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445nm test load questions 1000mA. (revised)

AJ_Dual

AJ_Dual

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Hi.

I know I've been all over the map with this... first this thread here: http://laserpointerforums.com/f51/445nm-test-load-questions-53839.html I put it in Tutorials Help & Repairs, completely missing that there was the Drivers/Test-Load forum here. :p

Then I've been reading what Dr. Lava had to say in this thread: http://laserpointerforums.com/f67/micro-boostdrive-vs-flexdrive-18650-driving-445nm-ld-52913-2.html

Mainly:
drlava said:
NO! 1N4001 diodes have a variable voltage drop depending on current. At 1A they drop about 0.9V! this plus the resistor (which should be 2 1 Ohm resistors in parallel for 0.5 Ohms total) is why I suggest the red dummy load range with 4 diodes.
Click to expand...

And when it came to the resistors:

HIMNL9 said:
The quantity of smoke that they produce, and the time for which they produce it ..... :p :D

Seriously, the resistor need to hold the current that you are testing, and to dissipate the resulting power ..... easy ohm law, power is volt*ampere, so, if you use an 1 ohm resistor, for test a 500mA drive, it have a dropout of 500mV across it, and need to dissipate 0,5*0,5=0,25W (1/4W), if you test it with 1A, it cause a 1V dropout, and need to dissipate 1W, if you test 1,5A, it cause 1,5V dropout and need to dissipate 2,25W, and so on .....

And, ofcourse, more high is the power of the resistance, more it's robust and affordable, and less risk to smoke out it .....

So, is always better to use at least an 2W resistor, for currents under 1A, and at least 5W resistor for higher currents.
Click to expand...

So, putting together an order from Futurlec.com, I think I have what I want finally for the Microboost, so I can make the final pot adjustments to 1000mA for my 445 build.

testload.jpg


Comments? (I ordered 6 1N4001's in case I need more.)

Thanks.
 





Man, just crank the pot till it stops turning! The 445's can handle it!

It looks good though, but I think the voltage will read a little different on the resistors since you changed the resistance.
 
Okay. I'm just going off of what Dr. Lava said in the other thread about making a test load for his own microboost. I was more concerned about fine-tuning the mA, since the voltage is just needs to be greater (within reason) than the Vf/drop the diode has, no?

I have no idea why two 1 ohm resistors in parallel is "better" @ .5 ohms, instead of one. Just that Dr. Lava recommended it. And two ceramic bodied wire-wrap 5W resistors seems the way to go as others said that lower wattage resistors got hot fast, and you had to read and adjust the pot in quick bursts. Two 5W resistors seems like it'll let me take readings and make adjustments in a more leisurely manner.

I can follow a schematic, but knowing why "what does what" is not my forte. :D (if that isn't obvious already)

What voltage should I want to read, (if I should even worry?) since the Vf of a 445nm is around 4.1-4.4? All I know is that I could use a flexdrive or a microboost, but Dr. Lava thought the microboost was a bit more forgiving in a few ways for a 445nm diode running at high mA. (more shrug) So that's what I bought.

Although I see what you're saying. It's going in the Kryton group buy as the host with direct heatsinking no module, so as a portable, I'm not imagining any kind of continuous duty-cycle. Maybe a few minutes for some long exposure photograpy. So if I'm higher than I initially wanted, the 445 diode should survive for a decent life-span. It's not as if this is some continuous duty-cycle labby.
 
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Alright,

The voltage you read across the resistor is actually the current running through the circuit. When you use a 1ohm resistor and you read 1000mV your driver is outputting 1000mA. The driver is a current regulating driver so the diode will control the voltage, you don't have to worry about setting that.

Two 1ohm resistors are better than one because two in parallel will have double the wattage rating of one by itself. I would think two 2ohm resistors would be better, because that would equate to a 1ohm resistor with double the wattage. a high wattage resistor is needed because you are pulling a lot of amps, if you use a little 1/4w resistor by itself it will overheat (possibly burn out) but either way the resistance will change and your reading won't be right.

Honestly, the limit of the boost drive is well within reason for these diodes. The max current of the highest jumper setting is 1000mA, so just turning the pot till it is maxed will put you at or extremely close to 1A.

I wouldn't worry about heatsinking if you are using a Groove, there is plenty of that on the Groove. My hosts (which are an inch shorter or so) run over two minutes before they start to get warm. You should have an awesome duty cycle with a maxed boost drive.
 
Sounds more like I'll be using the test load to make sure I've got the pot maxed then without over-turning it and wearing it out more than anything else then. :D

So would I expect to read 500mV with .5 ohms of the two 1 ohm resistors splitting the load in parallel like that to know I've got it adjusted for 1000mA, right?

Since it seems the test load will not be as useful as it might be in other builds, I did order the components with a small breadboard and a jumper wire kit so I can reconfigure everything and have nothing set in stone.
 
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Remember that the rated current limit for 1n400x diodes is 1 amp, and not more than that for continous loads. I'd suggest 1n540x series drop diodes to handle the current safely in this type of dummy load.

As far as the the resistors go: if you use 1/4w type resistors, it is prudent to limit their current as well - 2 0.5 ohm pieces in paralel seem like a good idea but you must multiply the mV reading across those by 4 to get the proper current reading.
 
^ Oh yeah,("I'd suggest 1n540x series"). My larger "barrel" diodes sting my fingers after a couple of minutes. LOL
 
They sure get hot - the 1n400x and 1n540x are rectifier diodes, and normally conduct only half of the power cycle. They survive running continous current and 1 and 3 amps respectively (with some air flow), but at that point they get hot enough to burn your fingers on.

Also: Solder these drivers, dont build them on a breadboard (the kind you press components into without soldering): i've noticed that the contact resistances in such boards are big enough to throw your measurements way off at 1 amp currents.
 
Benm said:
Remember that the rated current limit for 1n400x diodes is 1 amp, and not more than that for continous loads. I'd suggest 1n540x series drop diodes to handle the current safely in this type of dummy load.

As far as the the resistors go: if you use 1/4w type resistors, it is prudent to limit their current as well - 2 0.5 ohm pieces in paralel seem like a good idea but you must multiply the mV reading across those by 4 to get the proper current reading.
Click to expand...

I figured if I was trying to dial it in for 1000mA, there'd be lots of heat, so that's why I was using 5W ceramic resistors. I never thought about the diodes too. So I'll take everyone's advice to switch to 1N5400's as well.

And dur... I KNOW that it's I = V/R, but when doing parallel resistance, my brain keeps wanting to ADD, not multiply .5 x. .5 = .25, so 1/4 the mV is read. So 4x the mV to get mA.

And the solder connections makes sense, that breadboard and jumpers are "lossy". At like $1.50 in components, I think I can afford to make a dedicated 1A test load for 445nm. :p

This is all the great kind of help and advice I'm looking for, thanks for chiming in, and any other thoughts or ideas, I'm glad to hear it!
 
Plenty of ways to build them :)

For me it depends on what i have lying around in components too - using 10 0.25 watt 10 ohm resistors in paralel to get a 1R/2.5W works just as well... but if you need to buy the components you might as well get a 1ohm/5W resistor or something similar.
 
I threw my 445 load together the other day and go figure I had no 1ohm resistors that I could quickly find. However I found a bag of 3ohm 2 watts. So 1N5402's and 1ohm 6watts of overkill FTW!!

fojbtl.jpg
 
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