lights help

[Hairyeyeball]

Hi, Not sure if im in the right place or not! sorry if im not.... If this isnt the right place could someone point me in the right direction please?

anyway, i'm in need of a bit of help with a light....

I have a 12v light that I am wanting to put on my bike (bicycle)
I was wanting to use it as a rear light and a brake light but not sure what I need or where to start!!!

This is what I have

1 x 12v 15w/30w bulb it has 2 fillaments and 2 wires that connect to it.
1 x 12v 2.8Ah battery
1 x contact switch

I know that when I have it as just the rear light it will need a lower voltage going threw it and for the brake light to work it will need the full 12 volts going to it.

I need to know what else I would need and how would I wire it up?

ANY help or advice would be fantastic!!!

Thank you all in advance
Trevor

 

[rezer]

You could use a series dropping resistor to limit the current thereby increasing the life of your battery. However, this will dim you bulb. Your battery needs to be rechargable. With just the bulb hooked up to the battery, your battery will discharge in a little over an hour. Another option would be to go with a bigger battery.

I would go with just the rear light setup. I don't know where you are from but why use a break light on a bike? Where are you located? That may answer my question.

 

[Hairyeyeball]

Thanks for your reply...
i'm into custom bikes and I wanted somethiing a bit different with the lighting.
I'm usiing a rear tail light from a '59 Chevy and thought it would be a nice touch if it worked as a brake light too.
Could I use a series dropping resistor for the main rear light and then run a second wire from the battery to the light via the contact swith to act as the brake light when the switch makes contact?
I'm from the UK btw

 

[rezer]

Thanks for your reply...
i'm into custom bikes and I wanted somethiing a bit different with the lighting.
I'm usiing a rear tail light from a '59 Chevy and thought it would be a nice touch if it worked as a brake light too.
Could I use a series dropping resistor for the main rear light and then run a second wire from the battery to the light via the contact swith to act as the brake light when the switch makes contact?
I'm from the UK btw

Yes. But, your battery probably won't last very long with a lot of stop a go biking. You will want to charge it up after use.

 

[Hairyeyeball]

That'll be alright. It wont be used on a daily basis.
Do you have any idea which series dropping resistor I should be using?
Thanks for your help btw

 

[rezer]

That'll be alright. It wont be used on a daily basis.
Do you have any idea which series dropping resistor I should be using?
Thanks for your help btw

If you decrease your amperage to 0.57A. Your battery will last about 2 hours long. With a bulb resistance of 9.6Ω, you'll need a 12Ω resistor rated for 5W. You can use a ceramic resistor for this. This will only supply about 1/2 the voltage to the bulb, but it will be a good starting point. You'll have to test the brightness of the bulb to your liking. Obviously, being such a critical item, safety first. If it's not bright enough decrease, the resistance until it is acceptable. You won't have to increase the wattage of the resistor though.

 

[kchriste]

1 x 12v 15w/30w bulb it has 2 fillaments and 2 wires that connect to it.

What you need to do is ground the "case" of the bulb holder ( Connect it to battery - ). One of the wires goes to the battery through an regular on/off switch and the other through the brake switch. Choose the wire that lights the bulb the dimmest for the running light. I wouldn't use a resistor to dim the light. You'll waste way too much power that way. Use a lower wattage bulb or LEDs to save power.

 

[rezer]

What you need to do is ground the "case" of the bulb holder ( Connect it to battery - ). One of the wires goes to the battery through an regular on/off switch and the other through the brake switch. Choose the wire that lights the bulb the dimmest for the running light. I wouldn't use a resistor to dim the light. You'll waste way too much power that way. Use a lower wattage bulb or LEDs to save power.

He will burn more power using just the bulb (15W). Using a resistor, he is only consuming 7W of power. Thereby, extending the charge of his battery. True, resistors are very inefficient, but you either loose the power with the resistor, the bulb or both. Perhaps you meant a resistor would wast too much power as opposed to using LEDs or lower wattage bulb? If that's the case, I agree (As long as the bulb is less than 7W) But my concern was the brightness of the bulb itself, since the current has been reduced by 55%. This is something the OP will have to check out and decide.

Smaller wire won't hurt anything, but it won't have the effect you think it will. This run will probably be less than 5'. As an example, if he's using 5 ft of 20ga wire, and that's a liberal estimate, the wire resistance is only 50mΩ. This won't drop hardly anything. He will still have the same power consumption at the bulb.

That said, I agree using LEDs would be the most efficient method. Evidently I thought it, but didn't post it (I keep reading the blasted thing but it isn't there. Bummer).

Hairyeyeball,
You might consider using LEDs. Since you work with custom bikes, this will have a snazzier appearance. This is another option you could check into unless your dead-set on using the bulb.

 

[Hairyeyeball]

OK so LED's sound a bit more simple than the bulbs.... If I use the LED's instead what would I need to do?

Say I have 15 LED's would I have say 10 connected all the time to act as the normal light and have the other 5 switched to act as the brake light so when I pull the brake all 15 are lit up?

If thats the case what would I need to use between the battery and LED's?
Wouldn't they burn out if they're connected straight to the battery?

Thank you for all your time and help with this.....
Trevor

 

[rezer]

OK so LED's sound a bit more simple than the bulbs.... If I use the LED's instead what would I need to do?

Say I have 15 LED's would I have say 10 connected all the time to act as the normal light and have the other 5 switched to act as the brake light so when I pull the brake all 15 are lit up?

If thats the case what would I need to use between the battery and LED's?
Wouldn't they burn out if they're connected straight to the battery?

Thank you for all your time and help with this.....
Trevor

No, the irony of this suggestion is you will still need a resistor, except in this case, one per. But this is what I wanted to avoid. The wiring will be more complex and there will be more work involved. It will be more effiecient though. You can use super-bright LEDs in the same manner you were going to use the bulb. A resistor would be in line during non-brake use as the tail-light. When the brake gets applied, it would switch another resistor in-parallel with the first, thereby inc. the current flow and the brightness. Regardless, both states will require resistance.

 

[Hairyeyeball]

Oh I see lol
give me a spanner over a soldering iron any day lol
do you have any idea what resistors I would need or is that dependant on how many and what type of LED's I use??

You mean I would need a resister on each LED?

 

[Hairyeyeball]

Would this work? sorry for the poor drawing but think you guys should see what I mean!!

**broken link removed**

 

[rezer]

Would this work? sorry for the poor drawing but think you guys should see what I mean!!

**broken link removed**

The value of your resistors will depend on the current draw for the LED. In you drawing, only 1/2 of the LEDs are lit during non-brake use. Then when the brake is applies, the other 3 light. Is this right? I recommend using one resistor for each LED in series, otherwise there will be an imbalance between them. One may be brighter than the others and so on. It's just a better design. To me, it makes more sense to operate the LEDs, all on, at a lower current (with a series dropping resistor), then when the brake is applied, the switch would short across the series dropping resistor, thereby increasing the brightness of the LEDs. With this design, you could use 280 ohm resistors for your branches drawing 15mA with a main series resistor of 47 ohms, 1/2W resistor. This would operate at 1/2 brightness. When the brake is applied, the branch current would inc. to 30mA. This will depend on what LEDs you acquire, but I believe super-brights will draw about 30mA with a 3.6V drop. You can google it and check the specs.

 

[audioguru]

Ordinary little 5mm red LEDs are 1.8V to 2.2V. white and blue (and some very bright green) LEDs are 3.3V to 3.6V.

Their absolute max current at room temperature might be 30mA and enclosed in the sunshine they will overheat.

 

[Hairyeyeball]

Yes thats right. I thought it would've been easier to have it lighting up with 3 then 6 when the brake was applied lol

So you mean I should do something like this?
**broken link removed**

My brother has been helping and he went out today and bought these **broken link removed** instead of individual LEDs so I am presuming that what I have drawn out will be no good now? (think it was prob wrong anyway lol)

 

[Willbe]

a rear light and a brake light
1 x 12v 15w/30w bulb it has 2 fillaments and 2 wires that connect to it.
just the rear light it will need a lower voltage going threw it and for the brake light to work it will need the full 12 volts going to it.

The 1034 and 1157 lamps have a high wattage filament (brake) and a low wattage filament that both get the 14.4 V from a running engine.

 

[Hairyeyeball]

The 1034 and 1157 lamps have a high wattage filament (brake) and a low wattage filament that both get the 14.4 V from a running engine.

I have decided to go with REZER's suggestion and go with LED's instead.
I just need to know if the diagram I have done is correct and will work

 

[audioguru]

Six 2.2V LEDs in series won't light when the battery voltage is less than about 14V.
Six 2.5V LEDs in series won't light when the battery voltage is less than 15.5V.

Use two strings of 3 LEDs in series and each string in series with its own current-limiting resistor for bright Brake lights. Add a resistor in series with both strings combined to reduce the brightness for the tail light and the brake switch shorts it.

 

[rezer]

I have decided to go with REZER's suggestion and go with LED's instead.
I just need to know if the diagram I have done is correct and will work

Gurus got it figured. Go with it.

 

[Hairyeyeball]

Thanks guys, but im a bit confused now! lol Dont suppose you could draw me a diagram? and tell me which resistors to use could you? bit of a cheek I knnow but im not very good when it comes to all this electronic stuff............