ebay power supply

[irving2008]

Just some thoughts around the 55v 9.9A power supply (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=380071301709) I bought off ebay for £22 inc postage as a result of this thread (http://www.mycncuk.com/forums/showthread.php?t=768&page=5)

The two questions being asked were, how do you connect to it and how can the output voltage be reduced below 50v.

The first is easy, standard 4.8/0.5mm LUCAR connectors fit perfectly, so no need for an expensive socket.

The second less so... but I'm working on it. The attached datasheet shows that the Inhibit line must be between 5.5v and 11.5v approx which controls the output voltage between 50 and 57v approx. As the inhibit line drops below 5v the output volts is fixed at 42v until at some point (to be determined) the output is turned off. At 42v the supply is out of regulation (but exactly what that really means is open to experimentation). The circuit diagram below shows one way to set the output voltage.

In the meantime here are some pics.. these are quality supplies..

Pic 1 shows the unit, Pic 2 the connector block.

Pic 3 shows the two main circuit boards when stripped out of the case. Note the substantial heatsinks.

Pic 4 shows the input RFI filter - a sign of quality

Pic 5 shows the daughter board which is a separate switch mode supply to provide internal intermediate voltages. The adjustment does not control the main output volts.

Pic 6 - another sign of quality - a temperature sensor on the main input bridge rectifier heatsink. The 25A bridge rectifier below it converts 240v AC to 330V DC

[Tom]

Hi Irving,

I was just logging on to PM you that I'd received my PSU this morning, when I found this thread! Thanks for the review!

Looks like a nice unit - I've had the covers off, but didn't get it down to the same state of undress as you... :whistle:

The datasheet shows that if the inhibit line is left at 0V the PSU will sit at 42.8V (out of regulation). You also mention that it might turn off at some point, but I can't see that mentioned in the data - is this from experience? I'm thinking of just trying (leaving it plugged in in the corner) it to see what happens... You'll probably remember that I need 50V max for my drivers (aiming at 42 to 45V).

Need to get some 4.8mm spade connectors first though - I only have 6.3mm and they're not secure on the terminals...

Tom

[irving2008]

...The datasheet shows that if the inhibit line is left at 0V the PSU will sit at 42.8V (out of regulation). You also mention that it might turn off at some point, but I can't see that mentioned in the data - is this from experience?
No I haven't tried it - but whats the point of an 'Inhibit' that doesn't? Need to put a 100mA load on as well for test so need to find a 470ohm 10W resistor...

...
Need to get some 4.8mm spade connectors first though - I only have 6.3mm and they're not secure on the terminals...Maplin's do them N35CY (Blue) and they do red as well...

[HankMcSpank]

No I haven't tried it - but whats the point of an 'Inhibit' that doesn't? Need to put a 100mA load on as well for test so need to find a 470ohm 10W resistor...
Maplin's do them N35CY (Blue) and they do red as well...

or if you're nowhere near a Maplin a pack of 25 for £1.99 delivered.....

http://cgi.ebay.co.uk/4-8mm-blue-female-crimp-spade-terminals-Pack-of-25_W0QQcmdZViewItemQQ_trkparmsZ65Q3a15Q7c66Q3a1Q7c 39Q3a1Q7c293Q3a2Q7c294Q3a25QQ_trksidZp3286Q2ec0Q2e m14QQhashZitem20ac6cf92aQQitemZ140331776298QQptZUK Q5fBOIQ5fElectricalQ5fComponentsQ5fSuppliesQ5fETQQ salenotsupported

(PS I've emailed Minibea UK on the off chance they have a schematic)

BTW If there's any interest in the from other living here in the Great Smoke, (ie a 'group buy')...he saying he can give more discount - plus I can use my own courier (£7.50 for up to 25kg in weight - which should get about 7 of these in there!). So each could work out as low as £13 ...which for that spec of PSU is just insane.

[Robin Hewitt]

Looks wonderful, but... :naughty:

All the cheapy stepper drive boxes clack out just passed 50 volts to protect themselves and you really don't want one axis to pause waiting for the volts to come down a tadge :whistle:

[irving2008]

Looks wonderful, but... :naughty:

All the cheapy stepper drive boxes clack out just passed 50 volts to protect themselves and you really don't want one axis to pause waiting for the volts to come down a tadge :whistle:
Which is why I am working to figure out the mod to control the volts down to 35 - 45 instead of 50 - 57. It may be as simple as changing the resistor controlling the current sink device in the feedback loop...

[Robin Hewitt]

Which is why I am working to figure out the mod to control the volts down to 35 - 45 instead of 50 - 57.

Aha ! :clap: :heehee:

[HankMcSpank]

Top quality PSU at a great price! I think it will be set to 45V soon.....Just keep giving Irving a prod...or a :beer:

If you're setting up a group buy put me down for 3....might come in handy :)

I think the group buy would only work for those that can collect from my place here in North London ...ie savings to be had from lumping the one delivery together (or they could be collected from my work nr the Barbican in London)...don't really want to proceed until Irving works his magic though.

The seller will give a discount (though I've not asked/pushed him on this), & Parcel2Go will deliver upto 25Kg in weight door to door for about £7.50.

That aside, if you want to go your own way & can beast him down to a tenner each for 3, then with Parcel2Go as the courier, then that would only be £12.50 per PSU to your door!

[Kn8]

Hi I would be interested in joining in on a group buy and will be happy to purchase four supplies at the right price.
Ivan.

[HankMcSpank]

Hi I would be interested in joining in on a group buy and will be happy to purchase four supplies at the right price.
Ivan.

Once again...due to the weight of these, I reckon a 'group buy' will only work if people can collectin person, from North/Central London. In other words, the win here is mainly the £10 saving he's charging on the P&P ...by grouping these PSUs in blocks of 25kg, then some useful saving can be made on the P&P (plus whatever discount he offers on volume)

I've now emailed the seller for price break points. (but like I say, not worth pursuing unless the voltage output on these PSUs can be tamed to more usable levels)

[HankMcSpank]

I,ve just been quoted £16.00 Del for 3 of these to yorkshire from the seller and they are on there way as we speak.:yahoo:

Mental!

Forget group buys. ....we may as well all fly solo with that kind of offer - stupid price!!!

[irving2008]

Mental!

Forget group buys. ....we may as well all fly solo with that kind of offer - stupid price!!!I paid £19 del for 2, so £22.49 a PSU... cant be bad...

It may take me a couple of days to work out the answer to the volts. Its a TI UCC2985 phase-shifting PWM controller driving 4 x F740 500V 20A HexFETs in a full-bridge, running at 340vDC supply, driving the output transformer, the output being rectified by two BYT16P dual fast 20A rectifiers. Feedback from output to PWM is via a pair of opto-isolators. As such it is not far different to the reference circuit for the 2985 PWM but so far not been able to identify the actual voltage regulation mechanism.

There are a pair of FA3624 PWM controllers on a daughter board each driving an FP460L hexfet as a single ended flyback converter to provide logic voltages of 5v and 12v (I'm guessing based on the other chips around there, but it would seem logical).

There is another daughter board with SMT parts on that is made in UK (rest is made in Germany) which suggests this was bought in. Havent been able to fathom its purpose yet.

[Lee Roberts]

check the Tec doc out on the listing page irving.

"500W Telecommunication 19“- Module"

:)

[Tom]

TI UCC2985 phase-shifting PWM controller driving 4 x F740 500V 20A HexFETs in a full-bridge, running at 340vDC supply, driving the output transformer, the output being rectified by two BYT16P dual fast 20A rectifiers. Feedback from output to PWM is via a pair of opto-isolators. There are a pair of FA3624 PWM controllers on a daughter board each driving an FP460L hexfet as a single ended flyback converter to provide logic voltages

Crikey! I'll just be happy if I manage not to set fire to it when I plug it in!!
Thanks for the investigations Irving - i've got a couple more weeks of fiddling with leadscrew and alignment then I think I'll suck it and see what happens at 42V. (unless your reverse engineering gets finished before my machine)(possible) :whistle:

PS. cheers for the ebay spades link Hank - i'm nowhere near Maplin :(

[irving2008]

check the Tec doc out on the listing page irving.

"500W Telecommunication 19“- Module"

:)and your point Lee? Thats the tech spec I included in my first post in this thread... thats where i got it... it doesnt say much tho...

[irving2008]

MTBF @ +25°C ambient temperature MIL HDBK 217 F >20 years

Found that in there :)Yes, this is designed for the telecoms market... as I said, a quality supply....

note also elsewhere in doc... "Designed for free convection" No fans needed!

[HankMcSpank]

I emailed the manafacturer (Minebea) to see if they had a schematic, here's their reply...



thank you for your request.

Sorry to tell you that NMB Minebea gave up that business years ago. No more drawings, spare parts or schematics available anymore,

Regards

[irving2008]

I emailed the manafacturer (Minebea) to see if they had a schematic, here's their reply...


thank you for your request. Sorry to tell you that NMB Minebea gave up that business years ago. No more drawings, spare parts or schematics available anymore, Regards

Yeah, good try, but I thought that was wishful thinking. These were built around 10y ago I think.

[John S]

So Kip's only got 5 years warranty left. :yahoo:

.

[irving2008]

Well I managed to get the power supply wired up and it does what it says on the tin... no noise, no fuss, just 500w of power....

The variable output is, well, variable... and it doesn't get switched off...it sits at 42v when the 'inhibit' line below 5v or above 11v, although the SysOut line does switch off when out of regulation.

Also needs no load resistor.... works happily with no significant load.

Will continue to investigate....

[HankMcSpank]

I,ll second this my, 3 ps arrived today and i,m well chuffed they just look and feel quality.
Thanks Irving and Kip.:clap:

Edit: ended up costing me £17.38 each inc delivery that was for 6 supplies.


I,ve just been quoted £16.00 Del for 3 of these to yorkshire from the seller and they are on there way as we speak.:yahoo:

Could you clarify (so I can put on my best haggling hat :biggrin:) - excluding delivery...what did he charge per PSU?

[HankMcSpank]

Thanks (& sorry for labouring the point! :smile:)

For anyone wanting to order a few of these - the seller will allow collection via your own courier.....& Parcel2Go will deliver upto 25kg to your door for about £7.50 in total (the ad says they weigh 2.5KG each, so factoring in some 'headroom', you could therefore get 9 PSUs into the one Parcel2Go delivery - can't imagine you'll be popular with the driver though!)

[John S]

So after the sage of parcel farce, parcels 2 go etc was it possible to get to around the 40 volt mark ?

.

[irving2008]

So after the sage of parcel farce, parcels 2 go etc was it possible to get to around the 40 volt mark ?

.
Still working on it John, looking promising but haven't had much time this week...

[HankMcSpank]

Still working on it John, looking promising but haven't had much time this week...

Old thread - what was the outcome? (did anyone manage to tame the voltage?) The seller is still knocking these out at £12.99 per PSU (his wife must be a tad miffed at them laying around the house by now!) ....


http://cgi.ebay.co.uk/NEW-UNUSED-50V-DC-POWER-SUPPLY-9-9A-MINEBEA-/380071301709?cmd=ViewItem&pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item587e03d24d knockout price.

[Swarfing]

Hank

i bought two of these a while a go before seeing this original thread and still not got round to powering them up let alone start to tweak them. i would be very interested in anything further found out about them on the voltage drop front. My drivers can do the full 50v volts but would be happier at a few volts lower to save the possible crispy bacon burn factor. By the way i picked mine up direct from the old fellow (i live in Swindon)

[ecat]

Adding up the costs of a diy cnc machine continues to make my eyes water so finding these makes for a refreshing change :)

In theory the output from the opto isolator should be wired to a feedback pin on the main PWM controller chip. If memory serves me correctly and the chip follows convention then the function of this feedback pin is very simple:

if the voltage on this pin is above a certain threshold value (around 2.5v perhaps) the PWM controller switches off and if the voltage on this pin is below said threshold the PWM controller switches on - this is how the output voltage is regulated.

As the PSU already has some way of varying the output voltage there may be some additional complications but all that should be needed to decrease the output voltage is a change to a single resistor such that the voltage on the feedback pin is increased by about 20% for a 40v to 47v output range (ish).

Disclaimer: I know enough to hurt myself and nothing more :)

[HankMcSpank]

I'd have thought the way they do this is to modify the duty cycle of a PWM stream. I'm tempted to order one - it appeals to the lazy mountaineer side of me ("I want to climb it because it's there" or transposed to this particular situation "I can't be arsed to climb a mountain, so I want to get the voltage down on this 50V PSU because erhm it's not 45V")

[irving2008]

Old thread - what was the outcome? (did anyone manage to tame the voltage?) The seller is still knocking these out at £12.99 per PSU (his wife must be a tad miffed at them laying around the house by now!) ....


http://cgi.ebay.co.uk/NEW-UNUSED-50V-DC-POWER-SUPPLY-9-9A-MINEBEA-/380071301709?cmd=ViewItem&pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item587e03d24d knockout price.
I managed to blow one up and to fry the input of my PicoScope.... (cost me £300 to replace it :redface::sad: ) due to selecting a reference point that wasn't the ground potential I thought it was!

The problem is that the design doesnt directly match the reference application schematic for the controller chip, and has a third-party board full of SMT parts that appears to do the opto-isolated feedback with at least one custom chip on it... Also there appears to be three power supplies in there, the main 50v job from a 400vDC rectification and two others, one of which is a -ve rail.

As we know there is a input pin who's voltage controls the output. This goes into the SMT board and I believe this voltage drives a current source (as per the reference model) that controls the feedback circuit, however I was unable to identify that part on the board and suspect its inside the custom chip. Also there is obviously some sort of comparator on it to drive the 'in regulation output and control the current limit' but again suspect this is inside the custom chip too.

The result of all of this is I was unable to find an easy way to change the control range. I believe the necessary resistor(s) to change are on the SMT board but I cannot yet identify them. And then other pressures overtook the time I had available...

[Tom]

I bought one ages ago (as a result of this thread) and just plugged it in. It's been running the machine ever since.

Open circuit my supply measures 42.7V (the data sheet spec is 42.8V +/- 0.5V, so no worries).
The data sheet calls this voltage "out of regulation" (ie. there's less than 5.5V or more than 13.5V on Ucr). I haven't checked what happens when I put voltage on Ucr, because the "out of regulation" voltage is the one I want, and it seems to cope with load OK at 42.7V. The 4.3 signal diagram on the datasheet (attached) is the useful one.


On my machine Ucr (pin 28) is just floating, but I should probably tie it to ground to avoid surprises. I haven't bothered because, well, it just works.

Happy days.

[HankMcSpank]

Thanks for the feedback - have you measured how much the 'out of regulation' 42.7V moves when your stepper motors are going at full tilt?

[Tom]

It doesn't flinch at maximum speed. I can't measure it under cutting load at the moment because there's some dust-sensitive stuff in the room, but jogging at max speed I can't even measure 0.1V variation on the output pins of the supply. Steppers under load should only consume marginally more power i'd have thought.

I'm running with the 3Nm steppers that everyone sells, along with the 4.2A drivers.

One test I can't do is a hardware e-stop, to see what voltage gets pushed back through the drivers with a sudden stop. I'm still only wired into software e-stop circuit (not good), so I can only decelerate at the max values EMC2 allows. Still, with 7V of headroom to the 50V max which the drivers can cope with, hopefully no problems...

[John S]

Tom,
You say 42.7 volts but the spec says 50v ?
Is this with it turned down as far as it will go ?

[irving2008]

John,

The PSU is variable 50 - 56v but with no control input it runs in a 'unregulated' state at a fixed 42.8v +/-0.5v. it appears this isnt unregulated as such, just outside the voltages for which the very low noise/ripple spec is guaranteed (these PSU were originally intended for telecoms phone lines so are very low noise).

[Tom]

Hi John,

Yeah, basically. Plug it in and it'll whirr away at 42.7V happily.

I think they were originally intended to be used by some sensitive rack-mounted equipment, which needed really close voltage control somewhere between 50V and 56V. The exact voltage within the 50V to 56v range can be adjusted with a control voltage to pin28. I guess some closed-loop control (in a different box) would increase the control voltage slightly when the unit was under peak load, to keep the voltage seen by the sensitive equipment stable.

We're all using them in "cheap whacking great power supply" mode, without any need for the regulation voltage on pin 28. I've just bought 2 more (in case they run out! one for the lathe and one spare).

[ecat]

Just bought two :)
I may be away next week but I'll have the cover off them as soon as I can :)

[GeorgeD]

Was thinking of going for one of these? thats not too bad considering its amperage and some 15amp jobs are getting knocked out at around £35 to £40
http://cgi.ebay.co.uk/21-30volt-power-supply-up-34amp-output-NEW-/150467654119?cmd=ViewItem&pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item23089231e7

[John S]

Why do you need all those amps at a puny voltage ?

[GeorgeD]

WellI'monly going to un my drivers at 24volts so thats adequate and the amps are there if and when its needed.

[irving2008]

It will never be needed... you wont find a driver capable of more than 4A tops thats limited to use at 24V so the most you'll ever need is 3 * 4 *.66 = 8A unless you plan a 4th or 5th axis... but by then having only 24V will be a serious limitation anyway...

[John S]

I'm nipping down to Swindon one day next week, anyone in the East Mids want any bringing back but you will have to collect from me.
I'm not shipping out.

Price is £12.99 for the PS, no other costs.

[Tom]

Aargh,

Cheers for the offer John, I would've done but paid for mine earlier. In fairness he only charged £12 shipping for 2 units so it's all good.

[Swarfing]

John

Pop on in if for a mug of tay and knobs if you do, and i might even get some of those things you like so much in as well.

[John S]

Will do and send a PM when I get a reply on times and dates.

[ecat]

Well, they have arrived. Impressive beasts, especially the big hole in the middle to facilitate passive cooling.

irving2008, could you possibly link me to the UCC2985 application note or spec sheet, google is not helping :(

(http://www.mycncuk.com/member.php?125-irving2008)

[irving2008]

No, I cant find it again either... but if memory serves (and I'll have to look when I get home) I didnt find it before but a near match - enough to give pinout and reference circuit clues... but I dont recall offhand what it was or where I found it...


*edit* might have been a typo.... UCC2895 datasheet (http://focus.ti.com/lit/ds/symlink/ucc2895.pdf)

[ecat]

thank you anyway.

An older part perhaps? There is certainly enough info on the, what I suspect to me similar, ucc2884, 3884.

If I can track down a comparator feeding the opto-isolators then the switching chip may be irrelevant. You mention a second opto, could this be for over-voltage?

Output -> voltage divider -> comparator -> opto... if nothing else the feedback circuit could be replaced.... heh... maybe :)

Guessing again, the comparator - in custom chip or not - is running from +5v or +12v, so there must (-ish) be a voltage divider external to the custom chip/comparator etc.

Anyway, we know these are good for 42v.
Drivers that can cope with the full 56v are not so expensive (?)
On a personal note, if the worst comes to the worst, I now have the makings of +/-56v psu @ 500w which will make for a stonking sub-base amp :)

[ecat]

Some initial investigation:

PWM controller : http://www.digchip.com/datasheets/parts/datasheet/477/UCC2895N-pdf.php

The interesting parts on the surface mount board are, guessing here as I've not buzzed things out or even applied power yet!!! :
Op-Amps : lm224 equivalents
Comparators: lm239 equivalents

Now I guess the fun can begin :)

[irving2008]

well I got as far as setting up my test bed again yesterday to restart the investigation but got sidetracked (watching TV while probing 400V isnt a good idea)... This link (http://focus.ti.com/docs/prod/folders/print/ucc2895.html)gets you to datasheet and applications notes.

[ecat]

probing 400v at any time is not a good idea imo!

Anyway, that daughter board is a nightmare, everything is way to small and the board would be trouble to remove: I think I have the comparator outputs to the 2 optos, via 2 transistors so looks good :) The bad news is all the fun gubbins for this is behind the capacitor bank making it almost totally inaccessible :(

Undeterred, lol, I moved on to the inputs to the daughter board and here I may have hit the jackpot... maybe.. The op voltage is divided down by a factor of ten and fed to the daughter board. Yay. These dividers are on the main board and not surface mount. Yay. The bad news is there are two voltage dividers and I have no idea what the second one is for, then again I have no idea which of the 2 we need anyway.

Divider 1 feeds op div 10 (measured) to daughter board pin 12
Divider 2 feeds op div 10 (measured) to daughter board pin 8

You should be able to trace the resistors I'm talking about from these pin numbers.

If I'm right about the lm224 equivalents then pin 12 feeds to a unity gain op amp, pin 8 feeds to a different opamp that actually 'does stuff'. I've no idea what it does but it's not unity gain.

So, why two dividers and two opamps ? 1 to catch the default 42.9v and the other for the variable feature? I don't know. Do I need to change both? I don't know.

These boards were not made for easy disassembly so I've measured the divider resistors in circuit, of course the values measured this way do not match the values required for a div 10 series pair. Ho-hum. One resistor in each pair is big and easy to see - they are not quite under the heatsink and just behind the output coils, I can't see a ref number now the thing is back together :( -, so if you have reasonable colour vision perhaps you can let me know the value?

Anyway, before I risk life and limb by snatching the soldering iron from the coals (should be hot enough by now) I'd like your opinion on which of the two possible modifications would be most suitable...

1) Configure the psu so the variable range works over, say 43v to 47v (ish)
2) Configure the psu so the 'non-regulated' voltage can be set to XXv and the variable input can be ignored.


I'm off to try and find a zener...

[irving2008]

Where did you think the optos are?

Ideally would want to be able to force the voltage down further, tho that might not be viable...

Where were you going to put the zener?


Since I've fried this board anyway I think I'll pull it to bits, get easier access to the parts....

[ecat]

A couple of hi-res images if needed ...

http://www.i2net.me.uk/files/cnc/mine/ebaypsu/TopBoard-hires.JPG
http://www.i2net.me.uk/files/cnc/mine/ebaypsu/BackBoard-hires.JPG

Back of the board showing the 2 optos (2 x 4 pins), the track feeding pin 20 (Error Amp) on the PWM and the 4 res making up the 2 voltage dividers. (ignore the pencil marks, they may or may not be correct!)

http://www.i2net.me.uk/files/cnc/mine/ebaypsu/BackBoard-800-Markup-1.jpg


Top of board, only 1 of the optos is visible.

http://www.i2net.me.uk/files/cnc/mine/ebaypsu/TopBoard-800-OptoMarkup.jpg


Close-up of output coils, one of the two large voltage divider resistors marked (R34). The large resistor from the second divider (R11) is right next to it.

http://www.i2net.me.uk/files/cnc/mine/ebaypsu/opCoilsAndResistor-800-ResMarkup.jpg

The zener is just so I can set up your test circuit... still not found one :(

My idea is to modify one or both of the voltage dividers by fitting parallel resistors, this is a nice easy modification and so long as we don't ask for the impossible the whole of the control circuit should play along with us :)

Example:
In fixed mode the op voltage is 42.9v and the voltage at the centre of each divider pair is 4.29 volts. This 4.29 is the critical voltage in fixed mode, the control circuit will do every thing it can to maintain 4.29 volts at the centre of the divider pair. If we reduce the value of the lower resistor in the divider then this resistor will drop fewer volts and the divider ratio will effectively increase. If we select a value that gives us an 11:1 divider for example, in order to maintain 4.29v the output voltage would have to be 47.19 volts. Yay, in theory :)

Reducing the value of the upper resistor in the pair reduces the divider ratio which should allow us to modify the output voltage range in variable mode.

What I don't know for certain is the value of the resistors in the pair, my colour vision is not so good so I can't read the value of R34 or R11.Once we know the value of one of the resistors we can calculate the rest :)

[irving2008]

OK, going to whip the heatsink and daughter board off this dead one so i can get a good look... be back later...

[irving2008]

Right, decimated the board lol

Attached is circuit diagram for the wiring to the daughter board. Q1/Q2 are the opto, the 6-way connector to the top left is the connection to the output connector. Also attached are pics of daughter board, will start tracing that through later this evening/weekend, and main board after decimation.

On the 6way, pin 1 is the control volts Ucr, pin 2 is SYSOUT, pin 3 is the 50v rail internal to the PSU (via temp compensation so can be used to control output voltage on load in a system), pin 4 and 5 I suspect are +/- voltages to the control board and pin 6 is common.

It is likely as ecat says that R11/R12 and R33/34 are the dividers providing upper and lower voltage control limits, why there are two isn't clear. Adjusting either R11 or R33 may not change the output voltage, but merely adjust the levels at which the SYSOUT function changes state... some experimentation needed there... but getting closer...

[ecat]

I was getting worried that you had probed the 400v line again!!

You have been busy. Indeed, R11, R12, R33, R34 are the ones I'm looking at, 9.1k and 1k make the 10:1 divider. Lovely. So, I'll stick a 10k resistor across R11 and or R12 and we'll see what happens. Why 10k? As my old man said one day 'it's always 10k', in this case it may, or may not, give us a fixed output of 47v. Good enough for you?

:)

501 1j in the middle od the daughter board is a variable resistor, I may twiddle it if I'm feeling brave.

All I know about the daughter board...Err, from memory :blush:

http://www.i2net.me.uk/files/cnc/mine/ebaypsu/DSCN1884-marked%20up.jpg

Note to self: Work out how to do thumb nails

[ecat]

It's alive!!! Muhahahahhahaha

Whenever I put something back together I'm always delighted if it still works, from that point everything else is gravy :)

Ok, in fixed mode I now have 47v output :naughty:

First attempt was across R12, I don't know what it is supposed to do but it doesn't affect the fixed mode voltage.

Second attempt I used 9k4 in parallel with R34 and the result is close enough to my calculations. Always a good sign. Why start with 9.4k? Simple, I found a bag of 4k7s.

Calculations:
Top divider resister is 9.1k
We are changing the value of the divider resistor, call this value x.
Desired output voltage is op
Ratio is the ratio of the divider
These calculations are based on k ohms

op = 4.29 * Ratio
Ratio = op / 4.29 : Required Ratio

Ratio = (9.1 + x) / x
x = 9.1 / (Ratio - 1) : Required resistance

As we are creating the value x by placing a resistor in parallel with the existing 1k resistor we need a bit more maths. Lets call the parallel resistor rp.

x = 1 / (1/rp + 1/1)
rp = x / (1 - x)

N.B. In the case of THIS power supply, the existing resistor is 1k. As x is the value resulting from paralleling a second resistor, x will always be less than 1.


Ok, now to work through for my measured 47 volts:

47 = 4.29 * Ratio
Ratio = 47 / 4.29 = 10.956

x = 9.1 / (10.956 - 1) = 0.914

rp = 0.914/(1 - 0.914) = 10.63

Hum, 10.63k is not the 9.4k we expected, lets work the calcs the other way:

rp = 9.4

x = 1 / (1/9.4 + 1/1) = 0.904

Ratio = (9.1 + 0.904) / 0.904 = 11.07

op = 4.29 * 11.07 = 47.49v

Less than 0.5v difference, maybe my calcs go wrong somewhere or my meter is worse than I thought, but I think the result is close enough.

[irving2008]

yes... but it could equally be setting the current limit! might be worth twiddling....

I've identified all the parts on the daughter board with the except of U102 and U105 which are just above the variable resistor, marked A012. All the other transistors on the board are generic NPN (1Bp = BC846) and PNP (3Dp = BC856) but these are designated like ICs - I have a suspicion they might be band-gap current sources or something...i dont think they are mosfets as these are designated 'Q' types elsewhere and diodes are 'D' (there are 6 generic small signal types and 2 zeners).

I've imported the diagram into Visio and populated it... now just putting in the links.... see attached WIP...

[Tom]

Guys, all this electrickery is terrifying! :confused::smile:

Keep up the good work!:beer:

[ecat]

That's some mark-up irving, thank you :)

It could be the current limit, it could be almost anything, lol. I'm just looking at the system as a black box controller and I'm especially trying to avoid that daughter board, I suspect it may be more clever than I am ;)

The current limit should be quite easy to trace. R30 is used to sense the current, this feeds to daughter board pin 7. I have no idea what d13 is doing in there.

That big daughter board VR has me puzzled, but you know what curiosity does to cats and ecat is especially suspicious of the intentions of the 400vdc lines.

@Tom,
Thanks for your support.

k, I'm off to kill some zombies :)

[hmaki]

Hi,
How long it takes when yours power supply arrived?
I ordered a supply three days ago and nothing yet happened.
Usually ebay seller has sent message when you buy something, but he has´nt sent anything.

[irving2008]

Hi,
How long it takes when yours power supply arrived?
I ordered a supply three days ago and nothing yet happened.
Usually ebay seller has sent message when you buy something, but he has´nt sent anything.

Well its holiday season, he may be away. You are in Finland, he may have to sort out additional shipping. Why not contact him on eBay and ask?

[hmaki]

Yes I have asked shipping time on eBay,but he have not answered yet.
i´m so impatient because that is last part and then I can test my machine.

[GeorgeD]

You sound like Chinese origin,Hmaki...where abouts are you?

Have you emailed the seller? he could be on holiday/have problems??




Oops! pays to look at the last post.

Finland it will take at least 4 to 5 workin days to et to you...or more?

[Ricardoco]

Ahh now that power supply looks familier to me, is it because that communications company i work for uses them to generate the 50v dial tone you hear every day when you pick up the phone (assuming you are not on cable that is, lol)...


Rick

[irving2008]

Ahh now that power supply looks familier to me, is it because that communications company i work for uses them to generate the 50v dial tone you hear every day when you pick up the phone (assuming you are not on cable that is, lol)...


Rick
Well its a Mineaba supply for telecoms, c 1995/96... no longer manufactured...

[Ricardoco]

Well its a Mineaba supply for telecoms, c 1995/96... no longer manufactured...

I knew it!! and maybe its not manufactured any more but they are still used, remember this comapany still has bakalite fixtures because they believe "if it aint broke dont fix it because the shareholders need the cash), they do replace them with farnell units when they go bang though....lol

[irving2008]

I knew it!! and maybe its not manufactured any more but they are still used, remember this comapany still has bakalite fixtures because they believe "if it aint broke dont fix it because the shareholders need the cash), they do replace them with farnell units when they go bang though....lol
Dont suppose you'd have any documentation on them?

[Ricardoco]

Im not back at work till next week so i will have a look for you then (if there is i will have to send you some scans) although small there is a chance.. :)



Rick

[GeorgeD]

(if there is i will have to send you some scans) although small there is a chance.. :)

I can see lots of rubbing of hands and faces being lit up here. :heehee:

[hmaki]

Im not back at work till next week so i will have a look for you then (if there is i will have to send you some scans) although small there is a chance.. :)



Rick

I finally received my supply.
Now I wait instructions how I can rise supply voltage:)

[ecat]

It's early to bed for me tonight and a long day tomorrow, I'll see what I can do. I've tested a range of voltages BUT I cannot test at anywhere near full load so cannot comment on when the current trip will kick in. What voltage are you looking for?

[hmaki]

Hi,
Irving:
Can you explain me how that schematic works on your first post in this thread?
Also I like to know what is this value on potentiometer.

I want to rise my supply voltage to 57V thats why I asking these questions.

BR

Juha

[GeorgeD]

Juha,doyou know what you're doing? sorry for that but the pot is lablled as 1.5k variable.

[routercnc]

Hi Juha,

I'm not great at electronics, but the usual way to write these things is to put the 'K' in the middle e.g.:
1.5K = 1K5
7.5K =7K5
I suppose this avoids costly mistakes if the small dot '.' is missed. My knowledge ends somewhere there . . .

[GeorgeD]

I can't understand why he doesn't connect the suppy to whatever he wants 57volts for? the supply according to the pics Irving has posted,the first pic is showing the voltage output as 50v to 57.6 peak so it should be adaquate for his needs?

[hmaki]

Hi!
It makes me little confused because I read that value 1V-5:redface:
But now voltage divider is almost ready.

Thank you very much Routercnc!

[Mad Professor]

Can the voltage output of this unit be droped to <30vdc for use with the TB6560 driver board, Unto I upgrade to PM752 Drivers?

[Jonathan]

Would it be safe to put a few of these power supplies in parallel? Maybe put small resistors / diodes(?) in to balance the load.
I ask because it's occured to me that these are the right voltage for my big 48V brushless motor/spindle. It claims to take over 100amps but obviously I'll never need anywhere near that amount! I think 3 PSUs in parallel would be plenty.

[ecat]

@Mad Professor

<30v humm, possibly or possibly not. I'll review my notes and maybe give it a try :)

[Mad Professor]

I got my power supply this morning, so now looking at how to drop the voltage for my TB6560 driver board.

Back on page6 you said you adjusted the value of R34 to adjust the voltage out the PSU when in safe mode.

So I am looking at removing R34 (9K1) and in it's place putting a 10K multi-turn pot + a 2K resistor.

Do we know yet what the 2nd voltage divider is for?

[ecat]

The power supply has two modes of operation:

Variable, where the output is controlled by a voltage applied to pin 28 (i/Ucr) on the main connector. This control voltage is to be set somewhere between 5V and 11V.

Fixed, if voltage applied to pin 28 is lower than 5V or above 11V the power supply output is fixed to 42.8 (+/- 0.5V). It appears that leaving pin 28 unconnected is sufficient to force the supply into fixed mode.

The resistor pair (R33, R34) provide the feedback voltage used when in fixed mode. I think, but never did prove, the resistor pair (R11, R12) provides the feedback voltage when in variable mode. All comments from this point on will assume fixed mode is selected.

Without modification the R33, R34 pair act as a x10 divider so whatever the voltage at the output one tenth of that voltage appears at the junction of R33, R34. The PSU is designed to hold the voltage at this junction at 4.28 volts.

For a given output voltage the R33, R34 pair are chosen such that 4.28 volts appears at the point where they join.

For an output of 24V, R34 must drop (24 - 4.28 =) 19.72V, leaving 4.28 volts across R33. Leaving R33 at 1k this would give us a value of 4k6 for R34.

Without modification the current through R33, R34 = 42.8 / (9k1 + 1k) = 4.28mA. The power dissipated by R33 = 4.28V * 0.00428A = 0.018W and the power dissipated by R34 = 38.52V * 0.00428A = 0.165W (so why do they use such a chunky resistor for R34 ?)

For a 1k + 4k6 24V modification the current through R33, R34 = 24 / (4k6+ 1k) = 4.29mA. The power dissipated by R33 = 4.28V * 0.00429A = 0.018W and the power dissipated by R34 = 19.72V * 0.00429A = 0.085W (most resistors/multi-turns would appear ok, but keep a close eye on the temperature of the multi-turn)

Another thing to look out for is ripple, how much the output voltage varies as the switch mode switches. Indeed, the minimum duty cycle of the switching circuit may even limit the minimum voltage to something greater than 24V. Only testing will tell.

Finally. Beware of the 400 Volt lines!!!

[Mad Professor]

Thanks for your reply.

As I type the PSU is running at 26volts, I have connected up scope, and the power output looks very clean, I have not yet put any load on the psu.

I will be connecting the PSU to my control board later on today.

[ecat]

Would it be safe to put a few of these power supplies in parallel? Maybe put small resistors / diodes(?) in to balance the load.
I ask because it's occured to me that these are the right voltage for my big 48V brushless motor/spindle. It claims to take over 100amps but obviously I'll never need anywhere near that amount! I think 3 PSUs in parallel would be plenty.

In theory, my interpretation of the theory at least, any switch mode PSUs of similar nominal output voltage can be paralleled without the use of resistors or diodes. Since similar is not the same as exact and exact is impossible, initially one PSU will attempt to handle the full load. It will reach its limit and the OP voltage will drop, at this point another PSU will kick in and try raise the output voltage back to what it should be. Ripple may be a problem, especially when the PSU kick in and out, so test the setup and see.

N.B.
When dealing with switch modes, mains voltages or anything else dangerous I recommend wearing safety glasses, safety gloves, standing well back and getting a friend or loved one to throw the switches ;)

[ecat]

26V with no load, if this is low enough for you then the job should be done. Lovely :)

As you have a multi-turn already set up, can you go any lower?

[Mad Professor]

The lowest I have tried taking the PSU down to is 20volts.

I have been running the TB6560 board at 24volts fine unto my old psu gave up.

I would like to run how much voltage as possible to gain the extra speed out of the stepper motors.

I am slowly going to work my way upto 30volts.

I don't know how much, or if I will get any extra speed out of the stepper motors going from 24 to 30volts.

[ecat]

Cool.

Remember to make some allowance for the peek voltage generated by the motor when the driver stops driving, heh. There is a thread around here somewhere with more details. There's also a thread relating voltage to stepper speed.

[Bodge]

I bought three of these 500W 50.5V power supplies for £12 way back in 2009.. as time has passed I mislaid the documentation.. A google search Found the missing PDF here. My Lazy way of solving this problem was to buy three 20 Amp bridge rectifiers to limit the output Voltage to Less than 50V therefore solving the slightly higher than 50v output.
My reason for this solution is messing with switch mode PSUs is quite dangerous. (a friend of mine was hit in the temple by a flying electrolytic case when delving into a switch mode psu. With such force it caused a tear in his retina.)

Your circuit hacking/reverse engineering provides a more elegant solution thank you.

Is their any reason why my "Lazy solution" of 2 x the diode volt drop was not considered as a solution in regulated mode?




The power supply has two modes of operation:

Variable, where the output is controlled by a voltage applied to pin 28 (i/Ucr) on the main connector. This control voltage is to be set somewhere between 5V and 11V.

Fixed, if voltage applied to pin 28 is lower than 5V or above 11V the power supply output is fixed to 42.8 (+/- 0.5V). It appears that leaving pin 28 unconnected is sufficient to force the supply into fixed mode.

The resistor pair (R33, R34) provide the feedback voltage used when in fixed mode. I think, but never did prove, the resistor pair (R11, R12) provides the feedback voltage when in variable mode. All comments from this point on will assume fixed mode is selected.

Without modification the R33, R34 pair act as a x10 divider so whatever the voltage at the output one tenth of that voltage appears at the junction of R33, R34. The PSU is designed to hold the voltage at this junction at 4.28 volts.

For a given output voltage the R33, R34 pair are chosen such that 4.28 volts appears at the point where they join.

For an output of 24V, R34 must drop (24 - 4.28 =) 19.72V, leaving 4.28 volts across R33. Leaving R33 at 1k this would give us a value of 4k6 for R34.

Without modification the current through R33, R34 = 42.8 / (9k1 + 1k) = 4.28mA. The power dissipated by R33 = 4.28V * 0.00428A = 0.018W and the power dissipated by R34 = 38.52V * 0.00428A = 0.165W (so why do they use such a chunky resistor for R34 ?)

For a 1k + 4k6 24V modification the current through R33, R34 = 24 / (4k6+ 1k) = 4.29mA. The power dissipated by R33 = 4.28V * 0.00429A = 0.018W and the power dissipated by R34 = 19.72V * 0.00429A = 0.085W (most resistors/multi-turns would appear ok, but keep a close eye on the temperature of the multi-turn)

Another thing to look out for is ripple, how much the output voltage varies as the switch mode switches. Indeed, the minimum duty cycle of the switching circuit may even limit the minimum voltage to something greater than 24V. Only testing will tell.

Finally. Beware of the 400 Volt lines!!!

[ecat]

I bought three of these 500W 50.5V power supplies for £12 way back in 2009.. as time has passed I mislaid the documentation.. A google search Found the missing PDF here. My Lazy way of solving this problem was to buy three 20 Amp bridge rectifiers to limit the output Voltage to Less than 50V therefore solving the slightly higher than 50v output.
My reason for this solution is messing with switch mode PSUs is quite dangerous. (a friend of mine was hit in the temple by a flying electrolytic case when delving into a switch mode psu. With such force it caused a tear in his retina.)

Your circuit hacking/reverse engineering provides a more elegant solution thank you.

Is their any reason why my "Lazy solution" of 2 x the diode volt drop was not considered as a solution in regulated mode?

Good question, I think at the time my list of solutions looked like:

Plan A
Modify existing circuit.

Plan B
There should always be space for a plan B even if it lacks a concrete definition ;)

Plan C
As the required voltage drop is small use one or more semi-conductor junctions (diodes or transistors)

-------------------

Plan A
The PSUs were quite cheap so it didn't really matter if I blew one up. In fact the 'spare parts' alone would be worth more than £12.

I had two PSUs to play with, potentially losing one was not a problem. In fact I did lose one, I left it in the office and forgot to bring it home when the company closed down - Grrrr

The whole idea of switch-mode PSUs is to efficiently convert one voltage to another. Modification is the correct solution.

After all that, any modification had to be as simple as possible, as safe as possible and not involve anything near the high voltage side.

Should only be attempted by those who are aware of and acknowledge and are are happy with the risks involved in opening a SMPS


Plan B
Very simple solution.

Does not involve opening the PSU

Safe to implement but in use this sense of safety is somewhat deceptive:

1) The forward voltage (Vf) drop of a semiconductor junction (diode) is not a fixed value. Buy rule of thumb we often assume something around 0.6v, 0.7v but look at the datasheet for the device you intend to use and you may find that Vf = 0.7V at 1A but up to Vf = 1.0V at 10A and as low as 0.4V at <0.1A. So two diodes in series may give you a 1.4V drop or they may give you a 2.0V drop or a 0.8V drop - over 50% variation depending on current draw. Whether or not this matters is entirely down to what you are trying to achieve, but I'm sure some bright spark is certain to attempt to use 10 to 15 diodes in series for 7V to 10V drop - well, at 50% or more variation this is when the magic smoke can escape.

2) Heat! If each semiconductor junction drops 1V at 10A draw then each and every semiconductor junction will dissipate 10W at 10A draw, for continuous use we now need heatsinks and possibly insulation.

-------------------

That covers most of the risk / reward assesment. Two diodes are great if you've done your homework and everything checks out, in my case I was happier making the mod :)

[Bodge]

Cool.. I was trying to imagine some reason I had not thought of.
The devices in question were KBPC5010, I was wrong saying they were 20A it was 50A.
With FVD variation <0.5v over the current range 0-10A. (0.5v to 1v)

They will now be put to one side for my next Green energy project.





Good question, I think at the time my list of solutions looked like:

Plan A
Modify existing circuit.

Plan B
There should always be space for a plan B even if it lacks a concrete definition ;)

Plan C
As the required voltage drop is small use one or more semi-conductor junctions (diodes or transistors)

-------------------

Plan A
The PSUs were quite cheap so it didn't really matter if I blew one up. In fact the 'spare parts' alone would be worth more than £12.

I had two PSUs to play with, potentially losing one was not a problem. In fact I did lose one, I left it in the office and forgot to bring it home when the company closed down - Grrrr

The whole idea of switch-mode PSUs is to efficiently convert one voltage to another. Modification is the correct solution.

After all that, any modification had to be as simple as possible, as safe as possible and not involve anything near the high voltage side.

Should only be attempted by those who are aware of and acknowledge and are are happy with the risks involved in opening a SMPS


Plan B
Very simple solution.

Does not involve opening the PSU

Safe to implement but in use this sense of safety is somewhat deceptive:

1) The forward voltage (Vf) drop of a semiconductor junction (diode) is not a fixed value. Buy rule of thumb we often assume something around 0.6v, 0.7v but look at the datasheet for the device you intend to use and you may find that Vf = 0.7V at 1A but up to Vf = 1.0V at 10A and as low as 0.4V at <0.1A. So two diodes in series may give you a 1.4V drop or they may give you a 2.0V drop or a 0.8V drop - over 50% variation depending on current draw. Whether or not this matters is entirely down to what you are trying to achieve, but I'm sure some bright spark is certain to attempt to use 10 to 15 diodes in series for 7V to 10V drop - well, at 50% or more variation this is when the magic smoke can escape.

2) Heat! If each semiconductor junction drops 1V at 10A draw then each and every semiconductor junction will dissipate 10W at 10A draw, for continuous use we now need heatsinks and possibly insulation.

-------------------

That covers most of the risk / reward assesment. Two diodes are great if you've done your homework and everything checks out, in my case I was happier making the mod :)

[Bodge]

From all the great work done a lot earlier (Many thanks guys)... we could calculate the replacement for R34 this way :-

Given that the PSU spec says "If the PSU is out of regulation then Uout=42.8+/-0.5V DC."

Taking the potential divider made from R34 and R33 is 9K1 and 1k with a +/- 1% tolerance

Applying 42.8V to this divider gives us a Junction voltage of 4.238 +/- 1%

Calculated by (R1(1k)/(R1(1K)+R2(9.1K))* 42.8V = V divider = (4.238V)

So rough calculations for 49V +/- 0.5 we need a resistor R2 of 10K561 or 10.561K (which ever standard you prefer)

The nearest we I could get with standard values (1/R1)+(1/R2)+(1/R3)=(1/Rtotal) was (1/22K)+(1/22k)+(1/270K) = 10.569K or 10K569 (which ever standard you prefer)


Thus this should give an output voltage of 49.025 +/- 0.5V eg +/- 1%


To change R34 for the 3 parallel resistors this was my process.

Warning make sure the PSU has been off for a good time as the PSU capacitors hold High voltages for a considerable time 400v DC is a skin splitting voltage and quite a Deadly!! thing to touch.

Remove the 5 outer screws, remove the cover, Unscrew the top board another 4 screws, disconnect the connector connector on the end unscrew the two screws holing the grey i/o connector disconnect the mains link connector and the other 4way connector

Remove the two PCBS.

Un screw the two screws holding the Heat sink down unscrew the screw that you can reach on Diode de solder the other diode remove the heat sink.
De-solder R34 replace it with the new resistor made from 2 x 22k 1/4W 1% and the 270k 1/4W 1% resistors connected in parallel re-solder R34 Re-assemble in reverse order...
Now to test it.. the result of this change gave me an output voltage of 48.9V very slightly out from my calculated value but well within the +/- 1% tolerance on the resistors used.

excuse dyslexic spelling


pictures to follow.

[Swarfing]

This may help and save you having to open it up :tan:

[Bodge]

Yes that is a nice way to avoid opening it up.

Unfortunately when I bought the PSUs I also bought the stepper drivers & Stepper Motors .. from Arc Euro Trade (bought with redundancy pay out )

Anticipating being to OLD to get a new job.. to allow for automating part manufacture for a start-up a business. 3 years later I now need to make parts without spending much.

The stepper controllers I have are 50V max supply..

I'm building a

CNC 1.2m x 600 CNC for cutting PLY and MDF.

a CNC type lathe for drilling and cutting 15mm PTFE bar. It would be nice to be able to do 5mm or 6mm bras studding as well but think it will not be man enough to do that.
I have the Seig micro lathe but this can not take a feed through bigger than 10mm diameter so maybe this could be automated for Brass studding.

An Aluminium cutting CNC based around a SEIG X0 micro Drill/Mill is also under construction the starting Time and Precision Ltd 3 axis x 55mm/2.20inch cubed aluminium positioning stage 0.00125 resolution on X & Y at 200 steps or 0.000625 Resolution @ 400 steps. x,y,z. Table needs to be sped up its threaded drives are very fine think it was for a microscope originally.

I have a 300mm x 300mm CNC for cutting PLY and MDF. for PCB engraving its OK it can cut as it cut its own T slot Bed but its far too "SLOW".

Picture of all these bits and bobs bodgeitquicktools.blogspot.co.uk