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2-way radio causing voltage to spike

We had to install a new voltage regulator in the alternator in one of our fire trucks. We can now not key the Motorola 2-way radio in our truck without the voltage spiking. Do you know what could be causing this and is there a way to block the radio transmissions from affecting the alternator?

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Hi and welcome to FixYa,

Your described problem indicates that the RF from the Motorola is being received by the electronic regulator of the alternator and is erroneously factored in as sensor/triggers. Simply stated, the RF causes the regulator transistor to conduct more allowing higher voltage output. There could possibly be two ways of addressing the issue: regulator/alternator side and/or the Motorola side. Things that you could try:

  • shunt a reverse protection diode across the output of the alternator to the ground;
  • install filter condensers on all the wires leading to and from the alternator;
  • wire a ground strap (not a ground wire) from the firetruck's - terminal of the battery to the alternator housing;
  • check/improve (lower down) the SWR of the antenna;
  • if you are using a magnetically mounted antenna, replace with a gutter mount or similar mounting brackets;
  • wire a ground strap (not a ground wire) from the antenna mount to the radio to the body of the firetruck to the alternator to the - terminal of the battery.
A ground strap is a flattened braided electrical wire unlike the common stranded auto electrical wire.

Pls post back results. Good luck and thank you for using FixYa.

Posted on Jan 26, 2009

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