Need help with motor home batteries

Greetings. I have an older motor home with two GC2 6v house batteries and separate engine starting battery.
Jacks and 5000w generator are started with house batteries.
That’s original equipment.
5 yrs ago I paralleled two more GC2’s in adjacent compartment, added 1100w excelltech inverter and 600w solar.
Works great very happy. BUTT!
Time to play with lifepo4.
I’m thinking….keep original two gc2 for starting jacks, generator and 12v accessories. Packing adjacent compartment with lifepo4 only for inverter 120v. Totally separate.
How to charge both banks??
Can I parallel two victron scc mppt to two separate battery types?? Or do I need two separate solar arrays??
In winter with furnace gc2’s may occasionally run low. Can I give them a boost with a B2B from the lifepo4. Or is that just for an alternator??
Thanks greatly appreciate any response I’m open to any ideas

Are you planning on a 12v Lifepo4 battery bank?

Each charge controller needs their own solar array.

Thanks Bobert. Yes my inverter is 12v. What were your thoughts?

Thanks camelcase. Is that for Pwm also or just a mppt thing?

Let me throw out a few ideas… I full-time in a Class A and built my own lithium house bank 1-1/2 years ago. Here is a link for my build. It may have some ideas (or not) for you.


You need to find out how many amps the jacks take and how many amps it takes to start the generator.

I would think you do not want three different battery banks in your rig - chassis, house lead and house LiFePo4. Keep it simple.

A good lithium bank will have no trouble running the jacks and will probably be able to start the generator too. If not you could move the generator

Are you wanting to build your own pack or buy drop in batteries?

Good Luck

Keep the system 12 volt. Ditch the second set of house (lead acid) batteries. Keep the starter battery lead acid. This simplifies your system a lot. Add a DC-DC charger to keep the starter battery charged.

As stated above, you need to know the maximum amps that your jacks draw. That's a more sustained draw - more than a couple of seconds. The generator is a quick draw, but can be more than 200 amps. As an alternative, you could start the generator from the same battery that the engine starts from.

Here's a recent thread on using LiFePO4 for starting a generator:

Thanks rocket man. Will have to spend some time studying your system. Forgot about insulation and heat. That brings my adjacent compartment down to 20x17x10!!
I think I’ll pass on moving the generator. I found 350 cc amps for generator and “adequate battery” for H&H 310 jacks.

Thanks hrgkd. Yes 12v systems, second set of gc2’s are gone. Engine battery is in front under hood. Original gc2’s are in exposed compartment. Those two batteries are sometimes combined with solanoid switch. Adjacent compartment is now empty waiting for lifepo4.
I’m not understanding add dc charger for starting? Doesn’t alternator do that?
350cc amps for generator. Does that require 400ah bms?

Mgr said:

I’m not understanding add dc charger for starting? Doesn’t alternator do that?
350cc amps for generator. Does that require 400ah bms?

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If you add a DC-DC charger, you can keep your engine starting battery charged up. That's handy for situations where the motorhome might sit for weeks or months without being started.

Thanks hrtkd. That is a handy tip. I found That onan generator could be 350 amps. Searched hwh jacks even called them and no luck. I’ll just assume it’s Large. I assume Those numbers are for determining bms size.
Is four 100ah lifepo4 Enough? Wait that won’t even fit in that compartment anyway.
Two will fit easily. But won’t even start generator and may blow up with jacks.
Maybe I’ll just stick with 400ah of lead. No wait this is just a hobby anyway and I could use a few more amps so maybe Two separate banks would work.
Ok I’m back to 400ah lead and will go to the desert for a couple weeks and try to consolidate Compartments for more batteries. I’m thinking the wife’s desert rock and beading compartment will be perfect for batteries…my tools…where will lawn chairs and barbecue go? Bigger motor home. No wait what if I rewire two of six solar panels to those two 6v those will start anything.
Just thinking
That sok 206ah might fit perfectly. Could that dc to dc thing maybe smooth out two separate banks??
Can I ask what dimensions are your DIY battery build??
Thanks appreciate

Move your generator lead over to the chassis/starting circuit. Remove the isolator/combiner solenoid, keep the two circuits separate.

Alternator should charge the starting battery, replace the solenoid with a dc-to-dc charger so you can charge your house battery when driving.

Separate solar controllers for separate solar panels.

I just did this exact conversion for a 2005 Winnebago and it works just dandy. 2 starting batteries in parallel - their own 100W panel and SCC, they start the engine, run the leveling jacks, slideouts, power awning, and power entry step. The house circuit is seperate, has 600w of solar, a dc to dc charger, a 12v converter/charger set for lifepo4 parameters, and a couple of 120V inverters.

Starting:



House:

Mgr said:

That sok 206ah might fit perfectly. Could that dc to dc thing maybe smooth out two separate banks??
Can I ask what dimensions are your DIY battery build??

Click to expand...

Dimensions will vary depending upon which brand and size of cells you purchase. Usually you can find cell dimensions.

I found that if I looked a little deeper at the compartments in my RV I could find unused space. Clothes hamper? Not used, could hold batteries. Many cabinets with drawers don't have the drawers going all the way to the wall. I ended up using a drawer compartment, eliminating the drawer.

Thanks browneye.
Is that a entry step.
Two inverters?

Mgr said:

Thanks browneye.
Is that a entry step.
Two inverters?

Click to expand...

DIY lifepo4 pack moved in under the sofa, with 12V converter/charger and 600W inverter. The inverter has their own receptacles, marked as such - one in the master at the makeup desk, one outside with the radio, and one behind the co-pilot seat. If I were to do it again I would have gone with a bit larger inverter with a transfer switch and connected it into it's own 120V circuit going to existing outlets. Hindsight is 20-20. It works fine for what we want though, charging some electronics, the ebike batteries, and a box fan. The coach already had a 300W inverter just for the front TV and receiver/turner/surround sound. TV is now an LED flat screen - with the surround sound and TV on the smaller inverter, it pulls about 6A on 12V. So four hours of TV is about 25Ah off the battery.

The original battery compartment under the entry steps now has room for two starting batteries in parallel, their own 100W solar panel and controller (in view) and the Victron Orion dc to dc charger is there - that is a way cool unit. Victron BT app is really nice.

Originally the 12V converter/charger was under the refer in a closed compartment, and quite some distance from the new battery location - about 10' of cable. But worse the old wiring was 6awg, which was also supposed to carry the inverter feed. Moving them both next to the battery and connect with 4awg wire gave me pretty much zero voltage drop. The whole setup works killer. The lifepo4 cells just keep going and going and going - just amazing.

I got a LOT of help here putting it together - would not have attempted a battery build without some of the very generous forum members.

We've gotten by with a pair of golf cart batteries over the past 17 years we've owned this coach - mostly dry camping. That's about 100A usable, our average overnight consumption if the furnace has to run - it pulls about 11A running, so overnight it can use 40-50Ah by itself. A 230 lifepo4 battery gives me double the capacity for half the space and a third the weight:

Originally I was going to replace the seven year old golf cart batteries - one cell was coming up short on specific gravity. A pair of Trojan T125's run at least $300 now, maybe more. Building a DIY battery cost me about twice that, perhaps a little more, with tools and materials, wire and connectors, fuses and switches and stuff. But as mentioned, I get twice the storage capacity, and longevity likely means it's the last battery the coach will ever need. I saw it as a good investment for preparing to retire and use the motorhome a lot more. Our water tanks and holding tanks fill up before we would ever run out of power.

Browneye. Great thanks no huge battery banks no humongous inverter nice and simple. No bms problem
About that victron Orion dc charger. Will that actually bulk, absorb, and fully charge a lead battery from a lifepo4 battery. Equalize?

The Smart version of the Orion can be set to whatever charge parameters you want. I'm not sure about the non-smart version. The data sheet for the non-smart doesn't go into details, but the Smart version data sheet does:

I exchanged the one I had for a smart charger version. You can set all of the parameters on it with the app. Download it here if you want to see how it works:


Usually it's used the other way around though - input from starting/chassis battery to charge your house battery when the engine runs with its alternator.

I also do not leave the 12V converter/charger on, only used when needed, when connected to shorepower or running the generator for 120V. So far I haven't had the need - solar panels keep the batteries charged up each day. Even in storage - there's just no need to plug in to shorepower any longer.

Thanks browneye. Good tip, I will move converter charger closer to battery compartment. O wait that is a 20 yr old charger. Now I have to shop for a new charger for lifepo4.
I’m actually liking your minimalist approach. A larger transfer switch system would be a distant future build. No large appliances. Just crockpot small toaster etc
So my system will be like yours only in reverse. Am I the only one
Just curious if you’re starter bank was to somehow get low could you boost it with lifepo4 bank? With orian?