Power Supply 0-30V 2mA-3A Troubleshooting

[Growling_Mango]

Hi!

I'm trying to build a variable voltage DC regulated power supply that is 0-30v and 2mA-3A. The problem I'm having is that as soon as I plug it into get a reading on my multimeter it reads 34v, even if I try turning the pot it does not change. I've rewired the pots and made sure the transformer is working so I believe I might have wired something wrong on the board itself. This is a kit that I bought to get some experience with soldering components and kind of learn a bit about how circuits work so I'm a bit in the dark and can only troubleshoot so far. I'm not exactly sure what I did wrong and any help would be appreciated.

 

[berkeman]

Hi!

I'm trying to build a variable voltage DC regulated power supply that is 0-30v and 2mA-3A. The problem I'm having is that as soon as I plug it into get a reading on my multimeter it reads 34v, even if I try turning the pot it does not change. I've rewired the pots and made sure the transformer is working so I believe I might have wired something wrong on the board itself. This is a kit that I bought to get some experience with soldering components and kind of learn a bit about how circuits work so I'm a bit in the dark and can only troubleshoot so far. I'm not exactly sure what I did wrong and any help would be appreciated.

Welcome to the PF.

Can you use the UPLOAD button to show us the schematic? If you could post a picture of the finished kit, that would help as well.

 

[Growling_Mango]

Here are the photos.

 

[berkeman]

Here are the photos.
View attachment 99169 View attachment 99170

Nice!

So the schematic has node numbers on many of the nodes. Does the documentation give typical DC voltages for each of those nodes with respect to ground that you should be able to measure? That would help a lot in troubleshooting the circuit. What do you use for the transformer input to the bridge rectifier at the left of the circuit?

 

[Growling_Mango]

They do not have DC voltages for the nodes unfortunately. I may be misunderstanding the last question but the transformer I'm using is this http://www.newark.com/hammond/166m24/isolation-transformer-24v-72va/dp/51R4207, if that answers your question.

 

[Growling_Mango]

I actually just found out what the problem was! It turns out my solder job wasn't has good as I thought and after closely inspecting it found a few dry joints.

 

[dlgoff]

... after closely inspecting it found a few dry joints.

Were those for the power diodes by chance? A good rule of thumb, for me anyway, is apply enough iron/solder contact to see the solder coming completely up the thru-holes.

Nice work, BTW.

 

[Averagesupernova]

Yes this does look like nice work. I think kits are probably given less credit than they deserve as teaching tools. Now that it is up and working go ahead and make some measurements at various places in the circuit and write those figures down. Then work through it and get it straight in your head as to WHY those figures are what they are.
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To add what dlgoff said, the power diodes as well as some of the headers probably have the largest amount of metal to heat which would make them the most difficult to get enough heat into to get a good solder joint.

 

[Growling_Mango]

Were those for the power diodes by chance?

To be completely honest I'm not too sure which connection it was. I ran through a bunch of them again just to make sure everything was set. I jumped into this thing with a very limited amount of knowledge so it's been fun working through it and figuring everything out, even if it's little by little. Thanks for the help guys!

 

[Averagesupernova]

I didn't do much, but you're welcome. Sometimes my frustration with beginners is off the scale. Not here. You asked the question, did what you were asked, and in the meantime you went about it by yourself and solved the problem. Again, your work looks nice.

 

[Tom.G]

Nice job Growling_Mango, you did it! ...and welcome to the crowd of electronikers!

 

[jim hardy]

I think kits are probably given less credit than they deserve as teaching tools.

Agreed to the Max ! We learn 10X more by doing than by only reading about doing.