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Drop In LiFePo4 Batteries Round 2

4757 Views 30 Replies 6 Participants Last post by  colemj
I saw some to me unbelievable low priced 100Ah drop in LFP batteries on Amazon today ( At least low priced to me who got my last set of batteries only 2 years ago and was comparing costs of LFP to the FireFly batteries I got. Now I read Rod's article slowly this morning:

and chased down the full spec sheet attached.

To my reading this seems a good LFP battery spec compared to the items Rod's article


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Just bought 2 Ampere Time 200 AHr Plus LiFePO4 batteries from Amazon. When I purchased them on October 20th there were 742, now 690 each when buying a two pack. Wonder if I can get the difference back. I purchased those batteries mostly because of the good reviews and Will Prowes tear down on YouTube.

Are they drop in? NO! I have added a DC-DC from the alternator to the lifepo4, removed the AGM charger and replaced it with a inverter charger, added 3 160 panels and a MPPT charger.
Looking at the Ampere Time specs, those have max charge/discharge of 100A, so perhaps this 0.5C rating is common among dropins.

For comparison, the higher quality cells used to build batteries have 1C charge and 2C discharge ratings.

The 100 amp rating might be for the non plus model. We purchased the Plus model. From the plus model with the 200 amp BMS:
recommend charge current 40 amps
max continuous charge current 200 amps
max continuous discharge current 200 amps
max discharge current for 5 seconds 400 amps
cycle life 4000 times

What I don't like are the operating temps 0-50C charge -20 to 60C discharge and storage temps of -10C to 50C but that is due to the chemistry.
So how do the max charge currents work when a BMS drops out a drop in battery? Lets say you have 3 batteries that can accept 50A each and your alternator + solar could do 120A. When the batteries are charged 1 of the batteries BMS drops it out and now there are only 2 50A acceptance batteries on line with a 120A supply. What if another battery drops out????
I'm assuming the batteries are wire in parallel. In our case the MPPT controller is limited to 40 amps, the DC to DC is limited to 20 amps (didn't want to overload the alternator) and the inverter charger can do 100 amps but is settable in 5 amp steps. So even if all three devices are pumping in amps the BMS limit is not reached in our application. The alternator is always connected to the lead acid battery so it is never unloaded.

For the case you stated the battery voltages track each other very closely within 10's of millivolts so the case of having 2 batteries charge completely then the entire 120 amps flows into the one battery won't happen because the current will decrease as the battery voltages rise. Which is way it is recommended NOT to mix old LiFePO4 with new ones.
Since the 3 batteries are wired together they are charged with the same voltage for the same amount of time. When the two batteries are fully charged the BMS doesn't disconnect because the charger voltage has not risen to the over voltage trip point. The third battery's voltage is so close to fully charge voltage the charger can not rise the voltage enough to push the 120 amps into the remaining battery, assuming all the equipment has been setup correctly and is functioning within manufactures specifications and all three batteries have been slowly charged so the BMS had time to equalize each cells voltage.
A lot of features for the price, bluetooth and cold temp shut down. Considering the reviews on Amazon I'm a bit skeptical of the cell quality BUT the company did respond with replacements. Maybe someone can jump in on why advance warning of BMS disconnect is needed.
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