Author Topic: another NiCad to LiFePO4 conversion  (Read 3205 times)

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dnix71

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another NiCad to LiFePO4 conversion
« on: March 27, 2013, 11:43:14 PM »
I have two led shed lights bought from Home Depot several years ago. They use a 3 cell AA nicad pack to power 5 leds. The battery pack is identical to the one used in many older cordless phones.

The original plastic rocker on/off switch on both failed after a few weeks. Since I knew it to be a defective design, instead of returning the lights, I went to Radio Shack and bought 2 proper metal toggle switches and fixed both.

The shed lights are solar charged from a small thin-film panel that has a 10 foot cable for remote mounting. Fully charged when new the lights would run for at least 4 hours

The one in my bathroom worked well for a while and then on cell on the outside of the pack went bad. I replaced the bad cell. Today I noticed a second cell was getting weak and decided to try a LiFePO4 cell instead of tearing the pack apart again.

It works. The AA sized 3.2v LiFePO4 cell was put in a AA holder and the original pigtail connector cut and soldered to the new cell holder.

The second pic is a closeup of the circuit that drives the leds. The diffuser was removed so you could see the leds clearly.




vtpeaknik

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Re: another NiCad to LiFePO4 conversion
« Reply #1 on: April 09, 2013, 03:40:20 PM »
Is this "AA sized 3.2v LiFePO4 cell" a standard (?) 14500 (or 14505) cell? Does it have a built-in circuit to prevent overcharge?  I wonder how well it will work in cold conditions.  My outdoor solar LED motion-sensing light worked OK for a year or two but then stopped working most of the time in the winter, when I actually need it.  Perhaps I should put a Lithium cell in it like you did.

dnix71

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Re: another NiCad to LiFePO4 conversion
« Reply #2 on: April 10, 2013, 05:57:09 PM »
The cells I use are plain cells. They are physically an exact match for a common AA cell. Rechargeable outdoor led lights use lipo cells now. Just take the light apart and you may find it uses something Radio Shack sells. I can get these cells at Radio Shack, but they don't sell chargers. That's not a problem if you are just replacing a cell in an outdoor solar light.

vtpeaknik

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Re: another NiCad to LiFePO4 conversion
« Reply #3 on: April 11, 2013, 10:19:36 AM »
Well if the solar panel is in a sunny spot it may over-charge the battery, and Lithium batteries are famous for fireworks.  I was even worried about the NiCad battery overcharging, so put the panel of my motion sensing light in a location where it gets limited sunshine.  That turned out to be not enough light in the winter, perhaps.

Any easy way to add a simple "charge controller" of some sort to this?  E.g., a zener diode of about 3.6V in parallel with the battery?  (If there is such a zener diode available.)

Harold in CR

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Re: another NiCad to LiFePO4 conversion
« Reply #4 on: June 17, 2013, 02:33:25 PM »

 From my very recent search for the Radio Shack cells, they are no longer available ???. Not in the Solar application anyway. ?

 I had to go to Hong Kong and buy a pair of 700MHR 14500's. Got them in less than 10 days to Florida. Now, to get them sent down with other goodies, in the next 3-4 days.