Want to use car battery to be source for my Cobra GMRS radio

[gamefish]

HI!

I have in the past used recharable AAA battries to power my
Cobra PR 950 DX GMRS Radios. The problem was that the batteries did'nt last to long and had to be recharged often. I use the radios between RV's while on extended vacations. The question is: Can I build a circuit that can be pluged into the cigarette lighter and have the voltage droped down to 6 volts to allow me to bypass the battreies in the radio?
Is there a simple circuit that I can obtain and build from?

Thanks for your help in advance,

Gamefish

 

[jrz126]

Is there anything listed on the radios about how much current they draw?
a 7806 V-reg should do it, but you might have to add some extra capacitors to smooth out the output.


It might just be as simple as this (of course I'm just a 2nd/3rd year EE student, so there might be more to it):

 

[gamefish]

Is there anything listed on the radios about how much current they draw?
a 7806 V-reg should do it, but you might have to add some extra capacitors to smooth out the output.


It might just be as simple as this (of course I'm just a 2nd/3rd year EE student, so there might be more to it):

Thanks for your quick input!

The specification Book indicates that it has a "POWER" output of 2 watts on high power and at low power its 500 milliwatts.
The battery operating range is listed as 4.0v to 6.0v.

Thanks again,

Gamefish 8)

 

[jrz126]

that's more than likely the transmitting power. Do you have an ampmeter so that you could measure the current draw?

You'll need to buy a voltage regulator that can supply enough current. I would think something in the range of 1-2 amps would be sufficent. If you only use the 'low' power mode, you could get by with less.

I'll bet that someone sells a cig. lighter adaptor with a regulator built in. If you dont want to build it yourself, maybe try to find one of those with a sufficent rating.

 

[gamefish]

Thanks for the help!

I built the circuit using the 7806 regulator schmatic and it seems to work great. I am measuring the temp of the regulator as I transmit and the temp goes up to ~115 degrees. Tomorrow I think I'll add a heat sink and see if it runs cooler. The voltage did not drop during the transmitting, so I assume that I am not overloading the regulator.

Any comments will be welcomed.

Thanks again for the help.

Gamefish

 

[Nigel Goodwin]

Thanks for the help!

I built the circuit using the 7806 regulator schmatic and it seems to work great. I am measuring the temp of the regulator as I transmit and the temp goes up to ~115 degrees. Tomorrow I think I'll add a heat sink and see if it runs cooler. The voltage did not drop during the transmitting, so I assume that I am not overloading the regulator.

A 1A regulator should be fine for a 2W transmitter, but you should certainly add a decent size heatsink to it - bear in mind that the tab on the regulator isn't ground, so you will need to insulate it.

I presume you added the two capacitors shown on the circuit?, they are essential in these 78xx designs.

 

[stevez]

I was having some trouble (noise) with a handheld amateur transceiver that I was powering from my cigarette lighter. A friend who services commercial mobile equipment noted that battery operated equipment often does not have the power conditioning circuitry that mobile equipment does - so he was not surprized that I was having some problems. A choke (inductor) and a large capacitor solved the problem. In my case I did not need (or use) a regulator since the transceiver input was 13.8 vdc. If noise isn't a problem (as heard by the person listening to you) then I wouldn't worry about the choke and capacitor.

Be sure to fuse the lines from the cigarette lighter so that in the event of a problem that the wiring doesn't overheat. Some plugs have a built in fuse holder.