Energizer Ultimate Lithiums in 10S2P configuration?

[HuckMeat]

I have a high drain outdoor light I built (6 XPG's, maxflex driver) - I'd like to stretch the runtime between having to fiddle with the batteries.

Am I going to get into any problems with two series strings of 10 (15-16V per string) connected in parallel? This reduces the overall discharge rate on each string, which helps, plus doubles my capacity.

For various reasons, I'm springing for energizer ultimate lithium AA's for this application. The weight of the battery is important (1/3 less than alkaline, and lighter than my LiIon rechargeable waterbottle packs), plus if we have to play games with them, we can modify/swap AA's within a pack to keep some light coming out of the system.

It the past, we used packs of these to run a 10W HID, and the 6x XPG light appears to be brighter.

Any cautions/warnings? I'd be building the packs into holders, taping them, vac sealing and then heat shrinking them to help protect the packs from the elements.

 

[lightseeker2009]

I don't know the size of the package etc, but I would have just bought a high capacity 4S Lipo RC pack. You will get the voltage your looking for, even more capacity, and it will be way cheaper in the long run. Plus you only work with one battery at a time, not 20 AA's.

 

[HuckMeat]

Thanks for the reply!

This pack will get full of nasties (river/snakes/alligators/bugs) and weight is a premium, I'm not worried about the cost in the long run. Just enough mass to run the light for 3 nights. Smaller packs are better in general because 1) if a pack fails, we can fall back to another at a lower power level 2) As we depleate a pack, we can give it to our support team so we no longer have the weight in the boat.... However, we have to start out with all of our batteries up front in the boat, no resupply.

I've not found a LiPo/LiIon pack, assembled, that comes close to the weight of Energizer AA lithiums. If you find something, I'm all ears - Money is no object here, within reason, but weight and energy density are key. I have a few waterbottle batteries of the LithIon and LiPo variety I use for day to day. For this particular canoe race, we usually assemble 3 packs of 8 energizer lithium AA to run bilge pumps, and then other packs to run lighting for 2-4 nights.

 

[lightseeker2009]

No problem, we are all here to help out.
I understand your weight concern, but 20 of the AA Lithiums will weigh at least 260 grams. A 5000mah 4S lipo pack only weighs 187 grams. And that includes its package etc. With the AA's you still need to have a holder for them, with springs and wiring that will add even more weight.

I hear you money is not an option, but one set of 20 AA's will cost you the same as the mentioned 4S Lipo pack. And the Lipo pack is rechargeble. To me its sounds like a win win situation, and you will be a little greener to the environment.

 

[Benson]

You said 6xXPG, so I'll assume 1.3Ax3.5Vx6=27W, 27W/20=1.4W, but the Energizer L91 datasheet only shows up to 1W discharge yielding 3.8Wh at room temperature and 3.1Wh at freezing -- I'm assuming temperatures are reasonably high at night, since you mentioned gators, so let's extrapolate from room temperature to 1.4W, say 3.6Wh.

3.6Wh/14.5g = 250Wh/kg


The most energy-dense Li-ion polymer battery I know of is this 11.1V/2.65Ah pack.
Don't have specific discharge data, so let's assume 11.1V*2.65Ah=29Wh corresponds to your discharge rate.

29Wh/157g=190Wh/kg

Energizers do win, but not by a whole lot, and there's still wires, shrinkwrap, etc. needed to get them in the same state as the Li-ion pack.

(Also that Li-ion pack is somewhat cheaper than L91s per-Wh, but you said money is no object, anyway.)

 

[Benson]

Heh, we typed a lot of the same stuff.

A 5000mah 4S lipo pack only weighs 187 grams. And that includes its package etc.

But this? I haven't seen them anything like that light at all -- you saw my numbers above for a low-power (1C), high-capacity pack, which is the best I know of. Link, please? ;)

 

[lightseeker2009]

Heh, we typed a lot of the same stuff.
But this? I haven't seen them anything like that light at all -- you saw my numbers above for a low-power (1C), high-capacity pack, which is the best I know of. Link, please? ;)

Seems the site made a typing error:whistle: http://www.hobby-xpress.com/products/154-turnigy-5000mah-4s-30c-lipo-pack.aspx
I got the weight from this site. I dont use 4S cells so weight is never a factor for me, otherwise I could have seen it is wrong.

Here is the exact same battery, with its correct weight, ie 536 grams: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9177

Sorry for the confusion, it was not my fault, I just quoted:D

 

[HuckMeat]

Thanks! I'll soak this in and reconsider.

The weight is important as we end up portaging our boat around dams, etc and the ounces add up. We are already loaded with 70-100 hours of food (water is the only thing we can get from support). I want to size the packs ideally so we can get through a night on a 10 watt setting, and then give them to our support (i.e. get the weight out of the boat) in the morning - With a fresh pack for the next night.

The 3x XPG will run in the high 20 watts when we run it full out, but we usually only crank it up when things are about to go south real quick (i.e. about to wrap a 4k carbon boat around tree or some such stupidity).. - Normally, we will run a 10watt +/- lower current setting.