# What could you reasonably run with 2 6v batts tied together and 370watts of panels?

Bass-O-Matic
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**45**✭✭
I made a spreadsheet with my usage for my little Trailer. Not much. Some LED Lights, a small DC Fan, occasional water pump. But I have room on my roof and in my trailer for 2 6volt batts tied to 12v and 370 watts of solar.

I feel like I could run more if I put in an inverter.

Thanks so much!

I feel like I could run more if I put in an inverter.

- I have an AC mini fridge that draws Power: 85 W/1.3 A. If I add an inverter... could I reasonably run this 24/7?
- What about the 5000 BTU ac? 500 to 650 watts I saw a guy run one off 250 watts solar panel I guess also connected to a batt? That doesn't seem right.
- How big an inverter would I need to run the AC and the Fridge? Or just one or the other? I came up with 300w for the fridge.
- How long could I run the AC off the batts? or is this totally nuts.
- Would the batts get hot and explode?
- Why do people use temp sensors on batts? Do I need one?

Thanks so much!

## Comments

80✭✭767✭✭✭✭So no, a 370w of solar will likely not be nearly enough. Ideally the battery only charges during the day and the panels can handle all the loads and charge the battery all the way up.

How big is the battery?

That panel is likely just big enough to power the fridge by its self, assuming you have enough battery power.

To power an air conditioner you need more like 1.5 to 2kw of panels minimum and a lot of batteries.

Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

245✭✭✭What is the amp hour rating on them? Are they deepcycle or marine or starter batteries?

What is your other power consumption in watts hours besides the intended AC and/or fridge.

45✭✭So, yea, forget the AC.

Is there any hope for the fridge? Power: 85 W/1.3 A.

Let me put it another way. If I wanted to run that fridge 24/7 what would you suggest? I'll add the extras later....

767✭✭✭✭Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

3,741✭✭✭✭A pair of golfcart batteries stores 225 ah X 12 volts = 2700 watthours. The less of that you use each day, the longer the battery will last.

You can probably run the fridge on those batteries for a day without ruining them... but it depends on the duty cycle which depends on ambient temp and how often you open and close the door and how much warm food you put in it.

--vtMaps

45✭✭how big an inverter? I heard 3x the watts. so 300? Then I heard more from some other source.

45✭✭196✭✭✭196✭✭✭3,741✭✭✭✭Don't forget that a large inverter has tare (self consumption) losses. My inverter uses 20 watts just being turned on (not bad for a 3500 watt inverter). Over a day's time that's 480 watthours... just a bit less than my fridge uses in the summer.

In your system, a conventional fridge becomes a defining load. That one load forces a number of design decisions that you wouldn't otherwise make. One possibility is to get a variable speed compressor fridge. They come in AC and DC models... the DC ones need no inverter. The AC ones do not have high startup surges and will work with a small inverter.

Variable speed compressor fridges are more efficient... it's better to run a compressor at 1/3 speed all the time, than to run it at full speed for 1/3 of the time.

--vtMaps

45✭✭80✭✭767✭✭✭✭Get a pure sine wave inverter. Those cheap modified sine inverters are garbage.

Normally we size battery systems to power the load for 2 to 4 days.

Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

175✭✭✭With the new camper we just bought my two 100 watt panels take about 6 hours of sun to keep up with the fans, two led lights, and the water pump. Battery bank is unknown beyond it's 2 - grp 27's labeled D27DC - 160. Best guess is they may be 95 Ah each.

45✭✭5,974✭✭✭✭✭Figure you are producing 120 watts and you have average 4 hours (that is going to be generous this time of year with flat mounted panels unless you are on the equator. You can produce 4 hour x 120 watts for 500 watt hours and your fridge uses 50 watts per hour while running. Add your inverter using 10-12 watts an hour and if you are running off battery you will lose 20% storing the energy. You aren't left with much to run the fridge.

- Assorted other systems, pieces and to many panels in the closet to not do more projects.

45✭✭45✭✭Well, if I had a 600 watt pure sine wave ( I assume you mean minimum with a max of 1200 or so ) I could at least run the fridge for a few hours while we traveled to our next AC Plug eh?

118✭✭✭https://www.amazon.com/Wagan-EL6224-12V-Cooler-Warmer/dp/B00NHBYOA6/ref=sr_1_2?ie=UTF8&qid=1510206647&sr=8-2&keywords=12V+cooler+for+car

* And only on completely cloud-free days, of course.

32,921adminHow much energy the fridge uses in a day (Watt*Hours or kWatt*Hours) is still in question... A warm room with already cool food--typically run around 50% duty cycle. Or:

- 50 Watts * 24 hours per day * 0.50 duty cycle = 600 Watt*Hours per day = 0.6 kWH per day

That actually seems pretty low for energy consumption... I would have guessed closer to the ~800 WH per day range.If this is the correct refrigerator:

https://www.energystar.gov/productfinder/product/certified-residential-refrigerators/details/2213650

- Annual Energy Use (kWh/yr):
215
- 215,000 WH per year / 365 days per year = 589 WH per day
- 589 WH per day / 24 hours per day = 25 Watt average load

The manual says "This unit is not designed to be installed in an RV or used with an inverter."....2x 6 volt @ 200 AH "golf cart" batteries will reasonably supply:

- 12 volts * 200 AH * 0.50 max discharge * 0.85 inverter eff = 1,020 WH max

Your two batteries would supply this fridge for almost 2 days of "no sun"--Not bad.Say you mount your solar panels flat to the roof, 170 Watts, in the Austin Tx area:

http://www.solarelectricityhandbook.com/solar-irradiance.html

## Austin

Measured in kWh/m2/day onto a horizontal surface:Average Solar Insolation figures

- 170 Watts * 0.52 off grid AC system eff * 4.0 hours of sun per day = 354 WH per average "October day"

Or, working the other way, your 170 Watt panel would need "hours of sun" per day:- 589 WH per day * 1/0.52 off grid system eff * 170 Watt panels = 6.7 hours per day "break even" with 170 Watt panel

Or, if you assume Feb-October camping, 3.41 hours of sun (Feb):- 589 WH per day * 1/0.75 "fudge factor" * 1/0.52 off grid AC system eff * 1/3.41 hours of sun = 443 Watt "recommended" solar array

Obviously, tilting panels towards sun, where you will be camping (farther north or south), warm weather=longer fridge run time, etc... A bunch of factors that can effect your power generation and needs.-Bill

45✭✭