Solar 12V Lead Acid Trickle Charger

I have a couple of things which have 12V (lead acid type chemistry) batteries which get used irregularly. I know well that these batteries need to be kept 'groomed' for optimal life and to avoid disappointment when you go to use the item.

For quite a few years I've used a small 5W solar panel similar to the one above with great success. For instance my "ride on" lawn mower battery is over 6 years old and still acts like new. This is not an accident.

In the past I've gone with the "KISS" (keep it simple stupid) approach of having a 5W panel just directly (well via a diode) connected to the battery. Now I know that a "12volt panel" is not going to put out 12 volts, and I now that to charge a 12 volt (lead acid) battery you need to give it more than 12 volts and all that stuff you can read elsewhere (such as here) if you don't know. A typical 5W panel will not be able to over-charge a 12V battery unless that battery is very small. Instead (probably at worst) it will hold the battery at about 15V for the peak sunlight period and that's it. Some intelligent positioning of the panel will help you to avoid this (taking advantage of the movement of shade and the angle of the sun).

So my last panel died (no idea why, I suspect one of those fine solder joints broke or eroded) and so I went to ebay and bought the one above. Having had them before I just wanted to test the outputs (to ensure it was working) and put it into service. I'll circle back to that, because that led to some discoveries.

The first discovery was that this panel is actually (totally without fanfare) incorporating a mini PWM solar controller in it:

yes, you can see that LED blink when you initially hold it up to the light. The  "Chinglish" is a bit misleading however. When one carefully cuts the back off (held by what is similar to black Sika-Flex) one finds the controller and the LED on the board.

one can test the actual panel (hardly coinvently) of the PV+ and PV- tags (which literally solder direct to the lugs on the back of the panel).

 But one can not test the output of the panel directly by the battery clamps because this is not a simple panel: its instead a system.

This is because a solar controller typically requires an "order of things" when connecting it.

1. connect the controller to the battery (allowing it to know what voltage its dealing with, as many are 12/24V). This is also a "safety" thing for the electronics because an unloaded and cold panel  in full sunlight may exceed the safe voltage input limits of the controller.
2. connect the panel to the controller (charging now begins if there is enough light)

So, because this panel is always directly connected to the panel the above order of connection sequence can't happen. Thus the system shows nothing (yes 0V) on the battery clamps which may (incorrectly) lead you to think that the "bloody thing is broken". (guilty)

Clearly a case of "ignorance is bliss"

So, once I understood this I connected it to the battery via my Amp meter and voilla!! Current flowed and as well voltage began ticking upwards on the battery (yes, I have 2 meters).

Fantastic

Looking on the back of the panel (if one could be bothered to look and think) we see some give-aways here.

In the Specification we see a few lines we wouldn't expect to see:

• Over-charged Protection Voltage (sic) of 14.5V
• Over-charged Recovery Voltage (sic) of 13V

one would simply not expect to see these two on a plain panel, as this is the sort of stuff a controller provides.

It would have been better if the seller had made it clear that this was the case (because then they wouldn't have had to send me a second one because this one appeared faulty).

So basically I can fully recommend this little guy for simplifying my life of keeping my batteries well groomed. Something my motorcycle needs because there is a little 50mA parasitic drain which needs addressing if I don't ride it every day (I don't). 50ma sounds small but after 5 days that's 6Amp Hours and the new capacity of a AGM battery for the bike is about 8Amp Hours, so in winter, a week of not using it during the week means on Saturday you've got a dead battery.

So I can just hang it off the number plate and plug it in to the bike and my battery is kept "groomed". Naturally I had already made up a small DC jack plug to connect my previous (panel and controller) system to the bike.

This streamlines things enormously (because I don't have to connect the controller to the bike and then the panel to the controller) and instead only have one thing to plug and play.

Naturally it works well on the lawnmower too

Win Win