# 7.4V on a 6V Halogen?



## secretspy711 (Oct 12, 2010)

Simple question... can I use a 2-cell LiPo battery (7.4V nominal) on a 6V 15W halogen MR11-type bulb? How much will that degrade the bulb life?

Thanks!


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## mvyrmnd (Oct 12, 2010)

I suspect it would work. For how long depends a lot on the quality of the bulb.

The easy way to find out is to sacrifice a bulb to the gods of experimentation!


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## fivemega (Oct 12, 2010)

secretspy711 said:


> Simple question... can I use a 2-cell LiPo battery (7.4V nominal) on a 6V 15W halogen MR11-type bulb? How much will that degrade the bulb life?
> 
> Thanks!



*If bulb life is rated more than 100 hours at spec, then you can overdrive it by 2-cell LiPo battery. 
7.4 nominal voltage will drop to about 7 volt under the load (Depending on overal system resistance and battery internal resistance).
Rerated bulb life depends on bulb life at specs and actual voltage at bulb pins.

Note: most of MR11 and MR16 bulbs are rated over 1000 hours but not all.*


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## Linger (Oct 12, 2010)

1)Most likely.
2)I don't know, WA has a re-rater, but it will depend on your specific bulb what its performance will be.

In favour of it, I have a 6v 20w mr11 bulb plugged into a 3s (~12.4v) 20c pack. Very bright, very white.
Against it, I've also had a 6v d26 lamp assembly poof on 2s LiFePo (6.6v). Very dark, very sad.

Am I correct to presume your bulb was meant to be run from a dc converter plugged into an AC source? If so it actually takes 6v @2.5A. (as opposed to a 6v bulb meant to be run on primary cells that quickly sag well below this.) If your bulb was mean for long runs actually at 6v, it should have some capacity for over-voltage.

*Soft-start always helps prolong bulb life, especially when hotwiring (over-volting it)


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## secretspy711 (Oct 13, 2010)

Thanks for the replies!

This will be for a bike light, and I can get/make either a 6V NiMH or 7.4V LiPo in similar capacities for about the same price, but the LiPo would be lighter-weight. They both have their advantages though.

Linger, I'm not sure of the answer to your question. This is a NiteRider Trail Rat I scored on Craigslist for $16 without a battery, so I need to come up with one, hence this thread. I assume the bulb it comes with is one of the stock bulbs (found here), but there's not a lot of information on them. When I get to replace the bulb, I guarantee I won't be paying $20 for it though!

You put a 3S LiPo on a 6V bulb?! woah... any guess on how many lumens you squeezed out of that?

How do you soft-start? I'm not really an electronics guy -- I just know enough to be dangerous . Was thinking about using a switching dc-dc converter to get me back down to 6V if necessary... would the inductor in the circuit provide the soft-start characteristic? But then I wouldn't really need the soft start anymore...


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## secretspy711 (Oct 14, 2010)

ok, so my light arrived today, and so I did some testing. Man, overvolting it really makes a huge difference! :twothumbs Check out these beamshots (I used MTBR's "standard" beamshot camera settings)

Control (sorry, a bit out of focus):






6V Alkaline "Lantern Battery"





7.4V 2S LiPo


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## mvyrmnd (Oct 14, 2010)

See? Fortune favors the brave


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## jh333233 (Oct 15, 2010)

arent incan bulbs very sensitive to over voltage?
my sf p60 burnt with 2x 16340 (2x4v fullcharged)


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## fivemega (Oct 15, 2010)

jh333233 said:


> arent incan bulbs very sensitive to over voltage?


*Not necessarily.
Depending on designed bulb life, they can be overdriven pretty hard up to 160% of designed voltage.* 



jh333233 said:


> my sf p60 burnt with 2x 16340 (2x4v fullcharged)


*Don't you think 8 volt for a 5 volt bulb (30 hours life) is too much overdrive?
Each primary CR123 has voltage of 2.5 volts under 1.2 Amp current draw of P60
Voltage of 2 IMR 16340 is perfect match for P90 but will severely overdrive P91*


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## lightseeker2009 (Oct 19, 2010)

I'm using a 7.2V Nicad RC car batterypack to power a phillips HPR50 6 volt lantern globe. This combo has survived 3 charging cycles so far. Nice increase in light!


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## KiwiMark (Oct 19, 2010)

jh333233 said:


> arent incan bulbs very sensitive to over voltage?
> my sf p60 burnt with 2x 16340 (2x4v fullcharged)



I run an Osram 64430 6V 30W bulb at 10V - very bright & white.
I run an Osram 64458 12V 90W bulb at 20.2V - VERY bright & white. (fivemega Elephant II body & fivemega 3" throwmaster head - fantastic light)

Some incan bulbs can tolerate quite a lot more voltage before 

The Pelican 3854-H & 3854-L bulbs are rated at 6V and work quite nicely from 2 Li-ion cells - this is the classic ROP setup.


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