Thread: Dual battery with solar panel.

Hi Lewy, and first off, if you have the solar panel mounted to the vehicle and use it while driving, during daylight hours, both the alternator and the solar panel will be charge will charging your batteries.

NOTE this is common practice with motor homes and you will not damage either your alternator or solar regulator, when you set up this way.


If you are at a camp site, and the solar panel is connected ( via a solar regulator ) to the auxiliary battery, then the auxiliary battery will charge, but unless the isolator has the reverse charging function, and most do NOT, you will not be charging the cranking battery.

If your isolator does have reverse charging, then both batteries will be charged from the solar panel.

Originally Posted by drivesafe

Hi Lewy, and first off, if you have the solar panel mounted to the vehicle and use it while driving, during daylight hours, both the alternator and the solar panel will be charge will charging your batteries.

NOTE this is common practice with motor homes and you will not damage either your alternator or solar regulator, when you set up this way.


If you are at a camp site, and the solar panel is connected ( via a solar regulator ) to the auxiliary battery, then the auxiliary battery will charge, but unless the isolator has the reverse charging function, and most do NOT, you will not be charging the cranking battery.

If your isolator does have reverse charging, then both batteries will be charged from the solar panel.

Hi Tim - can we assume all of your dual battery systems/isolators have reverse charging ability?

Originally Posted by gavinwibrow

Hi Tim - can we assume all of your dual battery systems/isolators have reverse charging ability?

Hi Gavin, the older Isolators would remain on for up to around 30 days before the battery voltage reached 12.0v and this would allow the use of a solar panel connected to either battery to keep both batteries charged.

But once the older isolators shut down, you either made sure the solar panel was connected to the main battery, or you stated your motor to link the batteries back together again.

The DT90 from its inception, had a maximum Shut-Down time of 72 hours from the last time the motor was running, but they were also the first of my isolators to have Reverse Charging ( automatic turn on ) when a solar panel or battery charger was connected to the auxiliary battery.

Not long after this, all SC80s were also supplied with Release Charging.

All my isolators now have Reverse Charging.

For the OP: if your redarc controller is 'newish', it's dual acting so you would connect the solar regulator to the aux battery, and the redarc will sense that it's at 13.2v and then switch on to also charge the start battery too.
ie. it doesn't matter which battery you connect solar too, it will charge both(eventually).

There are older redarc controllers tho(I have one in my D1) and it only charges one way, where I'd have to connect solar to the main battery to charge both.
In the D2 tho, it's the newer version that is dual acting.

I can't see any difference in their respective markings .. just both marked SBI12.

Originally Posted by AK83

For the OP: if your redarc controller is 'newish', it's dual acting so you would connect the solar regulator to the aux battery, and the redarc will sense that it's at 13.2v and then switch on to also charge the start battery too.
ie. it doesn't matter which battery you connect solar too, it will charge both(eventually).

There are older redarc controllers tho(I have one in my D1) and it only charges one way, where I'd have to connect solar to the main battery to charge both.
In the D2 tho, it's the newer version that is dual acting.

I can't see any difference in their respective markings .. just both marked SBI12.

cheers i am not sure what model it is but i didn't know that they would switch to "reverse" charging.This would explain why i had the feeling that the start battery was working better than usual as the famous D2 parasitic draw would be lost with the use of the solar panel keeping the start battery charged.I mainly was concerned that if i hooked things together i would let the smoke out somewere or burn up the solar controller.

reverse charging or reverse mode is probably an incorrect way to describe it, but anyhow, you understand.

The only way to know if yours is a D type model(the type that 'reverse charges' is via serial number, then searching .. and I reckon there's an easier way.

On the D2, I sometimes have it sitting for ages(and drive the D1). Other times I have the D1 sitting and drive the D2 instead.
While sitting, I have the sitting Disco connected to a solar panel to keep it topped up.

So I found: the D2 I connect the solar(spring clips) to the aux, and eventually after the aux has charged, it clicks on the solenoid and the main then gets it's charge.
It can take a bit of time, and there may be some hysterisis, where the main gets connected, it then drains the aux a bit, aux then dips below cutoff voltage and redarc turns off(and main stops charging).
This can happen both ways too tho, nothing specific to connecting to the aux battery. I think it's that the solar sometimes ponly puts out say 2amps or something.
So this will cycle like that for a bit, but then come good and both charge fine.

On the D1, I did same, but main never connected via the redarc, so I have to connect to main battery so that both get a charge.

This is how I discovered that both types exist. And they look identical(other than age). and too hard to remove it off its mount to read the serial numbers.

But I would 'guess' that if you bought it recently(and in say up to about 5 years ago), it's more likely a D model.

My D1 one came courtesy of brother who got it off marketplace s/h, and the guy already had it for years prior to that... ie. much older.

Hi lewy and if you have easy access to the two studs on your isolator. simply swap the leads over.

In other words, connect the auxiliary battery lead to the main battery stud on your isolator and connect the cranking battery lead to the auxiliary stud on the isolator.

With the leads swapped over, start your motor.

If the isolator turns on, your isolator has the Reverse Charging function.

If it does not turn on then the obvious.

Originally Posted by AK83

reverse charging or reverse mode is probably an incorrect way to describe it

Not sure why you would say that?

Reverse Charging is exactly what goes on.

An isolator with Reverse Charging capability allows the isolator to operate in REVERSE to its primary function.