New build with recycled parts on a ridiculous budget 120cm*60cm work area

Can you take a resistance measurement at the coil that you do not have continuity? If you put your multimeter at continuity scale you get a bazing sound of a reading only if resistance is low,I think up to 10 ohm but I am not sure if it is a little higher or change between the brands of the meters,if resistance is higher you have to take a measurement with the ohmmeter.

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Originally Posted by Nickhofen

Can you take a resistance measurement at the coil that you do not have continuity? If you put your multimeter at continuity scale you get a bazing sound of a reading only if resistance is low,I think up to 10 ohm but I am not sure if it is a little higher or change between the brands of the meters,if resistance is higher you have to take a measurement with the ohmmeter.

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I've ordered another transformer, will check the existing transformer though

https://www.maplin.co.uk/p/2x50v-100...nsformer-a74qj

It's 50v per output core

I hope there's no issue going oversized with a 1000va transformer but I didn't realise they had 625va one and this was 1/2 price same make as rapid.

Saved enough cash on the transformer that I just managed to buy a new AM882 as well with fast shipping.

Normal version not am882h.

One good bit of news the new parallel port card came I fitted it and parport recognises it so linuxcnc should at least work and I bet mach 3 does to.


Attachment 23166

I got it wrong before there's no continuity between blue and grey OR violet and brown but there is continuity between grey and violet I guess this means both thermal fuses are blown.

One question about the new transformer I know I wire on the input side the brown and blue to the mains, the grey and violet together as before. On the output I wire the orange to the black and the yellow to the red then wire them to the the rectifier is that correct?

Would wiring a 5amp plug fuse to the PSU input give some protection to without tripping out in normal usage?

Omg that's some low price transformers :D
Good find and I'm happy that you are back on track!

Wish they delivered to Sweden ;)

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For the fuse question.. think it might blow when charging the caps..

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Quote:

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Originally Posted by Desertboy

Would wiring a 5amp plug fuse to the PSU input give some protection to without tripping out in normal usage?

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I suspect that 5A might be a bit small and might blow on switch-on, although you will probably get away with it. Typically, a standard fuse will blow within 10sec with a 2x overload, so that might be OK. For normal running, you are unlikely to be drawing anything like 1000VA (which is a touch over 4A in practice) most of the time, if ever, so that's well within the fuse rating. I use a 10A MCB on my own machine feeding all the PSUs (although the stepper driver PSU is the most power-hungry) and I haven't had it trip yet.

Unfortunately, the fuse is very unlikely to protect the equipment and that's not really why it's there. In practice, the fuse blows just after the equipment fails! It's really there so that in the event of a serious fault that draws excess current, the wiring isn't going to burst into flames. In the case of elecronic components, it's well-known that the transistor is the fastest fuse on three legs...

Right I'll get 1 of these mcb's tomorrow to wire the PSU through
https://www.toolstation.com/shop/p26107

and 2 10 amp ones, one for the spindle and one for the twin 3 pin wall sockets.

I am going to wire 32amp to the junction box soon so might as well plan for the future.

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Originally Posted by Desertboy

Right I'll get 1 of these mcb's tomorrow to wire the PSU through
https://www.toolstation.com/shop/p26107

and 2 10 amp ones, one for the spindle and one for the twin 3 pin wall sockets.

I am going to wire 32amp to the junction box soon so might as well plan for the future.

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I think you might want a D rated one with that big transformer:beer:

I think I use a C type MCB - more surge-resistant than a B (the usual domestic type) but trips a little more easily than a D. But that's with a 650VA transformer. However, without analysing in too much detail, I doubt that the transformer difference is that significant and it's the size of the capacitors that matters more. I would tend to go with C type, I think.

Just an observation - are you running the primaries in series (240v) or parallel (115v) ??

If series the you need to connect supply to blue and brown with grey/violet joined.

If parallel then connect blue/violet and grey/brown then connect supply to to those pairs.

Just an observation as said but easy to ignore those little dots on the transformer winding pictures ;)

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Originally Posted by Davek0974

Just an observation - are you running the primaries in series (240v) or parallel (115v) ??

If series the you need to connect supply to blue and brown with grey/violet joined.

If parallel then connect blue/violet and grey/brown then connect supply to to those pairs.

Just an observation as said but easy to ignore those little dots on the transformer winding pictures ;)

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I had it wired blue and brown to mains 240v, grey and violet joined on the input side. On the output side orange and red to the rectifier, yellow and black joined. This was a dual 25v output core.

This time with the 1kva transformer I'm going to wire the input the same (it's a dual core 115v input). The output I will join the orange and black and then wire to rectifier, join the yellow and red and to rectifier. (Dual core 50v output, I want 50v out to feed into the rectifier so I get my 68-70v out for my drivers.)
Attachment 23183

If I add a precharge circuit to this, could I use a type B mcb I guess the capacitors have a large inrush which might trigger the type b mcb but when charged you would have better protection with a type b than a type c? I have some adjustable time delay relays (0-30mins) 10amp I could use so the precharge circuit always comes on say 1 minute before the PSU powers on.

If so how the hell do I make one I read something about precharge resistors but have no idea where to start.

Came today but missing the top metal plate! I think the one on my old transformer will work fine but still poor maplins I do have both rubber protectors.

I was hoping it would straight swap but not so sure it will I might just get away with it and a hammer ;)

Attachment 23184

Not going to wire it up until I have an MCB, replacing the rectifier as well, going to leave the caps in place.

Think I traced the problem to a poor crimp causing the initial problems and we think my friend reconnected the bridge rectifier backwards on the output but no one can be sure.

There's a reason transformer manufacturer's usually recommend slow blow/time delay fuses, and this thread has just proven why.

Fit a 10A MCB to a 1KVA transformer, and there is a high probability the transformer winding will fail before the MCB trips.
1KVA roughly equals 4 amps, so taking a type B MCB, it takes a minimum of 6 seconds at double the rated current for it to trip. So taking that 10A MCB, that's 20A, 5 times the transformer rated current, or over 4KW flowing for 6 seconds. Do you still think that MCB will do much good?

I personally just use a time delay fuse rated around 120% of the transformer rating. If you blow it, you're doing something majorly wrong, and it's far cheaper than a MCB.

As for cheap multimeters, they rarely have a fuse for the amp setting, which is likely what will of caused the problems. A sudden short on the power supply, as well as causing the transformer to fail, will of likely burnt something out in the power side of the AM882. If you were to strip it down, you could at least check the main power supplies are still functioning.

Also, if you strip the outer covering of the transformer, you might find the fuses near the outside of the windings, so it could potentially be a relatively easy repair.

I am going to have a look at fixing the transformer, there's a good vid on you tube it doesn't look that hard if the fuse is near outside but at £41 for a 1kva I couldn't resist. Maplins still have a new 625va transformer (50v) for £30 which I'm seriously tempted (Have enough bits to make a 2nd PSU) and also try and fix the original one or they have an 800va (45v) for £35. I have 7 caps now and 2 new rectifiers so it's cheap PSU for betty bigger sister Already planning ;)

Would these be suitable slow blow fuses?
http://www.ebay.co.uk/itm/5-CERAMIC-...A3euImkU3PFBZg

These look plug compatible in which case I'll put the PSU on a plug for ease.

When I first got the Am882 it had a dodgy connection I changed the plug and it was fine but I do wonder if the connection is dodgy on the board open it up couldn't see anything from the top need to take it out properly and look underneath

I am going to complain to Chinese I bought it off as they "offered" 1 year warranty but also got it on my CC so will see if I can get a refund through them.

At the moment this is going to a normal plug socket which is connected to an MCB in the board (16amp) on a side note my shitty 24v psu tripped it so I chucked the PSU in the bin was £7 ebay special. But it didn't trip whenthe psu blew in fact it didn't even blow the 13amp fuse in the plug and my pc stayed on connected to same power in.

I would not bother with pre-charge, this supply is not big enough to need it, as long as the rectifier is big enough to take the inrush as well as a slow-blow fuse in the input it should work fine.

Pre-charge is easy with a resistor in the output before the rectifier, maybe 10r 25W and a timer relay which shorts out the resistor after maybe 2s would do it but i wouldn't bother myself. Pre-charge is more used with supplies that have very large capacitors/higher voltages.

Quote:

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Originally Posted by Davek0974

I would not bother with pre-charge, this supply is not big enough to need it, as long as the rectifier is big enough to take the inrush as well as a slow-blow fuse in the input it should work fine.

Pre-charge is easy with a resistor in the output before the rectifier, maybe 10r 25W and a timer relay which shorts out the resistor after maybe 2s would do it but i wouldn't bother myself. Pre-charge is more used with supplies that have very large capacitors/higher voltages.

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Right wired up properly and tested 78.2v out so a little high what's the best way to reduce this voltage my AM882's 80v is max input.
Attachment 23190

I daren't plug it in to the AM882's.

Got it wired to a 13 amp switch finally so I can turn it on/off without killing power to pc.
Attachment 23189

Got a free enclosure some damage to the front but better than what I have, will transfer the AM88's and BOB's across PSU will stay in PC case.

Attachment 23191
Attachment 23192

Quote:

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Originally Posted by Desertboy

Right wired up properly and tested 78.2v out so a little high what's the best way to reduce this voltage my AM882's 80v is max input.

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If it were my supply i might unwind a couple of turns off the transformer secondary, but thats just me ;)

Not too many ways to fine tune the voltage really.

Maybe also look at an autotransformer in the primary circuit - a multi-tapped primary only transformer with the input going to the normal 240v tap and then take an output from the neutral and a tapping a little lower like 220v.

https://en.wikipedia.org/wiki/Autotransformer

Just an idea though. ;)

Or just run it at 78v's and hope ;) I turned it on off a few times and tested the voltage each time, and I noticed my input was 250v at the time it seems to vary at work from 238 to 250v this is the highest reading I've had so far and I think the max allowable is like 252v.

I need to check what the ac voltage going into the rectifier is didn't think that but was gutted as I was expecting to get something like Joe Harris 68v giving he has 25v output coils in series and I have 50v in parallel.

I wonder why I'm getting such a high reading is it because I have a high input voltage? This is mains fed, to an industrial unit, is it possible other things could affect voltage on the line? I'm going to have a dedicated line put in for the machine I seem to remember getting 240v when I was working on the 3 phase sockets (I tapped 1 phase for my plasma cutter)

Could I be getting a high reading because it's Saturday and the demand is lower on the estate?

Quote:

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Originally Posted by Desertboy

Or just run it at 78v's and hope ;)

I wonder why I'm getting such a high reading is it because I have a high input voltage?

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Yes, output is directly related to input, that is a very high input.

Quote:

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Originally Posted by Davek0974

Yes, output is directly related to input, that is a very high input.

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Will have to check Monday morning see what it reads.

I think the voltage will drop when you connect a load on the secondary side. Now you only have the caps connected right?

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Assuming input voltage is at rated 230V, your output voltage open circuit is going to be at 52VAC (rated output voltage plus the regulation rating of 4%).
Multiply that by root 2, gives 73.5V peak voltage.

Now if your input voltage is at 250, which puts it around 8% above the rated voltage, so your output voltage will be proportionally higher, at 79.4V peak.

Now all you need is a sudden deceleration on a couple axes, and the energy dump back into the DC side can potentially push everything overvoltage.

If you search for my Triac retrofit thread, there's a big post there explaining all this.

Quote:

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Originally Posted by m_c

Now all you need is a sudden deceleration on a couple axes, and the energy dump back into the DC side can potentially push everything overvoltage.

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Thats the important bit, i would get this voltage down before connecting drives.

Have ordered a 45v 1kva which will solve the problem whilst I'm waiting I took the time to start stripping out the box and recovered some nicer wiring conduits. Also fitted a proper stop switch to it.

Friend is going to fibreglass repair the damage for me I might even paint it ;)

Attachment 23193
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There's loads of space in here should I put the transformer in here as well and fit a 4 120mm pc fans two blowing in across the am882's and two sucking out the side of the transformer and leave a nice gap so the air can flow, I want to make sure the caps get good air flow over them.

It would be good to fit the transformer at the top of the box but it weighs 8kg making the box top heavy so it'll go at the bottom if i do fit I think the key will be good air flow and lots of it. I have a better on/off switch which is rated to 2hp (I think might be 3) ac3 so I think should be ok for the PSU.

Quote:

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Originally Posted by Desertboy

Have ordered a 45v 1kva which will solve the problem whilst I'm waiting I took the time to start stripping out the box and recovered some nicer wiring conduits. Also fitted a proper stop switch to it.

Friend is going to fibreglass repair the damage for me I might even paint it ;)

Attachment 23193
Attachment 23194
Attachment 23195

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If you can cancel the order and reorder a 625Va as it should suite you better 45V is a good choice

None of my CNC modules get hot, i would think one fan would be ok, filtered inlet then fan with a vent at other side of cabinet.

Caps will/should not get hot or even warm.

Quote:

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Originally Posted by Davek0974

None of my CNC modules get hot, i would think one fan would be ok, filtered inlet then fan with a vent at other side of cabinet.

Caps will/should not get hot or even warm.

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They won't get warm until you put a load on them. I have two control boxes the router with 4 drives does not have any fans in the box is 500x500x250 and is fine.

It's easy to worry about overheating but in practice, it's not a big problem on our size machines. On mine, I have two 12V fans just so that they cover a larger area and push a bit of breeze across the stepper drivers but I have wired them in series so that they run fairly slowly. Moves more than enough air. Similarly, I run the 12V spindle cooling pump on 5V and that works fine as well.

I also bought a 50V transformer for my machine (from Rapid Online), then realised that it was going to be a bit too high. Once you take into account the fact that input voltage can be some way above nominal, and the output voltage is a few per cent high to allow for voltage drop at full load, then it's easy to start nudging that 80V. In my case, I rang Rapid the day after the transformer arrived and they were happy to swap it for 45V, and even arranged a courier to pick up the old one. Good people to deal with. I'm now running at a nominal 68V which is bang on the money.

I'm going to fit a inrush current limiter ntc thermistor
https://www.ametherm.com/blog/inrush...s-got-you-down

I think this is suitable
https://www.ebay.co.uk/itm/282728849186

as far as I can tell I just wire this inline to the mains, anyone had any experience of them?

I wouldn't bother, unless the power on surge is a problem, as it's just something else to give potential problems.

Looks like I'm going to have wait at least another day the AM882 will come from China quicker lol

Attachment 23211
Been on phone will either be redelivered tomorrow (If it's ok which it will be of course, things are like house bricks) or new one sent out for Monday

My Hermes claimed they tried to deliver it today although I was there with the roller shutter door open so they are lying bastards, have to wait till Monday, would have been quicker to order from China lol.

Using the 50v transformer as a pattern (the 45v will be identical) so started to think about kitting out the box, anyone see any issues having the transformer under the stepper driver? I am going to fit 2 pc fans one sucking in and 1 extracting.

Attachment 23218

Going to use new capacitors as I have them and am going to need to fit everything a bit tighter.

You can just see the breakout board in the corner on a bit of ply will fit it roughly there and chop a hole with a cutting disc for the parallel port and USB to stick through.

Not sure I will fit the other BOB as I really don't need extra the input pins, good to have a spare though.

What's everyone set there AM882's microstepping up at?

Transformer came finally! didn't get round to soldering it but will have it up and running tomorrow ;)

Attachment 23225
Damn just realised I wired this up wrong lol but turned it on yet. The orange and black should be joined as well as the red &yellow.

Was tired this evening only just come home from work glad i decided to leave it till morning.

Almost there, got some connectors on a din rail for sorting out the wiring to the BOB, still need to solder the capacitors but will get that done tonight. Looking for my holesaw set at moment so I can make the fan holes in the enclosure.

Attachment 23226

The non working AM882 isn't bolted down just there for reference.

I have got a current inrush thermistor which hopefully is the right one if it cause problems I'll ditch it but it was £2 so I thought worth a punt. Hopefully with one fitted I can then use a type B mcb which I can just fit in the box ;)

I now feel it's starting to look like cnc electronics ;)

Got the capacitors soldered on a 2nd time, ready to test output voltage, need to get my mate tonight and borrow his hole saw so I can fit the fans and he's helping mount the box and the wires can be connected ;)

Attachment 23227

Now I need the new AM882 was quoted 10 working days delivery tomorrow is the 10th day :(

Ordered
one of these
http://www.ebay.co.uk/itm/230689466731

So I can fit it inside the box and take the mains in from the same feed as the transformer. Then I can wire first to a junction then on to the pc fans and BOB. This way if the toroidal transformer is one then the fans are running and less leads coming into the box.

I hope 1amp is enough, PC fan's are ~0.2amp I guess it doesn't need much to generate the control signal for the vfd.

Can I wire the stall detection output from 1 AM882 to the next then the last AM882 in the chain to the BOB?

Short answer - no!

Longer answer - the AM882 use an open-collector output. Think of it as being a normally-open switch that closes when there is a fault (like a stall). What you can do is wire them all in parallel and then to the BOB input. I do this with the EM806 on my machine and it works fine.

Attachment 23229

A little bit closer, ready to mount the box and start running the motor's and home switches. Need to mount the VFD as well so I can run the wiring 12v adapter won't be here till Monday.

Need holesaw for the fans mate has my cheapo set so going to see him tonight little bastard keeps forgetting it.

Does this look correct it's the pulse and dir +'s connected to BOB pc 5v

Attachment 23237
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