Hello,
I have a police unit that is having a problem with his radio I will explain.
About 2 months ago this problem occured and they replaced the battery and it stopped but now its started back and now its worse than it was the first time.
He is running a TK-760HG High Power 45 Watt VHF Radio.
When the car is running there is a loud distinct hum when he transmits but when the car is off there is no hum and the radio sounds good.
I will be looking at how things are wired up tomorrow but I suggested to him that he could have an alternator going bad or one that is leaking
He is running a Ford Crown Vic and this vehicle is the only radio in the fleet that is acting up...
Radio Problem
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Is it a whine that varies in pitch with engine speed? Sounds like a really sick Q?
If so, it might be bad diodes in the alternator which means the thing will fail completely soon. Another possibility is a bad ground. Check the ground cable from the battery. Both ends - at the battery and at the block. If the cable is fraying and corroding that could be it.
That they changed the battery and it cleared up for a while tells me it could be either. Maybe the new battery took enough load off the alternator for a while or maybe the change jiggled a corroded battery cable enough to last a bit.
If so, it might be bad diodes in the alternator which means the thing will fail completely soon. Another possibility is a bad ground. Check the ground cable from the battery. Both ends - at the battery and at the block. If the cable is fraying and corroding that could be it.
That they changed the battery and it cleared up for a while tells me it could be either. Maybe the new battery took enough load off the alternator for a while or maybe the change jiggled a corroded battery cable enough to last a bit.
Chris,
Hamming 31 years
http://www.wa2zdy.com
Wesley Chapel, Pasco County, Florida
Snow? What's that?!
The human race is proof that Darwin was wrong.
Hamming 31 years
http://www.wa2zdy.com
Wesley Chapel, Pasco County, Florida
Snow? What's that?!
The human race is proof that Darwin was wrong.
Alternator whine is a real whine, not a hum; it is caused by the high speed switching of the field current, which the regulator does in order to set average field current to the level necessary to produce the alternator output necessary to maintain setpoint voltage.
If the hum sounds more like a 60 Hz ground hum, my first question would be: is there an inverter somewhere in this car? Maybe one of those small ones that plugs into a cigarette lighter socket?
If the hum sounds more like a 60 Hz ground hum, my first question would be: is there an inverter somewhere in this car? Maybe one of those small ones that plugs into a cigarette lighter socket?
My money would be on a bad alternator.
You could also do a fast check with a voltmeter on the battery posts. Put one meter lead on the battery post and the other on the battery connector. I have seen poor connections between the battery post and the battery terminal cause this problem. Turn the headlights on and let the engine idle. You shouldn't see any voltage at all. Maybe just a couple of millivolts at the outside.
Jim
You could also do a fast check with a voltmeter on the battery posts. Put one meter lead on the battery post and the other on the battery connector. I have seen poor connections between the battery post and the battery terminal cause this problem. Turn the headlights on and let the engine idle. You shouldn't see any voltage at all. Maybe just a couple of millivolts at the outside.
Jim
If an alternator has one of the six rectifier diodes short (or open), you'll get a much lower frequenct alternator noise than your typical alternator noise. It will still vary with RPM.
A shorted doide will put some AC into the system. You will need a scope to find this. Look at the output at the alternator stud. You'll see a typical pulsed hi-line DC signal with a "1 in6" spike.
A shorted doide will put some AC into the system. You will need a scope to find this. Look at the output at the alternator stud. You'll see a typical pulsed hi-line DC signal with a "1 in6" spike.
The problem with later vintage alternators, is that the diode pack is now a module, but if one or more is shorted or open, you should measure a voltage drop into the battery.
14-14.6V is within the ballpark, but if the output voltage is lower, by at least 1 to 2 volts, then your regulation is shot and this will cause whining, with a poorly 'charged' battery that will fail over time from insufficient votlage/current supplied to the battery.
If you masure 13 volts with the engine running, then the alternator is in need of repair.
If it's a late model ford, you MUST replace the pigtail along with the alternator as those are well known to be fire starters and the warranty will NOT replace any ford alternator that has not had the pigtail replaced at the same time.
This is not the case with GM or Chrysler alternators.
14-14.6V is within the ballpark, but if the output voltage is lower, by at least 1 to 2 volts, then your regulation is shot and this will cause whining, with a poorly 'charged' battery that will fail over time from insufficient votlage/current supplied to the battery.
If you masure 13 volts with the engine running, then the alternator is in need of repair.
If it's a late model ford, you MUST replace the pigtail along with the alternator as those are well known to be fire starters and the warranty will NOT replace any ford alternator that has not had the pigtail replaced at the same time.
This is not the case with GM or Chrysler alternators.
"If you masure 13 volts with the engine running, then the alternator is in need of repair. "
Not always true. Many PCM controlled alternators can adjust output from battery voltage to near 15 volts. Just because it is low, it is not bad.
Many of the PWM (pulse width modulated) units will back down charge voltage when not needed to increase CAFE standards.
New GM trucks (first used on 05 Tahoe/Burbans) use an inductive loop on the battery ground to provide reference to the PCM to control charge. This system produces some bizarre charge results. They also turn the charge totally off under certain conditions and you will see under 13 volts. Some also turn off the charge during certain hi-load events such as ABS pump activation or engine fan motor starting. Also note that these alternators do not charge immediately after you start the engine. Expect a 10 to 30 second delay on the start of the charge with these.
"If it's a late model ford, you MUST replace the pigtail along with the alternator as those are well known to be fire starters and the warranty will NOT replace any ford alternator that has not had the pigtail replaced at the same time. "
True to a point. The mid/late 90s Fords had this problem. A replacement alternator came with new pigtails. Per Ford, replace the pigtails if visible heat damage can be seen. I've seen very few with a visible problem. Also look for morons that do install the pigtails with butt splices instead of soldering them. Butt splices are for car stereos and have no place in production auto electric work or emergency vehicle conversion.
Things are changing. Wait for the 36/42 volt systems coming soon!
Not always true. Many PCM controlled alternators can adjust output from battery voltage to near 15 volts. Just because it is low, it is not bad.
Many of the PWM (pulse width modulated) units will back down charge voltage when not needed to increase CAFE standards.
New GM trucks (first used on 05 Tahoe/Burbans) use an inductive loop on the battery ground to provide reference to the PCM to control charge. This system produces some bizarre charge results. They also turn the charge totally off under certain conditions and you will see under 13 volts. Some also turn off the charge during certain hi-load events such as ABS pump activation or engine fan motor starting. Also note that these alternators do not charge immediately after you start the engine. Expect a 10 to 30 second delay on the start of the charge with these.
"If it's a late model ford, you MUST replace the pigtail along with the alternator as those are well known to be fire starters and the warranty will NOT replace any ford alternator that has not had the pigtail replaced at the same time. "
True to a point. The mid/late 90s Fords had this problem. A replacement alternator came with new pigtails. Per Ford, replace the pigtails if visible heat damage can be seen. I've seen very few with a visible problem. Also look for morons that do install the pigtails with butt splices instead of soldering them. Butt splices are for car stereos and have no place in production auto electric work or emergency vehicle conversion.
Things are changing. Wait for the 36/42 volt systems coming soon!