LiFePo4 batteries in 12v applications

[jkaetz]

https://a.co/d/fhFwnNZ

Has anyone substituted these for 12v applications? They claim to have a built in BMS to prevent over discharge but aren't as clear on charging, do they need 14.6v to charge them or will the BMS boost a 12 -13v charging voltage? I'm looking at the kids ride on toys and my various UPS units around the house. They list plenty of info on discharge and cycles but don't mention a lot about charging. I have a good charger for my RC equipment that would do the job but it would be better if the standard 12v lead acid chargers would do the job.

 

[Dave A]

Depending on the quality and features of the BMS it will limit the discharge percentage and the max charge percentage, discharge and charge rate, cutoff output at high and low temperatures. As for charging voltages you have to check the specs provided with the battery(the Amazon link you have list those parameters). They would be best at replacing lead-acid batteries in the right environment. A guy named Will Prowse on UTube does good videos reviews on LiFePO4 batteries.

 

[DoggyDaddy]

 

[jkaetz]

View attachment 213387

LiFePo4 batteries will give similar capacity to lead acid with less weight and more cycles in a deep cycle application. They have slightly different charge and discharge requirements though. Thus the BMS (battery management system) to prevent overcharge/over temp or over discharge.

 

[DoggyDaddy]

LiFePo4 batteries will give similar capacity to lead acid with less weight and more cycles in a deep cycle application. They have slightly different charge and discharge requirements though. Thus the BMS (battery management system) to prevent overcharge/over temp or over discharge.

I got nuthin'... But I can sorta understand this version in principle at least. So thanks for dumbing it down for me.

 

[snapping turtle]

I think there are two kinds one has like a heater in the battery because they don’t like to take a charge if the temp gets down to a certain level. The other has no internal heater.

 

[laf]

I have a couple LiFePo4 for ham radio. They require a different charger than one you have for your SLA or Gel batteries. The charge cycle isn't even close to what a lead acid is. Now there are some expensive battery chargers that you can set up for different chemistry types and those will work but your $30 big box special will not fully charge a LiFePo4.

They hold nearly double a lead acid of the same rating. The BMS will keep it from over discharging and damaging itself unlike the SLA/Flood/Gel. The voltage as it discharges is a lot more stable as well unlike the lead acids. They're also very light compared to the same lead acid capacity.

If you're planning on stuffing this into a cheap UPS you will not be happy with the results. The onboard chargers are for lead acid and not LiFePo so it will not fully charge a battery. The more expensive ones have configuration that you can change for Gel/Flooded/LiFePo/etc.

So kids toys will get close to double the run time, UPS you'll be unhappy with, and you need a charger scaled for your battery capacity. You shouldn't use the same charger for a 20Ah battery as a 100Ah one.

 

[jkaetz]

I have a couple LiFePo4 for ham radio. They require a different charger than one you have for your SLA or Gel batteries. The charge cycle isn't even close to what a lead acid is. Now there are some expensive battery chargers that you can set up for different chemistry types and those will work but your $30 big box special will not fully charge a LiFePo4.

They hold nearly double a lead acid of the same rating. The BMS will keep it from over discharging and damaging itself unlike the SLA/Flood/Gel. The voltage as it discharges is a lot more stable as well unlike the lead acids. They're also very light compared to the same lead acid capacity.

If you're planning on stuffing this into a cheap UPS you will not be happy with the results. The onboard chargers are for lead acid and not LiFePo so it will not fully charge a battery. The more expensive ones have configuration that you can change for Gel/Flooded/LiFePo/etc.

So kids toys will get close to double the run time, UPS you'll be unhappy with, and you need a charger scaled for your battery capacity. You shouldn't use the same charger for a 20Ah battery as a 100Ah one.

Excellent info, thanks. Unfortunate that they are not true drop in replacements if you have to alter charge circuits to get full capacity. Given that the batteries have a bult in BMS to cut off the charging, wouldn't it simply be a matter of increasing the UPS charge voltage to 14.6? Mine are mostly old APC units certainly not built with LiFePo4 in mind. I have modified the oldest (probably 20 years or so) to adjust the charge voltage because it had drifted a little high. Charge current would only impact recharge time yes? For the most part I don't think they need to be charged quickly, we don't usually have outages longer than a few minutes. I can only think of one where it would be tempting to go from 10 - 12 AH to a higher capacity.

 

[laf]

They'll physically drop in, but you're right you will not just skate by with the old chargers. In the case of kids toys it may not matter since the batteries usually have to come out anyway and you can use the dedicated LiFePo chargers.

The BMS on the LiFePo4 aren't total charge controllers, they mostly make sure that the batteries aren't fully discharged, that it isn't delivering more charge than the pack is capible of, that the temp is ok, and that the pack stays balanced. The whole charge cycle on the lead acids may not give you the bulk current charge because when the lead acids are fully discharged they'll be closer to 11.5v but LiFePo will be around 12.8-13. So when the APC sees that it's at 13v it will think it's a lead acid in float charge not bulk charge and my not allow enough current to go into the battery.

A good site on battery charging rates and voltages. You may get away with it charging without modifying your APC but I wouldn't hold my breath. I've been reading more about them for RV's and there is plenty of stories on "I ruined my battery" or "it never charged" because the RV's charging was designed around flooded lead acid chemistry.

 

[jkaetz]

The BMS on the LiFePo4 aren't total charge controllers, they mostly make sure that the batteries aren't fully discharged, that it isn't delivering more charge than the pack is capible of, that the temp is ok, and that the pack stays balanced. The whole charge cycle on the lead acids may not give you the bulk current charge because when the lead acids are fully discharged they'll be closer to 11.5v but LiFePo will be around 12.8-13. So when the APC sees that it's at 13v it will think it's a lead acid in float charge not bulk charge and my not allow enough current to go into the battery.

Right, I have an RC charger that will happily charge the kids stuff, not too worried there. The UPS is more of a wishful thinking project to see if it can be made to work. I know most of them can adjust their float voltage, but I don't know by how much yet. The only one I would likely do this with is the one powering my home network in case of a longer outage. Most UPS are setup only to allow a graceful shutdown of systems instead of a longer runtime. Granted with lead acid batteries you'd need a ridiculously sized battery to match the capacity of LiFePo4.

 

[laf]

If you could disable charging from the UPS and have a separate charger for those batteries, it'd be ideal. But you can always try adjusting that float voltage in conjunction with a smaller capacity LiFePo4 and if you toast it, you're not out $100 for a decent sized battery pack. Also keep in mind the smaller you go, the less you can have for total draw on the battery. Smaller packs may limit you to 10A out so the cells don't overheat. So if you do get a test battery, don't try to run a lot off it. Good luck, the future is LiFePo but we're still in the present.