# solar battery

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I have a mighty mule 500 opener and a 10 watt solar panel can I use a 12 volt deep cycle marine battery with this ? I live in western Washington and we do not get a lot of days in fall and winter with direct sun.   10ft  gate and it will be opened and shut about 3 times a day at most.

I would suggest, at least a 2% to 5% rate of charge and a small PWM solar charge controller. If you have a 100 AH @ 12 volt battery (good size), then:
• 100 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.02 rate of charge = 38 Watt panel minimum
• 100 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 94 Watt panel nice size
• 100 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 188 Watt panel (gate running all of the time)
• 100 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 244 Watt array "cost effective" maximum
For most people, they only use the gate a few times a day, and a 38 Watt panel (38 Watts or ~30-50 watt panel, what ever is a good deal for you) is probably more than enough. Battery wise, they would like a 5% minimum rate of charge at 94 Watts--But that is probably overkill.

And a simple charge controller like this (with a smaller 4.5 amp maximum output panel):

https://www.solar-electric.com/sg-4.html

Will the Mighty Mule Open During A Power Outage?
Yes. A fully charged FM500 or FM502 battery will provide an
average of fifty (50) cycles (open and close) and the FM350 battery
(12 Volt car or marine battery not included) provides up to 1500
cycles during a power outage. This number can vary depending on
factors such as the type of gate, number of accessories added, and
weather conditions if using solar panel(s) (FM121) to charge the
battery.

Ok, from the quote, a "car battery" will run the gate up to 1,500 times on a single charge... Generally, don't want to discharge more than 25% per day for two days, so say 1/4 of that or ~375 times per day:
• 100 AH * 12 volts * 1/1,500 cycles = 0.8 WH per cycle
A 94 Watt panel in bad solar conditions for Olympia looks like:

### OlympiaAverage Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 28° angle from vertical:
(Optimal winter settings)  Jan Feb Mar Apr May Jun 1.72 2.79 3.37 3.80 4.01 4.10 Jul Aug Sep Oct Nov Dec 4.51 4.65 4.43 3.10 1.99 1.56
A 38 Watt panel would "operate" the gate on an average gloomy December day:
• 38 Watts * 0.61 DC off grid system eff * 1.56 hours of sun per day (Dec) = 36 WH per day
• 36 WH per day / 0,8 WH per cycle = 45 cycles per day (break even)
• 1,500 cycles * 0.25 nominal discharge of battery = 375 "easy on battery" cycles without sun
• 375 cycles from battery / 45 cycles per day (Dec charging) = 8 days of no sun, no strain on battery at 45 cycles per day
• If 4.5 cycles per day, that is 80 days of stored cycles
Assuming a week or more of bad weather (almost no direct sun), and you probably only run 4-8 cycles per day on the gate--You should be very happy with the setup.

Check the battery state of charge in the evenings (after sun sets) with a volt meter. If the battery is >~12.4 volts in dead of winter, you are doing OK. If lower, it should probably be put on an AC battery charger and given a boost.

Note that Lead Acid batteries do not like to sit (be stored) at less than ~75% state of charge or they sulfate and eventually fail. 75% State of charge is roughly 12.37 volts (use a hydrometer for more accurate readings):

https://www.solar-electric.com/learning-center/batteries-and-charging/deep-cycle-battery-faq.html

State of Charge 12 Volt battery Volts per Cell
100% 12.7 2.12
90% 12.5 2.08
80% 12.42 2.07
70% 12.32 2.05
60% 12.20 2.03
50% 12.06 2.01
40% 11.9 1.98
30% 11.75 1.96
20% 11.58 1.93
10% 11.31 1.89
0 10.5 1.75

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Posts: 103Solar Expert ✭✭✭
sure it will work but you'd be better off with a ~100w panel, you'll wind up having to haul it to the house and manually charge it sometimes with a tiny little 10w panel ..
• Posts: 4,670Solar Expert ✭✭✭✭
johnG said:
I have a mighty mule 500 opener and a 10 watt solar panel can I use a 12 volt deep cycle marine battery with this ? I live in western Washington and we do not get a lot of days in fall and winter with direct sun.   10ft  gate and it will be opened and shut about 3 times a day at most.

If you are using their solar setup but are worried about the long periods of shade, you likely would be better off with a larger panel and the same battery. I think most sealed batteries can take a higher charging rate, often it will be on the battery case. I think these tend to come with a 20 Ah 12 volt battery, from my faulty mind. if It could handel a 1/5th charge 4 amps. a 50 watt panel might work for you, you would get more charging on overcast days and yet be within specs (if it can handle that) on sunny days.

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
• Posts: 2Registered Users, Users Awaiting Email Confirmation

Thanks for the info everyone