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Help with 8a driver and load

Imotox

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I have tried to find out how to set the 8a black buck driver for 7W+ NUBM44-81/NUBM47-A1 450nm Laser Diode. I know a test load to set the driver but not sure how to build one. All the info I can find is so confusing. Please help. Using a 12v power supply and going to be ttl on a cnc machine.
 



Gazen

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Search "test load" in the search bar at the bottom of the page, there are several threads that should be helpful. If you have any specific questions about them ask here.

Look at the spec sheet of the diode for its forward voltage, then use diodes to match it and a 1 ohm resistor. Make sure these components can handle the power.
 
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diachi

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If you don't want to learn how to build one you can buy this: https://www.survivallaser.com/20A_Heavy_Duty_Selectable_Test_Load/p556088_14651126.aspx

Here's a schematic for one if you want to build one. Just uses a 1 ohm resistor and regular silicon rectifier diodes.



Number of diodes sets the voltage drop, that should be selected based on the forward voltage of the diode you're using, which will vary depending on the current you're using. You'll need to beef up the diodes and 1 ohm resistor for the current requirements of a NUBM44. Heatsinking of the diodes/resistor may be required. Voltage drop per diode will depend on the diodes used and the current, but somewhere around 6 or 7 will be about right. Doesn't hurt to check voltage/current graph on the datasheet for whichever diode you pick.

Here's an example, my DIY 20A adjustable test load.



If you're not experienced with electronics and soldering I suggest either using the pre-built test load or buying a diode/driver combination that is already set.

Final note, do you have experience with high powered lasers? Do you have laser safety glasses? The NUBM44 is seriously powerful and is not something to mess around with.
 
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Imotox

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Ok so if i used 4 1N5404 Diodes and 5 watt 1 Ohm ceramic resistor, would that work? That is the same load i used on my 3w laser. So when setting the current on the driver I hook up power and run TTL to max and set that to what? Just making sure to do it right and safe.

I do have safety glasses from survival laser. I just need a little more power with this diode laser than the 3w.
 

diachi

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Ok so if i used 4 1N5404 Diodes and 5 watt 1 Ohm ceramic resistor, would that work? That is the same load i used on my 3w laser. So when setting the current on the driver I hook up power and run TTL to max and set that to what? Just making sure to do it right and safe.

I do have safety glasses from survival laser. I just need a little more power with this diode laser than the 3w.
What current are you setting it to?

Connect your test load, apply power and then apply 5V+ to the modulation input. You can use the 5V+ reference on the driver for this if you need to. Once you've done that, set the current by adjusting the pot and measuring the voltage drop across your 1Ohm resistor. 1V=1A.

 

Imotox

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Im not too sure how many amps to run for this laser. 5? 5.5? 6?
 

Encap

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Im not too sure how many amps to run for this laser. 5? 5.5? 6?
See: https://sites.google.com/site/dtrlpf/home/diodes/6w-nubm44-445nm-laser-diode

"My meter does not read past 6.8W but this diode is clearly doing well over 7W but I will call it 6W till someone can show some testing further than I can with my meter. @ 4.5A it does 6.8W and I ran it for about two minutes @ 5.5A with the meter pegged at max the whole time never a drop in reading so there is a very good chance it is doing much more than that." ~ DTR
 

diachi

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Im not too sure how many amps to run for this laser. 5? 5.5? 6?
Keep in mind that the 1N540X series rectifier diodes are only rated for 3A and a 1Ohm 5W resistor is only rated for about 2.2A in this configuration. At 5A your 5W resistor will be dissipating 25W. It'll also be dropping 5V at 5A, so your load voltage will be 5V + the voltage across your diodes. Remember to account for that. You want the load voltage to be close to the voltage your laser diode will be running at.

Neither component will hold on for long when pushed that far past their rating. The diodes will be OK for a short time with some heatsinking but I'd probably go with a 0.1Ohm 5W resistor. That's good to around 7A and will introduce a lower voltage drop to the test load.
 
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Imotox

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Keep in mind that the 1N540X series rectifier diodes are only rated for 3A and a 1Ohm 5W resistor is only rated for about 2.2A in this configuration. At 5A your 5W resistor will be dissipating 25W. It'll also be dropping 5V at 5A, so your load voltage will be 5V + the voltage across your diodes. Remember to account for that. You want the load voltage to be close to the voltage your laser diode will be running at.

Neither component will hold on for long when pushed that far past their rating. The diodes will be OK for a short time with some heatsinking but I'd probably go with a 0.1Ohm 5W resistor. That's good to around 7A and will introduce a lower voltage drop to the test load.

Wow i feel stupid right now. I know once i get it ill get it but seems greek at this point. Any suggestions for good diodes and resistor would be good to make this thing.
 

RedCowboy

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paul1598419

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You have a typo, RC. E=I X R, not I/R. Imotox, you can buy 10 amp silicon rectifiers for ~$5.00 for fifty of them. I don't have a link handy, but they can be found on eBay.
 

Benm

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Keep in mind that the 1N540X series rectifier diodes are only rated for 3A and a 1Ohm 5W resistor is only rated for about 2.2A in this configuration. At 5A your 5W resistor will be dissipating 25W. It'll also be dropping 5V at 5A, so your load voltage will be 5V + the voltage across your diodes. Remember to account for that. You want the load voltage to be close to the voltage your laser diode will be running at.

Neither component will hold on for long when pushed that far past their rating. The diodes will be OK for a short time with some heatsinking but I'd probably go with a 0.1Ohm 5W resistor. That's good to around 7A and will introduce a lower voltage drop to the test load.
I agree with this: The diodes can easily be substituted for ones that can handle more current, but choosing a different resistor could be a good choice here. The 1 Ohm value was good for currents at 2 amps or so, but is not very realistic when testing for performance of a driver on a 7 watt laser diode running 8 amps.

So choosing the resistor correctly matters. If you have a datasheet for the diode you can roughly derive from that how many diodes and what value resistor you would need to approximate the laser diode best.

I think 1.0 ohm is definitely too much, but 0.1 ohm may be a lit low to reflect the actual diode. Perhaps something in the order of 0.22 or 0.33 ohms would be best (1 to 1.5 extra volts dropped for a 5 ampere increase).
 

paul1598419

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For higher current diodes, I use a 0.1 ohm 5 watt 1% tolerance resistor so you can use 500 mV for 5 amps. Also, since we are talking about DC values here, the 10 amp rectifiers will work, but only for short periods of time. They will overheat if you allow them to draw 5 amps for more than several seconds. But, that is plenty of time to set up your driver.
 

Benm

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Oh sure, but as i said the choice of diodes is pretty free. If you want a test load that can run an unlimited time you can dimension the diodes (and heastinking for them) accordingly. There are plenty of power diodes on the market that can be mounted to a heatsink in TO-220, TO-247 packages.

Another thing to consider is what type of diode you want at these currents. Perhaps you may want to use schottkey ones - you'll need more of them but have a more precise control over the current/voltage curve as well. And you can use things like MBR1645 diodes mounted on a heatsink. Those cost under a dollar a piece (and are mostly used in solar systems and such) , but have the downside that their heatsinking flange is connected to one of the terminals, so each diode would need it's own heatsink, or you'd have to mount them electrically insulated. The do handle 16 amps though.

You can get case-insulated diodes of similar specs though at decent prices, so you could use a single heatsink for all diodes and the resistor making it easier to build.

But whatever you do, keep in mind that you just want to build something that mimics the electrical characteristics of your specific diode as best as it can, at least around the current you actually plan to operate the laser diode at.

The goal of a dummy load is to act like it was the actual laser diode, but just not be susceptible to driver mishaps like current spikes, and even if it is damaged by one to be much cheaper/faster to replace than the actual laser diode.

As a concept this as been around forever - even back to when people were using dvd writer diodes and the dummy load could just be something like 2 or 3 1n400x diodes in series with a 1 ohm resistor, which mimicked the electrical performance of that diode pretty well, and also provided the resistor to connect a scope over so you can look at the current.
 




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