NiMH performance in cold weather

[sssamcz]

My first post on this forum so forgive my if this seems like an overly simple question to you lighting buffs. I have a NiMH cell powered bicycle light, and have recently noticed severely decreased runtimes (roughly halved) in weather not that much below freezing. Is this normal? Is there anything I can do to reduced the effect of the cold on my battery (insulate....).

Thanks in advance for any insight you might be able to provide.

Sam

 

[mrme]

For cold weather performance, Lithium is king. They are really expensive, though. I doubt retrofitting the light with li-ion rechargables would be very practical for you, but it is worth considering when you choose another light. I think they perform well in the cold.

A common solution is putting the batteries in a pouch that is worn around your neck under your coat. It keeps the batteries warm.

With rechargable battereis, I doubt any of these measures are justified. Just keep your ears to the ground for higher capacity cells, I guess.

 

[andrewwynn]

run the light at higher power so they heat themselves.. do you leave the batteries on the bike in the cold or are the inside before you go out? my NiMH batteries.. they say to put them on the charger to pre-heat them if using in cold weather.... and.. yup.. batteries do self-heat so just a little 'coat' of some kind.. insulated enclosure should do the trick (to help at least somewhat).

-awr

 

[Lurveleven]

I turned on my Tri-star Phazer and put it in the freezer and got the same runtime as when not in the freezer. No change in light output either. My freezer is -25°C and I was using Vanson 2300maH NiMHs. The Tri-star is producing a lot of heat and wasn't very cold to touch after 40 minutes in the freezer so I also tested just the batteries by measuring the current from them (when used in the Tri-star) before and after freezing them, and I saw no difference.
Maybe there is a difference in how different NiMH cells behave in the cold?

 

[sssamcz]

Thanks for the responses and particularly your experiments Lurveleven! Anyhow, this is definitely a real problem for me so perhaps different cells do behave differently in cold. I will try the insulation and wearing on the body suggestions and see how that goes. Failing that, it sounds like the lithium batteries could be the way to go. How hard could it be to hook up some new batteries??

Thanks again,

Sam

 

[andrewwynn]

re: hard to hook up.. the problem is that Li and NiMH of course have different voltages, capacities, etc.. if you make your own pack it can be easy to get around.. it's almost exactly a 3:1 ratio.. 3NiMH series batts = 1 LiON bat. Then there comes the charging.. need a LiON charger.

I'm a big fan of LiON.. it'd be worth it to have LiON, but it makes sense to just do some testing with what you have first.

-awr