Combined Solar Powered Gate and Radio Dog Fence

Carsenio

Hi,
I am not yet very knowledgeable about solar power and am trying to figure out a solution for my 40 acre property in Colorado that combines a solar powered gate and a radio dog fence. I am looking at this gate kit, that come with 24V batteries and 30W solar panels ( http://www.alekogates.com/ALEKO-AS1300-Solar-Kit-Swing-Gate-Opener-p/as1300solfull.htm ) and this radio dog fence ( http://www.sportdog.com/support/in-ground-fencing/in-ground-fence ).

To combine these two systems, is it as simple as installing a 24VDC to 120VAC inverter between the batteries off the gate opener and the dog fence transmitter? I assume the radio transmitter draws very little power and the gate batteries ans solar recharger will more than enough to keep the fence powered, since gate will be used only a few times a day.

I would appreciate any advice and guidance on how to do this right.

Thanks.

BB.

Re: Combined Solar Powered Gate and Radio Dog Fence

Welcome to the forum Carsenio,

The answer is you probably will not be able to use the gate power system for your fencing system as is...

I looked through the fencing information and could not find anything about its power consumption... If you just buy a small 120 VAC inverter--The inverter itself will probably draw at least 6 watts. Lets guess that that entire inverter+fencing transmitter takes 10 watts total. Sizing the battery for 2 days of storage (bad weather) and 50% maximum discharge:

• 10 watts * 24 hours per day * 1/0.85 inverter eff * 1/12 volt battery bank * 2 days of storage * 1/0.50 max batt discharge = 94 AH @ 12 volt battery bank

Next, sizing a solar array to charge the battery bank. 5% to 13% is the nominal recommended rate of charge:

• 94 AH battery * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 89 watt panel minimum
• 94 AH battery * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 177 watt panel nominal
• 94 AH battery * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 230 watt "cost effective" max solar array

Next, lets assume a minimum of 2 hours of sun per day (poor winter weather). The minimum solar panel to keep up with the load would be:

• 10 watts * 24 hours per day * 0.52 system eff * 1/2 hours of sun per day minimum = 230 Watt array minimum (based on 2 hours of sun per day)

You can do the same thing as above, but with a 24 volt battery bank--Just two ~47 AH 12 volt battery in series would be the same thing... And the gate would probably be easily powered + fence transmitter from such a system.

Note, I guessed at the 6+4 watt inverter+fence transmitter... You would need to contact the factory to find out how much power it really uses, or measure it yourself (Kill-a-Watt meter, DC AH/WH meter, AC/DC Current Clamp Meter, etc.).

Also, I used 12 volts as you can easily get a smaller 12 volt/good quality AC inverter with 6 watts of "tare loses"... As you go up in battery bank voltage, it can be more difficult to find small/low tare loss AC inverters.

Cost effective use of solar power is a combination of conservation, knowing your loads/power requirements, and doing several paper designs to see what works best for you.

As you can see, powering the equivalent of a 4 watt Christmas light can take quite a bit of solar design/money to run 24 hours per day / 12 months a year.

In the end--If you have 120/240 VAC utility power--You are probably better off powering from your utility power. If your property is off grid--It would probably still be better to power such a system (fencing, possibly electric gate) from your main/home off grid solar setup. Such small loads do not usually put too much strain on larger off grid power systems--Plus you will be monitoring/have a backup genset too.

-Bill

Carsenio

Re: Combined Solar Powered Gate and Radio Dog Fence

Thanks, Bill, for the detailed analysis. I have contacted to dog fence company to get their specs. If I am reading your reply right, are you saying this setup would work if I upgraded the 12v batteries from the 12ah ones included to 47ah or greater? Unfortunately the gate is in the corner of my property, so getting AC power there is A big task. Since I have to have it solar powered, I am trying to kill two birds with one stone and have the same setup power the dog fence. I pulled up this basic inverter ( http://www.northerntool.com/images/downloads/manuals/457300.pdf ) and it shows a 0.35A (at a 12V input) battery drain. That calculates out to 4.2W, correct? So that would leave me almost 6W for the radio transmitter, right?

BB.

Re: Combined Solar Powered Gate and Radio Dog Fence

Yes--You are reading the specifications correctly... Less losses on the AC inverter, smaller system/more power for loads.

Also note that this is a 12 volt AC inverter--Will not work with a 24 volt battery bank. And you NEVER want to split 12 volts from a 24 volt battery bank--One battery will always be undercharged, and the other will always be over charged (there are reasons and ways this can be done--But the added costs pretty much never make sense except in large bus chassis RV conversions and such--sometimes).

However--That is a MSW (modified square/sine wave) type inverter. Many small "wall wart" type transformers (and many digital switching supplies) do not operate well on MSW inverters--They can overheat and have low output voltage issues (because of the MSW wave form).

And it is difficult to tell if any particular AC device will have problems or not with MSW... Something like 80% of AC devices will work OK on MSW, and some 10% will have early failures (minutes to days to months). You can read about MSW/TSW-PSW inverters here:

All About Inverters
Choosing an Inverter - Home Power Magazine

If reliability is very important for your loads--I would highly suggest a TSW/PSW (true/pure sine wave) AC inverter. However, TSW inverters have, very roughly, 2x the losses of a MSW inverter (and are more expensive too).

Regarding batteries... You want to use Deep Cycle batteries, not Marine or Automotive batteries...

And, remember that Power = Voltage * Current

So, if you double the battery bank voltage and 1/2 the current (or AH storage), it is still the same mount of power:

94 Amp*Hours * 12 volt battery bank = 1,128 Watt*Hours of storage energy
47 AH * 24 volt battery bank = 1,128 Watt*Hours of stored energy

Picking an AC inverter is going to be a pain... The physics (higher DC bus voltages tend to create more idle losses) and marketing departments (people with higher voltage battery banks are less common, usually want more power/larger inverters, and have more money) are "against" you. Here is an example of two Samlex 300 watt inverters, one at 12 volts and the second at 24 volts:

http://www.samlexamerica.com/documents/product-specs/12001-PST-300-12-24-0413.pdf
http://www.solar-electric.com/samlex-pst-series-pure-sine-wave-inverters.html (pricing from our host)

12 volt 500 mAmps of draw => 0.5 amps * 12 volts = 6 watts idle draw
24 volt 400 mAmps of draw => 0.4 amps * 24 volts = 9.6 watts idle draw

For very small systems--Finding/figuring out out how to run small loads off of DC direct power is sometimes seems like the best answer--But when you see that a 12 volt battery bank can run from ~10.5 volts (dead) to near 16+ volts (equalization/charging)--Most DC input devices cannot accept that wide of DC voltage input range--So you are back to looking at AC inverters or DC to DC converters (which are sometimes just as expensive as AC inverters).

It would be very nice if the mfg. put a wide range capable DC input on their transmitter--But most companies do not. A little bit of extra design work and a few bucks more in mfg. costs.

-Bill

I would ask the company if the system will run on a "MSW Inverter" or not... Also, it is possible to get DC power supplies that can run from MSW and simply replace the one that comes with the transmitter--But more costs, more pain, more talking with the vendor about their DC input power requirements.

Carsenio

Re: Combined Solar Powered Gate and Radio Dog Fence

Thanks again Bill for all the info and recommendation on the inverter. Lots to think about. I'll post my final setup if I get this put together.

BB.

Re: Combined Solar Powered Gate and Radio Dog Fence

Feel free to ask more questions if they come up. There are lots of ways to address your needs.

-Bill