Thread: Old Redarc dual battery isolator is really hot and won't turn off...any suggestions?

Hi Angus and the first thing you need to do is measure the voltage of both batteries.


You need to see if the battery voltage has actually dropped below the Cut-Out level of the isolator.


The Cut-Out voltage is somewhere between 12.5v and 12.7v. But Yellow top batteries can hold the voltage higher than that for quite a few hours.


If the isolator is still on, the voltages should be very similar. If there is a difference, say half a volt or more, then the isolator is stuffed ( see below ).


Also, if it is your isolator, they are renown for contacts sticking, but you can clean them up and all is well again.


So don’t rush to replace it just yet.

Originally Posted by drivesafe

Hi Angus and the first thing you need to do is measure the voltage of both batteries.


You need to see if the battery voltage has actually dropped below the Cut-Out level of the isolator.


The Cut-Out voltage is somewhere between 12.5v and 12.7v. But Yellow top batteries can hold the voltage higher than that for quite a few hours.


If the isolator is still on, the voltages should be very similar. If there is a difference, say half a volt or more, then the isolator is stuffed ( see below ).


Also, if it is your isolator, they are renown for contacts sticking, but you can clean them up and all is well again.


So don’t rush to replace it just yet.

Ahh okay thanks for that quick info, I just also spoke to someone about buying a new version of this little isolator and they mentioned that possibly these little isolators are mainly for use with lead acid batteries...is this true? He wasn't sure so he was checking but it got me thinking do I maybe need a slightly different system to maintain two Optima gel batteries as opposed to my old batteries that were lead acid that were in the car when this little basic isolator got installed?

Or is it possible that the Yellow Tops are just great at holding a higher voltage and because of that the isolator will never cut out unless I'm running fridges and other things off it with the car off while camping?

Hi again Angus and the Optimas are AGMs and not gels, and if working properly, your isolator is fine.


Gels would actually hold their voltage at a much lower level.


If it is the Optimas holding the voltage high, your isolator uses a fair bit of energy to keep itself on and this will draw the batteries down to the Cut-Out level eventually.


BUT, you need to get some voltage readings or all of this is just guesswork!

We probably have the same isolator. Small flat red opaque area on the small protrusion that lights up to indicate connection(ie, it's on).

Turn on lights and fan and whatever else to drain main battery a little.
Cutout is at just below 12.7v. That is, if you have 12.7v at the main battery, it stays on. Once it(self) senses less than 12.7 it then cuts out and you'll hear the clunk sound of the solenoid disconnecting.
Now main battery is isolated from aux battery.

Mine can take a few hours after stopping to switch off too.
Sometimes after a few hours, where it's still on, I open the door to the D1 and just the interior lights are enough to drop voltage on the main battery to just under the 12.7v cutout and it switches off.

Normal operation.

I've never checked the isolator for heat while it's connected tho. Will do if I can remember too.
What location is the isolator.
I fitted mine to the small area between battery-radiator-aircon pipes, so it gets a lot of heat there anyhow.
Are you checking it a long while after switching engine off?
How hot are other bits in the engine bay near the isolator. eg. expansion tank could still be quite hot after a few hours .. etc, etc.

Young Angus, listen to Drivesafe. He sells dual battery systems for a living, and he's telling you your system will probably be OK. That sounds like good, honest advice to me. Something you don't always get from retailers.

Originally Posted by AK83

I've never checked the isolator for heat while it's connected tho. Will do if I can remember too.
What location is the isolator.

Hi AK, it is normal for relays and solenoids to become VERY hot while on, even when there is no load passing through them.

Originally Posted by drivesafe

Hi again Angus and the Optimas are AGMs and not gels, and if working properly, your isolator is fine.


Gels would actually hold their much lower voltage.


If it is the Optimas holding the voltage high, your isolator uses a few bit of energy to keep itself on and this will draw the batteries down to the Cut-Out level eventually.


BUT, you need to get some voltage readings or all of this is just guesswork!

Thanks so much everyone for the advice, and thanks for clearing the battery type up for me...I was just regurgitating what the guy at ARB told me but now that I think about it I think I knew the Optimas weren't gel batteries...oops

So I went down and the voltage on both batteries was pretty much spot on 12.8 the first time I measured...then a little later I measured both and they were both reading about 12.74, both readings while car was off and hadn't been started in between.

Also the retailer from ARB just earned some points because he went away after I said I might need to buy a new system and he did some research for me, and came back and actually told me that my system was probably fine and that the red light is meant to stay on and it will get a little hot and that it's all probably working properly so don't buy something new...how about that hey ARB in Brighton that was, apparently an alright bunch of blokes!

So thank you very much Mr. Drivesafe and thanks very much everyone else too, great advice and I now understand a little more about my car Bunch of legends all of you!

Thanks Drivesafe for being so honest with this guy.

I know your isolators are superior in a lot of ways, but Redarc are not rubbish as I can tell you appreciate.

It is indeed refreshing to read expert advice on a 'problem' with a maybe competitor's product that doesn't bag the crap out of it!

cheers,DL