Solar to starting or house battery?

[James86004]

I am permanently mounting a solar panel on our 2023 Defender. I would like to have it charging the starting battery, since systems draw several amps of power every time you open a door, and can drain that battery when you are out in the field for a couple days.

If I do this, will any excess solar power go through the dc/dc charger to the house battery? Is this a bad idea?

Sent from my moto g stylus 5G (2022) using Tapatalk

 

[Joe917]

Generally you want your solar going to the house batteries.
Any well made vehicle should be able to go a weeks without starting without issue as long
as all your house loads are on the house battery. In an failed start you can always jump from the house battery.

 

[fratermus]

I would like to have it charging the starting battery

That would be highly unusual. Providing power to the starter side causes weird behavior unless charging power is greater than the DC-DC's rated output:

1. solar charges starter batt at 10A
2. starter batt voltage rises to DC-DC cut-in
3. DC-DC starts charging house bank at 30A
4. starter battery voltage drops to DC-DC cut-out
5. repeat until the sun goes down

If you are concerned about keeping the starter battery topped off you could use a combo DC-DC/MPPT that has starter battery maintenance. In this scenario when solar is present and the house bank is charged the charger sends the starter battery a maintenance charge.

If you are concerned about getting stuck with a dead starter battery then a relay end-around the DC-DC will let you self-jumpstart.

 

[James86004]

Thanks, all. I will charge the house battery.

A problem with many modern vehicles is the radio/navigation computer takes a while to boot up, so they are set up to boot as soon as you open a door. They draw a lot of power, so if you are camping and open and close the doors several times a day, it can flatten the battery.

 

[llamalander]

You can try this, not a huge investment if the computer/alternator don't like it.

SI-ACR Automatic Charging Relay - 12/24V DC 120A - Blue Sea Systems

Automatically combines batteries during charging, isolates batteries when discharging and when starting engines.

www.bluesea.com

I use one with an optima starting battery and a marine deep-cycle house battery, 380w. of solar with a Victron MPPT and my stock alternator.
About 30 seconds after either charging source reaches a voltage threshold, the batteries combine, and both are charged by either or both sources.
This seems to work well because the batteries have a similar chemistry and charging capacity, I don't know if it would play well with lithium, or rather prevent the alternator from killing itself to charge one.

I think the cable + fuses (one at each battery, ACR between) to connect the batteries may cost as much as the ACR.

 

[pluton]

Maybe look at a smaller 'maintainer' type solar charger for dedicated use on the starting battery. I got a Renogy 10W MPPT unit for $40 and change, and it does a really good job of keeping the starting battery charged. It's small (about 10x14") and can be placed on the top of the dashboard and do it's job.

 

[DaveInDenver]

That would be highly unusual. Providing power to the starter side causes weird behavior unless charging power is greater than the DC-DC's rated output:

1. solar charges starter batt at 10A
2. starter batt voltage rises to DC-DC cut-in
3. DC-DC starts charging house bank at 30A
4. starter battery voltage drops to DC-DC cut-out
5. repeat until the sun goes down

This is right.

I have a Victron DC-DC charger, specifically a 220 watt Orion, to maintain my house and have a 15A Morningstar solar controller. As a test I tried feeding into the starter but I have only 100W of solar, so I don't come close to saturating my solar controller and am much lower than the bulk current capability of the Victron.

I expected the sequence you describe and wasn't surprised when it occured.

There may be ways to alleviate this using voltage turn-on, turn-off and restart values but it will never work completely seamlessly unless you set the ride-through, e.g. DC-DC has turned on but you set the under voltage turn-off, so low that the starting battery must draw down to keep the DC-DC on.

Ultimately using ignition sense to hold off or manually enabling (or perhaps a disable when using solar) the DC-DC is the only way around this.

My Victron does have an external on/off switch just for this purpose. It is jumpered from the factory so that it only runs based on the software settings. I put a small switch on it so I could control it just in case but it's rather inconvenient and doesn't really efficiently use the solar since the house battery is discharging while the starter is mostly sitting at float.

I'm feeding my solar into the house and if I need to jump, as has been suggested, I'd just use the (mostly) topped house to do that but you could I suppose alternate days charging the starting battery with days drawing it down deeply forcing the DC-DC to stay on.

I'm very surprised if a new Land Rover would draw down it's battery that fast that you couldn't spend a few days parked.

 

[Wallygator]

I would do one of these to maintain the starter battery and a different panel for the house battery/batteries.

https://www.lensunsolar.com/Hood-Solar-Panel/Land-Rover-Hood-Solar

Cascadia also makes something similar.