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

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.

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

I put a 2x18650 together with a fuseholder and 2a minifuse with the snap from a dead 9v battery.
Done originally for a radio that had a 6 c holder with 9v snap that was killed by alkaleaks.
Not wanting to give alkaleaks another shot at killing this late 50’s radio i made this adapter.
Customer loves it.
I made a few more.

If its something that doesn’t have to be mobile, I found these on Amazon. I have one for 9v and another for 2 AAA batteries. The thin flat ribbon cable even allows the battery compartment to close. Haven’t had a problem yet.

Lenink AC Power Supply Adapter for 9V Battery

Lenink AC Power Supply Adapter for AAA Battery

Necro Bump, It’s Alive - Alive…

I got lazy trying to match battery voltage to various low current devices.
So I got some of these things. I use old laptop 19v power supplies or enough old 18650s to make sure the supply voltage is high enough for the buck converter to work. Need to make sure the input V stays 2v (or more) than the desired output.


From Amazon, like 3 for $14? Cheap and you take your chances on them being DOA according to the reviews.

Or the DROK Buck that can be Voltage or Current limited. 1 for about the same price.
All the Best,
Jeff