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Jbones · 01-17-2025, 08:53 PM

I have 800w of solar wired for 12v, and a new 12v 4000w pure sign wave inverter.
I also have a12v, 400ah lithium po4 battery.

Can I buy another 400ah 12v lithium battery, wire them for 24v & use the 4000w 12v inverter, or do I have to stay with the batteries wired for 12 volts?

If I can use the 12v inverter with a 24v battery supply, will I have to rewire the solar panels to 24v?

twinboat · 01-18-2025, 05:14 AM

You can't use a 12 volt inverter, or anything else with 24 volts.
Wire the batteries in parallel, suppling 12 volts with 800 AH of capacaty.

shoreco · 01-18-2025, 05:15 AM

Keep the batteries in parallel and remain 12v

Jbones · 01-18-2025, 08:26 AM

Thank you. Obviousl, this solar instalation is all new to me. After I get it all is installed, I will have it checked by a qualified solar tech before activating it.

SafariBen · 01-18-2025, 01:31 PM

You already have a lot of battery for that amount of solar, what are you trying to do that more battery will accomplish?

Every battery maker I've seen says to never mix batteries of different ages, I don't know if that info is out of date or not? don't mix different brands if at all possible.

Jbones · 01-20-2025, 05:35 PM

I was asking about adding another battery if I went to 24v. Since I can't go to 24v there is no need for another battery at this time.

Eventually, I might add more solar pannels, and if I do, I might consider adding another battery of the same type, which would eventually give me 800 ah of storage if needed.

TravelSolo · 01-21-2025, 03:46 PM

The solar voltage is independent of the battery voltage. The solar charge controller takes the solar input however it comes in, then converts that to the battery voltage you program (or it senses).

If you change from 12v battery to 24v battery you need to get a new inverter that will accept 24v since there is no efficient and inexpensive way to convert the 24v to 12v at the amperages the inverter can pull. So stick to 12v unless you want to change more components and add a DC-DC to drop the 24v to 12v for the trailer house circuits use.

d23haynes57 · 03-02-2025, 08:01 PM

Quote:

Originally Posted by Jbones

I have 800w of solar wired for 12v, and a new 12v 4000w pure sign wave inverter.
I also have a12v, 400ah lithium po4 battery.

Can I buy another 400ah 12v lithium battery, wire them for 24v & use the 4000w 12v inverter, or do I have to stay with the batteries wired for 12 volts?

If I can use the 12v inverter with a 24v battery supply, will I have to rewire the solar panels to 24v?

Another installation without due diligence engineering up front. What is the surge capacity of that inverter? A 4,000-watt load will require 400 amps at 12 volts DC. Even for Lithium you design the system supplying battery capacity going for no more than a 4-hour rate of discharge. For Lead Acid this should be 6 to 8 hours. In addition, for Lithium you need to consider the design limitation of the built in BMS. The next part is trying to use as few batteries in parallel to meet the requirements and most battery manufacturers will limit that to four. Also consider what other loads may need to be supplied while the inverter is loaded. Lighting, heating systems, entertainment, etc.
Based on battery value pricing I would probably go with three, 300 A/H, (900 A/H total), batteries with 200 A/H BMS.
Hopefully your inverter/charger has a 150 amp or larger charge section. That would put you at a 6-hour rate for this bank. For engine alternator charging, going direct from alternator to the battery bank @14.2 volts figure 25%to 40% of the A/H capacity to be potential load. Isolation methods, relays, diodes, cable size and length will reduce that. For a bank this size you need close to 300-amp alternator. If going with DC-to-DC chargers you want at least 10 A/H for 100 A/H battery capacity. This sis still only a 10-hour rate. Note that for this theoretical bank you 90 amps. Now keep in mind that when alternator voltage drops these devices will increase current draw to compensate. If the DC-to-DC chargers or solar supply is limited the parallel batteries may actually charge in stages, one at a time.

For most RV applications 3,000-watt inverters are sort of the sweet spot. 150-amp charger sections. 10-gauge 30-amp circuits in/out are practice and easy to install. Usually excellent transfer switch capacity and reliability. Battery cable 3/0 or 4/0.

Stircrazy1 · 03-03-2025, 08:21 AM

Quote:

Originally Posted by Jbones

I have 800w of solar wired for 12v, and a new 12v 4000w pure sign wave inverter.
I also have a12v, 400ah lithium po4 battery.

Can I buy another 400ah 12v lithium battery, wire them for 24v & use the 4000w 12v inverter, or do I have to stay with the batteries wired for 12 volts?

If I can use the 12v inverter with a 24v battery supply, will I have to rewire the solar panels to 24v?

keep the batteries at 12V like mentioned, the problem you might rung into depending on the batteries is if the BMS will put out enough amps to run a 4000 watt inverter just running at 4000 watts you could be pulling up to 366amps when accounting for the ineffeciency of the inverter, if it has surge capability it could be higher. so by adding a second 12V in parralel you are doubling your amorage capability. so if your BMS was 150amps (just picking a number) now you can go to 300amps. and if that is the case with that inverter I would be tempted to run 3 of the batteries to give me about 450 amps of capability. now this is all asuming that you have 150amp BMS if they are 200amp then you should be ok as long as you don't use much of the surge capacity.

as for your panels, if you have a MPPT solar controler I would rewire then solar panels to 24V anyways. it has nothing to do with the batteries and will still put 12V charging tot he batteries. what it does is make it a little more efficient. well in some cases a lot more efficient.