Using Leisure battery solar panels to charge starter battery

[Grim Reaper]

I am thinking of adding a solar charge controller to my setup to allow me to charge the starter battery from my rooftop panel should the need arise. Has anyone done something similar?
I am thinking of adding another battery cut off switch to the solar feed so I can disconnect it from the Redarc solar input (set up to feed a lithium battery under the seat) and connect it to a (probably Victron) solar charge controller to charge the starter (AGM) battery via the cables already in place between the starter battery and the redarc alternator input.
The battery cut off switch arrangement would require a single key to be removed from one switch and reinserted into the other so I can't feed both the Redarc and the Victron at the same time. Any thoughts on problems that may arise?
Currently have 100W (21.9V/6.14A) panel on the roof, and I have a 200W (23.4V/10.7A) panel ready to fit (Redarc limit is 32V so no issue with voltage) so I'm thinking a 75/15 charge controller over the 75/10 version? would you go for the BlueSolar or SmartSolar version?

 

[Dellmassive]

Defo smart solar as it has Bluetooth built in.

And I'd go for the 75/15..

Or even a 100/20, then you could run the whole 300w through it if you wished.

The only difference if the physical size of the units.and power obviously.

 

[Dellmassive]

I use a 50w fold kit plugged into the dash socket....

That helps charge the starter battery.

I use the 75/15 smart on AGM profile.

 

[Grim Reaper]

Completed fitting of the new charge controller today, squeezed it in beneath the inverter under the driver's seat and wired it all in. Was a bit of a pain getting it all in but seems to be working OK, now have the option to keep the starter battery topped up throughout the year.

 

[Dellmassive]

Love it.

Looks like you have......

Victron mppt.
Victron inverter.
Redarc DC-DC.

What's the operation modes?

I'm assuming it's all charging the leasure battery all the time.... How do you switch over to charging the starter battery.?

 

[Grim Reaper]

The victron smart solar is set to AGM for the starter battery, the Redarc is set to Lithium for the leisure battery. By moving the red key from one isolator to the other the solar panel input from the roof mounted panel can be diverted to either charge controller but not both at the same time (you'd have to insert another key to do that which would not be recommended)

The third isolator is to disconnect the fuse box feed so everything (except the fridge which is permanently live) can be turned off in one go (so no drain from usb converters or diesel heater controllers that are fed off the leisure battery)

 

[Dellmassive]

Gotcha... Nice.

 

[Grim Reaper]

At 09:14 I have about 40W going into the starter battery.

 

[Dellmassive]

Lovely.... The starter is normally kept at 80% SoC by the power management system .

So expect to dump about 20% or 20ah into the starter battery before it shows 100% full. (Every drive cycle)

 

[Grim Reaper]

So, slight issue (or potential issue)...
Just pulled the old solar panel off and hoisted the new one into place and I find the new panel has a curve to it that is in the wrong direction to what it needs.
Does anyone think if I leave it up there for the night that it might relax and fit a bit better? It may put more pressure on it than is desirable to go ahead and glue it down like it is.

 

[Dellmassive]

Yeh.... No worries.


The sun and heat will relax the substrate... And it will drop to the curve of the van.

Nothing to. Worrie about

 

[Grim Reaper]

I have a few lead shot bags from my scuba diving days, I'll put them on the corners to help out.

 

[osman]

I use a 50w fold kit plugged into the dash socket....

That helps charge the starter battery.

I use the 75/15 smart on AGM profile.

That’s interesting .. you can use the dash 12 v socket to charge the starter battery ?

 

[Pete C]

Yes. Obviously it needs to be one that is always on (as opposed to on with the ignition), and you really don’t want to put more than 8 Amps through it, so 50W is pretty safe.
We have charged ours this way with a Ctek 5A charger.

Pete

 

[Dellmassive]

That’s interesting .. you can use the dash 12 v socket to charge the starter battery ?

Yes. As above.

Stick with 8A max as the plug will get hot.

You can also charge through the obdw port as well.... But again lowish power.

 

[dcpen43]

Planning some off grid trips so installed solar last month. Ample energy for the LB. Decided to add an isolating switch to the MPPT output to redirect energy to Starter Battery. Appears to be working nicely.

Anyone think I might run into issues. Going leave the Starter hooked up to Solar for a couple of days and see what happens.

 

[Grim Reaper]

I think the only thing to be sure of is that the charging profile of both batteries is the same if you don't plan on altering the charger settings when switching between them. I used a different unit for the leisure battery (lithium) and the starter battery (AGM) and just switch the solar input between them as required.

 

[dcpen43]

Yes, that thought popped into my mind too. Thankfully I had previously changed the LB to AGM so I think I am ok on that front. Will see have it goes and keep an eye on the BM