NJG-18 Current dropping issue

Hi,

I've been having problems with some NJG18's I have, I can't for the life of me seem to set the current on them with out having problems.

I put together a 6A universal testload using a 0.1ohm 10W resistor (keep voltage drop low), 3.1k resistor in parallel to drain the drivers caps, then the diodes I am using are rated for 6A, and according to the data sheet have a Vdrop of 0.8V @ 1.5A, so 5 of those were set on my test load (+ a little extra voltage drop from my 0.1ohm resistor) and to double check the test load I hooked it up to a flex drive with a known output and confirmed it was reading correctly.

The problem I am having with this current NJG-18 driver is I hook it up to my converted computer PSU which is outputting a confirmed 4.2V with a maximum load of 3A (LM350 circuit inside.) This is too make sure I don't have problems with batteries dying and effecting current readings, and when I read the current on the NJG-18 the current reading just constantly drops off and won't settle.

The driver is setup to bypass the modes, with the negative output on the edge of the driver, positive output at the positive hole then bridged to C1. The positive input from the PSU goes to the spring, and the negative is bypassed to the negative output as described by DTR:



I've got a video I took of the problem to make it a bit clearer: (note, that the reading is the actual current reading eg. 800mA)



If anyone could help me out I'd really appreciate it

Anything heating up like it's being overdriven?

BShanahan14rulz said:

Anything heating up like it's being overdriven?

Click to expand...

It's not the PSU or test load as I double checked it with a flex drive and getting accurate readings.

I've double checked the voltage from the PSU to the driver as being exactly 4.2V, I made sure I kept the driver on it's stock pot settings as I wanted to confirm it wasn't anything I was doing whilst turning the pot, and the driver doesn't feel hot to the touch so I don't think it's heat issues either.

What is the voltage drop of your test load? I use the red setting on my test load with the NJG because of the funky voltage current ratio thing it does and since the blue setting simulates the voltage drop of a blueray diode it lowers the output current significantly. If you hooked up a blueray diode the 800mA you are reading is probably what you would get but on a 445 it may be 1.4A.

DTR said:

What is the voltage drop of your test load? I use the red setting on my test load with the NJG because of the funky voltage current ratio thing it does and since the blue setting simulates the voltage drop of a blueray diode it lowers the output current significantly. If you hooked up a blueray diode the 800mA you are reading is probably what you would get but on a 445 it may be 1.4A.

Click to expand...

According to the datasheet on the diodes, they have a voltage drop of 0.8V@1.5A, the 0.1ohm resistor has a voltage drop of 0.15V@1.5A, so 5 diodes is 4V+0.15V from the resistor and that's about right isn't it?

What total voltage drop am I aiming for? I was going for about 4.2V

Cheers for the help

here's the data sheet for the diodes I'm using in my test load:

http://www.maplin.co.uk/media/pdfs/Module 46413.pdf

I've just noticed they're rated 50-1000V? not sure if thatll be causing the problems?

EDIT:

I gave it another go this time with 6 diodes, and I seem to be getting a slightly more stable reading of around 750mA, although now the current seems to be increasing slightly.