Originally Posted by seeker333
You should look at this before you buy one.
http://forums.mtbr.com/showthread.php?t=78470
Evidently there are many frustrated tt owners out there. It appears that the tt company lacks the expertise to design and implement a reliable control unit for the light. The link indicates they are on a 3rd generation controller which is still problematic. Batteryspace has a workaround: they sell the light with a lower voltage battery, which eliminates the need for the controller ( is 11v vs 14.4v, i think, working from memory). Pros: no controller failure, no loss of light and return hassle, lighter battery to carry, lower cost, longer lamp life. Cons: lamp is not overdriven, so less light produced.
Overdriving a HID doesn't make more bright, it just burns out the ballast. The light itself runs on fairly high voltage (I think they need several hundred volts to start, and around 100V to run) which is switched up by the ballast from the input voltage. Since that's a solid state regulator, it runs the light on the same voltage regardless of the input voltage. I did some testing with mine and the light runs the same brightness until it kicks out, all the way from 14.5v down to about 7 volts (where I stopped the test; the light was still running but the voltage was dropping by 0.2 volts per second, and I didn't want to damage the battery).
The problem with overvolting is that the ballast is only designed to handle up to about 14.8V, and if you give it more than that, you're stressing and overheating the components.
Overdriving works with incandescent lamps because it makes the filament burn hotter.
I have a TrailTech light. I bought just the light, and at first hooked it straight to my 14.4V NiMH battery. It ran about 6 hours before frying the ballast.
When they say "14.8V max input" do not assume that a 14.4v battery is OK. If you put a voltmeter on there, you'll find that a 14.4v NiMH puts out nearly 16 volts at first, and doesn't drop below the max 14.8v for over an hour (on my 4.5 AH pack with the HID and a strobe turned on).
I sent it back, TrailTech replaced it, and then I hooked it to a 12V battery instead. It ran all winter and is still fine. On the 14.4v battery it ran very warm to the touch; on the 12V it's a tiny bit warm but hard to tell.
If you buy a TT light and hook it to a 12V NiMH it should do fine.
Bottom line: if you use it the way they say to use it, you'll be fine.