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Steve Gavitt

Member
Hi I installed my fuel gauges as per VANs and during the calibration process (Dynon) everything seemed fine ? indicators work. However upon taxing out I noticed that the left indicator showed a lower amount than previously indicated and a minute later showed 0 fuel. I thought it was the wires but everything seemed to check out okay. When I tested the gauge on the plane I was not getting any connection (Ohms should have been between about 270 and 30). So I figured it was a bad gauge and ordered a new one. Got the new one and tested it both on the bench with the multi-tester and prior to installing in the tank with the Dynon hooked up ? everything okay. Installed the guage and added fuel ? indicator seemed to work okay. However again when taxiing out the indicator went to 0. Tested the gauge and got no connection. What gives? Anybody have this problem? Thanks, Steve.
 
The flange of the sender needs to have a good airframe ground (near zero ohms between it and the airframe)

If this is your problem it can be fixed a number of different ways. When I install float type senders I put a star lock washer under teh head of one of the crews.
This will dig into the screw head and teh sender flange and give a good ground even if their is a film of proseal there. You can also add a ground wire between one of the screws and the airframe but you still need to make sure it has good contact with the sender flange
 
That's what I thought too - even sanded a little spot on the flange to test. Put the multi-meter probes on the center post and the sanded spot - nothing. Thanks Steve.
 
When you say you installed fuel 'gauges' I assume you mean fuel senders since you are using the Dynon as your actual gauge.

A couple things to note: when ohming or measuring the resistance of the sender when it is connected to the Dynon make sure the Dynon is powered off otherwise the bias voltage/current provided by the Dynon unit will affect your ohm meter reading and could make it appear to measure much higher (or lower) than it actually is. Best to disconnect the Dynon when measuring resistance of the sender. How much fuel do you actually have in the left tank, what does it measure on level ground before taxie? If you don't have a lot of fuel, depending on your taxie way and turns, the fuel will slosh around quite a bit and the Dynon dampens the slosh so you could end up with a significanly lower reading than actual however once back on level ground and stationary, the original reading should return after a minute or less. My fuel readings are all over the place when I taxie.
 
Yes, I tested the fuel sending unit with the Dynon disconnected and did not get any connectivity. My problem is the unit works when I first install it -correct reading - but after the first taxi it seems to have a problem and goes to zero fuel and then stays at 0 no matter what. I thought it was a wiring problem but when I tested the sending unit on the tank I can't get any indication that it works. I thought maybe its not grounded correctly and sanded a little spot on the flange to test but still don't get any contenunity (sp?) with the center post and the flange. I've flown the plane and it doesn't give any reading at any fuel level. Seems like I got a couple of bad sending units. Thanks for the response.
 
Could it be that 12 volts power from your electrical system is somehow getting out onto the sender line? I think 12 volts from the power system would probably exceed the wattage and open up the potentiometer in the sending unit. Seems strange you had 2 units fail the same way by opening up after taxieing. You should be able to inspect the failed unit(s) and see if that is happening. If so, could be a safety issue also.
 
So you put a multimeter on the first (now removed) unit and you can't repro the issue on the ground? If you can't repro it with the removed sender I would suspect that the problem has to lie somewhere else. These are relatively simple devices with little mystery involved as to how they work.
 
Stupid question, but did you make certain that the float is secured properly in the sender? If not properly secured with the correct bends it can turn and be upside down or sideways and will not show properly. Ask how I know.

greg
 
My recent issues.

After 300 hours or so I had a sender go intermittent on me. Not the exact same symptoms but the sender unit checked out just fine when I removed it but would not work in the airplane. A new sender fixed the problem. Odds of you having an out of the box bad sender are long, but could happen. Having them check out fine out of the airplane then not work when installed can happen. Dont ask me why, but that was my experience.
 
When I tested the failed unit on the bench it seemed to work but there was a dead spot in the middle of travel and near the end. I don't recall getting that before. Also when I tested the voltage from the Dynon the working side was 1.2V and the non-working side was 2.72V. Maybe its the Dynon? Thanks Steve.
 
The Dynon voltages sound about right. The Dynon unit actually supplies a constant current (more or less) as would an analog gauge and the measured voltage accross the sender will vary according to its resistive value. The non-working sender (if open) would provide no load and the voltage would be high compared to the working side. Given identical resistive loads, the voltages measured accross them should be approximately equal.
 
Steve Gavitt said:
When I tested the failed unit on the bench it seemed to work but there was a dead spot in the middle of travel and near the end. I don't recall getting that before. Also when I tested the voltage from the Dynon the working side was 1.2V and the non-working side was 2.72V. Maybe its the Dynon? Thanks Steve.
Click to expand...

Could be. A simple swap of the wires in the connector on the EMS should give a definitive answer. If the problem persists on the same tank on the EMS you know that it's a fault in the EMS.
 
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Okay I think its the float getting stuck. Checked the voltage on the currently installed unit (one that doesn't work) and it read 2.71V (there's 13 gals in the tank - dynon shows 0). Removed the wires and connected the "bad" sender and moved the arm. Dynon showed correct values as I move the arm. I also checked the voltage and as Joe points out the voltage changes with resistance - a full tank shows about 0.6V and empty its 2.70V. So it has to be the float/arm. But how? When I added fuel after I installed the float the last time it showed correct reading on the Dynon. So I assumed the float was in the correct position. Is it possible that when taxiing the float became stuck and could not get released? I have flowed the plane several times including in some turbulance and you would think that it would release. In any case I removed the sending unit and it looked like the arm/float wasn't exactly perpendicular with the flange. So I bent it back and also I moved the float so that the clip is now on the forward side - not sure if this is correct. We'll see. Thanks, Steve.
 
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