# converting 12 volts to 4 volts

Discussion in 'Misc Electronics' started by Locoaudio, May 29, 2008.

1. ### LocoaudioGuest

Hi
I have a classic motorcycle and I have updated the old alternator to a
Permanent Magnet Alternator,
but the motorcycle has a starter safety relay ( which basically stops
the starter motor from reengaging once the engine has started)
which is activated by 4 volts from the old style alternator
now i need something small rugged and vibration proof to step down
the voltage from 12 volt to 4 volt
any ideas
Jamie

2. ### GMGuest

See the following which is for 12V to 3V

http://www.coolcircuit.com/circuit/12v_to_3V/12V_to_3V.GIF

I guess you have to find a zener diode that is about 4.7V and of course
you should recalculate R1. Look @
http://www.diodes.com/products/catalog/list.php?parent-id=9

3. ### GMGuest

See the following which is for 12V to 3V

http://www.coolcircuit.com/circuit/12v_to_3V/12V_to_3V.GIF

I guess you have to find a zener diode that is about 4.7V and of course
you should recalculate R1. Look @
http://www.diodes.com/products/catalog/list.php?parent-id=9

4. ### JamieGuest

A resister?
Need to know the coil resistance of the relay for proper calculations

http://webpages.charter.net/jamie_5"

5. ### S K MandalGuest

hello friend
You can use voltage regulator LM7805 (NATIONAL Semiconductor/
FIRCHILD) , so the output of the regulator will be 5Volts @ 500mA max.
Then you can connect a diode or a resistor with a filter capacitor to
drop further by 1Volt.
Good Luck.

REGARDS
SUBIR KUMAR MANDAL
SCIENTIST 'B'
DRDO

6. ### S K MandalGuest

YOU can also try LM317, adjustable voltage regulator, Aand to drive a
relay you need 10mA to 20mA depending upon their types.