My bike light

[EscourtU]

Ok I have searched the forums and just need a quick "It's ok" from someone. I have a 12v 55watt light and hooked it up to a 12v 9.5ah battery. I am guessing that this setup will give me "about" 2 hours runtime without running completely dead. Is this calculation correct or am I way off? Thanks..

[tedsti]

You are correct on your run time estimate. Make sure you have some heavy gauge wire on this set-up since you will be pulling 5 amps. I would guess that you would want 14G or bigger. Is it a lead acid battery?

The real question is are you sure you want to run a 55W bulb? That is a lot of light. Even a 35W is borderline overkill. Is it an MR16 bulb?

[bigwheel]

Ok I have searched the forums and just need a quick "It's ok" from someone. I have a 12v 55watt light and hooked it up to a 12v 9.5ah battery. I am guessing that this setup will give me "about" 2 hours runtime without running completely dead. Is this calculation correct or am I way off? Thanks..

As ted said, you are pretty close with your calculations, AND you will need some decent thickness wire (probably #14~16 or so), AND that you will have lots of light with a 55 watt bulb. I'm not going to say "too much", because that value is undefined.

However, the 9.5ah battery will not give you 9.5 amp hours at the 2 hour rate. Deep Cycle batteries (Sealed Lead Acid) are rated at a C/20 or C/100 rate. In other words, they put a small load on them when they measure. There is something called Peukert's equation where you can estimate for different loads if you really wan to. Anyway, you will be lucky to get 1.5 hours. Also, you are not supposed to run a SLA battery way down, except under special (emergency) circumstances. It is really hard on battery life.

Finally, a 9.5ah battery is going to be pretty big and heavy. You will get a decent workout, and need a big bag to carry it.

[EscourtU]

It is actually from my spare running/fog light. They are the smaller ones that I bought from walmart a few years ago and just never used them. I am using the wire that came with them and the switch also. Yeah I am sure I don't need so much light but I had them laying around and not being used. It is a sealed battery and unsure what the exact terminology is for it.
I carry the battery in my backpack.

[Ish]

....they put a small load on them when they measure. There is something called Peukert's equation where you can estimate for different loads ....

http://im1.shutterfly.com/procserv/47b6db31b3127cce88ad4f366c7600000016108AauW7hy3ctD

[ibismojo2001]

As ted said, you are pretty close with your calculations, AND you will need some decent thickness wire (probably #14~16 or so), AND that you will have lots of light with a 55 watt bulb. I'm not going to say "too much", because that value is undefined.

However, the 9.5ah battery will not give you 9.5 amp hours at the 2 hour rate. Deep Cycle batteries (Sealed Lead Acid) are rated at a C/20 or C/100 rate. In other words, they put a small load on them when they measure. There is something called Peukert's equation where you can estimate for different loads if you really wan to. Anyway, you will be lucky to get 1.5 hours. Also, you are not supposed to run a SLA battery way down, except under special (emergency) circumstances. It is really hard on battery life.

Finally, a 9.5ah battery is going to be pretty big and heavy. You will get a decent workout, and need a big bag to carry it.


What the .......!:D

[bigwheel]

It is actually from my spare running/fog light. They are the smaller ones that I bought from walmart a few years ago and just never used them. I am using the wire that came with them and the switch also. Yeah I am sure I don't need so much light but I had them laying around and not being used. It is a sealed battery and unsure what the exact terminology is for it.
I carry the battery in my backpack.

If it gets you out night riding, then go for it. Just take the opportunity to shut off the lights whenever possible.

If the group gets way ahead of you, just wait for the next opportunity where the trail curves back, then look them in the face and giggle. :crazy2:

[EscourtU]

Took it for a ride tonight and there is certainly much more light than my last night ride. It lights up a nice 20ft wide path. My battery lasted 2 and a half hours without noticeably dimming. Makes it much more fun to ride at night.

[Tegra54]

As ted said, you are pretty close with your calculations, AND you will need some decent thickness wire (probably #14~16 or so), AND that you will have lots of light with a 55 watt bulb. I'm not going to say "too much", because that value is undefined.


here is a good wire table: http://www.pupman.com/listarchives/1998/April/msg00189.html

your 12v 55w system will be pulling nominally 4.5amps of current, so you should be able to get away with a #16 wire

[bigwheel]

Glad it works for you. Are you sure it is a 55 watt bulb?

55 watts / 12 volts = 4.6 amps (rated amperage)
12 volts / 4.6 amps = 2.6 ohms
13 volts / 2.6 ohms = 5 amps (This is what your light will draw)
9.5ah / 5 amps = 1.9 hours Theoretical run time. Actual should be less.

If I had to guess, I'd say it was a 35 watt bulb. Still, an excellent choice for a home brew.

[EscourtU]

I am no electrician but the box says (2) 55 watt Halogen Off-Road/Racing lights. I only use 1 on my helmet and nobody makes eye contact with me so it must be bright.

[SprocketHead]

If that was the one you had on Wed at the "secret location", it's a nice light!

The problem I've run into is that a light that works for 2 hours at 40 degrees, quits in ~1 hour at 0 degrees... Good idea to bring a small emergency light.

[EscourtU]

Ha ha ha I keep the mongo battery inside and wrap it with a cloth. Not to keep it warm but for some cushion on my back. I had a great time riding. Hope to see ya next week. Maybe we could work on some wheelies. I need the practice. I have a deep cycle on stand by.:shocked: