Voltage stabilizer

[middleagecrazy]

Help
Dad left the Spitfire with me to try and straighten out the wiring. Here is the issue. Number one is that the gas gauge moves with the blinkers. It is a new gauge and sending unit. I can't find anything in the manuals about the voltage stabilizer that is in the circuit that is on the back of the tach. I check Moss Motors and they list the Voltage stabilizer as NA. I understand that NA means "NO LONGER AVAILABLE" This is the same issue we had before replacing the sending unit and the gauge. Doe's anyone know the function of the stabilizer? I Ohm'ed it out and it only has .003 ohm of resistance across the terminals however it has .008 ohm from the terminals to ground/earth. It seems logical that the purpose of the stabilizer would be to filter line noise from the circuit. Anyone have a suggestion as to a solution.

Thanks in advance
Anthony

 

[Dave Russell]

The so called voltage stabilizer is litte more than a specialized blinker. It's contacts open & close to maintain an AVERAGE voltage of 10 volts or so as measured over a period of time. If you just put a meter on it, it would go from 12 volts to zero periodically but the average would be 10 volts. Since the gages are thermal, it takes time for them to respond to the changes of supply voltage & they don't respond to the relatively rapid blinker/regulator switching changes.

I don't think anything but the gages should be connected to this circuit. It appears that the turn signal feed may somehow be connected to this circuit, instead of to a solid 12 volt supply.
D

 

[Adrio]

I ran a bench test on a gauge to and sender unit to determine what voltage would be "equivalent" to the old thermal voltage stabilizer. What I cam up with is a 12V solid state regulator with the ability to deliver enough courrent for all your gauges works great. That is what I used for mine in place of the thermal unit and it has been working perfect for over 10 years. I built mine but I think I saw some for sale online some place.

 

[70herald]

HI Anthony
As was pointed out, the "stabilizer" really just turns the power on and of at a high frequency. The equivalent "steady" voltage to get the gauges to read correctly is about 10 volts.
The easiest way to get this is to use a 7810 voltage regulator. It only has three leads. Input, ground and output. It has more than enough capacity for all the gauges on a spit. The data sheet says you need a capacitor and other stuff, but for this application it is overkill all you need is the regulator. Note that the heat sink is connected to ground so be careful where you place it. I just soldered mine into the can from the old regulator and hooked it up with the original contections. This is what I have in my Herald.
By the way, the standard regulator is available but is harder to find and will cost way more. The 7810 is probably available at Radio Shack or other elecltronics supply shop. you can probably get it for about $1.
Yisrael

 

[danmas]

Keep in mind that the solid state regulators won't have the temperature compensation that the original does, so your gauges will be off a bit as the temperature changes.

 

[dklawson]

Dan, you've made the temperature compensation argument before... but I'm curious how much error this will make on Smiths instruments. I've seen Smiths stabilizers with outputs ranging from 9 to 11 volts. Would you expect more than such a 10% error from temperature compensation?

As for the 7810, that chip isn't available from Radio Shack but it is available from sources like Mouser, DigiKey, and Newark Electronics (all of whom will sell through the web).

Download my PDF from:
https://home.mindspring.com/~purlawson/files/SmithsVoltageStabilizer.pdf
It should help you troubleshoot the gauges and help you either calibrate or replace your stabilizer.

 

[Dave Russell]

I think you're missing the original question.

"Here is the issue. Number one is that the gas gauge moves with the blinkers."

Not which IVR is the best. The "blinkers" were never meant to be run off of the IVR & should have no effect on the gages.
D

 

[dklawson]

Sorry Dave. Good point.

As Dave said, make sure that you have hooked the blinker/flasher relay up correctly. It shouldn't have a direct connection to the voltage stabilizer... certainly not to the 10v side of it. BTW, the 12v side of the stabilizer has spade lugs marked with a "B" for battery while the gauge terminals on the stabilizer are marked with "I" for instruments.

 

[middleagecrazy]

Thanks for the response. I have disassembled the stabilizer and found that there was corrosion inside at the point of Ground/Earth. I have cleaned the unit and plan to install it for a test this evening. While I had it out I did the ohms test to verify that the unit was not broken. There was also corrosion found on the inner points. This was cleaned up also. I should be able to respond with the test results tonight.
Thanks Anthony

 

[dklawson]

The points inside the stabilizer are factory preset to give a time averaged 10v on the "I" terminal. Once you sand or dress them to remove corrosion/pitting you will probably need to recalibrate the stabilizer. That procedure and the necessary equipment is discussed in my PDF (link above).

 

[middleagecrazy]

Well after reading the information supplied by everyone. I find that sense the Gauge is an aftermarket unit the Voltage Stabilizer was not needed. However it was necessary to correct the voltage to obtain the proper read out of the gauge. I found that in my particular instance this could be accomplished by installing a 100 Ohm resister in the power wire that feeds the gauge. Now when I have a quarter of a tank the gauge reads one quarter. I thank everyone that fed me the information needed to diagnose and resolve my dilemma.

Thanks
Anthony