Charging Trailer Batteries with VAN Solar System

[FloridaNativeMike]

Your best bet appears to be to replace the absorption fridge with a 12v compressor fridge. If not using the absorption on propane, then a 12v compressor fridge is a far better option with far less current draw.

-Mike

[Craig Alan]

No, you DON'T have a lot of solar. At least not when we're talking powering a fridge.

When running at 12v your fridge draws about 10 amps, or 10 amp-hours/hour. Unfortunately, we need to run our fridges about 24 hours per day. That makes 10 amp-hours/hour x 24 hours/day = 240 amp-hours/day. Your trailer has 2, 70 amp-hours batteries (lead acid, I assume) that you don't want to run much lower than 50%, providing about 70 amp-hours of the 240 your need per day. Your lithium batteries can be drawn to 75%, giving you another 150 amp-hours. Together, your batteries provide a total of 220 amp-hours/day, which is about 20 amp-hours shy of what you need for JUST THE FRIDGE.

[Aside:
Hmm...I wonder if that fridge calculation includes the 0.5 amps required to run the control circuitry? If not, that's another 0.5 amp-hours/hour x 24 hours/day = 7 amp-hours/day.]

If you figure out the cabling, etc. I suppose your proposed solution would be maybe-sorta-but-kinda-iffy solution. Rain and clouds will dampen your plan, as would all the other electric draws (parasitic and useful) you probably want to fulfill.

I've read that average solar RV'ers use 75-150 amp-hours/day day. My wife and I own a 17-foot Casita and limp by with 200 watts of solar and a single 85 amp-hour lead acid battery (curse you, Casita, for making a 1-battery enclosure when there's room to make a second bay just to the rear of the factory bay). We conserve as best we can and rarely drop below 50% discharge, using 40-50 amp-hours/day. If inclement weather is in the forecast, we spend a night at a campground or RV park to charge with shore power, fill the water tank, and dump the other tanks. We also bask in the air-conditioning for a night.

Eliminating the big electric draws is possible. Namely, we kiss goodbye the A/C and microwave, running the fridge, water heater, and furnace on propane. The remaining big draws are things that have moving parts - fans especially. I learned my CPAP draw can be reduced from 5-6 amps to 2-3 amps by turning off the humidifier and heater. After a couple weeks of getting used to this configuration, I'll never go back - even at home.

The other major electric draw is for recharging our electronic devices. We've learned to charge in the tow vehicle when the next day is a drive day, and also to charge using the "extra" solar capacity that is unused on many mid-late afternoons when charging is in it's final stages. My Bogart Engineering Tri-Metric battery monitor tells me how many watts are going unused. I love that device.

As others have said, there is is ONE BEST ANSWER to you issue. Explore your hesitation with propane and see if you can overcome your reservations. You'll never look back.

[redbarron55]

The above post is correct.
Either use propane or swap for a compressor fridge.

I have 300 watts of solar on the Scamp roof and while it will charge the batteries fairly quickly there is not enough power to just willy nilly blow through it.

I would like to have a nice LiFePO4 battery setup with maybe 150 Ah capacity, but I don't.

I have a compressor fridge and when dry camping in national parks it seems that we are always in the deep shade. Perhaps out west where there are fewer trees it would be relatively easy to maintain reserves.

My wife is also against LP in the trailer itself (heaters, ovens cooktops etc.) so the tankless water heater is mounted on the tongue with no other appliances.

We do have a dual fuel ,LP or Gasoline, inverter generator that we can use the second LP tank to power when we need it. That directive about LP gas is why we have a compressor fridge! Plus it cools better and while driving down the road. We usually have enough sunlight on the solar panels while traveling to easily keep the batteries charged, especially since we also have the +12 Vdc from the TV. The solar would do by itself, but it does make up for the voltage drop on that circuit.

[Defenestrator]

Looks like the fridge in the Parkliner might be a bit small with no separate freezer compartment? 600W of solar might actually do the truck on cool sunny days, depending on what else needs power. Searching around, it seems that's a relatively small fridge with no freezer? That might only need around 150W to keep it running and run a bit lower duty cycle than most, like 50-70% on a cool day. On the lower end of that, you need 1800Wh/day, which works out to around 360W worth of panels. On a hot day, you'd need 720W of panels just for the fridge. Similarly, in the winter the panels might produce only about half as much power and you're falling well short.

So.. for the most part it'll be enough to cut your propane usage a fair bit, but not enough to actually run the fridge off of solar power alone. If you want to run it off solar I'd say step 1 is to replace it with a compressor-driven fridge that'll be significantly more efficient. At least 3x, and maybe more like 10x.

[Huck]

Originally Posted by redbarron55

The above post is correct.
Either use propane or swap for a compressor fridge.

I have 300 watts of solar on the Scamp roof and while it will charge the batteries fairly quickly there is not enough power to just willy nilly blow through it.

I would like to have a nice LiFePO4 battery setup with maybe 150 Ah capacity, but I don't.

I have a compressor fridge and when dry camping in national parks it seems that we are always in the deep shade. Perhaps out west where there are fewer trees it would be relatively easy to maintain reserves.

My wife is also against LP in the trailer itself (heaters, ovens cooktops etc.) so the tankless water heater is mounted on the tongue with no other appliances.

We do have a dual fuel ,LP or Gasoline, inverter generator that we can use the second LP tank to power when we need it. That directive about LP gas is why we have a compressor fridge! Plus it cools better and while driving down the road. We usually have enough sunlight on the solar panels while traveling to easily keep the batteries charged, especially since we also have the +12 Vdc from the TV. The solar would do by itself, but it does make up for the voltage drop on that circuit.

I don't believe it is correct because it leaves out the 800 watts of solar panels.

[Huck]

Originally Posted by FloridaNativeMike

Your best bet appears to be to replace the absorption fridge with a 12v compressor fridge. If not using the absorption on propane, then a 12v compressor fridge is a far better option with far less current draw.

-Mike

I will probably compromise and use both propane and dc. The problem I have run into at the beach on several occasions is the wind blows the pilot light out on the refrigerator.

So I will probably use propane unless the wind is a problem and then I can switch to DC. If I could find a compressor fridge that would fit in the same space as current refrigerator, I would probably swap it out.

[Lynn Eberhardt]

So, back to where we started, only now you know more about batteries and capacities than when we started.

Keep in mind that most 3 way fridges are constantly on when operating on 12 volts. That is because on and off high amp dc switching tends to cause arcing that welds the switch contact points together. Operating a 3 way fridge on electricity would probably use less power overall on 110ac from an inverter, even considering conversion losses. Just watch your battery levels.