Narco MK12D pulling 15 Amps?

[RONSIM]

SOLVED:!! (but not understood) I started getting "High Amp" alarms on my Dynon EMS 120 when I used the "push-to-talk" on my Narco Nav/Comm. Thinking it was stray RF, or something, I started looking in that direction. This morning, I used a clamp-on DC Ammeter to measure current pulled from the battery by my various systems --- everything as expected until I did the "transmit" on the Nav/Comm --- measuring on the down-stream side of the circuit breaker, I was showing 12-16 Amps (5 Amp breaker did not trip on the momentary transmit) ---

The Nav/Comm receives and transmits normally ---- I am assuming I have something going on in the transmitter ---- any ideas?.

Solved this immediate issue by switching the Comm antenna coax out of the Narco to a Comm antenna I installed on the bottom of the airplane for my handheld radio. Connected with a length of RG58 and a coupler. Everything back to normal and Navcomm pulls about 3.5 - 4.0 Amps.

When I get a chance, I will try to track down the original coax/antenna issue and do some more "experimenting" and look into the 5 amp breaker issue!

I appreciate all the help I have received and some of the suggestions on wiring I intend to implement at the next chance.


Thanks,

Ron

 

[BobTurner]

now you have two problems!

If you held down the PTT long enough to read the meter, the 5 amp CB should have tripped. So either the radio and the CB are both defective; or stray RF is fooling your meter and the Dynon; or there's a problem elsewhere. What else is controlled by the PTT? audio panel? receiver mute?

 

[RONSIM]

Bob -- thanks for the reply

I would have suspected RF on the meter, but I took similar readings on my strobes, pitot heat, GPS, TXP, lights, etc --- all of those readings were where I would expect ---- the breaker is 6 months new (switch type). Nothing else on the breaker.

And, I do think it weird breaker did not trip --- I will try another breaker.

 

[Mike S]

Couple things here that catch my eye.

First off, any chance you missed a decimal point on the meter reading??

If not, then;

Second, if the 5a breaker is the correct one for the radio---------not only is the breaker bad, but something is causing the circuit to draw extra amps ------ if it is in fact pulling 12a

Fixing the breaker is only half of your problems, you need to find/fix the cause of the extra amp draw.

Couple big "if"s in there, but better to be sure ...............................

 

[RONSIM]

Mike -- thanks

Decimal points, and I, have always had issues ---- (slide rules as an Engineering student was the big one!) ------ but I did triple check that one. The breaker issue will be easily investigated --- I have another I can quickly (thank goodness for a Tip-up) substitute.

I am going to pull the Nav/Comm and check the tray and connectors -- I cannot believe the unit is pulling 15 amps and still working.

On my other amp checks, the Dynons showed about 3.5 amps, the strobes about 7 amps, the pitot heat about 6 amps, etc., so I think my meter is working OK --

R.

 

[flightlogic]

older transmitter current draw

Mike raised a good point, but it seems you are reading the correct digits. A clamp on meter might not be the best tool for DC in this circuit though.
The Narco is specified to draw 4.3 amps on a 13.5 volt aircraft.
My guess is you are really not pulling the current showing on the meter. To have a faulty radio and breaker that allowed the excess all occur at the same time would be rare.
I would clean up all the connections and then put a current meter inline... at the breaker terminal if that is handy. See what that shows.
Report back and then some more "experts" can jump in as well. Best of luck.

 

[RONSIM]

Good suggestions

I will be giving those a try-------

Thanks for the help, all --

Ron

 

[RONSIM]

Check OP --- Solved but not understood (yet)

Traveling to WV to ferry an -8A to FL ----- will try to figure out the "why and wherefore" of the antenna and breaker issue when I get back in town.

R.

 

[RONSIM]

Not the antenna?

Well, after switching to the bottom antenna, with a new section of RG58, and, finding everything worked as designed, I attached the new coax to the original antenna (Comant 121, in perfect (looking) condition). Same issue -- getting high amp readings on my meter and on the Dynon EMS120.

So, this led me to believe the antenna was bad, for whatever reason. At Sun n Fun, yesterday, I bought a new Comant 121. Today I removed the "old" antenna and installed the new antenna, ensuring a good ground plane interface. Using the new coax that worked well with the bottom antenna, I ran the same tests ------SAME RESULT! High amp readings on the meter and on the Dynon when transmitting. While I was at it, I did my clamp on meter on other aircraft circuits (GPS, TXP, lights, etc.) On all of them, I got an amp spike on the meter and the Dynon when transmitting with the navcomm.

I put the old antenna back on and relocated the coax back to the belly antenna.

I will continue to look at what is picking up the RF from the top antenna and giving me the screwy reading ----

 

[RONSIM]

REALLY solved

Thanks to some good advice and suggestions from the RV gang, I was put on the right track ----- yes, my (I thought expensive) meter, was being affected by the RF coming off the comm antenna, and would give me a 15 to 40 amp reading without being clamped on anything ------ and, Jake Jansen (aeroassist, aussie land) suggested I should make sure my Dynon EMS120 wiring was as short as possible and excess not looped or stowed.

Yesterday, I removed my access panels and trimmed unused wiring and rearranged the other wiring (to the EMS).

A test flight today showed everything working normally ----

Thankfully, I can now move on to other challenges, which may pop up.

Thanks for everyone's help.

Ron