Smiths "voltage stabilizer"

Jim Rosenthal · 27th November 2010, 09:51 PM

When Ron wired the instruments for my GT40 he used the "authentic" Smiths gauges that I had bought several years ago. This included an oil pressure gauge, a fuel gauge, and I think a water temp gauge which are all supplied with (I guess) a modulated 12 volts from the Smiths voltage stabilizer. We have just started to get everything working, and it seems to be evident that the three gauges that are wired to the voltage stabilizer don't work as they ought to.

Does anyone have any particular knowledge of these items and what they do, and is the voltage stabilizer necessary? I will call Nisonger Instruments on Monday, but I thought I might get some information from those more informed than I (which is just about everyone, on this particular topic) We followed the wiring diagram provided by Smiths exactly. I have no idea whether the thing itself is working as it ought to be. Also, does anyone know whether the case of the voltage stabilizer needs to be grounded? (I don't have the wiring diagram handy as all the cars' paperwork is with the car, not here)

Alan Watkins · 27th November 2010, 10:43 PM

Quote:

Originally Posted by jimbo

....supplied with (I guess) a modulated 12 volts from the Smiths voltage stabilizer. ....Also, does anyone know whether the case of the voltage stabilizer needs to be grounded?

If you want to know what the voltage stabilizer story is, there's a good description here: How To: Replace Your MGB Thermal Voltage Stabilizer

Upshot is they put out an average of 10V, but that average is established over a very long interval by oscillating between battery voltage and zero (!). OK, nothing unusual about that; that's called switch-mode voltage regulation and it's ubiquitous now (since the 90's or so). What's odd to us modern folk is that the oscillation takes place at a humany observable rate, unlike modern ones that run anywhere from 10s of kilohertz on up.

I don't know if your particuilar Smiths gauges require 10V. While you're figuring that out you could just connect them to battery voltage. They'll work but may read high. If they don't require "stabilisation" but you use it anyway they will read low. Actually, that might be a way to tell if you need one.

The voltage stabilizer definitely needs to be grounded somehow. The Lucas unit in the article definitely needs its case grounded so yours probably does as well.

Jac Mac · 28th November 2010, 01:12 AM

The unit is usually earthed by fitting to the body of the gauge cluster in the car in question ( I worked in a Ford Service shop during the late sixties/early seventies & Im talking all english fords from that era... MKI/II Cortinas, Zephyrs, Escorts etc etc.
As Alan has pointed out if one was to observe the fuel or temp gauges while the key was on the needles of these gauges would move slightly due to the voltage change.... even got the odd customer who would notice & ask for it to be corrected!

Having said that Im not 100% sure that some of the aftermart 2" gauges required 10 volts, might have been 12v.

Jac Mac · 28th November 2010, 01:15 AM

The unit is usually earthed by fitting to the body of the gauge cluster in the car in question ( I worked in a Ford Service shop during the late sixties/early seventies & Im talking all english fords from that era... MKI/II Cortinas, Zephyrs, Escorts etc etc.
As Alan has pointed out if one was to observe the fuel or temp gauges while the key was on the needles of these gauges would move slightly due to the voltage change.... even got the odd customer who would notice & ask for it to be corrected!

Having said that Im not 100% sure that some of the aftermart 2" gauges required 10 volts, might have been 12v. Temp gauge sender units also had variations for different cars etc, strange since they were being used with the same gauge in the panel...eg a MK3 4cyl Zephyr would require a different sender to its 6 cyl stablemate.

Jim Rosenthal · 28th November 2010, 07:32 AM

Thanks to all. After I posted this thread, I surfed around a bit and came up with some other articles; there's a good one in Mini Mania, a site I am somewhat familiar with since I have a classic Mini Cooper as well. From what they describe, the voltage stabilizer may be working, but possibly its case needs to be grounded, at least to the gauges it supplies. Or maybe just to the grounding lug of the chassis. We'll see, and I am interested to hear what Nisonger says- they are supposed to be the Smiths authorities in the USA. Thanks to all for the help, and I will report back as soon as I know something.