Charger Recommendation for LiFePO4 backup system.

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Solar Enthusiast
Nov 28, 2019
I plan to build a 12 V LiFePO4 backup system to power a refrigerator.
I would like to run my refrigerator off grid during peak hours (4 p to 12 am, or 8 hours).
I plan to build a system based on 280 Ah Cells, and have a maximum discharge of 80%.

I plan to charge the battery during off peak hours, or for 16 hours a day.
So the charge rate in this case would be: (280 Ah) x (80 %) / (16) = 14 Ah.
Charging rate would be: 14 Ah / 280 Ah = 0.05 C charge rate.

I noticed some type of car battery trickle device such as:
but I wonder if this is the way to go?

- So what charger would you recommend for my application?


Happy Breffast!
Oct 26, 2021
Given that you've calculated you need 14A of charging, two of the options you've listed can't provide that; however, you don't need to charge the entire capacity in 16 hours.

Assuming this is a typical residential fridge, you are looking to provide about 800Wh of energy per day.

280Ah * 3.2V * 4 = 3584Wh = 4.48X the amount of energy you need on a daily basis, so you're only looking to restore 62.5Ah over that 16 hour period, not 280Ah. You only need a 4A source.

IMHO, given the low amount of discharge, to maximize life, I would simply "float" the battery at 13.6V. This would gently charge it to 95% SoC and likely improve the already ridiculous cycle life.

There is a 15A version of this converter for $129:

It can operate as both a 14.6V bulk, 13.8V absorp and 13.2V float charger OR it can operate as a constant voltage supply.

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Solar Enthusiast
Nov 28, 2019
@sunshine_eggo thank you for your reply.

Thank you for pointing out the PowerMax converter device.
This would be a perfect way to keep the battery charged.

I checked my refrigerator and the compressor power is about 190 W.
I am now running a Wattmeter for a full day to determine the daily consumption.
I noticed when re-starting my refrigerator that the defrosting ran for about 30 minutes consuming 390 W.

I plan to use this project as a base framework for developing larger power generators.
In particular, I would to monitor the consumption using a Modbus power meter (based on this design).

Modbus Power Meter .jpg
I would like also to develop some battery control mechanism to stop the battery charging when completed,
and to disconnect the load when the battery charge is too low and switch back the load to the grid.
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Photon Sorcerer
Dec 30, 2019
I would suggest using the sun to charge it 😎.

Can you install solar panels or is that not an option?