Duracell plus D cell mah?

[Paul Baldwin]

Hi,
I've tried searching but the information is proving elusive! I'm just trying to work out a rough runtime for a 2d mag using the KD Q5 drop-in with the 2-4.5 volt boost buck converter. I've found the online calculator and erring on the side of caution @ 2500ma and guessing at 80% converter efficiency that gives a runtime of 2 hours 20 mins. Is this anywhere even close? I'll buy some decent NIMH cells when I get chance, its just that the Duracell are readily available.

Cheers

Paul.

[ltiu]

Hi,
I've tried searching but the information is proving elusive! I'm just trying to work out a rough runtime for a 2d mag using the KD Q5 drop-in with the 2-4.5 volt boost buck converter. I've found the online calculator and erring on the side of caution @ 2500ma and guessing at 80% converter efficiency that gives a runtime of 2 hours 20 mins. Is this anywhere even close? I'll buy some decent NIMH cells when I get chance, its just that the Duracell are readily available.

Cheers

Paul.

If these are alkaline D cells. Then Energizer publishes their specs at 18,000 mAh:

http://data.energizer.com/PDFs/E95.pdf

Assuming Duracell has similar capacities.

It all depends on your discharge rate. The higher the current you subject the battery to, the less capacity it will have in the end.

[metlarules]

http://www.duracell.com/oem/Pdf/new/MN1300_US_CT.pdf

[mdocod]

Don't use duracell D cells,

Use a true D NIMH cell, they are 10,000mAH or greater.

Eric

[VegasF6]

As you have gathered, despite the fact that alkaline D cells may be rated as high as 18,000 mAh that is at very low discharge rates, hence the recomendation for nimh cells. Seeing them rated at only 9000-11000 mAh you would be led to believe they are inferior cells, but just the opposite is true.

Take a look at this runtime graph for a stock mag 3D cell with krypton bulb. I am pretty sure this lamp is manufactured by Carley from what I have been able to find. So, if the specs I linked are the right ones, the draw is only 2.6 watts, yet you can see how quickly the brightness drops. With only a 2D and a boost circuit your current draw will be even higher so runtime will be less.

I don't really know much about the circuit used in the KD drop in, you may be better off with 3 C cells instead of 2 D. The circuit will probably run more efficient at the higher voltages.

[Paul Baldwin]

Hi,
thanks for all the info I Have been looking at the cell options before I got the drop-in, my trouble is that they will have to be imported too as the choice in the uk seems very limited. The Tenergy 10000mah ones seemed like a good choice? Then I'll need a charger! The Duracell are readily available in the local garage for £1 each so I grabbed a pair of those just to test it.
I had thought of buying the 3 cell mag but again I couldn't find one I could just go to a shop and buy for reasonable money, the cheapest 2 cell was £20, I've never owned a mag before.
I wish I had measured the light output with the fresh cells. After only 15 mins use I'm only getting 18,000 lux @1m

Paul.

[VegasF6]

Normally I am a big fan of the LSD technology like many others here. I bought the accupower evolution D cells. I don't know if you are aware of the LSD or hybrid batteries? Essentially you give up a little capacity in exchange for a low self discharge rate meaning that you can leave them sitting around and when you get back to them they will still be charged. I am sure you could find a discharge graph somewhere here, but should be along the lines of only losing 15% after 12 months. It's linear though, so they lose the most in the first month and slows down after that.

In your case you may want the maximum runtime and not be worried about self discharge. Some comparisons have been done, the more traditional nimh cells can vary a lot. Some will run down in only a few weeks and some can go several months and still have more capacity than the LSD cells. This is affected by both the brand and the age and condition of the cell and just how it has been treated.

If it was me, I would be more interested in what I could buy in the UK even if it wasn't the very best. I mean sure, you might get a battery that is 10 or 15% better at a huge premium if you had to have it shipped from US, but I would be interested in a cost to performance ratio. Perhaps something from Ebay UK? Someone has probably written a thread about what is availible to you locally.

Stay away from energizer, duracell, etc in this case, as they are just selling a AA battery in a D package, a 2500 mAh D cell. Yuck.

Speaking of, another option is to run AA's. If you haven't seen them they sell some pretty cheap adapters you slip an AA battery in and fit them in a D size holder. One comes to mind that holds 2 AA's side by side, doubling your capacity. So in your case you could run 4 AA nimh batteries in a 2x2 configuration. 2.4V at 4000 - 5000 mAh. The cheap ones aren't good for higher current applications, but yours isn't that high a current in the grand scheme of things. The only concern there is it seems like I remember there was a contact problem either at the top or the bottom of the light. So you might have to do a slight modification to either your top spring or bottom spring of your mag.

Do you happen to already have an AA charger and or batteries?

[Paul Baldwin]

Hi,
I have got a cheap charger that handles aaa,aa,c and d cells. It's ok for small batteries but the charge time for 2500mah d cells is up to 30 hours lol. I also have a 1 1/2 hour uniross charger for aaa and aa but only the 1000mah aaa batteries to go in it. I've just looked and they do make some 2700mah aa's, the aaa's seem to perform well in my X2000 torch so maybe this is the way to go?
Ebay UK have 2 adverts for 10,000mah batteries lol, both makes I've never heard of, I'd rather not risk it. A google uk search mainly brings up Ansmann batteries, they are all £10-11 each plus postage! Then I need a charger on top of that
Another downside is the 2.4 volts I'll get with 2 cells, it looks like the 3xd mag was definately the better choice for a half decent runtime.
I have seen the LSD options but charging batteries before I need to use them generally isn't a problem. Do you know where I can get a cheap 3xaa to d convertor that will handle 1 amp?
Cheers,

Paul.

[VegasF6]

Another downside is the 2.4 volts I'll get with 2 cells, it looks like the 3xd mag was definately the better choice for a half decent runtime.
I have seen the LSD options but charging batteries before I need to use them generally isn't a problem. Do you know where I can get a cheap 3xaa to d convertor that will handle 1 amp?

I haven't seen any parallel adapters, only the 2xAA, which would give you in the neighborhood of 5400 mAh. Or the 2xD cells like you mentioned which could supply 10-12000 mAh. Or you can use 3xC cells at 4500-6000 mAh but at a higher voltage.

I am not familiar with the performance of the KD drop in to tell you if it would run better at the higher voltage or not, but quite probably it would.

If you look at Mdocod's reply a little ways up in his signature line you will see the adapters he manufactures and sells. I have a couple and like them very much. I certainly can't speak for him, but you could ask him to build you a 6XAA parallel adapter. Then you could potentially have 2.4~3.00V with ~8100 mAh's available and only need an AA size charger.

About the only other option I can come up with is to try lithium cells. You could do 1 18650 protected cell with a spacer, 1 of AW's C size lithiums with a spacer, or potentially 2x18650 parallel. As far as I know, no one makes the parallel adapter for in-line use, so that would be something you would have to rig up, a bit tricky.