hi all, i have a problem of over charging on my 65 s type. i changed the voltage regulator for a new after market one same as what was on the car and also tried a friends genuine lucas one and they all read the same. i get 18.3 volts at the battery at 1500 revs and 19.3 volts at 2000 revs. anyone got any idea as to what the problem could be. i have another old car and that goes to 14.7 to 15 volts tops. im lost.

 

I am not an expert. All entries should start with that but unless you have changed to an alternator the 65 S Type should have the old generator producing those sorts of figures but it sends it through the RB340 voltage regulator which is the black box on the left side inner wing. The RB340 then reduces the voltage produced by the generator down to a constant 12v which it sends to the battery via the ammeter. The volts that the RB340 sends to the battery can be adjusted on the regulator but it is not something I have done. It requires taking the top off and fiddling with a couple of screws but it can be adjusted to drop the voltage going to the battery.
If you have a service (Blue book) page P26 and beyond in Electrical and instruments describes how to adjust the voltage. I don't have the facility to reproduce it here but if you go to this link on the S Type register the manual is in a PDF document which you can down load and read.
THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM - S-Type Documents

 

thanks for your reply cass but 3 regulators are giving me the same reading so it has to be something else.?

 

You have me stumped then because if you think about it logically there is nothing else that can effect the voltage. The generator produces the volts and as a generator these vary with the RPM that the generator is turned at by the engine. More RPM means more volts produced. An alternator does the same but has a built in voltage regulator where as the generator relies on the RB340 voltage regulator to drop the voltage to 12volts when the generator is working at high RPM and producing up to 25 volts. The volts go from the generator to the RB340 then via the ammeter to the battery. There is nothing else in the circuit that could increase or decrease the volts other than the RB340. I hate to say it but logic suggests that all three of your RB340s are not correctly set. If you follow the directions in the manual you should be able to tweak the RB340 so the voltage coming from the generator, through the RB340 then going to the battery is dropped to 12v.

 

Regulators should ideally cut at 14.2 volts in the modern world of the alternator. This is most unusual. 3 X RB340's giving the same crazy readings but I have to concur with Cass. There is nothing else in the circuit. Are you sure your multimeter is not buggered or at the wrong setting.

 

I had an issue on a frogeye sprite once where some of the wires on the regulator were on the wrong terminals and that was then outputing a voltage above 20 volts, it turned out that whoever made the new wiring loom had used the wrong colour wires for some of it.

I went up the road at night and when I got to about 30mph both headlights went pop and I had to drive back (slowly) on a combination of main beam and side lights, luckily I had only gone about a mile.

 

I would check the points in the regulator (any regulator) and make sure they are not stuck shut, and or they are clean.
Use a points file, not fine glass paper to clean them, the grit from the paper gets imbedded in the points.
One of those micro cloths dampened with acetone works well enough to clear the filings away.

Don't over do it with the file and keep it "square" as possible.

 

Check that you haven't mucked up the wiring between the generator and regulator.
The voltages you are quoting are roughly the same that you get when testing a generator in the car by shorting the field winding to the generator output (with the wires to the regulator removed and engine running)
Don't rev the engine any higher than you have as you can easily burnout the generator and cook gauges, bulbs etc with excessive voltage!.

 

The latest RB340 replacements you get from Barratts & the likes are preset at build & not easily adjustable.

 

Original:







High Res pdf below:

 

Three duds seems unlikely though not Impossible. I'd follow Bill and Homer and look for something wrong in the wiring. Check against Glyn's diagram that the cables are connected as they should be.

 

hi chaps, all sorted, dynamo was shorting out inside. took apart cleaned it all up , replaced wire inside and all working fine. charges steady at 14.7 volts. thanks all.

 

glad to here it!

...was going to suggest that maybe the measuring instrument may have been faulty. but seeing now that that wasn't the case, i think i'll save myself the embarrassment of offering useless information... once again. so forget i said anything.

 

Excellent its solved!! I'm sure everyone else concurs that it's great to hear when a problem is solved - this forum is great when it comes to solving the many conundrums (conundra?) of old cars that we all experience!!!!

 

conundri.

 

Very funny - the 471 page Mk2 service manual doesnt refer to conundrums, conundra or conundri. Probably assumed 60 years of happy, trouble-free motoring despite there being more service bulletins than one could poke a stick at.......