Is it OK to Parallel an AGM battery with a Lithium once engine is running? (1 Viewer)

[Fisher23]

Is it ok to run my main battery connected to my lithium once the vehicle is running?

I have my new lithium battery which is 12.8v and 40aH Valence connected to run my fridge.
Eventually I'm going to get a solar panel, and a solar controller, but do not have these yet.

Can is run the Lithium in parallel with the main AGM battery when driving to charge the lithium back up? Then when I turn off the engine the batteries are are disconnected from each other.

Is there any harm in doing this?

 

[Greg_B]

Two different battery types that need different charge profiles so I would suspect problems in your future if you do this. Mismatched batteries are talked about in this thread with the discussion starting near the bottom. The video that is linked talked about wet cell batteries and starting and deep cycle differences, but the principle would be the same afaik.

hth's
gb

 

[Fisher23]

Thanks!

 

[terrx]

I bought some of the same 40Ah batteries. Planning to use at least two in my 40 charged by a Victron blue solar MPPT controller. The input to MPPT will be switched between PV (two panels in series) or 48v (5A) output from a boost converter to engine/alternator: PV when camping (usually day+) or traveling (usually 2-8 hours).

 

[e9999]

OP: I suppose if there is some sort of battery separating / monitoring system, there could be some issues with that, but otherwise I don't see that connecting a ferrophosphate lithium battery in parallel in a pinch would be a critical mistake since they can be charged up to 14.6v safely (from memory) and the alternator should not exceed that normally (I think). There may be some protection circuit on the battery though which could have an effect, and the alternator could behave differently, but aside from that, voltage is voltage so if the alternator output stays between 12.8 and 14.6 you are probably fine I would think. Now whether the battery would charge optimally or not is a different story. But yea, if I were in the boonies and needed to recharge the lithium battery in a pinch, I would try it. I'd monitor the voltage the first time, though...

 

[terrx]

Do not charge a U1-12RT over it's 13.8v float voltage once the battery is fully charged. You can use max 14.6 until then. Because it's not simple to tell when fully charged, I set all charge voltages (bulk/absorption/float) to 13.8 and not worry about 14.6 which means it doesn't get a full charge (more like 90%) but that doesn't hurt LFP and actually extends the charge cycles. The battery has internal low voltage disconnect at 10.5 which is safe but you may want to use something like Victron BatteryProtect to set it higher, which leaves a bit more reserve and also extends charge cycles.

 

[Fisher23]

Do you have a recommendation on a dc to dc charger?

I run a fridge, and that is the main purpose. Have a bunch of camp lights, and other stuff I run also but the main item is the fridge.

My plan is to put a 100 watt panel on the roof that charges the Lithium, (to keep the fridge running) but that panel is waiting on a roof rack which could be months before I figure out which one I want to get.
Then have some central charge controller that can take charge from the alternator from while driving, and from the solar panel when it has sun.

Currently I have the fridge hook up to an AMG aux battery. When the LC is running the two AMG's which are in the engine bay are in parallel, and when turned off the one aux AMG is running the fridge. The problem with this setup is the AMG takes way too long to charge the aux AMG back up, and the fridge can only run about 2 days like this without traveling about a 1/2 day.

So I was thinking of paralleling the lithium with the aux amg for this next trip (4 days) until I get some kind of DC to DC charger installed.

I was looking at the new redarc BCDC1250D a 50 amp charger but was wondering if there is something like that that is not so expensive.

 

[spressomon]

FWIW, I just purchased a Sterling 1260 (12v, 60A) DC to DC charger (also serves as the isolator) for a new LiFePO4 pack going into a trailer project. IIRC 9-different preset/programmed profiles plus custom profile ability. Best price from ElectricCarPartsCo.