Minimum & Maximum Voltage For Mobile Radios

henryg · Post by **henryg** » Wed Sep 14, 2005 4:50 am

Hello. As a general rule or guideline, for mobile radios, what is the minimum and maximum voltage that the radio needs or can take? We were doing our annual fire pump tests and the voltage on one of our older engines has dropped from previous years. I was wondering what is needed to make the radio work or blow up for that matter. Thanks. Henry

nmfire10 · Post by **nmfire10** » Wed Sep 14, 2005 9:55 am

I don't have a specific answer for you, but I would be more concerned about what caused the voltage to drop rather than whether the radio will be ok.

thebigphish · Post by **thebigphish** » Wed Sep 14, 2005 7:02 pm

look at the product manual for each radio, and look at the operational voltage requirements....you will probably see something like 11.8 to 13.4 vDc, anything out side of that and i would be hellaconcerned that you are gonna be replacing a lot more than a piddly radio.

kg4ere · Post by **kg4ere** » Wed Sep 14, 2005 8:38 pm

Jim202 · Post by **Jim202** » Sat Oct 08, 2005 4:55 am

You may be surprised to see just how high the new auto electical systems are running. The days of the old 13.8 volts are history. Today you will find the voltage at or above 14.2 to 14.6 volts. Seems these new Detroit engineers have something about higher voltages in the auto systems today.

As far as the fire trucks go, I find the battery maintenance is the cause of most of the electrical problems. No one pulls the cover off the battery compartment very often. Only when the truck fails to start. What you find is green and white growth on most of the connections. The grounds are very prone to just falling off. When you get high resistance joints, a 200 amp alternator or larger and the engine running, your bound to see electrical problems.

On top of bad battery maintenance, they tend to forget that battery life is only 2 to 3 years at the outside in this type of service. As the battery ages, it's internal resistance goes way up. This also causes problems for the alternator to maintain proper voltage in the system.

Jim

kg4ere wrote:you need to be very careful to try and maintain voltage between 11.8- and 13.8 volts. anything over or under can damage the radio. i work at a local installation company and we actually have had 2 of the local ems trucks fry their radios because of a flaw in the trucks electrical system. the electrical system would send a spike though the radios essentialls locking them and, and causing us to have to reinstall the firmware on them.

nmfire10 · Post by **nmfire10** » Sun Oct 09, 2005 8:44 pm

Or you have the ladder truck downtown... The alternator had a massive meltdown. Boiled over all the batteries. Smoked the computer (like the whole truck computer) and fried the load manager. With these fancy pants new trucks, without a computer, you have no apparatus.