Powering a 120 VAC gate opener off grid

Panapat

I have a spare 165 W, 35 - 36 VMP solar panel. I am looking for advice on how to match it up with a charge controller and high efficiency inverter. The motor draws 300 watts running, so I would think the motor has some sort of inrush protection, otherwise the 10 amp fuse would blow. If possible I would like to use a 12 Volt Battery, or do I have to feed the 36 Vols into a 36 VDC battery?

BB.

Your better bet would be to get a DC powered gate opener. Then a relatively small solar panel+12 volt battery+small charge controller should work fine.

The problem with running the AC gate opener, is the AC inverter's "tare" losses... A typical AC inverter uses ~6 Watts just turned on and no loads... Assuming the 120 VAC gate actual energy usage hardly matters):
http://www.solarelectricityhandbook.com/solar-irradiance.html

Panama
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 81° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
6.10	6.23	6.12	5.45	4.58	4.33
Jul	Aug	Sep	Oct	Nov	Dec
4.14	4.22	4.40	4.37	4.22	4.94

• 6 Watts * 24 hours per day = 144 WH per day
• 144 WH per day * 1/0.52 off grid system eff * 1/0.52 off grid system eff = 67 Watt panel (July "break even")

So, your 165 Watt panel looks to be large enough to run the inverter (and gate) through bad weather.

A 300 Watt AC motor/AC inverter would need a minimum suggested flooded cell lead acid battery size of:

• 300 Watt AC inverter * 100 AH * 1/400 AH per 1,000 Watt AC inverter = 120 AH @ 12 volt battery minimum (based on starting surge current)

And, based on WH per day of usage:

• 6 Watts * 24 hours * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/12 volt bank = 56 AH minimum (based on energy storage)

To charge the battery, need 5% to 13% rate of charge. 5% would probably work OK, but suggest 10%+ for longer battery life. Use the 120 AH @ 12 volt minimum battery sizing (because of 300 Watt starting surge support for inverter--Typical inverter will support 2x rated wattage for starting surge):

• 120 AH * 14.5 volts charging * 1/0.77 solar panel+controller derating * 0.05 rate of charge = 113 Watt array minimum
• 120 AH * 14.5 volts charging * 1/0.77 solar panel+controller derating * 0.10 rate of charge = 226 Watt array nominal
• 120 AH * 14.5 volts charging * 1/0.77 solar panel+controller derating * 0.13 rate of charge = 293 Watt array typical "cost effective" maximum
  

So, your 160 Watt panel would be "enough" for a 120 AH @ 12 volt battery... But would need to be re-evaluated if using larger batteries (such as 2x 6 volt @ 200 AH golf cart batteries for a 12 volt @ 200 AH battery bank).

For use with your Vmp~30 volt panel, you would need a small MPPT type solar charge controller. A "cheaper" MPPT type charge controller would be about 50% efficient charging a 12 volt battery. This is an example of a smaller MPPT controller:

https://www.solar-electric.com/mosumpsochco.html

For a 300 Watt AC inverter, this 12 volt TSW one is nice:

https://www.solar-electric.com/residential/inverters/off-grid-inverters.html?nav_inv_input_voltage=436&sine_wave_type=549 (bunch of 12 volt inverters)

https://www.solar-electric.com/morningstar-si-300-115v-ul-inverter.html (has been a good rugged unit for many folks)

Links are starting points for your search--Finding something local may be best for you vs importing from US, and/or want to use less expensive units.

If your gate operates a bunch of times per day (like a commercial lot/loading dock), you may need to take into account the actual gate operating energy... A Kill-a-Watt type meter would be a good start:

https://www.amazon.com/s?k=kill+a+watt

I still would be suggesting looking for a 12 VDC gate system if you can justify it... Running a 6 Watt load 24x7 will (usually) require the larger battery bank and chances of running the batteries dead during bad weather/more batteries to replace (batteries get "murdered" by usage/poor maintenance, or simply last 3-5 years, and you you need a new bank from aging/cycling in hot climate--batteries do not like heat).

-Bill

mike95490

I have a large gate opener, and it runs of a 20w panel. (opener is on concrete pad, and has rotary arm to pull the gate open and closed) It's got a 20ah 12v battery in the housing.  6 years going strong.

Panapat

Thanks BB for your extensive reply. Unfortunately I already have two 1800 Kg 120 VAC gate openers I bought some time ago. They are the sliding type, looking at the spec provided by the manufacturer its rated at 350 Watts not 300 Watts as I said. Mike, I suspect your gate opener is DC.

So I dont believe a 300 watt continuous output will be up to the task. The gate is on my farm and wont be used many times a day, maybe open and closed a maximum 4 or 5 times. The MPPT charger I have opted for is the 20 amp EPEVER with Wifi option. https://www.ebay.com/itm/302378028095. The battery I am looking at is this one, 12 VDC 100 amp/hrs Lithium https://ewtbattery.en.alibaba.com/product/60679172617-213144720/Bestseller_lithium_ion_battery_12v_100ah_deep_cycle_lifepo4_battery_pack_for_motor_home_marine_industry_solar_panel.html?spm=a2700.12243863.0.0.2ce83e5fstCSmR Price is $280, waiting info on the shipping costs to USA and BMS requirements.

Still looking at 500 Watt fan less inverter options, have not been able to find any.

Additionally, I have a solar tracker, which holds 4 165 Watt panels for my solar water pump. I intend to install the spare 165 watt panel onto the tracker to optimize solar charging.

BB.

I would guess that 4-5 times a day is a "few" operations per day... And the inverter I suggested is good for 600 Watts for 15 minutes at 600 Watts.

https://www.solar-electric.com/lib/wind-sun/SureSine.pdf

And I would guess that the opener runs for less than 30 seconds to open and 30 seconds to close, or 1 minute per cycle. And, I doubt it take 300 Watts to run... But let us say it does take 300 Watts:

• 300 Watts * 1 minute * 1 Hour/60 minutes * 5 times per day operation = 25 WH per day
• 25 WH per day * 1/0.85 AC inverter eff * 1/12 volt battery bank = 2.5 AH per day (at 12 volts)

And your 165 Watt panel under 4 hours of sun per day would supply an average daily energy harvest of:

• 165 Watt panel * 0.52 average off grid eff * 4.0 hours of sun per day = 343 Wh per day
• 6 Watt inverter tare losses * 24 hours per day = 144 WH per day

So, 5x per day gate operation is 25 WH per day, just running the inverter 24 hours per day is 144 WH per day and the solar harvest is 343 WH per day (December daily average)... And the 5x per day gate operational energy is a small fraction of total daily load, and much less than the energy harvest per day.

So, assuming that a 300 Watt or similar small AC inverter can start the gate, and the gate probably takes 1/2 or less of 350 Watts for the cycle (other than a second for starting surge)--The system should work.

The hole in the discussion is the starting surge. If you have to go with a larger inverter (here is a 1,000 Watt AC inverter), the Tare Loss is going to be a lot more:

https://www.solar-electric.com/samlex-pure-sine-wave-inverter-pst-1000-12.html
https://www.solar-electric.com/lib/wind-sun/PST-1000-specs.pdf

This larger inverter take ~800 mAmps or 0.8 amps @ 12 volts to run:

• 12 vols * 0.8 amps = 9.6 Watts
• 9.6 Watts * 24 hours per day = 230 WH per day

Significantly more than the 144 WH per day of the 300 Watt AC inverter, but still less than the 343 WH pe day of average harvest in December... But now you are looking at a 1,000 Watt AC inverter would would need closer to a 400 AH Flooded Cell Lead Acid battery bank to "reliably" surge 2,000 Watts for the larger AC inverter... Or 2x 6 volt @ 200 AH "golf cart" batteries in series x 2 parallel strings for 400 AH battery bank (4x golf cart batteries total). You could possibly get away with 2x 6 volt @ ~200 AH AGM batteries for a 12 volt @ 200 AH battery bank (AGM batteries do support higher surge current vs Flooded Cell Lead Acid batteries).

Back to the 5% minimum rate of charge for the larger battery bank:

• 400 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 377 Array minimum (for larger FLA bank)
• 200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 188 Watt array minimum (for smaller AGM bank)

If the starting surge is much higher than I guess, and you need a larger AC inverter and battery bank to support that surge, even with a 200 AH @ 12 volt AGM battery bank, the 165 Watt panel is pretty marginal. And you would need 2-3 panels minimum for an FLA battery bank.

And here we land... I am making lots of guesses on how much power (starting surge/running Watts) a gate opener I have never seen/installed. And I do not know if the first 300 Watt system is way undersize or the second 1,000 Watt system is way oversized. Or even if the 1,000 Watt system is large enough (if the gate motor has serious starting surge issues).

So, do you build the smaller system and see if it works. And build a second larger system if it does not? Or build the larger 1,000 Watt (and more expensive) system first.

I do not know... But this is the issue with supplying 120 (or 230) VAC power 24 hours per day for a system that runs maybe 5 minutes per day. The starting surge is, more or less, sizing the solar power system---And making it much larger vs the running 5x per day energy (which is relatively trivial/small).

You could get a Kill-a-Watt meter to measure the average Wattage... And you can get a current clamp meter that measure starting surge current to better estimate the starting surge. Here is an example of an AC current clamp meter with Inrush current measurement:

https://www.amazon.com/Amprobe-4560555-AMP-310-Clamp-Meter/dp/B00OYFJ5FI
https://www.amazon.com/s?k=current+inrush+AC+current+clamp+meter (some other meters that may have Inrush function)

Even with the inrush current measurement, you really do not know how the AC inverter responds to high output surge current (does it turn off or simply drop the AC voltage some) and how the gate opener+electronics behave (do the gate electronics fault or ride through the few cycles of AC voltage drop)...

And here is where the math and guesswork cannot give you a 100% accurate answer. And you are left with buying/borrowing some hardware, installing the gate, and see what works--Or if you can find somebody else that has already installed a system similar to what you want to do (xxx Watt Solar AC power system).

I am sorry I cannot give you "the answer". Too many variables. Starting surge/inrush current is a killer for off grid power systems... For example, a standard refrigerator with a ~120 Watt motor needs a 1,200-1,500 Watt AC inverter and battery bank to start (>600 Watt starting surge for the refrigeration compressor--Compressors usually require high starting surge because of the back pressure from pumping refrigerant). Such a battery bank and inverter system is "seriously" large vs buying a DC gate opener and a small battery+solar panel.

You might even check with the gate opener company and see if they have a DC motor+controller "conversion kit" you can retrofit the gate.

Another option is to just dig a trench and bury a few hundred feet of 120 VAC wiring from a building to the gate... If you are over 1,000s of feet/100s of meters from utilty power--May not be cost effective to bury utility power to the gate...

-Bill

Panapat

Thanks again BB for your reply. We are totally offgrid so no utility power. I have an electric gate in the main house which is tied to power and rated for 800 kg, 250 watts at 3 amps. I used a clamp on and operated the gate, it never registered over 2.25 amps. Correlating that information with the bigger motor of 350 watts it would be reasonable to deduce that the spec of the 300 watt inverter you suggested would do the job. However, the manual states – Wiring location for 12V lead-acid battery input-, not lithium, any reason for that?  I will check back with the manufacturer and see if they have a retrofit kit to DC.

Estragon

+1 on checking the motor with a kill-a-watt type meter.  As well as the unknowns Bill mentioned, I wonder about the AC motor "power factor".  The meter has a function to estimate PF.

Basically, if the current and voltage wave are pulled out of sync by the inductive motor load, the inverter has to produce more Volt-Amps for a given wattage.  Although inverters are spec'd on wattage, they really should be V.A. rated.  For example, a 300w load with a .5 PF would need 600VA inverter capacity to run properly.

mike95490

If this is at a remote location, remember - Lithium batteries CANNOT EVER be charged when it's below frost temps.

 Charge rate should be throttled back below 40F

So if you are in the south, great.  if you get frost - no Lithium.  Most don't have heaters, and a heater would consume even more power on cloudy days !!

BB.

Mostly, because that inverter was designed and spec'ed before Li Ion batteries became "popular".

If you are thinking of using LiFePO4 or similar batteries, as long as they stay within the operational voltage of the AC inverter (typically 10.5 to 15.0 volts), then they will be fine... That inverter, as I recall, has a switch setting to 11.5 volts battery cutoff. That could be helpful for both Lead type and Lithium type batteries (deep cycling is hard on batteries--A remote gate that is not actively monitored--The higher cutoff voltage can save you an expensive battery bank).

Lithium chemistries are known to supply much higher surge current. However, there are many Lithium batteries with internal over/under voltage protection built in... And many times, this limits the available surge current from the battery bank. For example, if limited to 100 Amps, that is P=V*I=12v*100a=1,200 Watts...

As Estragon states, measuring current can tell you the VA rating of the motor/load... 2.25a*120v=270VA.

Note that Watts is always equal too, or less than VA rating... For smaller inverters (residential), they are typically rated for Watts=VA max (300 watts = 300 VA). However, the "real equation" for Watts is (assuming you are running ~120 VAC):

• Power (Watts) = Volts * Current * Power Factor, where PF is between 0.0 and 1.0 and for induction motors is typically 0.65 to 0.80
• P = 120 Volts * 2.25 Amps * 0.70 PF (guess) = 189 Watts
• 189 Watts * 1/0.85 AC inverter eff * 1/12 volts battery bus = 18.9 Amps "nominal" 12 volt Battery Bus current
• 189 Watts * 1/0.85 AC inverter eff * 1/10.5 volts Battery cutoff = 21.2 Amps "worst case" when battery voltage is low

The AC wiring/inverter is designed for VA rating... The DC wiring and Battery wiring is (mostly) designed based on Watts. Poor Power Factor means a "larger inverter". But poor power factor also means a smaller battery bank is possible.

The problem with most Kill-a-Watt and current clamp meters is that they take a "sample" every ~1 second or so... To accurately measure inrush current, you need to sample a 1/2 cycle of current.. or 1/120th of second... So, much of the time, a "standard" current/power meter misses the surge current peaks.

There are a lot of details and guesses being made here... The rules of thumbs we use here are used to get "close enough" for a "reliable and longer lived" system over time/state of charge/etc. We try not to do too much in the way of a lot of "fudge factors"--We try to use the "real numbers" as much as possible to give you the most "cost effective" system we can and reduce the risk of a system that won't meet your needs. But other variables (like how the inverter and loads react to "corner conditions") can be the make/break difference. And without testing/experience, it is pretty much impossible to make a "reliable" guess as to what will 100% work (i.e., the 300 Watt vs 1,000 Watt, or greater, system design for this specific gate operator).

It is possible that the gate company can also tell you what size inverter will run their gate too.

And you cannot run solar AC power from your home/office/etc. to the gate? The gate load would probably be near trivial for a larger AC solar power system.

-Bill

Panapat

Thanks again folks, yeah, I am in Panama, no frost problems. I think what I am going to do if the supplier cannot answer my various questions, is to install the gate and motor and run it off a generator I have.  I can then get some real figures with either the clamp on or kill o watt. The House with the main solar is 60 meters away, at the top of a hill. The gate is 15 meters from the solar water pump equipment. Seemed like a good idea to put it there. The gate is another 30 meters or so from where I took this picture.

 

Panapat

Quick up date, manufacture came back with an answer to my questions. no DC conversion kit. Absorbed power 638 Watts. A little over the SureSine™ Inverter full load of 600 Watt.

BB.

I would be looking at your solar water pumping system... If you have a battery bank + AC inverter, then running 15 meters from gate to pump area would not be too bad?

And if the present water pumping system is not large enough battery+inverter, I would prefer to put your hard earned $$$ into making the pumping solar power system larger, than building a second (overly large/expensive) solar power system just for your AC gate.

If you only have solar panels + DC water pump, then there is nothing "easy" that can be done to interconnect and provide 120 VAC for your gate system (I would not go to a battery based pumping system if it is presently solar panels only powered).

-Bill

Panapat

Your last point is exactly where I am, solar only water pump. The expense will be the MPPT controller, Inverter and battery. I have everything else.

Panapat

Hi everyone, here is an update on my gate project. After installing gate and motor I hooked up a generator and tested the current draw, see snaps. It requires 1000 Watt surge and 600 continuous. I tried a Chinese  $75 inverter 1600 watt surge and ,  800 watt continuous. It didn't work, just kept tripping. I ended up buying a Zantrax modified sine wave inverter for $135, 1500 Watt surge. It worked fine, moral here is, don't believe sticker ratings on these chinese brands.

BB.

Sounds like you have a good solution for your needs.

A couple of observations:

Make sure the battery wiring is short and heavy enough for the DC surge current (is possible that voltage drop in DC wiring caused the inverter to shut down--Use your meter to measure DC input voltage).

MSW inverters are kind of hard on induction motors. One way to look at the problem... An induction motor is designed for 60 Hz (or 50 Hz) sine wave--With a sine wave, all off the energy is at 60 Hz and the motor uses that to rotate. 

With MSW inverters, there are other frequencies (harmonic distortion). Those other energies are not at 60 Hz, but usually at "odd numbered harmonics" above 60 Hz. The end result is that is energy that goes into the motor, but does not help the motor rotate--And it goes into waste heat--That makes the motor run hotter.

https://electricala2z.com/renewable-energy/inverter-harmonic-distortion/

https://en.wikipedia.org/wiki/Power_inverter

A "pure sine wave" inverter typically is less than ~5% total harmonic distortion. Or less than ~5% wasted energy in the motor (transformer, wiring, etc.). A Modified Square Wave inverter is around 24% THD... Or around 24% of the motor energy is wasted as heat inside the motor.

Since you have an electric gate--The motor only runs for 30 seconds at a time, and typically an open/close cycle, then nothing--So the motor should not get too hot and it has time to cool down too.

So, just watch the motor temperature--But it should not be a problem (sealed motor, not good cooling airflow/heat dissipation. Build a sun shade over motor/electronics/battery bank would help a lot too--Heat is the enemy of just about everything.

Old engineering rule of thumb... For every 10C over 25C, life of electrical equipment falls 1/2... Keep at 35C, the "stuff" will age about 2x faster/last 1/2 as long.

-Bill

Panapat

Hi Bill. thanks for the tips. I tested both inverters off my car battery, both leads where the ones supplied by the inverters. I know MSW are not ideal for motors, it does run noisily, but they are half the price. The motor is oil filled so should help cooling but I will monitor it, the shade is a good idea here in Panama. Thanks again.

mike95490

> The motor is oil filled so should help cooling
I think not.   The torque converter in a car is oil filled and both half's spin.  Filling a motor with oil would not work well.
  The motor may use an Oil Filled capacitor.  That is a real thing.

Panapat

Update on the 120 VAC 800 Kg gate opener, I ended up buying a 115 Amp Hr GEL/AGM battery connected to the 1500 Watt MSW inverter, Solar is a 165 Watt panel connected to a EPEVER Tracer charge controller.

To operate this gate, I have the usual 433 mhz remote and to open it from the house, I installed inside the motor housing, a 12 Vdc power supply and the Sonoff SV switch, modified for dry contact operation. https://www.youtube.com/watch?v=osKyMUXwKpo

Getting WiFi to the gate required the installation of a Kuwfi CPE Access Point, this allowed me to control the gate via Ewelink cloud control. As I am in the middle of nowhere internet is not available so, I ended up buying a Huawei 4G Router and installed a Unlimited Data SIM, $39 a month and on a good day I get 20 mbps up and down.

It was suggested that the MSW inverter would overheat the motor during operation, I tested this and I can confirm the motor never even got warm during a couple of open close cycles. The current draw on the battery whilst the gate is in operation,  is around 40 amps, and after a week of operation, maybe twice a day, the inverter tripped on low voltage, 10.5 Vdc, the battery was around 12.3 Vdc when I checked it.

The panel was delivering 1.5 Amps on a cloudy day, to be sure I fully charged the  battery with a normal charger, after 12 hours it was still only reading 12.3 Vdc. Looking online, this battery should read around 12.8 Vdc when fully charged, so I took it back to where I purchased the $300 battery.

They put a battery tester on it and was able to load it up to 200 amps, I noticed the voltage dropped from 12.3 to 12.1 Vdc during this short test. Off course they told me there was nothing wrong with it, but I explained that the battery specs written on the side of the battery says it should be at least 13 Vdc in standby, additionally, I informed them that they need to test the true capacity.

This is what they are doing and I should hear from them on Monday. I will let you know, any comments greatly appreciated as usual.

Panapat

Turns out the battery is good. The single 165 watt panel only puts out a max of 4.5 amps at 32 volts. I have installed another one in parallel. Still only producing 3 amps with early morning sun. Must be the cheap chinese panels I bought. Lets see how the state of charge is after a couple of days. 

Panapat

An update on my modified sinewave Xantrex 1500 watt inverter, first issue I had with it was it was tripping on high voltage, so I reduced the MPPT charge controller to accommodate. After just one year and no issues the inverter kept tripping on low voltage of 12.2 VDC (shown on the MPPT Charge controller), which is much higher than the quoted less than 10.5 VDC. I put a fully charged alternative battery on to test and same result. Looking online I couldn't find any solution to this issue for Xantrex. So, it looks like I will have to buy a new inverter, this time a pure sine wave variety.

mike95490

Panapat said:

An update on my modified sinewave Xantrex 1500 watt inverter, first issue I had with it was it was tripping on high voltage, so I reduced the MPPT charge controller to accommodate. After just one year and no issues the inverter kept tripping on low voltage of 12.2 VDC (shown on the MPPT Charge controller), which is much higher than the quoted less than 10.5 VDC. I put a fully charged alternative battery on to test and same result. Looking online I couldn't find any solution to this issue for Xantrex. So, it looks like I will have to buy a new inverter, this time a pure sine wave variety.

Check your battery wires for a poor connection.  Voltage drop in the wires can trip the inverter ofline