Pro-197 operating voltage question...

[AAFC]

I recently purchased a Pro-197 and decided to make up cigarette lighter power cord for occasional use in my truck. The radio came with an extra power cord which is intend to be "hard wired" into a vehicle.... I'm not doing a permanent installation so I just put a cigarette lighter plug on the cord. Works great! However, while doing this I wanted to verify the polarity of the 120 volt "wall wart" power supply so I could make sure that I wired the cigarette lighter adapter correctly. I used my digital FLUKE multi-meter to check polarity and I got a reading of 20.4 volts from the wall wart. The output spec written on the power supply says the output should be 13.8 volts. The Pro-197 manual says operating voltage should be between "12-14.4 VDC, 13.8 nominal, 16 VDC Maximum". My questions is.... Should I be worried that the factory supplied wall wart is putting out 4 volts over the maximum specified operating voltage?

AA/FC

 

[gewecke]

I recently purchased a Pro-197 and decided to make up cigarette lighter power cord for occasional use in my truck. The radio came with an extra power cord which is intend to be "hard wired" into a vehicle.... I'm not doing a permanent installation so I just put a cigarette lighter plug on the cord. Works great! However, while doing this I wanted to verify the polarity of the 120 volt "wall wart" power supply so I could make sure that I wired the cigarette lighter adapter correctly. I used my digital FLUKE multi-meter to check polarity and I got a reading of 20.4 volts from the wall wart. The output spec written on the power supply says the output should be 13.8 volts. The Pro-197 manual says operating voltage should be between "12-14.4 VDC, 13.8 nominal, 16 VDC Maximum". My questions is.... Should I be worried that the factory supplied wall wart is putting out 4 volts over the maximum specified operating voltage?

AA/FC

Did you check the voltage under a load or right from the wall wart? I would connect the wart to another device requiring the same voltage and see if it drops under a load.
If not then, purchase another wart or perhaps use a regulated supply which is what I do with my pro-197.

73,
n9zas

 

[K9WG]

Yes, the wall wart will read higher without a load (e.g. the radio). A regulated power supply is a good idea as N9ZAS has suggested if nothing more then to help prevent power surges.

 

[AAFC]

Thanks for the replies!

Yeah, I realize as amp draw goes up, voltage will go down. Without doing any calculations, it doesn't seem like this scanner can draw enough amperage to bring the operating voltage into range. (drop 4 volts) I'm going to do a bit more testing.... I'll let you know what I find out. I can't believe that Radio Shack would send a NON-regulated wall wart along with this scanner. Just because it's a wall wart, doesn't mean it can't be regulated.

 

[gewecke]

Thanks for the replies!

Yeah, I realize as amp draw goes up, voltage will go down. Without doing any calculations, it doesn't seem like this scanner can draw enough amperage to bring the operating voltage into range. (drop 4 volts) I'm going to do a bit more testing.... I'll let you know what I find out. I can't believe that Radio Shack would send a NON-regulated wall wart along with this scanner. Just because it's a wall wart, doesn't mean it can't be regulated.

Well you can place the blame on GRE, since the radio is actually produced by them. True, they COULD produce a regulated wall wart but then how much do you think our overall price would increase as consumers?
This again is why my pro-197 is powered by my astron switched supply at 12.8vdc +/- 2volts. :wink:

73,
n9zas

 

[AAFC]

Well you can place the blame on GRE, since the radio is actually produced by them. True, they COULD produce a regulated wall wart but then how much do you think our overall price would increase as consumers?
This again is why my pro-197 is powered by my astron switched supply at 12.8vdc +/- 2volts. :wink:

73,
n9zas

Yes, I realize the scanner is made by GRE. Considering everything is produced in China, I suspect that a regulated wall wart would cost GRE less than a dollar extra to produce. It's up to them if they want to charge the consumer more for such a cheap upgrade to ensure the life of their product. There is already plenty of mark-up to absorb the extra dollar. But hey, if they want to charge more, I'm sure people would still buy it. It's not like we're talking about a $20 piece of electronics. These scanners range from 3-4 hundred bucks (depending on sale prices) so the extra cost of a regulated power supply should be the least of their worries. Hell, they may even save money if the regulated power supply helps cut down the number of warranty claims.

I understand why you are using a dedicated power supply on your equipment. I also have a similar power supply.

73, (yes, I'm a ham too)
AA/FC

 

[gewecke]

Yes, I realize the scanner is made by GRE. Considering everything is produced in China, I suspect that a regulated wall wart would cost GRE less than a dollar extra to produce. It's up to them if they want to charge the consumer more for such a cheap upgrade to ensure the life of their product. There is already plenty of mark-up to absorb the extra dollar. But hey, if they want to charge more, I'm sure people would still buy it. It's not like we're talking about a $20 piece of electronics. These scanners range from 3-4 hundred bucks (depending on sale prices) so the extra cost of a regulated power supply should be the least of their worries. Hell, they may even save money if the regulated power supply helps cut down the number of warranty claims.

I understand why you are using a dedicated power supply on your equipment. I also have a similar power supply.

73, (yes, I'm a ham too)
AA/FC

At the value these radios hold today, any effort to baby them is a smart move. My original wal wart for my 197 is still the box with the packing,should I ever want to sell it to upgrade to something new.

73,
n9zas

 

[sphipps]

The wall wart should be outputting about 16-18 volts under no load. 20 volts is really on the high side with no load. I wouldn't lose sleep running it like that, but I'd highly consider taking it back to Radio Shack for a replacement to protect from damage in the long run. Unfortunately you'll probably have to exchange the entire bundle for another one... not just the wall wart.

 

[AC9BX]

That wall wart isn't particularly well regulated. I suspect it isn't regulated at all. 20V is nominal for that supply without a load. If you're so inclined you can open the radio and measure the voltage in use. You'll find it is closer to 16V. That may still seem high but it's okay. The radio has it's own regulators inside, 8V and 3.3V. I bet if you measure the output of every one the store has in stock you'll find they're about the same. Most modern three terminal linear regulators will not float high with no load and often the circuit design places a small load on it for that very purpose. They wouldn't use anything special beyond that. If they would use a more expensive switching regulator they'd just use a switching supply instead. Be glad it has a linear supply. They are far more robust and switchers make a bunch of radio energy, very bad for powering a scanner.
I'd worry more about exceeding the 16V in the car. Typically it won't go above that but modern vehicles tend to have voltages near 16, especially after starting to increase the charging current. Plus it can supply a lot more current than the wall wart, thus the use of a fuse. It's fine. Enjoy your radio.