Temp and Fuel Guage

[LLAngus]

I have a temp guage and fuel guage giving me fits. Can it be the voltage stablizer? If it is where is it and how can I test it? Any help would be appriciated.

 

[David_DuBois]

The voltage stabalizer is on the forward bulkhead behind the speedo and tach. To test it, you should see system voltage (12 to 14 volts) on the green wire. The green with tracer color on it will have an on and off voltage that is the same. The way the stabalizer works is by switching the input voltage on and off such that the average voltage is always about 10 volts. The switching is accomplished with a switch that is comprised of a bi-metalic blade that is wrapped with a resistance wire (just like the turn signal flasher). As current is drawn through the resistance wire and the switch, the bi-metalic blade is heated, causing it to bend out and brakes the contact. As the blade cools it straightens and again makes contact. The more current drawn, the faster the on/off cycle occures, giving a higher average voltage to make up for the voltage drop caused by higher current flow. The on/off cycle is such that the average is about 10 volts, regardles of current draw within specification of the system. If someone has replaced the original stabalizer with a solid state unit, the stabalization is done by varying the output of a transistor and will have a steady output voltage (instead of the on/off cycle or the original) of 10 volts.
Cheers,

 

[PAUL161]

[ QUOTE ]
I have a temp guage and fuel guage giving me fits. Can it be the voltage stablizer? If it is where is it and how can I test it? Any help would be appriciated.

[/ QUOTE ]
If the stabilizer is original, 30+ years old, I'd get a new one and change it. That will eliminate that problem. There not expensive and easy to change. Usually over your left foot on the inside fire wall. If they start to go bad, your gauges won't work right and their not repairable, their a throw away item. /ubbthreads/images/graemlins/cheers.gif PJ

 

[dklawson]

Others have described the system well above so I won't repeat anything they've said except to reinforce the point that because the stabilizer is switching on/off very fast, a digital volt meter won't be able to measure the output well if at all. Even analog meters can't always measure the stabilizer output voltage.

For more information on the stabilizer and how to test it and your gauges download my PDF from:
https://home.mindspring.com/~purlawson/files/SmithsVoltageStabilizer.pdf

 

[David_DuBois]

"Even analog meters can't always measure the stabilizer output voltage." I am going to disagree with Doug's statement above (although he and I may be saying the same thing different ways). An analog meter is the only thing that will give a reliable measurement of the output. A digital meter will only give a reading of what the voltage is at the sampling time of the meter, so it will try to read instantanoius voltage during the sample period. This many be zero, 12 volts or anywhere in between (unless you have one of the really expensive digitals that will read true RMS voltage) . The analog meter will read average of the voltage at the output, which is slightly lower than the RMS voltage and for this application, is a much more accurate indication of what the instruments are actually seeing. Generally, the stabalizer will be working and the output voltage will be somewhere around 10 volts (taking into account of the inaccuracies of the meter used) or not at all, giving an output of zero volts or the full system voltage. I have not seen one of the adjustable stabalizers, but one of those would sure make calibrating the gauges easier.
Cheers,

 

[dklawson]

Dave and I don't disagree at all, but perhaps I should clarify what I mean and comment on what I've seen.

As Dave said, the digital meters have a sample rate that may only be a few times a second and they really can't hope to display the average voltage coming out of the stabilizer. As mentioned, the analog meter will average the output and give a steadier reading... to a point.

I've worked on a couple of stabilizers where the output was switching on and off SLOW enough that there were perceptible swings between 0V and +12V. Think of this as the stabilizer switching on and off like a clock (tick-tock-tick-tock) as opposed to their normal high speed on/off (which is more like "buzzzzz"). When the switching is really slow like that the analog meter needle will swing wildly up and down and it's hard to determine what the average stabilizer output voltage is.

That still may not be clear but I just want to point out that I agree with Dave. It's just I've seen a few instances where even an analog volt meter couldn't display the stabilizer's output.

Regarding the adjustable stabilizers... I think they are all adjustable but some of the earlier ones had the adjusting screw pass through the insulator plate. The screw was secured with glypt or glue so it wouldn't move. Remove the goo and you can adjust the gauge on the fly. I believe it was the later stabilizers where the adjustment has to be made by opening up the stabilizer case and turning the contact with a pair of needle nose pliers. It's not convenient but it can be done. I repaired one like that for a friend with a positive ground Mini.

 

[PAUL161]

Doug, I took one apart just to see how it was made and what made it go bad. The points had a white powder on them and wouldn't make contact. After cleaning the points, it started working. But for 17 bucks, I couldn't see putting it back. It still was 30 years old. I put a new one in and it works fine. PJ

 

[dklawson]

I had to resurface the contacts in my friend's stabilizer to clean them up. Your old unit sounds similar to his. I also made him a positive ground solid-state regulator for his gauges... but he wanted to use the original part. To each his own.

Another of my Mini owning and servicing friends has told me that he has seen as many as 4 out of 5 NOS units turn out to be DOA. I suppose that's why I started poking around inside them. I wanted to understand what could go wrong if the failure wasn't associated with parts burning up.

 

[David_DuBois]

Doug - You are correct, a slow operating stabilizer would still be switching to quickly for the needle on an analog meter to follow, but not fast enough for it to obtain an average reading. Obviously the only solution is to get a $900 o'scope to view the pulses - hmmm, makes a new stabilizer or a solid state replacement look much better. By he way, I saw somewhere of somebody placing a solid state regulator inside the original case.

The contact degradation is the same thing that plagues the points style SU fuel pumps. The points will develop a film that, if not cleaned off by the current passing through them, will eventually insulate the contacts one from the other. This is especially a problem with cars that are not driven regularly. Plus, over time, the points will just flat out wear away.
Cheers,

 

[dklawson]

In most installations the solid-state regulator or Smiths stabilizer isn't visible once installed. For those applications I've encouraged people (with negative ground cars) to simply solder leads to the u7810 chip and use the hole on the chip for an earth/mounting screw. Where the stabilizer remains visible (like on the Mini and certain Triumph models) I've put the 7810 chips inside the old Smiths cases. It's more work but if looking correct is necessary, it's worth the effort.

 

[LLAngus]

I understood everything you guys were saying. Use to work as a manager at the "old" Radio Shack where we had actual parts. (once got a local radio station back on the air with a small capacitor). I will get a hold of Tony as soon as I get the rest of my parts installed. Thanks again guys.
/ubbthreads/images/graemlins/thirsty.gif