Solar charging the starter battery

[vomhorizon]

I've been evaluating various options as far as beefing up my 4Runner's electrical needs are concerned since I'd be adding a 40-50 Liter fridge and a couple of camp lights soon. I've looked at a number of options and tried to best match my budget, my usage (how long I planned on being off-grid and how long stationary with the engine running) and the power usage from my accessories. I've decided to not go for a dual battery setup for now as I think that with solar and a AC 10 Amp charger as my secondary source my Group 34 AGM should be able to handle my needs when the car is on and running and when substituted with a 30-40 AH (400-500 Watt) Lithium solar generator which I would be buying for my rig and for use around the house.

I intend on mounting a MPPT charger under the hood of the vehicle, and plan on having a 50 or 100 Watt panel on my roof rack. Being not very familiar with solar set ups, I wanted some help in understanding how the solar charger (say a Victron smart solar MPPT) would interact with the smart alternator and the Noco 10 Amp charger that I plan on using. Will my battery accept charge from 2 sources simultaneously (Solar charger and alternator when the engine is running, or solar and the AC charger when it is plugged in)? I don't want to end up in a situation where my solar charger is prohibiting my battery from being charged by the alternator when I have the engine running and my battery being worst off compared to not having the solar set up at all.

 

[Martinjmpr]

I've been evaluating various options as far as beefing up my 4Runner's electrical needs are concerned since I'd be adding a 40-50 Liter fridge and a couple of camp lights soon. I've looked at a number of options and tried to best match my budget, my usage (how long I planned on being off-grid and how long stationary with the engine running) and the power usage from my accessories. I've decided to not go for a dual battery setup for now as I think that with solar and a AC 10 Amp charger as my secondary source my Group 34 AGM should be able to handle my needs when the car is on and running and when substituted with a 30-40 AH (400-500 Watt) Lithium solar generator which I would be buying for my rig and for use around the house.

I intend on mounting a MPPT charger under the hood of the vehicle, and plan on having a 50 or 100 Watt panel on my roof rack. Being not very familiar with solar set ups, I wanted some help in understanding how the solar charger (say a Victron smart solar MPPT) would interact with the smart alternator and the Noco 10 Amp charger that I plan on using. Will my battery accept charge from 2 sources simultaneously (Solar charger and alternator when the engine is running, or solar and the AC charger when it is plugged in)? I don't want to end up in a situation where my solar charger is prohibiting my battery from being charged by the alternator when I have the engine running and my battery being worst off compared to not having the solar set up at all.

I'm not an expert by any means but I'm a bit confused by your setup. What is the 10a Noco charger going to be plugged into? A generator? Or are you planning on camping at campsites that have electrical hookups that you could plug the Noco charger into?

I'm just not seeing where the 10a AC charger fits into this. If you are at a place where you can plug in an AC charger, you could also plug your fridge into that same outlet and not use any battery power at all. Instead of spending $50 - $100 on a 10a charger you could spend $15 on a long extension cord to plug in the fridge.

This is exactly what I have been doing for years, BTW. I carry extension cords and if we are at a place that has power, the fridge gets plugged into the 120vAC outlet, not the truck. It does mean one extra step when leaving for the day (unplug the fridge from the 120v outlet and plug into 12v) but that literally takes 30 seconds or less.

I don't have any specific recommendations but I would say that if you plan on running with a single battery, it's a good idea to have a backup jump starter pack in the event that your fridge draws your battery down enough to keep it from starting.

 

[vomhorizon]

I'm not an expert by any means but I'm a bit confused by your setup. What is the 10a Noco charger going to be plugged into? A generator? Or are you planning on camping at campsites that have electrical hookups that you could plug the Noco charger into?

The 10 Amp AC charger charges my starter battery when shore power is available and stays in the truck since I plug in my AGM in from time to time to keep it topped up. You are right, if I'm at a campsite that is electric, I'd just plug it in and be happy (that will be rare though as I like to avoid camp sites). However, would I need to disconnect my MPPT in that case? Same when the engine is running. Would I need to disconnect the MPPT to ensure that the battery is being charged adequately by the alternator? My understanding with solar setups is limited but I do think there should be an MPPT out there that should be able to smartly manage between multiple sources of power going into the battery, detecting that the alternator is supplying power and allowing the alternator to charge the battery when engine is running and moving over to the solar panels when it is not.

 

[NatersXJ6]

I have no official knowledge or authority in electrical things, but I do have small experience.

I recently added 200w solar to the roof of my Jeep and the Victron SmartSolar 75/15 MPPT to fill the gaps left by a fridge running 24/7 in the heat. I do not unplug when I drive. The solar controller senses the alternator voltage at the battery and either stops charging or boosts voltage above that to allow charging (I don’t know which), but it works transparently. I’ve been running it maybe 3 months now and haven’t noticed any low battery instances, where last summer I was on a charger every 4 days.

one note in your plan, I suspect depth of discharge will be a problem with a 34M battery, and you won’t ever recover it all the way. I went to a 27M, and it seems to have made a big difference.

I also put my controller in the passenger footwell instead of under hood due to temperature concerns.

Good luck and have fun!

 

[craig333]

You can have multiple charging sources.

 

[vomhorizon]

I have no official knowledge or authority in electrical things, but I do have small experience.

I recently added 200w solar to the roof of my Jeep and the Victron SmartSolar 75/15 MPPT to fill the gaps left by a fridge running 24/7 in the heat. I do not unplug when I drive. The solar controller senses the alternator voltage at the battery and either stops charging or boosts voltage above that to allow charging (I don’t know which), but it works transparently. I’ve been running it maybe 3 months now and haven’t noticed any low battery instances, where last summer I was on a charger every 4 days.

one note in your plan, I suspect depth of discharge will be a problem with a 34M battery, and you won’t ever recover it all the way. I went to a 27M, and it seems to have made a big difference.

I also put my controller in the passenger footwell instead of under hood due to temperature concerns.

Good luck and have fun!

Thanks! My set up will be very similar to yours and if too may end up placing my MPPT in the footwell if I go for one that doesn't have adequate thermal or weather protection. I had also shortlisted the Victron 75/15 for my needs. I guess one could always get a 5 ft extension from the solar panels if needed. I don't envision depth of discharge being too much of a problem for me currently because I will be substituting it with a Lithium 500 Wh solar generator that I'll be taking along with me on trips. Worst case, Just disconnect the power source to the fridge and connect the solar generator and have it run the fridge overnight and then plug it into the car when it is running the next day. But if that does become an enduring issue, I could always upgrade my starter batter to something like a Group 31 as it fits my rig (though not ideal given the weight).

 

[john61ct]

Did not read all.

There is no need to set a goal of charging a Starter batt from solar.

You should have all significant energy sources designed to maximise charging your House bank.

Then keeping the Starter topped up becomes trivial - it should hardly ever go below 99.9% SoC in a proper design.

Obviously a proper ACR/VSR/combiner or DCDC charger connection between the two circuits as usual.

Now vehicle kept **stored** unused, away from grid power is another story, all the House batteries should be fully isolated from loads

and a small $30-50 panel can be added if needed to keep everything topped up even with the ECU, stereo presets remaining connected.

 

[DaveInDenver]

You should have all significant energy sources designed to maximise charging your House bank.

He doesn't want to go with dual batteries so the starter is the house. Using a modest solar system makes sense and having a shore charger is smart to keep the battery conditioned. Not sure about needing everything - an MPPT solar controller with 50 ~ 100 W panel, a 40 A-hr lithium solar generator and a 10A shore charger.

 

[vomhorizon]

He doesn't want to go with dual batteries so the starter is the house. Using a modest solar system makes sense and having a shore charger is smart to keep the battery conditioned. Not sure about needing everything - an MPPT solar controller with 50 ~ 100 W panel, a 40 A-hr lithium solar generator and a 10A shore charger.

I agree with the last bit. If I was designing something specifically for the rig, I'd probably ditch either the solar panels or the solar generator. But the Lithium solar generator is going to be used for a lot of stuff at home and outside as well so it isn't exclusively for long trips with the rig though it will be there on most occasions if I need it. I guess for redundancy and peace of mind if for nothing else.

 

[john61ct]

Yes just Starter batt no House storage at all to me means keeping a phone charged, an LED or two only, maybe a small fan used a few hours.

If you have good charging capacity IMO silly not to capture it, store 2-3 days' usage.

A couple Deka GCs gives you 200+ Ah for ~$200 can serve well for 6-8 years.

And no risk of getting stranded with a flat starter.

But, that's me

 

[dreadlocks]

an oft overlooked alternative is downsizing the starter battery, I used a Deka ETX20L on a 3L V6 just dandy.. gives >300CCA and is the size you often find in Jump Starters.. they got an EXT30L w/>400CCA.. this takes advantage of AGM's ability to power big loads w/little batteries, none of us need the 1000CCA more typical sized AGM's can give, freeing up the rest of the vehicle to be wired to an automotive format deep cycle battery and not needing to rewire the whole vehicle. All while guaranteeing you can always start even if someone leaves the lights on.

 

[DaveInDenver]

Yes just Starter batt no House storage at all to me means keeping a phone charged, an LED or two only, maybe a small fan used a few hours.

If you have good charging capacity IMO silly not to capture it, store 2-3 days' usage.

A couple Deka GCs gives you 200+ Ah for ~$200 can serve well for 6-8 years.

And no risk of getting stranded with a flat starter.

But, that's me

Fitting 200 A-hr of golf cart batteries would leave no room for a fridge in a 4Runner! Not everyone drives a 4wd motor home with every imaginable appliance. I ran an Engel MT45 from an Optima Redtop group 34 for several years using a 100W solar panel (a pair of 50W in a DIY suitcase) and a Morningstar SS-MPPT-15L. This battery is rated 50 A-hr @ C20 and the MT45 consumes about 1 or so amp-hour so pulling into a camp spot fully charged with just he fridge load and solar in mostly sunny Colorado never left me stranded in weekend warrior usage.

That said I now run dual batteries mainly to give redundancy, a group 25/35 paired in the stock location. This was for convenience since they fit in the group 27 location on my Tacoma. If I was starting from scratch I'd give serious thought to just going with a smaller and lighter starter like @dreadlocks says and find a place for a bigger second battery. But the layout of my engine bay wasn't conducive to this easily. But I also like having the option for either or both to start or run a winch by having the option to connect or isolate them.

 

[vomhorizon]

Yeah lugging around heavy batteries isn't going to happen in the 4Runner given that space and weight are at a premium. This is also the reason why I want to mount the solar panels as opposed to a briefcase.

 

[DaveInDenver]

Yeah lugging around heavy batteries isn't going to happen in the 4Runner given that space and weight are at a premium. This is also the reason why I want to mount the solar panels as opposed to a briefcase.

Keep one of those jump packs in the glove box for back up. Or the solar generator might serve for that. There are options for good battery monitors these days that knowing consumption and charging with better resolution should help. I just watched voltage, which is a very poor guesstimate for state of charge. A worn out 22R-E doesn't present a tough starter load and being a stick shift pop starting was my plan B.

 

[dreadlocks]

yeah if you've got a winch in the equation then having a dual battery setup you can combine for a large amp reserve is the most desirable design.. otherwise, if the only electric motor is a half second load like a starter then capacity size is mostly moot since its always gonna be >98% Charged.

If you've wired your own aux circuitry to run off starter battery and your backing it with solar and determined to make this work, I would suggest two safeties.. First line of defense a Low Voltage Disconnect (LVD) like a Victron Smart Battery Protect that you can set to cut off your loads automatically before your starter battery loses its ability to start, and lastly a nice jump starter just incase, make charging it up a part of your routine.. make nice phone chargers too.