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DaveBell
Moderator
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# Posted: 20 Apr 2024 20:34
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I am a little concerned. The RC lawnmower I bought says to do not leave it unattended while charging. Do these batteries ever have problems when charging?
Shenzhen 12.8V LiFePO4 Battery 42Ah
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gcrank1
Member
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# Posted: 20 Apr 2024 22:04 - Edited by: gcrank1
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Probably a CYA thing, especially if it really isn't an LFP battery but one of the other Lithium chemistries.
LFP has proven to be very safe, but not the same can be said for all chargers.
Fwiw, I monitor all my rechargeables to get a sense of the charging curve and don't leave them on charger past a reasonable time or 'full charge indicator'. I don't even like leaving my cell phone or laptop plugged in overnight.
You could use an inexpensive household timer to run the charger for x hours and shut off. That would give you the rest of the 24 as a buffer.
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travellerw
Member
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# Posted: 20 Apr 2024 23:38
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LiFePO4 is super safe.
but it is a battery. I'm super careful with all of them as I have even seen FLA melt down.
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Steve_S
Member
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# Posted: 21 Apr 2024 09:04
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I also feel that is a CYA thing, most especially due to the E-Bike shenanigans which has been hyperinflated by the fear mongering chicken littles. E-Bikes are NOT LFP either !
Gcranks Timer Idea is a GOOD ONE if you have any doubts and until you have confidence.
There is a catch... Sorry. But some of these "chargers" are not the best, usually the cheapest & simplest they can use of course. FAR TOO MANY companies push an envelope of stupidity by pushing the charge voltage too high. Make sure to take a Voltage reading on the chargers terminals to see what voltage it's at, it should NOT be over 13.8V (3.450V per cell X 4 cells). If it is higher, that is overdriving the LFP beyond Working Voltage spec.
It would be useful if ou could post a photo of the Charger & it's specs or a link to the info on this product.
Just in case anyone else comes along. Keep in mind that LFP (LiFePo4/Lithium Iron Phosphate) cells can be either: Pouch, Prismatic (big blue square) or Cylindrical in formats with various AH ratings.
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paulz
Member
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# Posted: 21 Apr 2024 10:18
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Agree, CYA thing
Quoting: Steve_S NOT be over 13.8V (3.450V per cell
Ok, just lowered my solar charger to 13.8. Actually saw 14.1 on the MY50 display yesterday. Suns finally out!
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DaveBell
Moderator
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# Posted: 21 Apr 2024 22:31
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Yeah, E-bike fire and recently battery powered scrub brush fire. So much junk coming out of China. The mower sat in my garage for a year (one initial charge before winter) because I hate mowing short grass. This year it got about 14" tall so wife gave me marching orders, get the mower going.
I was worried that not charging it (don't know if the charger is also a maintainer) would have harmed the batteries. But they came right back. The batteries measure 13.8 after 5 hours charging, they measured 12.5 after sitting one year.
Folks at Super Droid Robots could not tell me if the charger would function as a maintainer also.
"It is generally safe to keep these batteries on a charger, but we recommend to not over extend charging time to keep the life of the battery healthy and to keep yourself and the unit safe." Yeah, CYA.
The mower is now living in the backyard under the roof overhang with a cover to keep rain off. The day I mow, I hook up the charger and wait five hours. I'm surprised the batteries didn't die waiting for months in the garage. Do LiPoF04 survive not being charged better than other batteries?
Thanks for the responses guys!!
Dave
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gcrank1
Member
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# Posted: 22 Apr 2024 08:20
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YES, they do. The self discharge (as long as there are no active or phantom draws) is very low. The recommendation for long life is to not store at full charge, but 60ish%. Also, unlike LA, LFP does not need to be recharged asap after use.
Was the 13.8v observed right after charging or after settling a few hours? You want to wait a bit.
Note that voltage is Not a good good way to measure the state of charge of LFP. It will give you an indicator of the high and low ends but the usable power range is so flat that it is very hard to tell just were in that band you are.
If I were you, Id use the mower as needed, just for drill take a note of the voltage after it sits for some hours and store it.
Before use I would charge it, but sans a state of charge indicator on the unit, keeping an eye on the voltage rise. Once it reaches 13.8 stop rather than continuing. The amps will have fallen off and you will have probably 95% soc.
After a few cycles of use the battery will settle down too and you will have a better sense of how long to 'top it up' prior to use.
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Steve_S
Member
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# Posted: 22 Apr 2024 08:27
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LFP is actually one of the best when it comes to retention. BUT they must have some charge, generally between 30-50% when being put into storage for a period of time. They can sit at 50% for over a year "inside" without much loss at all *(IF the BMS is not drawing power). If the BMS is pulling, it will be minimal but can draw down the battery.
At year end, leave the battery at 12.8V +/- a wee bit and no worries. IF the battery drops to 10V it will shutdown (proper BMS function) and should be wakeable with an incoming charge. This depends on the quality of the BMS though.
As an FYI:
I have had LFP cells frozen solid in storage at -30C with 30% charge in them. Once thawed they were fine and still are. LFP can continue to discharge up to -20C but cannot take a charge until they are at +5C internal temp. Limited low charging (0.2C Rate) can happen from 0C to 5C after which full charge rate can be applied.
LFP does NOT explode or catch fire. Worst case that can happen is they overcharge & offgas, at which time they become scrap.
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old greybeard
Member
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# Posted: 27 Apr 2024 14:03
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Just put a LifePo4 battery in my camper. 100AH with a low temp cut off BMS. About $200. Prices have dropped dramatically. When I put new batteries in my cabin 8 years ago they didn't have BMS's available with the low temp cut off. And the batteries were very expensive
When I upgrade definitely going LifePo4
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DaveBell
Moderator
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# Posted: 30 Apr 2024 02:07
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Gcrank1, time for the experiment.
Its been 9 days, time to mow the grass. I measured the voltage, 13.3. Put on the chargers, light is red (charging). Waited two hours, charging lights are green, voltage measures 13.3. Mowed the grass. Next week i'll charge for only one hour.
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