Help me design my solar/battery bank for camper

[Joe917]

Flat mounted panels produce plenty of power, you may have issues in Alaska. In overcast conditions there is no advantage to tilting.
Any hard shadow on a panel well affect output.


Flat mounted panels will make very little output in the winter months due to low sun angle. Even less if there is equipment casting shade on them in the morning or afternoon.[/QUOTE]

 

[swduncan]

I started out thinking that 100w & OEM battery in the truck was plenty for my ARB 83qt fridge, but several days on a beach last year and a few days in moderate shade since have changed my mind. On the beach the fridge was using upwards of 800wh a day - that's with kids opening it, cycling lots of water through it to get it cold, etc. so surely at the worst case end of the spectrum. But, that's why we got a fridge instead of a cooler - to make warm things cold. The panel was putting out 75 to 85 watts, when I kept it aimed, but between the mist and blowing sand and heat it was not as panel friendly as you might think. Plus we were in a remote area and killing the battery was a bit riskier than usual, so it all added some stress to an otherwise awesome trip.

Since then I've had two trips where because of weather or trees there was less than full sun and had to fiddle around to keep the fridge running. In one case I had to wait for the panel to recharge the truck enough to start in the morning - only took about 20min, but I don't need that.

I just added 100w, and a small SLA battery so I can separate from the truck if I want to. I'm not going to do dual battery in the truck, and I'm waiting for the lithium batteries to drop a bit more before I make a larger power pack. While time will tell I think it will work better.

You do not need 200-400w of solar for a 50L fridge and a few LEDs. That's insane. Nor do you need dual 6v golf cart batteries. Waaay overkill. But some guys here love overkill so whatever. 100w panel and a Grp 27 or 31 AGM or Lead Acid will handle that all year long unless you park in the forest everyday in which case you need to move no matter what batteries or panels you have.

He's in Phoenix. It's sunny everyday for a long, long time. lots o juice to recharge.

If you have the room and dollars to burn go with dual golf cart batts and 200 watts because that combo is cheap these days and never think about it again. But I'd be surprised if you ever, ever get below 75% charge.

 

[Bayou Boy]

I started out thinking that 100w & OEM battery in the truck was plenty for my ARB 83qt fridge, but several days on a beach last year and a few days in moderate shade since have changed my mind. On the beach the fridge was using upwards of 800wh a day - that's with kids opening it, cycling lots of water through it to get it cold, etc. so surely at the worst case end of the spectrum. But, that's why we got a fridge instead of a cooler - to make warm things cold. The panel was putting out 75 to 85 watts, when I kept it aimed, but between the mist and blowing sand and heat it was not as panel friendly as you might think. Plus we were in a remote area and killing the battery was a bit riskier than usual, so it all added some stress to an otherwise awesome trip.

Yea, if you've got kids going for drinks in the fridge that'll kill stuff fast. We only do food in the fridge. I keep a Yeti 50 with a good slurry going for drinks. Beer tastes better out of an ice slurry anyway.

 

[john61ct]

Also loading warm stuff in the fridge should mean 100% cycling for many hours, can take 24hrs without opening to get back to normal.

For that scenario I'd go with multiple boxen.

On a budget maybe the drinks / all-day opening one could just be a cooler with frozen water jugs, the other a big freezer only gets opened 1-2 times per day.

At some point in cost / space / weight you need to realize compromises are required being mobile, not all home luxuries are worth trying to duplicate on the road.

 

[Bayou Boy]

At some point in cost / space / weight you need to realize compromises are required being mobile, not all home luxuries are worth trying to duplicate on the road.

Wise words right here. Camping is not the same as cooking at home with your 36" wide all fridge.

 

[1Goat]

I have a 50lt NL, running off an old 100a/h batt, attached to a 100w panel (through a controller) for 3 years and have never run out or had to charge the battery.

Sent from my SM-G950F using Tapatalk

 

[Joe917]

I have a 50lt NL, running off an old 100a/h batt, attached to a 100w panel (through a controller) for 3 years and have never run out or had to charge the battery.

Sent from my SM-G950F using Tapatalk

How often do you move? (vehicle charging)
How long do you go out for?
How many times a year do you use it?
All makes a huge difference.

 

[1Goat]

How often do you move? (vehicle charging)
How long do you go out for?
How many times a year do you use it?
All makes a huge difference.

The fridge/batt setup is in my camping trailer. The trailer is connected to the 105 whilst towing only.
Twice a year we camp in 1 spot for 10 days. Don't move. I remove the solar panel and keep it in the sun with extension cord I've made up. Same when the trailer is parked at home. Fridge is off but batt connected to solar panel.

Sent from my SM-G950F using Tapatalk

 

[1leglance]

According to an older Overland Journal article I found the NL 50L Twin uses 45amps/24 hours, that means if I use the National Luna Power Pack I already own with a Duracell FLA Deep Cycle which is 105 AH, then I am good for overnight as long as I get sun during the day on the solar, or drive/run truck for a while.
If I hold to the 80% rule then I am in trouble without sun after 24-36 hrs unless I drive.

The AGM batteries don't seem to offer more Amp/Hr and I am worried about charging profile out of the National Luna Power Pack and Victron 75/15 Solar controller....

I would prefer 1 battery after seeing how much 2 Golf Cart batteries weigh....

 

[john61ct]

There is no fixed AH/day number for a fridge or freezer, too many variables fluctuates widely.

Battery weight per AH is basically fixed for lead, in fact heavier the better.

LFP is lighter but costs 5-7x more.

2x 6V GCs 200+AH is the minimum I would use for a fridge powered by mostly solar.

If you had a genny you didn't mind running every cloudy day, get away with less, but still need solar to get bank longevity.

 

[swduncan]

Yes, for drinks a cooler and ice + water is the way to go! Space is at a premium for us and as the only beer drinker I settle for cycling cans through the fridge.

Usually the making warm things cold part happens on the long drive between places where power and opening is not an issue. Looking back on the beach trip I wish I'd brought some insulated containers (hydro flask or the like) because that would've helped a lot with the frequent opening. We have them now

Yes, it was running 80+% of the time, based on the WH records from the Victron charger. I had it set to 34F. We had very cold water, and I never felt the food was at risk. We had three 1l nalgene bottles that we rotated - one drinking, two cooling. The fridge met high expectations. It was the solar + battery that was edge case.

The big discovery for me was how far reality was from the math. For example the ARB draws about 4 amps nominally, and that was what I had in mind when sizing things. But that is at full voltage. At 12v it's closer to 5-6 amps, and below 11.5 you can be looking at 7+. This means that getting the battery low is not just bad, but bad^2. This is why so many AH for the battery. The voltage drop as the battery drains can be a killer.

I'm not concerned about abusing my cheap deep cell that I got to use with the fridge, so I'll give the 200w a try for a while and then decide what to do next.

Yea, if you've got kids going for drinks in the fridge that'll kill stuff fast. We only do food in the fridge. I keep a Yeti 50 with a good slurry going for drinks. Beer tastes better out of an ice slurry anyway.

 

[Bayou Boy]

I see you have a Ram. An Rtic 40 soft ice chest fits perfectly between the center console and the back seat if you are only traveling with 4 people. We do that a lot on road trips.

 

[1leglance]

So 2 6v Golf Cart batteries will give me 235AH for 136 lbs of battery wgt.
The Blue Sea M-ACR and Victron 75/15 will give me the ability to have the factory alt charge things and the solar keep things topped off if I understand correctly.
At least with extra power I can add the cellular booster I have been thinking about

 

[john61ct]

Well on your way! That SC will handle 220+W just fine, even 250-300W if you get a crazy good deal on panels, just giving up a little rare peak output.

Make sure to get the FLA Duracell GCs, not sealed.

With the ACR make sure to size fat enough cables to minimize voltage drop.

With the CTEK you can do a longer run of thinner wire, but at lower current, slower charging.

 

[pdavitt]

This is also why multiple smaller panels can be better than one large panel since you can wire it up so that shade on one does not take them all out.

I agree. The optimal panel setup for "12V" panels is four, two panels in series with those two groups paralleled, if you have the roof real estate. With a good MPPT charge controller you want the panel voltage to considerably higher than the "Battery Voltage"
A standard 12V panel has a Vmpp of around 17-18V so two of them in series will give you panel voltage of about 34-36V, which is perfect for a MPPT controller charging a 12V battery system. Why? The higher the panel voltage the sooner battery charging can start.
Most MPPT chargers have a "start charging" voltage. With Victron equipment it is Vbat + 5V, not sure about other brands. You may not get much during the early morning or late afternoon, but you'll get something.

Hope this helps,
Pat