DIY PSU build query...

[joe.ninety]

Hi,

I've been reading the following thread:

http://www.mycncuk.com/threads/11628-First-Proper-CNC-Router


and I've got a question regarding a DIY bulit power supply that is mentioned in post #9 and my question is regarding the current output....

Jazz recommends against using the Zapp Automation one (in post #8) as it maxes out at 6A, but from what I can tell the specs for the DIY version that is recommended and built using a 500VA 45V are exactly the same and it's output is 6A too.

The only 230V single primary that they (Rapid) sell is a 500VA one.

So my question is...

What kit/parts do people use if they want their DIY PSUs to provide more than 6A output? To enable future use of additional motors?

Cheers

[AndyUK]

https://www.rapidonline.com/single-primary

Are you sure they only sell a 500VA one?

Edit: oh I see. You're saying only one that has two 45V secondaries.

In that case you just have to play around with the secondary voltage, e.g. using 2x25V in series, or go to a different supplier.

[joe.ninety]

Hmmm, the more I think about it the solution seems to be to wire the two 45V outputs from the 500VA tranny in parallel thereby doubling the output amperage to 12A.

[AndyUK]

Yes sorry didn't do the maths on your numbers and didn't realise you were only talking about a single secondary. Wiring in parallel was assumed. 500VA will net around 12A at ~64V.

[Clive S]

and I've got a question regarding a DIY bulit power supply that is mentioned in post #9 and my question is regarding the current output....

What will the drives take as max voltage and will the drives take AC and well as DC

[Doddy]

Wiring secondaries in parallel is a perfectly acceptable solution - just remember you need to make sure the phase of each secondary is matched (you normally find one end of each secondary marked on any schematic with a 'dot' - wire dot-to-dots and non-dots-to-non-dots... if that makes sense). Don't worry, if you get it wrong your fuse will politely inform you.

The only issue to consider is that the power loss in a system rises as a square of the current drawn - you'll have less losses for a given wiring CSA if you can distribute your load across individual secondaries, rather than wiring everything to parallel secondaries. But, provided you over-spec the wiring, and/or avoid daisy-chains on the power distribution then you shouldn't have problems.

[joe.ninety]

I should explain...

Probably like most people who are new to CNC'ing, once the bug bites I just want to get on with something ASAP. Unfortunately, I've come to discover that every decision seems to rely on another until you've gone full circle and are back at the start ;-) Well that's how it feels anyway.

I was hoping that the PSU would be something that it was possible to get started on, and that it would be possible to 'spec' one up that could work across a variety of motor choices, and also still be usable in the future on possibly a larger machine. So essentially an over engineered/spec'ed one.

My curiosity was piqued by Jazz saying that a 6A PSU didn't allow much leeway for expansion. So as I stated, I just wondered what people were using if they wanted 45V but at a higher VA output. Was the reason that 45V was recommended over 50V simply because the 50V version has a lower current output... 5A on the 50V compared with 5.56A on the 45V?

The simple answer might be to just buy another brand as Andy suggested.

Cheers

[Desertboy]

I built my own PSU there was nothing to it just a transformer, bridge rectifier and 3 capacitors.

It sounds far scarier than it actually is took about an hour including time to smoke cigs and drink tea.

I have since quit smoking so I think 30 mins is realistic.

[AndyUK]

Yeah, it's not difficult just be aware of the safety.

Plus, if you get AC drivers it's just the torrodial. Nothing else.

Doing it beforehand however is not your best plan, bit of a false economy because you'll end up with something that isn't quite right or you'll make compromises on the rest of the build to suit.

First, figure out what you want to cut. Materials, sizes.
Then work out your physical constraints on machine size.
Then find a similar build log and start CADing. As you come up against different problems look to other build logs for solutions then add your own twist. It's just not worth spending time and money until you know what you want and have speced it out across the board.

[Kitwn]

I should explain...

Probably like most people who are new to CNC'ing, once the bug bites I just want to get on with something ASAP. Unfortunately, I've come to discover that every decision seems to rely on another until you've gone full circle and are back at the start ;-) Well that's how it feels anyway.


Every answer raises two new questions. You'll have to get used to it I'm afraid!

There are plenty of sources of transformers. Have a look at RS Components for example. Even if you don't buy from them, you'll get an idea of the range available. Note that the DC voltage (that's appalling English, but everyone knows what it means) you will get from a finished supply is higher than the RMS voltage rating of the AC transformer, if a DC supply is what your drivers require. I've linked to the site linked below before but it's a good intro to DC PSU design. A supply for a CNC machine can be allowed to have quite a high ripple voltage and thus less capacitance than would be needed for, say, a hi-fi audio amplifier.

http://www.skillbank.co.uk/psu/

[JAZZCNC]

My curiosity was piqued by Jazz saying that a 6A PSU didn't allow much leeway for expansion.

This here is exactly why you shouldn't buy anything until you fully understand what's been said and why.!

My suggestion to that person to use a toroidal over a the 6A PSU would have been based on them using both the secondary coils.

Building a PSU isn't difficult and the best choice for a CNC machine but you can't just guess at it.

My strong advice is DONT buy anything until you have researched exactly what your building and what components your going to use. Even then the electronics are best left until the end of the build.

If your not sure what you need then ASK don't read posts taking bits from here and there because often you'll put 2 & 2 and end up at 6 because there are so many different ways of doing this it's easy to misunderstand, even if you think you do.! So Unless your 100% sure it's correct for your needs then just ASK for a second opinion before buying.

[Desertboy]

This here is exactly why you shouldn't buy anything until you fully understand what's been said and why.!

My suggestion to that person to use a toroidal over a the 6A PSU would have been based on them using both the secondary coils.

Building a PSU isn't difficult and the best choice for a CNC machine but you can't just guess at it.

My strong advice is DONT buy anything until you have researched exactly what your building and what components your going to use. Even then the electronics are best left until the end of the build.

If your not sure what you need then ASK don't read posts taking bits from here and there because often you'll put 2 & 2 and end up at 6 because there are so many different ways of doing this it's easy to misunderstand, even if you think you do.! So Unless your 100% sure it's correct for your needs then just ASK for a second opinion before buying.

Wise man that Jazz you should listen to him.

[Clive S]

I was hoping that the PSU would be something that it was possible to get started on, and that it would be possible to 'spec' one up that could work across a variety of motor choices, and also still be usable in the future on possibly a larger machine. So essentially an over engineered/spec'ed one.


You still haven't answered post #5 What will the drives take as max voltage and will the drives take AC and well as DC

You have not said what drives you want to use as a lot of drive these day only need AC input ie just a toroidal

[Desertboy]

You still haven't answered post #5 What will the drives take as max voltage and will the drives take AC and well as DC

You have not said what drives you want to use as a lot of drive these day only need AC input ie just a toroidal

That's the $64000 question isn't it.

I built a 70v PSU which means if I change my drivers they would have to be in that range or I need a new transformer.

I think mine is 1kva so I think I could run pretty much anything in the Nema23 profile on all 3 axis (4 motors) without blinking.

[joe.ninety]

You still haven't answered post #5 What will the drives take as max voltage and will the drives take AC and well as DC

You have not said what drives you want to use as a lot of drive these day only need AC input ie just a toroidal

I've haven't said because I don't yet know :cheerful: I thought me saying the bit about making something that was over 'spec'ed' and that could work with a variety of choices would make that clear but I guess not and I'm sorry for misleading you. It would seem Desertboy in #14 has done exactly the sort of thing I was alluding to.
Anyway, I'm not going to ask any more questions until I've put more flesh on the bones, but that in itself is difficult if i don't know what I've got in mind is possible. I'm just trying to gather some underlying info and knowledge that means I don't end up wasting either my time or others in coming up with designs that don't have a hope of being good.

Cheers

[JAZZCNC]

That's the $64000 question isn't it.

I built a 70v PSU which means if I change my drivers they would have to be in that range or I need a new transformer.

I think mine is 1kva so I think I could run pretty much anything in the Nema23 profile on all 3 axis (4 motors) without blinking.

First let me say I'm not having a go at you or anyone with this post, it's just to make my point.!

Posts like these are what confuse folks and lead them to add up the wrong numbers. The Va rating won't kill your drives but choosing the wrong Voltage will fry them in a heartbeat.

Likewise, some of the other posts that are overly technical and made by people who know electricity don't always help either and add to the confusion because they talk in technical jargon that the person seeking information doesn't understand, or really needs to know to build a PSU suitable for CNC.

Sometimes I just wish those posting would take into consideration the knowledge level of the person seeking help and answer accordingly, in ways that don't blow people's minds. Or at least try to find the persons knowledge level and then explain in such ways that explain the technical jargon.

We all try to help with the best of intentions, which is great, but I do think that often the more technical minded could answer in simpler ways. This is why often some of my posts can bang on a bit because I'm always trying to answer in the simplest ways possible mindful that for every 1 person asking the questions there will be 10+ silently watching who say nothing. It's these people who often fall foul of misunderstandings because we can't know there knowledge level and answer accordingly.
Yes it's there fault not ours, they should speak up, but we can keep the jargon to a minimum, or at least explain it clearly so there's no confusion.

So ASK is the message to all those reading who never speak up.! . . . . . But to all you clever bugger who know it all just keeps it simple please and the jargon down.

[dazp1976]

This one matey. 2*50v 1000va. Bosh.
https://uk.rs-online.com/web/p/toroidal-transformers/1234006/

[JAZZCNC]

Anyway, I'm not going to ask any more questions until I've put more flesh on the bones, but that in itself is difficult if i don't know what I've got in mind is possible. I'm just trying to gather some underlying info and knowledge that means I don't end up wasting either my time or others in coming up with designs that don't have a hope of being good.

No don't stop asking questions. Start a Build thread and ask all your questions in there. Don't worry about asking what may feel like dumb questions or offering up weird and wonderful suggestions. This way everything related to your machine is in one place and others coming to the party late can look back and see what's been said before.


This one matey. 2*50v 1000va. Bosh.
https://uk.rs-online.com/web/p/toroidal-transformers/1234006/

Not sure who that's aimed at but 1000Va is on the large side and not really needed for anything but larger motors on typical 4 axis machine. Also for anyone with 70Vdc drives then 50Vac Secondaries are too large because they will be right at the 70Vdc mark so not enough safety margin. Always leave roughly 10% safety margin from the drives Max volts. Only use 50Vac secondaries with 80Vdc drives.

[dazp1976]

I would forget places like zapp automation. The u.k. has some junk available.
If I did my mill again I would:
1. Go closed loop.
2. I'd get AC powered drivers 20-80vac like:
https://www.ebay.co.uk/itm/EU-Ship-Wantai-CNC-Closed-Loop-Servo-Motor-Driver-SS880-8-2A-20-80VAC-/223484030824
3. Get 2 toroidal 35vac supplies wired in series for 70vac (7.14A) and wire them direct to 2 drivers each for 4 axis. These would leave headroom as the idle voltage would be above 80v. like:
https://uk.rs-online.com/web/p/toroidal-transformers/1233994

[Desertboy]

No don't stop asking questions. Start a Build thread and ask all your questions in there. Don't worry about asking what may feel like dumb questions or offering up weird and wonderful suggestions. This way everything related to your machine is in one place and others coming to the party late can look back and see what's been said before.



Not sure who that's aimed at but 1000Va is on the large side and not really needed for anything but larger motors on typical 4 axis machine. Also for anyone with 70Vdc drives then 50Vac Secondaries are too large because they will be right at the 70Vdc mark so not enough safety margin. Always leave roughly 10% safety margin from the drives Max volts. Only use 50Vac secondaries with 80Vdc drives.

I use 45v secondary's when wired in serial and rectified gives me 72v without load and 68v with load.

I also have a 50v one I don't use which gives 78v without load and 73v with load, I bought 2 because when Maplins went bankrupt they sold them 1/2 price and that's when I built the PSU.

Also I blew up the first transformer I bought which I paid full whack from RS for, wired the rectifier the wrong way round I seem to remember. So buying 2 was my insurance policy lol.

It's also the reason I got 1Kva transformers there's was a limited choice of what was left, was in the voltage range and was cheap.

[Doddy]

I use 45v secondary's when wired in serial and rectified gives me 72v without load and 68v with load.

I also have a 50v one I don't use which gives 78v without load and 73v with load, I bought 2 because when Maplins went bankrupt they sold them 1/2 price and that's when I built the PSU.

Also I blew up the first transformer I bought which I paid full whack from RS for, wired the rectifier the wrong way round I seem to remember. So buying 2 was my insurance policy lol.

Sorry, pedantic mode (it might be important for someone blindly following this to avoid damaging drivers etc.):

Wired two 45V windings in series and you get 72V DC off load?, there's something amiss there. Perhaps in parallel? - I'd expect a 45Vrms winding to present around 64Vpk-pk, probably 62V after rectification and smoothing. Add 10% for the 220VAC rated primary and the nominal 240VAC UK supply and you're getting within a gnats of the 72V.

Two 45V windings in series you should expect 90VACrms, leading to around 128Vpk-pk, around 126V after rectification and smoothing. And then you can play games with the 220VAC primary versus nominal UK supply.

For reference, I also bought a toroidal tx from Maplin on closure...

27463

That pokes out 72V off-load, rectified and smoothed, measured with cheap Chinese current/voltage DMM panel meters. Two secondaries driving two separate circuits - but this should give the same voltage as two secondaries in parallel (not series). The maths for mine = 50VAC * SQRT(2) - 2 * Vf(rect) = 69V - within about 5% of measured - I'm happy with that.

[Desertboy]

Sorry, pedantic mode (it might be important for someone blindly following this to avoid damaging drivers etc.):

Wired two 45V windings in series and you get 72V DC off load?, there's something amiss there. Perhaps in parallel? - I'd expect a 45Vrms winding to present around 64Vpk-pk, probably 62V after rectification and smoothing. Add 10% for the 220VAC rated primary and the nominal 240VAC UK supply and you're getting within a gnats of the 72V.

Two 45V windings in series you should expect 90VACrms, leading to around 128Vpk-pk, around 126V after rectification and smoothing. And then you can play games with the 220VAC primary versus nominal UK supply.

For reference, I also bought a toroidal tx from Maplin on closure...

27463

That pokes out 72V off-load, rectified and smoothed, measured with cheap Chinese current/voltage DMM panel meters. Two secondaries driving two separate circuits - but this should give the same voltage as two secondaries in parallel (not series). The maths for mine = 50VAC * SQRT(2) - 2 * Vf(rect) = 69V - within about 5% of measured - I'm happy with that.

The bridge rectifier drops the voltage, it converts AC to DC you connect both outputs in series run it through the rectifier and 72v out the other side in DC.

You need capacitors to clean up the DC.


In center tapped full wave rectifier, only one diode conducts during each half cycle. So the voltage drop in the circuit is 0.7 volts. But in the bridge rectifier, two diodes which are connected in series conduct during each half cycle. So the voltage drop occurs due to two diodes which is equal to 1.4 volts (0.7 + 0.7 = 1.4 volts). However, the power loss due to this voltage drop is very small.

https://www.physics-and-radio-electronics.com/electronic-devices-and-circuits/rectifier/bridgerectifier.html

[Clive S]

I use 45v secondary's when wired in serial and rectified gives me 72v without load and 68v with load.



Are you sure you about the serial or do you mean parallel ?


The bridge rectifier drops the voltage, it converts AC to DC you connect both outputs in series run it through the rectifier and 72v out the other side in DC.

You need capacitors to clean up the DC.


I think you need to re visit this as I don't think you understand it. It is also misleading for others.

Doddy is correct.

[JAZZCNC]

The bridge rectifier drops the voltage, it converts AC to DC you connect both outputs in series run it through the rectifier and 72v out the other side in DC.

You need capacitors to clean up the DC.



https://www.physics-and-radio-electronics.com/electronic-devices-and-circuits/rectifier/bridgerectifier.html

You need to SHUT UP until you know what your talking about because your going to cause people serious damage with your WRONG information.

[Desertboy]

I should just link the Clive S build it's how I built mine, 2 years ago bad memory.

Whatever I did I did it right I just copied Clive S's build, 3 capacitors to smooth the DC.

This is what it tests out at without load
27464

[JAZZCNC]

I should just link the Clive S build it's how I built mine, 2 years ago bad memory.

Whatever I did I did it right I just copied Clive S's build, 3 capacitors to smooth the DC.

Yes, you should have because Clive S knows what he's doing unlike you.!

Giving information out like you are doing without actually knowing what you did or why is dangerous. The only reason it works for you is that Clive S does know what he's doing and knows the difference between Series and Parallel so sized the transformer secondaries correctly.

If you had wired those 2 x 45 in series then your drives would now be toast and anyone reading your WRONG information would also fry their drives because of you.! . . So please don't post anything about anything electrical unless your 100% sure you know what your doing or why you have done what you copied from someone else because your not helping, your actually dangerous.!

[Doddy]

I should just link the Clive S build it's how I built mine, 2 years ago bad memory.

Whatever I did I did it right I just copied Clive S's build, 3 capacitors to smooth the DC.

This is what it tests out at without load
27464

Refer to post 330 of your own build log - you wired your secondaries in parallel.

[Kitwn]

You need to SHUT UP until you know what your talking about because your going to cause people serious damage with your WRONG information.

A little knowledge is a dangerous thing. Sometimes you really do need to make the effort to understand the subject correctly. Read the information in the first page or two of the link I gave in post #10.

It's also worth noting that anything other than a 'True RMS' meter can give false readings of voltages that are neither continuous or sinusoidal, as seen at the output of a rectifier without smoothing capacitors.

[joe.ninety]

Posting error.

[Doddy]

Posting error.

Maybe, but a good price, if they’ll honour it!