keybaud Posted July 20, 2012 Share Posted July 20, 2012 My previous fuel tank didn't have a fuel sender, so the fuel gauge permanently read full as the cables are not attached to anything; however, if I short the cables, the guage reads empty, so I assume that the gauge is working correctly. The non-earth cable reads +4 volts, as does the output of the fuel gauge that this cable is connected to. I've received a sender from Caterham, but when I attach the cables to the sender, the gauge reads 'half full' when it should read 'full' and it reads 'full' when it should read 'empty'. The resistance across the sender is 275 ohms at what should be the empty position and 19 ohms at what should be the full position. The gauge doesn't start to change from 'full' until the arm has travelled about 50% of its movement, which is at a resistance of approx 90 ohms. Can anyone shed any light on what I need to change to make it all work properly? i.e. Is it simply a matter of rewiring the gauge or is my gauge not compatible with the sender, etc? /edited with more details and removed my faulty voltage reading. Edited by - keybaud on 20 Jul 2012 18:19:53 Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 20, 2012 Member Share Posted July 20, 2012 -4V relative to what? Jonathan Link to comment Share on other sites More sharing options...
keybaud Posted July 20, 2012 Author Share Posted July 20, 2012 Quoting Jonathan Kay: -4V relative to what? Jonathan Relative to the earth, but I'm wrong, it is +4 volts. I've also added extra details above. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 20, 2012 Member Share Posted July 20, 2012 Phew, I'll cancel the call to CERN. :-) Jonathan Link to comment Share on other sites More sharing options...
keybaud Posted July 20, 2012 Author Share Posted July 20, 2012 OK, it looks like I may have found the problem. The gauge is a Rochester 5-90044 aircraft fuel gauge, which has a working resistance of 0-30 ohms. The Caterham fuel sender appears to have a working resistance of 20 to 250 ohms, which implies that they aren't compatible. /edit Found a fuel gauge on demon tweaks described as "240 Ohms empty, 22 Ohms full", which is what my sender is doing, so my theory is correct. Sort of 'Hurrah', as I now need to buy a new gauge. Off to the wanted section I go. Edited by - keybaud on 20 Jul 2012 20:15:05 Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 20, 2012 Member Share Posted July 20, 2012 Are you sure you want a new fuel gauge? How about a unique BC crowd-sourced adaptor circuit? I'd start with a Wheatstone bridge with the fixed resistors giving a ratio that matches the resistance ratio of your sender and gauge... Jonathan Link to comment Share on other sites More sharing options...
keybaud Posted July 20, 2012 Author Share Posted July 20, 2012 Quoting Jonathan Kay: Are you sure you want a new fuel gauge? How about a unique BC crowd-sourced adaptor circuit? I'd start with a Wheatstone bridge with the fixed resistors giving a ratio that matches the resistance ratio of your sender and gauge... Jonathan Making my own rheostat for the sender and reversing the motion of the float would be easier, but I can't be arsed to do that either. /edit But you've got me thinking now... /edit 2 And heres one somebody else prepared earlier: https://www.spiyda.com/magento/index.php/fuel-gauge-wizard.html Edited by - keybaud on 21 Jul 2012 00:39:38 Link to comment Share on other sites More sharing options...
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