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Old 03-12-2023, 12:05 PM   #1
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Wiring Between Batteries

Hi

Kind of a long post, I apologize.

I've been asking a lot of electrical questions and been getting helpful information.
I have yet another question. I took my 2 105ah Lion LFP batteries to the dealer to have them installed on our Geo Pro 20BHS while they do some pre-delivery work.
They tied the two batteries together in parallel with what looked like 8g cable (looked pretty small to me). I mentioned I thought it would be larger, but they said the existing wiring would be fine. Now, I'm pretty sure that the cabling between batteries needs to be bigger, but even after reading quite a few solar/battery articles I'm still a little unclear about the sizing.

Should I base the inter-battery cabling on the max draw that the battery bank could see, or base it on the total AH's of the battery bank. Mind you, I'm just talking about the wiring for the parallel hook up.

The trailer has a 1000w inverter ( approx 85a draw), WFCO 8735ad converter, 380w of solar in parallel with the stock 30a charge controller. I have a third 105ah battery to add to the bank when I figure out where inside to move them to.

By my reckoning the batteries should be wired in parallel with 0 or 2/0 cable. Am I on the right track?

Once again, thanks for any input you can provide.

Kip
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Old 03-12-2023, 01:08 PM   #2
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As it is right now the largest draw on your 12v system will be the inverter. Current draw, allowing for inefficiency will be more like >90 amps. This will be in addition to the usual 12v load for lites, refer, t-stat, etc. I'd use 100 amps for determining wire size as a minimum.

Using an average total wire run from load to batteries of 20 ft, and using a chassis ground, a #1 awg wire would be minimum. #8 wire doesn't even make the chart with a 1000w inverter but no surprise a dealer would think so.

If you see a larger inverter in your future go as large as you'd need in the future. More $$ for the larger wire initially but cheaper in the end as you'll only be buying wire once.
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Old 03-12-2023, 01:10 PM   #3
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I always thought manufactures used the smallest allowable and have upgraded for personal preference. Here is a good page for reference. https://battlebornbatteries.com/battery-cable-size/
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Old 03-12-2023, 01:18 PM   #4
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OK, thanks for the replies. The 8awg was just between the batteries, not sure what's running from the batteries to the load, as I don't have the trailer here yet.
Nonetheless, you've confirmed my instincts on this: Go big or go home. I'm expecting to have to upgrade a lot of wiring when I move things around.
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Old 03-12-2023, 01:24 PM   #5
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Thanks for the Battleborn link. Very informative.
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Old 03-12-2023, 03:05 PM   #6
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for intra-battery jumpers for two batteries in parallel wouldn't the amperage flow be 1/2 of the flow going out to the load? for three in parallel the intra-battery flow could b 2/3 of the flow going out to the load.

all that being said i'd go with jumper cables at least as large as the cables carrying the load. just makes is consistent.

as stated the inverter will be a large load but don't forget to add in the slides / jacks as they could easily be run while the inverter was also drawing current.

another way to check would be to look at the specs of the batteries. the bms will have a limit on how many amps it will allow. in parallel double that as each bms will could allow the max, times the two batteries.
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Old 03-12-2023, 03:13 PM   #7
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CHIKDOE

Thank you. That info on how power draw is shared by the batteries is just the kind of info I was looking for. I had not seen not seen that explanation before, maybe because it is so common sense, but it hadn't occurred to me. I think 2/0 is the way to go and will allow for some expansion.

Kip
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Old 03-12-2023, 03:17 PM   #8
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If you use high quality welding cable it can handle higher current then standard home wiring
https://windynationstore.com/product...-shrink-tubing
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Old 03-12-2023, 03:41 PM   #9
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Quote:
Originally Posted by kcmusa View Post
If you use high quality welding cable it can handle higher current then standard home wiring
https://windynationstore.com/product...-shrink-tubing
On this note Victron goes as far as to state an actual strand size limit for wires used with many of their products that carry heavy currents. The manuals for both my Phoenix IP43 and Orion chargers state strand size:

Quote:
Use flexible multi-stranded copper cable; the diameter of each individual strand should not exceed 0.4mm (0.016 inch) or a
surface area of 0.125mm (AWG26).
Welding cable will meet this "standard". Also, welding cable will be far more flexible than wires for residential/commercial use in same sizes.
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Old 03-12-2023, 03:47 PM   #10
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Quote:
Originally Posted by kipkohl View Post
OK, thanks for the replies. The 8awg was just between the batteries, not sure what's running from the batteries to the load, as I don't have the trailer here yet.
Nonetheless, you've confirmed my instincts on this: Go big or go home. I'm expecting to have to upgrade a lot of wiring when I move things around.
There is a remote possibility that the factory used a larger wire if the Inverter was factory installed. I would feel comfortable in guessing that it is only the bare minimum size.

Take into consideration that with LiFePo4 batteries they will draw a lot more charging current than lead/acid batteries, and will do so for almost the full charging period. In short, if you have a 55-60 amp converter, LiFepo4 batteries could well draw >50 amp while charging for a couple hours. Lead acid will draw half that and even taper the charge current down as SOC rises.
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Old 03-12-2023, 03:57 PM   #11
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Another good source for battery cables is the local auto parts store. Most, such as Auto Zone, NAPA, etc have a good selection with various terminations.

Bob
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Old 03-13-2023, 05:31 PM   #12
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I was in harbor freight the other day and noticed they carry a set of 2 2/0 "inverter cables", each 3' long, for $45. not a bad price given the high cost of copper cables these days.
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Old 03-13-2023, 05:36 PM   #13
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Boy, thanks for the helpful replies and the heads up on the wiring sources. I've already ordered 2/0 welding cable and connectors. Now I have find a good deal on a crimper. I'm leery of the hydraulic units that I can afford so it might have to be a hammer crimper.
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Old 03-13-2023, 05:42 PM   #14
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Quote:
Originally Posted by kipkohl View Post
Boy, thanks for the helpful replies and the heads up on the wiring sources. I've already ordered 2/0 welding cable and connectors. Now I have find a good deal on a crimper. I'm leery of the hydraulic units that I can afford so it might have to be a hammer crimper.
Home Depot Tool Rental
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Old 03-13-2023, 05:46 PM   #15
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Spot on , Larry. Thanks
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Old 03-13-2023, 06:13 PM   #16
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hopefully the PEX crimper at the HD tool rental will do the job, but when you receive your copper terminations you'll see how heavy they are.

several years ago I helped my son outfit his sprinter for full-time living and I purchased a hydraulic crimper from amazon.

https://www.amazon.com/gp/buyagain/r...UUifQ%3D%3D%0A

recently when I installed an inverter connected to my new 200Ahr Li battery I used it again to crimp the terminations on 2/0 cable.

another option if the PEX crimper doesn't do the job is to return the cable and terminations if you can and buy the 2/0 inverter cable set from harbor freight.
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Old 03-13-2023, 06:20 PM   #17
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Faithie999, your link didn't work for me. Which brand did you buy?
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Old 03-13-2023, 07:07 PM   #18
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I see the brand i purchased is NLA. Here is one the looks identical to the one I bought and is $20 cheaper.

On Amazon google this:

KERTY 16 Ton Hydraulic


$32.99
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Old 03-13-2023, 07:17 PM   #19
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What Titan said


get the biggest cables you can fit
that way if you decide to UPGRADE inverter you won't have to redo expensive wires.

dry fit your cables and lugs use felt pen to mark how the lug is to be positioned to lessen twisting

Good list of different tools ..
https://www.mobile-solarpower.com/tools.html




'
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Old 03-13-2023, 07:29 PM   #20
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Oops.

Quote:
Originally Posted by faithie999 View Post
hopefully the PEX crimper at the HD tool rental will do the job, but when you receive your copper terminations you'll see how heavy they are.

several years ago I helped my son outfit his sprinter for full-time living and I purchased a hydraulic crimper from amazon.

https://www.amazon.com/gp/buyagain/r...UUifQ%3D%3D%0A

recently when I installed an inverter connected to my new 200Ahr Li battery I used it again to crimp the terminations on 2/0 cable.

another option if the PEX crimper doesn't do the job is to return the cable and terminations if you can and buy the 2/0 inverter cable set from harbor freight.
Oops. I searched for "rent cable crimper" and didn't notice that Google ignored the adjective.
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