Battery Options

[Stickney]

I am looking to build an inexpensive lighting option for commuting. I only need 45 minutes of run time on a daily basis as it is only dark during my night-time commute. My commute is a combination of street, bike path and highway, with both well lit and dark areas as well as busy intersections.

I have been looking at a variant of the very popular Pond Scum design as it seems like a good way to get a bright option for less cost (the dark areas and busy intersections are where I feel a bright light would be helpful).

However, I have been struggling with battery options, and thus, I thought I would ask some of you with more experience how you might proceed with building a commuting light system for which you only need 45 minutes of run-time. I won't be using the system for any mountain, single-track, or trail riding. I might use the system for night riding, but not for more than an hour. A lighter system would be nice, but weight isn't a huge issue to me, though mounting/carrying the battery is a bit of an issue.

Would overvolting a 6 V light be as effective as overvolting a 12 volt light? (ie could a 7.2 volt battery work for me)

Thanks, and, I am a newbie to light building, so feel free to be blunt if you think I am off-track in my thinking.

[jeff-o]

Would overvolting a 6 V light be as effective as overvolting a 12 volt light? (ie could a 7.2 volt battery work for me)

No. I'd stick with the traditional overvolted 12V MR16 bulb. Besides, 6V bulbs are pretty hard to find, especially if you want a specific beam pattern.

[wmodavis]

Side effects of 'overvolting'. Yup! there are side effects so weigh the good and the bad. What is good for someone's application may not be good for yours. So evaluate based on your own requirements.

Side effect 1.
Overvolting results in more light output. That may be good if you need more light.
Side effect 2.
Overvolting results in shorter light bulb life. That may be OK if you only need more light for a shorter period of time and the bulbs are cheap enough to replace often.
Side effect 3.
As a design practice taking reliability into account - it is not a good principle to follow. But your requirements may outweigh good design practice which is a 'relative' thing anyway. I.E. - good design is in the eye of the beholder.

[Stickney]

Thanks -- it looks like the difference in building a NI battery or buying a prebuilt one is roughly $30 (using batterspace estimates) -- would my application work ok with cheaper lead acid models? I am trying to get buy cheaply on batteries, but I am starting to think that buying a pre-built model in a bottle may make more sense long-term.

[jeff-o]

A bottle battery is great because it's sealed against the weather and fits into a space you already have. Buying prebuilt also means you can get the voltage you want.

[cyccommute]

No. I'd stick with the traditional overvolted 12V MR16 bulb. Besides, 6V bulbs are pretty hard to find, especially if you want a specific beam pattern.

I'd disagree on the overvolted 6V lamps. Overvolting a 6V lamp to 7.2V is a 20% increase and you'll get similar light output. The advantage is that you only have to carry half the batteries of the 12V system. The disadvantage is a reduction in run time. A 3.3 Ah 7.2V battery pack will power a 20W bulb for about 1.1 hours. A 3.3 Ah 14.4V battery pack will power a 20W bulb for 2.3 hours but you have to carry twice as many cells to get that run time. You could just carry 2 7.2V packs to get the same run time.

Battery Space carries the 6V MR-11 bulbs.

If you want to do MR-16 (larger bulb but much better light output), then 12V is the only thing available.

[jeff-o]

I'd disagree on the overvolted 6V lamps. Overvolting a 6V lamp to 7.2V is a 20% increase and you'll get similar light output. The advantage is that you only have to carry half the batteries of the 12V system. The disadvantage is a reduction in run time. A 3.3 Ah 7.2V battery pack will power a 20W bulb for about 1.1 hours. A 3.3 Ah 14.4V battery pack will power a 20W bulb for 2.3 hours but you have to carry twice as many cells to get that run time. You could just carry 2 7.2V packs to get the same run time.

Battery Space carries the 6V MR-11 bulbs.

If you want to do MR-16 (larger bulb but much better light output), then 12V is the only thing available.

Ah, but it's the fact that a 6V bulb will be in an MR11 form factor that makes it not worth using. The reflector isn't as efficient so even with the same amount of power, the light output isn't the same.

[Stickney]

Thanks -- excellent input -- does anyone know if with that Pond Scum design, if a MR11 bulb will fit in the Harbor Freight light without boring it out, which I believe is needed to fit an MR16 bulb?

Ultimately, the 14.4V and MR16 design seems best, but I am on a limited budget, and if I can get by with a 7.2V and 6V bulb, I may have to make do.

Again, Thanks!

[Sir Bikesalot]

I've tried over-volting the 6V MR11s from batteryspace at 7.2V (6AA NiMH). They suck. I had to go to 10V (8AA) to get any decent output (I tried 10W, 15W and 20W bulbs). At that amount of over-volting though, the bulb wouldn't last very long at all.

Over-volting 12V MR11s from batteryspace yielded similar results. But when I went with a really high-quality 12V lamp from JetLites, light output was significantly better. My conclusion was that lamp quality makes a huge difference, and that high-quality 12V (vs 6V) lamps are easier to find. However if you end up going 6V, I hear Nightrider carries some quality lamps.

[cyccommute]

Ah, but it's the fact that a 6V bulb will be in an MR11 form factor that makes it not worth using. The reflector isn't as efficient so even with the same amount of power, the light output isn't the same.

The MR-11 is standard issue in all commercial systems. It's not horrible...not as good as the MR16... but, if you have the headlamp to start with, it's a workable system. I've spent many hours riding with a 7.2V MR11 in 10W, 15W and 20W configurations. They were relatively bright...much brighter they running them at 6V.

But I'll agree that if you are going to build a system, start with the MR16

[cyccommute]

Thanks -- excellent input -- does anyone know if with that Pond Scum design, if a MR11 bulb will fit in the Harbor Freight light without boring it out, which I believe is needed to fit an MR16 bulb?

Ultimately, the 14.4V and MR16 design seems best, but I am on a limited budget, and if I can get by with a 7.2V and 6V bulb, I may have to make do.

Again, Thanks!

The Pond Scum is for a 12V MR16. To get the best output, overvolt to 14.4V. Jumping from 12V to 14.4V goes from a 'it's bright' light to a 'My eyes! My eyes!' light:D

[acroy]

I am looking to build an inexpensive lighting option for commuting. I only need 45 minutes of run time on a daily basis as it is only dark during my night-time commute. My commute is a combination of street, bike path and highway, with both well lit and dark areas as well as busy intersections.

I have been looking at a variant of the very popular Pond Scum design as it seems like a good way to get a bright option for less cost (the dark areas and busy intersections are where I feel a bright light would be helpful).

However, I have been struggling with battery options, and thus, I thought I would ask some of you with more experience how you might proceed with building a commuting light system for which you only need 45 minutes of run-time. I won't be using the system for any mountain, single-track, or trail riding. I might use the system for night riding, but not for more than an hour. A lighter system would be nice, but weight isn't a huge issue to me, though mounting/carrying the battery is a bit of an issue.

Would overvolting a 6 V light be as effective as overvolting a 12 volt light? (ie could a 7.2 volt battery work for me)

Thanks, and, I am a newbie to light building, so feel free to be blunt if you think I am off-track in my thinking.

My hombrew system might be exactly what you're looking for:

10W 6v system running off a 7.2V r/c car battery (so 12 watts). About 1hr runtime, yes it's okay to overvolt, yes the bulb will die sooner, yes the light is whiter & brighter.

I built mine from the remains of a Nite Hawk SLA system, a couple Tamyia r/c car connectors, and an extension cord. worked great. ran it both on the helmet (battery in pocket, wire up the back of my shirt) and on the bars (battery in old water bottle).

cheers

[dbs]

The Pond Scum

What is the Pond Scum design? Would someone enlighten me?

Thanks.

[cyccommute]

What is the Pond Scum design? Would someone enlighten me?

Thanks.

This one (http://forums.mtbr.com/showthread.php?t=245737) by Jay Buthman. A very nice design.

[Stickney]

All -- thanks so much -- I will see what battery options I can find -- at this time, that may be the deciding factor. Ya'll have been very helpful!

[joshandlauri]

I use the pondscum light as is, out of the box and I have no problems using that light. not as bright as my 50 watt mr12 but plenty bright for a commute