AJay 1 Posted April 29, 2009 Report Share Posted April 29, 2009 (edited) I have been experiencing increasing problems with my temperature gauge and fuel gauge and have decided to do something about it. After some investigation i found that the gauges operate a a regulated 10volts, this is controled by a very archaic device called a voltage stabiliser........ The Smiths voltage stabiliser is a mechanical voltage regulator that reduces and maintains the instrument operating voltage at 10v dc. Inside the stabiliser is a bimetallic strip, an insulated heating wire coil, and contact points. 1) The contact points are located inside the stabiliser housing. One side of the points is on the “B” terminal, the other side is on one end of the bimetallic strip attached to the “I” terminal. 2) The bimetallic strip carries current between the contact points and the “I” terminal. 3) The heating wire coil is wound around the bimetallic strip. It is connected between the contact point on the bimetallic strip and chassis ground. “E” terminal (ground or Earth) “I” terminal (to Instruments) “B” terminal (from Battery) Contact Points (inside, not visible When the ignition switch is turned on, the “B” terminal sees full battery voltage. Initially the stabiliser points are closed. Current is carried across the contact points, through the bimetallic strip, and provided to the “I” terminal. Thus, when the ignition is first turned on, full battery voltage appears on the “I” terminal of the stabiliser. Remember that one end of the heating wire is also attached to the contact point on the bimetallic strip. Thus, when the ignition is switched on, current also begins to flow through the heating wire to chassis ground. The resulting heat causes the bimetallic strip to change shape and “open” the points. This breaks the current flowing to the “I” terminal and through the heating wire. The voltage on the “I” terminal drops to zero (0) volts when the points open and the heating wire cools. Without heat the bimetallic strip returns to its original shape closing the points. This restores current flow to the “I” terminal and the heating wire. The cycle repeats several times a second. The result of this on-off cycling produces a reduced “average” voltage on the “I” terminal. The voltage is not a steady 10v, but switching occurs with a frequency that approximates 10v. Because of this fast switching, it is virtually impossible to measure the operating voltage of a stabiliser directly using a volt-ohm meter. Now for the interesting bit....... All the above can be replaced with a little device called a 10volt regulator This little device can be fitted within the old Stabiliser for an origional look The old unit can be dismantled by bending back the tabs on the side of the casing and removing the bottom section. This shows the old bimetalic strip as discussed above. This is bimetalic strip is removed and the regulator replaces it being soldered to the contacts. Carefully place the circuit board back into the housing. Use pliers to gently fold the sheet metal back to secure it. DO NOT allow the short wire to become pinched. Test your work. Connect your vehicle’s ground to the case of the stabilizer. Connect battery voltage to the “B” terminal. Connect a volt-ohm meter between the “I” terminal and chassis ground. If you do not observe 10v you will need to open the unit up and check the circuit again. Edited April 30, 2009 by AJay Quote Link to post Share on other sites
matk 17 Posted April 29, 2009 Report Share Posted April 29, 2009 Sounds like an excellent solution to a constantly recurring prob, well done! Quote Regards Mat Link to post Share on other sites
AJay 1 Posted April 29, 2009 Author Report Share Posted April 29, 2009 The finished item This can then be reinstalled in the car with the case attatched to origional fixing as this provides the ground throught the case. The Voltage stabiliser filter (a small black box installed between the regulator and the instruments) can now be removed, this was used to proved the instrumenst with something resembling a smooth dc supply. The whole cost of this conversion was 49p The voltage regulator came from CPC http://cpc.farnell.com/stmicroelectronics/...equestid=531009 I now have rock solid water temp and fuel gauges Quote Link to post Share on other sites
eengel1 0 Posted April 30, 2009 Report Share Posted April 30, 2009 well done, and well documented ! Quote Link to post Share on other sites
USAndretti42 314 Posted May 1, 2009 Report Share Posted May 1, 2009 Or you could buy a solid-state regulator that looks just like the original piece from JAE in California. Quote S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE Link to post Share on other sites
AJay 1 Posted May 1, 2009 Author Report Share Posted May 1, 2009 Or you could buy a solid-state regulator that looks just like the original piece from JAE in California. For less than a Dollar?? Quote Link to post Share on other sites
deverett 9 Posted March 31, 2012 Report Share Posted March 31, 2012 Just followed the link to the regulator. This part will stop regulating when the input voltage drops below 12.5v. That means at 12v you are getting out 9.5v and at 11.5v you get 9v. Worth noting when you are idling or just have accessories on. These things are known as linear voltage regulators. If you want stable voltage even when the battery is discharging, you need a switch-mode regulator. Dave Everett Quote Link to post Share on other sites
civi 0 Posted May 26, 2014 Report Share Posted May 26, 2014 @Ajay, as mentioned in the post above, it can’t work at lower voltages. It can only work if you already have a stabilized 15V power supply in your car somewhere. Since most models probably will just have a 12V supply to operate from, a small voltage regulator circuit has to be used in that case. Most switch-mode supplies will require a small circuitry with it which won’t be that easy to fit it. Quote Link to post Share on other sites
pete 1,913 Posted May 26, 2014 Report Share Posted May 26, 2014 @Ajay, as mentioned in the post above, it can’t work at lower voltages. It can only work if you already have a stabilized 15V power supply in your car somewhere. Since most models probably will just have a 12V supply to operate from, a small voltage regulator circuit has to be used in that case. Most switch-mode supplies will require a small circuitry with it which won’t be that easy to fit it. original posts are 5 years old Quote hindsight: the science that is never wrong Link to post Share on other sites
sanj 12 Posted May 30, 2014 Report Share Posted May 30, 2014 The LM2940T-10.0 only drops 0.5V, or 0.2V at lower currents. Quote Visit Sanj's Lotus Esprit Turbo SE pages Link to post Share on other sites
davidmgoodson 0 Posted March 9, 2015 Report Share Posted March 9, 2015 Thanks for your post. I have a 1967 Series Land Rover with similar gauges and the voltage regulator recently shorted out (in the middle of a busy intersection, naturally). I followed your instructions except I did not bother to incorporate the regulator housing since I am not concerned with aesthetics. The regulator I used is a 1.0 amp 10 V (NTE1953) . The problem I have now is that the gas gauge reads "full" at all times. Since I am not an electrician I am not sure why. I tried reversing the polarity but then it reads "empty." Thanks for any advise. I would really like to keep a solid state regulator if I can figure out this issue rather than go back to the old fashioned one. Sincerely, Dave G. Quote Link to post Share on other sites
redshift 32 Posted March 17, 2015 Report Share Posted March 17, 2015 Hi Dave The gauges are really quite voltage sensitive and a few 100mV will have them moving. Yours are clearly over-reading with the regulator that you've made which suggests the voltage it too high. Have you checked the output because it sounds like it could be short-circuit and giving you the full battery voltage? Quote Link to post Share on other sites
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