I need to power an irrigation system with a portable 12v battery. The battery is recharged by a solar trickle charger.
The battery powers the arudino connected to data logging shield which logs every 30min. It also powers a 12v pond pump for about 30 minutes each day.
I'm having trouble keeping the system successfully charged and trying to find the solution.
I assume I need to determine the amperage pulled by the whole circuit and ensure the battery has proper amp.hrs to fulfill the demand. Does anyone know how I could successfully determine this amperage??
Any other suggestions would be greatly appreciated.
With a multimeter. Measure the current drawn by each thing independently, then multiply by the time
each will be on per day - that will give you the capacity used.
Solar power depends on the number of hours of sun, which is highly variable depending on weather
and season. Best to assume battery capacity should be many days, not just one day.
Also, assume the charging circuit is only something like 80% (I forget exactly) efficient. If you take 80 AH out of the battery and put 80 AH back in, you will come up short - you will have to put more like 100AH back into the battery to make it work (up here in the Seattle area, you need to put a little water wheel at the bottom of the solar panels to let the rain charge it when the sun is not around )
The best place to put the multimeter is in series with one of the battery wires (with the solar panel disconnected as you do the test).
You want to measure:
The current drawn by your 12V motor. Multiply that by 0.5h, and that's how many Ah/day you'll need to run your pump. This amount will likely be 80% of your total Ah required.
The current drawn when the system is idle (should be almost nothing) and multiply it by 24hr. That's how many Ah/day you'll need just to keep the Arduino alive.
The current drawn when you're logging. You'll probably need to make special code that logs continuously in order to measure the current with a multimeter, as I imagine it's going to be a short spike of current during a short logging process that won't accurately register on a multimeter. You need to multiply that current by the amount of time logging actually takes, and multiply that by 48 since you log every 30min. That's how many Ah/day you'll need to log with your Arduino.
Add the 3 Ah together and that's the amount of Ah you'll need per day. You'll want to size your battery to be 3-4x this amount to deal with days without sun. You'll want to size your solar array so that under optimal conditions it provides 1.5-2x this amount so that it can catch up for days without sun.
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