Wednesday, June 25, 2014

Solar Regulator Testing

A quick post today.  I've been roped into another project for my Dad.  This time he wants to use a solar panel to keep a battery on a generator charged.  Before installation, I wanted to test how it performed as I had suspicions about the quality of the solar regulator.

To test the panel it was set up at ground level pointing to the north (southern hemisphere) on the installation bracket.  An old electrical cable was used to connect it to the regulator that was protected from the weather.

Solar Panel
Solar Panel in Test Position

Cheap Regulator Under Test
The connections are simple.  Two wires come from the solar panel, two go to the battery, and two go to a load that only comes on at night, I connected a low power 12 V LED strip to this terminal as an indicator.  When the voltage from the solar panel drops below a certain point for a set amount of time, the regulator switches to night mode and turns the light on.  Under test this feature didn't seem to work.  The load seemed to stay on permanently, day and night, this was enough to make me question the operation of the whole device.  Over the week of testing it didn't seem to charge the battery at all either.

I've since learned that some regulators discharge through the solar panel at night if a diode isn't installed.  This seems ridiculous to me.  That should be built into the regulator.  So it's possible that it was charging during the day and discharging at night.

Cheap Regulator
As the operation and construction of the regulator seemed a bit iffy, I decided to just buy another one.  I got a decent quality one from Jaycar, the MP3720.  This one also has an extra wire that lets the regulator know if it's charging a wet or sealed battery, this seems to just set a different charge voltage.  For a wet battery it's connected to the negative terminal of the battery, for a sealed battery it's left unconnected.  The regulator is also constructed well, it's potted for splash resistance and it feels solid.

Jaycar regulator
I've connected the new regulator and have been testing it for the last couple of days.  The battery seems to be charging, the night light hasn't come on yet, but I think the battery voltage is still too low for that to happen.

I think this will do the job,  I should know after a week or two of testing.
MP3720 under test


  1. The mp3720 is an excellent controller and doesnt need testing. If the night light feature has not worked yet, I would straight away try to charge the battery full using a proper battery charger, then measure the voltage of the battery the next day, see if it holds charge or not. It might very well be that the battery is failing. For solar, I avoid using wet cell batteries, this is just a personal preference, but I understand you might not have control over that.

    Another issue, that solar panel looks like a baby one, I would guess 5watts to 10watts? What happens is that your system is not 100% efficient, and I am not sure how much power you are using / losing daily (some larger batteries do lose a bit of power daily on their own) -> so maybe re-consider your needs and if you need to, get a larger panel.

    I plan to post some of my solar rigs I have done one of these days at easysolar (dot) solutions... I just need to get a roundtuit.

    1. Thanks for your thoughts. The night light feature has started to work and easily lasts all night, it took a couple of days for the battery to charge to a level that allows it work. The voltage on the battery is holding steady. You're right, the panel is small, it's only 8W, but the battery is quite small and the night light is only a couple of small white LEDs. Everything has been working well for the last week now. So yeah, I'm quite happy with the MP3720.


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