AA cell to D cell convertor

[Gundam]

AA cell to D cell convertor

are there AA cell to D cell convertors available off the shelve?

it's more economical to have one type of rechargeable batt like AA than to have a few types of batt and different chargers to cope with it.

the dimensions of a D cell can easily accommodate 3 AA cells as there are some pics in CPF showing 3 AA cells in series, but I'm thinking if there are convertors that run the 3 batts in parallel. will there be any increase in current that might overdrive LEDs in particular?

 

[Gundam]

upz

 

[Slick]

Yes, I purchased a Panasonic NiMh charger that came with AA cells and adapters to put an AA cell into either a C or D size.

Thes adapters fit only 1 AA cell to each adapter, so voltaqge remains the same. I don't use them because I don't want a rechargable D cell that's only 1700Ma.

 

[Slick]

Here's the exact kit that I bought...

You can see the C and D adapters towards the bottom of the blister card (2 each)

 

[Empath]

Sweet Adaptations

American Science & Surplus

 

[Gundam]

Slick ,
how abt squeezing 3 AA in a D cell convertor and run them in parallel.

will i get 1700*3 = 5100mAh

thinking of making a convertor but will the hassel be worthwhile?

Empath,
thanx for the link

 

[CiTY]

Actually they sell that Panasonic kit at Costco. With a rebate.

 

[Slick]

Originally posted by earwax:
Slick ,
how abt squeezing 3 AA in a D cell convertor and run them in parallel.

will i get 1700*3 = 5100mAh

thinking of making a convertor but will the hassel be worthwhile?

Empath,
thanx for the link

<font size="2" face="Verdana, Arial">These adapter's wouldn't offer you any advantage over just building them from scratch. If you want 3 AA's in a D carrier, see MrBulk's posts on the eBay flashlights he bought just for the 3AA to D battery holders. A pair of these holders makes 2D flashlight potential mod material for the 5W Luxeon.

I bought mine at Costco like City sez.. $14.99 after a $5 mail in rebate.

 

[Lucien]

I'm interested too, but for other reasons. I was wondering what is a safe level of discharge of a given battery? If the current load is unreasonably high, then using 3 cells in parallel would mean each cell having to support 1/3 the total load.

There might be problems with a parallel set-up though, I think somebody mentioned something about it on another thread, cross current something or other, wiring packs for RC use in parallel, but I can't find the thread now...

Then there is total capacity to consider, I believe GP batteries has a 7000mAh D cell, and the largest capacity AA cell they have is 2000mAh, so at best the 3xAA solution would be short 1000mAh. Would lower current load offset this? (For comparison, an Engergizer D cell alkaline is rated at 18000 mAh)

A custom built AA-D cell converter would be interesting, especially for a 5W LS Maglight mod. Even more interesting, a single peice converter that could replace 2 (or 3) D cells. I'm not aware of any on the market though. Designing one would be a easy task, getting them made on the other hand...

 

[Steelwolf]

I haven't seen any D-cell adapter that takes in 3 AA cells in parallel. Fortunately, it is not a terribly hard adapter to make yourself, since you basically need something to hold them together (sticky tape?) and something to provide a single point of contact for positive and negative terminals (metal disc, probably with springs soldered on to contact the AA batteries). This may need some refinement to make it work but I have done something similar a couple of times with 2x35mm film canisters (the plastic tub holding the can that holds the film.)

I had two neoprene disks covered with a flexible wire mesh. One disk was wedged in to the bottom of each plastic tub. A hole was punched through the bottom of each tub and the appropriate nipple and flat contact surfaces were put in place and connected to the flexible wire mesh using wire, solder and hot glue. So the final set up has one tub on the bottom, with the appropriate flat contact surface and the 3 AA batteries wedged inside. Then the other tub is placed over the top (+ve) of the batteries. The fit is a little tight, so it should stay together, but the flashlight battery compartment should be able to provide the rest of the compressive force. The individual tubs can be wrapped with paper to make up the rest of the diameter.

I hope that was simple enough to understand. The real difficulty is making a holder that can take 4 batteries in a 3V configuration. There is insufficient space to have a tub go around the batteries.

As for off-the-shelf stuff, I have a bunch of adapters from GrandCell, but they only take a single AA battery, though they are for both C and D cell applications. I got them for the C cell configuration which allows me to use lithium batteries with my UKE-SL4.

 

[Steelwolf]

Oh yeah, there might be an increase in current available, since the internal resistance of batteries are just like any other resistance value. ie, you add the resistances if they are arranged in series, and use, 1/sum of resistances, when they are in parallel.

On the other hand, D cells are able to deliver more current per hour anyway, so you might not really get any performance improvement.

 

[Gundam]

Woohoo! Steelwolf u got the bull's eye.

intuitively i felt that there would be some change in current but i guess u confirmed it... u see i sux big time in my circuits.

so wif this parallel configuration there will be lower internal resistance thus current will increase. since LEDs in particular are sensitive to current then there will be a problem

 

[Jonathan]

The internal resistance of AA cells as compared to their capacity is much lower than the internal resistance of D cells compared to the D cell capacity. But D cells store much more energy, and so a single D cell will have lower internal resistance than a single A cell.

But if you look at datasheets for alkaline batteries, you will pretty much find that 3AA cells in parallel have lower internal resistance than a single D cell, so that at moderate to high currents (say 1/2A and above) the set of 3 parallel AA cells will deliver more energy to the load than a single D cell. This is why the 'double barrel' flashlights would often work better than D cell based lights.

-Jon

 

[dilettante]

For 2D applications, Willie Hunt makes a sweet "AA conversion stick" that holds 8AAs and incorporates a voltage regulator. I stuck it in a 2D MagLite with 8 Lithium AAs and the bulb he provided. The results re much better then 2Ds and an aftermarket Krypton bulb. I posted details elsewhere if you are interested.

 

[sunspot]

dilettante. I am interested in the stick. Where can I find more info on this?

 

[Gundam]

Lucien,
did u find GP 7000mAh D cell in the local hardware shopes? i believe that it's rechargebles. most of the time i find BP rechargeble D cells wif less than 1000mAh

dilettante,
yeah i'm interested i that 'stick' too. where did u get it?

 

[Lucien]

earwax,
I haven't actually seen the GP 7000mAh D cell on the shelves yet, it is listed on the GP webpage though. And yes, it is a rechargable (NiMH).

I have seen the rechargable 2000mAh AA cells, they're a little pricy, so its up to the individual as to whether they're worth it over a set of 1800mAh units.

Jonathan & Steelwolf,
So, in the final analysis, 3 (or 4) AA cells in parallel would be better than 1 D cell for a high current load? Say 0.5 - 1.5 A? I didn't really get what Steelwolf meant by "D cells are able to deliver more current per hour anyway".

Also, does anyone have any info on "reasonable" current loads for batteries? How much is too much?

 

[txwest]

Ccrane sells 9000mAh NiMh's for $9.95, shipped. TX

 

[Alan]

I have been using GP 9000mAh on a few lights for sometimes. Charging them takes forever on my Saitek smartcharger - around 24 hours for a set of 4:-(

Alan