I've been following Abe's topic, but I have a similar but different problem.
I have a 60A alternator/ammeter, and have just totally rewired the plane(be nice! ). The ammeter pulses only with the engine running and does show a charge. It does do it without anything turned on. The frequency of the pulsing varies with engine speed and above 1500RPM or so it's not noticable. I'm guessing I have a bad diode in the alternator. Also, I have an ICOM IC-A200 and a VAL 760 radio, in the VAL, which I believe is older technology, I can hear radio noise pulsing with the pulsing of the ammeter. I did use shielded wire where needed and have good grounds. Above 1500 it's just a continuous squeal, but no noise in the ICOM. Any thoughts?
I'm not sure how your alternator system is wired, but what you describe is very common in '70s vintage Cessnas. The ammeter wiggle happens because regulator power, field current, and voltage sense are all supplied to the regulator by a single circuit. Resistance in the circuit causes a sense error, which the voltage regulator chases, setting up an oscillation. The usual fix is to replace the master switch, but any resistance in the circuit will do it. Check the whole path from main bus through the breaker/fuse, the master switch, overvoltage relay, connectors ... whatever is in your setup. In the late 70s Cessna eliminated the wiggling problem by changing over to voltage regulators that have separate sense and power terminals.
There are so many different alternator conversions, with so many possibilities of error/failure, that it's virtually impossible to diagnose over the internet.
You might wish to :
1) CONFIRM your alternator/regulator wiring is completely in accordance with STC instructions. If the conversion was done on a "field approval" or other individualized installation, then you have the type installation most likely to have difficulties. (One of the reasons STC's can be well worth their expense.)
2) Remove your regulator and alternator and have them tested individually for failure.
Remember that if you used shielded wires, that only ONE end of a shielding is actually connected to ground....NOT BOTH ENDS. Connecting both ends of a shielded wire's shielding to ground creates what is called a "ground loop fault" which can result in audio squealing.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
My conversion appears to have been done via a field approval back in '76. It used Cessna drawing 0500062, which is for a 172I. All components - master switch, cicuit breakers, noise filter, and wire are new, but I'll check any for resistance in the the curcuits. Maybe a new style solid state VR would fix it?
I'll double check my sheilding grounds -I know all avionics wires are properly grounded on one end, but the wiring diagram shows the VR wires grounded at the noise filter and again between the VR and alternator. I'll try disconnecting one of them and see what happens. Thanks.
Here's a troubleshooting chart produced by Zeftronics. Dr. Femi Ibitayo is the electronics engineer who is principal at Zeftronics/Hazotronics that I have referred folks to previously. He's a good man.
Cessna Alternator Troubleshooting.pdf
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'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
I got out to the hanger today and used the troubleshooting info -thanks George! At first I found high field resistance at the pin and alternator so desided to change out all the VR wires(they're the only wires I haven't replaced yet besides the + batt cable which will be next!). After replacing the wires now the resistance is within normal range! With the engine running the ammeter is alot better, now it's just a small flicker below 800RPM. I can live with that.
The VAL radio still has noise, may be coming from ignition or alternator. I also noticed the wing strobes cause noise in it too. But nothing in the ICOM, I writing it off as a radio problem with the VAL. Maybe I'll have to get that 430 after all!
That "little flicker" might entirely be caused by the strobes as they draw a charge to build up the capacitors and then discharge the capacitors when they "fire" the lamp. (And of course stobes that cause noise in a radio is probably a shielding problem or a power-supply problem.) Your radio may not be the problem at all,.... but go ahead and get the Garmin 430, send me your VAL and let me troubleshoot it for you.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
Cessna® is a registered trademark of Textron Aviation, Inc. The International Cessna® 170 Association is an independent owners/operators association dedicated to C170 aircraft and early O-300-powered C172s. We are not affiliated with Cessna® or Textron Aviation, Inc. in any way.
). The ammeter pulses only with the engine running and does show a charge. It does do it without anything turned on. The frequency of the pulsing varies with engine speed and above 1500RPM or so it's not noticable. I'm guessing I have a bad diode in the alternator. Also, I have an ICOM IC-A200 and a VAL 760 radio, in the VAL, which I believe is older technology, I can hear radio noise pulsing with the pulsing of the ammeter. I did use shielded wire where needed and have good grounds. Above 1500 it's just a continuous squeal, but no noise in the ICOM. Any thoughts?
