# Solar power for 1 amp relay board

Hello , I want to power “XXX-Channel 1-Amp SPDT Signal Relay Shield” with photon, with solar power/battery, any project I can use as a guide?

thanks

Hi Sergio,

That board will draw about 46 mA at 12VDC continuously if it is to maintain communication with the Particle Cloud. When the relay is energized there will be an additional current draw of approximately 12.5 mA at 12VDC.

Thanks Travis, a question, 12.5 mA is per relay?

That is correct. Each energized relay will draw 12.5mA when energized.

What are you powering with the Relays? The 12.5 mA per relay is in addition to the actual load.
If you share your load and estimated duty cycle, a simplified power budget can be calculated with the info Travis posted.
That will point you in the right direction for Solar Panel and battery size.

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I thought about tagging you on this one @rfontaine since you have some good recent experience with Solar projects. Didn’t want to seem pushy though

@rfontaine, the relays will turn off/on a already powered 12v electric fence.

10-4
The Quick Version:
Calc’s will assume 12.0V, even though your battery will hopefully stay well above that.
Also assume 1 relay powered 24/7.

Per Travis’ measurements = 46+ 12.5mA = 58.5 mA = 0.0585 Amps
Watt = Amps * Volts
Watts = 0.0585 * 12.0 = 0.7 watts.
For 1 day = 0.7 watts * 24 hours = 17 watt hours.
In a perfect world, a 17 Watt Solar Panel would recharge your battery with 1 hour of full sunlight.
The quick approach is to de-rate any Solar Panel 50% (I’d be happy to explain in more detail if ya care to read it).
For Instance, if you want to use a 12V 10 watt Solar Panel, go ahead and de-rate it to 5 watts.
We calculated that you need 17 watt hours per day, so you hope for 3.5 hours of Sunlight (17/5) each day to maintain the battery. That’s pretty optimistic, but can be done if your battery has enough reserve capacity for Cloudy Days.

Battery Capacity:
I’ll use a 7 amp-hour SLA battery for an example.
To prolong the life of the battery, you don’t want to cycle it below 50% capacity.
So de-rate the Battery Capacity 50% (similar to Solar Panel). For the Simplified Calc’s, this battery now has a 3.5 amp-hour effective capacity.
3.5 amp-hours / 0.0585 Amps = 60 hours of runtime, without Recharging. That sounds like a LONG time, but that’s only 2 cloudy days.

A full Power Budget gets much more involved, but this shows you how to get a decent idea pretty quickly.

Decide the minimum # of hours of sunlight that you expect in the Winter to size your Solar Panel.
Decide the maximum # of Cloudy days in a row that you expect in the Winter to size your Battery Capacity.

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Perfecto! you are the best!