Transformer calculation

[CNCDevil]

Hi,

I'm going to build an unregulated PS for my new router. Even though I'm quite sure that this is correct, please confirm that the calculations are ok:



Transformer:

2/3 (bipolar) * 4 steppers * 6 A/ph = 16A

40VAC secondary * 16A = 640VA

The closest match in this range is a 625VA transformer.


Capacitor: (50Hz)

(100,000 * 16A) / (40*1,414) = 28,000 uF



4 (or more eyes) are always better than 2.


Thanks

[CNCDevil]

Read and lean!

I have read some papers concerning the ripple voltage, which is why the filter capacitor must be added. I conclude that the bigger the capacitor is, the better.

I can't get hands on any capacitors larger than 3300uF where I live, but I'll just put 10 in parallel.

There is actually no reason for writing this, but now the thread at least have a little value for others that seek info on this issue.

[Al_The_Man]

Originally Posted by CNCDevil I conclude that the bigger the capacitor is, the better. I can't get hands on any capacitors larger than 3300uF where I live, but I'll just put 10 in parallel.

A little known fact is that if you when you run close to the maximum current capacity of the supply, any increase in capacitor size requires an increase in transformer VA sizing.
Al.

[CNCDevil]

Do you mean that the transformer power will decrease when using a capacitor larger than the calculated, when running close to max. rated amp?

Would you please explain why this is happening or give me a link to where I can read this stuff?

I guess you are saying that the best thing to do, is just keep the ripple voltage withing 10% of the rectified voltage. at max. amp. output of the transformer?

[Al_The_Man]

Here is my divshare link, the pdf was too large to post.
http://www.divshare.com/download/8224888-77e
Al.

[CNCDevil]

Nice document. I will probably need to read it trough a couple a times to get the hang of it, but it's definitely worth it.


Thanks so far Al