Solar charging the starter battery

[vomhorizon]

Thanks for all the help and advise guys. I'm new to solar and have mostly ever camped with ice boxes (or worst) so all this is new to me.

For sure any battery used for deep cycling (as opposed to dedicated to Starting only)

should be from a known - good maker and a model designed for longevity in true deep cycling usage.

Odyssey's PC-2150 is such, very rare in that it truly lives up in reality to the "dual use" label.

That's G31 size, they likely have others in that line.

In my case, If I'm on the road for 3-4 hours a day while running the fridge from the alternator and also providing a supplement from the trickle charge coming from the solar controller (I can accommodate both a 100 Watt and a 160 Watt panel given the current space I have on the roof rack) while also getting a few hours of stationary solar ONLY charge in, how much will I be cycling? [ knowing that once I'm done with most of my outdoor camping needs with a lithium pack,I could always disconnect the fridge from the battery and connect it to the lithium unit for the 8-9 hours of no or little sunlight].

If I assume 6-8 or so hours of fridge usage w/o alternator or solar, how much will my battery be depleted before solar panels start back on and before I hit the road? I'm assuming that 3-4 hours of driving plus any solar input coming from the charge controller should be adequate to top up the battery assuming its fairly topped up when I shut off my car and assuming a 3.5 Amp draw (hypothetically speaking because it factors say one or two camp lights being used for say an hour of when we're cooking etc) with a 50% duty cycle for the 6 - 8 hours (that's roughly 12-15 Amps of stationary draw in 24-hours of usage which a 100 or 160 Watt solar panel should be able to put back into the battery throughout the day).

I think I need to figure out whether:

A) Connecting the Victron solar controller and solar panels directly to the starter battery is OK from a battery and car electrical system health perspective (I'm new to this so am still wondering what the net impact of two regulated chargers working concurrently will have). Last thing I want to do is muck up car electrics and void the warranty.

I see most folks running solar setups with the auxillary battery that is being charged by a DC to DC system with a built in solar regulator (like a red arc) or solar charge controller being separate. I know a few who take a solar briefcase and clamp it to the starter battery when stationary but in that case only one system is charging the battery at a time (alternator when engine is on, and solar when engine is off and solar is connected).

B) Can I wire my solar + and - input (coming from the panels down to the solar charge controller) via an anderson plug so that I disconnect it when driving and plug it in when I camp? I guess I need to understand whether it is safe and OK to disconnect monocrystalline (both + and ground terminals) panels form the charge controller and just leave them on the roof like that.

If possible, this would be like taking a solar blanket or briefcase but not having to lug it around in the trunk or set it up when camped. I also really like the idea of trickle charging the battery via solar when I'm parked outside (my work parking is outdoors) as this should basically take care of topping off the AGM (given the charge profile relative to what the Toyota alternator) and saving me the hassle of plugging it into an AC charger every now and then. This will probably be even more important when I upgrade to a group 27.


My reason for avoiding a dual battery system has to do with cost, weight and all the wiring that I'd have to do (I guess you could always get it done via pre assembled kits but those are even more expensive). For the price of the Red Arc DC to DC, I can pretty much buy my entire solar set up (160 Watt panel, 10 AWG wires, and MPPT) and even if I have a dual battery system, I would kind of still need a portable Lithium system because of away-from-car power needs (so I can't really save money by avoiding it) and other general purpose usage around the house or when camping with others.

 

[broncobowsher]

OK, I am about a week late to this party...

I have been doing exactly what the OP discussed. My '10 Xterra has had solar since the end of '11. Only battery is the starting battery. No good way to package a separate house battery unless I want to undersize my starting battery. I have an ARB freezer fridge, the old original one from '08. Add in a 70W solar panel (math said 100W would be a better safety margin but packaging says 70W fits the roof better). PWM charge controller (Sunkeeper SK6) mounted in the passenger kick panel. No temperature probe. In the cabin protects from severe engine compartment heat but is still roughly the same temperature while parked for extended times.

The battery that is known for only lasting 2 years in these trucks lasted almost 7. One winter morning it was slightly slow to crank over so I pre-emptivly replaced it. The solar is connected 100% of the time, no isolation from the trucks normal electrical system. I think this is what actually kept the battery around for so long, it stayed on the charge controller while the truck was off.

Live in AZ, I use the fridge for a grocery store run. Inside the cab with all the windows closed it will never freeze, the ambient (cabin temp) is too high. But in the mountains it is fine. Even parked in shade it keeps up. Fridge it is just fine. If it is cool enough to sleep it doesn't draw enough battery to be a problem overnight. Next day there is more than enough solar to run the fridge and recover from overnight. I have accidently left it on freeze overnight, my bad. Fridge runs full blast all night long. Forget to turn it off after a grocery store run. Next morning the truck will still start on its own. Not happy doing it, but it will do it. That is pushing it too far in the name of planning. Still no plans of changing anything in how it is laid out. After 100k+ miles and almost a decade the solar panel is starting to suffer some damage to the cells. Found some new 100W panels that fit my packaging needs, the panels are getting more efficient. Might upgrade sometime. But for now the 70W panel still gets me by.

 

[67cj5]

OK, I am about a week late to this party...

I have been doing exactly what the OP discussed. My '10 Xterra has had solar since the end of '11. Only battery is the starting battery. No good way to package a separate house battery unless I want to undersize my starting battery. I have an ARB freezer fridge, the old original one from '08. Add in a 70W solar panel (math said 100W would be a better safety margin but packaging says 70W fits the roof better). PWM charge controller (Sunkeeper SK6) mounted in the passenger kick panel. No temperature probe. In the cabin protects from severe engine compartment heat but is still roughly the same temperature while parked for extended times.

The battery that is known for only lasting 2 years in these trucks lasted almost 7. One winter morning it was slightly slow to crank over so I pre-emptivly replaced it. The solar is connected 100% of the time, no isolation from the trucks normal electrical system. I think this is what actually kept the battery around for so long, it stayed on the charge controller while the truck was off.

Live in AZ, I use the fridge for a grocery store run. Inside the cab with all the windows closed it will never freeze, the ambient (cabin temp) is too high. But in the mountains it is fine. Even parked in shade it keeps up. Fridge it is just fine. If it is cool enough to sleep it doesn't draw enough battery to be a problem overnight. Next day there is more than enough solar to run the fridge and recover from overnight. I have accidently left it on freeze overnight, my bad. Fridge runs full blast all night long. Forget to turn it off after a grocery store run. Next morning the truck will still start on its own. Not happy doing it, but it will do it. That is pushing it too far in the name of planning. Still no plans of changing anything in how it is laid out. After 100k+ miles and almost a decade the solar panel is starting to suffer some damage to the cells. Found some new 100W panels that fit my packaging needs, the panels are getting more efficient. Might upgrade sometime. But for now the 70W panel still gets me by.

In a test your fridge was subjected to extreme heat where it was put in a chamber and heated to 60*c / 140*f and it still managed to keep all it's contents frozen, So does it get hotter than 140*f in your Truck ??

 

[jonyjoe101]

inside my van in the front uninsulated section with the windows closed it gets up to 150 f, this is in southern california. I don't have the ARB fridge but the 26L 12 volt fridge I have when it gets in the 90's (back of insulated van) it has to run more to stay cold. I measured the temperature from the fridge air vents and it reaches 110 degrees while running. It heats up the interior of the van.

I hotglue 3 layers of half inch foam to my fridge exterior, that does help in reducing the power usage. I keep the fridge set to 12 degrees f, and depending on the vans inside temp it will use from 18 to 26 ah per day. I found 12 degrees will keep my fish sticks and other frozen food cold enough. Taking the temp down to 10f increases power usage to over 31ah per day, so i keep it at 12f. Before I hotglue the foam it was using up to 44ah per 24 hours at 12f.

 

[NatersXJ6]

In a test your fridge was subjected to extreme heat where it was put in a chamber and heated to 60*c / 140*f and it still managed to keep all it's contents frozen, So does it get hotter than 140*f in your Truck ??

In Arizona, yes, temperatures in a car with the windows up can easily exceed 140. Same here in California, outside ambient temps before considering sun can reach 115 plus in my area. Not hard to believe the interior blows past 140 when the car sits in the sun. I accidentally touched the inside of my Jeep hardtop one time... burn baby burn!

 

[vomhorizon]

The battery that is known for only lasting 2 years in these trucks lasted almost 7. One winter morning it was slightly slow to crank over so I pre-emptivly replaced it. The solar is connected 100% of the time, no isolation from the trucks normal electrical system. I think this is what actually kept the battery around for so long, it stayed on the charge controller while the truck was off.

Thanks for providing feedback on the set up. I will be running a single battery set up as well and will supplement with solar to keep it topped up. Plan on ruining either an Engel 40 L Combi or a Luna 50 and I am budgeting a nominal need to replenish about 35 Ah (38% of a Group 27 battery capacity), between the alternator and solar, over a 24-hour window. I should be fine with a 100 Watt panel but am seriously considering up-sizing it to 160 Watt. I'll also have some portable power handy in case of overcast days and for contingencies in case I make that rare longer trip.

Just in case someone stumbles upon this thread looking at the same issues, in addition to what the members here have so well articulated, here are some other web links describing charging the batteries concurrently via multiple sources -

https://amsolar.com/diy-rv-solar-instructions/edfaq

What happens when I have multiple charge sources charging a single battery bank

shop.pkys.com

 

[vomhorizon]

So as far as a battery upgrade, my options include upgrading from my current Odyssey Group 34 to a Group 27 battery to get the additional 25 or so Ah in capacity. Alternatively, for about the same price (or slightly more), I can keep my Group 34 as is (it is about 2.5 years old and is regularly topped up by AC) and mount a second Odyssey Group 34 using a aux tray and run the two in parallel. This, in theory, would provide me with 40% additional power. Would the same architecture (solar charge controller connected to starter battery and solar+alternator concurrent charging) still hold even when the two batteries are connected in parallel? And is there reason to be concerned with the fact that one of the batteries will be new while the other old?

In that case, I would just build my power setup with the existing Group 34 battery (running wires to the back, connecting fuse block, terminal mount fuse, and a breaker etc) and when I install the fridge, I can install a second battery and connect its + and - terminals to the corresponding terminals of the original starter battery for a parallel setup. Is it just that simple, or have I overlooked anything?

 

[john61ct]

Sorry missed this

In my case, If I'm on the road for 3-4 hours a day while running the fridge from the alternator and also providing a supplement from the trickle charge coming from the solar controller (I can accommodate both a 100 Watt and a 160 Watt panel given the current space I have on the roof rack) while also getting a few hours of stationary solar ONLY charge in, how much will I be cycling?

For purpose of selecting a lead battery that will withstand deep cycling, "how deep" is irrelevant. 99.99% of lead batteries sold are only suitable for Starter duty, and consumer / automotive channels are rife with fraudulently labeled and marketed crap that will only last* a couple/few years at most.

What is a Deep Cycle Battery? - Marine How To

Light Cycle vs. Deeper Cycle NOTE: This article deals with FLOODED marine batteries, not AGM or GEL batteries. The Problem: The problem, as I see it, is one of dishonest marketing where multiple battery types wear the same clothes (sticker) and will perform differently when

marinehowto.com

* EoL defined by % loss of capacity, aka SoH

Once you have a suitable battery, then yes, you can murder it by drawing down too low, usual guideline is a 50% limit.

You need an Ah counter to tell.

> disconnect the fridge from the battery and connect it to the lithium unit for the 8-9 hours of no or little sunlight

all depends on total capacity vs energy drawn per hour, and that will vary **a lot** depending on the temp delta at the time, putting warm contents in, how often you open etc etc

You need an Ah counter to tell, get a feel by experience

A fridge needs to run 24*7 for efficiency, letting it power down will increase total Ah per 24hrs

You won't hurt anything charging from multiple sources,

leave everything solar hooked up, no harm

but the solar input is largely irrelevant while any ICE source is running.

Nothing to do with monocrystalline.

Do take advantage of mains AC charging whenever possible while cycling.

In storage outdoors, even tiny solar is plenty to counter ECU discharge rate.

> My reason for avoiding a dual battery system has to do with cost, weight and all the wiring that I'd have to do (I guess you could always get it done via pre assembled kits but those are even more expensive). For the price of the Red Arc DC to DC

Dual battery can be handled with a $50 solenoid if you keep the design simple.

DCDC is only needed for different voltage needs, or very long wiring runs.

 

[broncobowsher]

In a test your fridge was subjected to extreme heat where it was put in a chamber and heated to 60*c / 140*f and it still managed to keep all it's contents frozen, So does it get hotter than 140*f in your Truck ??

Sorry for the delay. I'm not here all the time.
No
The ARB fridge maxes out at 100°F drop. At 140° the fridge will run 100% and will warm up to about 40°

If you want a true freezer, you need more battery and find a way to keep the fridge cool.

My experience is only running fridge overnight. And overnight is cool enough I can sleep. Which means the fridge only runs part time, guessing less than 50% duty cycle. A single battery will not survive a fridge running 100% (freezer)

 

[vomhorizon]

I don't plan on running the fridge as a freezer constantly, and definitely not when I have just one single (wired) group 27 battery. The two fridges I'm considering are the Engel MT45 or the Luna 50L. My math may be a bit fuzzy but I'm assuming a worst case scenario of 15 hours of no sun (low sun) and no alternator and a 3 Amp draw with a 80% cycle. This over a 24 hour period where the remaining 9 hours are spent either using either the combination of alternator and solar, or just solar to keep the battery topped up. Others, elsewhere, have experience about a 25-28 Ah draw per day from the 40 L Engel but I assume that is across a range of temperatures and daily fluctuations. My worst case is about 50% higher than that average.

This comes to 36 Ah capacity used for every 15 hour cycle when nothing is being put back into the battery. A 92 Ah Northstar will fit in my starter battery location. This gives me a fair bit of room before I hit that 50% SOC below which I would just turn off my fridge and plug in the portable battery. I would have to do this manually, add a LV disconnect or rely on the fridge's LV disconnect feature, which for the Engel at least is quite low though it probably accounts for losses.

So based on my style and camping needs where we are rarely stationary for more than 24 hours at a time (most of the time just over night before hitting the road in the morning) this combination should suffice. For solar I've decided to settle for a 160 Watt panel because I have that additional space to spare compared to a smaller 100 W. We use a ground tent as the parking at where we live would not allow us to mount a RTT so I have space once I factor in some fuel, recovery boards, my ground tent and a few chairs that I usually thrown on the rack. The idea being for the alternator and solar, or just the solar to get the battery back up on its feet quickly even if we are only driving for a few hours. The portable lithium is a handy device which we will also be using when camped away from the vehicle but could also double up and power the fridge when needed.

 

[67cj5]

Sorry for the delay. I'm not here all the time.
No
The ARB fridge maxes out at 100°F drop. At 140° the fridge will run 100% and will warm up to about 40°

If you want a true freezer, you need more battery and find a way to keep the fridge cool.

My experience is only running fridge overnight. And overnight is cool enough I can sleep. Which means the fridge only runs part time, guessing less than 50% duty cycle. A single battery will not survive a fridge running 100% (freezer)

Well in that case your fridge needs re-gassing, because it says in the manual that it will can handle temps of 122*f or 43*c, And in the Tests I have seen it was put in a Chamber and the room was heated from 25*c up to 60*c / 140*f. and back down to 25*c over a 24 hour period, All the fridges were set to 4*c The ARB 47L temp varied from 1*c to 8*c with an average temp reading of 4.5*c which is 0.5*c above what it was set at NOT set to -18*c / 0*f So if it achieved 4*c when it was set to 4*c in temps of up to 60*c / 140*f then no doubt it could of achieved Sub Zero internal Temps if it had been set lower, So yours either need recalibrating or regasing, There are a few other tricks you can do to make your fridge behave differently,

On Page 50 of your Manual it states that It can Cool 50*c / 122*f below the Ambient Temperature, So seeing as they tested it in Temps of 60*c / 140*f and it still went colder than it's Target temp then your fridge should be able to do the same,

Another thing to note is how you load a fridge has a big impact on how well it cools, You need to leave an Air Gap between your food and the walls of the fridge, If you pack it like you would a Suit case or a card Board box then it will not Cool as well as it should, This is Vital when using them as a freezer.

In fridge mode if you are carry a load of Cokes etc or Beer put a layer of cans in the bottom because the metal cans attract the cold and they will give you longer off cycles so you use less power and then load your food on top of the cans, There are many ways to pack a fridge Some will give you shorter run times and shorter off times and some will give you average run times and longer off times and some will give you longer run times and longer off times and sometimes they can give you shorter off times,

This might all sound a bit daunting but your ARB can keep food fresher longer than any domestic fridge on the market I have proved this over and over using 2 of our most favourite Items having them last up to 10X longer than what a domestic can achieve.

Regardless of what money grabbing sales men/women say, No one in their right mind would ever try to run a 4x4 fridge from a single battery unless it is in the winter months where the ambient temp is around 15*c / 59*f, Much warmer than that is only asking for trouble unless you have a backup plan and Or a Noco Jump pack along for the ride,

But remember we both own the same fridges and so does a 1000 other people here and we could run them all side by side and we would all get different results because of how we set them up, and that applies to every brand on the market, And to date Snomaster are the worst fridges I have come across because there is no way to get them to use less power, Yes they are very fast at cooling but they eat Batteries, and the compressor Rattles will drive you nuts even in a 4x4 let alone in a vehicle more quieter.

Hope that helps.

 

[vomhorizon]

Regardless of what money grabbing sales men/women say, No one in their right mind would ever try to run a 4x4 fridge from a single battery unless it is in the winter months where the ambient temp is around 15*c / 59*f, Much warmer than that is only asking for trouble unless you have a backup plan and Or a Noco Jump pack along for the ride,

Are you saying that it would be impossible to do so without killing the battery for EVERY possible use case? Are you referring to just running it off of a starter battery, without solar and for extended periods of time without turning the vehicle on? I'm just trying to figure out what an efficient 40L fridge will draw over say 12 hours of no solar and/or no alternator. 20 Ah? 30Ah? 100Ah? There has to be a reasonable range and if your main AGM can support that you should be able to replenish that the next day by using solar or running the vehicle (or both). Threads here that go back 5 or more years provide a pretty decent average range given various combinations of ambient temperature and usage. They usually range from 28 Ah per day to 40 Ah for an Engel 45. Let's assume that you are 15 hours without solar or altnerator (evening through the next morning). This depletes your battery between 18 Ah and 25Ah from night time usage. Why would you need to jump start the battery the next day if you have a 90 or 100 Ah battery? Just not sure whether I'm missing something here given that folks here on this forum seem to be able to meet their fridge needs off of just one Group 27 or Group 31 battery (for a couple of days between charges) and I'm pretty sure they aren't just using it in the middle of winter.

 

[67cj5]

Are you saying that it would be impossible to do so without killing the battery for EVERY possible use case? Are you referring to just running it off of a starter battery, without solar and for extended periods of time without turning the vehicle on? I'm just trying to figure out what an efficient 40L fridge will draw over say 12 hours of no solar and/or no alternator. 20 Ah? 30Ah? 100Ah? There has to be a reasonable range and if your main AGM can support that you should be able to replenish that the next day by using solar or running the vehicle (or both). Just not sure whether I'm missing something here given that folks here on this forum seem to be able to meet their fridge needs off of just one Group 27 or Group 31 battery (for a couple of days between charges) and I'm pretty sure they aren't just using it in the middle of winter.

I would never run any of my fridges from my Starter battery, And if you hook up a solar panel to your starter battery you could end up doing damage to the vehicles electrics because you should never charger a starter battery with it still connected to the vehicle,

If where you are going gets full sunshine for most of the day you could get by with a single battery of around 100Ah+ when hooked up to a 100w Solar panel, For every Ah of battery power you have you want at leased 1w of solar power, 120w would be nice 150/200w would cure all your future problems should you need more power,

Look at it this way, you have a 100Ah Battery but when the ambient temps get right up there any fridge can use up to 60/70Ah+ per day, @ 70Ah per day your battery is now down in the danger zone of 30% SoC which is what my batteries are rated to being 30% at 600'cycles, A 100w panel can put out around 5.56Ah X that by 6 is 33.36Ah going back in the battery, A 150w panel will max out at around 8 or 9Ah @ 8 Ah = 48Ah going back in the battery, If you get 8 good hours of sunlight then you are going to get around 64Ah back in the battery, These are all extreme figures including the fridge draw figures, In reality a fridge in hot temps is going to draw around 40 to 55A So in order not to take the batteries down too far 2X 100Ah batteries would be a good starting point to give you some reserve power to carry you over if you don't get the Solar hooked up first thing in the morning, So a 150w Panel and 2X 100/120Ah Batteries is what I would looking at,

A lot of folks also run DC to DC chargers for their second batteries as well as solar, I do not use my Starter battery for anything but starting, I have 2X 110Ah Batteries plus another for a spare and I also have 2 Dometic Lithium PLB-40 Packs plus other power options if needed.

In cooler Climes A fridge can use as little as 8Ah in 24 hours, But in hot climes try to keep the fridge cool and well ventilated and you can half it's power draw, Ok.

Hope that helps.

 

[vomhorizon]

y, And if you hook up a solar panel to your starter battery you could end up doing damage to the vehicles electrics because you should never charger a starter battery with it still connected to the vehicle,

This is interesting and a contradiction to what most everyone here has said and what I've been able to find on the net while specifically looking at whether solar and alternator charge can co-exist. In fact there are members here who have been running this set up for a number of years. I have yet to encounter anything that suggests that an MPPT concurrent to the alternator will damage the vehicles electrics. Could you point me towards something to that end if you have come across something?

 

[67cj5]

This is interesting and a contradiction to what most everyone here has said and what I've been able to find on the net while specifically looking at whether solar and alternator charge can co-exist. In fact there are members here who have been running this set up for a number of years. I have yet to encounter anything that suggests that an MPPT concurrent to the alternator will damage the vehicles electrics. Could you point me towards something to that end if you have come across something?

Well the Alternator is made to put power out, when you hook up a solar panel you are forcing power back down the system, that's not good for the alternator, And If this is not True then why Does the Hand book and every vehicle manual tell you to disconnect the Battery before charging, Also if such people know better than the Motor Companies they Why have these Motor Companies not offered these people a Job,

There is a good reason why it says disconnect before charging, and just because some do it does not make it right It can work fine doing that a dozen times but there comes a point when it says enough is enough and a 1000 miles from no where is no time to find out the hard way.