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the12volt's install bay
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onthethreshold
Joined: December 19, 2011
Location:
Ohio,
United States
Posts: 3 |
| Posted: December 19, 2011 at 12:13 AM - IP Logged |
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| I need to reduce 14.3 volts to 8 volts to run an indicator lamp. Basically I'm a mechanic who can solder .Can someone tell me what size resistor I need and the values I need to achieve this.The alternator puts out roughly 100 amps and as stated 14.3 when charging .I'm thinking I can just solder in a resistor to the positive feed to the lamp.Thank you in advance . |
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onthethreshold
Joined: December 19, 2011
Location:
Ohio,
United States
Posts: 3 |
| Posted: December 19, 2011 at 12:16 AM - IP Logged |
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| The forum rules requested I add this info, 1979 Chevrolet K-10 . Sorry,new guy here . |
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oldspark
Joined: November 03, 2008
Location:
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| Posted: December 19, 2011 at 4:33 AM - IP Logged |
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R=V/I where V is the voltage drop required (eg, 4-6V) and I is the current (Amps) of the bulb and R is Ohms (rounded to the nearest preferred value.
The Wattage rating needs to exceed VxI (or IxIxR or VxV/R).
The output capability of an alternator has nothing to do with what its loads take. A 3W bulb still takes 3 Watts (0.25A @ 12V) irrespective of whether it's a 35A or 250A alternator.
(Or to paraphrase, a vehicle's electrical system is voltage based. Specifically, the battery requirements is what alternator voltages are set for.)
You can add the resistor to either side of the lamp.
And whether using 12V or 12.7V or nominal 13.8V-14.4V should not make much difference to the bulb (unless at 8V it is close to its limit). |
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onthethreshold
Joined: December 19, 2011
Location:
Ohio,
United States
Posts: 3 |
| Posted: December 19, 2011 at 2:35 PM - IP Logged |
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| Thank you ,no disrespect but could someone just tell me in laymans terms what value resistor I need to buy from Radio Shack to accomplish this task . Merry Christmas to all . |
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oldspark
Joined: November 03, 2008
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Posts: 2,855 |
| Posted: December 19, 2011 at 11:59 PM - IP Logged |
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Sure. What current or Wattage is the bulb?
(That's why I couldn't give a value - you didn't provide the lamp data.) |
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Topic: voltage reduction
