Current draw of small solar controller?

[HeadedToTexas]

The 15 hp Yamaha on our dinghy is tiller steer with no alternator. I wanted to add sonar to the dinghy for exploration and I chose a simple Hawkeye depth sounder that draws 200 mAh when it’s on. I chose a 2000 mAh battery and a small 2 watt solar panel with a simple solar charger.

Here’s my math. The 2 watt panel puts out 2 watts / 12 volts = 0.167 amp or 167 mA. As long as I run the depth sounder for less than half of my typical solar day here at 40° north, the 2000 mAh battery should be good.

Unless the little solar charge controller draws more amps than I figured. It has LEDs that indicate charge state. Guessing they are part of the problem. Do I even need a charge controller for this application?

 

[DavidM]

You probably don’t need a solar controller with your setup. You are drawing more than the 2 watt panel can replace.

Realistically that 2 watt panel will produce a lot less than .167 amps due to the sun angle and clouds, less than .1 amps. A 5 watt panel would work better.

 

[HeadedToTexas]

With such small values, what are the consequences of simply wiring the positives from the panel, battery, and sounder all together and same with the negatives?

 

[Bmarler]

With such small values, what are the consequences of simply wiring the positives from the panel, battery, and sounder all together and same with the negatives?

Depending on the open circuit voltage of the panel, over long periods of non use with solar left connected, the voltage might rise to a high level and dry out the battery. Note that I said “might”, the two amp output of the panel might not be enough to do anything bad.

 

[HeadedToTexas]

It’s not even 0.2 amps, right? And that’s at peak which here at 40° north isn’t long.

 

[DDW]

A 2W panel isn't very big, but there are small controllers (like the 5A Genesun) that draw only microamps.

 

[HeadedToTexas]

And it’s a NiMH battery.

 

[Bmarler]

And it’s a NiMH battery.

You should have lead with that. Makes a big difference. I wouldn’t sweat it, just hook it all up parallel. I would include a volt meter so you can see how it holds up over time.

 

[HeadedToTexas]

Just an update. I have wired the battery, solar panel, and sonar (switched, of course) together in parallel. So far, so good.