3 amp power power supply

[overcashier]

Last week Caswell informed the 3 amp power supplies were back ordered. I got great response from them and they found me a returned unit. I unpacked the unit tonight there was no documentation so I plugged it in and figured I put a meter to it. When I power up the voltage reads .5 and when I turn the knob to the right it goes to zero. When i turn the current knob to the right nothing happens. If I play around with the knobs occasionally the unit will make a couple clicking sounds and the voltage will jump up to 8.5. If i turn the current knob down to the left the unit will click and the voltage drops down to .5 again. No matter what I do the current always reads zero. They had mentioned the unit was returned and the guy just didn't have the fuse in properly. I checked the fuse in the back of the unit and it seems fine. Any ideas?
Thanks
Greg

[seanc]

Greg:

... so I plugged it in and figured I put a meter to it.

What kind of meter, volt or amp? Doesn't the unit have it's own meters?

To check the volt meter:

1. turn voltage knob all the way down
2. turn current knob all the way up
3. turn the unit on
4. turn the voltage knob up gradually. The volt meter should go up proportionate to the knob.
5. current will ALWAYS be zero during this test.

To test current, you have to connect a load of some sort: eg. a resistor, a small light bulb, your plating tank, etc. A small value resistor is ideal, something from 1 to 10 ohms, smaller is better, but requires higher power rating, say 5 watts or more.

eg, with a 1-ohm resistor:

1. set the voltage to @ 2 volts, as per above procedure
2. turn the unit off
3. turn the current knob all the way down
4. connect the resistor (or other "load")
5. turn the unit on
6. gradually turn the current knob up. The meter should go up in proportion until the unit hit it's voltage limit (it should click here), then the amp meter will stop increasing. With a 1-ohm resistor, it should stop at 2 amps. You'd need a 4-watt or more resistor.

If it passes both these tests, it's working.

You can use larger value resistors, just have to do some math to determine what the amp meter should read:

eg #1, if you use a 10-ohm resistor, at 2v,the current meter will stop at 0.2 amp, but you can use a very light weight resistor, 0.4 watts.

eg #2, if you use a 10-ohm resistor, and set the voltage to 5v, the current meter will stop at 0.5 amp, but you'll need a slightly larger resistor, 2.5 watts.

The "clicking" you hear is the unit switching between CC (constant current) & CV (constant voltage) modes. This is normal.

Make sense?

Sean

[overcashier]

Thanks Sean,
Makes a lot of sense. Unit tested perfect. I can finally plate this weekend.
Thanks again
Greg