Confirming PSU spec for steppers.

[Rogue]

So...

...this 500VA 35V-35V transformer would let me connect the two outputs in series to get [email protected]. By the time it has lost a few volts through the additional components (rectifier etc) I would have 68.6V (I think it's 1.6V drop for suitable rectifiers?). This 30V-30V would give me 58.4V - with 57.2V being the minimum rather than the optimal that I had thought it represented - so it would be the bottom line option.

Daft question, is it feasible to knock the output down a bit from a transformer, short of fiddling with the number of turns?

[JAZZCNC]

No the 35V is AC so needs to be rectified which makes it times 1.4 so that would be 35 +35=70 x 1.4= 98Vdc. . .Boom.!!

You need 25V to give 70Vdc.

Yes can fiddle with turns but why would you.? Just buy the appropriate transformer.??

[Rogue]

No the 35V is AC so needs to be rectified which makes it times 1.4 so that would be 35 +35=70 x 1.4= 98Vdc. . .Boom.!!

You need 25V to give 70Vdc.

Yes can fiddle with turns but why would you.? Just buy the appropriate transformer.??

Ahh, yeah that might not be what I'd want then. I was asking about the fiddling because I was wondering, I certainly don't want to fiddle...

[Jonathan]

Ahh, yeah that might not be what I'd want then. I was asking about the fiddling because I was wondering, I certainly don't want to fiddle...

You can wind a few extra turns on, or vice versa, then add the appropriate insulation. It's a crude but successful way of tweaking the voltage of a toroidal transformer that's not quite what you want...it shouldn't be needed here though as you can just buy the right one.

[Rogue]

Ahh hold on, wait a second. It would be 25V if the outputs were connected in series (thereby doubling the V while maintaining the A), so 25+25*[email protected]. If a transformer with 50V-50V 625A had the outputs wired in parallel, would this give 50V*1.4=70 @ 625+625 / 70= 17.8A?

[JAZZCNC]

Yes 50v wired parallel is double the amps but they are half the rating of the 25V so workout the same.

[Rogue]

Could you just clarify what you mean by rating in that context? VA? I ask because the only way I understood that the 25V wired in series would equal the amps from the 50v wired in parallel would be for the 25V to start with double the VA, ie

50V-50V 500VA parallel would be: 50*1.4 = 70V@500+500 / 70 = 14.2A
25V-25V 500VA series would be: 25+25*1.4 = 70V@500 / 70 = 7.14A
so you would actually need 25V-25V 1000VA to get: 25+25*1.4 = 70V@1000/70 = 14.2A

There's clearly something fundamental I'm missing here.

I really appreciate both of your inputs, time and patience, just in case I didn't mention it already!

[Jonathan]

When you put the windings in series add the secondary voltages, but at the same current. In parallel you get the same voltage as for one winding but twice the current. Either way the VA rating has to remain constant for the same transformer.

[JAZZCNC]

Just what Jonathan says but to make it clearer look at the transformer output current ratings for these two transformers.

Both are 625Va but first is 2x25V second is 2x50v.

Standard Range Toroidal Transformers: CM0625225: 625VA 230v to 2x25v

Standard Range Toroidal Transformers: CM0625250: 625VA 230v to 2x50v

If you wired the 2x25V in parallel not series you'd still have 25V but @ 24A So obviously 2x50V in paralle is 50V @12A (6A x 2)

[Rogue]

Now, are you agreeing with me or correcting me? Because what you said is what I thought I said, if you follow me.