# Thread: Smart people, help me calculate

1. ## Smart people, help me calculate

I know a burn-time calculator has been posted (many times even) for overvolting halogen bulbs but I can't find it. Please help me with this scenario:

6volt 5 watt MR11 bulb (NiteHawk Nomad), driven by a 9.6 volt 4200 mAH NiMH battery pack?

http://www.batteryspace.com/index.as...ROD&ProdID=199

2. Linear approximation for burn time:

Burn Time = Volts * AmpHours / Watts

9.6V seems a bit high for over-volting and those sub-c packs are rather bulky and heavy. Why not get a higher wattage bulb if you need brighter? 5W isn't typically bright enough to use off-road, even with over-volting. The best option for a low voltage system would be a 15W and over-volt at 7.2V. That burns for over 2 hours with a 4500mAh battery and should provide minimum lighting for riding off-road at daylight speeds.

3. Homebrew,

I remember someone using the Nomad 5 watt and overvolting with 12volts which ran for 40 minutes. He descibed it as his "god light" or something like that. I have three Nomads with 3 hardly used 5 watt bulbs and was thinking of making into a "god light" or at least psuedo-god light to use as augmentation for steep techinical areas. Also, when I first got a Nomad for shytes and giggles hooked it up to my 14.4 volt pack. The pack was far from full charge but the light output was amazing, super white and brighter than my 14.4 volt MR16 20 watt lights.

4. My understanding is, because of Ohm's law, at 9.6 volts you will be drawing 12.8 watts and 1.3 amps. This would give you less than an hour's run time, and might make for short bulb life. As Homebrew said, you will be better off at a lower voltage and higher rated bulb.

Tim

5. Thanks guys, I appreciate the input.

6. Originally Posted by TCW
Homebrew,

I remember someone using the Nomad 5 watt and overvolting with 12volts which ran for 40 minutes. He descibed it as his "god light" or something like that. I have three Nomads with 3 hardly used 5 watt bulbs and was thinking of making into a "god light" or at least psuedo-god light to use as augmentation for steep techinical areas. Also, when I first got a Nomad for shytes and giggles hooked it up to my 14.4 volt pack. The pack was far from full charge but the light output was amazing, super white and brighter than my 14.4 volt MR16 20 watt lights.

That was DeeEight with his "dog light". You never know what the Un-Politically Correct Canuk is cooking up there in his mom's basement. You can give it a shot if you have some higher voltage batteries laying around but I certainly wouldn't put any serious money into the idea. Instead of buying expensive new batteries, I would save up a few bucks more and get something like a 15W Planet Bike system on sale (you just missed the Nashbar closeout for \$80 last month). That will come with 4500mAh battery, smart charger, mount, really nice bright bulb and guaranteed to work.

7. Originally Posted by TCW
Homebrew,

I remember someone using the Nomad 5 watt and overvolting with 12volts which ran for 40 minutes. He descibed it as his "god light" or something like that. I have three Nomads with 3 hardly used 5 watt bulbs and was thinking of making into a "god light" or at least psuedo-god light to use as augmentation for steep techinical areas. Also, when I first got a Nomad for shytes and giggles hooked it up to my 14.4 volt pack. The pack was far from full charge but the light output was amazing, super white and brighter than my 14.4 volt MR16 20 watt lights.
That would be me... 12V Gelcell SLA from princess auto for \$20, Nomad 5W light for \$20 (cdn, and this is like a decade ago I started doing this) equals drowning out most HID's for a change (as in, if you ride behind someone using an HID with this thing, you cast shadows past him for a change). The downside is of course the power consumption shoots up dramatically.

The luminous flux goes up to the exponent of 3.5 with whatever nominal voltage (so 2 to the power of 3.5 in the case of my 100% overvolting), the consumption squares and the bulb life goes to an exponent of -10. Take your typical 5000 hour, 5W-6V rated MR-11 bulb. Expect about 10-20 hours of bulb life (which at \$4 a bulb isn't bad given the light you get... you'd have to burn out a LOT of bulbs to justify buying an HID for anything other than burn time per ride), around 55W equivalent of light (so like a car headlight), and about 20W of current draw. The SLA's I use are only 2.2 and 2.3Ah ones, so with the 5W bulbs I get a bit over an hour of god-light, and when I run the 6V-10W bulbs (which become bright enough to light up not only past your friends with HIDs, but the shadows of their bike are usually extending further than their light normally projects) get about 30 mins.

Many brand name light makers use the over-volting trick (well, not so much a trick but taking advantage of the increasing efficiency curves of higher voltages) to get more light than the "competitor" from a given bulb. Turbocat, Nightsun, Niterider, and Vistalight have all done it in the past. The normal setup is things like a 7.2V battery pack with a 6V bulb (20% over), 13.2V on 12V bulb (10% over) or 6V on a 4.8V bulb (25% over).

At 25% overvolting, the light output jumps 118%, the current draw increases 56%, and the bulb life shortens to about 10% of normal. Now given that these are halogen bulbs its being done to usually, 10% of 2000 to 5000 hours is still... 200 to 500 hours of life. Vistalight's VL5xx lights are the ones that ran the 25% overvolt. The nightstick battery packs were all 6V batteries and the standard bulbs were also 6V, but they had these special "high-output" bulbs you could order, which were actually 4.8V bulbs.

To figure out what the actual jump in lumens might be to compare to say, buying a new higher-output light system (whether the now discounted 15W Planetbike Alias lights, a cheap HID, or a DIY LED setup using Cree XRs or something), you'd first have to figure out what the bulb originally was rated for in the light housing you're using. Halogens being typically around 20 lumens per watt though is why with back in the old days most of us found running a pair of 10W lights plenty for most riding. You quickly realize with a 100% overvolt, and the accompanying 11.3 times as much light as to WHY I call them god lights. A single 10W bulb suddenlly going from 200 lumens to over 2000 will tend to give you an edge on the trails.

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