[bertvk]

I'm building the power supply for my stepper motors and seem to get very strange readings on the output. I'd like to have your thoughts.

Here's the setup:
transformer converting 220V to 30V at 5A (regular resin cast transformer)
6A diode brigde rectifier
3 capacitors of 3300 µF, 50V in parallel (9900µF in total)

The output voltage of the transformer is 34V AC. The DC voltage behind the capacitors is 47V DC, which is normal and to be expected (1.4 * 34).

Here's the strange thing: I also get an AC voltage of 104V on the output!!!! What can be the cause of this? If I were to hook it up I guess I'd frie my stepper board.

I checked everything twice. There are only 5 parts to check, so it doesn't take that long.

[tachus42]

You have a cheap meter which dosn't really read the ac. It just switches in one diode in series with its input and then doubles the reading to account for the fact it's only getting voltage for half the cycle. Try reversing your meter leads when you make the AC measurement you should see zero then.

[Al_The_Man]

One possibility is to look at what kind of VOM you are using to measure, if it is a modern low impedance electronic type, most are only accurate on the AC range with a true rms voltage. And can give all sorts of odd readings if used otherwise. If you have an older moving coil meter that is around 1000 ohms/volt it will probabally give a very different reading. The other thing that alot of users of Hi Imp meters is reading due to leakage such as through a solid state relay that is in the OFF condition showing like it is conducting due to a full voltage indication. Also put a fairly high load on the output of the PS and see if that makes a difference.
Al

[bertvk]

Thanks guys.
It didn't make any sense to me and I didn't want to blow up my electronics, so I wanted a second opinion. I have no degree in electronics, so I wasn't sure if I overlooked something.

I got me a better DMM and now everything is spot on. I guess the cheap DMM I used first had a bit of a problem with the ripple on the voltage.
All's wlel now and I can continue putting the electronics in the case. :-D