Lucas Generator and Control Box tests

(John Burke) #1

Over the winter I’m going over all the major systems in my new XK140 MC OTS. I’ve replaced some cooling hoses that were starting to crack, had the radiator cleaned and pressure tested, rebuilt the C45PV-5 generator and bench tested the RB310 Control Box. I’m now going through the “Lucas Generator and Control Box Tests” as described in the link below to make sure my charging system is within spec. I’m up to test 5 on the current regulator but am stumped as to how to measure the amperage. The test indicates a C45PV-5 Generator should put out 22 amps +/- 1 amp at 4,500 rpm (I assume that is engine rpm as opposed to generator rpm, but I am not positive). My conundrum is that my multimeter only goes up to 10 amps and goes off scale. I can’t even find a multimeter that goes up to the 40 amps DC indicated in the test. Do people just connect the ammeter in the car? If so which wires are those in the engine compartment? Any help from someone who has completed these tests is greatly appreciated.

(Roger McWilliams) #2

Ammeters come in a wide range of maximum current measuring capability. Multimeter ammeters maxing out at 10 amps is common. Using the ammeter in the car makes good sense since it supposed to cover the normal operation range. One potential drawback would be knowing the current to within 1 amp of accuracy or precision is a bit unlikely using the ammeter in the car. I would use the car ammeter in my car, I have confidence in it based on each past drive, but I don’t worry too much about getting the current to within one amp.

(Andrew Waugh) #3

Get a clamp on Ammeter. You can get inexpensive ones (mine was about 50$, but they’ve gone down in price). Clamp types aren’t terribly accurate, but they’re close enough for what you’re trying to measure.

You can also get a clamp attachment which you use in conjunction with your multimeter.

The clamp types are very convenient in use, as you don’t have to disconnect anything to take a reading.

(John Burke) #4

Thanks guys. A clamp meter is on the way.

(Clive Jervis) #5


I don’t think that calibrating the current cut-out is essential to begin with. As long as the voltage parts are correct, then you should be good. You can observe the charge current on the car’s ammeter.

Unless you are planning running at night in the rain with a discharged battery, I doubt you will need anywhere near the max output.

If the meter is pegging I would suspect the voltage cut-out is set too high. If you believe the battery is good and the voltage settings are correct and the meter is showing a large charge, then you can adjust the current regulator.


(John Burke) #6

I suspect the ammeter in the car isn’t hooked up properly. It shows about +5 to +10 amps when the car is running but does not move at all when I turn the headlights on, yet they shine brightly.

(Clive Jervis) #7


When the engine is not running and you turn on the lights does the needle show discharge?


(Rob Reilly) #8

I once had occasion to run my XK120 all night in the rain, although with a good battery, got lost in Kentucky looking for my reserved campsite on the way to the national Jag show in Franklin TN, but the car did fine. Lucas can be a Prince in the Darkness.