DIY PSU build query...

**JAZZCNC** · 20-02-2020

Originally Posted by joe.ninety

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** · 20-02-2020

Originally Posted by JAZZCNC

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** · 20-02-2020

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** · 20-02-2020

Originally Posted by Clive S

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** · 20-02-2020

Originally Posted by Clive S

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

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** · 20-02-2020

Originally Posted by Desertboy

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** · 21-02-2020

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

**JAZZCNC** · 21-02-2020

Originally Posted by joe.ninety

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.

Originally Posted by dazp1976

This one matey. 2*50v 1000va. Bosh.
https://uk.rs-online.com/web/p/toroi...rmers/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** · 29-02-2020

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-W...-/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/toroi...ormers/1233994

**Desertboy** · 29-02-2020

Originally Posted by JAZZCNC

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.