Nope, I plan on just having a plug similar to that as a port to plug in the solar panel.

Depending on how power hungry the alarm clock is (I'll be testing this) will determine what I do. It might be easier to just plug the solar panel in for a charge up every month or so. 4 hrs of charging at 200 mah should get the batteries around a third charged, 8 hrs is 2/3rds charged. This is how my outdoor thermometer station works and I like it. If it is more power hungry than I anticipate, I'll just mount the solar panel on a window and run a wire across the room to the clock so its charging at every opportunity.

In any case, the plug just would make for a nicer setup.

Continuous trickle should extend battery life, no?

Yes, you are right. Less deep cycling will extend battery life. That is the way I originally thought of when I designed the charging system (solar panel hooked up 24/7). I probably will still do it that way.

Measuring the power draw will give more info on how flexible I can be with things.

Interesting. Going to hook it up to a digital multimeter for the DC current draw test?

Yeah, something like that. I'll pull the batteries out of the clock and wire them seperately. I'll have one multimeter measuring voltage and another meter measuring current. That should give me pretty precise power draw with and without the backlight on.

I got around to taking the clock apart and measuring power draw. The results were encouraging.



http://ecorenovator.org/forum/attach...1&d=1357942682

http://ecorenovator.org/forum/attach...1&d=1357942682

Using a 4.55V alkaline battery pack (nimh will be lower voltage), the clock uses a pretty impressively low 20 uA (microamps) with the back light off.



http://ecorenovator.org/forum/attach...1&d=1357942701

With the back light on, power consumption increase 11X to about 235uA! This isn't real surprising. The majority of the power consumption of even laptops is the back lighting for the screen.

However, even 235 microamps is still a very tiny draw. The batteries I'm using are rated for 2200 milliamp hours. That is the equiavalent of 2,200,000 microamp hours. So, even if the back light was on 24/7, the batteries should theoretically last 390 days! But, that is not the true case, in reality the current draw will be even lower, lets say 128 microamps (average of 20uA and 235uA). This almost doubles the battery life to 716 days. Still, this isn't realistic because nimh batteries are known to 'self discharge' on their own.

So, the solar panel must compensate for the draw of the clock plus the self discharging cells. I'll note you can buy low self discharge cells (aka precharged). Mine are not precharged cells, so I'll have to deal with this.

It was also mentioned on the blog post that my solar panel voltage may not be high enough to sufficiently charge the batteries. The commenter says you need at least 2 volts above the battery pack voltage to get a charging to happen. Testing will have to be done to ensure that the solar panel is in fact charging the batteries.

I reassembled the alarm.

Before doing so I soldered in some wires to the positive and negative battery leads and routed the wires out the back to hook up to the solar panel.

http://ecorenovator.org/forum/attach...1&d=1358089874


Tied the wires in a knot to stop them from being ripped out and/or putting stress on the soldered joints.

http://ecorenovator.org/forum/attach...1&d=1358089808


Drilled a hole in the back of the case for the wires to exit the case.

http://ecorenovator.org/forum/attach...1&d=1358089808


Then reassembled the clock.

http://ecorenovator.org/forum/attach...1&d=1358089808

http://ecorenovator.org/forum/attach...1&d=1358089808



Next up I'll have to find me some sunshine to test out weather the solar panel is actually going to charge up these batteries or not. Since the clock uses so little power it shouldn't take much to keep a sufficient charge.

You know you're an ecorenovator when... you put this much time into avoiding plugging your alarm clock into the wall. :D

Just kidding. Enjoying the project.

Haha, thats pretty true! It is a learning experience though, and a fun one. As you well know I quite enjoy this kind of tinkering.

I realized that I never finished writing up this little project. The last update was in 2013 and it has been working incredibly well ever since then. The nimh batteries plug away for months on end due to the awesomely low power consumption of the clock. One day in the sun literally powers this clock for months if not an entire year.

Here are some pictures of how I hooked up the 5V 200mah solar panel. The solar panel got a little pigtail and connector that I had kicking around. I forget what they're called, but its what computer fans use. I did not use a diode. I later wished I had gone with a higher voltage panel, so I did not add a diode as that would lower the voltage that the panel outputs. I simply plug the panel in when in use, and unplug it when its not in use.

https://ecorenovator.org/forum/attac...1&d=1564579415

https://ecorenovator.org/forum/attac...1&d=1564579432



Here is the full setup.

https://ecorenovator.org/forum/attac...1&d=1564579493

https://ecorenovator.org/forum/attac...1&d=1564579576