A question of capacity

Hi all,

First up I'm a battery noob. So please be patient with me.

I sort of covered what I'm about to ask elsewhere but my question is a little more specific/basic this time.

What would give me greater run time: 4s 4500mAh C-Cell NiMh batteries or 4s4p 2000mAh AA's?

I'm pretty sure it'd be the AA's (4x2000mAh = 8000mAh total capacity as opposed to the straight 4500mAh for the 3s C-cells).

Is my maths right or am I making some ill-judged assumptions here?

Just to clarify I require 4.8V for my driver so either solution will output the right voltage. I'm considering making a battery pack from Eneloops or possibly higher capacity AA cells by just taping/heat-shrinking the AA's to each other in the required pattern. Although a holder of some sort might be better because recharging this super-pack might be a tad difficult. I'm assumning at least anyway.

Good or bad idea?

Any help would be appreciated.

Thanks

- Matt

Your maths is correct, but I hope you aren't trying to fit 4s4p AA's in a C sized space!

lol no I'm using these in a D Mag. The only reason I mentioned C-cells is because I was planing on using a battery tube for 4 C-cells in a 3D Mag. I've even made the tube but after finally deciding to grab some good rechargeable batteries I've realised that using AA's is much more convenient from a price/availability perspective.

My only decision now is to plump for 16 eneloops or these Vapex one's I found on theBay. I did a little research and they are viewed under good light most of the time. The extra capacity is what is enticing me and although they won't last as long as the Eneloops for holding that capacity on the shelf, I'm not the kind of guy who really cares...maybe I should go for the 2900mAh Vapex ones the same store is selling (same price). Plus it's an Aussie seller so I won't have to wait 4 weeks to get them.

If you had no plans for this to be a BOB light or shelf queen, go for the capacity. If it's a toy, then having to recharge to play is not so bad.

Keep in mind that 4 AAs will not fit side by side in a D-mag. 3 max standard bore.

Here you can see how numbers compare.

RepProdigious said:

Keep in mind that 4 AAs will not fit side by side in a D-mag. 3 max standard bore.

Click to expand...

They do fit, albeit without an adapter (so just loose in the tube) if I can't make an adapter that will fit with the batteries then I'll jsut shrink wrap them into one super-cell type of battery. No idea how I'd charge that but i'm sure it could be done...

Then again they might not fit length wise - 4s C-cells fit because they are narrower than the internal tail cap diamtere, allowing them to sit inside the tail cap a bit and thus providing greater length. 4s4p AA's may be too wide to fit inside this gap.

I better investigate a bit more.

Thanks for the link as well - sort of clarifies my estimates some what.

EDIT: So 4s4p won't fit into the tail cap as they're too fat, and they won't fit under the tail cap as 4 AA length is too long, so I will have to use a 4s3p, but the pack will have to be 3 AA long and 4 wide....if that makes sense.

To do this I need to shrink wrap them all together. I can't use a normal charger for this as the packs voltage will be 4.8V. How would I go about charging this custom pack? Something like this maybe? But that's for 6 cells max - Mine will be 12. Does this mean I'd have to charge each series pack seperately? Easy enough to do I guess.

Man I need to learn more about batteries and charging principles. *sigh*

Mattaus said:

They do fit, albeit without an adapter (so just loose in the tube)

Click to expand...

That's not true. Some rechargeable AA batteries are slightly fatter than alkiline batteries. This thickness may varry from one to other brand or capacity batteries.
Also some M*g "D" bodies have slightly larger ID than other M*g "D" even if all have D+seril number. Older version M*g without D in front of serial number has larger ID and all AA batteries will fit 4 side by side.

Mattaus said:

if I can't make an adapter that will fit with the batteries then I'll jsut shrink wrap them into one super-cell type of battery.

Click to expand...

Even if you find 4 rechargeable to fit in M*g "D" body side by side, after shrink wrap they may not fit or cause restriction.

fivemega said:

That's not true. Some rechargeable AA batteries are slightly fatter than alkiline batteries. This thickness may varry from one to other brand or capacity batteries.
Also some M*g "D" bodies have slightly larger ID than other M*g "D" even if all have D+seril number. Older version M*g without D in front of serial number has larger ID and all AA batteries will fit 4 side by side.


Even if you find 4 rechargeable to fit in M*g "D" body side by side, after shrink wrap they may not fit or cause restriction.

Click to expand...

Yeah this is all correct. I'm getting increasingly frustrated that I can't get the required 4+V at a capacity greater than 5000mAh. I'll keep looking but I'm not holding much hope :-(

Mattaus said:

Yeah this is all correct. I'm getting increasingly frustrated that I can't get the required 4+V at a capacity greater than 5000mAh. I'll keep looking but I'm not holding much hope :-(

Click to expand...

3x32600 will give you 5000mAh at around 11 volts......

RepProdigious said:

3x32600 will give you 5000mAh at around 11 volts......

Click to expand...

I was thinking along similar lines. You say you need 4.8V. Is that a minimum or maximum input?

I'm using the Shiningbeam 2.8A driver. It's maximum input voltage is 6V, and apparently just above 4V is the sweet spot. I guess I could change the driver over, but that's almost a complete rebuild.

3x32600 gives me 5000mAh, but then so does a few rechargeable C-cells I've found - and that's at 4.8V. So kind of a waste of time. Unless I'm missing something.

It's looking more and more difficult. Maybe a longer mag?

What's the lesser of 2 evils: 3p32600 giving a combined mAh of 15000 but at only 3.7V, or 4s C-cells giving me 5000mAh but at 4.8V?

Now that I've been forced to think about it, I'm willing to sacrifice performance (it's rediculously bright for my needs anyway) for run time. 15000mAh should give me over 5 hours at full power, but seen as the Forward current the driver can supply below 4V is less efficient and not as powerful then it will be slightly less bright.

I'm probably going to give up and use normal D-cells for this, and plan a new flash light at some point down the track - with a little more thought put in before hand!