Recently purchased an RV-8 with a King KX-125 Comm and noticed that when you depress the PTT to transmit the ammeter will deflect to the negative side and remain there for as long as you transmit. It will show anywhere from 5 to over 10 amps of discharge! The charging system seems to be working fine otherwise. If you turn on any of the accessories the ammeter responds normally. I ohm'ed the antenna to the airframe to see if there was some kind of short but there doesn't appear to be a problem. Any ideas?
Van's Air Force
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PTT Causing Ammeter To Show Discharge
- Thread starter SuperDave
- Start date
Norman CYYJ
Well Known Member
Yes, RF is probably getting into the system. Try transmitting on 118.0 and then 135.9. See if there is any change. If so probably a mismatch in the antenna system somewhere. Is the antenna properly bonded to the aircraft skin? You can not find the problem with an ohm meter. Some antenna manufactures use open DC circuit antenna and some are DC shorted.
FORANE
Well Known Member
Is the ammeter digital?
I have a digital EGT by aerospace logic the EGT-100-4P like here:
http://www.aircraftspruce.com/catalog/inpages/EGT1004P.php
Every time I hit either PTT the EGT will read "cold" and stay there until I hit a PTT again and the EGT will read correctly again. The folks at aerospace logic said it sounded like a ground interference.
I have a digital EGT by aerospace logic the EGT-100-4P like here:
http://www.aircraftspruce.com/catalog/inpages/EGT1004P.php
Every time I hit either PTT the EGT will read "cold" and stay there until I hit a PTT again and the EGT will read correctly again. The folks at aerospace logic said it sounded like a ground interference.
terrykohler
Well Known Member
Had The Same Problem With Vans Ammeter
After a number of failed attempts at fixing the problem, I bought an EI volt/ammeter. Problem solved.
Terry, CFI
RV9A N323TP
After a number of failed attempts at fixing the problem, I bought an EI volt/ammeter. Problem solved.
Terry, CFI
RV9A N323TP
Terry,
I think you nailed it. It is a Van's ammeter and nothing made sense, even to my EE brother-in-law. I am going to try a few more easy tests like the aforementioned frequency test just for giggles.
fixnflyguy
Well Known Member
Mine does it also
I have the stock Vans guage, and recently installed the Fliteline 760 com in a hole next to the guage..does the same thing, and Im used to it now. When I had a handheld mounted on the armrest, it did not do it, and I am using same belly mounted antena.
I have the stock Vans guage, and recently installed the Fliteline 760 com in a hole next to the guage..does the same thing, and Im used to it now. When I had a handheld mounted on the armrest, it did not do it, and I am using same belly mounted antena.
