COB (chip on board) led 50w warm white


Ahhhh lol sorry! Yes if they would be good but I wanted the one with the potentiometer it’s on rapid led I’ll get diver part number could you see if it would work?

Also could I somehow use the computer tower power 12v but it doesn’t have a potentiometer lol would it run too hot? I really want that dial though, it would be ideal


I’ve never tried to under power a cob like that, 12volt power supply with 36 volt cob. So I’m not really sure if it just wouldn’t come on, or it would try to pull curent through the roof. Either way, I wouldn’t advise using it.


Okay I was just asking for the correct driver with dimmable option, and I was not aware you couldn’t under power a cob like that. I didn’t know it wouldn’t turn on…lol thank you for that out of likes :+1::+1::+1::+1:

Looks like I’ll be looking up how to wire a computer 12v supply to a cob :+1::+1::smirk_cat:


I’m not sure if it will or won’t, just saying I haven’t tried. If it does turn on, it’s not going to perform to it’s potential. So it’s never been on my list of things to do. @1BigFella has a more extensive electronics background than me, perhaps he would have some knowledge on that.


Yeah I hear ya. Thanks for the tid bit @dbrn32 thank you for tagging @1BigFella too. I found the meanwell npf-40d-36 on amazon for 32.94 and .99 cent shipping


Did you look for it at arrow?


It’s a buck cheaper, free overnight shipping. Up to you, I don’t really care where you get it from.


No I forgot about arrow thank you! Your the best bro. I really truly appreciate your knowledge :+1::fist_right: @dbrn32

It’s 31.54 on arrow :crossed_fingers: I’ll pull the trigger on this next paycheck


No problem! You could do quite a bit cheaper if you didn’t need the dimmer. Not sure how important that is to you.


The dimmer is very important to me lol it’s for my sprouts and seedlings :wink::+1: @dbrn32 also I don’t want to overhear using the PC heatsink I pictured above it will be active cooled though…thoughts?


I would think at that power level the pc cooler will be fine. Like any active cooling system, it’s heavily dependent on the fan running. So you can bet a fan failure will directly result in the cob failing as well.

The good news is, you’re really only into it for cost of driver right? So if that happens, the replacement cost would be the cob and you can go to a passive heatsink then if you want. Or just replace the fan, that’s really up to you. Could run for years that way too.

Did you look at those strips @BIGE put together? You can probably do one or two of those for cheaper than that driver.


Yeah I agree, I dont think the fan should fail :crossed_fingers:that is true the cob would fail as a result of the fan failing, it relies on the active cooling. I’m not concerned with failures obviously it can happen but I’m now concerned with building this kit as a “starter” build before I go all in on a full passive heatsink cob build! :+1::wink: yes I saw @BIGE build in the “let’s talk diy lights” thread. I wonder if he could chime in on the parts and cost of his cob strip build :+1:


I think he spent about $130 for 120 watts, but he has extra of build materials for future use.

If you were looking to do something around 30 or so Watts for seedlings, 2 560 mm strips and a driver would be under $30. He used aluminum and double sided heat transfer tape to mount them, that stuff would be extra. But you’ll be running 160+ lumens per watt with the strips, as opposed to under 100 lumens per watt with this cob. There wouldn’t be any need for dimmer in that application since the light intensity so spread out, you can just run it a few inches higher or lower. Plus you could get whatever color temp you wanted, as opposed to being stuck with what you have.

It’s just another option to consider. You can move forward with the cob as well, makes no difference to me.


Thanks for the advise I can’t put together all these different options/builds in my head I’m not up to speed with the chip on boards just yet, I spent all last night catching up on your thread lol I learned a lot about cri and the types of different cobs and drivers :+1::+1::+1:I’m glad to have someone like you to ask for advice in this place. Thanks for everything I’ll post updates of the mini build before I go all out and get a whole setup. And it would probably be a 800w build for a whole grow :wink::+1: so looking to spend some good cabbage


That COB is 63 watts maximum (36 volts x 1759-0 ma). You just multiply the forward voltage by the current. Which you can also measure with a cheap multimeter. (You have to put the meter in 10 amp setting and put it in series with the COB to get current, then reconnect the COB to power and measure voltage across the COB terminals.) If you run it with an 1120 ma driver it will be less power. Around (1120/1750) x 63 = 40 watts.

That’s just an approximation though, because at that current it will not drop 36 volts. It might be around 31 volts, so that would be 22 watts. It is difficult to predict without the manufacturers voltage & current graph. LEDs are not linear. They start making light when the voltage reaches a certain level and above that they make more light. But as you increase the current the forward voltage rises and as they get hot more of the light is infrared. So they make more light but the lumens/watt line falls off and gets flatter.

The best thing to do is to find their maximum current and then run them at 1/3 to 1/2 of that. You get a lot of lumens/watt and usually buying more COBs is cheaper over the long run. You have to pay to run these at least 12 hours a day, you know!

So I would recommend running it at 850 ma. The driver should be able to supply 36 volts, though it won’t actually put more than 31 volts across the COB. Don’t worry much about the wattage: You’re not going to run anyway near the maximum. If you tried to run them at 12 volts they would do nothing.

Beware of random power supplies on eBay or sitting around. They will almost all be constant voltage and will either not run the COB at all or blow it up if the voltage is too high.


@1BigFella thanks for the formula DC Voltage x Forward current = wattage of cob :+1::wink:

Okay so what driver should I get then? Lol I do want dimmable capability though so keep that in mind. Thanks and the meanwell npf-40d-36 is I think 700ma or correct me if I’m wrong. I don’t have tabs on everything just yet. I should write this all down! Lol

Thanks so much guys for your assistance!


I think you’re still going to need to go with that driver. We certainly could’ve gone with bigger model, but I would never run cob at cob at max, so I certainly wouldn’t recommend anyone else do so.

There’s just not a lot of options for dimming drivers that small. I think there is a 25 watt driver, but that would mean 0-10 volt or pwm dimming. Just means more money to get you same result as using a pot.

Speaking of which, you realize that you’ll have to add that separately right? The driver comes with capability, but it’s up to you to add components to do it.

Back to the driver anyway. Once you install the dimmer, it will control the output current. So then you have the ability to run it wherever you’d like. Assuming pot is 0-100k, that should be linear. Wherever the pot reads 50k, the output current of driver will be 50% of the 1120ma and so on.


Thank you for that info. yes the one I saw that you recommended has screw terminals for the pot to be hooked up :wink::+1: thanks for reminding me :pray: @dbrn32


Somebody has a very nice automated selection tool that lets you select the maximum current and dimming option, and shows you the cheapest mean well options with specs. Damned if I can find it now! It was NOT Mean Well whose online catalog is a nightmare.


I’ve never used that model, so when the time comes post up some pics please.