Need help figuring out my battery system.

[Furyous68]

I'm converting to LiFepo4 batteries. My 2012 Freelander does not have a Lithium compatible converter. I purchased a Renogy 50A DC-DC/ Solar charge controller. My plan was to disconnect the convertor, & wire the charge controller to the alternator, install a solar port on the exterior (panels aren't on the roof), and then wire the batteries to the electrical panel.

Then I had a thought... the Lithium batts aren't supposed to be used to start an engine. I have an Onan 4000 genset... so I still need a lead acid battery for that. I need to be able to keep that battery charged... so is there a way to run my lithium batteries with the Renogy Charger & still have an SLA battery on factory converter?

I understand this is probably a "have your cake & eat it too" scenario.

[chopity]

The factory converter wont hurt the lithium batteries. Use it when they're low. To maintain and top off the lithium use your new solar controller. Assuming youre not boondocking 24/7. You want to top them off periodically so they can balance.

To start the genny some people buy a tiny starting lithium battery. Not a deep cycle but one designed for starting. Could use a regular 120v battery tender to charge it up when needed after a handful of generator starts.

[Soppy]

Depending onthe BMS in the battery, you could probably use it to start your generator. You would probably need a 200 amp BMS , although some 100 amp BMS's will allow enough current flow to start a generator. As long as the voltage on your old converter doesn't exceed 14.4 v , it can be used to charge the lithium batteries.

[hamm2018]

Originally Posted by Furyous68

Then I had a thought... the Lithium batts aren't supposed to be used to start an engine. I have an Onan 4000 genset... so I still need a lead acid battery for that. I need to be able to keep that battery charged... so is there a way to run my lithium batteries with the Renogy Charger & still have an SLA battery on factory converter?

I understand this is probably a "have your cake & eat it too" scenario.

We have a big 5th wheel, and the Lithium batteries start our Onan 5500 without any issues. Been working great since 2022, and we dry-camp for over 3 months straight in the winter.

[Persistent]

Originally Posted by Furyous68

I'm converting to LiFepo4 batteries. My 2012 Freelander does not have a Lithium compatible converter. I purchased a Renogy 50A DC-DC/ Solar charge controller. My plan was to disconnect the convertor, & wire the charge controller to the alternator, install a solar port on the exterior (panels aren't on the roof), and then wire the batteries to the electrical panel.

Then I had a thought... the Lithium batts aren't supposed to be used to start an engine. I have an Onan 4000 genset... so I still need a lead acid battery for that. I need to be able to keep that battery charged... so is there a way to run my lithium batteries with the Renogy Charger & still have an SLA battery on factory converter?

I understand this is probably a "have your cake & eat it too" scenario.

Your original plan is good, except, don't disconnect the old converter charger. It will still charge deeply discharged lithium batteries. It will also supply 12 volt power for lights and other things when on shore power.

The DC-DC replaces the old bridge circuit between house and chassis battery banks. It converts the alternator lead acid output profile into a lithium charging profile.

Install the new lithium batteries in place of the old lead acid house batteries. Chances are the new lithium will start the generator, but get advice from an expert. Contact Renogy for an OK. It depends on the starting current required and the Renogy battery BMS capability. Have the exact generator make and model number handy. Have the starting requirements for the generator handy.

The rule of thumb is you should not use small lithium RV batteries to start the RV engine. Starting a generator engine uses much less power.

Some Litime batteries come with a warning not to start generators or run leveling systems.

[whybother]

Originally Posted by Furyous68

My plan was to disconnect the convertor,

As others have said, just leave it for now.

Originally Posted by Furyous68

Then I had a thought... the Lithium batts aren't supposed to be used to start an engine. I have an Onan 4000 genset...

If you haven't purchased it already, make sure your battery has a 200A BMS. (Most of the smaller LifePo4 12v batteries only have a 100A BMS... not AH, the capacity, but A, as in the amount of amps the BMS is rated for continuous load.)

A 12v LifePo4 with a 200A BMS (or 2 x 100AH) should have no problem starting a genset. Even a 100A BMS would probably work. Where you'd run into trouble is trying to start the chassis engine.

[Tony Ramirez]

ONE batt w a BMS of 100A lets you draw 100A, but TWO batts w 100A BMS lets you draw 200A. Same theory w 200BMS, x2=400A.

I have 2 200A BMS & have NO PROBLEM starting my 10K watt deisel gen, even in mid 20 temps.

[twinboat]

Move the generator to the chassis battery and re-route your old converter output to it too.

That way, anytime your on shore or generator power, your chassis battery is being charged. Your new lithium converter can be just be used for the lithium batteries.