I would just go buy a solar usb charger and rig it up in series with the cells. The charger would not put out enough juice to fry any batteries. Since nimh batteries naturally dwell at 1.2 volts, they would float at 1.25 per cell in theory. If one battery hogs more volts, it won't hurt the others.

$15 from Hong Kong
USB 3W 550mAh Solar Panel Mobile Electric Source Power Charger for iPhone 5S 5c | eBay

For a few bucks more, you could just ditch the D-cell batteries and get a power bank widget to plug into the motor:
$30 from USA
10000mAh USB Solar Power Bank Charger for iPhone iPad iPod Samsung i9300 N7100 | eBay

I like the Solar panel idea
If the solar panels were hooked directly to a charger the charger would maintain the batteries, my minor brainstorm..

Many chargers use a wall wart with a dc jack that plugs into the charger itself , it could be easy to wire the panel to the charger then the charger to the batteries.

I agree with Nahoemike in that most batteries are "balanced to start with" or are at even spec.

I use a 5A RC battery charger that charges lipo , li-ion , nimh , nicad , Pb / Gell cells and ordinary led acid batteries with complete control over every aspect of the charging amps and voltage and charge durations, + a balancing board ( a mini external board with multiple input and output connections) for charging and balancing multiple battery packs and types at the same time.

Jeff88 I change my mind after more consideration.. I would not worry so much about balancing your rechargeable D- size batteries, its not worth the fuss in this circumstance and they will start off pretty well balanced to begin with.

I noticed the use of "heavy duty" batteries in the photo. They are VERY low capacity compared to alkaline batteries (about 1/4 the MAH !!) How long will 4 fresh alkaline batteries last?

Didn't notice the "heavy duty" and didn't know they don't last as long. I, too, would be interested in the service life of a regular battery, however, I really just want to come up with a more eco-friendly way to power it (e.g. rechargeable batteries).

Rechargable "D Cells" are mostly AA's with a shell around them. Real D rechargeables you are going to have to dig for. Hardwing the old cell charger is a good option :)

Commonly known secret: AA and C batteries are exactly the same length. The chinese christmas toys that run off C batteries now have AA batteries with foam donuts around them to keep them centered. D batteries are a couple of pennies longer... so the chinese toys that run off D cells have foam donuts and springy thingys in them now.

Any updates on this?

No, my new job has taken up most of my time. Some day...

Get a hobby charger... there's lot of them for less than 40$.


You can charge pretty much any kind of battery, just use small magnet on crocrodile end to charge your d batt...

Came up with a solution...
 

Finally had a few minutes to do something about this issue and finally made a decision on the direction I wanted to go. I toiled with plugging into a wall, using re-chargeable batteries and having to take them in and out for charging, using one of my airsoft batteries, etc. I finally decided on just plugging it into the wall, since the garbage can sits right in front of a plug which is otherwise unused. Once I made that decision, I went back and forth on how I wanted to get power from the wall to the motor. Here's what I decided on:

First was to use my multimeter to determine how many amps the motor used in normal operation and when under extreme load (like forcing the lid closed while it's trying to open). The amperage was something like less than 200 milliamps (I forget now).

I started with finding something with open leads and a nice female plug on the other end. Found this: DC Jack Adapter

Connected the leads to the battery springs:
http://i1289.photobucket.com/albums/...psty50bgdx.jpg

Allowed a little slack for the plug:
http://i1289.photobucket.com/albums/...psf8ysivou.jpg

Found a plug that fits into the female end of the other one: DC power to USB
http://i1289.photobucket.com/albums/...psjnrhbj0x.jpg

And then I plugged all that into this neat little gizmo that I have a thousand of, a good 'ol standard USB adapter for a cell phone:
http://i1289.photobucket.com/albums/...psjohljkqo.jpg

It was just that easy! Now, all I have to do is drill a little hole and epoxy the female plug in to clean it up a little. For now, I just have the wire sticking out a little bit.

For day to day use, I just flip the switch and may or may not unplug it, remove the lid and empty my trash. I don't have to deal with batteries, charging, or anything else.