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station240's 18650 projects
#1
Small pack I'm working on.
For now to be 12V nominal SLA battery replacement, for my under desk UPS.
These are A123 LiFePO4 (lithium iron phosphate) cells, recovered from faulty drill battery.



Long term projects/plans.
These mostly involve Project UPS aka Project Fridge
This should give you some idea of how large and heavy this UPS is.
a) 12/48V battery for DC Contactors, cell/voltage monitors, other electronics.
b) Powerwall for big UPS, which didn't come with any batteries. Did however come with a complete set of unused high current battery cables.
c) Project MPPT, inject power into the UPS from solar panels. Re purposing a mostly functional Grid Tie Inverter, which isn't able to be used for it's original purpose.
Could be repaired fully, but I'm not interested in spending the $40 needed to repair the inverter output.

Completed sub projects:
a) Teach the fridge to not require 3 phase power, my tricking the low voltage electronics. Suspect it may not power up with only battery power.
b) Disable the inbuilt charger for Lead Acid batteries. Turned out to be as simple as unplugging the connector to that half of the PCB.
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#2
If anyone in Australia has any of these A123 cells they would like to donate, let me know.
They are 3.2V cells rather than the usual 3.7V.
My internet is too shit to have a youtube channel, so everything has to be photos or text.
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#3
I think I've ditched quite a few of these.. I'll keep an eye out for more for you .. they are no use to me Smile
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#4
Found the TP4056 doesn't do LiFePO4 cells, so looking at either an alternative module off ebay or further modify a PSU to be a dedicated charger.
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#5
station240 Wrote:Found the TP4056 doesn't do LiFePO4 cells, so looking at either an alternative module off ebay or further modify a PSU to be a dedicated charger.

I use a computer psu with a 'step up converter' so it can be done.
Why not switch to 18650 before the project gets to big?

Good luck with the project and keep us up to date

Cheers
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#6
Still pondering what charger to use for individual cells, there are boards that use the MAX1879 IC, which also come with a polarity switching system so it doesn't matter what direction the cell goes in.
The reason for the MAX1879, is it has multiple charge voltages (select using wire jumpers), of 4.35V 4.2V 3.6V. The 3.6V is needed for LiFePO4.
Basic idea is to use those boards for charging untested cells, and build a higher current charger that can do multiple cells.

The A123 cells I have are good for 30A discharge, I'm going to have to devise a way of testing that.
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#7
Been working on various things, so far this is the only 100% finish part.
This transformer like part is an inductor from some Industrial equipment, which I kept for some reason.

Was difficult but I managed to dismantle it, without damaging the copper in the process (stretching or scratching).


dimensions: 1.2mm thick 28mm x 77cm

I really should have tried not to bend these connections.

My DIY battery charger, built almost entire from ATX PSU parts, mostly works.
However it's not stable at 3.6V needed to charge LiFePO4 cells, is perfect on 4.2V so can charge normal Li-Ion cells.
Todo is to add circuitry to add a max and min current cutout.
eg max current 1A min, min current 75mA.
The min current being how you are supposed to determine if an 18650 is fully charged.

The charge process for LiFePO4 cells is rather different, still trying to wrap my head around that.
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#8
If you are intending to use these packs within an existing UPS, how are you intending to alter the UPSs' charge process to suit the new chemistry ?
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#9
Sealed Lead battery: 6x 2V cells 12V battery 14.4V charge
LiFePO4 battery: 4x 3.2V cells 12.8V battery 14.4V charge

So the issue is not charging the new battery, but having the correct low voltage cutout.
This of course is the small UPS, which has a weird charging circuit.

The big UPS is no issue at all, I disabled the internal charger months ago, simply by pulling a plug out of the PCB.
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#10
it was more the cessation of the float charge
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