1N4001 Diode Question --- Building a Test Load

[NightRunner417]

Hahaha omg I have to share this with you guys, it totally cracked me up...

I killed my first blue diode last week, and not wanting to be held back in completing my build, I kept working on structural issues and heat dissipation issues. All seemed "ok", but in order to really give it a decent thermal test, I needed a diode in there. Since I don't have my replacement blue diode yet, I decided to build myself a dummy load as described in this thread. I carefully soldered five 1N4001 diodes, end to end, minding the anode and cathode markings (it's early and my mind is foggy, so I had to be extra careful), and finished them off with a single 1 ohm resistor. I built the little strip in a side to side type config to limit size and lead length (inductance may not even enter in, but I wanted to be sure). I soldered this neat little diode array to the leads for the laser diode, and placed my DMM between Vcc and the "hot" lead of the driver board.

I saw the amperage peg the 1.25A that I have the driver set to max out at, and watched it because without adequate heat elimination, the LM350 based design begins to cut itself off to avoid self destruction, and my recent efforts have been aimed at reducing or even eliminating this effect. I was pleased to see that the amperage only fell a couple of tens of mA over about ten seconds, which is a lot better than it was doing, but I started to smell something very hot anyway... and I thought, "But... the 350 is sinked! And... the current readings show that..." About this time, a sudden motion at the laser head caught my eye and I saw what the problem was right away.

The two middle most diodes in the array got SO hot that they actually melted their solder joints and flopped forward as a pair to rest against the casing of the laser, lol! Wowwwwww... Well... I'm impressed! I figure I was only pushing about what, five watts or so through the array, but apparently that's more than enough to generate hot spots capable of melting solder. I don't know yet if I blew any of the diodes, but I wouldn't be at all surprised if I have.

Anyway, found that one amusing and thought some of you might get a laugh and/or some use out of that little experience.

PS: A little update - I just checked the diodes and they appear to be fine... I get a voltage drop of about 0.57 to 0.58 on each, and no reverse flow at all. Tough little buggers!

 

[HIMNL9]

It's normal ..... 1N400x serie is rated for max 1A, and have a max dissipation capability of 1W ..... and yes, they can become hot enough to melt solder (i made the same with BY255 ones, once, using them for a 2,5A driver, and they are rated for 3A ..... always choose diodes that can hold and dissipate at least the double of that what you need )

 

[Benm]

They'll do that alright, especially if not held in place firmly by a pcb. They often survive, although i'd never use them in something critical or difficult to repair afterwards.

Its quite amazing how you can squeeze that much power into the tiny diode package and still provide enough thermal contact to make it work safely.

 

[Humphry]

Would this be the 'correct' 1N4001 type of diode?

http://www.mantech.co.za/Datasheets/Products/1N400X.pdf


The forward voltage drop does not seem to be listed anywhere. I am getting all worried :cryyy:

 

[HIMNL9]

Would this be the 'correct' 1N4001 type of diode?

http://www.mantech.co.za/Datasheets/Products/1N400X.pdf

The forward voltage drop does not seem to be listed anywhere. I am getting all worried :cryyy:

Yes, and the forward voltage is "listed" only as a graphic, cause it vary with the current, is not a fixed value ..... it's the graph called "forward characteristics", where you can see all the forward voltages for the different curves (ofcourse, for continuous use, you must read only til 1A)

 

[Humphry]

for continuous use, you must read only til 1A

Thanks for your help!
Would there be any harm in momentarily reading currents of about 1.8A?
Is the only reason why you say this because of the overheating story or are there inaccuracies/ other complications involved. I am thinking of heatsinking this test load which is why I am asking if heat dissipation will be the only issue, which I can easily solve.

I am also wondering if 1N400x means the value 'x' can be anything from 0 to 7 or what the story with that is?
I have two 1N4007 diodes lying around and was wondering if they would do the job if used hand in hand with the previous diode.

I apologize for being such a noob

 

[HIMNL9]

^ Probably you get no damage, if the time is realy short (for diodes, the total current depend also from the duty cycle of the voltage, as example, a square wave with 50% duty cycle can hold til 2A, a 25% duty cycle can hold til 4A, and so on ..... if you use it at 1,8A for like a second, probably it resist, also if become hot, but over this, it may be damaged.

Anyway, diodes are strange beings ..... i had 3A diodes working for a short circuit at 12A til they melted the solder, and still working, after cooled, and also had schottky receiver diodes damaged for "having looked too bad at them" (touched them without discharge static, no sparks, simply they died )

 

[beantastic]

I built my test load today and here it is. I just wanted to run it by everyone. I know it is not the best solder job but I was in a hurry on my lunch. All of the joints are solid though. The red wire is the + for red diodes soldered in after the 4th diode. The blue wire is for Blu Ray diodes and is soldered in after the 6th diode. The black wire obviously is connected to the other end of the other end of the 1ohm 10 watt resistor.

 

[mikey395]

im also on the same promblem as beantastic
i made my test load (first one) just some some one to check if the wiring is ok
sorry for the blurry vision on the photo
its 5 N41001 diode and 1 ohm 1/2 watt then the black and red wire