Centroid Fuel Sender

Most of us probably have the original Centroid fuel level sender in the tank. I believe the unit we have has continuous output of 2.33V empty and 0.54V full.

My fuel gauge is based on ohms (240 empty and 33 full). 240/33 is the factory default setting from Speedhut for the fuel gauge (it is programable). Since I'm not a rocket scientist or EE, I'm fairly sure the probe voltage converts to the gauge OHMs, so selecting the 240/33 OHM setting will send accurate fuel level signals to the gauge.

So to those of you who are more electrically inclined, is this correct?
 

Howard Jones

Supporter
A few things are happening. The probe tube itself is in effect a variable capacitor. The fuel level inside the tube changes the capacitance of the tube. (the two plates of the capacitor are changing area and capacitance value as the fuel shorts the two as the level rises.) Then the sender electronics converts the varying capacitance to an equivalent resistance value. If you have a standard length tube I believe the factory sets the calibration of the tube capacitance to the resistance standard. If you have a cut to length type like mine then the calibration happens after the tube is installed in the tank, wired to the gauge and you press calibrate. Doing this tells the gauge that whatever resistance the probe is when empty is being converted, producing 240ohms. Or the gauge is recalibrated to read the empty value as empty. This is what I suspect.

Now the gauge acts as a single range ohm meter that is calibrated in fuel level.

Ans: yes
 
Thanks Howard. Mine is stock (12 inches I think) , and I calibrated it manually (the hard way), but not real trusting on the programming. I took a picture of my fuel sender prior to install but it's blurry. I think Centroid puts the OHM values on the top sticker. Does anyone have their sender accessible to check that for me (post a pic)? While I built an access panel to mine, lets say its not easy to get to and I'm being to lazy to remove the seat.

Thanks.
 

Stephan E.

Supporter
Hello Dan,

I also have the Speedhut gauge with 240/33 Ohm. I had a new level sending unit made by Centroid to match the gauge. The SLC sender matches the Kozo Dash with 100/0 Ohm. I was not sure about the Speedhut being able to digest that. Also the SLC sender has the linearization module built in to compensate for the tapered upper tank section. The new gauge will be acting a little differently without that module and will show levels falling faster through to the taper until it hits the straight section of the fuel cell which is fine with me. Centroid mentioned that the module was specific to the SLC sender is not available for other units. I'll play with both units to see which one it will be before inserting the tub for good.
 
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I was taking a look at Kurts install and saw his fuel probe. He was kind enough to send me a picture of the top.

Perhaps his is not a stock probe from RCR, but I noted it shows OHMs of 240/33. After an exhaustive search of my many photos, I found one of my fuel probe. And as Stephen has indicated, I do have the one that is unique to the Super lite...100/0 ohms. This is not a selection option on the Speedhut program, however Speedhut designed a manual programming option for custom programing to the 100/0 ohm readings for full and empty.

Bottom line, I may be OK after all. Thanks for the data Stephan.
 
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Dan,

My probe came with my kit from RCR, not sure how or why mine is 240-33 unless it is because I removed the Koso gauge from my order. I’ll have to check on that with Bill.

I wonder how the 90-0 option would work with your gauge? That would be easier to setup than a custom program/manual calibration. Since my tank is currently empty I may do a manual calibration just to be safe.
 

Joel K

Supporter
Here is a pic of mine, looks like the standard 100-0 For the KOSO.

4E4D71AE-9103-4F95-9616-58CB2C8AAC84.jpeg
 
Good question on the 0/90 Speedhut option. I’m truly most concerned with empty versus full. IAW Speedhut the gauge is calibrated for 0 empty and 90 as full if you select the 0/90 option. If the KOSO sensor measures 0 as empty and 100 as full then I would guess it would stay full longer as the fuel is used and once it drops below 90, it would start reading accurately on its way to empty. We may not know exactly how much say 1/4 tank is in gallons, but it would be time for a fill up anyway.

Based on Joel's photo, the Centroid is listed as 100/0. If Centroids standard is listing ohms as empty/full, then the 100/0 is opposite the 0/90 option on Speedhut. That leaves me with manual programming as the only option with my configuration.

I think this makes sense?
 
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Howard Jones

Supporter
When I calibrated mine I set the "full" with 15 gals in the tank. It held about 15 3/4 if I remember correctly. Then I set the "empty" with 3 gals in the tank. That ought to get me back to the pits if I make a mental error. These sensors tend to react slowly, especially when using fuel at a high rate as on track. So a margin of error on the empty side is a good consideration..

When you do the full manual calibration you are using whatever the empty and full resistive value is being produced as you select the two settings, I believe, depending on how much fuel is in the tank for each setting. This is a good way to do it but it does take a bit of work since you need to do the full setting first and then drain the tank to whatever you want the empty setting to be. The "easiest" way is to full drain and then add back a known amount of fuel.

What I really would like is a separate reserve tank with 2 gals in it and a separate pump. I have room but just haven't got to that yet. Maybe someday.
 
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Howard. It never actually occurred to me to create a reserve by programming 2 or 3 gallons as empty....good idea. From Stephan’s responsive above the RCR Centroid accounts for the basic shape of our tanks. Guess I will reprogram my gauge to empty/full based on the 100/0 ohm sensor but use your reserve idea and set the fuel warning light for 1/4 tank. Don’t want to experience another flame out due to no fuel. This thing coasts like a rock.
 
I’m using a device to convert the fuel sender signal to a 0-5V signal for my Aim dash system. When I calibrated my tank level I added fuel at 1gal and recorded the sensor’s output. Between 0-1.9gal I measured no change in signal from the sensor - so I believe you already have that 2 gal reserve built in if you factor the difference between the bottom of the sensor and the volume in your surge tank (minus some amount for the portion your fuel out line isn’t able to transfer).

I was able to physically get almost 20gal of fuel into my tank, after installing my fuel fill line. I got about 17 gal before fuel started spilling when I hadn’t yet connected my fuel fill line.

Details here: https://socalslc.com/2018/08/24/45-taking-aim/
 
Classic Instruments makes a sender that is a bolt in replacement for that sender. But it actually works. It's very slick

I hope others have better luck with their centroids than I did, mine would consistently fail to hold the calibration settings. I bought a second one in hopes my experience was a fluke, unfortunately it wasn't. Preferably the one they sell now (if any different) is a whole lot more reliable.

I don't remember what I used to replace it as I type this, but it has been faultless.
 
I hope others have better luck with their centroids than I did, mine would consistently fail to hold the calibration settings. I bought a second one in hopes my experience was a fluke, unfortunately it wasn't. Preferably the one they sell now (if any different) is a whole lot more reliable.
I don't trust the stock centroids/Speedhut combo that came with mine. Maybe it's the anti-slosh foam causing issues but my gauges will sometimes ready accurately, other times will show empty when I'm near full or show full, when I know I'm about empty in that tank. Will look into the Classic Instrument sensors. Disappointing as the capacitance fuel level sensor is the type used on aircraft.
 
I have been thru 2 of the RCR SLC Centroid fuel senders. Neither was able to keep its settings for more than 5 weeks. A common failure was reverting to reading FULL while driving part full. Centroid sent me a data logger to watch what was happening. They never came up with a solution although they agreed that it was correctly connected to the Koso dash. I have electronic design skills and it is my opinion that either the circuit or the software in this sender needs a complete redesign, it should be able to store it's last setting under ANY condition.
For the last year I have been using KUS magnetic type KFL11A0110.09 sensor. It works just fine.
 
Jerry,
Thanks for the information. The replacement sender I am currently using is from the boat world and honestly I don't think the resolution is what it needs to be. BUT at least it functions the same way every time.

My issue now is that as the fuel gets to the last 5 gallons the gauge reads empty. Since the tank is so wide and the sender does not quite reach the bottom of the tank, it sees empty 5 gallons before it actually is. Which is about an inch of fuel IIRC.

Jerry, how is the one you are using work in this regard?
 
So the SpeedHut stuff is NOT a Centroid manufactured part and proven reliable? Then maybe that is what I need.

Thanks
 
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