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  #1  
Old 07-10-2019, 05:23 PM
DeltaVee47 DeltaVee47 is offline
 
Join Date: May 2017
Location: Houston, Tx
Posts: 46
Default Fuel tank sender

I know this problem has been beat to death but I canít find my answer in the files.
So I have the Vans supplied resistive float fuel senders hooked up to G3X.
I get 1.007V on L and 1.223V on right when I start the calibration per the G3X manual. Add 5 and 10 gal fuel, no change in voltage. I have tried all the tricks such as recommended by Scott and others without success. Good grounding both sides so far as I can tell with my meter. So Iím about down to pulling the units to see with my own eyes how I screwed up the install.
My question is can I do this without pulling the wings and any hints/tips greatly appreciated.

Thanks everyone
Greg Beckner
N557GB
140366
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  #2  
Old 07-10-2019, 06:18 PM
JDA_BTR JDA_BTR is offline
 
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Location: Baton Rouge, LA
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Make very sure you have the pins right in the GEA24. And you can measure the resistance of the sender to ground with the wires unplugged from the GEA24. If you check with it plugged in you are also measuring the path through the box and that is distracting.
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  #3  
Old 07-10-2019, 06:46 PM
Bavafa Bavafa is offline
 
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What the above poster said and we can simplifier even more by checking the resistance right at the sender. If you see resistance change at the sender, then the problem is on the wiring from the sender to the GEA24
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  #4  
Old 07-10-2019, 07:00 PM
JDA_BTR JDA_BTR is offline
 
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Yes - I did mean to check at the sender, just make sure the plug is off at the avionics side of the equation. Then you can also check the wire continuity at the plug. Keeps you from unscrewing/rescrewing the sender wire if you don't have to.

Should check resistance from sender terminal to shell of sender first. Then terminal to wing aluminum. Then plug pin to wing. Then plug pin to battery or ground tabs (the ultimate ground). Don't assume the ground from the sender to the wing and the wing to the fuse and the fuse to the battery is good unless it is all tied in.

Personally, I got the L and R backwards not knowing which Garmin called #1 and #2. Swapped the pins and was in business. Couldn't understand why gas in the left tank didn't change the reading - turns out it was changing the right side just fine!
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Last edited by JDA_BTR : 07-10-2019 at 07:04 PM.
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  #5  
Old 07-11-2019, 08:23 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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The standard kit supplied sensors have a resistance range from about 240 ohms empty, to about 30 ohms at full, when measured relative to airframe ground.
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  #6  
Old 07-11-2019, 08:40 AM
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bkervaski bkervaski is offline
 
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Location: Birmingham, Alabama
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Quote:
I get 1.007V on L and 1.223V on right when I start the calibration per the G3X manual.
Did both of your floats have the 16th clearance top and bottom when you were fitting the wire?

If one of them has bottomed out it would explain your readings.
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Last edited by bkervaski : 07-11-2019 at 08:45 AM.
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  #7  
Old 07-11-2019, 11:06 AM
DeltaVee47 DeltaVee47 is offline
 
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These are all things I have not checked but will do tomorrow when at the hanger. Its only about 125 degrees in there this summer. Houston is the best.

Greg Beckner
n557GB
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  #8  
Old 07-11-2019, 11:14 AM
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bkervaski bkervaski is offline
 
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Just about everybody I know who is or has built a 14 had to put an extra bend in those wires to keep the senders from touching the top and/or bottom of the tank, ymmv.
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  #9  
Old 07-11-2019, 11:25 AM
Bavafa Bavafa is offline
 
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Quote:
Originally Posted by bkervaski View Post
If one of them has bottomed out it would explain your readings.
Just curious about the logic on this?

We are reading the resistance and calculating based on that resistance. If the float is touching the bottom, then wouldn't this just be the resistance value the start of your empty tank. Granted, since it is a bit further away from the inboard area, one could still have a bit of gas in the tank and still read zero but that amount is even more with the 1/16th off the bottom.
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  #10  
Old 07-11-2019, 11:30 AM
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bkervaski bkervaski is offline
 
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Quote:
If the float is touching the bottom, then wouldn't this just be the resistance value the start of your empty tank.
Yes, but since those two wires are probably not perfectly bent at the same angles if they are bottoming out it will show different resistance.

Probably one of the reasons for the 16th clearance on the tops and bottoms of the floats is so the sensor bottoms out before the floats hit the skins.
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Last edited by bkervaski : 07-11-2019 at 11:35 AM.
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