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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
Member
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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
Member
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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
Member
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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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