LiBIM and DC to DC converter?

[wmsilva]

I will be upgrading my house batteries from lead acid to LiFePo4. There is currently a BIM so I have bought a LiBIM to replace it. I like the idea of having the chassis batteries connected so they stay charged and I can connect them to jump start if ever necessary but I don't like the idea of my alternator running at near max output even for 15 min.
Sometimes I come up with what I think is a good solution for a problem but have doubts when I can't find where others have done it.... so I ask

Is it possible to add a 30 or 50 amp DC to DC converter inline with the LiBIM? If I cannot find a bidirectional DC to DC converter then could I use a busbar to put two converters in opposite directions?

Any advice would be greatly appreciated.

 

[Reed Cole]

Depending on your vehicle and the size of your battery bank direct alternator charging may be totally fine. I have a Ram Promaster and a 200ah lifepo4 battery and it works just fine. Normally the batteries see about 40 amps, the alternator is rated at 185A, I believe, so plenty of headroom. Of course your mileage may vary, but it could be worth visiting a vehicle specific forum and see if others have any experience.

I'm assuming that you want your solar system to maintain the starter battery?

If so one of the Renogy mppt/dc-dc chargers will provide that function, and perhaps other combo units will too.

You could also just get a high amp 3 way switch, one input, two outputs. The starter battery would be connected to the input, and the bim or libim connected to one output and a dc-dc charger to the other. When you're driving select the dc-dc when you're sitting select the li-bim. It's slightly inconvenient but pretty simple and effective.

Running two dc-dc converters doesn't seem like a good value, and doesn't let you "jumpstart" the vehicle.

Edit: You could add dc-dc converter inline with the li-bim but it wouldn't achieve any of your goals except limiting the alternator output.

Err, maybe not though, not sure how those would work together, since I believe the li bim checks the voltage of both batteries before connecting.

 

[wmsilva]

Thank you Reed,
I did something similar on my last RV and it worked, I'm probably just over thinking it. I have 500ah of battery and a, what I believe, 165A alternator on a 2014 cummins 6.7. I have read a couple times that this alternator can be problematic.

 

[Reed Cole]

Thank you Reed,
I did something similar on my last RV and it worked, I'm probably just over thinking it. I have 500ah of battery and a, what I believe, 165A alternator on a 2014 cummins 6.7. I have read a couple times that this alternator can be problematic.

Well, a dc-dc charger is a pretty safe bet for the health of the alternator and the batteries. I wouldn't have gone with direct alternator charging if I hadn't found multiple examples of people doing it with my vehicle.

I have the li-bim but I typically don't go for long drives so the timing function is pretty annoying for me and I usually just override it with a manual switch, which unfortunately also overrides the overvoltage function. But it's nice that it kicks on when parked to charge the starter battery from solar occasionally.

 

[Aussieguy]

30amp dc-dc with correct sized wiring will be much better the LiBIM (15 min ON 20min OFF)
disconnect the BIM control wires BUT leave the wiring in place ... takes a couple of minutes to re-instate for an emergency