Re: Fual Gauge Resistance

Alan Smith wrote:
Jim Warren wrote:
Alan Smith wrote:
Jim Warren wrote:
Alan Smith wrote:
You guys are normally very switched on & helpful so thought I would ask here, might be the wrong place but shove me in the right direction if it isn't.

I'm making my own fuel sender for my kitcar, the system works in principle, using a float, reed switches, magnets & resistors. My only problem is the calibration, I'm using a Smiths fuel gauge out of a Triumph (that's the tenuous link to uk.rec.classic.cars) but I do not know what the range of the gauge is, how do I find out? other than buying loads of different resistors & using trial & error. I know when my tank is empty I have a reading of 80 Ohms & the gauge is showing 3/4 full, clearly the resistance is not high enough. Would I also be right in thinking the gauge should be also going through a 10V voltage stabiliser?

Thanks

Alan...
You definitely should be using a 10V stabiliser, because otherwise your readings will vary according to the charge going into the battery and the drain coming out of it.

Once you have set up your stabiliser, find out which way your dial works - it might read Full with an open circuit or it might read Empty. Vice versa with a short to earth. Probably as the gauge came from a Triumph it will read empty, but you don't say which Triumph, so either is possible.

Likewise, your tank unit showing 80 Ohms when empty doesn't tell me whether when it is full it goes to 0 Ohms or to a number higher than 80. Again, either is possible, and you need to find out which.

Once you have got this information, you are again faced with two possibilities - one of which is that dial and tank units work in opposite directions.

Find some answers to the questions above and I might be able to advise you further.

Jim

Thanks for the response, in answer to your questions, I don't know what Triumph it came from just a Fleecebay bargain, it reads full on a short circuit, it does has 382 on the side if that's any help & not just the QA testers number. My sender currently reads 80 Ohms on empty & 10 ohms on full these were just some resistors I bought at 10 Ohms each just to prove it's viability. Once I know what resistance makes the gauge show empty & what resistance shows full they will be changed, it's getting those numbers I'm struggling with.

Alan...


Provided you use a 10V voltage stabiliser, I reckon 50 ohms will just get the gauge to Full, and 1000 ohms will be just about empty. If you bought a handful of 10 ohm ones, you should be able to test this, but assuming your 80 ohms reading 3/4 full is when using a 12V battery, it is a working assumption that the full mark is reached when 200 ma are running through the meter. So that is what I based my calculations on.

You might want to make the 1000 ohm one a bit bigger so that when the gauge says empty there will be a little drop of petrol left in reserve. You could try 1600 or 1800 ohms.

Don't forget that the 200ma current running through the 50 ohm resistor will make it warm. To be on the safe side, get a 2W resistor for that one.

Jim

Once again thanks Jim, got a few busy days so might not get back onto it till after the weekend, but will call round at either RS or Maplins to pick some resistors up. If you recommend 2W for the 50 ohm, what do you recommend for the others.

Alan...

have a look at the reference I mentioned it has various ranges and you should be able to work something out from that.
.

Relevant Pages

  • Re: Fual Gauge Resistance
    ... I'm making my own fuel sender for my kitcar, the system works in principle, using a float, reed switches, magnets & resistors. ... My only problem is the calibration, I'm using a Smiths fuel gauge out of a Triumph but I do not know what the range of the gauge is, how do I find out? ... Once you have set up your stabiliser, find out which way your dial works - it might read Full with an open circuit or it might read Empty. ... your tank unit showing 80 Ohms when empty doesn't tell me whether when it is full it goes to 0 Ohms or to a number higher than 80. ...
    (uk.rec.cars.classic)
  • Re: Fual Gauge Resistance
    ... I'm making my own fuel sender for my kitcar, the system works in principle, using a float, reed switches, magnets & resistors. ... My only problem is the calibration, I'm using a Smiths fuel gauge out of a Triumph but I do not know what the range of the gauge is, how do I find out? ... Once you have set up your stabiliser, find out which way your dial works - it might read Full with an open circuit or it might read Empty. ... your tank unit showing 80 Ohms when empty doesn't tell me whether when it is full it goes to 0 Ohms or to a number higher than 80. ...
    (uk.rec.cars.classic)
  • Re: Fual Gauge Resistance
    ... I'm making my own fuel sender for my kitcar, the system works in principle, using a float, reed switches, magnets & resistors. ... My only problem is the calibration, I'm using a Smiths fuel gauge out of a Triumph but I do not know what the range of the gauge is, how do I find out? ... Once you have set up your stabiliser, find out which way your dial works - it might read Full with an open circuit or it might read Empty. ... your tank unit showing 80 Ohms when empty doesn't tell me whether when it is full it goes to 0 Ohms or to a number higher than 80. ...
    (uk.rec.cars.classic)
  • Re: Fual Gauge Resistance
    ... My only problem is the calibration, I'm using a Smiths fuel gauge out of a Triumph but I do not know what the range of the gauge is, how do I find out? ... Once you have set up your stabiliser, find out which way your dial works - it might read Full with an open circuit or it might read Empty. ... your tank unit showing 80 Ohms when empty doesn't tell me whether when it is full it goes to 0 Ohms or to a number higher than 80. ... Once I know what resistance makes the gauge show empty & what resistance shows full they will be changed, it's getting those numbers I'm struggling with. ...
    (uk.rec.cars.classic)
  • Re: Fual Gauge Resistance
    ... If you bought a handful of 10 ohm ones, you should be able to test this, but assuming your 80 ohms reading 3/4 full is when using a 12V battery, it is a working assumption that the full mark is reached when 200 ma are running through the meter. ... You might want to make the 1000 ohm one a bit bigger so that when the gauge says empty there will be a little drop of petrol left in reserve. ... Once again thanks Jim, got a few busy days so might not get back onto it till after the weekend, but will call round at either RS or Maplins to pick some resistors up. ...
    (uk.rec.cars.classic)
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