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Retlas "Manchester" Dynamo

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Alyn Foundry:
A little history.

A few will know that my background was in electrical engineering and with a passion for vintage machinery.

I had the privilege of both seeing and working on a wide range of " machines " that spanned nearly a century. North Wales has many hydroelectric stations one in particular dated at 1905 was the oldest that I had seen. The turbines and alternators now replaced by a single and highly efficient replacement.

After Vincent had completed his Retlas he found that a load " softened " the rather erratic running nature so we discussed various means towards this end. A dynamo was the obvious choice as you can easily place a given electrical load in the form of lightbulbs.

Vincent's choice was a " Manchester " style as they were of very simple construction. The base becomes one pole, either North or South and the two field coils are wired to provide the electromagnetic influence to the top and bottom. The choice of a Lucas dynamo armature was twofold, they were very common and cheap because nobody wanted them and a low output voltage was safe in the usually wet rally field environment.

The prototype was a very plain affair, a simple cross at the bottom and the top is the only bit that wasn't remodelled. All the other patterns were redone after the Dynamo was proved to work. I've forgotten who wound the coils but I think we scavenged the Copper wire from the donor machine. This ensured that we had the correct resistance.

You will notice that the " brushgear " can be rotated about the axis of the commutator. This was a method used on early DC machines to combat something called " armature reaction " . This effect happens as more load is placed upon the generator, bending the magnetic flux which, in turn moves the best output from the commutator. As a result arcing occurs which, if left unchecked quickly burns the segments. The operator would then rotate the brushgear to find the point of least arcing.

The Retlas Dynamo was also fitted with Brass gauze brushes and ring oilers for that extra look of authenticity. The overall finish was such that Vincent's Dynamo fooled many an expert eye over the years few believing that it was home made.

Cheers Graham.

Chipmaster:
Here are pictures of two Retlas dynamos that I copied from the Internet some time ago, I don't have any details about them.
Andy

rd2[1] by Andy, on Flickr

rdj2[1] by Andy, on Flickr

steam guy willy:
Hi , Interesting project..I was also an electrical engineer in the Army and they had quite a few old 'Machines" that the y use to start up.  including one with the handle for adjusting the brush position !!  Also there is a black wire connected to the frame  ? is this part of the electrical circuit ?? and are the  4 middle connections able to reverse the polarity of the output  ?...and on the green one the rotor wire seem to be coloured slightly red and black...havent seen that before ??


willy

Alyn Foundry:
Good morning Willy.

Like Andy I've seen these pictures before but the builders and their methods are unknown.

With the Black one I surmise that they have only isolated one of the brushes and the frame becomes a return to the terminal block.

I'd never noticed the different colours in the enamel insulation before, well spotted. The armature is however " proprietary " so this is something that the manufacturer might have used to designate the coil termination to the commutator?

Cheers Graham.

Admiral_dk:
To me it looks like it is a "Bifilar Winding" - means that there are two (or more) parrallel wires, wound together as if there where one. There can be several reasons for this - in this case, to easier to get the coils into place after they are wound.

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