ammeter

[Phil Read]

ever since I bought my 4A it has a wild ammeter. After starting it goes off the clock with a charge rate, if I switch on the headlamp it goes off the clock dicharge and then comes back to the centre. It always seems to be charging up to 15 amps when the engine is reving, some times settling back to zero. It apperas to have a newish delco regulator fitted

Any ideas welcome

[RobH]

Why a Delco regulator with a Lucas dynamo, or has that been changed too ?  

First thoughts are the regulator isn't working but the headlight thing makes it sound as though the ammeter could just be way too sensitive. Its difficult to explain how that could be as the instrument is really simple - I wonder if that has been got-at somehow?

If you can get hold of a clip-on ammeter it would show you whether the ammeter is telling porkies or not. 

With the engine not running what does the ammeter show if you turn the headlights on?  Should be about 10A discharge. 

Edited June 2, 2020 by RobH

[signalredshaker]

Had this very same issue- I changed the control box and it immediately fixed it. however, this didn't last long and after changing it again its been fine for the past 5 years.

James

[Opie]

Your ammeter is most likely working perfectly. And your battery is probably in need of a charge. Here is why.

Your dc generator will provide voltage and amps to battery only if there is enough to "give away." If voltage regulator threshold is not met, the regulator will disconnect from battery. That is when you see your head lights take all the amps they need. (Regulator gives to headlights and takes away from battery.) The ammeter will show charging amps when battery is being charged.  If battery becomes satisfied, the amps it absorbs will reduce and ammeter will go to zero at full battery.

This article explains it better.  LINK HERE

Opie

(at least, I think that is what's happening)

Edited June 2, 2020 by Opie
Edited to reduce bravado to acceptable limits of incompetence

[RobH]

Hmmmm.  The wild extremes of charge and discharge that Phil describes are the symptoms of a faulty or mis-matched regulator as James says,  not of a low battery. It sounds as though the dynamo (if that is what it is - we haven't been told) is not being regulated smoothly but is switching between giving excessive output (high charge) or being driven by the battery because the cut-out isn't switching as it should (high discharge).

The lights on/engine off test will demonstrate whether the ammeter is working correctly but we really need more info on what the system fitted to the car actually is. It doesn't sound standard. 

Edited June 2, 2020 by RobH

[Phil Read]

Hi Thanks for the inputs. The car has a new battery, dynamo is standard lucas and it is fit with a Delco regulator, I suspect its just an Indian/Chinese repro, I will try and get some thing better.

[John Morrison]

Hi Phil.

from memory a guy on here had a new original still in the wrapping.

Why not place a wanted in the, For Sale/Wanted Section?

John.

[lynchpin]

My ameter never used to move much towards the +   I had the dynamo rebuilt because of a noisy bearing and when I refitted it my mech' brother set up the regulator properly by using a piece of paper between 2 of the connections and adjusting the others, something he learnt back in the 60's  when it was part of servicing these sort of cars, it now reads high in the positive when started up and quickly settles when the regulator adjusts it, you can see the needle moving as things are turned on and when the engine speed increases,there must be something on you tube about setting it up..

                          Phil..

[ianc]

The instrument which we call the ammeter is really a voltmeter!

On the back of the instrument is a low value resistor, called a shunt.  The value of the shunt (in ohms) is adjusted by the supplier to suit the scaling of the instrument, which is probably +30 to -30 amps.

If the connection to the shunt becomes loose, the ammeter is likely to provide odd and inconsistent readings, and charging of the battery could be on/off.

That said, I would agree that the likely culprit in this case is the regulator.

I have noticed a number of posts stating that an electronic version of the regulator, which has the appearance of the Lucas box, seems to work very well.  In view of the fact that reproductions of the regulator seem to provide problems, if sticking with a dynamo, I would opt for an electronic version if I were unable to find an old (1950s/1960s) Lucas regulator.

Ian Cornish

[Phil Read]

Problem solved. I bought a replacement voltage control box/regulator. The ammeter now goes up to 15amps on start up and then falls back to zero. Thanks for the inputs.

[RobH]

Thanks for letting us know Phil - it all adds to the knowledge base.

[peejay4A]

On 6/3/2020 at 5:06 PM, ianc said:

The instrument which we call the ammeter is really a voltmeter!

On the back of the instrument is a low value resistor, called a shunt.  The value of the shunt (in ohms) is adjusted by the supplier to suit the scaling of the instrument, which is probably +30 to -30 amps.

If the connection to the shunt becomes loose, the ammeter is likely to provide odd and inconsistent readings, and charging of the battery could be on/off.

That said, I would agree that the likely culprit in this case is the regulator.

I have noticed a number of posts stating that an electronic version of the regulator, which has the appearance of the Lucas box, seems to work very well.  In view of the fact that reproductions of the regulator seem to provide problems, if sticking with a dynamo, I would opt for an electronic version if I were unable to find an old (1950s/1960s) Lucas regulator.

Ian Cornish

That's true for a moving coil ammeter where a shunt is required to measure current.  The TR ammeter is a moving iron instrument and all the current passes through a few turns of very thick copper wire.  The resultant magnetic field deflects the moving iron which is attached to the pointer.  Even with a low resistance shunt, maybe to extend the maximum reading, the meter is still measuring current directly, but not all of it.

Edited June 14, 2020 by peejay4A