Solar plus alternator?

[DiscoMick]

Hoping someone can help.
I saw a wiring diagram in a magazine for a solar rooftop setup. It featured a wire running to the ignition. The idea was that when the vehicle was started the solar feed was disconnected. When the engine stopped, the solar reconnected.
There was no explanation, but I assume the idea was to avoid cooking the battery by charging it with both the alternator and solar at the same time. The vehicle had a dual battery system. The solar went into an MPTT DC-DC unit and then to the batteries.
So, my question is, is that necessary? Is there really a problem? Could a battery really be damaged?
What do you think?

[drivesafe]

Hi Mick and the diagram shows one of the ( many ) drawback of using a DC/DC device for both alternator and solar power.

In reality, you are far better off using a conventional isolator and a separate solar regulator.

With this setup, you can be charging your batteries from the alternator and the solar panels at the same time while you are driving.

And no you will not cook or damage the batteries by doing so.

What will happen is, if the batteries are low, they will charge faster with both power supplies connected.

Once they reach a near fully charged state, either the solar regulator will go into float mode and not supply any more power to the batteries.

Or the solar will continue to supply a very low current to the batteries ( and to the rest of the vehicle ) and your alternator will not have to supply as much current, as the solar will by supplementing the power.

Using a DC/DC device, you can only source power from one supply at a time. From the alternator while the motor is running and from solar panels when the motor is off.

This is what the relay is for, to disconnect the solar when the motor is running.

[DiscoMick]

Thanks for your reply.
So, in our case, we have one of your units fitted between the start and second AGM batteries. The alternator goes to the starting battery.
If I added a solar panel with regulator on the roof, should I connect it to the Traxide unit or directly to the start battery?
From your comments, can I assume this setup would not over-charge the batteries?

[drivesafe]

Hi again Mick and your solar pos ( + ) direct to the starting battery pos ( + ) and the solar neg ( - ) to the AUXILIARY battery's neg ( - ) terminal.

Do not connect the solar neg ( - ) to the start battery's Neg ( - ) terminal.

Also, again, you will not risk cooking either battery because neither alternator or the solar regulator operate at a voltage that could go anywhere near cooking the battery.

[Homestar]

I've been running a permanently connected solar system in the 101 and now my caravan for a couple of years now. The solar output is never disconnected when the engune is running - if you look at the regulator with the engine running, it shows the batteries as being full and the solar doesn't do anything, so no dramas. I work on the KISS principle. Everything is connected to everything else - car battery, house batteries, solar and auxiliary batteries in a couple of my vehicles. Different batteries, etc - all no problems.

Don't get fooled into buying something you don't need. :)

[Blknight.aus]

and put the regulator as close to the battery you're hooking up to as opposed to the panel if you can.

[DiscoMick]

Hi again Mick and your solar pos ( + ) direct to the starting battery pos ( + ) and the solar neg ( - ) to the AUXILIARY battery's neg ( - ) terminal.

Do not connect the solar neg ( - ) to the start battery's Neg ( - ) terminal.

Also, again, you will not risk cooking either battery because neither alternator or the solar regulator operate at a voltage that could go anywhere near cooking the battery.
Thanks. The second battery is down the back in the drawers and linked to the Traxide by a thick connection with 60 Amp fuses. Can I just earth the solar negative to the chassis and the positive to the same starting battery terminal as the alternator?

[Eevo]

Hi again Mick and your solar pos ( + ) direct to the starting battery pos ( + ) and the solar neg ( - ) to the AUXILIARY battery's neg ( - ) terminal.

Do not connect the solar neg ( - ) to the start battery's Neg ( - ) terminal.




hi drivesafe.
why do you connect the sol -ve to the aux battery -ve and not the starter battery -ve?

[DiscoMick]

hi drivesafe.
why do you connect the sol -ve to the aux battery -ve and not the starter battery -ve?
I'm guessing to reduce the chances of fire from a bad earth or battery failure, but that could be wrong. Both my batteries have their own earth to chassis connections.