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How to bring down mobile voltage?

K

KD0NNB

Member
Feb 24, 2011
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Getting my ducks in a row to do a Yaesu FT-857 install in my truck and noticed the manual is rather adamant about NOT going over 15 volts on the power supply. Unfortunately, late model Silverados will often just barely go above 15 volts when charging. Does anyone have a recommendation on some kind of converter or regulator to bring this down to say the 13.8v range? I would need something capable of handling at least 25 amps, preferably 30.

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Looks like I'm safe up to 15.87 volts.
 

Simply way you can add couple of silicon diodes in series. Each diode will give you 0.7V voltage drop. Of course those diodes must handle current you need.
Mike
 
sp5it said:
Simply way you can add couple of silicon diodes in series. Each diode will give you 0.7V voltage drop. Of course those diodes must handle current you need.
Mike
Click to expand...

What he said but first I would question WHY the voltage is so high. The batteries are the same old nominal 12 volt batteries that fully charge at 14.2 -14.4 volts. At 15+ volts I would expect battery damage.
 
Did you measure the voltage or are you going off of the voltage gauge in the dash? The dash gauge does a good job of telling you whether you are charging/discharging but may not indicate voltage accurately. A good example of this is the gauge in my Blazer. It indicates a charging voltage of 15v but measuring the voltage at the battery shows 14.3v. Something else to consider is that the charging voltage may not be the same as what you'll find at the input of your radio. Other electrical devices in the vehicle drawing from the power source (battery) can cause the voltage to drop. The best way to determine the actual voltage the radio will be seeing is to install the power leads for the radio, start the vehicle and measure the voltage at the plug prior to inserting it into the radio.
 
In the past I have seen alternators have an adjustment to control the max
voltage that it would reach. 15 volts seems high to me and I have had a lot
of mobile installations.
 

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