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Dominator alternators

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Dominator alternators

Posted by Rob Bradley at March 05. 2017

Can a two-wire RM21 alternator be used in a 6v system with a solid state regulator such as the A-Reg Six?

My friend's 1960 Dominator which I am rebuilding for him has an RM15/18 alternator. I have a spare RM21 from converting my Commando to Alton electric start. I also have a spare A Reg Six from when I converted my own Dominator to 12v. I would do the same here, but my friend wants to keep the 6v system to avoid the expense of buying an A Reg One (12v) and new ignition coil.

I would imagine that the output of a 57 year old RM15/18 alternator would be unexceptional, particularly as he wants to fit indicators and a bright running light, though I expect these could be LED, if road legal.

Re: Dominator alternators

Posted by john_holmes at March 05. 2017

Fit a ballast resistor and the coil can stay 6V, that just leaves the A Reg 1 12V to worry about. 6V and bright do not go together but LED's have made a difference.

Re: Dominator alternators

Posted by Gordon Johnston at March 05. 2017

I am surprised that your friend would want to forgo the option of brighter lights for the sake of a few quid. These days you really need the best lights you can get to stand a chance amongst the mobile searchlight batteries that are modern cars. Time for a bit of persuasion perhaps?

Re: Dominator alternators

Posted by robert_tuck at March 05. 2017

My experience is that the early alternator can do the job as long as its on 12v.  A 50/40 halogen bulb from Geoffy fits the BPF  system and is about as far as you can go. Indicators are not a problem.

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