How to build a light triggered by a specific voltage?

U

UnorthodoxCreations

New Member

• Dec 28, 2008

• #1

I working on building a custom gauge cluster for my car. Do to space constraints I will no longer be able to have a voltmeter, digital or analog. Is there something I can build so that when voltage of the car/battery drops below a certain level a warning light will come on? The warning light could be a traditional bulb but I think I would like to use a LED. Any help would be greatly appreciated.

 

audioguru

Well-Known Member

Most Helpful Member

• Dec 28, 2008

• #2

The warning will come on when the car is started and when the rear window defogger runs when the engine is idling. It might even come on at night when you stop at a traffic light.
You want that?

 

U

UnorthodoxCreations

New Member

• Dec 28, 2008

• #3

I would expect that it would come on when the engine is starting. No, I wouldn't want it on anytime an extra load is placed on the car. I would basically want it as a warning that the voltage is dropping abnormally low. I'm not sure where I would want it yet, 10volts, 9 volts?

 

R

rjvh

New Member

• Dec 28, 2008

• #4

9 Volts then your battery is dead already so you don't need a light to tell you that Nothing will work at that time

What you want is easy to make but what Audio guru already said sertain loads can pull the voltage down in certain conditions and that will not indicate that your battery is broken or up for replacement

Robert-Jan

 

U

UnorthodoxCreations

New Member

• Dec 28, 2008

• #5

I have no idea what I would be building here. I imagine it would not be to difficult to adjust what voltage the light comes on, correct?

 

R

rjvh

New Member

• Dec 28, 2008

• #6

Hi attached schematic is a simple to build and adjustible voltage setting setting for your LED

a few components are crossed as you dont need them in your aplication

make sure that you do use the resistor in series with the LED

Robert-Jan

 

Attachments

• battery discharge protector.pdf

  273.1 KB · Views: 198

R

rjvh

New Member

• Dec 28, 2008

• #7

Sorry my mistake

the first schematic the LED will burn when the voltage is above the seting point

you desired a Indicating light when the voltage is below the seting point so I attached the corect schematic for that

Robert-Jan

 

Attachments

• battery discharge protector.pdf

  279.4 KB · Views: 165

H

Hayato

Member

• Dec 28, 2008

• #8

Knowing that you have a good battery, try to measure the lowest voltage possible.

Turn the vent to the maximum, turn the deffoger on, turn the radio on, the lights... Then measure the voltage over the battery terminals.

With the alternator running, the voltage must be between 13.0V ~ 14.4V. The fully charged battery will be 12.6V ~ 12.7V w/o the alternator.