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12-31-2022, 01:36 PM #1
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Adding lithium's for inverter only but keep lead acid for 12V circuits...
Hey guys,
Wife and I mainly use our TT for long summer trips to Alaska or out West. It is 2600RB and has a 30A hookup. We stay gone for about 3-4 months and we do a lot of dry camping. We have two inverter gensets and they work well. But I need to add an inverter because I just added some electric seats so I thought I would do it right.
OK...I have two 24series deep cycle batteries for my 12V systems. I also have 3 newer lithium's (50Ahrs each) that I want to install with an inverter to supply my 120V circuits.
How would you incorporate this and a few questions:
First - Would you use my existing on board charger that takes care of my lead acid batteries to charge the lithium's also? I know the lithium's may not achieve 100% because of the lower voltage but I don't know if that's a big deal? OTOH, I do have a lithium charger that I can plug into shore power.
Second - Would I need a disconnect switch for this setup when shore power is plugged in? Just curious because my Lithium's would always be supplying the inverter and nothing else and I didn't know if inverters have some sort of sensing relay built in to handle the transfer from shore power to inverter power. If so, what do you guys recommend?
Third - What inverter would you recommend? I'm not planning on running my AC or microwave from the inverter but my fridge is the propane/AC and I want that. Maybe a 2000W?
Fourth - What type of charging solar panels would I need to install? My truck charges my batteries when I run but obviously not my lithium's. Would you guys recommend a portable panel or roof mounted?
Finally - Where would you install the inverter and lithium batteries? I assume somewhere under the front passthrough is the standard place for most people? Anyone have any pics?
Thanks guys.
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01-01-2023, 11:04 AM #2
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My first impression is that you might be better off upgrading the whole system, but it sounds like you'd like to go a different route.
Your onboard charge should be able to charge both battery sets, as you note the LiFePo4 batteries won't fully charge. I'd recommend a transfer switch to switch between shore power and the inverter. How many Amps do the electric seats draw? A 2,000-watt inverter sounds like it would be adequate for the use you're describing. Solar would depend on how you're going to use the system. You could add a DC to DC charger to charge the lithiums when traveling. For the where, you'd like to have the batteries as close to the inverter as possible. I'm not familiar with your coach, but the passthrough is a popular option.Stephen and Judy
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01-01-2023, 11:36 AM #3
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01-02-2023, 06:23 AM #4
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Well...I will do work myself, I already have an AC lithium charger (if needed) so would assume I can get an inverter and some kind of switch for under $500. Does that sound right?
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01-02-2023, 08:32 AM #5
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The voltage difference is so significant, I’d run it as a second electrical system.
A lead-acid battery is typically 12.65V full charge voltage, about half a volt lower than the lithiums, and the lead-acid voltage will drop significantly more than the lithium as they discharge. A portion of the lithium charge will be spent charging the lead-acid batteries. That would stabilize between uses, but since there is always a small load on the 12V system, it just seems problematic to me.
A simple charger would be fine for the lithium bank since you wouldn’t be drawing 12V power from it for anything but the inverter. I’d think you’d want at least 30A.John & Kathy
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01-02-2023, 03:52 PM #6
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01-02-2023, 04:56 PM #7
Not sure what you get from having two separate battery systems. That seems to over complicate to me. Single system should easily handle both 120 and 12v with no impact to either. Just make sure you have enough battery to handle your needs in lean times and you should be fine. If you are taking the time to upgrade go Lifepo4 and don’t look back.
Bill2019 GMC 3500 SRW Sierra Denali Duramax
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01-02-2023, 10:25 PM #8
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Eh, I think you'll find that budget a bit hard to meet. What wattage inverter are trying to put in? A pure sine wave inverter is going to likely blow that budget by itself. Two separate 12v systems is a bit abstract and IMO unnecessary. I'd keep the battery chemistry the same.I'm planning two separate DC systems in my next rig. It'll be 24v and 12v. But have two 12v systems doesn't make much sense to me either.
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01-03-2023, 06:34 AM #9
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It's because I have the batteries on hand. As I mentioned...I don't want to mix lead acid and lithium's in the same circuit. It's not recommended. What's the harm in using the lithium's to supply inverter only? Not arguing...just curious.
Also...I think I can get a pure sine wave inverter for about $300. All I would need after that is a transfer/disconnect switch...right?
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01-03-2023, 08:08 AM #102021 398M Full Body Paint 8k axles. LRH tires. Disc brakes.
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