Alternator charging - Li-BIM vs. DC-DC?

[demongman7]

Apologies if this is redundant or the wrong forum location, but the information overload on both sides of this debate have been challenging for me to decipher. I'm attempting to determine whether I should go with a Li-BIM 225 or DC-DC Charger (Sterling 60A) for my alternator charging purposes. I already own a Li-BIM 225, so would be great to use that for cost purposes, but in past builds I've used the Sterling 60A and found it to be great. Details on my system / vehicle are posted below, but I'm generally comfortable with the differences in basics between the two types of charging. From my understanding, the Li-BIM will charge my batteries in ~15min intervals based on the max output of my alternator without reaching 100% house charge; this is the recommended option by BattleBorn. Reading suggests the Li-BIM has concerns on potentially overcharging the house batteries (1:49 here), or overdrawing the alternator. Given my Heavy Duty alternator, I especially worry about the latter considering the 70A recommendation from Ford (despite anecdotal evidence in that thread allowing pulls > 70A). Alternatively, the DC-DC charger appears to be a more sophisticated system - matching charge profiles and presenting a 'safer' draw from the alternator.

In summary - it seems like the advantage of the Li-BIM would be 'faster' charging to an extent (~80-90% of house capacity), whereas the DC-DC charger might be safer for the alternator, while also allowing to charge fully to 100%? Am I interpreting these options correctly? Would it be a major mistake / dangerous for my alternator or batteries to proceed to use the Li-BIM?

Despite the recommendation for Li-BIM from BattleBorn, it appears through various forums that the DC-DC chargers are more popular; it'd be great to hear any views this forum has specific to the Li-BIM and Transit / what my best option may be.

----

Vehicle: 2018 Ford Transit 350 HD
System voltage: 12V
Batteries: 4x 100ah BattleBorn LiFePO4
Alternator: Presumably 250A
Other electrical components (don't think they should matter but FYI): Victron SmartSolar 150 | 70, 500W Renogy Solar Panels, 3000W Victron Multiplus,

 

[Reed Cole]

I have a Promaster with 2 100ah battleborns and connect to the alternator via a li-bim 225. It works fine but a regular relay would probably be better for me because I don't often go for long drives. It has a signal input that allows you to override the voltage sensing and timing functions which is what I do so it just stays on.

If my batteries are nearly depleted <10% I might see 75 amps or so going to the battery but for the most part it's in the 50-30 amp range. Though SOC doesn't seem to be the only factor, maybe temperature of the starter battery, not really sure but the alternator seems to do a fine job of regulating itself. I've been running it this way for 3 years, though in the summer solar is adequate.

I'm able to achieve a full charge directly from the alternator, it gets up to 14.4 and the current tapers off to almost nothing.

People with DIY packs like to keep the voltage lower but I don't think it's as much of a concern with Battleborns because the cells are better matched.

Can't really go wrong with a dc-dc charger but they take up space and generate a lot heat, and with a relay you can charge or jump your starter battery in a pinch.

I would check on the Transit forum to see if anyone has any experience with a similar setup to yours. Or just hook it up and see how it goes. Make sure you have a shunt based battery monitor so you can see what's happening.

 

[Reed Cole]

alternator charging for lithium battery

www.fordtransitusaforum.com

 

[jberger]

I think you've summarized it really well.
The Li-BIM being time based, is very limiting, both when the pack is low and when it's at the top of the range. It's not reading the temp of the alternator so it's just turning on and off without considering the alternator at all.
It will keep your starting batteries charged as a priority, so that's a positive.

I'd go B2B in this case, you don't really need the BIM features and you know the sterling will work well based on experience.

 

[eXodus]

Batteries: 4x 100ah BattleBorn LiFePO4
Alternator: Presumably 250A

400AH / (250A -50A) = 2hrs

50A for vehicle draw.

What would be interesting to know - at what voltage your alternator is sitting most of the time. My 180A Alternator in my Chevy Van - was dropping to 13.8V after about 15minutes of driving.

That reduced the charge rate to my 200AH LFP battery bank to less then 50A. No regulator, no electronics. Just 25ft of wire and the frame as return path.

I've just connected the LFP bank with a 200A relay to the starter battery every time the engine was running. Worked for 4 years before I sold the Van. Never thought about the alternator. The charge rate was actually pretty slow for my taste - since it took 5 hours to charge fully.


Before you spend money on the "Li-BIM 225 or DC-DC Charger (Sterling 60A)" - just connect your LFP batteries directly - put a clamp meter on and measure how much current is flowing. If it's very high - kill the engine and order one - if it's low enough for your comfort level - just get a cheap relay.

 

[demongman7]

Thanks for the replies - for transparency, I called BB again today, and talked through the situation at length and my views - in short the technician stated that for my particular system, he thinks DC-DC charging has a slight edge, and would recommend that over the Li-BIM 225. Underlying factors include 1) If the alternator is in fact 250A (noting gregoryx's comment), there is a very small but nonzero chance I could overwork both the alternator (based on BEMM guidance) and the Li-BIM itself (as it's rated to 225A). While this is unlikely because the alternator surely won't routinely deliver 250A, the tech did mention that the 'wear and tear' on the Li-BIM over years could be considerable. He seemed to think that the DC-DC charger would be a 'sturdier' option, although less powerful for obvious reasons. 2) On this note, he did agree that the advantage of the Li-BIM would be faster charging, and confirmed that it would not charge the BB's up to 100%, more like 80-90%. 3) He confirmed that the BB's would in no way constrain the charge - the 'max charge' of 200A referenced for a 400ah battery pack is not truly a max - since the Li-BIM doesn't have a manner for constraining current, overcharging is a possibility although unlikely with any factory alternator (even the presumed 250A). He wasn't terribly concerned about overcharging, but acknowledged the reality. 4) He said for most Transits, a DC-DC charging setup would make more sense in the typical electrical systems we tend to put together. The advantages of charge profile, idling, etc. and the typical balance with other charge sources yields a more attractive use case for DC-DC - not to mention the fact that smart alternators in many Transits now could diminish the advantages the Li-BIM offers due to fluctuating voltages; generally, he saw the Li-BIM as a more suitable plug and play option for systems already wired with a high capacity (ex. class A RVs upgrading from AGM to lithium, now requiring the Li-BIM).

Overall - the tech's evaluation was that for my particular situation, a DC-DC charger will probably make more sense - however it's super dependent on the situation whether a Li-BIM or DC-DC charger is best, so there's no right blanket answer. Regardless of his comments, I probably would have ended up switching back to a DC-DC because I see it as a safer option, and don't need a massive current from my alternator because I have sufficient solar and shore to keep me topped up. Hope this helps someone else going forward.