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Stepping up the Bike Light
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Please be positive and constructive with your questions and comments.

Stepping up the Bike Light

by magician13134 on Tue Feb 24, 2009 8:15 pm

Hey everyone, I've been looking into making my own "flashlight" for a little while (I've started to become very obsessed with them lately). I don't want it to really be practical or useful, 10 minutes run-time would be time, I just want it to make people (even me) go "WOW!". I was looking around and saw a nice 12V/50W Halogen at RadioShack for $6. I then found a pretty decent-looking power supply on eBay: 12V, 6500mAh
Then I realized that I have no idea what the circuit is doing. I know it's limiting the current. But I want it the halogen to get 4+ Amps to get all 50W out of it. It says that Li-Ions "dislike giving burst charges", does this mean they won't or they just won't last long doing it? What would I need to update in the circuit to accommodate the new power requirements?

Any advice on this is greatly appreciated, thanks.
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Re: Stepping up the Bike Light

by Amberwolf on Wed Feb 25, 2009 1:39 am

Just remember, despite the 6500mAh rating, you won't get 6500mA for an hour, and the higher the discharge rate from a battery the more likely it is to wear it out faster than normal.

It might work for a short time, as long as that battery is rated to discharge at a high enough percentage of it's capacity. The ebay page doesn't specify anything other than voltage and capacity, so there's no way to know this for sure.
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Re: Stepping up the Bike Light

by magician13134 on Wed Feb 25, 2009 9:09 am

Right, right. But I'm hoping to get about 4000mA for 30 minutes, who knows, it may not work. Will the circuit provided be able to handle those currents, though?
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Re: Stepping up the Bike Light

by oPossum on Wed Feb 25, 2009 9:46 am

The flashlight experts are at CandlePower Forums. They can tell you what works and what doesn't.
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Re: Stepping up the Bike Light

by magician13134 on Wed Feb 25, 2009 6:40 pm

oPossum wrote:The flashlight experts are at CandlePower Forums. They can tell you what works and what doesn't.
I'm a member there, but I was too intimidated to ask :(
Everyone there knows SO much more than me (since it's entirely flashlights) and they aren't afraid to remind me of that, at least here I can keep up with the electronics.
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Re: Stepping up the Bike Light

by oPossum on Wed Feb 25, 2009 7:44 pm

magician13134 wrote:I then found a pretty decent-looking power supply on eBay: 12V, 6500mAh
Then I realized that I have no idea what the circuit is doing. I know it's limiting the current. But I want it the halogen to get 4+ Amps to get all 50W out of it.

I wouldn't get that because there aren't any useful specs for the cells, protection, or charging circuit. The wire looks like it is a low current coaxial cable that has a very small (#24 or higher) center lead - not good for high current.

A couple 7.2 V RC battery packs in series would provide plenty of current. NiCd batteries will tolerate deep discharge without significant damage and charging them is much simpler than Li-Ion.
Not a "high tech" solution and lower energy density, but safer than most Li chemistry. There are many examples of what can happen with Li batteries at CandlePower forums.
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Re: Stepping up the Bike Light

by magician13134 on Wed Feb 25, 2009 8:09 pm

Hmm... I guess I'll need another use for a 12V battery then ;)

Thanks
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