9V Device Powered By 2S 18650's

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garrybunk
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Location: Johnstown, PA
9V Device Powered By 2S 18650's

So I was looking for a way to power my 9v battery powered luxmeter during long tests without wasting 9v batteries (I really have no idea how long they last in the luxmeter). I looked into 9v NiMh batteries as well as Li-ion rechargeable 9v batteries, but just didn’t like those ideas. The 9v Li-ion battery tipped me off though to put 2 li-ion cells in series for 8.4v to power most 9v devices. So, I decided that this is a great way to get some use out of some junk 2S & 2S2P bike light battery packs (the low capacity, not worth using with a bike light types) that I’ve accumulated. I also have some battery cases to feed 2 or 4 cells in if I need to go that route. All I needed to do was buy some 9v snap connectors from Ebay and DC 5.5/2.1mm male connectors. I found and decided to go with these connectors which are a combination of the two, but needed polarity reversed. To reverse polarity I simply snipped the wires, and resoldered black to red / red to black, soldered, then used heatshrink over the joints. After testing on the luxmeter to be sure it worked, I modded the luxmeter case to allow the wiring and DC connector to exit the battery compartment. Here are some pics:

-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques


NOTE: Moving my photos from PhotoBucket to Flickr. PM me or post in the thread if you can’t see my images and need me to fix or send a gallery link. PhotoBucket images should remain visible until November 2018.
ImA4Wheelr
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Nice. Been wanting to do that with 3S lifepo4 cells that I have on hand.  Voltage should be closer to a fresh 9v battery.

If one doesn't want to wait for those 9v connectors, they can be easily fabbed by taking the top of an expired 9v cell.  Sometimes you find one dead AAAA cell in there and 5 good AAAA cells too.

garrybunk
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Last seen: 4 hours 41 min ago
Joined: 10/31/2011 - 09:25
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Location: Johnstown, PA

I also thought about snipping a lead off of some old device that ran on a 9V battery, but I couldn’t find anything. From what I’ve read on the voltage level, the majority of 9v run devices don’t actually require the full 9+ volts and that (along with the flatter discharge curve of a li-ion cell) is why the 2S arrangement works so well. FWIW – my 9v alkaline battery that I pulled out of my luxmeter was at 8.10v and still running the meter fine. I don’t know at what voltage “low battery level” trips though. I could check into that with an adjustable power supply, but I just don’t think it’s worth the effort.

-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques


NOTE: Moving my photos from PhotoBucket to Flickr. PM me or post in the thread if you can’t see my images and need me to fix or send a gallery link. PhotoBucket images should remain visible until November 2018.