Radios interferring with new alternator

d_clinton · #1 (**permalink**) 09-14-2009, 06:33 AM

Hey Guys,

I have a bit of an odd problem........

My car has 2 Simoco 2-way radios installed that I use for work. Both have a power output of 25w. One radio is 136-174mHz, the other is 450-500mHz.

I had a faulty alternator replaced with a brand new one last week.

Now if either of the 2-way radios are keyed up with the engine running (no problems with the engine off), the alternator warning light comes on, all the lighting on the car brightens and the car either starts to idle all over the place, or if driving engine power drops! It actually blew a headlight bulb tonight because of this problem.

It seems to be related to the RF power the radios emit. With the antenna's unplugged, the problem disappears. From what I can gather the RF must be interfering with the new alternator in some way. I had absolutely no problems at all with the old one.

None of the wiring for the radios was touched, except for being disconnected from the battery while the alternator was changed. The cables are connected to the alternator firmly and the earth strap between the engine block and chassis is fine. The coaxial cable for both antenna's is in good condition with no nicks or cuts anwhere. Any ideas on how to rectify the problem???? It's got me stumped.

Thanks
Daniel

d_clinton · #2 (**permalink**) 09-14-2009, 07:16 AM

Just checked the battery voltage with a multimeter. At idle I'm getting a constant 14v, which is normal. Key up one of the radio's and it's peaking to around 20-21v! No wonder the headlight globe blew! Obviously it's something to do with the regulator in the alternator, but what can I do to stop this happening??

rfradioconsult · #3 (**permalink**) 09-14-2009, 09:33 AM

Simple. Return the new alternator, most likely the internal voltage regulator is defective. The overvoltage condition is not normal and may burn out your on-board computer.

Squad10 · #4 (**permalink**) 09-14-2009, 09:40 AM

Check the reflected power for both transmitters, I've seen alot of crazy things happen in a vehicle having high VSWR.

mr_tunz · #5 (**permalink**) 09-18-2009, 04:22 PM

It ur alternator the volt reg is bad seen this happen serveral times. Just take it back and have them test and it will be faulty.

RodStrong · #6 (**permalink**) 09-23-2009, 01:37 AM

Hire an exorcist.

911scanner · #7 (**permalink**) 10-18-2009, 12:36 PM

Late to this thread....

While I agree with possibly being a bad alternator, there is something else that comes to mind for me.

Have you considered that you should check the +12v & Ground runs?

Whenever you troubleshoot any kind of electronics in a car, the last thing to blame should be the equipment. The first thing to blame should be the installation, even if an experienced person did the installation. Why? Because people make mistakes, connectors can fail and because plastic coating degrades, sometimes much faster than metal.

After troubleshooting all of the potential installation issues, you then start the process of elimination with components like the alternator, battery or batteries and the radios themselves.

(edited to add) I would then suspect the radio before the alternator. Why would the alternator be fine with everything else in the vehicle but the radio(s)?

MM