What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Capacitance fuel senders, no more?

tweiss

tweiss

Active Member
As I begin to build my -8 tanks, I have decided to ditch my float set up (parts still on shelf un-opened) and go with the capacitance plate route instead.

I called Van's to order the needed parts for switching over only to find out they don't support the capacitance fuel sending theory any more.

They recommended looking into venders that make up aftermarket units if I still wanted to go this route.

Anyone have any experience with other vendors capacitive kits?

Thanks,
Tom
 
No expert here but I was very impressed with the Van's supplied floats in the RV-10. With the calibration of the Dynon Skyview these floats provided dead accurate fuel quantities. We checked at each refuelling and the amount required was exactly equal to the deduction from capacity of the tanks to fuel remaining on the Skyview.
I've installed the float sending unit in my RV-14 wings. Hopefully I'll be as pleased.
PS I still don't rely on these indications for safe fuel quantities on board for flight, just as a reference. Always dip your tank before flight.
 
Cap Sender Plates

The kits Vans supplied were really mostly hardware and instructions for the cap senders. Basically, 2 plates for each tank, some plastic washers for standoff, nutplates, screws, wire, terminals and instructions. The real cost comes in the converters needed to work with your EFIS, which I haven't purchased yet.

You can fab the plates yourself fairly easily. In fact, for the 10, Vans never made a cap sender kit, so the builder has to fab the plates. They are basically sized like 1/2 a tank rib, minus the standoff distance all the way around (don't remember off hand what that is). You could use a rib to mark a flat plate, then measure and remove the standoff distance all the way around, buy the hardware and install yourself.

My advice is to find someone with an 8 who has installed them and get the instructions from them. They aren't that bad.

P.S. I installed the floats in my 10 ALSO, in case I ran into trouble with the caps. The weight is minimal, as both systems are very light.
 
Tom,

I beleive I have several of Van's capacative sender kits stored away with my HRII project. I don't want to sell them, but I'd be happy to loan you one so you could duplicate it. Like Mike says, it's not really very complex.
 
This is really weird if you ask me.

My question is WHY?

Why would Van remove this option? I have caps in the -6 that I fly and they are ABSOLUTELY PERFECT in EVERY WAY! Super accurate, no moving parts and incredibly simple.

I also have them in the -7 I am building and am looking forward to them working just as good there.

Does anyone have problems with their caps? Is my experience with them unusual? I don't recall seeing or hearing about any real problems with them.

Opinions? Thoughts? Insight?

:confused: CJ
 
Captain_John said:
This is really weird if you ask me.

My question is WHY?

Why would Van remove this option? I have caps in the -6 that I fly and they are ABSOLUTELY PERFECT in EVERY WAY! Super accurate, no moving parts and incredibly simple.

I also have them in the -7 I am building and am looking forward to them working just as good there.

Does anyone have problems with their caps? Is my experience with them unusual? I don't recall seeing or hearing about any real problems with them.

Opinions? Thoughts? Insight?

:confused: CJ
Click to expand...

CJ,

No idea why Vans would discontinue. I installed them in my 10, but not flying yet. They seem straightforward in every way. I like the no moving parts and the accuracy they (should) deliver. Back when I was researching whether or not to go with capacitance senders, I remember someone saying the plastic used to make the standoff washers would degrade in fuel over time, introducing the potential for false reads or no reads. I did some digging and found that the material vans washers are made of seems to test well in av gas. The only other caution was from people who had "problematic" installs and couldn't get them to work/calibrate/or other.. I would think, as long as they are installed correctly and wires are properly tested for continuity (all in the instructions) they should perform flawlessly.
 
Nothing wrong with my Van's Capacitive Senders.

Finding a good converter however that is optimized for them is another story....
 
ppilotmike said:
So, what did you use for a converter? What EFIS? Details..
Click to expand...

I have used the Dynon ones and the Princeton 2 point ones and next am going to try the Electronics International ones.

Both the Dynon and the Princeton convert the capacitance to a voltage output. The EI one converts it to a frequency output.

I have used em with both the Dynon Legacy series and the Garmin G3X.

Both of the ones I have tried work. Just not as well as I think they could if redesigned and optimized for the Van's plates.

The Princeton ones have wigged out once or twice for no apparent reason but have come back to life and worked again.
 
Last edited:
I've got 200 hrs on the Dynon convertors. The GRT H1 screens provide a way to tune for the odd shaped tanks if one wants to but the readings are not far enough off to make it a top priority to go to the trouble. I have the EIS set to be most accurate at the lower half of the tank so I'm happy.

They are already way more accurate than any spammer I ever rented.

I do believe the "hockey stick" voltage that comes out of the Vans plates / anybody convertor is partially due to the plates not following the full shape of the tank rib. They are cut short well before the nose so are pretty much rectangular. The gas follows the volume curve of the nose and the plates do not. Disparity, although small. If I were to do it again, I would make custom capacitor plates that cover the whole rib (following the same clearance gaps) all the way around. I think that would go a long way towards making the voltage output a single straight line rather than two lines with a bend in the middle.

Also, there are two plates in each tank. The upper plate provides fuel sensing well past where the resistive floats have hit the top of the tank.

Sold....
 
Last edited:
How does the capacitive sensor work when the "upper" plate is not touching the fuel, as in when the fuel level is low enough that the bottom of the upper plate is exposed?
 
Snowflake said:
How does the capacitive sensor work when the "upper" plate is not touching the fuel, as in when the fuel level is low enough that the bottom of the upper plate is exposed?
Click to expand...

Rob, the "upper" plate is connected to the "lower" plate. They are effectively in parallel.

They are both measuring the (ever-changing) capacitance from plate(s) to ground.

Does this make sense?

:) CJ
 
I have the capacitive plates, and the Dynon Skyview. I started with the Dynon converters, but got pretty poor results because it uses only a very small portion of the 0-5V range. Swapped them out for the Princeton 2-set-point converters and recalibrated...much better. Still a tad off in the mid-range, about 3/4 of a gallon, but I plotted the calibration data (Princeton uses almost the entire 5V range), and I know how to "tweak" the data in the Dynon to get them even better without doing another calibration.

I do wish I'd taken the time to make custom plates that more closely followed the entire airfoil shape, instead of just being square plates, as I think you're right, that would result in even more accuracy, but as someone said...waaaaaaay better than any plane I've ever flow until now.

I have no idea why Van's would discontinue such a simple, accurate and easy-to-install option.
 
I'm glad this thread was started at this time. I just ordered a pair of Princeton converters after learning, the hard way, that the converters that I recently installed and tested, were the wrong type to work with my GRT Hx display/EIS. I ordered the only converters that Van's sold for capacitance senders when I ordered my wings. I didn't know any better back then and thought they were what I needed. Unfortunately, these converters are meant to be used with a particular gauge made by Electronics International. They shift the frequency and cannot be calibrated. Not what I needed. As a result, my tanks read 2 gallons even though they are empty. I called GRT because I thought the problem was related to the EIS. That's when I was able to talk to Todd, the Princeton man, who told me that I needed the Princeton converters because they can be calibrated. He believed that it was a bit misleading for Van's to sell only the EI converters and thought that they should have been clear about what converter is needed for different installations. Anyway, I have wasted $90 for these converters and have just spent another $190 for the right ones. Hopefully, this will help somebody else to not make the same mistake when choosing their converter.
 
bacstabber said:
I'm glad this thread was started at this time. I just ordered a pair of Princeton converters after learning, the hard way, that the converters that I recently installed and tested, were the wrong type to work with my GRT Hx display/EIS. I ordered the only converters that Van's sold for capacitance senders when I ordered my wings. I didn't know any better back then and thought they were what I needed. Unfortunately, these converters are meant to be used with a particular gauge made by Electronics International. They shift the frequency and cannot be calibrated. Not what I needed. As a result, my tanks read 2 gallons even though they are empty. I called GRT because I thought the problem was related to the EIS. That's when I was able to talk to Todd, the Princeton man, who told me that I needed the Princeton converters because they can be calibrated. He believed that it was a bit misleading for Van's to sell only the EI converters and thought that they should have been clear about what converter is needed for different installations. Anyway, I have wasted $90 for these converters and have just spent another $190 for the right ones. Hopefully, this will help somebody else to not make the same mistake when choosing their converter.
Click to expand...

I think this is a good part of the reason they were dropped.
Van's is not a mfr of EFIS systems, so can not keep up with all of the different (and often changing) design requirements of the multitude of systems that are now available.
The EI converter has been sold ever since the cap sensor kit was introduced (because at that time I believe it was the only one available).
Only a small # of kits have been sold each year, with a high level of tech support required trying to help people work out compatibility issues, etc., not to mention that it was not an available option for QB wings....

There actually are a few of these kits left if anyone is still interested. Call the order desk.
 
Last edited:
rvbuilder2002 said:
I think this is a good part of the reason they were dropped.
Van's is not a mfr of EFIS systems, so can not keep up with all of the different (and often changing) design requirements of the multitude of systems that are now available.
The EI converter has been sold ever since the cap sensor kit was introduced (because at that time I believe it was the only one available).
Only a small # of kits have been sold each year, with a high level of tech support required trying to help people work out compatibility issues, etc., not to mention that it was not an available option for QB wings....

There actually are a few of these kits left if anyone is still interested. Call the order desk.
Click to expand...

That's a good reason to not sell *converters*, but there's no reason to not sell the plates and hardware. In any case, they're dirt simple to make. Somewhere I have a pdf of the instruction sheet/blueprint for them...if I can find it, I'll try to post it somehow.
 
GOT EM!!

Thanks everyone for all your advise, suggestions, and offers. And thanks Scott for advising that there are a few kits left over at the factory.
My friend needs to put some break-in time on his new engine in his Maule, so we flew it up to the Mother-Ship today and I shopped like a girl.
Got my Cap plate kit, Proseal, and a few hardware goodies while I was there.
Always fun to visit.
Now back out to the garage to get these wings done.
Have a great weekend.
Tom
 
Captain_John said:
Rob, the "upper" plate is connected to the "lower" plate. They are effectively in parallel.

They are both measuring the (ever-changing) capacitance from plate(s) to ground.

Does this make sense?
Click to expand...
As long as there is fuel between (and touching) both plates, yes. The fuel is forming a dielectric between the two capacitive plates. I'm just not clear as to how it works when the fuel level gets low enough that the "upper" plate is exposed just to air. The dielectric constant changes to that of just air, and it seems to me that this would result in a significant difference in how the system responds to fuel level.
 
I always thought the measurement was between the two plates also. However it?s actually between the combined plates and the surrounding structure.
 
Snowflake said:
As long as there is fuel between (and touching) both plates, yes. The fuel is forming a dielectric between the two capacitive plates. I'm just not clear as to how it works when the fuel level gets low enough that the "upper" plate is exposed just to air. The dielectric constant changes to that of just air, and it seems to me that this would result in a significant difference in how the system responds to fuel level.
Click to expand...

Not sure where you were going. Capacitance change is the whole idea. Fuel not required for capacitance. The Vans plate system measures 180 picofarad with air as the dielectric. With full fuel, it measures 360 picofarad.
There is a continuous change in capacitance between the two end states as the fuel level changes.

In regards to the two plates in one tank. They are hooked in parallel so they are electrically ONE capacitor that has an average capacitance of the fuel covered part and the air covered part.

The "converter" you have to add uses the fuel tank capacitor as a part of a voltage oscillator. The oscillation frequency changes as the capacitance changes. Via circuitry magic that is too long to explain, that frequency change can be reconfigured into a variable voltage that can be used to drive your panel instrument. You may be able to google Jim Weir's capacitance gages for the details.

I came very close to building my own convertors. Had them working on the bench breadboard but I saw the Dynon pieces and they are so darned elegant and simple, I just bought them.
 
Snowflake said:
As long as there is fuel between (and touching) both plates, yes. The fuel is forming a dielectric between the two capacitive plates. I'm just not clear as to how it works when the fuel level gets low enough that the "upper" plate is exposed just to air. The dielectric constant changes to that of just air, and it seems to me that this would result in a significant difference in how the system responds to fuel level.
Click to expand...

The fuel need not touch both plates.

The two plates are connected together, so therefore it will be measuring the contact between the plate(s) and the skin.

It doesn't matter if the upper plate is completely dry. The lower plate is determining the dielectric to be an even smaller value.

Make sense?

;) CJ
 
Fuel type matters

I have the capacitive system in my RV-6. It has been a pretty good system, at least up until last year. I now have a flaky right tank indication that goes from normal to zero gallons on most flights. I'm still tracking the problem down - I don't yet have a reason to believe the problem is in the tank itself. But if it is inside the tank, fixing it will be a bear.

Also, something to keep in mind is that fuel type matters. I've been using 100LL and 91 Octane auto fuel, and the dielectric constant for the two is significantly different. So now I have a re-calibrated left tank that reads accurately with 91 octane and the right one is calibrated for 100LL. But if I fill up the left tank with 100LL because that's all that is available, I no longer have an accurate reading. I don't know if any of the EFISs out there have the ability to save multiple calibrations (for different fuels), but that would be a nice feature to look out for. Float-type sensors do not have that problem, of course.
 
Jordan, I knew this was the case.

What do your readings look like in your left tank when you do use 100LL?

Does the gauge show more or less fuel?

Does it have a bell in the data?

Does it not show empty?

What happens with a 50/50 mix of 91 and 100LL?

...just curious. I have never burned 91 in the -6.

:confused: CJ
 
CJ and Bill, thanks for the explanation, that makes a lot more sense now. I thought the two plates were the separate sides of the capacitor, but if they're connected in parallel then they form "one side" of the capacitor and the tank itself forms the other. That makes more sense.
 
Np, you are welcome. I can see how you might think that too!

I was thinking that it might be a fun experiment to get a galvi pail and immerse some plates in it and experiment with different liquids to explore the various dielectrics!

Hmmmm, maybe when the plane is done and I have plenty of time on my hands???

;) CJ
 
JordanGrant said:
I now have a flaky right tank indication that goes from normal to zero gallons on most flights. I'm still tracking the problem down - I don't yet have a reason to believe the problem is in the tank itself. But if it is inside the tank, fixing it will be a bear.
Click to expand...

Had an identical problem with one of my tanks. Turned out to be an intermittent connection at the BNC connector at the tank root (exterior to the tank). I think the Princeton capacitive converter cable's BNC connector at the tank had a short pin or small dia pin that was making intermittent contact with the tank's BNC connector. My fuel level would occasionally go to zero, sometimes it would come back, other times not. Installation of a 90 degree bnc adapter solved the problem.

No other issues with my cap fuel level system in 350 hrs.
 
You must log in or register to reply here.
Back
Top