Changing from gel cell to Lifepo4 battery

[GregTN]

I currently have a small inverter that powers my TV and some lights when the grid power goes down and the 12v 100ah gel cell battery is in need of replacement.  I would like to use Lifepo4 batteries with a suitable BMS as a replacement but the inverters built in charger doesn’t seem to have any adjustable  parameters.  The maximum voltage the battery reaches after charging is 13.8 volts and that also appears to be the float voltage.  The charge current rating on the inverter is 15 amp max but it normally starts charging around 8 amps and reduces to around 600ma when it is floating.  Would this charger work with four 3.2v 100ah Lifepo4 batteries?  I could always purchase a new charger but the inverter operates like a UPS and everything is automatic without any intervention from me which is an option I would like to keep if possible.

[Crossy]

10 minutes ago, GregTN said:

Would this charger work with four 3.2v 100ah Lifepo4 batteries?

 

Yeah, I've found that LiFePO4 is close enough to lead-acid for the chargers to work OK, you won't get to 100% charge but that's actually better for the cells anyway.

 

[GregTN]

Great to hear that as I can get them for around the same cost as the lead acid on Lazada and effectively almost double my amp hours since I only discharged the old battery to 50%.

Thank you

[Crossy]

I'm using some used 200Ah LiFePO4 golf-cart batteries, 1,600 Baht each on Lazada, measured at about 80% of rated capacity!

 

Many sellers with these, imported from China (golf must be a big thing there).

 

[GregTN]

I found this on Lazada and if I am understanding correctly this setup will provide 12.8 volts at 72 amp hours for under 3000 baht.

https://s.lazada.co.th/s.4vjqr

Anyone have any experience with this type of battery?

[Crossy]

10 hours ago, GregTN said:

Anyone have any experience with this type of battery?

 

I've bought from the Lifepo4shop before and found them to be ok (not those particular batteries). I got my golf-cart cells from him https://www.lazada.co.th/products/calb-lithium-ion-lifepo4-32v-12v-grade-a-200ah-ups-battery-i2527489409-s8982895966.html

 

I still wouldn't assume you'll get 72Ah particularly if charging with a lead-acid charger but at that price you can't really go far wrong.

 

If you don't get the capacity you need just get another 4 and make a 2P4S pack on the same BMS and double the capacity.

 

Don't forget you'll need a 4S LiFePO4 BMS too.

 

[Muhendis]

GregTN needs to be aware that:-

1. The lead acid charger has a trickle charge cycle which is unnecessary with LiFePO4's. This is not a serious problem but you might notice it and wonder.
2. More of a potential problem is the BMS. If it cuts off because of a low battery voltage, the charger may think there is no battery connected and therefore may not start charging. It depends on how the charger is set up.

[Crossy]

Yeah ^^^, I have a UPS that does No2. Run it completely flat and it won't charge until the BMS is woken up. It's rarely an issue but worth remembering.

 

[GregTN]

I do have the ability to turn the charge off so after it charges to its max I can turn it off.  Thanks for that information as I didn’t think about that.

I think number two is covered automatically because the inverter shuts down due to low voltage at 10.5 volts and the BMS shuts down at 10 volts.

Thanks for the suggestions.

[GregTN]

On 9/28/2021 at 5:56 AM, Crossy said:

 

I've bought from the Lifepo4shop before and found them to be ok (not those particular batteries). I got my golf-cart cells from him https://www.lazada.co.th/products/calb-lithium-ion-lifepo4-32v-12v-grade-a-200ah-ups-battery-i2527489409-s8982895966.html

 

I still wouldn't assume you'll get 72Ah particularly if charging with a lead-acid charger but at that price you can't really go far wrong.

 

If you don't get the capacity you need just get another 4 and make a 2P4S pack on the same BMS and double the capacity.

 

Don't forget you'll need a 4S LiFePO4 BMS too.

 

They actual advertise these 200 ah batteries you purchase as “Brand new” but even at 80% of the rated capacity that is still a great price.  How did you come to learn they were indeed used?

[Crossy]

6 minutes ago, GregTN said:

They actual advertise these 200 ah batteries you purchase as “Brand new” but even at 80% of the rated capacity that is still a great price.  How did you come to learn they were indeed used?

 

If you switch to Thai then use google translate "*Beware of impersonating 200ah. But a 180ah battery, if you want to be sure, look at the series Lithium ion phosphate battery from CALB 3.2 V 200ah GradeA, good quality second hand batteries, GRADE A, carefully selected."