Voltage reduction via resistors?

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GalpinAudio

Copper - Posts: 44

Joined: February 20, 2003

Location: United States

Posted: June 24, 2004 at 4:34 PM / IP Logged

I was wondering if anyone had a chart or formula for determining voltage reduction using resistors. I am trying to reduce my 12V + to 5.4V. Any help or suggestions anyone could provide would be greatly appreciated.

Matthew

Never Let Those Who Say It Cant Be Done Stand In The Way While You Do It!

sandt38

Copper - Posts: 60

Joined: May 25, 2004

Location: United States

Posted: June 24, 2004 at 5:05 PM / IP Logged

That is totally current dependant Why would you want to do that? There are many 5 volt sources on a car, but my suggesting where to tap into it is dependant on why you choose to do it.

http://www.bcae1.com/ohmslaw.htm

Ohms law is your friend. Look at that link for the formula.

DYohn

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Joined: April 22, 2003

Location: Arizona, United States

Posted: June 24, 2004 at 5:12 PM / IP Logged

Here's a voltage divider calculator:

http://ourworld.compuserve.com/homepages/Bill_Bowden/r2.htm

Of course, another way to do it (depending on your current load) is using DC to DC converters....

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xetmes

Silver - Posts: 586

Joined: May 18, 2003

Posted: June 24, 2004 at 8:30 PM / IP Logged

I would highly recommend a voltage regulator for most cases, cheap and effective, resistors will always need a current requirments factored into the design..

kgerry

Platinum - Posts: 3,455

This member consistently provides reliable information

Joined: February 07, 2004

Location: Saskatchewan, Canada

Posted: June 25, 2004 at 10:42 AM / IP Logged

true...plus it's not a stable voltage value.... there are lots of good 5V regulators out there cheap.... go to any electronics supplier and ask for a 7805 regulator... probably cost you less than a buck

Kevin Gerry

Certified Electronics Technician

MECP First Class Installer

Owner/Installer

Classic Car Audio

since 1979

GalpinAudio

Copper - Posts: 44

Joined: February 20, 2003

Location: United States

Posted: June 28, 2004 at 10:06 AM / IP Logged

Thanks everyone for the help. I am installing an aftermarket deck in a 2004 Ford F150 with factory subwoofer. The remote turn on voltage out of the factory deck is only 5V. If I hook the remote turn on directly off the aftermarket deck it creates a pretty loud turn on pop when initially turned on. I'm assuming that the reason is the higher voltage to the factory amp turn on. I'm hoping that if I reduce the turn on voltage from the aftermarket deck to 5V this will make my turn on pop dissapear. Any additional info or ideas is always appreciated.

Thanks,

Matthew

Never Let Those Who Say It Cant Be Done Stand In The Way While You Do It!

xetmes

Silver - Posts: 586

Joined: May 18, 2003

Posted: June 28, 2004 at 1:03 PM / IP Logged

for that application i would probably just use a resistor voltage divider, Any idea what the current draw of the unit is? (at 5V)

GalpinAudio

Copper - Posts: 44

Joined: February 20, 2003

Location: United States

Posted: June 29, 2004 at 9:38 AM / IP Logged

I havnt actually measured the draw but i'd guess it's no more than 3 amps max. It's just a remote turn on for a very small factory amplifier powering a single 8" subwoofer .

Never Let Those Who Say It Cant Be Done Stand In The Way While You Do It!

kgerry

Platinum - Posts: 3,455

Joined: February 07, 2004

Location: Saskatchewan, Canada

Posted: June 29, 2004 at 6:13 PM / IP Logged

if it's just a remote turn on circuit i'd be surprised if it was more than about 500 ma.... any 5V regulator will give you a stable regulated 5V output and takes all of 6 seconds to hook up. 12V in, ground, 5v out...what could be simpler....?? this way if your input supply voltage floats the output stays at a stable 5V

Kevin Gerry

Certified Electronics Technician

MECP First Class Installer

Owner/Installer

Classic Car Audio

since 1979

xetmes

Silver - Posts: 586

Joined: May 18, 2003

Posted: June 29, 2004 at 8:30 PM / IP Logged

woah didnt think it was 3 A. You wouldnt want resistors for that. You could use a discrete regulator, use filter caps on the input and output for the best performance...

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