Charging Rechargeable D Batteries
 

My garbage can is one of those hand motion lid opener kinds and needs 4 batteries to operate. :eek:

I used one set of batteries when we first got it, but I don't want to keep replacing them. I want to get some rechargeable batteries, probably Duracell because my other rechargeable's are. The problem is finding a charger that can support the amount of charge a D cell can hold. From what I have read in reviews, even if it "fits" a D cell, that doesn't mean it will fully charge it to capacity (meaning I have to charge more often).

So I'm looking for (and thought of a few) options to charge the batteries as necessary. Here's a few I thought of:

1) Use a power supply/wall wart and cut the end off, strip the casing and attach the positive/negative to a case which will hold the D cells. Never doing this before, I don't know how best to do it. One D cell is 1.5 volts. If I charge them in series, that is 6 volts. Should I get a 6 volt power supply and charge them in series or get a 1.5 volt power supply and charge them in parellel? Or maybe charge a pair in series and another pair in series? Or maybe a pair in parallel and another pair in parallel? In either case, should I get the exact voltage (6 or 1.5) or should I bump it up a little (say, 7-8 or 2-3)?

2) Another option and one I would really like, is a small solar panel. The issue I seem to find is how long it would take to charge the cells. I can find a panel that will output the right voltage, but the mA of output would take daaaaays to charge them up fully. I would need a second set and I don't really want to do that. If I could figure that issue out, the same question applies here as well, how best to charge them (in volts, 1.5, 3, 6, series, parallel)?

Anybody have any ideas or a thread link that I missed?

You can remove the batteries, let them cool off for a few minutes, and put them back in for a second charge cycle. And only using part of the battery capacity makes them last longer - that's what the Prius does. (That applies to all types of rechargeable batteries I know of. You'll want to keep them somewhere in the middle of their SOC range, except for lead acid that likes to stay near full charge. Every once in a while, you'll want to do a full charge to allow the individual cells to rebalance.)

I would recommend ditching the batteries all together. A 5V cell phone charger should be fine to power it. That is 1.25V per cell which is about what NIMH cells run at, and they work in nearly everything. Only the pickiest of electronics don't like them.

Cool project though, I wanna see some pics. :)

I think I get what your saying... plug in the power supply, then strip the wire to attach to each side of the battery terminal... only problem is that there is no nearby power outlet. I like the idea though, that way I don't have to worry about it at all.

I'm still not sure how best to charge the batteries. Series, parallel, two pairs...

Here's what the battery compartment looks like if it helps:
http://i1289.photobucket.com/albums/...psa705997d.jpg
Dimensions are 9.375" X 1.25".

I also had another idea, which wouldn't require batteries or home power at all, but it would be more of a research and learn then put it back to normal type of thing... more to come on that concept!

Since you're DIYing, there is nothing stopping you from extending the wires... Unless you are really WAY too far from an outlet.

If you charge them individually each battery will get it allotted charge, when charging multiple batteries at once the charger will send a charge to equal the combined voltage of in your case 6v or 7v to the set of batteries.

Problem is one or two batteries could receive a overcharge at the same time 1 or 2 more batteries could be undercharged but the charger will not know it, it will happily charge until the whole pack of batteries reach its 6-7v, possible cooking a battery or two in the process.

For RC battery packs and the like , they use balance chargers which allows all batteries to be individually monitored while being group charged.

In your case charge them individually and the batteries will thank you.

Regards, Doug / ecomodded

A balanced pack, in practice, will stay balanced until near end of life. And unlike lithium batteries, NiMH will tolerate a slight overcharge if not done too often - that's how balancing is generally done.

I was thinking about the solar panel idea for charging, then I remembered something I saw here talking about by-pass diodes.

http://www.solar-facts.com/panels/bypassdiode.png

So it got me to wondering if I could install a by-pass diode between each battery (effectively each "solar panel"). If one battery becomes a higher resistance, then the current will flow to the next one until the second one becomes too high resistance and then so on and so on.

Here's what I am thinking:
http://i1289.photobucket.com/albums/...psa2f8e7cb.jpg
You can see the by-pass diodes between each cell, effectively making a path of less resistance to the next one.

Will this work, or is my electrical theory incorrect somehow?

I've been told this won't work at lower voltages (I looked into it while developing a lithium battery management system for my PHEV Prius kit a while back). Zener diodes do not work as well at low voltages as they do at higher voltages. Their transition from blocking to allowing current to flow is more gradual at lower voltages. At higher voltages (like 13V or so), its more like a switch, and that is what you want.

I was actually thinking of using a Schottky diode for it's relatively low voltage drop. I can't find anything about their characteristics based on the voltage of the circuit, would they have the same characteristics as the Zener diodes?

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.

Looks good to me.

Nice fix. That is much better than messing with batteries.

I agree. Easier and better for the planet! It's a win-win!

Jeff good job! I learned some things with your solution. But for the other poster who said D rechargeables are hard to find, not so. Walmart's got them for $10. Ebay even cheaper.

Thanks Leafgreen!

The batteries themselves aren't hard to find, it's the charger that allows for the size of the D batteries that is seemingly hard to find, at least in the States. Most only go up to the C size at most.

For C and D batteries, I use the empty holders that came with my charger. Finding a charger that will hold that size is difficult, but putting large capacity AA batteries inside the adapters works well.

Just use the highest capacity and quality AA rechargeables you can.
Even it doesn't last long enough, you could hack together your own holder that would hold 3 AA batteries for each D battery, basically making your own D battery out of AA

Also an old cell phone battery should be around that voltage; you'd have to keep the old cell phone nearby (taped to back of can) as the battery charger holder