Confirming PSU spec for steppers.

[Rogue]

Never being one to rush things, I've now got a toroidal transformer sitting on the bench ready to get wired up!

Specifically, this: Toroidal Transformer 625va 0-50v 0-50v --- link to Data Sheet PDF

I understand from the Data Sheet that:

• on the Primary side, I want to wire the Grey and Violet wires together, thereby wiring it in series to handle 230Vac from UK mains,
• the Blue wire is now 0V and the Brown wire is now 230Vac, then
• on the Secondary side, I want to wire the Orange and Black together, then the Yellow and Red together, and
• the Orange/Black is now 0V and the Yellow/Red is now 50Vac.

Wiring it in parallel will give me 50Vac @ 12.5A.
After being rectified this will give me 70V @ 12.5A (less voltage drop across the bridge rectifier)

Is anyone happy to cast their eye over the datasheet and confirm that I'm connecting up the right wires before this goes anywhere near the mains? The instructions look straightforward, but I've said that about lots of things that later went horribly wrong

The original drivers I was looking at from Zapp are now discontinued. The alternative (DM856) has a max supply voltage of +80, which I understand to be a comfortable margin for this PSU. The closest driver current options, however, are slightly different - 3.8A or 4.3A, whereas my steppers are 4.2A. The old PM752's would provide 4.02A as the closest fit. Is there a significant enough difference in the current provided that would make it worthwhile hunting for different drivers, or is 3.8A fine? These will now be driving an X2, which I'll be using as a stepping stone to my initial DIY design.

The good news is that I should be finished by 2016, possibly late 2015 if I pull my finger out...

[JAZZCNC]

The original drivers I was looking at from Zapp are now discontinued. The alternative (DM856) has a max supply voltage of +80, which I understand to be a comfortable margin for this PSU. The closest driver current options, however, are slightly different - 3.8A or 4.3A, whereas my steppers are 4.2A. The old PM752's would provide 4.02A as the closest fit. Is there a significant enough difference in the current provided that would make it worthwhile hunting for different drivers, or is 3.8A fine? These will now be driving an X2, which I'll be using as a stepping stone to my initial DIY design.

Spend little more and Get the AM882 with lead and you can program them to exact amps and much more, they are great drives.

[Clive S]

Wiring it in parallel will give me 50Vac @ 12.5A.
After being rectified this will give me 70V @ 12.5A (less voltage drop across the bridge rectifier)

..

A small problem with wiring the secondary in parallel is that if the amount of turns on them is not exactly the same the transformer is not as efficient.
I got around this by rectifying the two windings separately then combining them at the DC side.
Just a thought. ..Clive

[Rogue]

Spend little more and Get the AM882 with lead and you can program them to exact amps and much more, they are great drives.

Intriguing. I've seen a bit posted about the AM882 drivers but a lot of it didn't seem positive. On some further reading, most of the issues seem to be down to user error and misconfiguration. The price difference at this stage is minimal as well.

Is it better to match up the driver output with the motor rating exactly, or leave a bit of a margin?

A small problem with wiring the secondary in parallel is that if the amount of turns on them is not exactly the same the transformer is not as efficient.
I got around this by rectifying the two windings separately then combining them at the DC side.
Just a thought. ..Clive

Also intriguing, though how would you establish that? Would it be as straightforward as checking the voltage from each output separately? I suspect I will take the easy way out and just use the one rectifier, but I'm intrigued by the idea.

[Clive S]

Also intriguing, though how would you establish that? Would it be as straightforward as checking the voltage from each output separately? I suspect I will take the easy way out and just use the one rectifier, but I'm intrigued by the idea.

I have just joined the two outputs from the caps together with no problems at all. ..Clive

[Jonathan]

Is it better to match up the driver output with the motor rating exactly, or leave a bit of a margin?

In theory you should be safe to run any driver up to its rating, since that's the whole point of a rating, if you can trust it. In reality however it's always best to overrate the drivers if you can, since then they will run at a lower temperature which prolongs the life of the components.

Also intriguing, though how would you establish that? Would it be as straightforward as checking the voltage from each output separately?

Yes - the difficult bit is determining how much of a mismatch would pose a problem.

[Rogue]

In theory you should be safe to run any driver up to its rating, since that's the whole point of a rating, if you can trust it. In reality however it's always best to overrate the drivers if you can, since then they will run at a lower temperature which prolongs the life of the components.

Hi Jonathan, thanks for chipping in again. I'm still aiming to finish this before you finish at Uni so I'll need you to work towards a PhD, should give me enough time.

I was thinking about this from the point of view of the stepper motors (4.2A) rather than the drivers. Either of the two drivers discussed are rated higher than the stepper (up to 5.2A for the DM856, up to 8.2A for the AM882) so there is plenty of margin. My question was whether it's better to run the steppers at their max or give them a bit of a margin. If your answer still applies (which logic suggests it does) then it seems reasonable to set the drivers for a little under 4.2A.

[JAZZCNC]

In short it's extremely unlikely for the windings to be mismatched enough for either method to cause problems, so although I'd advise buying a transformer rated for half the voltage so you can put the secondarys in series, if you find one for the right price which has to be wired in parallel I wouldn't worry.

Agree here and I've built both ways and never seen any difference to machine which is what matters at end of day. I buy what's cheapest or available and don't care which.

Intriguing. I've seen a bit posted about the AM882 drivers but a lot of it didn't seem positive. On some further reading, most of the issues seem to be down to user error and misconfiguration. The price difference at this stage is minimal as well.

Is it better to match up the driver output with the motor rating exactly, or leave a bit of a margin?

Yes there have been but that's mostly been because they have little experience or never used digital drives before but trust me they are fantastic drives and give super smooth performance with great resonance handling. The Fact you can configure them thru software helps if you have problems with resonance or just want to get the best performance you can.

Yes it's always better to match current to motor ratings but not go higher. The only margin you want to leave is on the voltage but it's also always better if the drives are not max'd out on current IE max current setting = motor current so the drives not working flat out.!

[Rogue]

Yes it's always better to match current to motor ratings but not go higher. The only margin you want to leave is on the voltage but it's also always better if the drives are not max'd out on current IE max current setting = motor current so the drives not working flat out.!

That answers that question, I should have waited another minute or two before replying! There's approximately 10V difference between the transformer output and the driver max input which should hopefully be fine.

[JAZZCNC]

That answers that question, I should have waited another minute or two before replying! There's approximately 10V difference between the transformer output and the driver max input which should hopefully be fine.

Yes 10V will be fine and the fact your using toroidal transformer helps further still because the caps will absorb back EMF better.