So, I'm installing an old tractor light on my rat, and I realize that the sucker puts out 35 watts. It looks great hooked up to a 12 car battery, but I don't have a clue about how much power it will draw from smaller batteries....electronics is not my thing. I mean I know that it will draw 35 watts, but I don't think 8 AA batteries is going to do the trick. I'd like to keep the light intact, it looks cool as an incandescent, but how do I get 35 watts of power out of flashlight batteries??? Thanks for any help.
12 volt headlight...35 watts???
- Thread starter NewOrleansFlyer
- Start date
Help Support Rat Rod Bikes Bicycle Forum:
The brightness of the bulb will depend on how many watts it gets, I don't know what kind of batteries you plan on using but they probably won't put out 35W, so the bulb would probably not be very bright if it lights at all.
cut out the rear of the light, used a water cooled dremel cut off wheel. Install a LED unit.
NewOrleansFlyer said:
Search for sealed lead acid (SLA) batteries. PowerSonic and Embassy are 2 well known brands. There are a lot of different sizes of these things and they can be charged with a wall wart. I've seen 12v batteries the size of a half sandwich. And they're inexpensive.
12v and 35 Watts means 2.91 amps
I dont think AA batteries are gonna cut it.
Bottom line... Flashlight batteries wont cut it, sure you could put together a pack that will work.... but I bet it would be HUGE... and you would have to replace them every hour.
if you do stick with the light... consider a sealed lead acid battery, like one for a power wheels.
I dont think AA batteries are gonna cut it.
NewOrleansFlyer said:
Bottom line... Flashlight batteries wont cut it, sure you could put together a pack that will work.... but I bet it would be HUGE... and you would have to replace them every hour.
if you do stick with the light... consider a sealed lead acid battery, like one for a power wheels.
No way are AA (or any) dry cells practical, they have a high internal resistance and just wouldn't put out the Amps.
Rechargeable AA would work (for a short while). Heres a quick example..
I found 2900mAh NiMh AA on ebay; highest capacity AA that I could find. That is the same as 2.9Ah (just convention with small cells to rate in mAh)
As Ratfink calculated 35W at 12V is just about 2.9A
So a pack of 10 (1.2V each cell) would theoretically give you 12v for an hour.
Although the 2900mAh rating will probably be at 1/10 capacity draw, so reckon on a fair bit less than an hour.
I would guess at somwhere around 45 mins. This would depend on the quality of the cells.
Sealed lead acid (SLA) batteries have higher capacities but are clunky. You could go for bigger NiMh's a string of C or D cells could be dressed up as an extra frame tube :lol:
LiPo cells have a higher energy density (more electric for the size/weight) but have big drawbacks on charging and discharging. I am a radio ham and run LiPo's in my RC but they won't be anywhere near my ride :wink:
I am with you on wanting to keep the tractor light, they are cool and I have my eye open for an old one at the right price. WW2 saw my area stripped of any metal 'to melt down for spitfires' the home counties around London were right behind the war effort, so you won't find many 'treasures' around here
The suggestion of converting to LED is the best way to go if you can manage it. Higher efficiency = More light for less current.
Regards, Kev
Rechargeable AA would work (for a short while). Heres a quick example..
I found 2900mAh NiMh AA on ebay; highest capacity AA that I could find. That is the same as 2.9Ah (just convention with small cells to rate in mAh)
As Ratfink calculated 35W at 12V is just about 2.9A
So a pack of 10 (1.2V each cell) would theoretically give you 12v for an hour.
Although the 2900mAh rating will probably be at 1/10 capacity draw, so reckon on a fair bit less than an hour.
I would guess at somwhere around 45 mins. This would depend on the quality of the cells.
Sealed lead acid (SLA) batteries have higher capacities but are clunky. You could go for bigger NiMh's a string of C or D cells could be dressed up as an extra frame tube :lol:
LiPo cells have a higher energy density (more electric for the size/weight) but have big drawbacks on charging and discharging. I am a radio ham and run LiPo's in my RC but they won't be anywhere near my ride :wink:
I am with you on wanting to keep the tractor light, they are cool and I have my eye open for an old one at the right price. WW2 saw my area stripped of any metal 'to melt down for spitfires' the home counties around London were right behind the war effort, so you won't find many 'treasures' around here
The suggestion of converting to LED is the best way to go if you can manage it. Higher efficiency = More light for less current.
Regards, Kev
Thanks for all the great ideas and information. I'll be taking a look at converting it..I saw somebody drilled out the connectors and put in a couple of ultra bright LEDs.
As for the lack of availability of old tractor parts in the UK.......thanks for the sacrifice....God knows what it might be like if you guys hadn't. Keep an eye on Ebay....you might find something there.
As for the lack of availability of old tractor parts in the UK.......thanks for the sacrifice....God knows what it might be like if you guys hadn't. Keep an eye on Ebay....you might find something there.
Cut out the element and went to Radio Shack to get some LEDs. Not sure if the big one would fit (had to hot glue it to the back, but it is mega times brighter than the little one that fit into the vacant hole in the back of the light. I've got to look up what resistor I would need if I went with more than 2 AAs...I've got room in a "faux" vintage battery I made, so it really doesn't matter. Anybody got any ideas...thanks
I ran a 12v 35w halogen on my bike a few time. Hooked it up to a 14lb car racing battery and just mounted the battery on the rear rack. It was BRIGHT and I was able to use it for around 2 hours of riding.
Radioshack has 12v batteries the diameter of a AAA and half the length. I used one for some led's long ago. But they still won't do anything where 35 watts is required. I'm wondering if there is a small transformer that does this. If a car ignition coil can step 12v up to 30,000V, I would think something could increase the wattage as well, and probably be smaller than an ignition coil.
Isn't it possible to use the LED-lamp,as shown below? I don't think they'll use 35 Watt. It's a brake-light for a car,so it should be bright enough. And there's LED's all around,so the mirror in your headlight should reflect most of the light.
Haven't tried it myself yet. It's just a wild guess.
http://s7.directupload.net/file/d/2864/qp3dlf8b_jpg.htm
Haven't tried it myself yet. It's just a wild guess.
http://s7.directupload.net/file/d/2864/qp3dlf8b_jpg.htm
ozzmonaut said:
Well, simply put, wattage, voltage & amperage are all directly tied together, it's basic physics. Watt / volts = amps drawn. This is what wilcycle was working from.
If you have a 35W bulb that's 12V, then 35/12 = 2.9 amps. You can step 12V to 30KV in a car because the car's electrical system will support several hundred amps. A small battery cell cannot. The example wilcycle provided was a AA that was rated at 2.9 amps-hours, that's two orders of magnitude less. That means that if 2.9 amps was drawn from it, it would depleat in an hour. The bulb would certainly dim well before that.
The bottom line is that you need adequate current to support a given bulb, even if the voltage is correct. You can't cheat it, the laws of physics bend for no one...
Follow up to above post:
It looks like the 2 LEDs, a couple of resisters, and a 9 volt battery are the ticket. Thanks for all the help. I'll post pics when I get it together.
It looks like the 2 LEDs, a couple of resisters, and a 9 volt battery are the ticket. Thanks for all the help. I'll post pics when I get it together.
