DIY bike lights / AA battery current

Unless it only lasts 0.5s until the bulb goes pop! (You should be OK - The actualy bulb voltage will probably only be around 13.5, which isn't a massive overvolt). Capacity and run time should be fine - I'd expect you to be getting around 2 hours on a setup like that.

In my experience, that's right. I've made them work by replacing the springs and thin wires with metal plates, but you then need to put pressure on the outside to make sure contact is good. If you make a pair of 6 cell packs you can get a cheap 7.2V charger from

--
Dave Hughes | dave@hired-goons.net
"Some drink from the Fountain of Knowledge... Others just gargle." 
- Dave Aronson

"Travis"

** Huh ?????

When did your lamp change from 20 watts to 10 watts ???

Why do you now say 12 cells instead of 10 ???????

Cant read a maker's data sheet?

BTW

Spring contact battery holders are not 100% reliable at any current - let alone 1.7 amps.

A soldered pack far better idea.

Maybe buy a 10 cell pack intended for an electric drill.

...... Phil

Thanks Phil, Clearly you've given everyone a clear insight into your character. {:-).

A 12 volt cordless drill could be the go, you'd get a decent sized battery and the charger and you could make holes or impress your friends by carrying out on-the-road repairs with a cordless screwdriver :-) You'd need to make a custom connector to the light though.

Cheers, Sam

When someone here suggested that a 10W one would be adequate and could be powered fairly easily by a bunch of AA batteries, and someone else suggested that 20W would probably be too bright anyway.

The commercial systems are usually 10W, often with overvoltage. I originally figured 20W because there was a cheap 20W bulb available which seemed the right size to fit in my existing lamp case, but that's obviously not a major consideration!

Because someone else suggested the idea of overvolting it, which made a lot of sense to me, and also because an extra two 2500mAH batteries would add half an Amp hour, less resistence.

Sure, but it doesn't tell me everything I need to know about the resistance of 12 of them in series and how this resistance is a function of the total current flowing through them.>

I don't need it to be 100% reliable as I have other lights on my bike, like an LED flasher.

I'd trade off a small amount of reliability for a large amount of convenience.

The only question being whether or not it would actually work.

Travis

Actually, the resistance between the contacts is constant, no matter how much current flows. It's the amount of energy that is wasted due to contact resistance that increases with current, proportional to the square of the current, in fact

Cheers, Sam

Travis,

I have made a few sets of lights (check the version 3 and version 8 links for what you are talking about).

12V, 10W globes in the MR11 size can generally be found at lighting shops without too much drama and cost about $8 or so each. If you are going to go for the MR16 globe (50mm) to take the cheaper option, I would recommend going with the hose clamps and engine enamel method (like my version 3 ones) as it is pretty simple. I have actually got a spare one of the nylon frame bags that fit a 4.2Ah sealed lead acid battery and my original version 3 lights if you are interested. I would also suggest going for the tighter beam patterns globes (about 10 degree or so is pretty good) rather than the flood type ones.

If you were going to make your own lights, I would suggest going for a 6V system. Although the globes are about $30 each (Vistalite, NightVision, NiteRider, etc), you only need half as many batteries and so will save on battery weight. Of course you don't get anything for free and a 10W, 6V globe will need twice as much current as a 10W, 12V globe. I now run 6V lights and use battery packs made from 4.5Ah, 4/3A sized NimH cells with solder tabs that go pretty well.

I have also recently bought a couple of 3W luxeons and a "fatman" controller and all I have to do now is work out how I am going to put them together and then find the time to do it. Although the luxeons are a bit more expensive they give the advantage of a small form factor (my optics are 32mm diameter), light weight, and low current draw. I am looking at running the luxeons both in series using 4 x NimH cells (probably AA for weight savings and simplicity) and the fatman controller (this will boost the voltage up to the required level (about 7V) and provide a constant current to the luxeons).

Let me know if you are interested in the battery bag and/or V3 lights.

Gags

"sam"

** No way.

The "contact resistance" between clean metal surfaces is not constant - it

*reduces* with increasing current and contact pressure.

It will however increase with increasing contact temperature and surface corrosion resulting from high temperatures over time.

....... Phil

Ah, so metal conductors contacting with a constant pressure are non-ohmic? I didn't know that.

Thanks, Sam

"sam"

** That is dead right.

Contact resistance is caused by oxidation or sulphides on the metal surfaces.

The resistance is non ohmic - it tends to cause a constant voltage drop over a wide range of current levels.

....... Phil