Is the charge controller leaking power?

[Brae09]

I recently built an automatic duck coop door. The power for the actuator is from a 12 volt 7 amp battery which is charged by a small 3 watt solar panel. There is a pwm charge controller that both the battery and the panel are connected to. But the door operation keeps failing. Each time I found the battery in very low voltage, around 10 volt. The battery is new. The panel outputs 17 volt during the day. I wondered if the battery was being drained at night when the panel was not putting out a charge. So I did this test. With the battery connected to the controller and the solar panel disconnected, I measured the voltage on the terminals where the panel was connected to. It was 2 volt. Does this mean that the controller would be leaking power if the panel is connected but is not putting out a charge like at night? I would think there should be no voltage on those terminals if the controller is working properly. I would appreciate your thoughts on this.

 

[MisterSandals]

small 3 watt solar panel
The panel outputs 17 volt

Are you sure? 3watts/17volts is .176 amps

To charge a 7ah battery it would take 7/.176 = 40 hours of full sun. The earth spins way too fast for your application.

If your battery is sitting at 10volts, it may be irreparably damaged.

But the description/specs of your equipment sounds REALLY odd.

And pictures of the duck coop please!

 

[nosys70]

you need to plan to recharge what you drained from the battery on less than 5 hours (or less if lighting is less than ideal).
so if your battery goes from 100% to 60%, you need to get the missing 40% from the panel.
for a 7A battery it means 7x.4=2.8A.
2.8A divided by 5= 0.6A under 12V that means 7.2W panel.
since you probably loose in panel and conversion, let's round it to 10W panel.
you are far too low with a 3W panel.

you did not specify how much energy the door (and timer ?) require, but obviously each day you loose a bit of percentage in the battery, until it is totally empty.

 

[Brae09]

Thank you both for the thoughts and questions. I've attached a picture of the setup. The motor (actuator) is rated at 12 volt and 3 amp. From your calculation (nosys70), it would need a 10W panel. But does the length of the motor operation come into play? It takes 15 seconds for each open and close. So the total operation per day is only 30 seconds. I am not sure how much power the controller, the switch, and the timer consumes. The 8-pin electro-magnetic switch is only powered during the day. So is the switch in the timer.

So the panel does drain some power at night? If so, how much is expected? I mentioned that, when the panel was not connected and the battery was, there was a 2.2 volt reading at the controller's terminals. Is that normal for a controller?

MisterSandals, the battery can still be charged to over 12 volt and it would stay that level without load. I don't know if it means it is still good.

 

[Brae09]

What do you think about this calculation:

1. The motor rated at 12 volt and 3 amps is equivalent to 36 Watt.
2. The motor running for 30 seconds per day would consume 36*30 = 1080 Joule of energy. (Watt = Joule/second.)
3. The panel at 3 Watt would generate 1080 Joule of energy in 360 seconds or 6 minutes. 1080/3 = 360.

If this calculation is correct, the panel would have been more than adequate for the application.

As a test, I ran the motor 4 times, the battery's voltage barely dropped. Currently, I am testing to see if the panel is draining the battery when it is not receiving light.

 

[JoeHam]

No idea if this is your problem but years ago cheap solar panels did not have a diode installed to prevent what I call "backflow" current. Basically the solar panel acts as a load overnight.

 

[Supervstech]

you need to plan to recharge what you drained from the battery on less than 5 hours (or less if lighting is less than ideal).
so if your battery goes from 100% to 60%, you need to get the missing 40% from the panel.
for a 7A battery it means 7x.4=2.8A.
2.8A divided by 5= 0.6A under 12V that means 7.2W panel.
since you probably loose in panel and conversion, let's round it to 10W panel.
you are far too low with a 3W panel.

you did not specify how much energy the door (and timer ?) require, but obviously each day you loose a bit of percentage in the battery, until it is totally empty.

Your numbers are right, but you are mixing up ampdraw with amp hours... the 3 watt panel is totally sufficient, unless his door is operating constantly like a revolving door... doubtful.

 

[Supervstech]

No idea if this is your problem but years ago cheap solar panels did not have a diode installed to prevent what I call "backflow" current. Basically the solar panel acts as a load overnight.

This is the problem.
It is the solar panel’s job to ONLY produce power... not the charge controller. If you are losing battery power at night, you need a different panel, or you need to install a diode.

 

[Brae09]

My test didn't show any significant voltage drop overnight. Supposedly, the controller should prevent the backflow from the battery. And the panel is designed to work as a trickle charger for car batteries. So it should have the diode.

While a 3W panel should be enough, I am finding that on cloudy days it doesn't seem to have enough power to actually charge. For example, the panel on its own will measure 15.5 volt. When it is connected to the battery through the controller, the input to the controller is just 12.4 volt. In turn, the controller puts out 12.2 volt to the battery. In comparison, if I connect a AC based float charger to the controller, the input voltage can reach close to 13 volt. The float charger by itself measures 13.6 volt.

I am thinking I should get a 10W panel and it would have stronger "charging power" on the cloudy days, which we have many in a row in Oregon. What do you think?

 

[45North]

I am thinking I should get a 10W panel and it would have stronger "charging power" on the cloudy days, which we have many in a row in Oregon. What do you think?

Can't hurt to upgrade your panel. I have a trickle charger too but I'm not using it for this application.
I am running the same battery as you with a 25W panel which on the face of it would appear to be plenty but we've had a lot of cloudy, cold, snowy days here this past month so I've been having issues too. I'm starting to come to the conclusion that winter in the north is not really that conducive to solar energy.