How Does a Voltage Stabilizer Work?

[4129R]

I have no reading on either my fuel gauge or my water temperature gauge.

My first thoughts were the voltage stabilizer is not working.

I bought a new one, looked up how to wire it up. B = battery or ignition dark green wire, I = instruments = light green 2 wires, earth the casing.

Still nothing on either gauge.

I shorted out the dark green and light green wires and the temperature gauge started climbing.

I tested the voltage in at 12.5v and the voltage out was around 4v. I connected up the old voltage stabilizer and the voltage out was around 12.5V but neither gauge worked.

I am confused.

I can understand the fuel sender gauge might rusted up and giving no reading, but I cannot understand how the water temperature gauge works with ignition voltage, but does not work using the voltage from the I side of the stabilizer. 

[BDA]

In general, I believe the voltage stabilizer is designed provide a stable (max?) voltage of 10v. Since I’ve already exceeded my understanding this subject, I’ll refer you to an article that explains it better than I: http://lotus-europa.com/manuals/misc/electrical/gauges.html

Be sure to check out the link that explains how a “Lotus gauge works.”

[4129R]

I took both stabilizers into the garage and plugged them into a charging battery.

The voltage going in was around 13.5v.

On the old stabilizer, the voltage coming out at the I terminal fluctuated repeatedly from 12.1v down to 0 then back up to 12.1v at around a 1 second cycle.

On the new stabilizer there was 0v output all the time at the I terminal.   

[4129R]

In general, I believe the voltage stabilizer is designed provide a stable (max?) voltage of 10v. Since I’ve already exceeded my understanding this subject, I’ll refer you to an article that explains it better than I: http://lotus-europa.com/manuals/misc/electrical/gauges.html

Be sure to check out the link that explains how a “Lotus gauge works.”

Thanks for that information. A stable +10v comes out of the I terminal on neither stabilizer. 

[BDA]

Yeah, it appears that your stabilizers are toast but it's curious that your new one is since I believe all the new ones are solid-state which should be much more reliable than the old ones (I believe they were electro-mechanical but I think the articles I posted and mentioned explain that pretty well). Anyway, your new one is clearly busted and you should send it back or just try again with another.

There is an article on building your own if you want to go that route (http://lotus-europa.com/manuals/misc/electrical/vregulator.gif). I think the instructions in that article were published before the solid state stabilizers were commercially available but from what I can tell, the instructions tell you how to make what you get when you buy a commercially available stabilizer.

[Dilkris]

This is interesting - I have just been along this journey. Couple of days back I posted "Dilkris Update - Back at it!" (but I put it in 'Technical Articles' which was probably wrong) - anyway it was about me starting the engine finally after some time away from the project. 
I wired up a temporary temp gauge circuit,(without the voltage regulator), and upon the engine running it was showing 130 degrees - I then realized that this 'magic cube' was not an option as it does, amongst other things it seems, reduce voltage to the temperature and fuel gauges to 10V.
I have now installed it, (original item - see pics), and temperature now stabilizes at just over 90 degrees.
If you need any more readings please let me know as it is presently very accessible. 
Also in researching this component on line - (it was made by Smiths Motor Accessories BR1311/00) - it seems that how it is mounted is important to it's operation - ie: it appears it can only be mounted one way - please don't ask me why - I followed the instruction and it works... 
Please refer photo of BR1307-00NEG which I assume super cedes the original - read description               

[4129R]

Whoopsie..........

You are purchasing a Smiths Gauge Voltage Stabiliser For MGB, Triumph TR4 & Spitfire MK1-3

 Regulated 10 volt supply - Positive Earth ONLY

I never knew those cars were +ve earth.

[Dilkris]

You are purchasing a Smiths Gauge Voltage Stabiliser For MGB, Triumph TR4 & Spitfire MK1-3

I'm lost - where do MGB's, Triumph TR4's and Spitfires come into the equation.   
What have I missed?

[4129R]

You are purchasing a Smiths Gauge Voltage Stabiliser For MGB, Triumph TR4 & Spitfire MK1-3

I'm lost - where do MGB's, Triumph TR4's and Spitfires come into the equation.   
What have I missed?

Lucas 12v voltage stabilisers on eBay.

[RoddyMac]

You are purchasing a Smiths Gauge Voltage Stabiliser For MGB, Triumph TR4 & Spitfire MK1-3

 Regulated 10 volt supply - Positive Earth ONLY

If you do a search for the part number Dilkris posted, it is indeed a negative earth unit.  The NEG in the part number should be an easy tell.  From what I recall, the difference between various part numbers was the obvious positive/negative ground, and mounting tab location.  For the electo-mech units, you do have to keep them in the correct orientation, hence the arrow or the word TOP, the newer solid state units should be able to be mounted in any orientation.  Also, some units are still electro-mech, not all are solid state.

[BDA]

MGs and Lotus (Jaguar too?) both use Smiths gauges (I believe Jaeger and Smiths merged at some point). Besides gauges, Lotus utilized several parts from MG (inside door handles), Jaguar (TC outside door handles and tail lights), and Triumph (steering rack, front uprights, front hubs) and surely many other smaller parts.

As for the orientation of the gauge making a difference, I would guess that the weight of the needle and associated attachment could be the cause. Catching up on how Lotus gauges work (which is to say how Lotus Smiths gauges work) might help you understand (http://lotus-europa.com/manuals/misc/electrical/meterinfo.html).

[jbcollier]

Instrument voltage regulators come in two "flavours".  One that puts out 10V and the other then puts out a pulsing 12v.  It is very common to buy duds.  Sounds like your original one was working just fine.