Excess Solar Power.

[Pete and Tracey]

Hi there everyone,

My question is a technical one. We have a van with 4 135w solar panels and 3 120ah batteries. By mid morning to lunchtime the batteries are fully charged and want to use the extra power going to waste to charge the deep cycle second battery in the vehicle when we are free camping. The Engel runs in the car and it would be nice to charge the car so we can leave the Engel on.

My question is how do I do this? Do I just run additional cable and second anderson plug to the second battery? I have 13 v on the caravan side of the Andersen plug during the daylight. No voltage on the car side of the Anderson plug, there is a relay isolating the battery from the plug on the car and is activated with ignition on.

Any help and advice on this would be appreciated.

Thank you.

[RussnSue]

G'day Peter and Tracey

It is most likely that there is a battery isolator between the two batteries in your vehicle. However, the Anderson plug on the car should be connected to one or the other battery and therefore be showing 12 Volts-ish when measured. If not, it may be that the Anderson plug has been wired via the ignition switch.

In my set-up, I have all auxiliary appliances (GPS, Laptop outlet, car fridge, UHF radio) running from a direct connection to the auxiliary battery. The Anderson plug that I have mounted on the rear bumper is also connected to this battery by a very heavy cable. When the vehicle is not running, all of these devices run off the auxilliary battery and are isolated from the cranking battery - so that we always have full power in the cranking battery to start the vehicle.

I ran a separate, large diameter, cable from the batteries in the van (via a Shunt) to an Anderson plug on the front of the drawbar. The one that Kedron fitted when they built the van was too small in conductor size and had too much volt-drop. When we are travelling I always have the van and car connected by these two Anderson plugs. This way, we are charging all batteries by both Sun and vehicle when driving, or just the van batteries and auxiliary battery are charging when the engine is switched off. This way, all batteries are charging all the time whenever we have Sun, not just when the van batteries have finished charging and using a surplus of power to charge the auxiliary battery. I look at it from the point of view that I have a larger battery bank - it's just that one battery happens to be located in the vehicle.

I have a Plasmatronics PL-60 charger and strictly speaking, I should add the AMP Hour capacity of the auxiliary battery to the capacity of the van batteries so that the PL-60 knows what it is meant to be charging. That is, the 480 Amp Hours of van batteries plus the 65 Amp Hour auxiliary battery gives near enough 550 Amp Hours in total. I didn't bother to do this, though, as the figure would then be incorrect when the van and car were disconnected from each other. So, I have settled for having the total set in the PL-60 being 480 AH.

The van batteries are as good as new after three years and the auxiliary battery, which was two years old before we even got the van, is also testing reasonably well for a five year old battery. There are those whom will tell you that the auxiliary battery should be of the same type (ie GSM or Gel or flooded cell) as the van batteries, or that the batteries should all be the same capacity (ie, 120 AH) or that they should all be the same age, or made by the same manufacturer etc, etc, but this is nonsense. I won't go into the science, but lead-acid cells are pretty forgiving when placed together in a parallel connected set-up such as what you propose to do.

In summary, the key things to have are heavy cabling to avoid volt-drop, direct connection through the vehicle to the second battery (fused, of course) and direct connection (also fused) to the van batteries. There will be differences of opinion as to how the auxiliary battery and cranking battery should be connected to each other (some say that they should be always connected until one or the other drop below a certain voltage, others say that the auxiliary battery should be connected when cranking to assist the cranking battery - but should then disconnect until the cranking battery has regained a certain voltage, others like me leave the two separate until the vehicle has started and then join the two together) - it's entirely up to you. With a van full of batteries and four solar panels, I am never concerned that I won't be able to get my vehicle started.

Cheers

Russ

[Rod and Mavis]

Greetings Pete & Tracy.

Our set up is simply to have the Anderson charge lead plugged to the car via a 5 meter extension lead and thus putting the car into the battery bank of the van.

We did specify 25sq mm wiring and a 135a plug to allow full current flow and minimal voltage losses over the distance.

Our car and the van have the same heavy wiring.

We have been parked up for the last almost two weeks and the car fridge has been running happily with the car plugged in and not started

Beware of the small wiring usually fitted to van and car. We have proven that our original ex factory set up was only allowing 3-4 amps to pass through,totally unsatisfactory. This is a joke when you are trying to put power into 3 big AGM's from the vehicle while travelling,or back to the vehicle when parked up.

Regards and safe travels.