Second battery not receiving charge from solar panels or alt.

If I understand your wording correctly...you say the solar panels are charging the main battery ok...and obviously you have a multi meter at your disposal so the answer to your question is really quite straight forward for you to test

With the engine off (at least 30 mins)...allows residual charge voltage to drop
1) Read the voltage on the main battery
2) The voltage on the terminal of the isolater (the one that is direct from main battery to the isolator)..these should be the same...ie no voltage drop
3) Read the voltage on the terminal on the other side of the isolator ( the one connected to the aux battery)...at this stage this should be the same volatge as the aux battery
4) Read the voltage on the aux battery...these should be the same

Now

Connect either the solar panels (through its controller of course) to the main battery OR start the vehicle

Within 30secs or so the voltage on both terminals of the isolators should be the same...if so then the isolator is working correctly...(that is the open isolator is now closed and connecting).....the voltage on the aux battery terminals should be close to the same as well...you may have a slight voltage drop...its cable size dependant

From this you have successfully diagnosed the isolator working or not.......if is then I guess you most probably have an aux battery dead

Robyn,

Possibly the isolator has failed, preventing charge getting to the battery so that with continued use, or even non-use but no charge in normal driving, it has over-discharged. With your multimeter you could test for that with the engine running.

With a battery that flat many chargers and regulators won't charge them. Depending on what has happened to the battery previously, it may be unrecoverable.

A battery that low will sulphate pretty quickly if left in that state and that is usually terminal for the battery - at best there will be reduced capacity if the battery ever accepts a charge.

You could try to recover it with a charger that has a flat battery recovery program. They are usually mains powered, but I have seen some solar regulators that say they can do it. Never tested them, though. Someone else may be able to advise on brands - perhaps Ctek?

Good luck with it.

The previous owner might be of limited help, because its what happening now that matters most. The battery could have died due to age or neglect - the charge controller may be at fault too. You need to be sure that there is no load at all on the battery when it is idle - even a small load over sufficient time will of course flatten it. A good auto electrician can quickly assess the components and operation of the setup and tell you the most cost effective way out of it - you will otherwise just be guessing and wasting time in my view.

Robin,

Regardless of anything else, the first thing your sister (or technical assistant) should check, is the voltage at the auxiliary battery, with the engine running.
After one minute or so, the dual battery controller should have activated the auxiliary circuit and a reading of around 14.2 volts should be present.

If this is not the case, the first thing to check is any inline fuse that should be present to protect to circuit from a short circuit situation.
Failing that the isolator is probably the cause of the problem. Should isolators also have a fuse which should also be checked for presence and condition.

As far as the measurement of the auxiliary battery voltage is concerned, 10.4 volts is dead flat and if a reading this low, or lower is being observed, the battery is um, cactus.

Any battery retailer can check the condition of the battery, however, if an AC charger is available, it should be tried to see if the battery will receive and hold a charge.
When being charged, the voltage reading should again be around 14.2 volts and when fully charged, the voltage should be 10.8 volts (fully charged) when the charger is removed.

Hi All, I just wanted to let all of you that posted suggestions and advice that the car was taken to an Auto Elec and the problem was definitely the isolator. They fitted a new Redarc isolator and the battery has come back to life and is once again being charged. Thankyou all for your help.
See you all out there one day.
Robyn