Volts

[Guest Ted Grener]

I bought an inverter for 110v to Dc 15 amp for my 20 watt mobile. When I plugged it in it shows 12.9 volts. Will this lower my output as the vehicle outputs 13.8 volt. 

[BoxCar]

A lot of power supplies have an adjustment for the output voltage that ranges up to 15%. Does your supply have an adjustment? Post the model power supply and where it came from and we may be able to help you find an adjustment screw or give you better advice on what to do. I

[WRHS218]

This is purely anecdotal: I have a 20w mobile in my vehicle which gets 13.8v (minimum) when the truck is running and 12-12.8v when the truck is not running. While I have not done any serious tests to determine maximum distances, I see no difference in signal strength or clarity at known distances using the radio with the vehicle running or not. The maths would seem to show there wouldn't be much difference between 12.9v and 13.8v. If I remember correctly my 20w radio draws around 8-9 amps when transmitting.  I measured it years ago when I thought I really cared. These days, if it works and the magic smoke doesn't leak out, I don't worry about it. 

[SteveShannon]

12 minutes ago, WRHS218 said:

This is purely anecdotal: I have a 20w mobile in my vehicle which gets 13.8v (minimum) when the truck is running and 12-12.8v when the truck is not running. While I have not done any serious tests to determine maximum distances, I see no difference in signal strength or clarity at known distances using the radio with the vehicle running or not. The maths would seem to show there wouldn't be much difference between 12.9v and 13.8v. If I remember correctly my 20w radio draws around 8-9 amps when transmitting.  I measured it years ago when I thought I really cared. These days, if it works and the magic smoke doesn't leak out, I don't worry about it. 

You’re right.  Although a wattmeter might measure an extra few decimal points of outgoing power, it will make zero real difference in range.

[Guest WRXI733]

17 hours ago, Guest Ted Grener said:

I bought an inverter for 110v to Dc 15 amp for my 20 watt mobile. When I plugged it in it shows 12.9 volts. Will this lower my output as the vehicle outputs 13.8 volt. 

Like said the minute (insignificant) drop in wattage wouldn't be noticed on the receiving end but I would be curious to if it is lower than 12.9 on transmit.

3's

Greg 

[nokones]

Since, I have all my Saturday chores done, I decided to do a quick bench test.

I don't have a 20-watt Mobile to test, but I do have a 25-watt Mobile and I highly doubt that 5-watts of RF output power would make a difference in any farz or much of a power draw.  I used a Kenwood TK-880-1 UHF 25-Watt Mobile radio, Bird 43 that was recalibrated last year, EMC Corp 150-Watt 50 Ohm Power Terminator (Dummy Load), and a Powerwerx 30-amp variable power supply.

My first test was with the voltage regulated at 12.9 volts.  The stand-by power draw was .3 amp, the transmit power draw at 6.3 amps, and RF Output at 23 watts.  At 13.8 Volts the stand-by power draw was .3 amp, the transmit power draw was at 6.6 amps, and the RF output was 26 watts.

The voltage did not drop one iota 

That is .533 dBm difference in RF power levels and my Farz guesstimate for difference could probably be measured with a short tape measure or maybe a yard stick.

[AdmiralCochrane]

50 years ago my father's CB did become remarkably clear for a while.  Then he noticed he was replacing a lot of bulbs on his car.  Luckily he caught it before the battery was cooked, the voltage regulator (old mechanical type) had gone up to about 18 volts.