Starter battery solar charge

[Scarfaz1]

Hi, quick question for the electrics/solar experts on here. Currently connecting a Ctek charger up to the starter battery if I'm not going to use the van for more than a couple of days. This has the advantage of keeping the leisure battery topped up via my dc to dc charger. I've already got an mppt controller setup for a mobile foldup solar and was thinking it would be a lot easier to just install a panel on the roof.

Question is if I keep it as it is do I need to install an ignition controlled relay to disconnect the solar when engine is running and if so which side of the controller should it be??

 

[roadtripper]

Your best plan, and the one lots of folks here take, if you want to fit permanent solar is to have that charge the leisure battery and then fit an AMT12 trickle charger to keep the starter topped up from the leisure battery.

You can connect an MPPT charger to the starter battery if you wanted to, no need to have a disconnect it will simply stop charging if the battery is full. Keep in mind as you will have a smart alternator the van will normally only charge the starter to around 80% to leave space do regenerative braking, if you then top this space up with a solar charger it can't do that and will just stop charging until the engine uses up the charge you just put in. This is one of the reasons its normally done the other way around.

 

[manfrotto]

Intrigued about the regenerative braking system.
This as a useful thread -

Thread 'Battery charging through regenerative braking.'

9 Jul 2021

I'm led to understand that the battery doesn't charge from ticking over on the drive because the van uses regenerative braking energy to charge it. That's right yes?

I haven't used my van much over the past 18 months and predictably, the battery tends to be quite down on its SOC. (I base this on the speed the starter motor turns the engine rather than through a meter). I can also tell when the battery is sufficiently charged because my stop/start starts working!

Anyway, I decided to top the battery up by giving it a run down the motorway. Despite a couple of hundred miles the stop/start...

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Based on that, if the van is sitting for a while, maybe it is better that a solar charger keeps the battery at 100% ?

 

[roadtripper]

No, like all batteries Lead Acid batteries don't like being held at 100% at all times, which is why maintenance chargers use strategies like slow pulse charging (eg AMT12), or letting the battery fall back in charge before gently charging again (CTEK in long term maintenance)

Is this the heaviest activity that can cause battery wear? No heavy cycling and discharge below 50% will do much more wear and damage.

In the majority of vans on this forum that are sitting for a while will tend to be leisure based vans and highly likely to have leisure battery. That battery is the one that's going to take the wear anyway and the one that having fixed solar while camping is most useful so it's the one that's more suited to solar charging - because these chargers start fresh every day none of them to my knowledge have any maintenance approaches.

Then use a charger specifically designed to maintenance charge a starter battery to keep that in a healthy range.

There is a very advanced charging system built in to your vans electronics, it's best to work with that and not fight against it. Forcing 100% charge into the starter is going to be wasted effort the first time you start the van and leaving a high current DC-DC charger enabled to cascade the excess charge in to the leisure battery is risky, it will very quickly drain a starter battery if it makes a mistake.

That doesn't mean maintenance charging is the wrong thing to do. If you have a single battery van that sits for weeks solar is better than being stranded, but if you can charge with a mains based maintenance charger with a proper long term storage phase your battery will last longer.