DIY PSU build query...

[joe.ninety]

Hi,

I've been reading the following thread:

http://www.mycncuk.com/threads/11628...per-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

[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

[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/

[dazp1976]

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

[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.