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Old 08-30-2022, 09:22 AM   #1
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Alternator ruined charging lithiums

I have a 2004 Itasca Horizon 40KD. I have 4 battleborn lithium 12 volt coach batteries. I do not have a Battery Isolation Manager or DC to DC charger. My alternator quit on me and had it replaced to the tune of $1,000. The new one is now also toast a month later, I am quickly figuring out the alternator is overheating on long drives.

I need to get a BIM or DC to DC charger obviously. But in the meantime, can I disconnect all but one coach lithium battery to avoid overheating the alternator? Any suggestions on what I can do in the meantime? I have some long trips scheduled and deadlines to meet.

Thanks in advance!
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Old 08-30-2022, 09:43 AM   #2
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Only reason an alternator would overheat would be because it’s driving into a short or being asked to provide more energy than it was designed to provide.

Do you have a short somewhere or a low resistance in the alternator output line?

Otherwise, what are you powering while underway that is consuming so much energy?

Your not by chance using an investor to run the A/C units while underway are you? (Not sure the engine alternator could provide the needed power for that).
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Old 08-30-2022, 09:50 AM   #3
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Lots of videos on you-tube of alternators burning up with just ONE lithium battery.

From what ive found, you cant goto lithium without limiting current output...

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Old 08-30-2022, 10:05 AM   #4
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I don’t think the OP’s approach is a good one.

The cost of simply installing a BIM or dc to dc charger would both eliminate uneven charging of his lithiums (which probably wouldn’t be good), and much less costly than another alternator replacement.
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Old 08-30-2022, 10:47 AM   #5
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I have a residential frig, with a 2000 watt inverter. Not doing anything crazy like ACs. In fact I have been running generator and house AC on most travels this summer due to the heat.

I don't think there is a short anywhere, but I can't rule that out.

I got the lithiums when we were doing a lot of dry camping and they worked great. Currently only going park to park with hook ups.

I could also temporarily remove the lithiums and just go lead acid?
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Old 08-30-2022, 10:55 AM   #6
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I have a 2004 Itasca Horizon 40KD. I have 4 battleborn lithium 12 volt coach batteries. I do not have a Battery Isolation Manager or DC to DC charger. My alternator quit on me and had it replaced to the tune of $1,000. The new one is now also toast a month later, I am quickly figuring out the alternator is overheating on long drives.

I need to get a BIM or DC to DC charger obviously. But in the meantime, can I disconnect all but one coach lithium battery to avoid overheating the alternator? Any suggestions on what I can do in the meantime? I have some long trips scheduled and deadlines to meet.

Thanks in advance!
I am far from an expert on this, but here are some issues.

1) 4 Battle Born 100 amp hour drop ins can draw 200 amps or more while charging. That is enough to destroy many truck alternators.

The correct B2B charger can control this.

2) The BMI for lithium batteries can disconnect suddenly for a number of reasons. In automotive terms, that is a "load dump". When a load dump occurs an alternator will spike a high voltage. That voltage can not only take out the alternators electronics, but other devices on the chassis 12 volt system.

A lead acid battery connected to the alternator can dampen that voltage spike to some degree. It depends on the exact wiring and components.

There is a device that will clamp voltage spikes that can be added to fix this issue.

3) Lead acid and Lithium batteries should not be charged or discharged in parallel or in series with one another. Battle Born batteries have pretty good BMI function. They will disconnect to protect themselves causing voltage spikes on the alternator. They also may not get the equalizing charge they require. That can cause the BMI to disconnect prematurely.

A B2B charger can fix this problem

4) The larger the Li battery bank, the larger these problems become. Reducing from 400 amp hours to 100 amp hours will reduce but not eliminate the problem. Check specs for the Battle Born battery. How much current will it draw at 14.4 to 15.0 volts? Check specs for alternator. How much excess capacity does it have? A 50 amp load dump will be a lot smaller than a 200 amp dump.

In a travel trailer, resistance in the connection to the tow vehicle can further dampen the effects. In a motor coach it depends on how good the bridge circuit is. Many motor coaches have excellent bridge circuits. That of course increase the effects.

Do you feel lucky today?

Alternatives. Disconnect the bridge circuit. Only charge the lithium bank using generator or shore power. Many owners settle on this as a permanent solution.
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Old 08-30-2022, 10:56 AM   #7
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This is the first post I have seen about a chassis alternator burning up due to heavy charging current. I think it is because you have 400 amp hours of Li batteries, not the more typical 200 Ahs. The current demand of 400 amp hours of batteries is enough to overload your alternator.

Can you beg, borrow, steal or buy a DC clamp on ammeter (about $100 for a Klein unit on Amazon) and check the alternator current at various engine rpms. Alternators typically overheat at high current, low rpm since the cooling fan air flow is related to rpms. Also check the case temperature. Anything over 200 F would be a concern.

I don't much like the idea of disconnecting all but one battery. As noted above this could lead to balance problems. But couldn't you just disconnect the chassis alternator connection?

As you note the two solutions are a Precision Circuits Li-BIM 225 or a DC to DC charger. The BIM solution just cuts the average current in half by turning off the chassis battery connection for 15-20 minutes and then back on for 15-20 minutes. But that is the cheapest and easiest solution and doesn't change how anything else works.

The DC to DC charger is a more elegant solution because it limits the current to a specific value. But because it is not bidirectional you lose the ability to aux start the chassis engine or charge the chassis batteries from the coach's DC system.

The fact that you burned up the alternator in a month tells me that you need the more elegant DC to DC charger.

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Old 08-30-2022, 11:47 AM   #8
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Agree with the others - if those coach lithium batteries are substantially discharged when you start the engine, your alternator is going to deliver a huge amp load demand, enough so that it overheats fairly quickly. It may also be subject to the surge that can occur if the LiFePO4 batteries suddenly cut off charging. If you can make sure the batteries are always charged before starting the coach, you can avoid the problem, but just one mistake could kill another alternator. I'd go with DavidEM's advice.
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Old 08-30-2022, 11:49 AM   #9
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Wow, incredibly helpful. I am leaning towards simply disconnecting the bridge circuit and charging the batteries from generator or shore, which would be the perfect solution for now until I get the DC to DC charger, which is the best solution.

So if I disconnect my "battery mode solenoid" for now, it will not charge the house batteries, but will it still charge the chassis batteries?
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Old 08-30-2022, 12:03 PM   #10
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You still have the problem of the bmi's disconnecting under a high charge current. There has to be protection for your inverter and generator. Onans hate being disconnected under load.
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Old 08-30-2022, 12:41 PM   #11
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Two years ago I replaced my 3 wet cell batteries with three 100AH Battle Born batteries along with a Victron Orion 30 amp isolation charger which limits the output of my Alternator to 30 amps charging to the batteries. It has been totally maintenance and trouble free ever since. Battle Born, made in the USA has a tech line, a human actually will answer the phone. I'm sure they can professionally answer all your questions and temporarily solve your issues.
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Old 08-30-2022, 02:17 PM   #12
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I can’t get over the $1,000 for a alternator, mine was around $175.00
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Old 08-30-2022, 02:50 PM   #13
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Wow, incredibly helpful. I am leaning towards simply disconnecting the bridge circuit and charging the batteries from generator or shore, which would be the perfect solution for now until I get the DC to DC charger, which is the best solution.

So if I disconnect my "battery mode solenoid" for now, it will not charge the house batteries, but will it still charge the chassis batteries?
Yes, disconnecting the isolation/bridging solenoid will stop house charging but not effect the chassis charging.
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Old 08-30-2022, 03:43 PM   #14
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Yes, disconnecting the isolation/bridging solenoid will stop house charging but not effect the chassis charging.
Would the generator then still charge the house batteries?
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