Electronically controlled 12V 75W lamp

[Simian_196]

Hi,
I would like some help with a project that I would like to start.
I have a torch which I would like to control using an electronic circuit.
It would be preferable to have the circuit as an anologue set up, if this is not feasable then may a PIC set up would be more suitable??

Here goes!

The brief

I would like the lamp to do the following:-

Turn on but does not blow the lamp (soft start) operate at different levels and have a level of battery protection


Lamp function

a - Soft start (protect the lamp against the initial start up of the circuit)

b - Voltage monitor (10 LED bar?) this would give a visual indication of the battery level with a single push of a button (small switch on the circuit)

c - Reed switch, with a single operation of the reed switch the lamp should do the following- full power - half power - quater power then off or if the reed switch is left on for more than 3 seconds an audible warning should sound until the reed switch contacts are opened again.

Battery Protection

All of the below should not be affected by trying to switch off the lamp and turn it on to try and get full power

a - The lamp needs to be controlled so deep drain of the batteries does not occur i.e. when the battery level reaches 75% the lamp supply voltage is reduced to 75%, i would like an audible warning to occur over a period of 10 seconds every time this occurs probably pulse every 1 sec

b - When the battery reaches approx 30% then the lamp supply voltage should be reduced to 25% and an audible warning as above.

c - When the battery voltage reaches 10% above the min voltage the lamp should switch off, this should remain so until the battery voltage is at 100%

Current components

1 - 12V 75W halogen lamp
2 - 12V 3.2Ah Lead acid battery (2off in parallel)
3 - Reed switch

It seems quite difficult to a novice! but if there is any one that could help I would appreciate any comments even ideas

I will add more details of the battery min and max operating voltages

 

[ante1]

Hi Simian,

Welcome to our forum,

You need a PWM (Pulse Width Modulation) circuit; this will solve the control and soft start part of your project. Search for PWM here in the forum and in Google, you will get plenty of circuits to choose from. The voltage monitor (battery monitor) is another part of your project which can be found in numerous variations with a quick search.
Later you might need some help putting it all together.  8)

 

[Alun]

Your idea to measure the battery voltage is flawed, of course the voltage to the bulb will drop by 75% if the battery voltage drops to 75% but most rechargable batteries will be destroyed when the voltage gets this this low so it's pretty pointless. I would recommend if you want to protect the battery the circuit should shut off the power if the supply voltage drops below 80%.

The soft start is also very easy to implement if you use a potentiometer with a bulit in switch (like the ones often used in some radios) to control the PWM with.

We alrady have loads of PWM threads but these two in my oppinion are the most useful:
http://www.electronics-lab.com/forum/index.php?topic=2373.0
http://www.electronics-lab.com/forum/index.php?topic=2988.0

 

[Simian_196]

Thanks for your help, for info the min and max voltage of the batteries is as follows:-
min 11.8V
max 13.4V

The % i suggested would be between these voltages not between 0V and 12V.

I didnt think it would be clear when i wrote the original request....sorry for any confusion.

Si

 

[Alun]

It's better to simply cut-off the power to the bulb rather than dimming it when the battery voltage drops because the efficiency of an incandesent lamp drops dramatically when its power is reduced. I recommend sounding an alarm when the voltage drops below 11.9V then cutting off the power at 11.8V, a comparator circuit

 

[Simian_196]

Alun, thanks for you help. It has opened up a whole new world for me, sad i know.

I would like to here your thoughts about this,

My project spec has altered slightly although I will still pursue it. (So in effect I have 2 projects on the go but this one is slightly more important)
I am now going to attempt to build a torch for my bike using leds.  :-\
I know you can buy bike lights cheaper fully assembled but where is the fun in that. I would like to add a few features standard lights don't have I think?? and build it myself.... keeps me out of trouble

I would like to use the PWM circuit because of the dimming function, I intend to use this as part of the additional light functions. I have earmarked the circuit in the link below, if that is the correct way to go??

http://www.electronics-lab.com/forum/index.php?topic=2373.0

I would like to change the supply voltage from 12V to 6V. (Batteries are cheaper)
I am going to use 19 leds for this torch, I have chosen 5000mcd white leds.
I have also drawn up a preliminary layout for the led pcb see attached (not final) I will use SMT resistors for the leds to keep the physical size to a minimum (its approx the size of a 50pence piece) I will also sketch up the other boards when I get a chance

I am going to add a battery monitor which gives me a visual indication using a circuit I found on the internet

http://www.uoguelph.ca/~antoon/circ/batmon12.htm

I will post pics of the board when I make it and all of the stages of the light manufacture, if any one is interested??

Should I move this thread to a new location??

View attachment 37991

 

[audioguru2]

I would like to change the supply voltage from 12V to 6V. (Batteries are cheaper)
I am going to use 19 leds for this torch, I have chosen 5000mcd white leds.

What kind of 6V battery?
What max current for the LEDs?

 

[Simian_196]

Sorry, Doh' :
The battery info:-

voltage:  1.2 V
type:        Nickel Metal Hydride (NiMh)
capacity:  3500 mAh
function:  Rechargeable

Led info:- Attached file

led.pdf

 

[audioguru2]

Hi Simian,
Those LEDs have the narrowest only 10 degrees angle I've ever seen. You might be riding at night and ride over a critter or small child coming from out of the narrow beam.
I guess you could tilt each LED a little to make the beam wider (but then dimmer).

The battery cell's capacity seems to be higher than usual. What size is it and who makes it? Can you post its datasheet?

 

[Simian_196]

Hi audioguru

heres a link to the web site

http://www.budgetbatteries.co.uk/category/14/Industrial-Tagged-Batteries.html?cartid=3223_20Nov05_211718

there close to the bottom of the page dark green in colour

 

[audioguru2]

Hi Simian,
The battery cell looks like a fully-filled C size. Here, Energizer puts a little AA size battery cell in their C cells and rate it at 2500mA/hrs. ;D

 

[Simian_196]

;D I hope to purchase 5 of them, just need to get the funds released(the future wife controls the purse strings). Out of curiosity were is here? if you dont mind me asking?

 

[audioguru2]

I'm very close to Toronto, Canada. ;D

 

[Simian_196]

Im from a small place, the Isle of Man. UK. look it up on google earth "Douglas" lat=54.15, lon=-4.48333

What do you think to my proposal??

Is it feasible for a newbie ;D

I have a workshop at my disposal so I can make anything almost

 

[Alun]

I recommend a Lumiled - one would be brighter and more efficient than all of those small LEDs put together, you can buy them from Maplin and RS, Farnell might sell them too, try shopping around and rather than using a PWM converter and a power wasting resistor you could construct a high effciency constant current regulator.

 

[Simian_196]

Ok thanks I will have to look into your suggestion Alun.

Oh great some more research :-\

I will be back! for more help