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paulz
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# Posted: 22 Dec 2024 11:58am
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Great you’re having good results. I’m still unclear on the dangers of using LFPs with alternators. I’ve read they can overcharge/undercharge, spike..
Are those Antigravity’s special? Will a BMS Lfp normally handle abnormalities?
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gcrank1
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# Posted: 22 Dec 2024 01:14pm - Edited by: gcrank1
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The BMS is supposed to be the last ditch protector for the cells, think of it as normally a multi-use, self resetting circuit breaker on both high and low voltage.
But when one fails how do we know? Probably after something way amiss happens with the battery?
Depending upon the BMS as a voltage regulator is considered bad practice, the fusing along with proper wire size is primary.
As I understand it the real danger in a 'vehicle' situation is that when the battery is low the alt will output huge amps thus overheating/overloading the alt (BAD) and the belt(s) may fail.
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ICC
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# Posted: 22 Dec 2024 01:17pm
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Quoting: paulz I’m still unclear on the dangers of using LFPs with alternators
I believe the big danger only is with something like an RV that has LFP house or coach batteries. When those are depleted a good amount the alternator can pump a very high number of amps into the LFP batteries because of the low LFP resistance. For an RV situation, a person can invest in a super duty alternator which is made to handle a constant high amp current, or use a DC to DC charger that will charge from the starting battery system and have a lower preset maximum charge rate.
We asked about that and were told we would be trouble-free with our two Yamahas. I do not know the technical details. Perhaps it is because the batteries do not have a huge total capacity; not big enough to cause the alternator to overheat. ???
I have no idea how the available car and truck size LFP cranking batteries work or what dangers there might be. I would have to do some research if I was interested in one of those. But I have no interest in LFP for my cars or trucks.
I like the LFP very much for the dirt bike and ATV. I have strived to keep the dirt bike as light as possible. And for the ATV it was nice to remove some top weight as we have some trails where we traverse sidehill slopes and I feel better.
Quoting: paulz Are those Antigravity’s special
A little. They do have a full-feature BMS as well as a reserve function in some batteries. Sorta like the reserve gas tank feature. If a Re-Start series battery is run down low enough that the BMS cuts off any output, there is a button on the battery that when pressed releases the reserve to allow 4 or 5 starts. There is also a remote control, but who needs another remote control to keep track of?
Antigravity also has a series of mini jumpstart packs that are sized for small engines. Like 6 x 3 x 1 inch and 10-11 ounces.
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ICC
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# Posted: 22 Dec 2024 01:21pm - Edited by: ICC
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Oh, and in a RV, or any vehicle I guess, if the BMS cuts off the larger charge current because it is too high there is the added danger that disconnecting the alternator like that can damage the alternator.
Most people I know with LFP RV house batteries use a Victron DC-DC charger to charge the batteries from the engine. Most also rely on solar panels for much of the charging.
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paulz
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# Posted: 22 Dec 2024 05:24pm
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I do see some used cycles advertised with Lfp batteries, cars no. Maybe it is the weight savings, or smaller output. Two types of alternators I know of, one with permanent magnets, other energized magnets, those spin free when not powered. Does either make a difference for Lfp, don’t know. Seems like the higher output ones use the energized.
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paulz
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# Posted: 27 Dec 2024 10:02am - Edited by: paulz
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Very thorough explanation of vehicle alternators for Lfp battery charging. I’m on my second read and just beginning to understand. Basically, in opposition to my original thought, a charged field alternator is better than a permanent magnet field for Lfp charging. Has to do with frequency and amplitude.
url=https://earthxbatteries.com/engine-charging-systems-use-lithium-batteries/]https: //earthxbatteries.com/engine-charging-systems-use-lithium-batteries/[/url]
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Nobadays
Member
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# Posted: 27 Dec 2024 10:13am
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The LiTime 12.8/100ah LFP I just put in my Class B campervan specifically says "do not use for a starter battery. " It has a 500a/1s discharge ability, and I did use it to crank over the Onan 2800 under the van which draws <25amps. That said I'm going to run a new wire forward to the chassis battery for the generator. There must be a reason they say not to use it for a starter.
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gcrank1
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# Posted: 27 Dec 2024 10:31am
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I wouldn't charge a house type lfp off my vehicle alt, Id use a dedicated dc to dc charger powered off the alt.
Id much rather spend $100ish for the dc2dc than whatever a replacement alt is these days.
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paulz
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# Posted: 27 Dec 2024 10:53am
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I wonder why they say that, doesn’t the BMS shut it down if the amperage exceeds its setting?
I’ve done a bit of testing with my new cheapo 100ah Lfp. It starts my little Honda 20hp cart no problem (has no charging system connected). Then, before leaving the house for Christmas at the cabin, I tried it in the hot rod, little 125 cu. In. flathead. Started that too no problem. Next I want to try the Onan generator starter here but it also charges the battery when running, not sure what it has for an alternator but killing this cheapo Lfp I could get over.
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ICC
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# Posted: 27 Dec 2024 01:22pm
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Quoting: paulz I wonder why they say that, doesn’t the BMS shut it down if the amperage exceeds its setting?
Yes, the BMS should cut off the charging. But when the output from the alternator has no place to go the alternator may be damaged or killed.
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Quoting: gcrank1 Id use a dedicated dc to dc charger powered off the alt.
To be more precise, the DC to DC charger is running off the battery that the alternator is charging, not directly off the alternator.
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paulz
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# Posted: 27 Dec 2024 03:16pm
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My question was concerning the LiTime warning Nobs mentioned “my Class B campervan specifically says "do not use for a starter battery.” What happens, will the BMS turn the battery off, or will it slowly spin over until the Lfp cooks?
Both engines I’ve tried mine on spun over as well as with flas and for long enough to get the gas going.
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gcrank1
Member
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# Posted: 27 Dec 2024 03:47pm
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Good catch, Izzy 
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ICC
Member
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# Posted: 27 Dec 2024 05:33pm
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Quoting: paulz says "do not use for a starter battery
The only thing I can think of is that the LFP cells do have a maximum recommended discharge rate. The BMS should cover that rate and should cut off the discharge if that value is hit.
Perhaps that amperage has not been hit by the starter motors you tried? Why??.. perhaps the engines are small enough and maybe low compression that it isn't all that difficult for the starter to spin the engine? Just guessing.
Or perhaps the BMS isn't good enough to act fast enough to cut off the discharge before the engine starts?? If that was the case then the LFP cells might be degraded with each start, depending what
actual ampere discharge was hit?? Again, just guessing.
And all that is assuming that the battery has a fully functional BMS that covers all the things we would want it to do.
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paulz
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# Posted: 27 Dec 2024 06:21pm
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Nob’s Lfp says 500a for 1 second max discharge. Flas typically have 500 or better CCAs. My little engines likely draw much less as you say.
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paulz
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# Posted: 27 Dec 2024 07:34pm - Edited by: paulz
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Quoting: Nobadays I did use it to crank over the Onan 2800 under the van which draws <25amps
Found in my Onan manual it takes 360-450 amps to start. It’s a 2 cylinder.
Also saw some Onan Lfp discussion on diy solar.
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gcrank1
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# Posted: 27 Dec 2024 07:57pm
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Note: This is just my understanding, OR lack of it:
I believe the high rating is the initial 'get it to spin' load then drops off quite a bit quickly (but to what?). Temp, oil drag, etc will matter, as we all have likely experienced.....
Starting LA bats are made to quickly discharge/dump their power and quickly recharge upon starting and thus the charging system activating.
LFP will also discharge and recharge quickly, and as I understand it the BMS, if so equipped, will limit both; but the BMS is supposed to be the last ditch safety for the bat, not a regular use regulator. A fuse to pop before the BMS limit might be a good thing.
If your starting load would pop the fuse it is (duh) too much load.
If it does start the unit then the issue comes down to how long it cranked/how much it discharged the bat?
If it didn't crank long there wasnt much discharge so the charging system wont have to work long or hard to top it back up. The problem as I see it is that if the bat was heavily discharged and the charging system has to work hard, which causes heat, which burns it out.
OR, the charging system keeps on pumping amps into a fully charged LFP in a permanent install and hurts or kills the bat cells.
I haven't tried it but will have a chance to try this coming spring. I have several small engines with electric start and dead LA bats. Im pretty confident that I can use my 100ah LFP to start them, just not leave it hooked up and let the now running unit run itself (the ignition).
Questions, comments or corrections are welcomed.
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paulz
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# Posted: 27 Dec 2024 08:30pm - Edited by: paulz
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Good idea on the fuses. I drove the cart a couple times today with the Lfp, no problem. But it did start right up. I still have some halfway good flas but when they die LFPs would be nice. No heavy lifting, no battery tenders…
Found some leftover 50a breakers from my cabin wiring, I’ll try those.
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paulz
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# Posted: 6 Jan 2025 10:45am - Edited by: paulz
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My new lfp literature says they are fine down to -4 degrees. I thought the low was higher?
Or is that charging?
Low Temperature Protection: The 12V LiFePO4 lithium battery can operate smoothly in temperatures from -4°F (-20°C) to 158°F (70°C), and automatically shuts down below -4°F (-20°C), which is especially critical in winter.
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gcrank1
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# Posted: 6 Jan 2025 11:28am
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Common 'wisdom' has been Do Not Charge below 32*f though Ive read that calling it off at a bit higher might be a good idea. IDK, but like to choose to caution.
Certainly that -4*f sounds way too low to me, maybe its a bad translation from....?
Same with that 158*f for a high. Ive read that heat is a real killer on LFP.
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ICC
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# Posted: 6 Jan 2025 12:26pm
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Quoting: paulz ...12V LiFePO4 lithium battery can operate smoothly in temperatures...
What does the word operate mean? To them? To You? It may vary
I believe in this case it means the battery can discharge down to -4 F (-20 C). Somewhere in their specs they should warn against charging at something like 32 F (0 C). Some BMS will cut off the change about 40 F ( 4C).
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paulz
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# Posted: 6 Jan 2025 12:27pm - Edited by: paulz
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Ok so ‘operating’ and charging are different things according to them. That info is from the sales flyer, it came with a several page booklet I don’t have here at the moment, may give more info. I’ll check..
Sorry ICC, your post came up after I typed..
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ICC
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# Posted: 6 Jan 2025 12:52pm
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If they don't make it easy to find the charging temperature info, that is a company I would stay away from. My opinion.
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Nobadays
Member
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# Posted: 6 Jan 2025 01:25pm
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My LiTime batteries state roughly the same thing as Paul's. The self heating ones I have running my Starlink right now at the cabin will discharge to -4F but will stop charging at 32F and will use the incoming power to heat the batteries to 50F. If there is no incoming power they will just discharge until the -4F 9r LBD which ever comes first.
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paulz
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# Posted: 6 Jan 2025 04:13pm
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Wife says we’re staying at the grid today so no reading that booklet. I did find a bit more online;
Low Temperature Protection: Our battery also offers low temperature protection. Intelligent functions prevent charging below 0°C and operation below -20°C, safeguarding the battery core and extending its lifespan
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paulz
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# Posted: 7 Jan 2025 07:03pm - Edited by: paulz
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Back at the cabin. A couple bits from the booklet.
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