D Rechargeables

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spencer

Enlightened
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Jan 19, 2008
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Saskatoon, Canada
I am in the planning stage of making a multi LED light. Right now the plan is to have 8 crees running off of two sharks. Four LEDs in parallel for each shark. I need some suggestions for the batteries. As the title says I would like to use D cells. I figure that I would need either two or three 3.7 volt batteries. I haven't decided if I want to use two or three batteries yet. I was leaning toward getting KD's 7.4V 5Ah 2 cell battery pack but I just read something that is making me lean away from them.
Awhile ago I saw a thread on someone who was trying to get a group buy on these really high capacity D cell batteries. I never finished reading the thread and haven't been able to find it again. Maybe I should use those batteries?
Anyway, just wondering your suggestions on what I should use. Higher capacity is a plus but I know that at least in the AA world the higher capacity batteries are not nearly as high performing. As you can see this light will be fairly taxing and on high will pull 30 watts (3.7V/LED @1A so 14.8V/string at 1A and 29.6V/all LEDs at 1A). From what I hear I should probably use protected so I don't accidentally kill the batteries. Also, LuxLuthor's packs may also be an option.
 
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Hello Spencer,

Saft cells are excellent, but you may want to study the spec sheet, closely.

It looks like the maximum continuous current draw that gives you at least 50% of the cells capacity is 0.08 amps. They will handle pulse loads up to 0.25 amps, but if your needs are greater than that, you should look at different cells.

Tom
 
From my experience, the KD D twinpacks work but you have to do a lot more changes to the light in order to get them to work. In their standard form in a regular 2x D Maglite they only work with the ROP Low bulb.......Now the KD D individual cells work with less changes to the light and run the WA1111 in standard 2x D Maglite (at least in my experience) Having said that, I have installed AW multi level switch into my 2x D Maglite and now use the Philips 5761 in it.
 
I'm building up a light I want to use D cells for. I'm going to be using KD 3AA to 1D adapters with some eneloops for now although in the not to distant future I'll probably upgrade to a single 6aa to 2D adapter.
 
I found another Saft battery. I believe that this is more suited for my application.

The whole amp thing kinda confuses me. If I have 3 of these in series it will supply 8.4 volts under load. If I have four CREE's at 3.7 volts each thats 14.8 volts at 1 amp is 15 watts. There will be two of these strings so it will pull 30 watts. 30 watts divided by 8.4 volts is 3.6 amps. I should be within the capabilities of this battery.

Spec sheet here.

Please check my calculations. I think I should be good with these batteries but please advise. Also what should I use as a charger?
 
spencer said:
I found another Saft battery. I believe that this is more suited for my application.

...

Spec sheet here.

Please check my calculations. I think I should be good with these batteries but please advise. Also what should I use as a charger?
Click to expand...
To charge it? Nothing. That is not a rechargeable battery.

As you can see at the top of the data sheet, it says, 'Primary lithium batteries'. You probably have not picked up on it, but primary batteries are one time use disposable batteries, and secondary batteries are the ones that can be recharged and used repeatedly.

As the data sheet says, lithium-sulfur dioxide cells are a special kind of cell designed to be installed in inaccessible places so they can remain in place for a long time without attention. They are quite expensive and not really intended for consumer use.
 
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Yah Spencer, I had a 14500 one of those saft batteries back when I was un-enlightened :) Trust me, they are not for this application. They use a different chemistry altogether and besides not being rechargable they are only for low current draw applications.

I am not sure about your math below either. You say you are planning on running 2 banks of 4 leds in series-parallel. So, you will need to supply in the neighborhood of 3.6 volts at over 4 amps per bank. That leaves you no headroom for runtime however, so it would take more like 4.2 volts. If you are set on running the emitters in parallel I would think your only option would be to run AW's excellent D cells. They are probably the only protected cells that will allow 4 amps or better without tripping the protection circuit.

Without doing the math, I would think you may want to look at a 3D or 4D with 9 or 12 eneloops and 4 leds in series in 2 parallel banks.

Frankly that is a very complicated build to consider so I am not qualified to answer all the questions, but I have planned out a 5 cree on 9AA eneloops and I am right at the border of what the driver can do. The driver I have purchased by the way is the maxflex.

There are concerns with running the emitters in parallel vs series, among them being if one of the leds has a lower voltage forward than the others, it will get more current, possibly overdriving it. And, if one was to burn out, the other 3 would then be very quickly overdriven. My understanding of this is that in series it can be avoided. You should have no trouble locating discussions on it.

Good luck, can't wait to see your results!
VegasF6
 
I'm kind of not planning on doing series-parallel. I plan on running four CREE's off on one Shark in series. Then on a separate Shark I plan to put another four in series. Make sense?
 
Would you consider 4d nimh high amp/high current cells for your build? With the shark you do not need a high voltage input.
 
That would really be pushing it. I want a two D maybe three and definately not four because of the size. Also I read that the Vin to the Shark should start at 1/2 Vout and at the end of the battery life it shouldn't sag past about 1/3. With 4 NiHD at 1.2 volts each is only 4.8 volts, less than a third of the light on high.
 
If you really want to run 8 Crees and two Sharks I think the best power source is going to be 3 AW "C" Li Ions.

The next batch of Sharks will be able to sustain a 3 amp input. You could run 6 Crees off two Sharks with 3 Accupower LSD D cells.

Two cells aren't going to cut it.
 
Unfortunately I'm leaning back toward the KD cells. I'm liking the higher capacity of the D cells. If AW had some D cells I would definitely buy them. KD's cells are cheap enough and the charger is 10 bucks. If I end up completely blowing my batteries then big deal and I'll buy some more. Any other suggestions though?
 
spencer said:
I'm kind of not planning on doing series-parallel. I plan on running four CREE's off on one Shark in series. Then on a separate Shark I plan to put another four in series. Make sense?
Click to expand...

Well that is much better :) It is what I was saying as well, 2 banks of 4 in series. In your top post, you do say "Four LEDs in parallel for each shark. " probably just a typo.

I have read that buying the KD D's you should consider the 2 indivisual cells as opposed to the pack. I forget exactly why, I believe it was the safety circuit.

As far as the SAFT cells, most of us probably think of the low amperage cells in the typical green and white wrapper, I don't have any feedback for you on the one's you found. Look interesting.
 
May as well continue the old post because it is still relevant.
I now need a suggestion for D NiMH cells. I need two of them and I'm thinking of going for these. They seem to be decent. Any thoughts or other suggestions? A different supplier?

Thanks
 
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