Lithium's and protecting the alternator

[Richpatty]

Hey everyone. So as many of you know, last year I moved to 800ah of Lithium. As part of the project, I replaced my BIM with a Li-BIM which gives the alternator a break from charging the house batteries every 20 minutes or so. This is done due to the fact that Lithium's are very hungry batteries and will basically take every amp they can get. Some say that this type of draw can over-tax an alternator, thus the need for the Li-BIM.

There is a long running thread on the "other forum" where folks are making the argument that indeed the Lithium batteries can tax an alternator, but that a Li-BIM may not help that much. This is due to the "on/off" nature of its function. It is said that when the Li-BIM cuts off the connection between the Lithium's and the alternator, that the sudden drop in power can cause some kind of "dump" on the alternator and cause issues or even damage it.

So, if this is true, some folks have suggested that you use a DC to DC converter in place of the Li-BIM, which would limit the amount of power being pulled from the alternator. But it would probably impact the ability to charge the chassis battery while on shore power as well as the Aux battery jumper function (since the BIM would be removed from the system). So I don't like that option all that much either.

My other thought is to put in a battery switch (like this: https://www.amazon.com/gp/product/B07T288VN8/?tag=rvf01-20) which I could turn off while driving, but turn it on when on shore power. The other idea someone had was to put a 125amp fuse on the line, so if the batteries call for more power than that, the fuse would blow and protect the alternator.

So, I really don't like any of the ideas....so I am tossing it out to everyone to see what your thoughts are. I know some folks have said that the length and gauge of the wire between the house batteries and alternator is not enough to push much more that 60-100 amps anyway, so this may be a moot point. But is it something I should bet my alternator on? I have a clamp meter, which I suppose I could try (I believe it even has Bluetooth), but I have not worked very hard to master its use (embarrassingly). That could give me an idea if I have anything to worry about.

Thoughts anyone?
Thanks
Rich

 

[B52Bombardier1]

Hello Rich,

See what the MechMan people can do with setting you up with a heavier duty alternator.

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Their alternators are used by a lot of people in the old hot rod hobby that had to abandon their 37 amp alternators from the late fifty's and early 60's to support dual, high wattage electric radiator fans, electric water pumps, modern air conditioning and big wattage stereo systems. The MechMan alternators can also be setup with a profile that makes lots of amps at a low engine RPM. They can easily build you an alternator that will crank out 150-200 amps and still fit your existing alternator bracket.

Nothing is free here. You will consume more fuel to spin this alternator, of course.

Rick

 

[Neal]

If a solar charger such as we have can control amps to a limit is there not a way to limit the amp flow from alternator to house batteries?

Paging Dr. @Chuggs

 

[Richpatty]

Pretty sure my 2017 Ventana has 200+ amp alternator already…. So upgrading is not the answer. :-/

 

[Neal]

I seem to recall diodes can be used to limit current.

Current Limit Techniques

There are a number of current limit techniques, click here to see a quick description of the most popular ones.

www.sunpower-uk.com

 

[Kevin D Pem]

Neal you are on target!

But like is common, there is always an effort to limit in the wrong circuit. For those that want to develop a product that can fix this issue I would intertain a dialog to work on it.

 

[Guido]

I put 2 300amp lifeblue batteries on my 3709 Dutchstar . I did not change the Bim and everything has been fine on two trips. The batteries are usually not charging while I drive because I usually start with 100% charge but I ran an experiment. I can use the boost button to charge and the the battery built in monitor showed 40 amp per battery going in when I press the boost switch .

 

[Kevin D Pem]

I put 2 300amp lifeblue batteries on my 3709 Dutchstar . I did not change the Bim and everything has been fine on two trips. The batteries are usually not charging while I drive because I usually start with 100% charge but I ran an experiment. I can use the boost button to charge and the the battery built in monitor showed 40 amp per battery going in when I press the boost switch .

Problem is lithium offer no or little resistance. Basically a sink for the power produced by the alternator. Automotive alternators are not designed to charge a bank of deep cycle batteries that have resistance and do get overheated when used to do that.

The problem is exaggerated when that bank is lithium.

In this case the question appears to be, can I save the alternator so it will last as long as it would have had I stuck with lead?

The answer is yes! However proprietary information would have to be disclosed to discuss it in a forum.

 

[Neal]

If we have a charge controller for controlling flow from solar to house batteries would something similar work between the other path to the batteries? Whatever path that is?

 

[Kevin D Pem]

If we have a charge controller for controlling flow from solar to house batteries would something similar work between the other path to the batteries? Whatever path that is?

You must remember that the control you speak of is sized to accommodate the supply, not the other way around.

 

[Kevin D Pem]

When a solar controller is set for lithium it becomes a constant current device.
The controller is designed to protect the batteries, not the power source.
You need a device that is designed to protect both.

 

[Richpatty]

I like the idea of a diode to do this, but I am not just that knowledgeable of them and the many variables that happen between the alternator and lithium's.

Next time I go to Freightliner, I may ask them if they see many alternator failures with lithium's, but will have to wait until December.

 

[Kevin D Pem]

What you need to know!
Diodes drop voltage.0.5 volts. Basically a resistor in this application. 10 awg wire also a resistor, but resistance varies depending on heat buildup. .
The hotter the wire the greater the chance the insulation can melt. Although the wire will supply the resistance required for voltage drop needed for the 12vdc circuit I would use an automatic reset breaker at both ends of the wire.

Like I said, I have a unit that I use for my poor boy generator that offers me 12v or 24v battery charging that could easily be modified to protect the alternator. It would need a factory computer tweak maybe.

 

[Richpatty]

Thanks Kevin. I guess I am looking for something that would do something like a DC to DC charger and provide a consistent 30-60amp flow. I am not sure how many diodes I would need as I am not sure how much amperage is coming across....

It would also stop the charging of the chassis batteries on shore power and the function of the booster switch.

Wondering if the battery switch is the way to go....

 

[Kevin D Pem]

Thanks Kevin. I guess I am looking for something that would do something like a DC to DC charger and provide a consistent 30-60amp flow. I am not sure how many diodes I would need as I am not sure how much amperage is coming across....

It would also stop the charging of the chassis batteries on shore power and the function of the booster switch.

Wondering if the battery switch is the way to go....

The real problem is with dry campers and long weeks without charging. I would guess that really isn't what you do, so the switch would likely work for you.

 

[Joe Hogan]

We had 640+ amp of LiFePo and solar installed in our Canyon Star. Never had an issue with the alternator charging the batteries. The stock Bird failed once but other than that no issues. For whatever that is worth.

here is a good source of information

Careful - Alternator Charging Lithium - Victron Energy

Charging lithium batteries from an alternator, be that in a boat or vehicle, presents some challenges when compared to the straightforward nature of charging lead based batteries. The video in this blog highlights these lithium challenges and shows you what can happen when things go wrong –...

www.victronenergy.com

 

[Rich W.]

Solar makes all the difference - the batteries are almost never discharged very much when you hit the road. But even without it, I’d just make sure I’m charged up pretty well before driving to prevent an excessive load on the chassis charging system.

 

[Ventana]

Does a DC to DC charger address these issues?

 

[Richpatty]

Does a DC to DC charger address these issues?

Yes, but how do you put it in place without disruption the charging of your chassis batteries from shore power and the aux boost function? You would need to remove the BIM which handles those functions.

 

[Neal]

Are there any reports of an alternator failing? Would an alternator "fail" just because the demand for amps is higher than its output? I hear they are quite robust. I think I'd just let things go and if it fails then correct for next time around but my guess is it is not going to fail. Maybe over-engineering the situation? Maybe also someone that sells LifePO4 batteries for RVers can shed some light on this topic?