Convert from dynamo to alternator

[chastr4a]

When fitting an alternator instead of the original dynamo, do you need to change anything at the voltage regulator?

[Lebro]

Yes. Assuming you are going for an alternator with a built in regulator (Lucas ACR etc) you no longer need the external regulator. You can remove it altogether & simply join the thick wires which went to "D", "A" & "A1" together, & connect the thinner wire wire going to "D" to the field terminal on the alternator.

or some people rip out the internals of the old regulator, & re-wire it to act as a junction box, make the connection above.

Bob

[RobH]

This is one way to do it using the RB106 as a junction box with its internals removed and the three large spade terminals A1, A and D connected together with a heavy gauge link wire under the base.  There is no connection to E.  F is used just as a junction point.  (Note that the D and F terminals are shown in the wrong order, for clarity in the drawing )

 

 

 

 

Edited April 24 by RobH

[BlueTR3A-5EKT]

https://www.tr-register.co.uk/forums/applications/core/interface/file/attachment.php?id=59372
 

I put this in the Bonanza some time back

[Ralph Whitaker]

9 hours ago, chastr4a said:

When fitting an alternator instead of the original dynamo, do you need to change anything at the voltage regulator?

Don`t forget also that the Alternator is Negative earth, so you need to reverse the battery connections if you are not already Neg earth. Also radio if fitted will be affected .

Ralph

Edited April 25 by Ralph Whitaker

[chastr4a]

Thanks guys, a great help.  Any predictions on what might go wrong if regulator wiring was not changed over?

[Lebro]

A bit unkown ! you would be trying to regulate the output twice. best not to go that way 

Bob

[Chris Hubball]

I seem to remember Ian Cornish wrote an article in TR Action on this many years ago, he may be along soon to give us the details

Cheers Chris

[RobH]

2 hours ago, Ralph Whitaker said:

you need to reverse the battery connections if you are not already Neg earth. Also radio if fitted will be affected .

Another thing you will need to change if you are swapping polarity is the instrument voltage stabiliser if that is a modern electronic type rather than the original bimetallic.

1 hour ago, chastr4a said:

Any predictions on what might go wrong if regulator wiring was not changed over?

You can get away with not changing the wiring on the control box as long as you just insulate  the dynamo ends of the dynamo leads and take off the earth connection from E on the control box.  The box can't then do anything even though it remains connected.  

You would need to connect the alternator field wire to D so it picks up the ignition lamp connection and find a way of connecting the alternator output to A or A1.   Problem there is the remaining unused tags on those terminals are the smaller type and are not big enough to carry the alternator current so it would be necessary to make up some form of 2-into-1 spade adaptor.

 

[BlueTR3A-5EKT]

If the car is not negative earth now as has been said you will also need to swap the low tension leads on the coil.   The lead going to the distributor must be connected to the terminal on the coil that has the same polarity symbol as the earth of the battery.   
 

If…you have CB and SW notation on the low tension terminals of the coil, all bets are off.   Unless there is a statement of suitable polarity on the coil.    The correct connection can be confirmed by use of a lead pencil and the HT connectors and observing the start and finish places of the spark.   Again we await IanC

[RobH]

This is a bit of a 'can-of-worms'.   The coil has one end of the primary winding connected to the HT winding and is meant to operate with that connection point going to the distributor.  That increases the output voltage by a few hundred volts because when the points open, the windings are in series so back-emf in the primary adds to that of the secondary.  By swapping the connections of the coil over, you lose that small boost because the connection point is held at 12v above earth.  

What this means is that in correcting things to get the right spark polarity , you alter the operation of the system slightly. It's a bit academic and probably won't be noticed in practice - but then neither will having spark polarity the 'wrong' way round.   Either way, the system isn't working in quite the way intended. 

if you are going to the lengths of installing an alternator and changing the polarity, the right thing to do is go the whole hog and fit a negative-earth coil. 

 

 

Edited April 25 by RobH