Lifepo4 and lead-acid - common ground?

Submitted: Wednesday, Feb 07, 2024 at 11:48
ThreadID: 146915 Views:1178 Replies:5 FollowUps:6
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.
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Reply By: TrevorDavid - Wednesday, Feb 07, 2024 at 12:20

Wednesday, Feb 07, 2024 at 12:20
Andy

I have to lead acids & a Lithium in my Cruiser. Lead Acids are for cranking and cabin accessories, the Lithium for fridges, water pump, lights etc, all negative connections are to the chassis.

Regards

TrevorDavid
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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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Reply By: Allan B (Sunshine Coast) - Wednesday, Feb 07, 2024 at 13:04

Wednesday, Feb 07, 2024 at 13:04
.
Hi Andy, a simple answer…….. YES, you most definitely can.
Cheers
Allan

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Reply By: Andy Mac - Wednesday, Feb 07, 2024 at 15:00

Wednesday, Feb 07, 2024 at 15:00
Thanks for that guys. That means my plan will work perfectly! Looks like I'll be spending my weekend crimping wires ????
AnswerID: 645241

Follow Up By: Genny - Wednesday, Feb 07, 2024 at 17:29

Wednesday, Feb 07, 2024 at 17:29
Gather the popcorn! Crimping? :)
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Follow Up By: Andy Mac - Wednesday, Feb 07, 2024 at 18:31

Wednesday, Feb 07, 2024 at 18:31
Crimping terminals onto wires.
I've got new bus bars, isolator switches, fused switches, ground points and anderson plugs to install. Then there's the new dc-dc charger, and I need to change my solar panels from series to parallel connections to reduce the voltage for the dc-dc mppt.
Some would see it as a chore, but I'm quite excited to get into it!
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Follow Up By: Genny - Wednesday, Feb 07, 2024 at 23:22

Wednesday, Feb 07, 2024 at 23:22
Yes I know. I feared you may have ignited "The Great Debate" - crimping vs solder.
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Follow Up By: Andy Mac - Wednesday, Feb 07, 2024 at 23:33

Wednesday, Feb 07, 2024 at 23:33
Lol, gotcha!
In that case, I'll stir the pot a bit...
If they were solid wires, I'd solder them (I probably will solder the andersons), but everyone knows that a well crimped conector with a heat shrinked sleeve is superior in almost every way.
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Reply By: danni86 - Wednesday, Feb 07, 2024 at 21:29

Wednesday, Feb 07, 2024 at 21:29
Lithium iron phosphate (LiFePO4) and lead-acid batteries share a common purpose in energy storage, yet their chemistry and performance differ. Both play vital roles in various applications, catering to diverse power needs.
AnswerID: 645244

Follow Up By: Nomadic Navara - Wednesday, Feb 07, 2024 at 22:29

Wednesday, Feb 07, 2024 at 22:29
Any power systems you have can use a common ground circuit. Any problems only arise if you attempt to connect the positive sides of things together. If you keep the systems apart there are no problems.


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