Help with driver and test load

[Asherz]

Hi,

I could do with some help regarding a driver I just built, my first one which actually looks like it might work lol.

Basically it has:

LM317T
47UF 35V capicitor
4.7ohm resistor
1k ohm multi-turn pot (I can't find the end turning point of the pot it seems to go on for ever)
1N4001 diode

It's running of a 9V battery, and will be hooked up to a 16X DVD burner diode, and for the test load I have 4 1N4001 diodes and one 4.7ohm resistor (dont have a 1 ohm)

Now, to measure the current which will go to the diode I believe you measure across the resistor in MV with a 1ohm resistor, and because ohm law states I=V/R youll get the correct current.

Now my multimeter is not digital, it's an old one which someone gave to me but gets the job done and there is a mv measurement but it says (250mV) and when I measure across the resistor the needle doesnt move.

The only time it moves is when I set it to measure DC 5V from the positive cable, to the negative cable (with the 4 1n4001 diodes and resistor in series in the middle) and it measures from 0.6 upto 0.8 (LM317 gets hot at 0.8), probally will go further just cba to turn the pot lol, now according to my calculations, as V = 1000mV, if I * the 0.6 say by 1000 it = 600mV which is then divided by 4.7 ohms for the resistor according to ohms law and I end up with 123... does that mean my driver is running at 123Ma? or am I going completly wrong?

Just to sumarise I am measuring from the positive to the negative leads from my driver, not across the resistor.

Cheers for any help anyone can over, I would apreciate it.

 

[rog8811]

It is a long time since I used an analogue meter, It may be an idea to test it, what I suggest is to set up an LED with a resistor and a battery (use this to get a known current http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng ) see if it will measure mv across the resistor then do the maths.

The other option is to buy a new meter, a usable one needn't cost more than $10 to $15

Regards rog8811

 

[Asherz]

Hey Rog cheers for the advice,

Tomorow I'm going to see my uncle whos an electrician but often deals with minature electrics such as this He has all the equipment I'll need and he said he would see if he could sort it out and have a look.

Thanks.

 

[rog8811]

Result! Let us know what happens.

Regards rog8811

 

[Asherz]

Hey, got it all sorted out today Turns out I had soldered the 1N4001 diode the wrong way round so the current wasn't flowing through : But I sorted it out and set it to 150mw, then when I attached my red diode in guess what! I didn't work dammit lol, I think I may have killed it with my first driver as I didn't discharge the capacitor... Owell, works with IR but I'm sure I'll get another red soon.. go to the local computer store or something and see if they have some spare burners.