vehicle power

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Irishfirepics
New User
Posts: 10
Joined: Sat Apr 06, 2013 2:34 pm

vehicle power

Post by Irishfirepics »

Hi all

I have a motorola gm300 in my car running on 12v if i move it to a 24v truck would you know if it will work or will i blow the radio?
RFguy
Posts: 1357
Joined: Wed Dec 21, 2005 6:17 am

Re: vehicle power

Post by RFguy »

You'll let the smoke out of it.

You will need a 24 to 12-volt converter sized for the radio (25-watt radio, minimum of 10-amps at 12 volt. A 45 watt radio, minimum of 15-amps at 12-volts).

Don't try messing around with half tapping the batteries in an attempt to get your 12-volt radio to work. It will be on-going grief.
Jim202
Posts: 3609
Joined: Sun Sep 09, 2001 4:00 pm

Re: vehicle power

Post by Jim202 »

Unless the truck batteries are new, it is not a good idea to center tap the two 12 volt batteries at the center point where you would expect to find 12 volts. This point is only 12 volts under a low current draw condition. As current input or output goes up, this 12 volt point can fly around and be either low or high in voltage. Bottom line it is only 12 volts if both batteries have a low internal resistance.

The problem compounds itself as the batteries age. The internal resistance goes up and the voltage filtering ability of the batteries goes down. As this happens, the ability of each battery to hold the mid point tap goes lower. As an example, if you go to start the truck engine, this mid point tap voltage could go real low or even high due to the high current draw from the starter motor. Once the engine starts, the charging alternator will try to bring the total electrical system 24 volt voltage back to normal. If the low side battery that has one terminal grounded, has lost it's low internal resistance, there is the possibility that you might even see close to the 24 volts at this mid point tap.

As has already been mentioned, using a voltage converter power module is the way to go. These units are made to take the full 24 volt input and convert it to the 12 volts the radio requires. It doesn't rely on any battery internal resistance to keep the voltage going to the radio at 12 volts.

I have used the 24 volt to 12 volt converter power modules on many large trucks and big front end loaders. Never had a radio problem once they were installed. Just make sure you get one large enough to carry the transmitter current demand.

Jim
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Bill_G
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Joined: Thu Sep 17, 2009 5:00 am

Re: vehicle power

Post by Bill_G »

+1

There are many fine 24-12 converters out there. Newmar is an excellent choice.

We won't discuss using a GM300 in the post-narrowband days.
Irishfirepics
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Posts: 10
Joined: Sat Apr 06, 2013 2:34 pm

Re: vehicle power

Post by Irishfirepics »

thanks for the info guys, I'll pick up a voltage converter.
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