How to make a selectable Dummy Load - VERY in depth

[bobhaha]

@edy

The resistor is a 1 ohm load. With a 1 ohm load, we can directly convert voltage to current.

Using Ohms law...

V= IR
Since we know the resistance is 1ohm, we can re write the equation like this...
V=Ix1
Or
V=I
Where V is voltage and I is current.

So when measuring a voltage across the resistor, you are effectively measuring the current in the system.

-Adrian

 

[laserdelic]

Bravo post Bob!. Is just what I need. Im building one today

 

[laserdelic]

Using 1 Ohm/1w resistor and 1N4007 diodes.

I haven´t used it yet because Im using a analogic multimeter. My digital is half died. Im buying a new one this days to try it.

 

[bobhaha]

Nice job! Looks good.

I'm going to be making a new video/thread on how to build a 3A selectable dummyload for cheap! Should be up very soon.

 

[laserdelic]

I´ll follow that 3A, for sure.

Finally I added two cocodrile tweezers to conect the driver and I cut the unused board with the dremel.

Thank you for sharing. Bob.

 

[Cyparagon]

cocodrile tweezers

I laughed harder than I should have. How the hell did that r move over 4 spaces? I'm totally calling them cocodriles from now on.

 

[laserdelic]

In Spanish: Alligator, Crocodile>Cocodrilo )

 

[kuhny1]

how many diodes are used for a 650nm red laser LD

 

[izzzzzz6]

Hi, is anyone able to point me to a thread which explains how many diodes i need to connect in series to check the current for a
Nichia NDB7875 445nm LD? and also i have 1N4001 50V 1A DO-41 Axial Lead Rectifier Diodes and a 1ohm 5W resistor. Can i use these diodes with the correct results? Thanks.
James

 

[Zeebit]

http://laserpointerforums.com/f67/test-load-diagram-s-all-laser-diodes-65186.html

You should use 1N54xx diodes instead. These can handle up to 3A.

Next time, use the search bar at the bottom of the page. Chances are, your questions have already been asked and answered. And don't post the same question twice even if its on another thread.

 

[crazyspaz]

Use the search bar at the bottom of the page...."Nichia 445 test load" would be a great search term...

 

[Jmillerdoc]

I can't find the original thread where I mentioned this but this seems to be a good one. If you are looking to source very tight tolerance resistors for your pass resistor to measure the current across, Percy Audio carries some excellent choices for this. As you know the calculation for your current is directly related to the value of the resistor your using. Often times your standard RatShack resistors are more than 10% off labeled value. Having an exact 1 ohm is important if your current measurement is to be accurate. When your pushing some diodes at max and high current a 10% variance could be lethal. Percy carries both Vishay Nude foils (0.25%) and Mills (1%). I haven't asked in a while but IIRC Michael Percy, the owner, probably can even measure the resistor for you. Measuring 1 ohm accurately is generally beyond the ability of most of your standard (even high cost) Ohm meters and for this you really need a MilliOhm meter (expensive). So, of you really want a good tight tolerance resistor try here:

http://www.percyaudio.com/Catalog.pdf

Cheers!

 

[kuhny1]

Sooo I ended up useing a epoxy coated inductor that measured out at 1 ohm would that be alright reading wise

ps: this is just for making a 50-100mW laser so i dont need a beefy resistor.

 

[Bionic-Badger]

The inductance may affect your driver.

 

[thedoc8]

If you are using it to test more than 1A driver for say.. 445nm diode this dummy load will overheat...


You must use diodes capable of at least 2A (i use 3A 1N5408) + bigger wattage resistor ... I prefer 5W 1Ohm to keep it cool for a longer time. When you measure current on heated components it actually makes results inaccurate. Oh and the bigger the current the higher voltage drop across each diode

Why does the wavelength of 445 overheat a diode tested at .5 amper. What does the wavelength have to do with it, I don't get it. Thanks

 

[brendon7358]

Why does the wavelength of 445 overheat a diode tested at .5 amper. What does the wavelength have to do with it, I don't get it. Thanks

This is a very old thread, and therefore a necro post but I'll answer your question.
The issue is the high amperage of 1A plus causes it to overheat. 445nm was just an example because at the time that was pretty much the only diode that went that high I believe. So if you only used 0.5A for a 445nm it would be fine but (at least at the time) you would be way under using that diode to its full potential.