Redarc SBI

Hi all. I have a dual battery system in the nav using a Redarc SBI. This system was in the car when I purchased it but I have really known if its working or not. The red light on the unit itself comes on, but does anyone know if there is actually way I can test if the 2nd battery is being charged or if the unit is actually working?

I would highly recommend buying a multimeter.

It's easy to test with a multimeter. Set it to 50V range if you have multiple V ranges on yours (a lot of the new ones are auto-ranging).

If your car battery is sufficiently charged, the Redarc unit will start supplying power. Before you start the car, measure the terminal voltage of the aux battery. Start the car. If the terminal voltage rises (once the Redarc system thinks your starter is ok) everything is fine.

Watch that voltage - it should get up over 14V with the engine @ 1200rpm or so, preferably in the 14.4V-14.7V range (it should be close to what your alternator is putting out). If it's not, your cabling to the rear might be too small and you may be experiencing a voltage drop. Test this by measuring the voltage on your main battery - it should be similar to the aux battery voltage.

Don't forget that the isolator won't (or at least, it shouldn't) switch on until it thinks the starter battery has enough charge.

Yep got a multimeter but just wasnt sure if how i was checking it was right. Doing it as per Tonys post but im only getting around 10.5-11V at the rear battery at idle. Thats with the red light on the SBI on, which im pretty sure means that it is switched on. Was thinking of rewiring it and see how that goes. Not sure on the condition of the battery in the back either, would that have an effect on the reading?

A dying battery may not always accept a full charge so yes it could effect the reading.

You could do a cell test, or a hydrometer test (as well as others) to test the battery and how good it is. You could even do a load test with a light or something and see how long it powers the second battery for. There are a number of different ways to test how good the battery is and any one would be advisable before trying to hunt down problems in the car which may not be there.

Thanks all for your replies, give me somewhere to start.

Wanna test mine too. So, if I understand you. I should be able to disconnect the lead at the 2nd battery and test it, engine running and get 14 or so vlt. Eliminates the battery as a problem, and the wiring to it.

I was about to suggest that John, good call.

Disconnect the rear battery and test those leads - not the battery, but the wires that were attached to it. See what voltage you get there. If you're getting 10.5-11V there, the system is useless. You'll probably find that either the cable is too thin or it's relying on a chassis connection.

Thin wires are the most common cause of voltage drop. They're also dangerous - with less conductor providing a path for the electricity, trying to draw a high current heats the wire up and can heat it up so much it melts or catches fire.

If you remove those wires and don't have any voltage present on them, the Redarc unit isn't working as expected (again, it could be cabling).

Also, test the rear isolated battery - if the battery tests at 10.5V, it's sick and suffering badly every minute it's left like that. I strongly recommend that you find someone with a C-Tek charger and get them to do a recycle charge cycle on it. It will help revive the battery.

Ta mate, my battery and wiring tests ok. I also bought mine 2nd hand and was wondering too.
Cheers.

So if I were to go ahead and rewire it, what size cable for both earth and power would you recommend using? SBI is under bonnet, 2nd battery is in tray.

To be the safest, get 8 sq mm conductor cable. You can use 6 sq mm - that's what I'm using. In my case, though, I'm rarely drawing more than 20A down the cable, so I can get away with 6 sq mm (which is about 60A cable).

The heavier the cable the less voltage drop you experience, and it's critical to keep that to an absolute minimum.

Awesome, thanks for your help. Ill have a bit of a play this weekend and see what I come up with.

I installed a Super Crap Turbo Timer on my 3 lt Navara and the side benefit is that it shows the voltage going into #2 battery. Only $70.00. Cheap insurance too.

Just an update. Had a bit of a play this arvo, tested the leads while connected to the second battery and was getting around 10.6V. Removed the leads from the battery and tested again getting up around 13V, so im going with a stuffed second battery. Thanks again for your help.

I'd agree with that. Are you getting an AGM?

Not sure Tony, havent really had a look at a replacement yet. Probably not as I dont really use it alot, only there to run the odd light off and small things like that. No fridges or anything at this stage.

I said the something similar about my second battery, now I run everything off it CB's DVD's, GPS tablet and it's 19v power supply, aux power ports, usb power ports, rear aux power, reversing camera, and a battery meter all powered permanently. Everything electrical I've added to the car now runs off the second battery, not everyone's ideal way about it but I do remember saying I'd hardly use the second battery