Charging from another 100Ah battery

I have the new EB70, and am beginning to think about getting another battery, likely another “naked” LiFePO4 of about 100 Ah size. Can the EB70 take the input from such a battery via jumper cables to cigarette socket to EB70 “car charger” cable? Should I somehow be limiting the juice coming off of the 100Ah battery into the EB70? I am thinking forward to a time when I have a van or vehicle to build out, and would be utilizing likely separate components rather than a solar generator. Getting a larger “naked” battery now would give me some insurance when conditions do not allow for adequate PV solar charging, to get the EB70 back up toward full.

I did find this YouTube video and it looks pretty straightforward, especially if one uses a 12 to 24 converter.

Any thoughts?

Yes, you can use a “car” socket conneted to a 12 volt batter for charging. But…you will not see a high rate of charge since the voltage range will be around 12.5 or so and not the 13.5 to 14 volt range you would be getting from a running vehicle. To see your actual wattage rate, connect your EB70 to your vehicle car socket with the engine off and the key turned on to simulate what you want to do.

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I am more thinking of carrying a spare LiFePO4 battery in the vehicle, fully charged, in case I need to top off the EB70. I like what the fellow did in the YouTube video, by using a 12 to 24 volt converter, and then running the electrons in as though they were coming off of PV solar–faster at higher wattage, and gets around the potential issue of too low voltage coming off of the 12 volt.

If I also got a MPPT controller, I could also top back off the spare 100 Ah battery when the sun is available.

I don’t have a 12v to 24v converter, but I think it would work. And due to LiFePO4’s higher voltage curve over the lead acid types you’d get good results. Here’s a shot of my EB70 taking 100w from a LiFePO4.

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So would two battery’s in series (25.6v) pump in the EB70’s max 200 watts?

Yes, you should get approx. 200 watts of input charging by using two 12 volt batteries in series.

I doubt you’d get the same from static 12v lead acids. Their nominal voltage is lower and their voltage curve is not as strong as LiFePO4s. You’d need to be pulling from a car battery while the engine was running to get similar.

Tried this over the weekend. Connect my AC 200P via the 12volt connecter to my campervan leisure battery (110amps). Pulled 8amps @ 100watts without a problem. Drove for 2.5 hours - Campervan putting 20/30amps back into leisure battery (so no problem drawing the 8amps out)
On arrival at campsite, I have fully charged leisure battery and the AC 200P went up by 10/12%
Connect it the next morning using my solar panel on roof which only puts in 6amps. This worked fine, but now looking at 12-48 converter or adding more solar to the campervan.
AC 200P lasted 3/4 days of keeping my cool in 35C/95F heat using a fan.
Very pleased.

Sounds good. The 12-48 volt DC converter will put around 575 watts of charging power but consumes about 55 amps of 12 volt DC power from the vehicle so the source needs to be capable of handling an extra 55 amps. The wires from the vehicle battery need to be as thick as battery cables and keep the run as short as practical. The wires from the converter to the AC200 can be 10 ga. wires and the run can be extended as well.

Scott, I have a dc-dc charger providing the leisure battery with 30amps whilst the engine is running. I’m hoping that this will supply enough recharging of the leisure battery whilst the 12-48 volt DC converter draws the amps out of the leisure battery. The 12-48 volt DC converter will not arrive until the end of next week.

You will be using around 55 amps of power from the 12-48 volt converter so you will be losing 25 amps per hour out of your battery. Can you connect the 12-48 volt DC converter directly to your enging starting battery so you would be receiving full alternator power? This would require the converter be fairly close to the starting battery and that may not be ideal. In any case, 30 amps of incoming charge will not keep up with the 55 amp draw from the 12-48 volt converter. But…You will only be charging the AC200 for about 3.5 hours from dead so you may be able to charge the AC200 as long as you can run the engine longer long enough to re-charge your “leisure” battery.

Scott, most of the time the AC200P would only ever be 50% discharged. I will look at connecting the 12-48 volt DC converter directly to the engine starting battery and running cables to AC200P. The problem is the VW campervan has a “smart” alternator fitted so will have to check if it will supply enough power. More reading.

Thanks by the way for your help and advice.