need shopping list... advice.

fordraceboy
fordraceboy Registered Users Posts: 12
I just installed a Mighty Mule 350 opener on my gate, and terrain/distacnce/power outages dictate that solar would be the best option to power this opener.

Based on what I have read, not measured, I can get approx 1500 cycles per day out of a car/rv battery. based on number of cycles and the chart they provided, here in Oregon I would need 15 watts of power for my 10ish gate cycles a day. (and maintain the battery)

I got a smoking deal on a 45w/12v panel (free) and think that this should provide ample power to keep up with my gate use. I will also be adding a keypad, but my friend has the same one and only changes his 4AA batteries in it every 4-5 months. If opener draw is 3.5A, and cycle time open to shut is 1.5 minutes, that would be just under 0.9AH a day correct? so, 45w at 12v is 3.8ish amps. Even at 50% efficiency, that is still double what my usage is correct?

An then... the panel will be mounted approx 55' away from the battery. I'll build a small cover for the battery and charge controller to be dry and covered- but what size wire will I need from the panel to the controller? The controller is this one -- http://www.ebay.com/itm/Intelligent-30A-PWM-Solar-Panel-Charge-Controller-12V-24V-Auto-Battery-Regulator-/111338685302?pt=LH_DefaultDomain_0&hash=item19ec4d8376

Will that one be sufficient? What will suffice as a "dump load" (if needed) off of this controller when the battery is full?

I know how to measure draw, wire things, etc... But application and understanding of this is pretty foreign to me. I figure this little project woul dhelp me have a better understanding, and the kids think it'll be cool to have the gate "Off the grid.." LOL

Thanks in advance

Comments

  • fordraceboy
    fordraceboy Registered Users Posts: 12
    Re: need shopping list... advice.

    PS- 25mA idle draw rate, and my swing time is 16 seconds each way
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: need shopping list... advice.

    It sounds like you have a good installation/design there...

    I am a little confused about the cycling. 1.5 minutes vs 16 seconds * 10 times per day. But just to put some math behind your calculations:
    • 16 seconds per cycle * 10 cycles * 2 open/shut cycles * 1/60 sec per min * 1/60 min per hour * 3.5 amps operating = 0.31 AH per day operating
    • 0.025 Amps standby * 24 hours per day = 0.6 AH per day standby
    • 0.31 AH + 0.6 AH = 0.91 AH per day total

    The panel:
    • 45 watts / 17.5 volts Vmp = 2.57 amps Imp
    • 0.91 AH per day * 1/0.80 charging eff * 1/2.57 Amp Imp = 0.44 hours per day of "noon time" equivalent sun per day

    For the battery, if we assume a 5% rate of charge minimum:
    • 2.57 Amp Imp panel * 1/0.05 rate of charge = 51.4 AH battery

    You could go with a much larger battery (upward of 100-200 AH @ 12 volts)--But I would not recommend it. Batteries as they age tend to draw more charging current in float--And a 51 AH battery would last roughly:
    • 51.4 AH / 0.91 AH nominal use per day * 0.25 maximum discharge (long life/reduce sulfation) = 14 days without any sun at all

    Regarding the wiring to the solar panel, you do not want much more than 3% or (0.03 * 17.5 volts Vmp=) 0.525 volt drop. Below 1% drop is usually a waste of copper. Using a generic voltage drop calculator:
    • 55' one way run @ 2.57 amps => 0.5 volt drop @ 12 AWG cable
    • 55' one way run @ 2.57 amps => 0.2 volt drop @ 8 AWG cable

    For your system, 12 AWG would be a good size--You really do not need heavier. Don't forget a fuse at the battery to protect the wiring from the battery to the charge controller and gate controller. The battery can supply pretty high currents and melt the wiring/possibly even start a fire if there is dry grass for the melted wire/insulation to drop on (in the case of a short circuit somewhere).

    And you do not need a dump load ... Just a nice little PWM solar charge controller at the battery. It will turn on when the battery needs charging and off when the battery is full -- And on/off to float the battery when full and the sun is up.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • fordraceboy
    fordraceboy Registered Users Posts: 12
    Re: need shopping list... advice.

    OK- the numbers all make sense, except the Vmp. Where does that come from?

    My opener has an input for the solar panels, I'm assuming that is a charge controller of some extent, but I'm going to use the PWM one. What size fuse is acceptable between the battery and controller- 20A?
  • Plowman
    Plowman Solar Expert Posts: 203 ✭✭✭✭✭
    Re: need shopping list... advice.

    The 30-amp charge controller is a bit oversized. Something closer to 5 amps would be better matched to your panel.

    Vmp is the maximum voltage your panel will produce.

    If you used 12 AWG wire, a 20-amp fuse/breaker would be plenty. Put it as close to the battery as possible.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: need shopping list... advice.
    OK- the numbers all make sense, except the Vmp. Where does that come from?

    Vmp of ~17.5 to 18.6 volts is the marketing specification for the solar panel's operating voltage (~0.5 volts per cell, or a ~36 cell panel) needed to recharge a 12 volt battery bank.

    Vmp falls as panels get hot... And you can lose upwards of 20% of Vmp on very hot days (sun heating your nice black glass covered solar cells).

    17.5 volts * 0.8 thermal derating = 14 volts operating voltage

    And you need ~14.5 volts to recharge a deep cycle battery at room temperature (hot batteries also need slightly less charging voltage--Keep battery around 45-75F for best life/operation--Don't let battery "cook" or "freeze" if possible).

    Note that Vmp is not a sharp peak, but a gentle hump--And not every day is a windless "Death Vally" temperature day.
    My opener has an input for the solar panels, I'm assuming that is a charge controller of some extent, but I'm going to use the PWM one. What size fuse is acceptable between the battery and controller- 20A?

    For a PWM controller, the minimum fuse should be:

    Imp of the panel/array * 1.25 NEC Derating * 1.25 "very sunny day" derating
    2.57 amps * 1.25 * 1.25 = 4.0 Amp minimum rated fuse+wiring for charge controller

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: need shopping list... advice.
    Plowman wrote: »
    Vmp is the maximum voltage your panel will produce.
    Oversimplified.
    Voc (open circuit voltage) is the maximum voltage a panel will produce.
    At that voltage and no current, you will get no usable power from the panel.
    If you short circuit the panel, you will get the short circuit current, Isc. But at zero voltage, also no useful power.
    Calculus and even common sense, tells that somewhere in between 0V and Voc will be the sweet spot where you can get the maximum power from the panel.
    That sweet spot, called the Maximum Power Point, will be when voltage = V maximum power or Vmp. The current will be I maximum power or Imp.

    Typically for a silicon cell, Vmp will be about 80% of Voc and Imp will be about 80% of Isc.

    A grid tie inverter or charge controller that has the necessary smart input circuit to locate the MPP and follow it through light changes, temperature changes, etc. has Maximum Power Point Tracking or MPPT.

    With PWM, you have no such advantage, and the panel voltage will simply be the battery voltage minus the volts lost in the CC. The result if that if you try to use a panel with Vmp too far above the battery voltage you will waste more than half of the panel power. In the best case, you will still be wasting about 1/3 of the panel power.

    And there you have the related abbreviations. :)
    SMA SB 3000, old BP panels.
  • fordraceboy
    fordraceboy Registered Users Posts: 12
    Re: need shopping list... advice.

    Lots of info.. Lol.

    So I need to run 12 gauge wire to my controller, then 12 gauge to the battery with a 20A fuse right next to the positive post of the well insulated (temperature controlled) battery.

    I have the 30A controller already, will I be better off to pick up a 5-10A controller for this little setup? Is extra vampire power going to be that great between the two controllers?
  • Plowman
    Plowman Solar Expert Posts: 203 ✭✭✭✭✭
    Re: need shopping list... advice.
    Lots of info.. Lol.

    So I need to run 12 gauge wire to my controller, then 12 gauge to the battery with a 20A fuse right next to the positive post of the well insulated (temperature controlled) battery.

    I have the 30A controller already, will I be better off to pick up a 5-10A controller for this little setup? Is extra vampire power going to be that great between the two controllers?
    That sounds like it'd work fine. 20A fuse will protect 12 AGW wire as well as a 30A charge controller.

    If you didn't already have the 30A charge controller, I'd say go with something smaller, but I doubt it'll be a problem. I just looked up the self-consumption numbers for Morningstar's controllers. They say my Tri-Star 45 draws <20 mA. The Pro-Star 30 draws 10-12 mA. The SunGuard 4.5A controller draws 6 mA.

    I hadn't thought to include charge controller self-consumption in my system calculations until now. Luckily it doesn't even amount to a rounding error, <0.5 amp-hours/day in my case.
  • fordraceboy
    fordraceboy Registered Users Posts: 12
    Re: need shopping list... advice.

    Less than 0.15 AH/day between 30A and 5-6A controller. I think it'll be fine. Lol. Like you said- you can adjust/round numbers that far. 👍
  • fordraceboy
    fordraceboy Registered Users Posts: 12
    Re: need shopping list... advice.

    Just looked through the literature on my controller and it says self-consumption is 6mA.


    One more item----

    Stranded vs Solid wire? Is it really an issue?

    Some people say it is, others don't. From my readings and understanding, DC is usually stranded wire because the electrons flow through it, verses AC which flows around the wire. Is this correct, or am I being a jackass. Again. :-D
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: need shopping list... advice.
    Just looked through the literature on my controller and it says self-consumption is 6mA.


    One more item----

    Stranded vs Solid wire? Is it really an issue?

    Some people say it is, others don't. From my readings and understanding, DC is usually stranded wire because the electrons flow through it, verses AC which flows around the wire. Is this correct, or am I being a jackass. Again. :-D

    Electrically there is no difference between stranded and solid.
    You choose which based on what the installation will be: stranded is more flexible and so is used in areas where that is a consideration.

    Some people get confused about the skin effect of high frequency which "flows around the wire". That is why stranded is used for RF circuits; more little wires which have greater surface area to core space ratio. The extreme of this is lightning protection which uses flat, braided wire.

    For power systems only the mechanical difference matters. Even though some people who pretend to be NEC engineers may say otherwise on other forums where people are rude and advice is wrong. ;)
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: need shopping list... advice.

    At 60 Hz, the skin effect is minimal, and is usually safely ignored
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: need shopping list... advice.

    There is house wiring with a few thick strands. Ok to use.

    And there is very fine wire for cord/welding cables and such. Fine wire cables do not usually make reliable connections in hardware designed for house type solid or stranded cables.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • fordraceboy
    fordraceboy Registered Users Posts: 12
    Re: need shopping list... advice.

    All done, been running for a month. Battery stays topped up, and CC is in float mode every time I take a peek at it. Then again, with usage of the gate, it seems as though I was a bit high for initial figuring. Probably needing less than 30 min of sun a day to replace what I use.

    Next project? PV/Wind combo installation with large battery bank to power the lights/fridge/freezer, radio occasionally, etc..

    I'll drag out the Kill-a-Watt meter and factor all the needs and be picking brains again soon.

    You guys are awesome!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: need shopping list... advice.

    Sounds good... Just go out there with a good volt meter and make sure that float is somewhere around 13.2 to 13.6 volts or so... You don't want >~13.8 volts (at ~77F) or you can cook the battery.

    And watch the water level in the battery too--Check weekly until you are sure that you can go a month without having to add water.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • fordraceboy
    fordraceboy Registered Users Posts: 12
    Re: need shopping list... advice.
    BB. wrote: »
    Sounds good... Just go out there with a good volt meter and make sure that float is somewhere around 13.2 to 13.6 volts or so... You don't want >~13.8 volts (at ~77F) or you can cook the battery.

    And watch the water level in the battery too--Check weekly until you are sure that you can go a month without having to add water.

    -Bill

    I've checked a couple different times and I get 13.3 and 13.4, so it looks good.

    Thanks for the reminder on the battery level- totally spaced even thinking about checking it. :blush:
  • fordraceboy
    fordraceboy Registered Users Posts: 12
    Re: need shopping list... advice.

    So, I topped up my battery water level (down just a tad) and measured my voltage coming from the panels- at the charge controller. Voltage was 23.4. Output to battery was rock solid 14.2, and battery measured 14.2. It also showed a nice, bright, green Full charge LED.

    So, a couple questions-

    Why are my panels cranking out that type of voltage? I was under the impression that 12V panels put out 17.3ish...

    With my battery showing charge voltage of 14.2, and getting a charge of 14.2v- why would my controller LED blink to a yellowish/green on the battery meter when the gate is opening? Just because of the draw from the gate? I never really paid much attention to this, but I built a plexiglas enclosure for the controller so I can see charge state (flaot, charge, etc) and battery state at a glance. I work nights and noticed this when leaving at 2230 and the LED's really shine.

    Is there an easy way to check depth of charge? I assume that 14.2v means full charge, and since the battery is less than a month old, I would find it unlikely to be sulfated at the shown voltage..
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: need shopping list... advice.

    You can't accurately measuring PV Voltage on the input to a PWM controller because it is switching on/off to regulate the output Voltage when in Absorb or Float. At that point the closer it is to finish charging the less 'on' time there will be and the PV Voltage will spend more time at Voc (no load) than Vmp (loaded). Thus the high reading. It doesn't matter anyway, because it works.

    If the load on the battery pulls Voltage down, the controller will try to charge it up again. No power from PV (such as at 22:30 hours which I think you meant) and it just reports drop in Voltage (change in LED indicator).

    Flooded cells can be checked with a hydrometer. Sealed cells can't be checked without disconnecting them and leaving them sit then taking a Voltage reading (resting Voltage). 14.2 would be where Absorb is, not "no charge" Voltage.

    If you want all the bells and whistles of reasonably accurate in/out power measurement on a charge controller you have to pay the big bucks for the ones with meters. Not worthwhile in this application.

    You should check the battery Voltage in the morning before charging begins. That will tell you how much is 'left over' after nighttime usage. Also this is an application which will have irregular loading, depending on how many times the gate is opened and closed during the day. So keep an eye on it over time with changing weather and use. That will tell you if it's up to the job.