Battery wire up

Can anyone help with a question in regards as to whether or not I can set up an in car auxiliary battery (100amp) wired into already installed camper wiring and battery (80amp). All this to run thru a redarc bc112 being charged off the starting battery

I want to be able to have the camper and aux battery hooked up together.
The aux battery is thru the firewall and the camper wiring is under the vehicle using Anderson connectors.
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Reply By: Allan B (Member, SunCoast) - Friday, Aug 24, 2012 at 22:42

Friday, Aug 24, 2012 at 22:42
Hi Capnbazza,

Firstly, I don't think there is a Redarc bc112, possibly you mean a SBI-12 which is the solenoid battery isolator product. Alternatively, you may mean the Redarc BCDC-1220 which is a dc-dc charger. Either product will serve this application.

There is no major problem having an auxiliary battery in the engine bay connected to a second auxiliary battery in the camper. However in order to satisfactorily charge the camper battery you will need adequate sized cable connecting them. It is also essential to have a fuse at EACH end of the positive connecting cable as failure to do this could cause fire in the event of a short anywhere along that cable.

In saying the battery sizes of "100amp" & "80amp" I presume you mean 100ah and 80ah (ah = ampere hours which is the battery capacity). This is OK, the batteries do not need to be the same capacity. However they should be of the same chemistry, i.e. both deep cycle or both Absorbed Glass Mat for example.

Cheers
Allan

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AnswerID: 493549

Reply By: capnbazza - Saturday, Aug 25, 2012 at 15:48

Saturday, Aug 25, 2012 at 15:48
Thanks Allan, yes I did have the wrong item mentioned, it is the latter. The Aux battery will be inside the vehicle in the rear and the camper battery is as mentioned in the camper. Both batteries will be the same although the vehicle battery will be a fully sealed deep cycle 100amp and the camper battery will be a marine deep cycle 80amp.
As I asked before, I want to be able to charge both while driving, that means can I run both these batteries from the one contact point, joined together at the Red arc?
112
Cheers

Capnbazza
AnswerID: 493593

Follow Up By: Allan B (Member, SunCoast) - Saturday, Aug 25, 2012 at 16:10

Saturday, Aug 25, 2012 at 16:10
Yes Cap, you can connect both batteries together and charge them simultaneously from the alternator. The Redarc BCDC-1220 would be best positioned close to and just before the vehicle auxiliary battery and both aux batteries charged from its output.

You should note though that the BCDC-1220 has a maximum output of 20 amps which will be shared between the two batteries. There is also the problem of voltage drop in the wiring supplying the camper battery.

A more ideal solution is to employ two Redarc BCDC-1220's, one for each battery and positioned close to each battery with both BCDC-1220's supplied from the alternator. That arrangement overcomes volt drop in the wiring and will look after your batteries much better. The BCDC-1220 will operate with 20 amp output even though the input may be as low as 9 volts. This is not an excuse to use grossly undersized cables however as the losses with place a higher load on your alternator.

Cheers
Allan

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FollowupID: 769183

Follow Up By: capnbazza - Saturday, Aug 25, 2012 at 16:24

Saturday, Aug 25, 2012 at 16:24
You mentioned that the batteries can both be connected from the alternator via a single SB1-12 (got it right this time). Does this mean that I don't connect the Red Arc to the main battery, which in turn sends charge to both battteries. I will have 6BS cable to the Aux battery but the wiring to the camper is set up with plain auto 6mm. THANKS (not) to a well known off road company.

Cheers

Capnbazza
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FollowupID: 769185

Follow Up By: Allan B (Member, SunCoast) - Saturday, Aug 25, 2012 at 17:13

Saturday, Aug 25, 2012 at 17:13
Cap, I realise now that you are using a Redarc SBI-12 NOT a BCDC-1220. In that case ignore everything I said in the last response at 16:10. This is a different scenario altogether!

The SBI-12 is a voltage sensitive solenoid which joins the aux battery(s) to the cranking battery (and therefore to the alternator) for charging but disconnects them when the engine stops to prevent current drain from the cranking battery in order to preserve its charge to do the intended job of starting the engine. It does not boost the voltage to charge the aux batteries.

You can still connect both aux batteries in parallel to the outlet of the SBI-12 but this arrangement will not do a very good job of charging the camper battery due to the long cable run. It will certainly require a good-sized cable all the way from the SBI-12 to the camper battery and the existing 6mm cable is woefully inadequate. 6 B&S cable all the way to the camper battery would be more appropriate.

Cheers
Allan

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Follow Up By: capnbazza - Sunday, Aug 26, 2012 at 15:27

Sunday, Aug 26, 2012 at 15:27
Thanks Allan, looks like I need to upgrade the cable on the vehicle. It was supposed to be 6bs cable when the dealer had it installed thru a 4x4 company. It wasn't unil later that I found out only 6mm cable was used. Normal story from both, neither accepted fault with installing the wrong cable...lesson learnt...do it your bloody self !!!

Cheers

Capn Bazza
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FollowupID: 769251

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