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Old 09-04-2020, 01:44 PM   #1
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2 battery questions

Hi all,


I just got a second battery to hook up in parallel to my first to increase my amp hours.

I am using a 2 gauge wire going from engine power to the first battery. Do I need to match that wire size to the second battery?

I also have the power from the engine going to the first battery and the connection to the fuse block coming out of the first battery. Can I just connect the second battery to the first, or should I reroute the current cabling to go from engine to second batt to first batt to fuse block instead?


Thanks!
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Old 09-04-2020, 01:57 PM   #2
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I think I got the answer to my first question here:
https://modernsurvivalblog.com/alter...nk-cable-size/


Nicely explained. I'm assuming it applies to vans as well as solar.
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Old 09-04-2020, 04:20 PM   #3
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Based on all the information I've seen, wire gauge vs. amp capacity is a function of cable length. This would mean that the interconnecting cables could be a smaller gauge than that running from the "engine power" to the battery bank:

12 Volt Wiring: Wire Gauge to Amps | Offroaders.com

Also, does this help answer your second question?

http://www.gearseds.com/files/twobat_onechgr2.pdf
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Old 09-04-2020, 06:37 PM   #4
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Thanks for the information and the links. I forgot about the length aspect.
I think I am ok with using 8awg between the batteries. That's what I am using from the battery to the fuse block.


I was wondering more so about how the other items wire into the battery bank. If I just connect the second battery, it will look like the image on the left, but I think it may be better to pass through both batteries, in which case the image on the right might be more appropriate.



Then I am not really sure where to clip my battery tender. Maybe pos on #2 and neg on #1?
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Old 09-04-2020, 08:29 PM   #5
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I don't really understand your diagrams. Does this help:

https://caravanchronicles.com/guides...s-in-parallel/

In the above site, the "To Electrical Equipment and Charging Unit" from the positive terminal of battery A goes to the positive cable from your vehicle charging system and to the positive terminal of your "fuse block". The ground of the fuse block goes to the chassis as does the negative terminal from battery A.
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Old 09-05-2020, 06:43 AM   #6
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Put your battery tender anywhere. It is only a trickle charge which can do it's job with small gauge wiring and it can feed the system from anywhere.

As for cable size between batteries it's most important if you have an inverter. They draw big power and you need very large cable between batteries and from battery to inverter to feed them.

Personally, since your batteries are side by side I would change that 8 gauge out to 2 or at least 4 myself. 10 minute job.
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Old 09-05-2020, 09:25 AM   #7
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Great, thanks for the advice!

I can see how 2awg cables will be better. I was going to do that first then thought the flexibility of 8awg might help with placement and movement later. (I don't have any 4awg supplies and am broke with the upgrades I am doing).

Thanks for the additional link. I think the diagram below will be the best setup.

I am rushing to get everything done in a week and can't seem to focus through these issues (and I am screwing up a lot of stuff because of time). Plus my son is out of daycare while I am working, and I am lucky to get 1-2 hrs a day on this. So thanks for the clarity.
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Old 09-05-2020, 02:51 PM   #8
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I agree about the inverter suggestion. I have 4/0 copper going from house battery to house battery and then it runs to a high amp stud. This is where my 2000 w inverter connects. Hopefully you also have some kind of a separator relay between the engine battery/alternator circuit and your house battery system. It might be a saver down the road. This is basically how mine is wired except I have two 4-D batteries.
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Old 09-05-2020, 04:07 PM   #9
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Thanks a bunch for the image. I am hoping to add solar later this year and the high amp stud is a good option at that point. I have a relay between the main and house battery, so I think I am good on that part.
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Old 09-06-2020, 09:00 AM   #10
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In general this would be the difference between one battery and two batteries in parallel.



You move the ground connection to the last battery to improve the balance of the system. I show these going to a bus bar, but you could also consider the battery terminal a bus bar. That is not the approach I would take, but it is commonly done. A power post is also a very acceptable solution, the general rule of thumb is 4 connection to one post. The frame connection can be considered just that, a connection to the frame. It does not have to be the negative bus bar, instead it is just a path back to the battery.

The wire size for the frame connection needs to cover all the devices that are connected to the body for their path to ground. The wire from the bus bar to the battery needs to cover the current for all devices connect to the bus bar. I would generally use the same size wire for that for the battery to battery connection, although in theory the current load is shared across batteries. I also generally fuse the battery bank to bus bar connection, but that starts to go deeper than your original question.

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