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Why is my voltmeter and ammeter doing this?

blueflyer

blueflyer

Well Known Member
OK, this is admittedly not in my RV (wings still in the garage), but I can use this knowledge in the future to perform future maintenance on my RV. How is that for rationalization?! Anyway, here is my problem: I have a Dynon D-120.

When I start my plane, the amps fluctuate from the high end of normal to high voltage from say 13.0 to 15.5. At the same time, my amp meter will swing back and forth from 0 to 22 amps. I have my amp meter wired to show what the alternator is putting out. Both of these meters will settle out for a few minutes, but they always start acting up like this again within a few minutes.

When I perform a hot start (0-360), the amps will stay way up at 50-60, and sometimes peaking at 62-63.....I have a 60Amp alternator. It seems if I get the rpms up to about 1500 or so, the amps will trend down to a more normal level of about 6-8 amps. Also of note, the throttle cable gets really hot during hot starts. So much so, you cant hold it if you touch the silver part of the cable visible in the cockpit.

I have replaced the voltage regulator and added a 1.5" thick ground strap from engine to firewall. My battery is in the rear fuselage. All connections seem to be tight. After adding the new ground strap, I have not attempted a hot start. I still have to same problems after the new voltage regulator.

What else should I look for or try to replace/repair? Thanks in advance.
 
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Throttle cable hot is a classic sign that the ground current is flowing thru it. Check all alternator, regulator, and engine grounds.
 
Display?

You have not said what display you are using for your voltmeter and ammeter. Whatever is hooked up to measure those, you need to check that those connections are rock solid. Although my voltage stayed steady, I saw wild amperage fluctuations over 70 amps (from a 60amp alternator). It does not take much of a resistance variation across the shunt to cause wild swings.
I re-worked the wiring to the ammeter shunt and that took care of that.

Just one possible root cause.

Don
 
Dynon D-120

sorry, its a Dynon D-120. Shunt connections were good, but I will keep it in mind to re-crimp the shunt connections if nothing else turns up.
 
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I agree with Bob Turner. Check all grounds including battery negative to airframe. Voltage fluctuations are likely due to a bad connection in the alternator field circuit. For troubleshooting on the ground with engine off, disconnect the field wire from the alternator and connect that wire to a high wattage lamp. Then measure the voltage at various points between the battery and that lamp. An excessive voltage drop indicates a bad connection. Switches and terminals are suspect.
Joe Gores
 
thanks for responses. Turned out to be a loose connection behind the panel causing the volts and amps to fluctuate.
 
I think you should check to see if the alternator field wire (small 5A fused wire) and the alternator power wire (large wire) have been run closely parallel to each other and are not shielded. I would like to see them shielded at the least. (Had this problem with my RV3B and shielding the wires cleared it up.


blueflyer said:
OK, this is admittedly not in my RV (wings still in the garage), but I can use this knowledge in the future to perform future maintenance on my RV. How is that for rationalization?! Anyway, here is my problem: I have a Dynon D-120.

When I start my plane, the amps fluctuate from the high end of normal to high voltage from say 13.0 to 15.5. At the same time, my amp meter will swing back and forth from 0 to 22 amps. I have my amp meter wired to show what the alternator is putting out. Both of these meters will settle out for a few minutes, but they always start acting up like this again within a few minutes.

When I perform a hot start (0-360), the amps will stay way up at 50-60, and sometimes peaking at 62-63.....I have a 60Amp alternator. It seems if I get the rpms up to about 1500 or so, the amps will trend down to a more normal level of about 6-8 amps. Also of note, the throttle cable gets really hot during hot starts. So much so, you cant hold it if you touch the silver part of the cable visible in the cockpit.

I have replaced the voltage regulator and added a 1.5" thick ground strap from engine to firewall. My battery is in the rear fuselage. All connections seem to be tight. After adding the new ground strap, I have not attempted a hot start. I still have to same problems after the new voltage regulator.

What else should I look for or try to replace/repair? Thanks in advance.
Click to expand...
 
I actually had seen your post regarding this issue and it would have been one of my "things to try" if I had not found the loose connection behind the panel. They are both run together and are both unshielded.
 
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