Power Supply Question

[Citizen]

My base GMRS radio inside the house is getting its power from a relatively new DuraComm power supply.  Its measured output is 13.9 volts and everything seems to work fine. 

 

For my mobile radio, I notice the in-car voltage is 13.8 volts when the car is running, and somewhere slightly above 12v when the car is not running and there is virtually no load, with the measurement taken directly off the battery.  My mobile GMRS radio works fine in both cases.

 

Finally, I have a very old power supply that I would like to make use of inside my house for a second radio.  Like my other base unit, It would be a mobile rig, but used as a base indoors.  Unfortunately, when I measure the output voltage it is showing 14.5 volts.  The question is; Would a 14.5 volt output power supply harm the GMRS radio (or any other mobile radio) that only requires 12 volts?

 

I looked for a way to calibrate the old power supply so to lower the output down to say 13.8 volts, but the only control other than the On/Off switch is a reset button on the back of the unit.  There may be a rheostat inside the power supply that I could adjust, but I would have to open it up.  The brand name of the old power supply is “Micranta”, aka Radio Shack, vintage 1970s.  It's old, but its output is steady/constant, so I believe it is a good unit, I just don't want to damage a good radio.

 

Thanks in advance.

[JohnE]

if it was 16.5 I would say don't use it.14.5 isn't out that much I just don't think it will provide enough current to run the TX side. those old RS unit were only rated at 1.5 or 3 amps IIRC

[mbrun]

The absolute best way to know is to check with the radio manufacturer to determine what voltage range is acceptable. Some, but very few, manufacturers actually publish this information.

 

That said, you are probably ok, and here is why I say that.

 

Manufacturer’s have done us a disservice. They call the radios ‘12v’ radios but their radios are actually designed for use in a vehicle that is operating on 13.8v and not 12v. The higher voltage exists because the vehicle battery needs a higher voltage to be charged. Consequently 13.8v is the voltage most everything in the car is designed around. Also, when a lead acid battery is charged, a charger may delivery up to 14.4 volts under certain conditions to top it off, this exposing all other electronics in the vehicle to that as well.

 

So where does that leave us? I imagine you are measuring your power supply without a load on it and that you’re getting 14.5v. This is just slightly above the normal max that the alternator would generate to charge a battery. If you put a load on your power supply, you will find that the voltage drops, perhaps down to 13.8 or even lower, right where you expect to be.

 

The better the power supply design, the less variance in output voltage between load and no-load conditions.

 

I just recently read a spec on a mobile radio where the manufacturer actually published its usable voltage range for its 12v Radio. It was published as 13.8vdc +/- 20%. That is the exactly the way it should be stated. This eliminates all guesswork. This translates into a radio that manufacturer says will operate correctly within a voltage range of 11.04-16.56 vdc.

 

Hope this helps.

 

Michael

WRHS965

KE8PLM

 

 

Sent from my iPad using Tapatalk

[1URFE57]

Also check how many amps is the power supply some power supply have the correct voltage but has low amperage.

[Citizen]

I checked and the stated output is 13.8 volts and 2.5 amps.  I now know that's very low for my GMRS radio, but it does seem to power my cheap CB.

[1URFE57]

I checked and the stated output is 13.8 volts and 2.5 amps.  I now know that's very low for my GMRS radio, but it does seem to power my cheap CB.

CB are low power right like what 5watts max? for your GMRS stick with 13.8 most regulated power supply output are 13.8 volts make sure the PSU has higher amps.

[BoxCar]

You'll need to check the specs for your radio to be certain, but you'll need close to 600W to power the GMRS radio.

[IronArcher]

My mobile has a recommended input of 13.8 +/- 15% so it would be good up to 15.9v

And as low as 11.73.

Just adding this for a reference.

This radio is 45w out (claimed) so I went with a 30amp power supply.

I would think 450w should be fine for most.

In the manual, the radio asked for less than 15a (207 watts?). I figured it would be safer to just double that.

[1URFE57]

My mobile has a recommended input of 13.8 +/- 15% so it would be good up to 15.9v

And as low as 11.73.

Just adding this for a reference.

This radio is 45w out (claimed) so I went with a 30amp power supply.

I would think 450w should be fine for most.

In the manual, the radio asked for less than 15a (207 watts?). I figured it would be safer to just double that.

The radio will only draw its rated amps so you have a very good head room there and of course higher amps power supply gives you flexibility.