Best way to hook up auxiliary batteries.

[Scout1]

I acquired two AGM group 27 12v batteries. I'd like to use them as auxiliary/back-ups & keep them in my pickup bed. My plan was to wire them to a plug that matches the the female plug on my tow vehicle to plug the camper into when I wanted to use these batteries. Is this a reasonable way to do this, or should I wire it to my Airstream another way?

[Mollysdad]

Did you plan to wire them in parallel to the regular batteries?

[PKI]

Do not forget to include monitoring/switching/fusing/circuit protection in your cabling as well as a method to secure the aux battery box. Pat

[Scout1]

Thanks for the feedback, but maybe my question was unclear. What I'm wondering is will hooking up my auxiliary battery as shown in the attached picture be satisfactory, or is there a more efficient (electronically) way of doing it. Such as wiring it parallel with my house batteries. I'd like to do it the way I have pictured, just for simplicity's' sake. It is wired so it powers the trailer just like the tow vehicle would it was plugged into it.

[ROBERT CROSS]

That is doable, but not as efficient as 4awg wired directly to the coach batteries. You could use a high amp quick connect.

Bob
🇺🇸

[Scout1]

Robert, I have two 6v lifeline AGM batteries in the trailer mated with 470 watts of solar on the trailer roof. The auxiliary batteries will actually be two 12v AGM batteries. Your saying with this set-up it would be best to attach this 12v bank (using the plugs you referenced) in parallel with the 6v bank? That makes sense to me, but just want to be sure. I have searched, but not been able to find any reference to this type of set-up. Thanks for the help?

[batman]

I agree 4 awg welding cable is much better than the 10 ga wire that is used in the trailer to TV umbilical.

4 awg welding cable and Anderson connectors like the SB-50 or SB-175 would work better. Anderson connectors are great connectors for battery applications, wenches ,etc.

http://www.amazon.com/EWCS-Approved-...g%2C220&sr=1-3
It is not necessary to go marine grade, I just like overkill.

https://www.andersonpower.com/shop/s...k-keyless.html
SB-50 (50 AMP) would probably work fine, However SB-175 IS (175 AMP).

Best of luck with your project.

-Dennis

[PKI]

Does this all depend upon the specific use profile?

For a few amps, no or rather minimal problems. For the situation where the trailer bank is low, those batteries will pull power - possibly more power than the fusing on the umbilical will support.

Then, there is the charging profile, the battery state monitoring, and the lack of regulation associated with the proposed method.

In an emergency and with managed control, maybe. However, as a standard approach to normal use, this seems like a simple solution at first glance that gets more complicated as you consider the possibilities.

Backup battery bank - suggest you add a disconnect for the primary and also add a high amp plug connector. Then unplug the main when at minimum capacity and plug in the secondary. The disconnect eliminates the load for safe connection and the separate banks eliminate battery state conflict. Using 6 and 12 volt batteries in a combined bank may work - 12 volt is 12 volt, but the interaction between cells is normally considered at a minimum poor practice.

Not an expert - suggest you spend some time consulting with one. I'll be interested to hear that information. Your question is an interesting one as the proposal is simple to implement. Just not convinced it is the right way to proceed. Maybe the solution is as simple as disconnecting the battery cables on the main bank while you use the backup. Pat

[DLDINS]

Originally Posted by Scout1

Thanks for the feedback, but maybe my question was unclear. What I'm wondering is will hooking up my auxiliary battery as shown in the attached picture be satisfactory, or is there a more efficient (electronically) way of doing it. Such as wiring it parallel with my house batteries. I'd like to do it the way I have pictured, just for simplicity's' sake. It is wired so it powers the trailer just like the tow vehicle would it was plugged into it.

Scout,

That set-up would only work if you are counting on a couple of amps (maybe up to 5A) of current coming out of the aux battery. What that set-up would do would be to put the batteries in paralllel, but through a rather high amount of wire resistance. That resistance imbalance will kill any help out of the AUX battery at high current. The same issue is present when charging from solar, most of the current would go into the trailer battery until it is charged and then (and only then) would the external battery get any charging current.

A high current example: two 12V batteries wired in parallel properly (all current paths are matched. At 100A they both see 50A.

Now add an inbalance of 625 microohms (30" of #4 wire): trailer battery then delivers 83A and the 2nd battery delivers 17A! It does not take much of an imbalance in the wiring to totally foul up the matching of parallel connections at high current.

[Scout1]

Thanks for the help. I'll disconnect the house batteries before I plug in the auxiliary. Seems like the best option.