View Full Version : Guidance please ...

13-11-2010, 09:02 AM
Hi Guys, A little guidance please. I have a DIYCNC System 4 Board which states a 24V to 30V regulated (Absolute max) Supply input, with the onboard driver cards using 2.5A max. I would like to build my own, so ... I know I will need a transformer, bridge rectifier and a goodly size smoothing capacitor. That much I can remember from my dim and very distant past. I have seen transformers that output 10V,15V,35V, but not 30V, How do I go about building such a creature?

John S
13-11-2010, 10:10 AM
Best to err on the 24 volt side than go to 30 v.
However the Xformer you need is actually less than 24 volts because of the action of the smoothing capacitor.

From the figure you give, take a 15 volt Xformer, feed it thru a bridge rectifier and you still get 15v but now DC, now wang this thru a 11,000uf cap to smooth it and you get 21.2 volts which is a product of output volts X 1.414 [ formuales is lifth different to this but this is a good rule of thumb ]

18 volt tranny gets you 25.45
20 volt tranny gets you 28.28

but a 24 volt one will get you 34 volts.

RS do some decent trannies, to get an idea look at 671-9038 (http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6719038)

Robin Hewitt
13-11-2010, 10:20 AM
20VAC will get you 28.28VDC until the mains surge when everything goes pop!

Been there, done that :naughty:

John S
13-11-2010, 10:26 AM
That's why I advised an 18 volt tranny, gives a bit of breathing space, fitted a few of these to Roy's old system3 boards when he did them, not a big believer in all on one board but they worked fine in a cost critical application and more to the point, are still working.

13-11-2010, 12:30 PM
or just buy a 24v psu