The MR 16 is a halogen bulb. I use 14.4 Volt 2 Amp Hour Bosch cordless drill batteries. Is there a LED that has comparable brightness?
I would have thought so, now days LED's can reach 6 Watts and beyond. But considering they are much more efficient than halogen's the LEDs replacement for the MR16's would be comparable in brightness, but require lower power -> longer battery life. Because they are designed as replacements, not alternatives, I imagine that any manufacturers/sellers website would include additional information comparinbg the two..brightness, viewing angle etc...
You need a very bright bulb for mountain biking. I was hoping to be able to use a 35 watt bulb and dim it when I don't need it so bright, for climbing, etc. Do standard dimmer switches need line voltage?
As far as I know, they do. I think you can get dimmer switches for lower voltage bulbs used in home lighting systems but I haven't seen any. If you are indeed electronics savy, a simple PWM dimmer using comparators, a 555, or even a micro shouldn't be too difficult, there are plenty of example circuits on google, many with handy stripboard layouts and detailed explaination.
Whether you choose to use your standard halogen bulb or LED's, either way you would still need a device to switch it on and off at PWM frequencies. This should be a power MOSFET, or possilby a pwoer transistor. MOSFET's generally have a much lower on resistance so they waste less power. Not only does this mean you get a slightly longer battery life, but also they don't get as hot as standard power bipolar transistors...so you own't need a massive heatsink. (LED drivers have this built in as part of the power supply).
Bulb life isn't important as the light only will get used 10-15 times per year at 2 hours per ride. I need 2 batteries per ride for a 2 hour plus ride. I would like to be able to get away with one battery.
I'm sure that could be done.
I know it was mentioned that dimming would reduce halogens life, and I assumed as much, but it won't be a drastic reduction.
Now, I know it seems like the peeps here are pushing the LED idea, and of course if you already have some bulbs, and just need an 'add on' then perhaps the PWM dimming would be a good idea. However, they are coming into fashion for a reason, especially for portable applications: efficiency.
These websites seems to give some half decent figures as to the reduction in power LED's could make:
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As you can see, it depends on viewing angle (the more focused the beam, the brighter they say it is, but a narrow beam might not suit your application). But generally it seems you're saving a at least 60% power for the same brightness/viewing angle. And yep, that means 60% more battery life. Some even claim to use 5W to replace a 30W bulb (not sure I beileve that) so there thats 1/6th the power, or 6 times longer batt life.
YOu may have a tough time finding one that woudl be an idea replacement as your currepnt setup as far as power output/beam angle goes, but they don't seem to be too expensive. Their life is rated in thousands of hours, so I guess unless you fall off your bike onto a rock it'll last forever.
You mentioned your current setup lasts for over 2 hours, but requires two batteries. So lets say each battery provides 70 minutes of life. (for a 2 hour 20 minute ride). For a 60% increase in power (thats the minimum) using an LED replacement, each battery would last
70 mins + 60% = 1.6*70 = 112mins (hour 50 mins). Two batteries: 224mins (3 hour 40).
As I said, thats a minimum saving, some bulbs appear to be more efficient, meaning I tihnk you can get away with just one battery for 130mins.
Or hell, even get some higher capacity batteries
Hope that gives some food for thought.
Blueteeth