Wiring solar panel on car

Wire to the aux, that is where to loads should be. The starter battery should not have a requirement to be charged by solar. In fact the aux should be charged by the alternator through the VSR.

Have a look at the Cetek 250. This should satisfy your needs.

Rod, I did ask the guy why he wouldn't connect to the aux and it was 'just in case - better to ensure the starter has full charge'. And the aux will still get charged. Seemed logical to me, but I am not experienced in 12V setups.

Tlax
Whilst either method of wiring will achieve the results it is more usual for the solar charger to be wired to charge the auxiliary battery, and should you be using a DC to DC charging method then it will charge the auxiliary battery.

Should your car be fitted with a 'smart' alternator, or if you are using a Lithium battery for the auxiliary, then you will need a DC to DC charging system to make the system operate to the maximum potential.

Hope this helps.
Athol

Just to complicate it even further, if you really want to charge the main some VSR's are dual sense, ie solar panel connected to aux will also charge the starter battery.

Would there be any issue charging the starter battery by the alternator and solar panel at the same time?

If you have a DC-DC charger separating the batteries then connect a small charger (such as the solar panel) to the cranking battery, the DC-DC will suck the cranking battery dry because the small charge triggers the DC-DC charger to continue working.
Try it some time!
This guy alterted me to it - he demonstrated it with a Redarc. I've made it happen with a Projecta and an Enerdrive.
https://youtu.be/rDXixCzg6iw

In any case, should always connect to aux battery because the charge current that continues to top up the cranking battery at a couple of amps is not going to the aux that needs it.

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Tlax,

Cars are designed to have the alternator look after charging the starter battery and, properly maintained, it will do that job well. There should be no need to provide the starter battery with additional charge from a solar panel provided that you do not have 'auxiliary' loads connected to it, and you should not do that.

If you do not connect the solar panel directly to the auxiliary battery (via a controller of course) then the auxiliary battery will only receive its charge from the alternator when the engine is running. The solar panel connected to the starter battery will only be directing its efforts to the starter battery which will probably already be fully charged from the alternator as the car maker designed.

There are cute ways to configure these charging circuits but the conventional way I have described above is all that is really required for a reliable system. Just leave your starter battery and alternator as originally built, provide an isolator (or dc-dc charger) to the auxiliary battery and connect the solar panel via regulator to the auxiliary battery. If you have not already purchased the isolator and solar 'regulator' then there are dc-dc chargers with provision for solar input which carry out all functions in the one device.

It is easy to over complicate matters, and many answers is to get it form "pretty good" to "pretty damn good"
Theoretically if your starter is healthy then the charge will simply go through to the Aux. I can see the logic of your installer's thinking. And, at the end of the day, will not make that much difference.
Personally I would (have) connect it straight to the Aux. but no big deal IMO

As a simple and cost effective alternative ,in my vehicle with solar and dual batteries i replaced the original controller on the solar panel with a powertech mp 3700 dual battery solar controller.

This allows the power from the solar panel to connect to the powertech controller which has TWO power outlets,you connect one outlet to the starter battery (bypassing the voltage sensitive relay or similar ) and the second outlet to the second battery .

The ratio of charge supplied to each battery is adjustable . EG 10% to starter and 90% to second battery or other ratio as required.

In the above example above, 10% and 90% when either one of the batteries reaches full charge 100 %, all of solar charge goes to the other battery ( overriding the preset ratios as needed ) and both batteries are fully charged..

No need for a dc dc charger in many vehicles..

Cost well less than $100.

Allan in the second paragraph of my post i spoke of the vsr or similar ,i did not suggest to remove it but instead to simply run a wire from the controller to the starter battery to top it up when ignition is switched off , sometimes difficult to describe things in text alone.

There have been many times I have seen the start battery discharged accidentally, glove box left open for a couple of days or accessories turned on to power up sockets to charge phones and heater fan left on low speed, many things can do it.

Have a back up plan, set of jumper leads are a forgotten piece of gear these days, only the old fellas carry them these days.

Set up one panel that can be connected to the start battery if required.

My back up is a 6 inch shifter and screw driver, if the start battery fails I will just swap it out with one of my accessory batteries (AGM)

As Allan hinted towards, leave the original system alone and keep your accessory system as simple as possible, just have a back up plan for your particular set up sorted.

If you use an isolator for your second battery then you'll just be wasting solar power.
If you have a DC-DC charger, then it can actually flatten the cranking battery.

This video explains it well:

So where's RMD to sort this out!?.....LOL.


Cheers.

Tlax,
Sorry if you have mentioned these details before but what type are your batteries and what is the size of the solar panel you are intending to fit?

There is an issue which I don't think anyone else has yet mentioned. It is something which has arisen in a friend's Patrol recently & relates to battery types & usage.

In his case he had a maintenance free wet crank battery, & a wet auxillary battery able to be topped up. Problem was he rarely thought to top it up, & this combined with the fact that his aux battery was only ever used when away on camping trips meant that it remained at 100% charged, or close to it much of the time when the car was being used as a daily driver at home. When wet batteries are charged to 100% they bubble & gas, unlike crank batteries which are in regular use & rarely get charged above 70% to 80%.

The 'problem is that VSR 'reads' the crank battery voltage to determine when it connects/disconnects the two batteries to/from each other, so the situation arises that the aux battery is full or close to it, but each time the ignition is turned on the voltage in the crank battery rises in response to the input from the alternator, & the VSR joins up the two batteries , allowing the aux to receive charge.

This is not a problem when on camping trips because the aux has constant loads on it.
However in the 'daily driver' scenario the aux gets overcharged. Combine this with not keeping the wet aux regularly topped up & it is a recipe for premature battery death, most likely evidenced, as in my friend's case by a bulging swollen battery & green oxidation around the battery caused by it's excessive venting.

Some things will help to avoid this. Use of a Valve Regulated Lead Acid battery (VRLA) like an AGM (Absorbed Glass Mat) type which are less prone to venting (but need to be better shielded from heat, when under the bonnet) or a very regular routine of topping up the battery (& not over filling it). Also using the battery during daily driving (eg. switch the fridge on).
Alternatively incorporate a switch/relay so the two batteries only get paralleled when you choose, but you have to remember otherwise you can end up with an aux battery killed prematurely by under charging. A voltmeter in the cab off the aux provides a handy reminder of when to flick the switch.

If the solar panel with regulator is mounted on the car & attached to the aux, the switch allowing the VSR to do it's thing would probably never need switching on in daily driving - but useful on camping trips.

To follow up a couple of messages, I will likely have the fridge running all the time, and I have attached a pic if the starter and aux batteries.