Battery nerds come hither!

[IronWing]

I have a light that draws up to 2.6A (measured) at nominal 12V. The light is powered via a cigarette lighter plug. I had been using a 9 cell AA pack to power the light but it doesn't deliver sufficient current. The max measured current out of the pack is 1.8 amps and the battery pack gets hot to the touch. I found a few packs that look like they might work but I'm looking for suggestions. Here is what I've found so far. Each uses a different chemistry. I'd like to get the longest runtime possible for the money and the least hassles.

Lighter, longer lasting, more expensive:
http://www.batteryspace.com/lifepo4...thcarlightersocket28aratefastcharger3a-1.aspx

Shorter run time but less weight:
http://www.batteryspace.com/polymer...at12v-132vwithsoft-startchargercarsocket.aspx

Cheaper, heavier:
http://www.batteryspace.com/beltbag...10humpfastsmartchargerforportabledevices.aspx


Edit: Thanks, Red Squirrel. New criteria: I need to take it hiking so weight matters.

 

[Red Squirrel]

Get a small lead acid battery, like one that would be in a 500va UPS. If you have a local electrical/industrial shop they might have some. An alarm company may be able to sell you one too, they are typically inside alarm system panels are are rather small. If size does not matter, a marine battery from the hardware store should work.

 

[Ken g6]

Let's back up. If you need to minimize weight, would it be worthwhile to replace this light (whatever it is) with a more efficient LED light? Or is that what it is already? How much light are you looking to produce, and over what area?

 

[Gibson486]

wow...at 2.6 amps, you are going to need more than AAs for that thing to even last.... what kind of light are we talking about here?

 

[arkcom]

http://www.hobbyking.com/hobbyking/store/__7636__ZIPPY_Flightmax_2200mAh_3S1P_25C_.html

cheapest charger-

http://www.hobbyking.com/hobbyking/store/__14857__HobbyKing_50watt_5A_X_Charger_Balancer.html

 

[IronWing]

It's a dual longwave/shortwave fluorescent UV lamp with fan. Each lamp pulls 1.25A plus the fan. Longwave LED lamps are cheap and available. Shortwave LEDs are neither right now. I can turn each on/off independently but often it is best to have everything running. I figure that with 10 AH batteries I can get ~4 hours use from a charge which is good enough.

 

[Gibson486]

Well, for 10 AH @ 12V, Red hit the nail on the head. It's gonna have to be one those batteries that you buy for alarm panels.

 

[Rubycon]

It's a dual longwave/shortwave fluorescent UV lamp with fan. Each lamp pulls 1.25A plus the fan. Longwave LED lamps are cheap and available. Shortwave LEDs are neither right now. I can turn each on/off independently but often it is best to have everything running. I figure that with 10 AH batteries I can get ~4 hours use from a charge which is good enough.

You're a rockhound I presume?
You're right, LEDs at 400 ish nanometers are plentiful and have decent lifetimes. Sub 300 nanometer LED sources are expensive and have much shorter lifetimes currently. I remember my mains powered mineralight having two bipin FL tubes - the blacklight blue (long wave) and the bare shortwave (germicidal) lamp...

10Ah is not going to give you four hours unfortunately. Sealed Lead Acid (SLA) batteries are typically rated at the C/10 rating. If your draw is 2.5A and you want four hours initially you will need about 16Ah to be safe. That's going to be heavy to be lugging around the hills! Li-Ion is going be lighter and generally more robust. Fully charged cell voltages of 3.7 and 4.2V are common. Of course making a pack from cells, protection and proper charging add complexity to the mix. I suppose it all boils down to how sensitive you are to having the extra weight to lug around.

For Pb I'd recommend a six pack of Gates Cyclon BC cells. That will give you 12V with an honest 25Ah capacity. If you wire them with proper lugs you can also use it to jump start your car since they can deliver over 600A into a near short circuit. (be sure to fuse the wire as a pinch can turn it in to a cannon fuse!)

 

[Eli]

I recommend LiFePO4. You'll pay for it, but it will give you much, much better cycle life than Pb and also be easier on the back. Some ideas:

http://www.batteryspace.com/Poweriz...V-20Ah-240Wh-30A-rate-with-Balancing-PCM.aspx

http://www.batteryspace.com/lifepo426650battery128v136ah17408whwithcarlightersocket28arate.aspx

http://www.batteryspace.com/Powerizer-LiFePO4-Battery-12V-17Ah-204Wh-34A-rate-with-PCM.aspx

Edit: LOL, I just realized you were already looking around on batteryspace in your OP. The ones you linked to will be fine, but like Rubycon said you won't get as much runtime as you would think. Still good for the price though I think.

 

[Mark R]

I think your best option would be a Lithium polymer pack. Something like: http://www.batteryspace.com/High-Power-Polymer-Li-Ion-Battery-14.8v-10-Ah-148-Wh-30A-rate.aspx.

This has a roughly suitable voltage, which is comparable to the output of a car alternator. If your lamp is designed for in-car use, this battery should be suitable. If you are very worried about damaging the lamp, then you could go for a lower voltage pack (11.6 V), but lamp performance may be decreased.

Lithium polymer batteries such as the one I've linked are a much lighter alternative to the lithium iron phosphate (LFP) batteries (your link 1). My linked battery contains 33% more energy, while cutting 50% of the weight.

LFP is similar in price to Li polymer, but have a much longer cycle life (thousands of charge/discharge compared to hundreds) and better suited to high-currents. However, you pay for this in terms of weight - LFP are nearly 3x the weight of Li polymer; and LFP have a crystalline matrix, whereas Lipolymer is a polymeric film matrix, so LFPs can be damaged if dropped, whereas Lipolymer are a bit more resistant to mishandling. LFP is best suited to applications where discharge is very short and multiple recharges are needed per day (power tools, RC toys, etc.). LiPoly is better for portable devices where the charge needs to last the whole day.

As for taking lead-acid batteries hiking, rather you than me. I did a video diary of a cycling/canoeing trip years ago, and humping around lead-acid batteries was not fun.

 

[Red Squirrel]

Another thought, if this is just for a hiking light, why not just get one of those LED work lights that has a built in battery? They can last for hours. Or a simple flashlight with a couple ultrabright LEDs in it. Surprising how much light those can produce.

 

[Rubycon]

Another thought, if this is just for a hiking light, why not just get one of those LED work lights that has a built in battery? They can last for hours. Or a simple flashlight with a couple ultrabright LEDs in it. Surprising how much light those can produce.

I'm pretty sure this has been covered. OP needs a source of shortwave and longwave ultraviolet radiation to observe fluorescence in minerals. (and to spot scorpions!) :biggrin:

 

[IronWing]

I ended up getting a LiFePO4 battery, this one:
http://www.batteryspace.com/lifepo4beltbagpowerbattery128v68ah8704wh14aratefastsmartcharger.aspx
plus extra battery. I don't think I've been impressed with a battery before. I'm impressed with these. 2.6 amp output for better than 2 hours each and they fit in a cargo pocket.