Cranking Vehicle while radio is on

[Engineer209]

I have a CDM1250 mobile radio and I was wondering if it will really hurt the radio I it is on when I crank my truck. I notice that every Fire Apparatus that I have ever been in that when the master power switch is turned on the radio comes on, then the piece of apparatus i cranked. I have never heard of any problems resulting from this. Just looking for a little additional info. Thanks

[Jim202]

I have a CDM1250 mobile radio and I was wondering if it will really hurt the radio I it is on when I crank my truck. I notice that every Fire Apparatus that I have ever been in that when the master power switch is turned on the radio comes on, then the piece of apparatus i cranked. I have never heard of any problems resulting from this. Just looking for a little additional info. Thanks

Most installs, if done the right way, will use an ignition sense wire to control the radio on off. When you crank the
engine, the ignition control wire looses power and the radio is off. Ever notice that the auto radio goes off when
you crank the engine?

Jim

[Motoboy]

Watch out when using ignition sense on CDM's! We had a customer with several dead radios, some were jump started and some were not. We eventually found a SRN for the CDM series that said vehicles using large power solenoids, that have the ignition sense connected to the solenoid, can produce negative voltage spikes that can blow out some parts in the radio. Since then, we always install CDM ignition kits with HLN6325 diode kits. These are designed to prevent this by shorting those spikes to ground.

In other words, if something bad happens to your radio when you crank your engine, it is probably an installation problem.

[wx4cbh]

Use a Bosch 30 amp cube relay on the power lead for your radio and wire the coil lead to a master actuation switch you can turn off when you exit the vehicle. Crank the truck and turn on the master switch after cranking. You would have to remember to flip the switch, but to take the memory dependence out of the situation, wire an adjustable "on delay" timer from an ACC or IGN terminal on the fuse panel to the coil of the relay in place of the switch. The "on delay" timer starts its countdown when juice is applied to the actuation terminal, and only passes power to the radio when the countdown time is completed. You should choose a time setting that allows the required Diesel starting drill to complete.

For full control in special circumstances such as jump starting, add a master switch in series in the relay coil line before the timer so you can disable the timer. With the ignition on and the master off, the radios will be off until you turn the switch on to actuate the timer and let the timer count down. That setup allows you to just leave the switch on all the time except when someone else is driving your truck or working on it. You can also use a single pole double throw ON-OFF-ON master switch to allow you to bypass the timer for more special circumstances.