@FSH 210 Sport,
@srf32 and everyone else could I get your thoughts on this?
My thinking is that the cheap BMS in the Redodo is cutting off charge and discharge at the upper voltage cutoff while the BattleBorn batteries may only cut off charge while leaving discharge active. I have experienced this with inexpensive BMS circuits that I have used in building LIon battery packs and with LifePo4 batteries that I have used in wheelchair projects.
One of the pair of AGM batteries that I installed in 2014 is showing 12.25 volts fully charged so I am thinking that it is time to replace them.
I am thinking that I may install a pair of low cost LifePo4 batteries to replace the AGMs. I want to tackle the LFP starter battery hurdle.
I have two thoughts on how to make this work.
1. Install 20A buck convertors after the factory rectifier regulators to prevent the stators from fully charging the batteries.
2. Replace the rectifier regulators with LFP compatible versions. Likelly MOSFET based rectifier regulators limited to a lower voltage.
Lots of good info in this thread
https://jetboaters.net/threads/bad-stator-on-06-sx210-ok-to-run-rest-of-season-before-pulling-to-repair.29032/
This thread is interesting
https://www.advrider.com/f/threads/lithium-batteries-mosfet-regulators-big-shunting-probs.1503976/
See my posts
#’s 14 & 15 in this thread.
To reiterate, I’ve been running heated 100Ah Battle Born batteries in my boat since early in 2022, so going into my third season with them. There are three trolling motor batteries for my trolling motor which is its own separate system, and one house battery. See my thread on this here;
https://jetboaters.net/threads/conversion-to-lifepo-batteries.35834/page-3
In the scope of this thread I have had zero issues with the Battle Born house battery, it charges off of the OEM rectifier / regulator with zero issues. I think the greatest depth of discharge I’ve done on the BB house battery was around 20%, and since I have the Victron smart shunt I could watch how much current the alternators were putting into the BB house battery and watch the state of charge level climb as time passed. The highest rate of charge I’ve seen coming from the engines was 26 Amps combined, during the aforementioned charging on the water after a 20% discharge was 23 amps initially then held steady at 20 amps for sometime before tapering off, this was with the engines above 3500 rpm, at idle the charge rate was 13-14 amps combined. While I did not have the Victron smart shunt installed when my FLA battery was installed, the rate of re charging of the BB LFP battery is very fast and much faster than the FLA battery was. I base that on the voltage level of the FLA house battery as read from the connext screen while I was on the water after running the live well and electronics for most of the day then having to run the engines to bring the FLA battery up from low voltage to finish out the day before heading home and plugging in the chargers.
My understanding is that my TR-1 alternators are three phase AC and the rectifier is full wave, so as far as my 2020 model year TR-1 engines and their alternators are concerned, the marriage to the Battle Born LFP batteries is a good one. And as stated previously, our alternators are always at full output with excess voltage being shunted to ground, so there is no excess / damaging heating that can occur in our alternators as opposed to automotive style alternators. This is due to the fact our alternators have fixed magnetic fields (fixed flux density) on the rotor, or PMA permanent magnet alternators, and the rectifier regulator regulates the output by shunting excess output to ground, this is why the rectifier / regulator is always hot when the engines are running even when the batteries are fully charged, and why their mounting bases water cooled. Automotive style alternators use a variable magnetic field (flux density) VMA to regulate output, these alternators are capable of much greater output in a given size compared to a PMA, but most of these only have a duty cycle of 10% otherwise they will over heat and burn up. With low resistance of LFP batteries, the automotive style alternators and their regulators will charge at 100% output / duty cycle and will burn up. There are some automotive style alternators that can run at 100% duty cycle and others that have a thermocouple in the windings to roll back output when it gets too hot. This is where DC to DC chargers come into play, they are fed from the starter battery and will only allow a lower rate of charge to a LFP battery, this not only protects the 10% duty cycle automotive / VMA alternator it also extends the service life of the LFP battery by keeping the charge rate below the maximum charge rate of the LFP battery. This is what a lot of the Van Life folks do to charge their LFP batteries off of the vans alternators. Yes, a well designed BMS will cut off excessive charge rates to protect the battery, and if the charge rate is always too high the battery will not charge, and, just like keeping the depth of discharge at 80% or less will increase the service life of the LFP battery, so will keeping the charge rate at .25C (25% of the Ah rating) rather than charging at the maximum.50C.
I agree with your assessment that the Battle Born BMS is regulating as it should by not allowing the battery to be over charged but still allowing discharge.
Installing a device to make a cheap LFP battery work, to me, doesn‘t sound like a good idea. And as I have illustrated above, so far the BB house battery (as well as the trolling motor batteries) are performing well with the OEM Alternators and rec/reg’s so there is no need to install a different reg/rec.
NOTE: You do have to modify the DVSR to only be active while the engines are running or manually switch the DVSR (that’s how mine is currently set up) or the DVSR will stay closed due to the higher resting voltage of LFP batteries. This will keep the batteries in parallel and not isolate the start battery from house loads. If you have a lead acid start battery the LFP battery will charge that battery until the voltage drops to 12.7 which is when the LFP battery is essentially 90% discharged, and most likely will ruin the lead acid start battery. Recently one of our members with a 255XD installed two 100 Ah batteries for the house loads and has a FLA start battery I believe, could be an AGM, and he tapped off of one of the fuel pump positive leads to power the DVSR making it fully automatic with a “run” hot. I may switch over to that myself.
As far as having an LFP starter battery goes, I know that one member here is using Battle Born batteries for both starter and house with no issues since the starter draw is below the BMS cut offs. Having said that, Dakota Lithium has a group 24 starter battery rated at 1000 CCA that you could check out, I’m just not a fan of DL as they do not have tech csr’s that you can talk to, and they’ve committed an integrity violation by leading people to believe they are a North Dakota based company, they are not they are a Chinese based company. Also, if you watch the “Morgan’s on the move” YouTube video in my conversion to LiFePO batteries thread you’ll see that FLA batteries are better for starter battery applications, and that is why I stayed with an Interstate group 24 dual purpose AGM start battery.
Man that was a lot for a Sunday morning…
