View Full Version : Voltage Stabilizer (Mal)Function

12-23-2009, 04:31 PM

What role does the voltage stabilizer fill? In an earlier post, I determined the odd behavior of my fuel and temp gauges were due to a faulty voltage stabilizer - which I have yet to have time to address. In addition, despite having a good strong battery, I also experience these other issues at idle (but go away when engine revved): horns don't work, turn signals don't fire and headlights barely brighter than a candle. Normally, with low generator output at idle, I would still expect the battery to drive this ancillaries just fine.

My understanding of electrical issues is really basic. Is it possible these other issues are related to the faulty VS as well?



12-23-2009, 04:58 PM
The voltage stabilizer is a crude voltage regulator that is supposed to supply 10 volts to the gauges. They use it because of the fluctuations that can occur in the charging system, especially the usual drop in voltage at low engine speeds. I have a feeling the your battery at idle will show LOWER then ten volts. This would explain both the gauge fluctuations and the other electrical issues you're experiencing at idle.

Put a voltmeter on the battery connections with the engine idling and see what you get. The rev it up to where your problems go away and see what you get.

Edit: Do the lights and horn etc. work OK when with the engine not running?? What does the battery voltage read without the engine running??

12-23-2009, 05:01 PM
Aloha Bob,

The voltage stabilizer provides a constant voltage (usually 10V) to the fuel and temperature gauges. Without the voltage stabilizer, the gauges will fluctuate depending on generator output. It is most apparent with the temperature gauge where high engine revs at highway speed will indicate high temperatures on the gauge, yet stopping for a traffic light and the engine at idle the temperature will drop rapidly down into the cold range. Early voltage stabilizer were basically a thermal switch that opened and closed constantly with the result being a average voltage output in the 10V range. Newer solid state circuitry is available from most of the usual LBC parts supplier. They use a solid state voltage regulator and are specific for either positive or negative earth applications.

The voltage stabilizer I don't think is related to your other electrical issues. That seems to me to be low voltage output from your generator, poor/corroded connections in the wiring or a combination of both.

12-23-2009, 06:50 PM
Just to echo and maybe clarify what Art & Dave said; the voltage stabilizer has nothing to do with anything, other than the temp and fuel gauges.

Personally, I would start with the engine off, checking with a good voltmeter (or DMM) to see what is happening. Everything should work correctly just from the battery. This is also effectively "normal" at idle, the generator just doesn't do much at such low rpm.

If Art is right, and your battery voltage is going below 12v, then either the battery is defective (even new batteries are sometimes defective) or it is deeply discharged. Get it fully charged (either take it to a shop or put it on an AC powered charger) and check again. If it won't hold at least 12.0 even with the headlights on, double-check the voltmeter accuracy and then get another battery. With only a light load (just ignition say) you should see 12.6 volts.

Oh yeah, if the weather/battery is really cold, like freezing (0C/32F), you can subtract 0.5 volts from the numbers above. That still means you should be seeing at least 11.5 at the battery with the headlights on and a nearly fully charged battery.

Once the battery voltage is OK, then you can start checking the voltage drop to the various devices. For headlights, I'd check the voltage at the point where the subharness joins the main harness, near the horns on each side. Find the wire that powers the headlights, and meter the voltage from it to the wire in the ground clip. This should be within 0.5 volts of what you measured at the battery; if not, there is a bad connection or high resistance somewhere between there and the battery.

The horns & turn signals are sometimes very picky about system voltage; I've had similar problems on my TR3A. If the horns won't sound clearly with 10v at the terminals, you need to disassemble them to clean the contacts & pushrod, followed by adjusting the contacts.

One place where I've had trouble is where the wires join the ammeter. Vibration & old age seem to make the individual strands of wire break right where the screws clamp onto them, resulting in just a few strands actually carrying current. Might be worth taking those joints apart for inspection, as everything but the starter (on a 4A) sucks power through the ammeter when running from the battery.

Might also be worth checking the voltage between the A and A1 terminals on the control box, with the engine off and the headlights on. Should be less than 0.1 volts here, if it's higher there may be a problem with the control box itself.