Leaving aside any discussions on the pros and cons and the merits or otherwise of converting to twelve volts, am I right in thinking that all I need to do for the charging system is to fit a 12 volt cut out, such as this one 12 Volt Cut Out, and use the standard dynamo with a twelve volt battery? I realise that I would need to change the bulbs and take steps to provide six volts to the wiper motor. At present, I have no existing electrics, so can start from scratch.
27-05-2019, 02:32 AM (This post was last modified: 27-05-2019, 04:18 AM by Bob Culver.)
Most simply fit an equal value resistor in series with the cutout voltage coil (On later cars between E terminal and body, with any connections to the E terminal transferred direct to body.
The unit illustrated is a combined cutout and voltage regulator. Use of the latter function is a whole longer and fraught story.
The whole 12v topic been thrashed many times including recently. It is important to limit field current. Some apparently just retard the 3rd brush and take care to keep it that way. Others add a resistance about same as the field winding to reduce any accidental excess. As there is likely hidden additional current to field, it is especially important the no load ammeter charge is kept conservatively within normal recommended limit.
The cutout you refer to has no current limiting facility; it is purely a voltage regulator. You would be well advised to ensure that you use a cutout/regulator which can keep the dynamo output within its original rating. On most A7s this is 9 amps total (less on early ones and slightly more on very late ones). Assuming 2 amps for the coil anything more than 7 amps on the ammeter should not be allowed to continue for long, or the dynamo will overheat leading to failure. I have just had failure of an electronic regulator which allowed excessive current flow and the solder melted from the commutator connections on the armature. I may well be in for an expensive overhaul.
Robert Leigh
27-05-2019, 11:43 AM (This post was last modified: 27-05-2019, 12:14 PM by Peter Sweeney.)
Depends what you are using the conversion for. If its a special This is the conversion I made in the 80's using a mini alternator. I had a friend who turned a v belt pulley for the camshaft in Ali and a steel shaft to use the original dynamo end plates without the commutator. Then turned the fan casting through 180 degrees. It was a broken one so I could file the remains of the fan hole off. The bracket for the alternator is bolted to the fan casting. It has worked without problems ever since. The mini alternator dose not need a cut out as its built in. I have converted my big 7 in the same way the cut out is now only used as a junction box. Now I can blind Range rovers back!!
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I have had a good look at my dynamo and noticed that the insulation on the wires coming out of the body is split just where the leave the dynamo case. It is a C35M model. Does anyone have an exploded view of one these which I can study before taking it apart to repair the wiring? I have looked, but cannot find one.
On my special (up for sale at Brightwells Leominster on the 10th July) I used the existing fan pulley and a ribbed belt to drive a Kubota mini alternator mounted on top of the dynamo housing.
the only fabrication needed was brackets for the alternator!
29-05-2019, 11:04 AM (This post was last modified: 29-05-2019, 11:11 AM by Bob Culver.)
Sorry fellahs, but I cannot bear the sight of alternators on old cars. For those who cannot persist with the original how rare are Lucas generators in UK?. The one on my 1960s everyday car still carries the swapmeet price tag...$2 (1 pound).
One of the great attractions of the Seven is the total absence of electronics. And that from a radio tech (eons ago).
I changed my cars over to 12 volts and alternator as I am fond of my life. I had a horrifying trip back from Beaulieu to Colchester at night in the 70's. The 6 volt lights faded away getting dimmer and dimmer. The Dynamo could not keep up with the lights on. It was so bad every car coming towards me put their main beams on to see what was coming. I couldn't see my own lights just the shadow of my car in the light pools of following cars. Never again. As there is no way to easily drive a dynamo from the crank an Alternator will give a full charge at lower revs allowing a pulley on the cam to do the Job. It was bad enough then now days no way. Pretty or not I prefer to err on the side of caution.
08-06-2019, 10:53 AM (This post was last modified: 08-06-2019, 10:54 AM by Jamie.)
OK. I am happy to share my confusion and show ignorance: perhaps I am just missing the obvious or forgetting some basic electrical theory from school.
Most 12 volt conversions, such as those on the Cornwall Austin Seven Club site (12 volt conversion and Another Way) use resistors to limit the current flow and diodes to replace the cut-out. This I follow.
However, many articles state that the dynamo can produce up to 30 volts or so. What prevents the dynamo from doing this and putting excessive voltage through the system?
