Looking at upgrading my system to Lithium coach batteries. My system currently has a PD4560 converter charger and a Precision Circuits BIM allowing bi-directional charging to both coach and engine batteries, all batteries are flooded acid cell. Under new upgrades with Lithium coach batteries, the PD4560 would have to be changed to PD4560Li which no longer has the charge wizard and equalization mode and provides the 14.4v constant. This will cause an issue with the Precision Circuits BIM which allows bi-directional charging and engine battery boost function. The PD4560Li converter charger manual states "DO NOT USE WITH FLOODED ACID CELL BATTERIES" for obvious reasons of charging parameters. There is an expensive upgrade for the Precision Circuits BIM costing $500. Wouldn't just disconnecting engine battery from the BIM and isolating it work? Battery cable from engine battery goes to a fuse box first before running back to the BIM and is easily disconnected. This would provide engine battery charging, but no charging to the coach batteries while driving. However, I have 300 watts of roof top solar which would be charging the coach batteries. I'm not sure what's tied to the engine battery to draw it down. The dash radio with CD, DVD and navigation is wired to the coach battery and No power steps.Has anyone encountered this situation and if so what was your solution?

Something like what you're considering would probably be the simplest solution. The one obvious drawback is that you can't charge the coach batteries from the engine, as you pointed out, and if they're low the alternator would provide a lot more charge than the solar panels alone. One solution there is to replace the BIM with a plain old continuous duty solenoid wired to the engine run circuit (and maybe also to the emergency start switch if you have one) such that they connect when the engine is running. This is a simpler setup that many RVs use by design.The engine computer and some related bits are mainly what would consume power from the engine battery...that, and self-discharge. If you're worried about the engine battery running down during storage, you can either get a small solar panel to maintain it, or if on shore power just use a little battery maintainer charger of some sort. If you have a lighter socket connected to the engine battery that's live all the time, that may be a convenient place to plug in a maintainer charger.

I don't have lithium but have given it some thought including this issue if I where to upgrade. Bottom line yes you don't wan't a normal auto battery combiner. I know some use a manual combiner so they can charge from the alternator if needed and watch the system as necessary while driving.To automatically charge from alternator you would need a dc-dc charger like a Sterling. I wish someone would make a nice two way dc-dc charger so alternator can charge house and solar/shore can charge chassis with proper battery profiles on each. I haven't found that yet.Magnum smart combiner might work too.Victron makes an interesting BMS that works with their lithium batteries for charging from alternator but requires as DC-DC converter for house loads for reasons I am not entirely clear on: https://www.victronenergy.com/upload/documents/Datasheet-BMS-12-200-EN.pdf

You could go 'old school' and get a diode based charger for the starter battery. That would drop charge voltage by 0.7 from 14.4 down to 13.7.

I emailed PC photos of my BCC and called them this morning. The new Li BIM replaces the old BIM and relay but is a nightmare installing it. Replacing the entire BCC with the new lithium model costing $500 is also a wiring nightmare. But my question was how is charging handled. It seem to be the same. Converter charger on shoreline or generator will charge both engine battery and coach batteries at the same time if one is low. The alternator will do the same while driving but the coach batteries for 1 hour. I don't see how the Lithium charging parameters would work for both, as PD4560 Li instructions said don use with Flooded battery charging. Still seems simplest way is to detach engine battery from BIM and allow solar to charge coach batteries continually while driving and the alternator to charge engine battery. Just concerned about engine battery going dead while dry camping and no boost. But I could fire up generator and use my old Victor 100amp battery charger if necessary.It would be so much easier to make the Lithium upgrade if I didn't have the Flooded engine battery.

SFVdave wrote:It would be so much easier to make the Lithium upgrade if I didn't have the Flooded engine battery.Why not replace the engine battery with Lithium as well?

System upgrade for Lithium coach batteries issue

19 Replies

2oldman
Explorer II
Dec 20, 2018
SFVdave wrote:
Wouldn't just disconnecting engine battery from the BIM and isolating it work?
Yeah.. that's what I'd do. I'm sure the alternator will handle your engine battery like it's supposed to.

What Li batteries are you considering?
LittleBill
Explorer
Dec 20, 2018
im pretty sure the replacement is meant for both engine and house battery's to be LI, not separate chemistry.

i would not even remotely consider combining the battery's their charge profile are vastly too different if using a 18650 based lithium cell, over voltage on a LI pack is a death sentence, both to the battery and potentially you
SFVdave
Explorer
Dec 20, 2018
camperdave wrote:
Does the Progressive Dynamics charger continue to supply 14.4v even after the Li battery is charged? That seems odd to me, I thought Li's don't like being trickled like that. If it just charges at 14.4 then shuts off, I think you'd be fine with the lead chassis battery.

No, it shuts off when lithium batteries are charged. No trickle charging.
camperdave
Explorer
Dec 20, 2018
Does the Progressive Dynamics charger continue to supply 14.4v even after the Li battery is charged? That seems odd to me, I thought Li's don't like being trickled like that. If it just charges at 14.4 then shuts off, I think you'd be fine with the lead chassis battery.
STBRetired
Explorer
Dec 20, 2018
SFVdave wrote:

It would be so much easier to make the Lithium upgrade if I didn't have the Flooded engine battery.

Why not replace the engine battery with Lithium as well?
SFVdave
Explorer
Dec 20, 2018
I emailed PC photos of my BCC and called them this morning. The new Li BIM replaces the old BIM and relay but is a nightmare installing it. Replacing the entire BCC with the new lithium model costing $500 is also a wiring nightmare. But my question was how is charging handled. It seem to be the same. Converter charger on shoreline or generator will charge both engine battery and coach batteries at the same time if one is low. The alternator will do the same while driving but the coach batteries for 1 hour. I don't see how the Lithium charging parameters would work for both, as PD4560 Li instructions said don use with Flooded battery charging. Still seems simplest way is to detach engine battery from BIM and allow solar to charge coach batteries continually while driving and the alternator to charge engine battery. Just concerned about engine battery going dead while dry camping and no boost. But I could fire up generator and use my old Victor 100amp battery charger if necessary.
It would be so much easier to make the Lithium upgrade if I didn't have the Flooded engine battery.
pianotuna
Nomad III
Dec 20, 2018
You could go 'old school' and get a diode based charger for the starter battery. That would drop charge voltage by 0.7 from 14.4 down to 13.7.
jharrell
Explorer
Dec 20, 2018
I don't have lithium but have given it some thought including this issue if I where to upgrade. Bottom line yes you don't wan't a normal auto battery combiner. I know some use a manual combiner so they can charge from the alternator if needed and watch the system as necessary while driving.

To automatically charge from alternator you would need a dc-dc charger like a Sterling. I wish someone would make a nice two way dc-dc charger so alternator can charge house and solar/shore can charge chassis with proper battery profiles on each. I haven't found that yet.

Magnum smart combiner might work too.

Victron makes an interesting BMS that works with their lithium batteries for charging from alternator but requires as DC-DC converter for house loads for reasons I am not entirely clear on: https://www.victronenergy.com/upload/documents/Datasheet-BMS-12-200-EN.pdf
DrewE
Explorer III
Dec 20, 2018
Something like what you're considering would probably be the simplest solution. The one obvious drawback is that you can't charge the coach batteries from the engine, as you pointed out, and if they're low the alternator would provide a lot more charge than the solar panels alone. One solution there is to replace the BIM with a plain old continuous duty solenoid wired to the engine run circuit (and maybe also to the emergency start switch if you have one) such that they connect when the engine is running. This is a simpler setup that many RVs use by design.

The engine computer and some related bits are mainly what would consume power from the engine battery...that, and self-discharge. If you're worried about the engine battery running down during storage, you can either get a small solar panel to maintain it, or if on shore power just use a little battery maintainer charger of some sort. If you have a lighter socket connected to the engine battery that's live all the time, that may be a convenient place to plug in a maintainer charger.

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System upgrade for Lithium coach batteries issue

19 Replies

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