Realistic Expectations of Solar/Fridge Setup

[jimbono]

Howdy! I’ve read a ton of threads already in setting up my solar and fridge for my vehicle. I think I’m headed down the right track but if you have any input or suggestions on if I’m having realistic expectations that’d be great.

So, here’s what I have now:
2005 grand Cherokee, single group 94 starter battery.
Dometic CFX 40w fridge
Renogy 100 watt panel, with their “wanderer” 30 amp PWM charge controller.
NOCO gb40 jump pack

I don’t really run anything on battery except the fridge from the rear 12v outlet. I am not shy about making a direct to battery connection if it would be better.

Currently without solar, and the low voltage disconnect set at 12.1 volts (the “high” setting) the fridge will not make it overnight set at 34 degrees. I’m not sure I want to drain my battery further as it is my starter battery.

I will be installing the renogy panel under my roof rack (which is loaded when going on trips, unloaded when parked) and am debating on whether I need to be able to slide it out from under the 1/2” round bars that make up the roof rack or if it will be OK generating power underneath. I’m thinking the ideal setup is to set the panel up away from the vehicle and aim at the sun...but that is too much hassle for me and I won’t be doing that. I’d rather have ice in that case.

So, realizing that my fridge will be off due
to low voltage in the morning, is it reasonable to expect the solar to be able to charge the battery and run the fridge during the daytime from the rooftop? The temperature in the fridge is still sub 40 degrees when I turn the vehicle on so I know nothing has spoiled. I would like to keep it on as much as possible. I live in sunny Nevada, and I do camp in the sierras quite a bit where the vehicle may not be in the sun for the full 12+ hours of daylight right now.

The reason I decided on solar was that I don’t always drive every day to keep everything charged up, and just doing a dual battery night leave me in a similar boat. Also, space is tight. I don’t have any room under the hood so I’d have to rig something up under the car somewhere and there’s not a lot of room to work with. It’s a small vehicle on the inside and I have 1 child and a dog along with myself and my wife. I realize that ideally I ALSO install a house battery to give me the best of both worlds, but I’m wondering if the solar will be enough. It’s cheaper to just do one and I figured it was a good start.

Does anyone have experience using solar/fridge with just a starter battery? Is 12.1 volts still too much of a regular drain on my starter battery? Do I just need to buck up and install a 2nd battery? I did check with a volt meter and the voltage that the fridge is reading is dead on to what I get at the battery. I checked the fridges reading using the dometic wifi app.

Thanks for all of your advice. This forum has so much information and inspiration for these kinds of projects.

 

[luthj]

I don’t really run anything on battery except the fridge from the rear 12v outlet. I am not shy about making a direct to battery connection if it would be better.

Absolutely, the 12v cigarette style plugs are mostly useless. Use another type, just about anything is better. Or just use a direct connection.

I will be installing the renogy panel under my roof rack

Solar panels cannot tolerate any shadows, period. Even the narrowest of shadows can cut a panels output by 50-80%.

A group 94 battery will have about 75AH if you buy a deep cycle flavor. Do not bother with starting only batteries, they simply will not last being cycled more than 10% regularly.

A decent battery should start your van at 50% SOC. So that gives you 38AH usable capacity assuming your battery gets fully charged during the day (a big assumption).

Fridge power usage varies dramatically with temperature and loading. A rough estimate is a duty cycle of 50%. At 40W, that is 1.75AH per hour. So 21AH over night approximately. So in theory a good deep cycle 94 battery should be okay. If you can experimentally measure the duty cycle of your fridge you can get a better estimate. Some units will only run 25% of the time, some will run 75%.

At 12.1V resting, your battery is 50% discharged. For a starting type battery with spongy lead plates, that is going to kill it in 100 cycles or so. You need to confirm if your battery is actually at 12.1V or not though. If you have significant voltage drops in your wiring, the fridge may be cutting out way early. Ideally you want 1% or less voltage drop on your fridge power feed.


Now, on to charging. A 100W panel can recover 3-4AH per hour in ideal conditions while still running the fridge (panel aimed at sun, no shadows). In order to get to 100%, you will need the depth of discharge recovered, plus another 2 hours of charging to get to a true 100%. So at 50%, that is 38AH/4= 9.5 hours +2 = 11.5 hours total. Charging from the alternator can take care of the bulk stage pretty quickly.

What is your alternator voltage at the battery? If its over 14.0V, you can expect decent charge rates.

Ideally I would suggest going with a large battery. Can you fit a larger battery in the starting position? A 100AH battery would be better.

 

[jimbono]

That’s good to know. After a lot of reading I was thinking the battery was still going to be holding me back.

My voltage at the battery when the vehicle is running is 14-14.1 volts so it should charge just fine. I have a 160 amp alternator. I haven’t found anything on how long the alternator needs to be running to give a bulk charge? I’m sure the only accurate way is to measure but a general rule of thumb would be a helpful starting point for me.

As for a larger battery, I’m not sure really. The group 94 battery is really big and fills its space pretty tightly in the engine compartment.

Would something like a 2nd deep cycle battery connected with a blue sea ACR be a better route to go? I think I am mainly worried about the charge time with an alternator needing me to drive for a few hours every day. I wouldn’t mind abusing the heck out of the deep cycle battery to get more AH out of it and have to replace them in 2 yrs vs 5 kind of thing either so maybe that route makes more sense.

That and I think I’ll make sure I can slide the panel out from the rack. I guess for a longer stay of 5 days removing it isn’t that big of a deal, but I’d surely want to be able to stay out for 2-3 without that extra step.

 

[Willy G]

Also, with shade brought to light..... Its best to keep the Vehicle out of direct sunlight, to keep the solar heat gain lower, so having a detachable solar panel isn't a bad idea either.

If you plan on using it for 5 days straight, I would highly recommend 1 or 2 deep cycle batteries.

 

[luthj]

A separate deep cycle battery with beefy alternator connection and 100+ watts of solar would be the recommended approach. A deep cycle battery will last 10 times longer in such an application. The challenge is of course finding space for it.

The alternator will never really get a deeply cycled battery to a true 100%. But for the 99%, the charge time will vary with SOC and the batteries design (as well as the wiring). You will see C/4+ rates of charge up till about 80-85% SOC, from there the current tapers rapidly to about .04C at 99% SOC. So at 50% discharge on a 100AH battery, you can recover to 85% in 1.4 hours or so conservatively. It may be faster for lower resistance batteries. You still need solar to get them fully charge, as the batteries will need held at 14.4-14.6V (depending on brand) until the current drops below 2% of C.

For faster charge rates you could opt for a DC-DC charger like CTEK or STerling. They are expensive though.

 

[jimbono]

Are there any deep cycle batteries that I can install on their side? Or maybe 2 smaller batteries that I can connect in parallel and squeeze in separate small spaces?

I see a lot of people using group 31 deep cycle batteries, I think they are roughly 13”x7”x10” (just a hair under then add some room for connections). That’s a little bigger than my current battery. I think I could fit two smaller batteries if I put one under my starter battery and another on the other side of the engine compartment, although I can see how adding more wire to connect them is not ideal. Or I can fit something a little smaller under the frame in the back, though I haven’t measured yet. From what I’m reading the 12v batteries are larger size=more AH and there isn’t really a way around that.

I see some SLA deep cycle batteries but they look like bigger versions of the batteries in UPCs and im not sure if they are a good option? Or should I look for something that looks more like the standard auto/deep cycle in an AGM format?

 

[luthj]

AGM can be side mounted. The more expensive AGM batteries sometimes offer better capacity in the same footprint as flooded lead acid.

Underframe mounting can provide a reasonable option. If you're going to be using two batteries in parallel ensure that they are the same size age and brand. There's nothing wrong with using two batteries in parallel. It is important that if they are far apart to balance the wiring so one doesn't get more load than the other, that is possible even over large distances if necessary.

Brand reputation is much more important than appearances. As mentioned in other threads if you have the space the best value right now is 2x6V GC2 batteries by Duracell a.k.a. Deka sold at Sam's Club and batteries plus. 200$ or so, and bulletproof.

 

[Willy G]

AGM can be side mounted. The more expensive AGM batteries sometimes offer better capacity in the same footprint as flooded lead acid.

Underframe mounting can provide a reasonable option. If you're going to be using two batteries in parallel ensure that they are the same size age and brand. There's nothing wrong with using two batteries in parallel. It is important that if they are far apart to balance the wiring so one doesn't get more load than the other, that is possible even over large distances if necessary.

Brand reputation is much more important than appearances. As mentioned in other threads if you have the space the best value right now is 2x6V GC2 batteries by Duracell a.k.a. Deka sold at Sam's Club and batteries plus. 200$ or so, and bulletproof.

This is probably what I will be doing in the future.

OR you could spend the $200+ on one Oddessy battery. and mount it anywhere.

 

[Charles R]

The diesel version of your Grand uses an H8 AGM battery with 95AH rating. if you look at your plastic battery tray, there's a small tab/nub that aligns the smaller gasoline engine batteries. shave that down and you can put the bigger one in. That's what I've done with my own Hemi Grand

I've been building up parts for my own solar setup recently, but I've been running a Dometic 28L (I keep mine at 39F) on battery alone for 2-ish years now. I'm in the San Francisco south bay area, so I'm not dealing with your temps, so anything I say has to keep that in mind. I use my jeep daily. My fridge is where I keep my weekly lunch stock, and it's never off, and never empty.

I've always known the rear cig plugs kind of suck. I noticed early on that the fridge would never really make more than a half-day without going into an energy saver-ish mode. So I experimented with setting my unit to the lowest voltage cut. It works very well for me. I recently started thinking I had hurt the battery over time, because I could tell the starting (in my CRD, where the fridge lives) seemed a little more strained... but in replacing it with a new one of the same brand, (autozone Duralast Platinum/Deka) I noticed there's no difference. Further, that suspected battery is now in my Hemi, which along with the fridge I'm using as a daily driver while I do some repair and upgrades to the CRD. It's showing no signs of any weakness whatsoever.

That said...

The fridge will still not run for more than 24hours-ish without running the Jeep. So my solar plan is a Renogy eclipse 100w, that I'll mount right up near the sunroof at the front of a rack I'll build. I have a redarc dual input DC-DC charger, and I'll run a second AGM H8 house battery. I think for my purposes that will keep the fridge (pretty much my only draw) running well even if I've parked the Jeep for a few days.

 

[luthj]

AGMs are pricey, so if you can fit and water a deep cycle flooded, I would go that route. With a second bank seperated by an ACR or DC-DC, there is not need to match the batteries.

A 95AH deep cycle battery in the starting position would be acceptable. Generally flooded deep cycle batteries may not have the needed CCA (gasoline engines need less). AGM deep cycles will often have no trouble providing CCA needed (even if they don't actually list a CCA value in the specs).

 

[Charles R]

I just like the redundancy of the house and the starter being the same. Plus... I've made it the same for all in my herd of piles.

 

[jimbono]

So my solar plan is a Renogy eclipse 100w, that I'll mount right up near the sunroof at the front of a rack I'll build. I have a redarc dual input DC-DC charger, and I'll run a second AGM H8 house battery. I think for my purposes that will keep the fridge (pretty much my only draw) running well even if I've parked the Jeep for a few days.

Where are you going to put your 2nd battery? I’ve seen on the CRD putting it in the rear left quarter panel, but on the gas engines the evap canister is back there. I could probably put something on the right side but it’d be right above the exhaust pipe, might be hard to get in and out.

Sounds like a second battery is really the way to go here. The solar can help keep things topped off but using the current starter battery won’t really suffice for draining down to 12.1 volts regularly. I’ll try and stick the biggest battery I can somewhere and if I have to find two smaller ones. The starter battery now is almost brand new so id rather install a dual vs replacing this one altogether anyway.

Thanks for the tips. I’ll be sure to post anything I come up with. I’ll install my solar first while I have it and figure out the dual battery as I go.

 

[matt922]

I have a similar setup as you but probably a smaller battery. Mine currently has a group 24 batt and also a noco gb40 for backup. If you set the fridge to medium protection your rig will start just fine without the help of the noco. There are problems with voltage drop over 15ft so obviously having 12 awg or larger will make a big difference. We were able to get a solid 12-14 hours like this, but weather was favorable 65ish during the day and near freezing by the time we woke up in the morning.

The rear outlet on our 4runner wasn't up to the task of handling the fridge and would cause voltage to drop to 10.5 volts under load while the vehicle was running. The 10awg line i ran made all the difference. I also used a bluesea panel with a voltmeter, usb, and a cig outlet for the fridge so i could occasionally keep my eye on it. If you have the black/gray dometic cfx you may want to download the app and look at the voltage the fridge is reporting as i found it to be a bit lower than what the battery actually had.

 

[Charles R]

For my project, the house battery will be inside the cargo area, at the right rear corner. I've removed all those plastic trim panels, and will be building a camper style interior.

Although.... The area right in front of the fuel tank, behind the trans crossmember, looks to be a nice spot if I was to lay the battery on its side and build some protection for it.

 

[jimbono]

We were able to get a solid 12-14 hours like this, but weather was favorable 65ish during the day and near freezing by the time we woke up in the morning.

If I’m camping in the sierras, the weather is almost always like this. That’s where I think solar will have a hard time with the shade, but at least the temperature differential is much lower.

If you have the black/gray dometic cfx you may want to download the app and look at the voltage the fridge is reporting as i found it to be a bit lower than what the battery actually had.

I used the app and compared to the battery directly, and they were exactly the same. It cut off at 12.1 as well according to the battery measurement, and while running they read the same as well. I’m not sure if that means hard wiring/upgrading the wiring will make any difference or not? It sounds like good practice to do so anyway, so I might do it just to do it “right” but I’m not sure if I’ll see any changes.

For my project, the house battery will be inside the cargo area, at the right rear corner. I've removed all those plastic trim panels, and will be building a camper style interior.

Although.... The area right in front of the fuel tank, behind the trans crossmember, looks to be a nice spot if I was to lay the battery on its side and build some protection for it.

Hmm...I’ll have to take a look by the fuel tank tomorrow. How much room is behind the plastic trim panels in back? Do you think I could cut out a portion and tuck most of the battery in either side? Or is it going to stick out majorly either way?

My only real gripe with the WK grand Cherokee is the interior space, it gets right real quick. Makes for good packing and always trying to balance the size of what we carry, but it’s going to be hard. We did a 1 week trip with 4 adults through all of the national parks in Utah last year and using our backpacking tents/sleeping bags we were still comfortable. The roof rack was full and so was the back though! Now we have an infant and will probably be bringing our dog more often so space seems tighter now. I don’t mind downsizing but I also love camp gadgets as their own hobby, it’s fun to make it just a little nicer each time we go out