Home » Public Forums » GMCnet » Adding a potentiometer to system to adjust fuel reading
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| Re: [GMCnet] Adding a potentiometer to system to adjust fuel reading [message #311925 is a reply to message #311924] |
Mon, 09 January 2017 14:05   |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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You guys need to bore a hole through the floor in your coaches, through the
top of the fuel tanks. Then, just use a stick of wood placed through the
hole to measure the contents. When you are through, put a cork in it. (Grin)
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Jan 9, 2017 11:58 AM, "A." wrote:
> Atom Ant wrote on Mon, 09 January 2017 11:56
>> I came across an interesting idea on how to adjust your bad senders.
>> It's simply adding another potentiometer into the system, and setting it
> at a known fuel level.
>>
>> they're cheap and easy to add into the wiring.
>>
>> I thought I'd share as it might be something that a perpetual tinker
> that owns a GMC coach might be willing to check into. I may actually try it
>> myeslf.
>>
>> https://sites.google.com/site/shannonpowerlab2/home/
> calibrating-your-fuel-gauge
>>
>> Thoughts?
> You can get a little improvement, but it will never be right. Your last
> post on your measurements said 10 - 100 ohms. 900 ohms in parallel to the
> sender will get you 90 ohms at the gauge when the sender is at 100, but
> will only drop the 10 ohms at the low end to 9.9. Anything less than 900
> will
> lower the top end to less than 90. 500 ohms in parallel would give you 83
> when the sender is at 100 and 9.8 when the sender is at 10. The only way to
> lower the low end appreciably without messing up the top end is to get the
> sender low end down. There is no such thing as negative resistance. The 900
> ohm resistor will make your gas gauge start to drop sooner than it would
> without the resistor. The 10 ohms will keep the gauge at 10% when the tank
> is
> dry. No matter what you do, that 10% reading when the tank is empty is
> unavoidable unless/until you get the sender resistance down. With 100 ohms
> and
> no parallel resistor, 10% of your gas will be gone before the gauge starts
> to drop. All that 900 ohm resistor buys you is a more accurate/responsive
> gauge at the full end, it gets you next to nothing as you get closer to
> empty.
> --
> 73 23' Sequoia 4 Sale
> 73 23' CanyonLands Parts Unit 4 Sale
> Upper Alabama
> "Highest price does not guarantee highest quality."
>
> _______________________________________________
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| Re: Adding a potentiometer to system to adjust fuel reading [message #311926 is a reply to message #311924] |
Mon, 09 January 2017 14:44 |
Atom Ant
Messages: 170
Registered: October 2016
Location: Austin, TX
Karma: 0
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Senior Member |
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A Hamilto wrote on Mon, 09 January 2017 13:50Atom Ant wrote on Mon, 09 January 2017 11:56I came across an interesting idea on how to adjust your bad senders.
It's simply adding another potentiometer into the system, and setting it at a known fuel level.
they're cheap and easy to add into the wiring.
I thought I'd share as it might be something that a perpetual tinker that owns a GMC coach might be willing to check into. I may actually try it myeslf.
https://sites.google.com/site/shannonpowerlab2/home/calibrating-your-fuel-gauge
Thoughts? You can get a little improvement, but it will never be right. Your last post on your measurements said 10 - 100 ohms. 900 ohms in parallel to the sender will get you 90 ohms at the gauge when the sender is at 100, but will only drop the 10 ohms at the low end to 9.9. Anything less than 900 will lower the top end to less than 90. 500 ohms in parallel would give you 83 when the sender is at 100 and 9.8 when the sender is at 10. The only way to lower the low end appreciably without messing up the top end is to get the sender low end down. There is no such thing as negative resistance. The 900 ohm resistor will make your gas gauge start to drop sooner than it would without the resistor. The 10 ohms will keep the gauge at 10% when the tank is dry. No matter what you do, that 10% reading when the tank is empty is unavoidable unless/until you get the sender resistance down. With 100 ohms and no parallel resistor, 10% of your gas will be gone before the gauge starts to drop. All that 900 ohm resistor buys you is a more accurate/responsive gauge at the full end, it gets you next to nothing as you get closer to empty.
fantastic! Thanks for the info. I think with the range it's showing now, plus gauging the odometer, I;ll be okay.
1976 Palm Beach
Austin, TX
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| Re: Adding a potentiometer to system to adjust fuel reading [message #311929 is a reply to message #311924] |
Mon, 09 January 2017 17:30 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Fuel gauges are not a precision device and you are never going to get the gauge to read exactly what you have. As an example the rule on an aircraft fuel gauge is only one. The gauge must read empty when there is no fuel in the tank(s). After that there are no precise rules and a lot of variance in readings occurrs.
If you need a precise measure measurement then look at a fuel totalizer. They have a sender in the fuel line that senses the fuel flow through it on gas going to the engine. Then that amount is subtracted from the pre-programmed amount of fuel stored in the tank and displayed to the user.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Adding a potentiometer to system to adjust fuel reading [message #311931 is a reply to message #311921] |
Mon, 09 January 2017 17:50 |
Atom Ant
Messages: 170
Registered: October 2016
Location: Austin, TX
Karma: 0
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Nope, I've always driven used cars, with goofy this or not-working that on them. I'm not by any means needing a perfectly accurate gauge. The range I've got is fine, and until it completely stops working, will suffice. I shared simply because I thought it was an interesting and creative solution to an issue that seems to be a regular concern with these aging coaches.
1976 Palm Beach
Austin, TX
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| Re: Adding a potentiometer to system to adjust fuel reading [message #311952 is a reply to message #311921] |
Tue, 10 January 2017 10:38 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Do you want higher readings than the sender is calibrated for? It isn't going to be accurate in that instance. The sender is built to provide a stated resistance at full scale, full scale being the high pressure it's made for. The wiper on the resistance wire is all the way at the end when the rated pressure is reached. Higher pressure won't move it any further since all the resistance is already in place. Adding external resistance will - depending on the gauge - make it read higher but it will do so at the sender's rated pressure, not a higher pressure. Worse, added resistance will keep the gauge from reading zero when there's no pressure, because there will still be the added resistance in the line.
Now, if you have a higher reading sender, but want to keep the gauge at full scale when the higher pressure is reached,padding the sender with a resistance will accomplish this, and the zero point will remain the same. How well it might track throughout its range is open to question.
Probably the best approach is to use a matched sender and gauge, and not have to worry about adding stuff.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: Adding a potentiometer to system to adjust fuel reading [message #311957 is a reply to message #311924] |
Tue, 10 January 2017 10:47 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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"There is no such thing as negative resistance."
Negative resistance exists in plasma conduits (fluorescent light bulbs) and ionized gases (such as the junction between a brush and moving commutator in a motor or generator, or lightning or other electric arc).
The actual unit of measurement is "mhos".
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Adding a potentiometer to system to adjust fuel reading [message #311961 is a reply to message #311957] |
Tue, 10 January 2017 11:50 |
Neil
Messages: 271
Registered: July 2007
Location: Los Angeles and Magalia, ...
Karma: 1
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Johnny
Right as always.
Truth is my question was for a non-gmc application with mismatched foreign senders and gauges where once the motor gets hot the sender reads really low. I was just trying to sneak some general knowledge out of the brain trust. Best would be to put in a mechanical gauge but not ascetically feasible.
Neil
76 Eleganza now sold
Los Angeles
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| Re: Adding a potentiometer to system to adjust fuel reading [message #311969 is a reply to message #311921] |
Tue, 10 January 2017 13:34 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Neil -
In that instance, try to get the proper sender for the installed gauge - assuming the gauge is in a stock instrument panel which doesn't lend itself to modification. Somewhere in the world, there's a sender intended for that gauge. Acquire it, and adapt it to the oil pressure port on the engine you want to measure. In that the adapter is under the hood out of sight, you can get really silly with it if you have to.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Adding a potentiometer to system to adjust fuel reading [message #312000 is a reply to message #311999] |
Tue, 10 January 2017 18:06 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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I put drivers who run their vehicles on very low fuel levels as the same
guys who play Russian roulette with all the chambers loaded. Breathe easier
guys, fill the tanks, and note your odometer reading. Drive 250 miles, then
refill the tanks. Forget those inaccurate electric fuel gages, and fuel
tanks joined at the hip with a large manifold between them. There are much
more important issues to concern you in your coach.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Jan 10, 2017 3:54 PM, "A." wrote:
> Matt Colie wrote on Tue, 10 January 2017 17:41
>> ...The several times I have been able to take on more than 50 gallons, I
> was concerned, but far from panic.
> Gas pumps vary by calibration. I drove my daily driver for a couple of
> years and could never jam more than 12 gallons in it at my usual station
> when
> the low fuel light came on. One time I was across the street from a
> station that was the same price as my regular place when the low fuel light
> came
> on. So I pulled in a filled up. The pump said it took 13 gallons by the
> time it clicked off. I never bought gas there again, and every time I needed
> gas after that I went to my usual place and never stuffed more than 12
> gallons in it.
> --
> 73 23' Sequoia 4 Sale
> 73 23' CanyonLands Parts Unit 4 Sale
> Upper Alabama
> "Highest price does not guarantee highest quality."
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] Adding a potentiometer to system to adjust fuel reading [message #312106 is a reply to message #312000] |
Fri, 13 January 2017 18:07 |
kelvin
Messages: 608
Registered: February 2004
Location: Eugene, OR
Karma: 0
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Senior Member |
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I'm just getting into a groove at 350 miles!
Not all of us need to stop after 4 hours in the seat. Or we hit a rest
stop without filling up. I've gone 450miles without flipping over to
"AUX" a couple times. I think my record in the seat is about 8 hours.
Proper fluid intake (or lack thereof) is important. :-)
It is good to know your particular coach, though. My guage (VDO) is
reasonably accurate. My tank sensors were in great shape last time I
had them out.
Kelvin
'73 23' in Eugene, OR
On 1/10/2017 4:06 PM, James Hupy wrote:
> I put drivers who run their vehicles on very low fuel levels as the same
> guys who play Russian roulette with all the chambers loaded. Breathe easier
> guys, fill the tanks, and note your odometer reading. Drive 250 miles, then
> refill the tanks. Forget those inaccurate electric fuel gages, and fuel
> tanks joined at the hip with a large manifold between them. There are much
> more important issues to concern you in your coach.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
>
> On Jan 10, 2017 3:54 PM, "A." wrote:
>
>> Matt Colie wrote on Tue, 10 January 2017 17:41
>>> ...The several times I have been able to take on more than 50 gallons, I
>> was concerned, but far from panic.
>> Gas pumps vary by calibration. I drove my daily driver for a couple of
>> years and could never jam more than 12 gallons in it at my usual station
>> when
>> the low fuel light came on. One time I was across the street from a
>> station that was the same price as my regular place when the low fuel light
>> came
>> on. So I pulled in a filled up. The pump said it took 13 gallons by the
>> time it clicked off. I never bought gas there again, and every time I needed
>> gas after that I went to my usual place and never stuffed more than 12
>> gallons in it.
>> --
>> 73 23' Sequoia 4 Sale
>> 73 23' CanyonLands Parts Unit 4 Sale
>> Upper Alabama
>> "Highest price does not guarantee highest quality."
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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