Battery Life

[clarion]

We may have done this subject before (in fact, I'm pretty sure we have, but I couldn't find a thread that I wouldn't be taking off topic by asking this).

I've been very happy with my Hope Vision One till recently, when it has been ripping through batteries - rechargeable and alkaline.  It wouldn't be able to run for a full commute (almost exactly an hour each time) without needing a repalcement.  At first, I thought it might just be the cold, but life got so short I was worried it was my charger, so I tried alkalines, and the same thing occurred.  Annoyingly, I wasn't able to use my Hope through the mud, grit & puddles on saturday.

So I've become convinced it's the light itself.  Today, I got a chance to run a test, and switched the light on to see how long it would run.  At first, I stepped it up to level four, to see how long it would last, but I realised that wouldn't be a useful test, so I put it down to level two, expecting it to run maybe ten to twenty minutes.

Two things.  One, on the maximum level, with no air flowing past, it gets very warm very quickly.  Two, it's still running, and unexpected time later.

I'll refit it to the bike, alongside the Cateyes, and see how long it runs tonight

[TimO]

I can't comment on the battery life, but most modern high intensity LED bike lights will get hot when running.  They do depend on the air flow of cycling to cool them down, and some will switch themselves off, or into a lower power mode if they detect that they are overheating.  If they don't have the smarts to do this, it could damage the LED, battery and/or electronics, but I don't know details about the Hope Vision 1.

The manual for my older Exposure light says:

Overheating

EXPOSURE LIGHTS are equipped with a thermal cut out. If the unit detects it may over heat, it will flash till it has cooled down. This is to protect the circuitry inside the unit, as well as the SuperLED’s. With moving air flowing over your EXPOSURE light, thermal cut out should not occur.

[clarion]

I imagine that cycling, even pootling, will bring amply enough air across the body to keep it cool.

[frankly frankie]

When I was testing the Dinotte 5W, I had to do quite a lot of static assessment (runtime, beam photos etc) and it would heat up the whole (straight) handlebars very nicely, on a cold November evening.

I wouldn't expect the Hope to deliver much using alkalines BTW.  It has a low-voltage cut-out which would probably kick in well under the 1 hour mark.  The Hope circuitry is designed to work with NiMH.

[TimO]

I imagine that cycling, even pootling, will bring amply enough air across the body to keep it cool.

Oh yes, it was more just a comment on you talking about it getting hot.  It seems unlikely the Vision 1 will suffer from this as easily as the Exposure Race Maxx I generally use, since it has a significantly lower output power.

This is the reason that most of this class of lights have metal cases, they need a decent thermal path to dissipate the waste heat to the outside environment.

[alexb]

I found the cold weather was making mine drain its batteries more quickly. On fully charged batteries, no problem.
On partially charged batteries it did cut out on me once and was clearly not happy when running cold, so I suspect the cold is doing the batteries no favours.
Do you have a "smart" charger? If so, is it saying all the batteries are OK?
My smart charger has detected a couple of duff batteries amongst my older batteries.

[clarion]

My charger is supposed to be 'smart', according to the pack.  it's a Maplin one.

I noticed that, despite having been run for twenty minutes in the office yesterday, the current battery pack for the Hope has lasted two commutes without worry.  What this indicates to me is that there is a temperature point at which the battery life starts to decrease significantly, to an unusable point somewhere just below freezing.

I need a hub dynamo

[frankly frankie]

Chemistry innit.

[mrcharly-YHT]

My charger is supposed to be 'smart', according to the pack.  it's a Maplin one.

I noticed that, despite having been run for twenty minutes in the office yesterday, the current battery pack for the Hope has lasted two commutes without worry.  What this indicates to me is that there is a temperature point at which the battery life starts to decrease significantly, to an unusable point somewhere just below freezing.

I need a hub dynamo

You and me both.

After my experiences during the big freeze, I did some research.

NimH batteries have 40% their normal capacity when operating below 0C.

[clarion]

Those figures feel about right. 

[TimO]

A discharging battery will warm up a bit, and so long as it starts off warm, it probably wont drop to zero for a while.

Of course, the metal case of these sorts of lights works against this in cold conditions, since it helps to cool the battery which you don't want.

I assume you haven't left the lights on the bike when outside, since this will really not help.

If you want to aid the batteries, possibly a small insulating jacket around the light might help!  A cylinder made from high density foam, or even bubble wrap might do the job.

It does remind me that probably my lights aren't going to work so well on the Definitely Not The FNRttC next week, so I'd better use them rather conservatively (Especially since my piggy back battery has a wiring fault and needs to go back to Exposure for repair).

[clarion]

I was thinking a little neoprene jacket might be quite natty

[alexb]

A discharging battery will warm up a bit, and so long as it starts off warm, it probably wont drop to zero for a while.

Of course, the metal case of these sorts of lights works against this in cold conditions, since it helps to cool the battery which you don't want.

I assume you haven't left the lights on the bike when outside, since this will really not help.

If you want to aid the batteries, possibly a small insulating jacket around the light might help!  A cylinder made from high density foam, or even bubble wrap might do the job.

It does remind me that probably my lights aren't going to work so well on the Definitely Not The FNRttC next week, so I'd better use them rather conservatively (Especially since my piggy back battery has a wiring fault and needs to go back to Exposure for repair).

Tim beat me to it. Pipe insulation should be about the right size, you can remove it if there are any signs that the klight is getting too hot.