Solar Questions

pianotuna wrote:
Hi RJsfishin,

I get 17 amps from 256 watts of panels, if the battery bank is hungry enough. Mppt controller, and series/parallel wiring is what it takes to do so.

RJsfishin wrote:
Quote: I read that you can get approximately 30 amps from a 100 Watt solar panel,
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Dream on !! It has to be a very good day if I ever see 18 amps from my 3 100 watt panels. You will seldom if ever see 8amps per panel

I do believe the OP meant 30 amp hours per day with a 100 watt panel , not 30 amps per panel.

Sorry I made a typo....Boob Docker, you are correct, I read that you can get 30 AMP-Hours per day and not 30 Amps from a 100 Watt panel.....my bad. Is that a realistic assumption?

We have the typical RV propane/electric Dometic frig. The manual claims it draws 3 amps of DC power. I assume that is the DC draw when using propane....correct?

As for my power calculation, I wasn't planning to run the heat all day, just a couple of hours in the evening and morning if needed. We also have a small propane heater that we could use also. Having said that, we have no intention of camping off grid in really cold weather.

If we do get lithium batteries, I was planning to install them inside the trailer somewhere, possibly into the bottom of a lightly used cabinet or under the bed, but not outside. I know that I'd have to run all new wires. I read that these types of cells don't give off gasses like lead acid cells and they don't like to get very cold. So I thought putting them inside wasn't a bad idea. I also read that most lithium batteries have battery management systems (BMS) built in to them that allow you to almost fully drain the battery. From what I read the BMS will shut the power down before any damage can occur to the cell. So I was thinking that I count on getting 80 to 90 amp hours from a 100 AH cell. Is that not the case?

Based upon some of your responses I re-looked over my numbers thinking that I was way too high. Unfortunately I didn't have the frig running 24 hours, so my estimate went up! My new calculation is 180 Amp-Hours per day, so I'd assume 200 AH for safety. I included my power estimate below. I got most of power consumption numbers from the manual or off the appliances directly. Our TV and DVD only gave AC watts, so I had to convert them into DC watts. I read somewhere that you can get a fairly good approximation of DC watts by dividing the AC watts by 0.80. Is this true? So our TV and DVD draw a total of 72 watts of AC power. 72/0.8 = 90.75 DC watts. DC Amps = DC Watts/ 12 Volts. So 90.75/12 = 7.5 amps of DC. So if watch TV for 4 hours that equates to 30.25 AH of DC. If these number look off (high or low) let me know. The frig and the furnace seem to be the real draw. We are relatively new RVers so we're still learning.

TV & DVD = 30.3 AH (using and inverter for 4 hours)
Misc Lights = 5.0 AH
Furnace = 48.0 AH (4 hours at 12 amps)
Dometic Frig = 72.0 AH (24 hours at 3 amps)
Water Heater = 6.0 AH (6 amps for 1 hour)
Water Pump = 7.0 AH (7 amps for 1 hour)
Power Vents = 5.0 AH (5 amps for 1 hour)
Misc loads = 7.2 AH (LP and smoke detector, power awning use, antenna booster, etc)

Total: 180.5 AH

Assuming my power estimate is reasonable, how many 100 AH lithium batteries be needed to handle that load?

I am leaning towards a MPPT controller and pure sign wave inverter for the TV and DVD player, but I don't have any details on which I'd buy.

Lastly, I should have mentioned that we are definitely getting an inverter generator within the next few months. I'm leaning towards a 2000-2500 Watt unit just so I can lift it. The larger units (3000 Watt and up) are just too heavy. So I may even buy two smaller units and run them in parallel, so have AC.

I'm just starting to investigate solar and Lithium batteries. I agree that lithium's are so so expensive right now, I keep hoping that the prices to come down.

Thanks for all of your info!

"I am leaning towards a MPPT controller and pure sign wave inverter"

Good choices....my choices! lol

A fridge on propane pulls about 17AH per 24 hours.

Your daily AH use will be about 75AH for the intended day as described. No way will you be using 200AH.

The long thread on lithium (Battle Born) seems to have decided not to use so much of its capacity daily, but to do more like 20-80s (60AH from a 100) so you want two.

You could do it all with 200AH of AGMs as your bank and still keep them inside the rig. No gassing with them unless you way overcharge them and blow their vents (not very likely you would be that careless)
Why spend so much to get lithiums??? It won't make camping any better. You just want 200AH worth of battery bank.

Well 17 AH per day for the frig is heck of lot better than my calculation! Don't get me wrong, I think your number is correct. I can't see the frig drawing 3 amps all day for 24 hours. I can't imagine that the frig controls and light draw that much power.

Again, what is wrong with running the fridge on propane like 99% of us when not plugged in?

Lwiddis wrote:
Again, what is wrong with running the fridge on propane like 99% of us when not plugged in?

Absolutely nothing... Isn't that the idea? I was not questioning running the frig 24 hours a day. I was questioning whether or not the frig actually draws 3 amps 100% of the time.

Your average 8 cubic foot absorption fridge running on propane with out the freezer door heater operating will idle at approx 0.3 amps and approx 0.8 amps when cooling. So the average amp hours per day would be about 15 ah per 24 hours.

TY for the numbers, Boon.

BeerBrewer wrote:
Sorry I made a typo....Boob Docker, you are correct, I read that you can get 30 AMP-Hours per day and not 30 Amps from a 100 Watt panel.....my bad. Is that a realistic assumption?

No, it is not realistic.