How to test voltage regulator/stabilizer

[IIA]

I need to test the voltage regulator/stabilizer in my 1970 IIA. I guess the first question is which to I have? There's a black box on the engine side of the bulkhead that clearly says "voltage regulator" but inside the dash behind the instrument panel there's something that looks like it could be a stabilizer (see picture, yes it's upside down). Could I have one of each?

Then, how do I test it (them)? I read in another post (http://forums.roversnorth.com/showth...tage+regulator) that it should have 12-13v going in and an average of 10v going out. I know this is a basic question, but how do I test that? (I have digital and analog meters).

[lumpydog]

I need to test the voltage regulator/stabilizer in my 1970 IIA. I guess the first question is which to I have? There's a black box on the engine side of the bulkhead that clearly says "voltage regulator" but inside the dash behind the instrument panel there's something that looks like it could be a stabilizer (see picture, yes it's upside down). Could I have one of each?

Yes - trucks before a certain period (1972ish/pre-Alternator) have a Voltage Regulator (engine bay) and a Voltage Stabilizer (behind the instrument panel).

Then, how do I test it (them)? I read in another post (http://forums.roversnorth.com/showth...tage+regulator) that it should have 12-13v going in and an average of 10v going out. I know this is a basic question, but how do I test that? (I have digital and analog meters).

The Stabilizer is mounted to the bulkhead (behind the instrument panel) on 2As and on the back of the Speedo in Series 3 trucks. It does a simple task - turn 12V into 10V - which is what the temp gauge and fuel gauge need to run properly. It's a weird little device in that it rapidly cuts in/out so that an average of 10V get output. For that reason, a digital multimeter won't work to test it. An analog, when connected to the "I" post (light green wire on it to the gauge) should average 10V. If it doesn't, I'd recommend the solid state replica Voltage Stabilizer sold by Moss Motors. It puts out a rock steady 10V that can be read by a Digital Multimeter.

To test the Voltage Regulator, that's a little more involved. It has two jobs. First charge the battery and second, cut over from the battery to the generator (dynamo), as the vehicle's primary power source, at about 13Volts. You need to make sure that what the Regulator outputs to the the battery won't fry the battery. And - you need to make sure that the cut-out clicks over at 13 Volts. My Regulator is set to provide about 14.2V of charging power to the battery at about 2500 RPM. This is different than the published spec - which is higher but not needed for today's batteries. If you set the output too high, you will boil the electrolyte in your battery and it will seep out through the vents.

A few good articles on tuning the RB106 (model of Lucas Voltage Regulator in later model Rover):

http://www.mg-tabc.org/library/lucas..._box_tests.pdf

http://www.sabra.be/GB/Tecnics/RB106.htm

https://www.youtube.com/watch?v=SxJNCigb0uA (this is a series)

[IIA]

I just tested the stabilizer and the needle on my meter stayed about 11v for a second or two then started bouncing around from around 0 to 10v. So I guess I need a new one.

[kb1iaw]

I just tested the stabilizer and the needle on my meter stayed about 11v for a second or two then started bouncing around from around 0 to 10v. So I guess I need a new one.

I'm pretty sure that's how it should behave. That being said I replaced mine with a $1.50 IC-7810.

http://www.ken555.plus.com/gtm/regul...onversion.html

[SafeAirOne]

I just tested the stabilizer and the needle on my meter stayed about 11v for a second or two then started bouncing around from around 0 to 10v. So I guess I need a new one.

The voltage stabilizer is a bi-metal strip. It takes a second to heat up, then begins to bend and unbend, breaking and then making contact to complete the circuit repeatedly while energized. This calibrated turning on and off the 12v circuit makes it seem like 10v coming out of the stabilizer, though it is realy switching 12v on and off a lot of times.

A digital meter can react to the voltage change too fast and may not read this well. An analog voltmeter can't react fast enough to show the 0-10v switching and should read a steady 10v if all is well.

[IIA]

An analog voltmeter can't react fast enough to show the 0-10v switching and should read a steady 10v if all is well.

That's about what I thought. Since mine doesn't show a steady voltage, I went and ordered a new one from Moss. We'll see if that solves the problem I've been tracking down (weird fuel gauge readings).

[IIA]

Here's a great article on voltage stabilizers and how to test them - wish I'd seen this sooner:
http://www.minimania.com/Voltage_Stabilizer

Supplemental Information & Instructions forC34770A Voltage Stabilizer, Negative Ground 13H3554 Voltage Stabilizer, Positive Ground
A Little History

Many British cars produced through the mid 1960s have moving-iron gauges that are fed directly from the battery through a wire that is live when the ignition is switched on. Fuel gauges of this type have two characteristics; the needle jumps off empty as soon as the ignition is switched on, and the needle bounces all over the place when you hit a bump. The readings on these gauges are also affected by the battery voltage, which means they may be erratic or inaccurate as the voltage varies. The new gauges introduced by Smiths in the 60s were based on bimetallic heating elements, and they eliminated these problems. These gauges behave differently; the needles of the fuel or temperature gauge drift up off the lowest reading slowly when the ignition is turned on. The new gauges required the addition of a voltage stabilizer. The original Smiths voltage stabilizer is simply a mechanical voltage regulator that takes battery voltage (13.8 -14V) and reduces it to 10 volts. Inside the stabilizer is a bimetallic strip, an insulated heating wire coil, and contact points. Over time, they fail for a variety of reasons and repairing them is problematic. The Smiths voltage stabilizer came in many configurations- the type and number of terminals depended upon the application, but that all perform the exact same function, providing the gauges a steady 10V.

About the Voltage Stabilizer

The supply of genuine Smiths stabilizers has dwindled to a few part numbers. The ones we have carried in recent years have varied considerably, even when ordered from the same source under the same number. They have had a variety of terminal combinations, which is confusing, and the reliability of some has been suspect.

Reproducing all the original stabilizers would be cost prohibitive, so we set out to reproduce a stabilizer that would meet the needs of all the various applications. We also decided to go to solid state components to improve the quality and simplify the construction, which kept the cost down. The case (1A) is a clone of the housing used on the late Smiths stabilizers. It is grounded to the chassis through the mounting bracket (1B). The instrument terminals are indicated by an “I” (1C) and the power in or battery terminals are indicated by a “B” (1D) just as they always have been. We provide one male spade (3A) and one female spade connector (3B) for both terminals to make it
easy to hook up the original wiring connectors. The solid state components are polarity sensitive and we therefore have a positive ground and a negative ground version of the stabilizer. The polarity of the unit is clearly indicated (2A) and it must be strictly observed.

Before You Replace the Original Stabilizer…

Let’s make sure that is the problem, using the gas gauge to diagnose the problem.
Before you do any testing:

1. Locate the stabilizer. Consult your workshop manual for the location.
2. Remove the wires from the stabilizer, marking them clearly so you can connect them correctly later.
3. Remove the stabilizer and clean all the electrical connections, including the ground connection- the points of contact between the mounting tab and the body sheetmetal.
4. Reinstall the stabilizer, and reconnect the wires.
5. Using a voltmeter, measure the voltage at the battery (this is the battery voltage referred to below)

With ½ tank, Gauge Reads High

1. Remove the wire(s) from the “I” terminal
2. Connect a volt meter between the “I” terminal and a good clean ground on the chassis.
3. Turn on the ignition.
4. If the voltmeter shows
5. 
   
   • the same voltage as you measured in step 1, AND
   • it remains there for 20-30 seconds without changing it is probable that the points inside the stabilizer are not opening and you should replace it.
   
   

With ½ tank, Gauge Reads Low

Rule out a problem with the sending unit first.

1. Make sure the wire(s) are properly connected to the sending unit.
2. Verify that there is adequate fuel in the tank.
3. Disconnect the wire on the sending unit that goes to the gauge (usually green-black).
4. Switch on the ignition and touch the sending unit wire to a good clean ground- the needle should rise slowly to the full position. If it does, the sending unit or the sending unit ground is suspect and needs to be checked out.
5. If the gauge still reads low, the stabilizer output voltage is low and you should replace it.

With ½ tank, Gauge Reads Empty

1. Remove the wires from the stabilizer, marking them clearly so you can connect them correctly later.
2. Locate the wires that were connected to the “B” terminal
3. Connect a volt meter between the “B” wires and a clean ground on the body sheetmetal.
4. Switch on the ignition and observe the volt meter reading and compare it to the battery voltage.
5. If the voltage at the “B” wire is less than battery voltage, the wire connected to “B” is damaged or broken and that must be found and corrected.
6. If the voltage at the “B” wire is the same as battery voltage, switch off the ignition.
7. Measure the resistance of each of the “I” terminal wires from end to end. Resistance over a few Ohms indicates a problem in the wire that must be corrected.
8. If no problems are found with the wires and the gauge still reads empty, reconnect the voltage stabilizer.
9. Perform the “Gauge Reads Low” series of tests listed above.

Installation Tips

1. Verify that the polarity of the stabilizer you have matches to polarity of the vehicle.
2. Locate the original stabilizer. Consult your workshop manual for the location if necessary.
3. Remove the wires from the stabilizer, marking them “B” and “I” so you can connect them correctly later.
4. Clean the electrical connectors on the wires.
5. Remove the original stabilizer, and clean the ground connection on the body sheetmetal.
6. Install the new stabilizer in the original location, and secure it with the original screw and washer.
7. Connect the wires marked “B” to the “B” terminal. Connect the wires marked “I” to the “I” terminal.

[lumpydog]

Good doc. This is the Moss Motors trouble shooting guide - which they seem to have taken down. I have the PDF but it was too large to upload here.

[mearstrae]

Here's a good link to rebuilding a stabilzer with modern components: britishv8.org/articles/mgb-voltage-stabilizer.htm
I know it says MGB, but these were used in every early British car I've seen, my '70 Rover(car) has the same one.


'99 Disco II
'85 R.R.C. Lwb (Gone...)
'76 Series III Hybrid 109
'70 Rover 3500S

[ninescorpions]

that guide is freakin sweet! I will be using it in the coming days!