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Discussion Starter · #1 ·
Does a 12v halogen lamp draw more wattage when run at 14.4v than it would at 12v? My observed runtime would suggest it does. Thanks.

JZ
 

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The short answer is yes. You need to work out the amps for your light at the higher voltage.

For example a 12 volt 20 watt draws 1.6 amps. If you increase the voltage to 14.4 it then draws 2 amps and 28.8 watts. This is a good site for working out the changes: http://www.angelfire.com/pa/baconbacon/page2.html.

Plug in the 2 figures you know and then up the voltage while keeping the value for the ohms.

Tim
 

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Discussion Starter · #3 ·
Thanks Tim. That matches my observed numbers pretty well. I was estimating that my 32w setup (12w+20w) was pulling 40+. Nice and bright though!

I'll have a look at that site tomorrow....gotta get some sleep so I'm ready for tomorrow's night ride!

JZ
 

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Discussion Starter · #5 ·
Cool....I feel better about my brand new battery pack now :yesnod:

JZ
 

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Wombat said:
The short answer is yes. You need to work out the amps for your light at the higher voltage.

For example a 12 volt 20 watt draws 1.6 amps. If you increase the voltage to 14.4 it then draws 2 amps and 28.8 watts. This is a good site for working out the changes: http://www.angelfire.com/pa/baconbacon/page2.html.

Plug in the 2 figures you know and then up the voltage while keeping the value for the ohms.

Tim
Tim,

I'm new to this, so I thought I would ask...

I have a Jet Lites 20w halogen set up with NiMH batteries. The batteries have gone dead and I want to rebuild my own battery pack. I've ordered up some 4500mAh SC battery cells and was planning to build 13.2v pack to replace the Jet Lites battery pack. The Jet Lites are 3800mAh I believe. So I'm expecting longer run times, but was also wondering about overdriving the lights to 14.4v by adding a 12th cell to the pack. What is the advantage and disadvantage to doing this? Will the halogens burn brighter? Will run time drop? Will the bulbs burn out?

Mike
 

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Discussion Starter · #7 ·
michael9218 said:
I have a Jet Lites 20w halogen set up with NiMH batteries. The batteries have gone dead and I want to rebuild my own battery pack. I've ordered up some 4500mAh SC battery cells and was planning to build 13.2v pack to replace the Jet Lites battery pack. The Jet Lites are 3800mAh I believe. So I'm expecting longer run times, but was also wondering about overdriving the lights to 14.4v by adding a 12th cell to the pack. What is the advantage and disadvantage to doing this? Will the halogens burn brighter? Will run time drop? Will the bulbs burn out?
Mike
To answer the 3 final questions: Yes, yes, and eventually. Here's a chart I came across that addresses all 3 of those factors. Basically, going from 12v to 14.4v increases the brightness by ~85%, drops the runtime by 20%, and the bulb life by ~90%. The runtime can be addressed by using a higher mAh battery (I got a nice 5000mAh NiMH batt. from batteryspace.com for $65....your 4500mAh is close to that). The bulb life sounds bad, but considering the rated runtime for these bulbs is typically 2000 - 5000 hours, and the bulbs cost $3 to replace, it's not a biggie.

I've got a 32 watt halogen setup on the bars.....running at 14.4v I can get two 2 hour rides in on a charge, switching between 12w and 32w about 50/50. Haven't burnt a bulb yet. The guy who started the "DIY light - 1 year on" thread yesterday has been running 14.4v for a year and hasn't lost a bulb yet. Overvolted halogen is the best bang for the buck in bike lighting. (so why do I have a bunch of stuf on order for LED projects this winter? :confused: )

JZ
 

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