Lifepo4 and lead-acid - common ground?
Submitted: Wednesday, Feb 07, 2024 at 11:48
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Andy Mac
Hi campers. I've upgraded the house battery in my camper van to a 200Ah Lifepo4, but I'm retaining the dual lead-acid batteries for the van accessories and starter. I have one question left to answer about the setup before I finalise the connections and flip the switches.
Can I connect lithium and lead-acid to a common ground (chassis/body)?
I feel like I've spent forever scouring threads for a straight answer to this one, but every thread I find on the topic usually devolves into a discussion/argument about earth cable size (or something along those lines) by the second or third reply, and nobody ever seems to answer the question. Based on that, please assume that my setup is the most spectacularly put together world class wiring job, connecting the finest components ever conceived by man. The connection points I'll be using have been personally approved by every one of the Gods, and my van's body is forged from a single piece of the purest copper. Every part of the system puts out or uses exactly the same Volts and Amps, and the Gods (they've been really helpful) blessed the whole setup with zero resistance, anywhere...
I just need to know, can I have lead-acid batteries and a lifepo4 battery connected to a common ground?
Thanks in advance.
Reply By: Member - LeighW - Wednesday, Feb 07, 2024 at 12:39
Wednesday, Feb 07, 2024 at 12:39
Yep same as trevor. Car is powered by its own lead acid battery. Freezer and other non car accessories are powered by the Lithium.
In my case as I don't use a DCDC charger I ran a negative cable from the cars common earth point near the cars battery to the Lithium battery. I also ran a cable from the lithium negative to a body earth point near the Lithium and also one to the engine to minimise any voltage drops.
Positive and negative is run from the Lithium battery to a fuse block, positives and negatives then run to each accessory. If your using a DCDC charger to charge the battery the negative will most likely be connected to the cars negative negative anyway unless your DCDC has an isolated output.
It could be advantageous to have the negative of the Lithium not connected to the cars negative as then any short circuit from the Lithiums positive to the cars metal work etc wouldn't result in a short circuit but you would need to run positive and negative cables to each accessory and all accesories would need to be ones where the the accessory negative is isolated from any metal case and mounting brakets and again any chargers will need isolated outputs.
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Follow Up By: Andy Mac - Wednesday, Feb 07, 2024 at 14:56
Wednesday, Feb 07, 2024 at 14:56
Thank you for this. My current setup is much like you've described with the solar and "house" electrics all routed back to the lithium via the mppt charger, so they're fully isolated from the van batteries, but I'm changing the mppt for a dc-dc with mppt which has a common negative terminal. With that in place, I can connect the alternator and 13.8V dc supply (active when plugged into mains on a site) to the same circuit so I'm not stuffed if the weather turns bad.
I was 90% sure that it would be fine, but it's always nice to have some reassurance.
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