Testing Voltage Regulators
My Spit
Tips
Projects
Links
Know that somewhere, sometime, this demon of Lucas will leave you stranded on the side of the road scratching your head at a dead battery. You had better be on good terms with your charging system, and since this is the brains of the entire thing, it's a good place to start. This guide covers the identification, operation, and testing of the standard Lucas Control Box or Voltage Regulator installed on all Triumph Spitfires (and many other models) that have a DC Generator.
First off we need to identify the box. Go ahead and remove the cover of the unit. The interior should be clean and dry. It should be really shiney and look like it just came off the assembly line. It's a sealed environment so if it appears at all dirty, discolored, or has any odd odors to it, toss it into the rubbish heap and get another. It's been compromised and won't be reliable after that.
IDENTIFYING THE COMPONENTS
Looking at the unit, the relays each have a cam adjusting gear on the back of the relays. The 'front' will be the side that has the terminals for your wires to connect to and is also facing down when the unit is installed. From left to right, the relays are:
1) Voltage Regulator
2) Current Regulator
3) Cut-out
The terminals at the bottom/front of the unit where your wires connect are also labeled with letters.
E) Earth / Ground
D) Main generator connection (usually brown with yellow stripe and 12 ga wire)
WL) Warning Light. Also the ignition light on your dash board. This is raw unregulated power so don't use it for a power source. It's only for your warning light.
F) Secondary generator connection (brown with green stripe). Connected to field coil in generator.
B) Main connection to battery. This is also where all your car's power is supplied. Big heavy 12 ga wires.
That's the layout. Now let's cover a few points before we start poking about with test lights and meters so we aren't wasting time in one area where another one should be addressed.
1) Make sure that the drive belt is tight and not slipping.
2) Check the wiring between the generator and the voltage regulator for continuity.
That's the brown with green and brown with yellow wires. Check by using the Ohms scale on your
meter and disconnecting the leads from the regulator and generator, then connecting your leads to
those wires. Any break here and you won't get any power.
3) Check that the Voltage Regulator is grounded. It needs a ground too to operate correctly.
Paint, rust, and crud can get into the physical connections and create a poor ground.
4) Test that generator! Make sure it's working first before you move to the voltage regulator.
CLEANING THE CONTACTS:
It's recommended that you clean the contacts when you have the case open. Over long service, the contacts may build up a bit of crud that can inhibit proper performance. Originally you would use glass paper to clean the contact instead of emery paper. This was because it would not wear grooves into the contact surfaces like an abrasive could. Today we have more advanced materials available. I like to use a color TV tuner spray, or any electrical contact cleaner meant for automotive use to spray down the entire unit. If you use the TV tuner spray, it MUST be labeled safe for plastics. There is nylon in this unit that can be softened if you use the wrong stuff. Automotive electrical motor cleaner is ideal. Spray the unit thoroughly. Next using a fine thin paper towel, such as you get out of restrooms, fold the towel and soak with cleaner. You can now use the corner of this to clean the contacts themselves. They may look clean, but you'll be amazed at the dark grey gunk this will pick up. Spray the entire unit again when done to clear out any fuzzies left behind by the towel. Easy, huh?
TESTING THE REGULATOR:
During this initial testing it is very important to ensure that the testing any adjustments made afterwards are done within the FIRST 30 SECONDS of starging the engine, otherwise they settings may be thrown off. The measurements you get are dependant upon temperature and after 30 seconds the unit will heat up and throw your numbers off.
First off we need to disable the cut-off coil. Slip a piece of cardstock or thin carboard between the contacts of the cut-off coil (the one on the far right as viewed with the camgear in the back of the relay). Disconnect the Warning Light wire from the box (WL terminal). Hook a voltmeter between WL terminal on the regulator and a good ground.
Start the engine and idle it at 3000 RPM. Depending upon the temperature of the air, you should get something like the following:
Ambient temperature Open circuit voltage
50F (10C) 14.9 to 15.5 volts
68F (20C) 14.7 to 15.3 volts
86F (30C) 14.5 to 15.1 volts
104F (40C) 14.3 to 14.9 volts
If you find the voltages wandering much and the engine RPM is steady, it indicates you need to go back and reclean the contacts again. If it still fluctuates, replace the regulator.
Now if the unit is steady, but it's either too high or too low, then we need to adjust the limits for the voltage range. This is where the cams on the back of the relays comes into play. We need to adjust the voltage regulator relay, which is the one on the left side of the box with the terminals out the front/down. You will need to turn this camgear to adjust the setting. View the box from the top/rear and adjust this gear clockwise to raise the level and counterclockwise to lower the voltage level. Let the car sit for a few minutes before you restart it and retest the setting. Remember that 30 second rule! I didn't and ended up adjusting things while the car was running and had readings all over the board. When it is behaving correctly, remove the cardboard from the cut-out relay.
Congratulations, it has passed test #1! Now on to test the cut-out relay.
With the WL terminal still disconnected and your voltmeter connected between the WL terminal on the regulator and the ground, start up the engine. You don't have to worry about the temperature or 30 second rule now. That part is past. Start revving up the engine smoothly. The meter should show your target voltage, but increase with the RPM's, then drop back a bit when the cut-out relays CLOSE. They were open earlier, but when you revved up the engine, the regulator needed limit the output of the generator which can put out 20+volts from getting to your system. This shunts the system and limits it to your ideal voltage. According to manuals, the meter voltage should read between 12.6 and 13.4 volts ideally JUST before the cut-out closes, or cuts out the generator. Realistically I've seen it higher, but the most important part is that the relay actually does activate and keeps the top voltage down at a reasonable level when you rev the engine up. We don't want to be overcharging the system with high voltage.
But if this isn't working, shut the engine down and check the voltage regulator. The relay on the far right as viewed from the front/down view is the cut-out relay. You may need to adjust the gear on the back clockwise to raise the cutout voltage or counterclockwise to lower it, just like you did with the voltage regulator relay on the other side of the unit.
Restart the engine and confirm the corrected setting. If need be, readjust as necessary. If you cannot even get close to any of these voltage levels, replace the entire unit. Make sure you have reconnected all the terminals again when you're done.
That's test #2! Only a few more to check.
Now we need to test the drop-off voltage. That's where the regulator disconnects the generator from the system when the RPM's drop down too low. If you didn't, the generator could actively start discharging the system and your battery.
Disconnect the two large brown wires from the B or battery terminals on the regulator. Connect those two loose wires with a short piece of wire temporarily. If you don't then the car won't run since this is where all your battery power comes from. Now hook a voltage regulator between the B (battery) terminal on the regulator and the chassis ground. We aren't testing the battery, only the voltage from the voltage regulator itself and how it handles low RPM situations.
Start the engine and bring it up to 3000 RPM again. This time start slowing the engine down and watch the voltage level. When the voltage regulator relay (first one on the left while viewing from the front/down side) opens the points, the meter should drop to zero. Note what voltage was on the meter when this happens. It should be between 9.3 and 11.2 volts.
If it isn't in this range, we need to adjust the voltage regulator. DO NOT use the camgear for this adjustment though. Instead we need to manually bend the fixed contact arm for the regulator ever so slightly. Two pairs of needle nose pliers are good for this. Reducing the gap between the contacts will will increase a higher drop-off voltage. Increasing the gap will have a lower drop-off voltage. The arm should be bent at about 0.10 to 0.20 of an inch offset from one end to the other.
Once you have the drop-off voltage where you want it, reassemble the unit and reconnect your wires.
Test #3 is done and gone! Now on to test #4- the current regulator.
Let's start by once again disconnecting the brown battery wires from the B terminal and shorting the wires together with a short piece of wire. Now put a piece of cardstock/cardboard between the contacts of the current regulator relay, or the one on the right as you view it from the front/down location. This prevents the voltage regulator from running and lets us get a true reading for the amperage the generator and regulator are working with.
Connect a 0-40 amp meter between the shorted brown wires and the B terminal on the regulator. All current will flow through this meter so a true meter with a shunt will be better than a digital or cheap analog volt ohm meter. You don't want 40 amps running through your fancy digital meter!
Start the engine and rev up to 3000 RPM again. Now turn on all the electrical accessories you have. Headlights, heater fan, turn signals, wiper motor, radio, etc. You want the maximum electrical draw you ever expect to have and then some. The meter should read 22 amps, the maximum rating the generator can produce (GM alternators run 63 amps by comparison and are leading reason for why they are such a popular conversion project). If the meter fluctuates while the engine is steady, you need to clean the contacts of the current regulator.
If the reading stays steady, but the range is wrong- too low or too high, then you need to adjust it with the cam gear on the back of the relay just like the others. Clockwise raises the setting and counterclockwise lowers the range.
Test #4 is complete! Your voltage regulator is in perfect operating condition!
If your regulator fails any of these tests and the adjustments don't help it, then replace it. They only run $30 on average and it really isn't worth mucking about with a dodgy piece of Lucas components. These tests only are made available to ensure that the regulator you have is working on the car. It's assumed that the generator is good. If the generator and regulator pass the test, then your next step is to check the battery or wiring for problems.
I hope this helps out. It certainly did help me just to identify all the terminals on the regulator and figure out what they connect to and how they work.