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prkaye

Well Known Member
Did my first engine run today. All went well except I had no RPM reading. I'm using Vans tachometer transducer into my dynon. The tach trans takes power from the battery bus. After disconnecting the transducer wiring, I determined that I had no power to the red wire... I then found that the 2 amp fuse I had in there was blown. I put a 3 amp fuse in and tried spinning the tach trans with a drill... this blew the fuse again. I then put a 5 amp fuse in and the tachometer seems to work now (at least by spinning the transducer with my drill).
Question:

1) I can't seem to find any documentation about the current load of the tach trans. I'm not sure why i chose a 2Amp fuse to begin with. 5A seems pretty high though... how much should this transducer be drawing??

2) As others have found, you cannot tighten the transducer on the engine case too tightly or the key will push on the back plate and pop it off. I can only put mine on finger tight before this happens. Would there by any harm in using some blue loctite on this for security?
 
I am not familiar with the Van's transducer, however I'd like to say congrats on your first engine run!

I had several "bugs" to work out after my first run. You'll get this sorted out.
 
I had the same problem with popping the back off the transducer. Finally solved it by shortening the drive spline of the tranducer until I could tighten the tranducer firmly without popping off the back.
Now have almost 100 hrs on the tach and as of now, no problems.
 
Thanks Gator. Do you know what size fuse you're using for the transducer, or roughly how much current it should be drawing?
 
I am using this transducer with an EIS4000. The power (red wire) is connected to the 12V regulated output of the EIS which is unlikely to be capable of supplying more than a few hundred milliamps.

I very much doubt that your 5Amps is correct.

Try disconnecting the transducer (red and white wires) and measuring its consumption. Connect the white wire and remeasure- perhaps you have a short in the signal wire (white wire to your Dynon) that is being reflected in the supply side.

HTH,
Doug Gray

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Try disconnecting the transducer (red and white wires) and measuring its consumption.
Click to expand...

Not sure I follow...disconnect it and measure its consumption how? Unfortunately my ammeter is positioned so it only shows current from the alternator. I can't really do any more testing with the engine running until after break-in. The tach is working now, but I fear it must be drawing a fair bit of current. The ammeter with the plane running with only the EFIS and fuel pump turned on, the current from the alternator is showing about 13 amps... seems pretty high. When turn everything on, including all lights, it's up around 50 amps.
 
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Am using whatever size specified with the transducer and pretty sure it's not nearly as large as 5 amps.......will try and check the next time I have the cowl off but that may be awhile.
 
Measure the current with a multimeter - engine stopped. Set the meter to read current and connect it in series with the red lead. Turn on the master sw and whatever else is necessary to power the sensor.

The sensor does not require the engine running to see a representative current.

Doug
 
The sensor does not require the engine running to see a representative current.
Click to expand...

Ahhh... very interesting! I assumed the current powering the transducer would increase proportional to the RPM. But you're saying it's always drawing a constant current through the red wire? I have mine on my battery bus... if it's drawing much current it will eventually discharge my battery with the plane parked! I'll have to see if I have a dead battery next time i head out there! I'll put an ohmeter on it with the engine off as well. Perhaps it should be moved to the main bus.

I've ordered up a replacement transducer, but I'm really starting to suspect it was an electrical shorting issue. After rewiring it yesterday and putting a larger fuse in, the tach was working fine.

Question:
Is it a likely mode of failure for the transducer to be working fine (reporting accurate RPM values) but somehow be drawing a few amps of current? This seems like a strange (unlikely) mode of failure to me.

With it on the battery bus (always-hot), it's possible I kept shorting it out by accident when I was working on it.
 
It is very unlikely that your transducer is drawing 5 Amps - first things first - check the current draw of the unit alone.

I would suspect another path to ground but without knowing your circuit arrangement I cannot help.

Doug
 
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