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MG MGA - Earth..Pos to Neg.

I am changing to Neg earth and have read Barneys process and it seems easy enough. The only complication is that about 8 yrs ago I had an electrician replace the generator with an alternator. What do I do about latter....
Neil Ferguson

Yr in trouble!
Pos earth alts are rare as hen's tooths. Only appeared on a few Jags, Rovers etc in the mid 60s. I have heard rumors of some mid 60s MGB being fitted with them, with aircon, but never saw one. These systems have external regulators, field isolating relays, and other various complications.
Are you certain it is not already neg earth? IF the alt really is pos earth,then you have to change it, and anything associated with it.

FRM
FR Millmore

99.9% of the time, if it is fitted with an alternator it has already been changed over to negative earth. Check again to see which post of the battery is grounded on the chassis. Perhaps it is already negative earth.

If it is a positive earth alternator, those are so rare that you might never find a replacement if it fails, in which case you may want to convert it to negative earth and change the alternator anyway.
Barney Gaylord

As Barney suggests, probably converted to negative earth when the alternator was fitted.
J Bray

Neil - Look at which post of the battery is connected to ground - if it is the negative post, you are already running negative ground. If the car is indeed still positive ground, the switch to negative ground is not a big deal - any alternator available in parts stores today are negative ground and can be installed in place of the existing alternator. If your present alternator is, in fact positive ground, you can pay of several negative ground alternators by advertizing your positive ground unit on e-bay. Cheers - Dave
David DuBois

Once again I have been on the road to Damascas and seen the light. I installed my single 12v battery and it is definitely + earthed . I am now of the opinion that the electrician installed another generator/dynamo and not an alternator. I attach a pic.. ..and no alternator I view looks like this black tube cylinder . Please confirm. I am going to proceed with Barneys polarity change procedure ..but does anything else need changing. I have a facet fuel pump, no radio ,electric radiator fans, heater fan ..and all other standard gear.


Neil Ferguson

Take a close look at that. It might be a Dynalite Alternator. they look like the Lucas generator and are available in POS GND versions.
Chuck Schaefer

Neil, look at the numbers stamped into the body of the generator. If it is C40 something, it is a generator and can be flashed to change the polarity. The leads on the Facet pump will have to be swapped. The Facet pumps are polarity sensitive, but will not be harmed by the wrong polarity applied - it just won't work if the polarity is wrong. Cheers - Dave
David DuBois

FRM..interesting possibility but don't remember a bill for the huge cost involved. It was also a jobbing electrician in a small country town ... I note that he unit I have is hooked up to the standard MGA regulator. I also find a jumble of indentifications ( always on the dark side of the moon! ) and used my wee mirror but nothing that fits ...is there any way I can check with the mga fired up?
Neil Ferguson

Neil -
Wasn't me suggested the big $$$$ Dynalight, but I'd think you would remember. Besides, I've never even seen one, and it is a fair bet your backwoods man hasn't either.
Give us a pic of the back end of the generator. Should be one small terminal and one large, and you can see the commutator through the end holes. Lucas gen will have a 5 digit part number, C40 Model number, mfr date as wwyy. Dynalight might have those too if built in a real used Lucas unit!
Permanent magnet motors (rad fans maybe) will run backwards if you reverse polarity - just swap leads.

FRM
FR Millmore

The mystery deepens.
I removed the unit to investigate the dark side and found the following stamped
"Neg Earth
(merc symbol) 22715 5 2002
C400 12v "
I attach a pic of this ......
Unit has a black barrel length of 15cm and overall length of 23cm incl pulley .
To ensure sanity I checked the 12v single battery again ...it is pos earth and I have had this car 23 years and never changed the polarity.
Is this a generator/dynamo and the electricn has polarised to + earth?
Any ideas??


Neil Ferguson

Went onto net and found this current ebay offering....identical..http://www.ebay.co.uk/itm/Triumph-C40-Dynamo-Lucas-22715-C400-/330618810972#ht_500wt_1180

Does this mean I can just polarise back to neg using the simple procedure?
Neil Ferguson

Any indication of where this thing was made?
Sounds like the people reverse engineering it didn't know what they were copying.
If it isn't stamped "Lucas" it is a knock-off.(and maybe if it is!)
"Neg Earth" means nothing, as it is the polarization which determines that on these generators. They are whatever you polarize them to.
The (merc symbol) is leftover from the very early days (and patents) of electricity. I think it was originally from American Bosch, or possibly a prior license from maybe Westinghouse/Tesla, used as a license mark by Lucas for many years. Bosch use it too; It is a stylized schematic of a three pole alternator.
22715 is the "Lucas" part number
5 is the date = 5th day or week or month of 2002. Real Lucas numbering would be ww yy, but they did not use leading zeros, so it would be 5th week of 2002
C400 is an aberration of C40
12v They got that right!
The arrow is the direction of rotation.
Really nice looking drive end plate, pretty much the pattern of the last Lucas ones.

Just do your changes and repolarize it.

FRM
FR Millmore

I'd agree. I just suggested the Dynalite as a possibility. Might fool a beginner. If it is a generator, you should be able to see the serrated commutator thru the openings in the rear bracket. Somebody help me on this. I read that the Dynalite is machined from aluminum. Would this mean that the body is not steel? Might be easy to differentiate with the use of a magnet.
Chuck Schaefer

Dynalite has an aluminium body so easy to check.

Siggi
Siggi

Case is magnetic and can see the serrated commutator.....so all settled and will re-install and polarise today.....many thanks to you all for the wisdom of the ages! Also have decided to change to an alternator when I can find a good one at a cheap price .....
Neil Ferguson

Case is magnetic and can see the serrated commutator.....so all styled and will re-install and polarise today.....many thanks to you all for the wisdom of the ages! Also have decided to change to an alternator when I can find a good one at a cheap price .....
Neil Ferguson

Reversed my single battery, connections fitted, sparked the regulator terminals ,reversed wiring on my facet pump and twin radiator fans and vroom ,vromm the car started ....now neg earth!! Very easy ,30 min work ......now for electronic ignition.
Neil Ferguson

Wait till he finds out he has 4 speeds backwards and one forward!

FRM
FR Millmore

Also swap the primary wires on the ignition coil. The "+ terminal is now white wire, and "-" is now white with black stripe going to distributor (to ground through points). It will run with incorrect polarity, but may be about 15% shy on voltage at the plugs when spark jumps wrong direction across the gap.
Barney Gaylord

Barney..slavishly followed your notes... coil wires already reversed.
FRM..forgot about the gearbox wiring......do you have a wiring diagram for me?
Neil Ferguson

Not a wiring problem. Just swap wheels from left to right and vicey versey, which reverses the interaction of their magnetic flux with the earth's field.

FRM
FR Millmore

Just got back from the garage and could not find the magnetic flux generators on the wheels ...and the earth's field is 15m away from car ..are you extracting the michelle from a poor pommy ocker?
Neil Ferguson

Neil

You did not wait long enough. The Schuler loop magnetic field detection is on an 84 minute cycle - hence the name.


To implement Schuler tuning, the feedback loop is modified to rotate as the car moves in north-south and east-west directions. To do this, the torquers that rotate the wheels are fed a signal proportional to the vehicle's north-south and east-west velocity. The turning rate of the torquers is equal to the velocity divided by the radius of the Earth.

Steve
Steve Gyles

This poor wee scouse in the antipodes is confused by all the ''torquers ' in the northern hemisphere. Steve's description is totally wrong for the southern hemisphere and as he also knows
that the 84 mins is affected by my distance from the equator? I also know that for the Schuler Loop to work each wheel would need a commutator ring and all four wheels would need to be connected to a stigmifier inverter and I could not find any of this equipment on my car.
Neil Ferguson

Very Good FRM and Steve - should have saved this for April 1st!!
Cam Cunningham

know now the reason why I had to set the timing always when I crossed the road wheels...

Thanks!
Siggi
Siggi

Neil

You also need to convert the Jaeger speedometer to negative earth to ensure that its kalman filter continues to give the correct forecast mph. The kalman filter is designed to overcome waivering speedometer readings and damp it all down to a mean average. As Wikipedia explains:

"In each time step, the Kalman filter produces estimates of the true unknown values, along with their uncertainties. Once the outcome of the next measurement is observed, these estimates are updated using a weighted average, with more weight being given to estimates with lower uncertainty."

Steve
Steve Gyles

This thread was discussed between 10/02/2012 and 13/02/2012

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