Part time Dual Battery - Portable & Redarc Query

Submitted: Sunday, Feb 04, 2007 at 14:36
ThreadID: 41963 Views:2900 Replies:7 FollowUps:9
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Hey Guys n Gals,

Have read all the Dual Battery threads, have sussed out what I want - now down to one not so minor detail.

I have a Jeep Grand Cherokke WG (2000) with no room under the bonnet for a second battery for fridge etc. No biggie - will knock up a plywood box to fit the 120 A/h AGM - am aware of all the cable requirements etc.

Tricky part is this, my current cig lighters (front & in rear cargo) operate when ignition is off - suggests straight to main battery. Which is good for charging mobile phones etc. Now if I were to have a Redarc installed for the second battery, and bearing in mind that the second battery wil only be a part time thing, if the second battery is removed, I assume that the Redarc will look for the starting battery volts when switching off the ignition and then switch over to a battery that is not there?

Am sure that this is the case, so how best am I to wire things up, so that I can have the ease of the use of a Redarc (or similar) when I need it, and also have things back as they were without the second battery. I prefer not to use a manual switch as the primary source of control - maybe manually switch over to a solenoid one day and then switch back a few weeks later when solenoid not wanted anymore, type of thing.

May not have done a flash job of explaining, but essentially the fridge wont always be in the car - want the Explorer DC75 at 850x520x520 and couple that with the second battery in the rear - would rather have the room than carry around all the time - even just the second battery is not a small thing hence why I dont want it permanent - I work away so would rather chuck my gear in the rear cargo as opposed to have stuff on rear seat.

Any thoughts and help is greatly appreciated.

Cheers All

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Reply By: Member - Blue (VIC) - Sunday, Feb 04, 2007 at 14:42

Sunday, Feb 04, 2007 at 14:42
The Redarc will still function without the second battery in the loop. I have my second batt in the tub and often remove it using a 50amp anderson plug as the joiner. No issues so far running around for weeks on end with out the second batt in... Hope that's what you were getting at, just got in from a weekend away and fatigue is taking a steady hold...
AnswerID: 219672

Follow Up By: amcjavelinsst - Sunday, Feb 04, 2007 at 14:48

Sunday, Feb 04, 2007 at 14:48
Cheers for that BLue,

Yeah, thats what I am thinking, the Redarc will still function, but that is just it - it will switch to something that is not there - so then the car is not getting power to the cig lighters (say mobile charging or even fridge in for a day trip no need for second battery)

Cheer for your reply Blue, it is appreciated

FollowupID: 480235

Follow Up By: Member - Blue (VIC) - Sunday, Feb 04, 2007 at 14:55

Sunday, Feb 04, 2007 at 14:55
Graeme, I think the redarc only switches if it can sense a secondary "load", I'm happy to stand corrected as I'm the proverbial electronic idiot, I don't recall the trademark "click" when the second battery is removed. I have had no probs with phone chargers and the like while the second batt is removed.

FollowupID: 480237

Follow Up By: amcjavelinsst - Sunday, Feb 04, 2007 at 16:04

Sunday, Feb 04, 2007 at 16:04
Cheers Blue,

Thats helps me to know that all works fine even without the second battery in place.

Thanks for that.

Even though I do think (not know) that the Recarc goes off the starting battery volts, not the secondary battery - there is a mention below.

I appreciate your input mate.

FollowupID: 480251

Follow Up By: Jimbo - Sunday, Feb 04, 2007 at 17:19

Sunday, Feb 04, 2007 at 17:19
I've got the same set up as Blue, in fact installed by the same bloke.

I second all that Blue has had to say.

FollowupID: 480261

Reply By: Tim HJ61 (WA) - Sunday, Feb 04, 2007 at 14:56

Sunday, Feb 04, 2007 at 14:56

The Redarc voltage sense is on the main battery side of the unit, not the downside. When the up/feed/main line is high enough to kick it in, it will kick in and connect it's solenoid. It doesn't care what is downstream.

Just make sure any wires are either removed from the Redarc or protected as they WILL be live if the little red LED in the voltage sense unit on the side of the Redarc is glowing.

AnswerID: 219674

Follow Up By: amcjavelinsst - Sunday, Feb 04, 2007 at 16:12

Sunday, Feb 04, 2007 at 16:12
G'day Tim,

Yeah I gather you are talking about when the engine is running and the main battery gets it's boost from the alternator and then the solenoids joins with the second battery to also charge that, in that I think you are correct in what you say. And yes, it will be live at the connection - having a lead to the rear cargo with a 50A Anderson will look after any potential live wire probs.

My point is mainly when the engine is switched off, the Redarc will look at the start battery state, say ok engine off and switch over to second battery which is not there - maybe it is not a problem, just in my thinking it may be if I were to have a fridge in for a day trip say a picnic, and it switches to draw power from something that is not there.

Your input is welcomed, thank you.

FollowupID: 480252

Follow Up By: Gerhardp1 - Sunday, Feb 04, 2007 at 22:56

Sunday, Feb 04, 2007 at 22:56
I have a redarc which charges the trailer battery when it's connected.

When the trailer battery is not connected, the redarc still switches on and off according to the starting/main battery voltage. When it's "on", there would be voltage at the anderson plug at the rear of the vehicle.

I have cig sockets which are not wired through the ignition, and they are live no matter what the redarc is doing.

When the engine is switched off, the redarc may stay switched in for a little while after alternator votage stops, but will not switch back in until a short while after the engine is restarted and the voltage is up to the required level again.
FollowupID: 480340

Reply By: Tim HJ61 (WA) - Sunday, Feb 04, 2007 at 15:00

Sunday, Feb 04, 2007 at 15:00

If there is potential current draw when the ignition is off, might be an idea to put a battery cutout device, not unlike the Redarc, in the line to ensure these devices don't drain your battery too low.

Dick Smith and Jaycar, and Oakley Electronics, all have suitable kits if you feel like spending time with a soldering iron.

AnswerID: 219676

Follow Up By: amcjavelinsst - Sunday, Feb 04, 2007 at 16:15

Sunday, Feb 04, 2007 at 16:15

Yep, am aware of that if the way all gets wired up goes that way, but should not prove to be an issue as am trying to avoid any load on the main battery aside from minor ones that will be fine to do.


FollowupID: 480253

Reply By: Leroy - Sunday, Feb 04, 2007 at 15:01

Sunday, Feb 04, 2007 at 15:01
Where are you going to mount the redarc? Not to the cig lighter in the back I hope. I would mount it under the bonnet and run decent cables to the rear cargo area where you will have your battery.

AnswerID: 219677

Follow Up By: amcjavelinsst - Sunday, Feb 04, 2007 at 16:19

Sunday, Feb 04, 2007 at 16:19
Heya Leroy,

No, my intent is do just that and have the Redarc near the main battery - will even run the earth/negative to the Anderson plug properly as opposed to earthing on a ground point.

As a point aside, with adequately sized cables, there should not really be anything wrong with having the Redarc further away from the main battery - so long as the sizing does not allow voltage drop.

Thanks for your input

FollowupID: 480254

Follow Up By: Leroy - Sunday, Feb 04, 2007 at 16:41

Sunday, Feb 04, 2007 at 16:41
No probs just thought I'd ask the question. That's exactly what I did when i put a batt in the back of my Rodeo.


FollowupID: 480259

Reply By: Member - andrew B (Kununurra) - Sunday, Feb 04, 2007 at 17:17

Sunday, Feb 04, 2007 at 17:17
Gday Graeme

as a cheaper option, a simple solenoid under the bonnet hooked into the ignition will work well. (does for me any way). Its pretty easy to hook up, there is an ignition wire on the wiper motor you can splice into for this. Another option may be the waeco ciggie lighter thing (?). It has a switch to go from always live to ignition on only, is relatively cheap and fairly neat.

Cheers Andrew
AnswerID: 219702

Reply By: SCUBADOO - Sunday, Feb 04, 2007 at 18:28

Sunday, Feb 04, 2007 at 18:28

In my campervan, I have my "second battery" (Gel 150AH), 230V inverter, smart battery charger, solar charger , fuseblock, extra DC outlets, battery monitor and Voltage Controlled Relay (similar to your Redarc) all in the same ventilated padded "plywood box" with carry handles. Doubles as an extra seat.

The entire setup can be disconnected, unlatched and removed when not required.
It sits in my garage connected to 230VAC, charging ready for my next trip.

AnswerID: 219716

Reply By: Muzzgit [WA] - Monday, Feb 05, 2007 at 00:10

Monday, Feb 05, 2007 at 00:10
Graeme, yes what you are asking is true. As long as the connections are there then you will have power to the back of the car until you stop and the solenoid drops out.

I had a drama with my aux battery a few weeks back ( it died a messy death ) and the Redarc was continually clicking in,out,in,out,in,out,in,out as we drove along. I simply moved the connection on the redarc so everything was connected to the starting battery side. I took the terminal off the aux battery and taped it up with heaps of insulation tape so I had power to the camper and the fridge until we got to a town to get a new battery.

You just have to remember you have no flat battery protection.

AnswerID: 219794

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