Hi all, many thanks for your responses and thoughts ... very much appreciated. The 'alternator' I have in mind is the one supplied by the Octagon club as I assume it would have been 'spec'd' as suitable. I'm not intending to put a pair Cibie Oscars on me TC , just looking to help the situation when wipers and headlights are on together, so Graham's advice of 'suck it and see' seems to be the way to go.
Thanks again
Tweed.
From: "Roger Furneaux
roger.46tc@gmail.com [mg-tabc]" mg-tabc-noreply@yahoogroups.com>
To: Peter Cole pcoleuk@gmail.com>
Cc: Graham graham47tc@btinternet.com>; Tweed lizandtweed@yahoo.co.uk>; MG-TABC List mg-tabc@yahoogroups.com>
[b]Sent:[/b] Tuesday, 22 January 2019, 20:58
Subject: Re: [mg-tabc] Tacho Drive ..
hi Tweed - I had a look at BB Classics website, they seem to be the main sellers of these. Nowhere do they (or anybody else) give the dimensions of the body: they seem to equate Lucas p/n C45 with output, whereas it actually refers to body diameter, 4.5 inches. Also, in their table of compatibility, they list the TC as a [b]saloon[/b] made from 1944, and [b]not[/b] compatible.
A dynamator usually has a double armature, used to convert DC to AC (typically at a higher voltage). They could be used to convert AC to DC, but the ones we are talking about are probably alternators with solid-state AC to DC conversion and control. The good old RF91 is by-passed, thus solving the problem (and expense) of restoring them or converting to solid-state.
They cost around 160 (208$) which means they are probably being made in China...
cheers
Roger
On Tue, Jan 22, 2019 at 1:32 PM Peter Cole
pcoleuk@gmail.com [mg-tabc] mg-tabc-noreply@yahoogroups.com> wrote:
[u][/u] Tweed,
The story sounds a bit confused. I think the basis of this is the fact that a Dynamator is really an alternator, and alternators have always spun faster than dynamos. This is probably because they came along decades later and because the rotating part of an alternator is much lighter that that of a dynamo, hence it can spin faster without precision balancing.
You really need more data on the Dynamator to confirm its output verses revs to see if it will provide sufficient charge at the typical revs of an XPAG. If I remember correctly the standard pulley diameter causes the dynamo to rotate at 11% above engine speed.
If Dynamator are happy with that there's no pressing reason to change the pulley. Failing that, if they confirm you do indeed need to use a smaller pulley there were several different ratio gearboxes available at the time. You may be lucky enough to find one that will compensate.
Peter
On Tue, 22 Jan 2019 at 07:48, Graham
graham47tc@btinternet.com [mg-tabc] mg-tabc-noreply@yahoogroups.com> wrote:
[u][/u] Tweed,I had thought that the benefit of a Dynamator ,
i.e.an alternator, was increased output at lower engine speeds, so I would suggest it is unnecessary to mess about with pulleys.Keep the thing as standard looking as possible and try it and see how you get on.No need to introduce complications.
GrahamTC 3107Buckingham
Sent from my iPad
On 22 Jan 2019, at 01:50, Tweed
lizandtweed@yahoo.co.uk [mg-tabc] mg-tabc-noreply@yahoogroups.com> wrote:
Hi y'all, when replacing the dynamo on a TC with a dynamator, I understand it's advisable to fit a smaller diameter pulley to take advantage of the increased output at lower engine revs .. but as the cable drive will still be off the back through the same reduction box, the tacho reading will alter. I measured the actual crankshaft revs with digital laser tacho against the chronometric tacho reading and was impressed to see it was as near as damn it right!
I kind of wish it wasn't quite so accurate then I wouldn't be too bothered about deliberatly making it read fast. The easy answer I suppose is to fit a modern impulse type tacho, but I don't want to do that.
Any suggestions from those that have gone the 'dynamator route' will be gratefully received.
TweedTC 0632Cambridge UK
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