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Second Alternator Charging Lithium Battery Bank

ScottPC

Active member
Yes, i went through this exact conundrum on my 2020 Ram5500 project.

I special ordered my truck with the Dual Alternators for 440amp total thinking i would separate them, one for truck bats, one for house bats.

I quickly learned this is WAYYYY more complicated than it seems, on the newer trucks.

DISCLAIMER: I am NOT an expert in this field, and wont claim to be. Also, everything i have found out is based on the Ram 6.7 cummins, i have no idea if the Ford alts are setup the same way.

However, i have some friends that are, do this for a living, and even spent a couple hours at my local dealer talking with an OG guy there that loves my project, so gives me a bit more love than the usual customer.

Bottom Line i found out: The dual alternators are controlled by the computer to work together and split the charging (somewhat) and disperse the duties to cut down on heat and other things. If one fails, the other one can pick up the slack as needed until repaired/replaced.

There is a process to electronically remove the second alternator from the computer by deleting the sales code and that essentially has the truck setup as if it came with just a single one from the factory.

Electronically anyway... You still have a complicated array of wiring in the loom for alt 2, and redoing it all to serve a different purpose on a brand new truck just seemed like way too much headache and unnecessary work that may possibly effect warranty.

After lots of research, and going back and forth, i settled on a Sterling 60amp B2B and so far, it has been working flawlessly throughout all the crazy tests i've been putting it through. My Victron smart shunt, shows the Sterling is actually charging at the 60amps it claims as well.

This is all for a 300ah lithium LifeBlue battery. So far, its been great for all my needs (my entire truck is setup for everything electric and no propane). But now that summer is coming, and i will be running the AC a bit more, i will be keeping an eye on the usage and determine if i need more battery.

A friend of a friend runs a residential Solar company and builds his version of Tesla Walls and he's been yapping about building me a big silly battery bank for the camper. If i end up doing that, i will likely switch to the Sterling 120b2b and then i'd basically be setup for whatever i could possibly throw at it.

End of the day, B2B are simple to install, setup, and work great

Careful with the Victron and RedArc versions folks are using, for what they cost they arent available in higher outputs.

There is absolutely no reason you shouldnt put the biggest one you can fit on your setup. I believe the Victron and RedArc max out at 30 or 40amps or so.

Sterlings are available up to 120amps, its kind of a no brainer (i went with their 60amp at the time of my build because the 120amp version was on backorder forever, its available now)

I just looked up the LifeBlue website and they claim they are one of the only LiFePo batteries that don't need a DC-DC charger and don't require solar and converters set to a "Lithium" setting as they are a "true" drop in replacement.


I've used Sterling B2B chargers with another brand of Lithium battery and it worked great. However, LifeBlue doesn't require them and allows direct alternator charging that worth considering. Maybe this is only in their current BMS versions. I don't think it would hurt if the Sterling was installed too, but it may be unnecessary. Do you have any insights?
 

DiploStrat

Expedition Leader
Most lithium iron batteries can be charged with the output of most modern alternators. (Note the caveat, "most.") A decent BMS will act as a master fuse to protect against over voltage, over cell voltage, over discharge, temperature, etc. The two caveats that I would offer, one from experience:

-- A discharged lithium battery is like a back hole for amps. (That is why they charge so fast.) But a 100Ah battery, discharged down to the BMS disconnect point, can easily pull over 80A and may pull up to its full rating. This can melt your wires and fry your alternator. Most "normal" alternators should not be loaded to more than about 50% full time.

-- If something goes wrong and your BMS shuts down, it may generate a spike that may destroy your alternator. AB2B will prevent this. Having a lead acid battery in the circuit, e.g., your starter battery may also work.

Finally, there is a lot of chatter in the lithium world to the effect that lithium batteries actually like to be charged a bit slower.

As always, free advice is worth ... ;)
 

Verkstad

Raggarkung
If something goes wrong and your BMS shuts down, it may generate a spike that may destroy your alternator. AB2B will prevent this. Having a lead acid battery in the circuit, e.g., your starter battery may also work.
Would not ’running loads’ of a vehicle what includes starter battery be sufficient to prevent alternator voltage spike if the lithium BMS suddenly disconnects ?
Btw, I dont think starter battery would do much as its a fairly high resistance most of the time.
 
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RAM5500 CAMPERTHING

OG Portal Member #183
Sterling B2B units are available in more sizes and are infinitely adjustable, should you wish. (And know what you are doing.) They tend to be physically larger and require lots of air flow.
Good point

The Sterlings are fairly large physically and would be a nightmare to try to mount under a hood. Lucky, I have ample room Inside my box
 

Rando

Explorer
Before investing in a B2B, the best option would be to try your charging system with your lithium battery. If your alternator output voltage is high, and you have short and heavy wiring, then there is a slight chance of drawing more current than you want - but a test will reveal this. Assuming you have loads on the battery, a voltage spike is unlikely. However, if you are worried about this, then a transient voltage suppressor is the way to address this, not a B2B. The usual issue is not enough current to the battery - which a B2B can address.
 

DiploStrat

Expedition Leader
Would not ’running loads’ of a vehicle what includes starter battery be sufficient to prevent alternator voltage spike if the lithium BMS suddenly disconnects ?
I would think so, and I read to that effect, but, given the chance of destroying an alternator, I don't want to recommend that anyone try it.
 

Rando

Explorer
It is also not entirely clear how a B2B charger would protect against a BMS shutdown (aka a 'load dump')?

The issue here is not so much that you will damage the alternator, but that when you suddenly disconnect a large load from the alternator, the output voltage of the alternator will spike due to the inductance in the field windings. It is primarily other things attached to the same circuit (eg ECUs, accessories, maybe the B2B itself) that would be damaged. If the battery were to suddenly disconnect from the B2B, the load at the input to the B2B will also suddenly drop - leading to the same situation. Littlefuse has a couple of good application note on this, and how to protect against it.
 

DaveInDenver

Expedition Leader
It is also not entirely clear how a B2B charger would protect against a BMS shutdown (aka a 'load dump')?

The issue here is not so much that you will damage the alternator, but that when you suddenly disconnect a large load from the alternator, the output voltage of the alternator will spike due to the inductance in the field windings. It is primarily other things attached to the same circuit (eg ECUs, accessories, maybe the B2B itself) that would be damaged. If the battery were to suddenly disconnect from the B2B, the load at the input to the B2B will also suddenly drop - leading to the same situation. Littlefuse has a couple of good application note on this, and how to protect against it.
Does seem like either a BMS or DC-DC (B2B) power supply could potentially cause or prevent the alternator from going out of regulation. It's not the load dump per say but the sudden change in feedback (sense) to the alternator voltage regulator. It's the same damage that could occur if you were to pull the battery cable off while the engine was running, which isn't an unknown failure mode.


It would completely depend on the BMS or DC-DC as to whether they still present a sufficient load to the source, such as input filtering or OV protection like the TVS you mention, for this not to occur. If the designer assumed it would always have a stable supply just parallel to the intact stock charging system they certainly may not do anything to prevent going off the rails. In that case if one wanted to dedicate an alternator to a BMS you could perhaps use a TVS or active load to stay in regulation or simply hang a small battery on the alternator side of the BMS or B2B?
 
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DiploStrat

Expedition Leader
Worth noting in this:

-- REDARC, and, I suspect, Sterling Power, require that their B2B be fed from a battery, typically a lead acid starter battery. So the loss of the second (camper/house) battery would be on the other side of the B2B.
-- Neither will provide any protection to the alternator from a problem with the starter battery, which is directly connected to the alternator.

Just to be clear that we are only discussing a BMS shut down of a lithium camper battery.
 

RAM5500 CAMPERTHING

OG Portal Member #183
I just looked up the LifeBlue website and they claim they are one of the only LiFePo batteries that don't need a DC-DC charger and don't require solar and converters set to a "Lithium" setting as they are a "true" drop in replacement.


I've used Sterling B2B chargers with another brand of Lithium battery and it worked great. However, LifeBlue doesn't require them and allows direct alternator charging that worth considering. Maybe this is only in their current BMS versions. I don't think it would hurt if the Sterling was installed too, but it may be unnecessary. Do you have any insights?
I dont have any insights into that claim. But what i do know, is there is no way of monitoring or limiting the charge if its direct...

It also says the battery is rated to a max charge rate of 150 amps or so

If my dual alternators are capable of 440amps and the Lifeblue SOC is down to 50%, i cant imagine that ending well for either the battery or the alternator without something limiting it
 

Rando

Explorer
Worth noting in this:

-- REDARC, and, I suspect, Sterling Power, require that their B2B be fed from a battery, typically a lead acid starter battery. So the loss of the second (camper/house) battery would be on the other side of the B2B.
-- Neither will provide any protection to the alternator from a problem with the starter battery, which is directly connected to the alternator.

Just to be clear that we are only discussing a BMS shut down of a lithium camper battery.
If the B2B is fed from a battery, there is no issue from a 'load dump' as the battery up stream of the B2B is still in the circuit and will provide plenty of capacitance to the circuit. In the case where you have a LiFePO4 in parallel (and/or through an isolator) with the starting battery, there is also no issue as the starting battery is still in the circuit if the BMS shuts off.

The situation where you have an LiFePO4 charged on its own alternator, as the OP described, is where there is a potential for a problem. In this case I am not sure a B2B would help, and by the statement from Sterling and REDARC, it sounds like they wouldn't help, which is why they require a battery on the input side.
 

Rando

Explorer
I dont have any insights into that claim. But what i do know, is there is no way of monitoring or limiting the charge if its direct...

It also says the battery is rated to a max charge rate of 150 amps or so

If my dual alternators are capable of 440amps and the Lifeblue SOC is down to 50%, i cant imagine that ending well for either the battery or the alternator without something limiting it
Doesn't the LiFeBlue provide built in current monitoring (not control)? So you would know how much current it is drawing, and it will also shutdown charging if it is too high. To reduce the current, you can either dial down the alternator voltage, or add some resistance between the alternator and battery.
 

ScottPC

Active member
I dont have any insights into that claim. But what i do know, is there is no way of monitoring or limiting the charge if its direct...

It also says the battery is rated to a max charge rate of 150 amps or so

If my dual alternators are capable of 440amps and the Lifeblue SOC is down to 50%, i cant imagine that ending well for either the battery or the alternator without something limiting it
I'd be inclined to go the B2B route and not leave it to the BMS. B2Bs seem really useful for the Smart Alternators, particularly.
 

DiploStrat

Expedition Leader
If the B2B is fed from a battery, there is no issue from a 'load dump' as the battery up stream of the B2B is still in the circuit and will provide plenty of capacitance to the circuit. In the case where you have a LiFePO4 in parallel (and/or through an isolator) with the starting battery, there is also no issue as the starting battery is still in the circuit if the BMS shuts off.

The situation where you have an LiFePO4 charged on its own alternator, as the OP described, is where there is a potential for a problem. In this case I am not sure a B2B would help, and by the statement from Sterling and REDARC, it sounds like they wouldn't help, which is why they require a battery on the input side.
We are talking past each a bit. The point is that a B2B, connected to your starter battery is an alternative to a dedicated alternator for the camper battery.
 
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