Adjustable brightness torch??

[bikemech]

Hi I have a request from a friend, he uses a torch with separate 12v battery power supply which he carrys a in his pocket, reason for separate battery is it lasts his whole work shift,
He has asked me if it would be possible to fit a potentiometer ( dimmer as he put it) how easy would this be ?

 

[Gryd3]

Hi I have a request from a friend, he uses a torch with separate 12v battery power supply which he carrys a in his pocket, reason for separate battery is it lasts his whole work shift,
He has asked me if it would be possible to fit a potentiometer ( dimmer as he put it) how easy would this be ?

Depends on the current draw of the torch.. it may be too high for a potentiometer to handle. The potentiometer will also waste some power... so it will not give him twice the battery life at half brightness.

One other important question.. is the torch an incandescent or an LED?
I would suggest he looks for an LED replacement... or we need to look into a 'PWM' method to 'dim' the light. This will save a lot more energy, and does not really 'need' to be adjustable with a dial if there are 1 or 2 preset dimmer values.

Ideas, thoughts?

 

[bikemech]

Yeah good idea with the led, never thought of that, it's quite a high power torch , and the whole setup would need to be as compact as possible , will get some details about what he he is using now and get back, ideally looking for maximum brightness with around 6 hour life, battery can be changer so suite, as long as it's not too big

 

[KrisBlueNZ]

PWM is the sensible option. Can be done fairly simply using a 555 driving a MOSFET. See http://www.reuk.co.uk/LED-Dimmer-Circuit.htm for an example. It is designed to vary the speed of a motor but there's little difference. Here's the circuit from that page:


Replace MOT1 with the torch (bulb or LED). D3 is not needed because the load is not inductive. Connect another 0.1 µF capacitor (ceramic) directly between pins 1 and 8 of the 555. That circuit should work pretty well. Can be built up on stripboard aka veroboard. Google stripboard construction for info.

 

[bikemech]

Think it's called breadboard over this side of the pond,
But great Al have a look at that.

Where is the controll on that diagram,
Is it Q1?
I understand 555 is IC?? And everything else ,

 

[KrisBlueNZ]

No, a breadboard is a solderless prototyping system.



^ Breadboard

v Stripboard aka Veroboard

 

[bikemech]

You just taught me something new

 

[Gryd3]

Think it's called breadboard over this side of the pond,
But great Al have a look at that.

Where is the controll on that diagram,
Is it Q1?
I understand 555 is IC?? And everything else ,

Take a look at the yellow P1 on the left side of the diagram.
Q1 is the FET that will do the heavy lifting switching the light on and off incredibly quickly (to make it look half-on)

 

[KrisBlueNZ]

Google schematic symbols to find out what all the symbols are.

 

[Gryd3]

C# = Capacitor
D# = Diodes (D3 should be removed)
P# = Potentiometer
Q# = Transistor (Or FET.. Field Effect Transistor)
R# = Resistor Values.

555 = A very common IC used for .. You guessed it, timing applications, anything from signal generation (PWM) to momentary delays to hold circuits on, or hold them off.

 

[bikemech]

Ahh damn, P1 , potentiometer 1 ?

 

[Gryd3]

Ahh damn, P1 , potentiometer 1 ?

Exactly!
It's not a sprocket or chain.. so I guess you missed that

When you get some more details from/for your friend, we can help you move forward and learn/build this.

 

[bikemech]

Yeah I replyed before I read the last post , sorry guys

 

[bikemech]

Exactly!
It's not a sprocket or chain.. so I guess you missed that

When you get some more details from/for your friend, we can help you move forward and learn/build this.

Was that sarcasam I read in your text lol

 

[Owen Qin]

 

[bikemech]

am i right in sayind D1 and D2 are zenna diodes?

 

[davenn]

am i right in sayind D1 and D2 are zenna diodes?

Zener diodes, no, 1N4148 are just small signal switching diodes

Dave

 

[bikemech]

would this work on say 12v 12ah battery or would it be to much ampage for it?

http://www.ukledsdirect.com/mr16-12v-led-spot-light-dimmer-controller-217-p.asp

 

[bikemech]

would this work on say 12v 12ah battery or would it be to much ampage for it?

http://www.ukledsdirect.com/mr16-12v-led-spot-light-dimmer-controller-217-p.asp

yeah it says 8A on it!!!

 

[bikemech]

PWM is the sensible option. Can be done fairly simply using a 555 driving a MOSFET. See http://www.reuk.co.uk/LED-Dimmer-Circuit.htm for an example. It is designed to vary the speed of a motor but there's little difference. Here's the circuit from that page:

View attachment 17135
Replace MOT1 with the torch (bulb or LED). D3 is not needed because the load is not inductive. Connect another 0.1 µF capacitor (ceramic) directly between pins 1 and 8 of the 555. That circuit should work pretty well. Can be built up on stripboard aka veroboard. Google stripboard construction for info.

what caps are C1 and C2?