John Williams and 12 volts

[cardiffrob]

I've met John a few times and he gave me some good advice about his 12V conversion to go alongside the Bristol A7 Club webpage.  I'm currently trying to get my car finished off, if only to get it running enough to drive round the garden.  I'm unemployed so a new 12 volt kit is out of the question.  I have everything else in 12 volts available from Morris 1000s so I'd prefer to avoid the cost of equipping with 6 volt bulbs etc.

I've got a very late C35 dynamo all cleaned up but wanted to check the info out before I fire the car up again.  At the moment I think that the 3rd brush has to be removed and an added cable strung between the screwed terminals of the old 3rd brush and the earth brush which is shown in Woodrow as "Negative (earth) brush".  The 2 other brushes remain exactly as Austin designed them?

The mathematics mentioned by John don't seem to add up.  1.6 Ohms plus 3.4 ohms would be 5 ohms.  Am I right in aiming for 5 or for 6 ohms?

Lastly, I can find the F and D terminals on the control box but how do I ensure I have the righ terminals as they come out of the dynamo itself?  Mine has a block with 2 wires held by grub screws.

Many thanks

Rob Thomas

[John Mason]

Rob, Sorry to hear about your employment position at the moment but if you are short of cash as you must be why move from 6 volt to 12 volt. There has been a lot on this forum about running successfully on 6 volts if maintained properly with the correct heavier wiring and good sound earthing.

John Mason.

[cardiffrob]

  DSC00576.jpg (Size: 232.34 KB / Downloads: 509)
  roll2.jpg (Size: 235.62 KB / Downloads: 510) I'd need to buy a 6 volt pump, battery, regulator and bulbs whilst I already have them available in 12 volts so it will be cheaper to make the change now.  All the 12V parts are on the car from when I was planning to buy one of the new 12v dynamos.  It will be easy to do the conversion from here and I might be able to have the car running by the weekend.
I would have no problems staying with 6 volts if I didn't have to buy the parts.  This car last ran a good 40 years ago before being stripped as a spares source, hence the lack of 6 volt parts.

[John Mason]

If it is any help your 6 volt Dynamo should produce enough power to run 12 volts although not as efficient as one modified with a rewind.

John Mason

[cardiffrob]

http://www.ba7c.org/technicalArticles/dy...volts.html

This is the page I was referring to in post #1.

[Duncan Grimmond]

I ran my Benjaustin at 12v throughout with a 6v Dynamo. The lights were a little dim until I fitted LEDs as the consumption at night exceeded the input but in normal daytime running there was plenty to keep the battery topped up. The starter remained 6v but in intermittent use it didn't seem to suffer, I tended to start on the handle anyway.

[cardiffrob]

Thanks for the info, Duncan.
What did you do with the 6V dynamo and ancillaries to run the car? Was the dynamo adjusted to give a higher voltage, as per the webpage above?

[cardiffrob]

I have 2 terminals on the outside of the case of the dynamo marked 'F' and 'D'.  To which terminals do these 2 normally connect inside of the dynamo?  I assume they run to the 2 main brush terminals but which way round?  This dynamo was in pieces when I got it and Woodrow doesn't show the connections.  On the pic below the F is to the left but how do you know which of the 2 brushes it goes to.  One is on a metal bracket and the other is on a sort of Bakelite one.
I have 2 starting handle nosecones to weld up and then I can get onto making the 2 drop links for the lowered suspension, assuming I can find enough steel on the shelf.
Thanks.
Rob (on the home stretch

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Can I safely assume that the Earth brush is the one on the steel bracket and the 'D' brush is on an insulated bracket.  Sorry if this sounds like a silly question but I don't want to kill the dynamo today! Page 205 of the Green Book shows a picture but mine is covered with dirty finger marks.

[AustinWood]

The standard 3 brush dynamo operates fine on 12V. It needs the correct cutout and a 12V battery.
It is basically a constant current device and the voltage will rise until it reaches the current for which the wiring is set up.
This is the reason for the high/low charge settings. Low setting to try to avoid overheating the battery.

[cardiffrob]

I thought it was necessary to bypass the 3rd brush to allow the RB106 regulator to take full control of the dynamo output?