Using a fricking bench psu to drive a diode

[rthorntn]

G'day,

Please, please help. I have searched the forums for the answer.

Maybe I am just being thick but I cannot figure out how to get a voltage/current combination...

I have an extracted DT0811 diode and a WEP PS-305D PSU [0-30V 0-5A], it has an Amps/mA switch for a more accurate readout and fine/course dials.

I think I am trying to get around 5v and 100mA. The closest I can get to that by twiddling the dials is 9v and 100mA.

I cannot seem to set both the Amps and Volts, it's one or the other.

When I switch the PSu on with all dials fully anti-clockwise, I get 0mA and 0V and the C.C. led is lit, turning the voltage dials do nothing, turning the current dials a tiny amount switches to the C.V. led and the voltage dials work so I can set it to say 4.2v but now the current dials aren't working...

The only thing I seem to consistently be able to do is turn the current slightly clockwise from 0 and then turn the voltage dial to 9-10 volts, that then increases the current to 100 mA and I can see a dim beam

I am tearing my hair out, please help.

Thanks.
Richard

 

[ARG]

To drive a diode with a PSU set it to the max voltage the diode will need. Turn it off and turn the amps to 0. Then short the output wires and attach it to the diode. Turn the power on and slowly start turning the current up, it should always be in C.C. mode.

 

[rthorntn]

Thanks ARGlaser.

I was trying that, I seen a youtube video [by DTR] posted here showing it.

I follow the procedure:

Turn on PSU with nothing connected
Move the current knob until c.v. lights
Move the voltage knob to 5v
Turn the PSU off
Turn current knob to 0
Short the leads then attach to diode
Turn the power on [c.c. is lit and both readouts read 0]
I start to turn the current knob and it switches to c.v. and v goes to 5v and current stays at 0

The only way I can get current to 100mA is to adjust the voltage until the current reads 100mA which is around the 10v mark, at this point there is a weak but focused beam.

Is there some tests I can do to eliminate potential issues?

Thanks.

/Richard

 

[Cyparagon]

I suspect those leads are a stupidly small diameter wire so they save 30 cents on copper . That means the wires drop a lot of voltage and generate a lot of heat. The supply reads the voltage at the terminals, not at the load, so that causes a wonky reading.

It's hard to find good leads, and I recommend building your own. Use an old lamp cord for the wire and cut to the length you want. That is usually 18awg and is okay for 5A. Search ebay for "banana plugs" and "alligator clips" and solder accordingly to either end. Since you already have attachments, you can just replace the wire if you like.

 

[rthorntn]

Thanks Cyparagon

I just checked the voltage with a fluke at the terminals [10v] and the voltage at the diode [10v] they match...and i can see a beam if i put my hand in front of it.

I have the bogartman test load kit from ebay, can the 6 x 1N5404 diodes or 1 ohm wirewound resistor help me troubleshoot?

I should add that I haven't soldered any leads to the diode yet, I am touching the leads to the diode.

/Richard

 

[rthorntn]

The PSU seems to ignore where the voltage dial is set when it's power cycled.

I am completely confused, this is pretty strange.

This diode is probably toast.

This PSU seems to work differently to the units you are talking about.

I can't seem to get say 5v at 100mA, no matter what I try.

/Richard

 

[DTR]

Could you make a video of what you are doing. Also make sure you have solid connections to the diode an intermittent connection could kill the diode.

 

[rthorntn]

Thanks DTR

Anyway I think I finally blew the diode.

I was making a video and for some reason, with only a tiny turn of the voltage dial the voltage jumped to 12v and the diode was no more, it isn't drawing any current anymore...

I ripped it out of an HDDVD so it was less than ten bucks.

I think a green laser is the way to go for astronomy anyway.

/Richard

 

[DTR]

That would be part of the problem. You should not be adjusting the voltage dial while the diode is connected. You set the voltage with no load on the power supply and the current to zero. Turn it off, short the leads, connect the diode, power the unit on and then turn up the current slowly.

 

[rthorntn]

But no matter what I did, turning the current dial with the diode connected did not move the current past 0.

Pushing the voltage up to 10v would get some current flowing but the beam was crap. I think the diode was cactus.

Doing what you say with an LED works to a point in that I preset 2v and cycle power [the led lights properly when I increase the current but it ALWAYS switches it to c.v. so the only way to increase the current on this PSU seems to be to increase the voltage]

Maybe this is a dodgy PSU.

Thanks again everyone.

/Richard