Trying to run two COBs in parallel advice needed

[Scotty321]

I picked up a couple of Craftsman 1000 lumen 4xAA worklights on clearance. I wanted to see if I could power both off of the same switch, so I took the COB from one, and soldered it in parallel to the other. However, I was wondering if the board was limiting the current, thereby negating the reason for me adding the second COB. It's hard for me to tell if it made a difference, as I got home and just made the change without reminding myself what they looked like individually... I tested them a few months ago and tossed them in the closet.

I am attaching a pic of the circuit board in hopes someone might be able to recognize the components and suggest whether what I did is in vain or not. If so, I'll put the second COB back. I did test it for a few minutes, so I know it works as a unit. It just seems like I'm not getting the actual 2x brightness of what they were doing separately... tested with NiHM and Alkaline batteries.

If it matters, I was going to toss it inside a cheapo hand lantern and use it with 4 D cells (or 6 volt) as a crazy floody latern.

Thanks for any advice!

 

[Lynx_Arc]

It is quite possible that there is a current regulator buck circuit on that light the one way to tell is put an ammeter inline to measure current draw with 1 and 2 cob lights. Another way is to see if the LED is brighter with alkaleaks or nimh. I"m guessing that you probably can't tell the difference between the two. I wouldn't expect to get 2000 lumens off alkaleaks but nimh may possibly do it. Unless there are components on the other side it looks like a linear regulator not a buck circuit and the blank face chip leaves me clueless as to what it truly can do.

 

[Scotty321]

It is quite possible that there is a current regulator buck circuit on that light the one way to tell is put an ammeter inline to measure current draw with 1 and 2 cob lights. Another way is to see if the LED is brighter with alkaleaks or nimh. I"m guessing that you probably can't tell the difference between the two. I wouldn't expect to get 2000 lumens off alkaleaks but nimh may possibly do it. Unless there are components on the other side it looks like a linear regulator not a buck circuit and the blank face chip leaves me clueless as to what it truly can do.

Thank you for the info and suggestions! I'll give it a try!

Side note: the only thing on the other side is the button.

 

[Scotty321]

Update; just some notes:

Pulled out my old clamp meter and measured approximately 2A (@1.4V*4) with Alkaline and 4.2A (@1.31V*4) with NiMH with both COBs hooked up (parallel)... I'll pull a COB off and measure later.

 

[Lynx_Arc]

sounds like the alkaleaks are about 11.2w and the nimh are 22w so the alkaleaks aren't able to handle the load. having 2 LEDs in parallel won't to the eye look twice as bright because but should be noticeably brighter as to the eye it takes a lot more than twice the lumens to be look twice as bright it takes 4x the lumens instead as the eye perceives it that way.
https://www.candlepowerforums.com/v...scale-Twice-the-lumens-equals-twice-as-bright

 

[Scotty321]

Looks like the parallel idea is a no go. I measure the same 4.2A after disconnecting the second COB... I also checked the light output by mashing on the unsoldered wire for the second cob and didn't really notcie any difference in output. No biggy. I might still make something, as I do remember turning both on when they were both powered separately and noticing a significant increase in output from using two complete units vs one.

I'll add that I picked these Craftsman 4xAA's for about $13 each, and the plastic components seem much more robust than the $10 Luminore 4xAA COB I picked up at Cabela's. The Luminore's COB wasn't even secured to the heatsink... just slid around on the thermal paste... and was much bluer with significantly less output.

Thanks for the replies!

 

[Lynx_Arc]

COB lights are the bomb for me lately. I've picked up cheap lower output ones at a store running 3AAs for $3 each and have other lower output ones also. The higher output COB LEDs that I've seen available online take higher voltage and I am wondering if going to a cree XPL emitter would be a better idea as you can get more lumens ouf ot a properly heatsinked emitter in a smaller space plus I think the efficiency is higher too plus better tint choices but the cost is not dirt cheap.

 

[Scotty321]

Probably... However, I got these on the cheap, and figured I could get decent with my soldering skills with this setup before I start trying on more expensive components. 20 years ago I messed up my first PC build and fried my first processor because I didn't install it right and spent money I didn't have to get another one. I'd rather mess up on on this, and if this little project goes nowhere and I don't mess up to badly, I should still be able to put them back together and use them as they were intended... If I put them together I'm sure they'll work fine for some attic insulation work I have to do in the Spring.

I'm attaching a pic of one of the two COB's (they are the same). If anyone can shed some light on their specs (pardon the pun), I would appreciate it. I didn't come up with anything on Google.

 

[Lynx_Arc]

You can possibly figure out the specs by measuring them in mm and comparing them with those online for sale on ebay or alibaba sites. It is likely they are 3 or 5watt varieties. I've been sort of entertaining the creation of my own 2000 lumen 20v tool light using COB LEDs but I've found it hard to find decent compatible COB leds that match my requirements. The ~12v COBs go up to about 5W and about 1000 lumens so to get 2000 lumens you need a pair of them in parallel. I have seen a 10W 24v COB listed but it was out of stock everywhere it was listed. There are also neutral white COBs but most are cool or warm white variations the warm white is not suitable for me for work conditions and the cool white is fine but I am concerned that it is a lot more bluish. Since the only available 2000 lumen COB is 36v or so it makes them unusable to me. A 2000 lumen tool light runs about $90 or so but if I can make one for $20 that has some custom levels to it such that I can choose low, low medium, high medium,and high modes perhaps 20/150/500/2000 lumen modes and maybe even a spotlight LED separately and also a USB output for under $40 it would be ideal. If I could get the 24v COBs for cheap enough I may consider a pair of them so I can do 4000 lumens output as I have some dewalt 6 and 8A tool batteries that should give usable runtime.

 

[Scotty321]

Have you tried deconstructing one or two of the Astro Pneumatic clones with the variable output dials and scavenging the parts? The reason I was hoping to run these off of the same switch was so that I could retain the two brightness settings with one button.

IIRC, the Craftsman light I took apart was a little whiter (less blue tint) with the white plastic reflector installed. Have you tried something like this to alter the tint on what's available to you?

 

[Lynx_Arc]

Have you tried deconstructing one or two of the Astro Pneumatic clones with the variable output dials and scavenging the parts? The reason I was hoping to run these off of the same switch was so that I could retain the two brightness settings with one button.

IIRC, the Craftsman light I took apart was a little whiter (less blue tint) with the white plastic reflector installed. Have you tried something like this to alter the tint on what's available to you?

I haven't tried much yet I don't have the parts at this time and my funds are getting low.

 

[Scotty321]

Some other notes...

I upgraded the wire from the LED to the board and to the batteries with 16 AWG from the hardware store since I was messing around with the solder... they didn't have 18 and I wasn't sure that the 20 was much thicker than the stock.

I figured I would try the setup with one of my LG 18650's (unprotected) and read 6.5 amps with the clamp meter (4.08v). However the heatsink area became hot to the touch pretty fast. It definitely seemed like more output, but I am afraid it might fry the LED quickly.

I retested with 4xAA NiMH (measured 1.3v each) and the clamp meter read 4amps. Although the LED started to warm up a little, it wasn't nearly as hot or as fast as with the 18650... so I think I'm going to stick with the NiMH for now with this setup.

I'm going to replace the wires on the second, zip everything back up, and just keep them for portable work lights for my Springtime attic insulation project. I think it's also a good test to see if the NiMH's will burn the LED out if used for long periods of time... and get an idea of runtimes.