Cheap P/S questions: PS-305D

[outofstepper]

Greets all.
Great place you have here.  Love Dave's videos and those are what eventually brought me here.
I'm a hobbyist but even that sounds a little overkill.  Started when I was teen with the Forrest Mimms books
at radio shack . . . am coming back to the hobby and slowly building my kit.

So not wanting to spend a lot of money (don't know how many times I need to make this same mistake!) I
picked up a PS-305D for about $50.  I'm sure you all know it, import, 30V / 5A.

I just found Ciccio's review, too.. needless to say I'll be opening it up first chance I get.

I had some basic questions, though, and was hoping someone could help.

1. could someone explain the exact procedure for setting the current limit on these units?
2. is there any way to get dual output out of these things?
3. why is my neg (black) terminal shorted to ground?  What happens if I remove the jumper?
4. I'd like to add a on/off switch to the output terminals so I don't have to turn the whole unit
on/off.  Doesn't look like theres a lot of space, but I think it should be straight forward.  Any
words of warning here?

Thanks!
Tony

[metalphreak]

1. Since its not programmable you set the current limiter by essentially shorting out the terminals. Most banana leads will be rated for 10A so you can use those to short the terminals and set the current limit. Obviously you don't want to leave it like that for an extended period. A nicer way would be to use a high wattage resistor or a 12V light bulb. Alternatively, connect whatever your using after turning the current limiter all the way down, then slowly bring it up until the limiter doesn't kick in any more. Give it a bit of an extra turn for some headroom and you're good.

2. No not without adding another regulator circuit and possibly another transformer if it has to be isolated (see #3)

3. The Black and Red output terminals are there because it is an isolated DC supply. The black negative terminal isn't referenced to mains earth at all (much like a battery). This means you can use additional supplies in Parallel for more current, or in Series for more voltage. The link to the Green (Earth) terminal just makes it so the Red positive is now referenced to mains earth (whether you need this depends on what you are powering).

4. Any switch could work between the output terminals and the internal wiring, as long as its got a sufficient current rating

[T4P]

1. Since its not programmable you set the current limiter by essentially shorting out the terminals. Most banana leads will be rated for 10A so you can use those to short the terminals and set the current limit. Obviously you don't want to leave it like that for an extended period. A nicer way would be to use a high wattage resistor or a 12V light bulb. Alternatively, connect whatever your using after turning the current limiter all the way down, then slowly bring it up until the limiter doesn't kick in any more. Give it a bit of an extra turn for some headroom and you're good.

2. No not without adding another regulator circuit and possibly another transformer if it has to be isolated (see #3)

3. The Black and Red output terminals are there because it is an isolated DC supply. The black negative terminal isn't referenced to mains earth at all (much like a battery). This means you can use additional supplies in Parallel for more current, or in Series for more voltage. The link to the Green (Earth) terminal just makes it so the Red positive is now referenced to mains earth (whether you need this depends on what you are powering).

4. Any switch could work between the output terminals and the internal wiring, as long as its got a sufficient current rating

... Er how do i parallel/series a power supply

[metalphreak]

Well parallel isn't as easy since you need to get proper current sharing.

Series is easy. It's just like stacking multiple batteries end to end. Obviously you need more than the one power supply... (and they need to be isolated outputs)

[outofstepper]

Thanks for the clarification.

Took it apart earlier to have a look inside .. have read some rather frightening things about
the build quality.  To my untrained eye it was a pleasant surprise.  Solder joints all look good..
PCBs even appear nicely arranged / lain out.

-Tony