12 volt 4 amp MF battery
 

It is unbearably cold in my neck of the woods and I need electricity to keep my hands warm. I own a pair of motorcycle gloves that plugs directly to the 12 volt system on my Honda and would like to use them for my daily commute when the temperature goes below -12 degrees C on my bicycle. What I need to make these gloves work on the bicycle is a small lightweight battery that will fit into my backpack. Does anyone know if such a battery exists and where could one purchase it?

There's oodles of batteries to choose from.

However, if your gloves draw 4 amps (and looking them up, one amp each is typical, so two amps each seems reasonable) that's about 50 watts. You'll need a big honkin' battery if you want them to last any amount of time.

For example, this 7 Ah 12 v battery weighs just under 5 lbs, and would power your gloves for under two hours. It would fit in your backpack fine, but you might not like it, especially if you need more than one to get the desired runtime.

A 3s LiPo pack would probably work well and could cut down the weight/runtime ratio considerably (probably by 50% or so), but would cost a good deal more. For example. this would power it for a little more than an hour but weigh only a pound. You'd also need a $3 or so buzzer to warn you if the battery is getting low and a charger for it.

Back when I grew up in Anchorage, AK I just used ski mittens when it got really cold and that was fine. Mittens are a good deal warmer than gloves.

A whole lot depends on how you define "small" and "light-weight".

For safety reasons I would suggest you limit your options to either a 10-cell NiMH pack (10 x 1.2V = 12V) or a four cell LiFePO4 pack (4 x 3.2V = 12.8V). NiCd is outdated, heavy, and potentially dangerous, sealed lead acid is heavy and the "acid" part could become a serious problem if it goes from "sealed" to "not sealed" in your back-pack (casing cracks or such), and other chemistires of Lithium batteries (usually refered to as Li-Ion) can get hot enough to catch fire if they are damaged and then heavily discharged.

If I was going to carry a battery in my back-pack and have it working to run somthing at the same time as its it was in my pack NiMH or LiFePO4 (Lithium Iron Phospahate) batteries are pretty much what I would use to feel reasonable safe doing so although I would be slightly more comfortable with the NiMH then the LiFePO4 but they will be slightly heavier for the same amount of power then the LiFePO4. So long as they aren't being charged or discharged I have no problem carrying Li-Ion batteries in my pack especially if they are single cells not packs but personally I wouldn't trust a non iron (Fe) chemistry Lithium battery to be in use on my back (iron acts as a built in chemical stabilizer in a lithium battery but it also adds some weight compared to lithium batteries without iron in the chemistry).

Do you know how many watts of power your heated gloves use? Or how many amps or milliamps? How long do you want the battery to last for them on a single charge? With that information I can point you towards some places with packs that might work for you. An even better option (as far as safety goes) would be to use a pack that is built into a water bottle and put it in the water bottle carrier on your bike (good to have more then one water bottle rack so you can still carry a water bottle) and then the batteries at least wouldn't be on your back.

Do your gloves draw 4-amps or do you want at least a 4 amp hour battery?

It's pretty easy to google for these gloves. They use one to two amps each, so two to four amps total. I'm pretty sure he's telling us that his uses four amps.

NiMH AA cells can put out 4 amps, but they work better at lower discharge rates. Given Eneloop batteries, such a pack would power it for about 30 minutes. You could go with 8 cells instead of 10 -- that would make it weigh less, put out less heat (so the gloves wouldn't work as well) but it would last a little longer.

LiFePO4 isn't a bad idea.

NiCd isn't any more dangerous than NiMH (though it's bad for the environment if not disposed of properly), but the energy density is lower, so you'll need an even bigger pack for the same runtime. I wouldn't suggest NiCd.

You're right about gel cell batteries -- they could break in a crash. But they are the cheapest viable option, even if heavy and bulky. They were fairly commonly used in bicycle headlights before NiMH and LiPo/Li-ion took over, and are still used in some low end E-bikes today. (Not that they're stored on your *back*, of course.)

Note that any battery can get hot enough to start a fire if damaged -- short it out internally, and it becomes a "hot steamer". The difference with LiPo batteries is that they're made of flammable materials and can themselves burn if abused. Put then in a strong case and be careful when charging and it's generally fine -- after all, they're in our cell phones and laptops.

One problem with this idea is that if it's cold enough to need the gloves, the batteries may not work well fully exposed to the cold. In your backpack they might have some insulation, might be somewhat shielded from the wind and might get some heat from you so they might retain their warmth for a while, but in the water bottle cage they're going to basically be at most just a few degrees above the outside temperature almost immediately, which will slow the chemical reactions and make them not work well.

But certainly, I'd rather have several pounds of batteries on my bike rather than on my back. But considering that you'll need several pounds of batteries to power these things for any length of time, I'd suggest non-powered mittens instead. Or maybe lower powered gloves -- 50 watts of power is easy to find on a motorcycle, but not so easy on a bicycle. 25 watts would mean half the weight in batteries for the same runtime.

How about a dynamo hub? The common voltage is 6v/3w, but I also read about 12v ones, although I don't know specifics. That won't give you the amps though. Remember too that you're pumping out some watts yourself on a bike that you aren't doing on a motorcycle.

Maybe a more modest glove type would suffice?

I doubt a large capacity battery is required. Bicycles don't have to deal with a 100km/hr wind chill factor and the OP really just needs an ocassional input in maintain a comfortable temperature. A motorcycle rider is stationary. A bicycle rider is working and generating body heat.

My lighting system is 12V, I'm using 3S1P Lipo cells as well as AA's. Lipos are available in a variety of capacities and formats including hard-case versions. Obviously my experience is different than some other people. I've run up to 100W off a 5.6Ah RC battery without it even getting warm. And I have no issue carrying it in an inside pocket. These are rated for 165A CONTINUOUS USE so anything less than 10A amps is barely taxing its potential. The battery isn't much bigger than an iPhone and would probably be good for the day. If those gloves were run continuously at 2A they'd likely be to hot to put on.

That's a pretty big battery with a pretty low discharge rate (for a plane, anyways.) That said, assuming that this is a 3s pack, it can provide 100 watts for about 40 minutes. Which is a pretty decent flight (must be a 2m+ glider) but not very long for a heater.

That said, you're probably right about not needing to use the gloves much. Also consider that the bike is going 15 mph or so, not 60 mph. A 2s pack (or even 1s?) might be a better choice -- reduce the power level by about 55% or about 89% in the case of 1s. Going with a 5.6 Ah 1s pack would reduce the power level by almost a factor of 10, and so it could last for about twelve hours. Might not be warm enough, however.

Thank you for all the excellent ideas. Yes, the gloves draw a maximum of 2 amps each on the high setting. I found a waterbottle battery on line but the price is more then I am prepared to spend. Gell type batteries seem to be the best value but I am not so sure a regular low amp charger would work with these simply because the company selling the batteries is also pushing their $75.00 charger. Why would gell batteries require a special charger? As far as protecting the battery from damage in case of a fall, I could wrap it in bubble wrap.

Bill

Was the water bottle battery the 84WH, LiFePo4 that batteryspace.com sells? I've had very good results with it powering bike-mounted ham radio gear. They sell a smaller, 32 Wh version "A123" pack replacement as well. Neither are cheap but they are IMO the best combination of power capacity and size/weight with reasonable safety and quality of construction. I think I paid $120 for the larger battery + charger (also got some extra cables so I could cut & make the adaptors I needed) and $90 or so for the A123 + charger. I would wrap the A123 in someting if there was any chance of a drop as it is just cells in rubberized shrink tape. The larger version is already packed in a 500ml bottle, not much to add there.

How long do you need the gloves heated? If you included an on/off switch, you could leave them off when your hands are warm enough. That would save a lot of power.

Depends on the battery pack build. The more cells, the more you want a battery management system (BMS) involved in the charging end of things. The fewer the number of cells involved in the battery pack and the smaller the current drain - the less likely you are to run into cell balancing issues.

You're not going to find a $9.99 solution. Even if you used rechargable AA cells it would take 20 or about $50 worth plus multiple chargers to get you through a day. A single large capacity 3cell Lipo would be a lot less hassle and wouldn't need a high end charger. But would still need some kind of voltage limiter to protect it from over discharging cause you left it connected too long.

This is the waterbottle battery in question:
BatterySpace.com/ AA Portable Power Corp.
825 South 19th street,
Richmond, CA 94804
[h=5]Water Bottle Nimh Battery: 13.2 V 5Ah (66 Wh)[/h]Your Price: $60.95

The price has just recently been reduced so I may give this a try.
The gloves would not be on for much longer then 20 minuites between charging.

Before you spend any significant amount of money on this, I suggest an experiment.

Get a 4 cell AA holder from Radio Shack. It's a few dollars.
Put four rechargeable batteries in it, fully charged. (I'll assume you have these already, but if not, $10 for them and a few more for a charger.)

Wire this up to power your gloves. Yes, it's only 5-6 volts, but you don't need much heat and your gloves will not be picky about the exact voltage (there's no electronics, just heating coils.) The reduction in voltage will reduce the amperage by half as well (and the heat produced by a factor of four), so assuming new, fully charged decent AA batteries (2000 mAh), you're looking at about an hour of runtime.

This might be all you need, with no special charger required and it's small and portable -- put it in your inner pocket on your jacket and it'll even stay warm so no problems with cold batteries.

If you need more heat, try a six cell holder, though your run time will then be even less. (But still more than 20 minutes.)

For a NiMH pack I was not thinking AA size, Eneloop or otherwise. I was thinking a 10 cell brick pack made from industrial type sub-C or larger size cells all shrink wrapped and ready to go. Or a 12V cordless drill battery made from sub-C or larger cells.

That said I think this would work well for him, basically a high capacity sub-C industrial NiMH pack inside of a water-bottle all ready to go. He might even get luck and the plug is the same as his gloves and will plug right in:

http://www.batteryspace.com/waterbot...emaleplug.aspx
http://www.batteryspace.com/waterbot...bikelight.aspx

Considering that the gloves were made for use at motorcycle speeds, not bicycle speeds, and that they were made for somebody not really exerting themselves, a lot less heat should be required for bicycle use.

He could test with a AA pack easily enough. Total cost around $4 if he's already got the batteries. If four cells isn't warm enough, try six. Actually, if six cells works well, a sub-C NiMH R/C car pack would work well for "production". He'd need a charger, but I'll send him one for shipping costs if he needs it (I've got a few that I'm never going to use.) But AAs may be adequate at the lower voltage (and therefore lower amperage.)

I still suspect that batteries in the water bottle are likely to get so cold that they don't work well (depending on just how cold unbearably cold is), but if the pack is small enough, and he really does only need it for 20 minutes, he could probably have one small enough to put in his pocket, which has the added advantage of not having to worry about wires when getting off the bike.