# Thread: Confirming PSU spec for steppers.

1. Originally Posted by Rogue
Hand holding? I would rather throw my ideas out and be corrected so that my understanding improves, but I'm sure some handholding creeps in unwittingly. My apologies if it does because that's not what I want to do.
Yep I understand but Wasn't offering to do it for you just over look and backup.!! An experienced eye watching over never hurts only affirms you've learnt correct.

2. 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*1.4=70V@8.9A. 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?

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

4. 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!

5. 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.

6. 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)

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

8. Ahh, wait a second. Is the 625VA shared between the two outputs or per output?

9. Originally Posted by Rogue
Now, are you agreeing with me or correcting me? Because what you said is what I thought I said, if you follow me.
Who you asking Jon or Me.? Either way we are both saying series you 2 x volts 1xamps or parallel 1 x volts 2 x Amps. . . BUT . . the amp output rating for 25v transformer are double the 50V.!

10. So we were saying mostly the same thing. That's a good start :)

I think I've worked out where my mental block is for this element at least. I was treating parallel as increasing A rather than decreasing the division of A. In other words, I was thinking of two outputs, each with 50V 625VA. Parallel would make this one output of 50V 1250VA. Rather, I should be looking at it as two outputs of 50V sharing 625VA between them - effectively making it 100V / 625VA = 6.2A. Wiring it in parallel would then have the same VA but divided by less, which has the same end effect as doubling it: 50V / 625VA = 12.5A. When I look at it like this, your previous comments make more sense so I guess I'm on the right track.

And you wonder why I get jittery with mains power

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