Stuart dynamo rotation

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I've never seen a Stuart Dynamo, but if the brushes are angled no as they would chip off the leading edge in reverse. If they are straight, I can't so a problem other than the polarity of the terminals. John

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HI, I am not familiar with the Stuart dynamo but you should be able to do it. It depends on the excitation. Reversing the direction will reverse the polarity of the output. You may need to build up the remnant flux in the field coils in the opposite direction to make it work. Tom.

Dynamos are dynamos. We always ‘flash the field coils’ on vehicle dynamos when changing polarity or fitting a different one.

The spare parts list mentions a magnet which suggests a PM field., in which case it will happily run either way but polarity will reverse.

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I think so too, but some DC motors have offset brushes, which improves efficiency, and running them in reverse damages the brushes. The drawing is exaggerated but if the brushes are offset as shown on the right, don't run in reverse.

Is it likely a Stuart Dynamo is designed to maximise efficiency? Probably not! Never seen a DC motor with offset brushes either, but my experience is tiny. They do exist.

Dave

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I thought AC series wound motors can have offset brushes to improve efficiency given the inductance in the windings - and they are not reversible. DC motors uness made for a very specific application may be required to run in either direction so would not have offset brushes. Anyway this is a model dynamo to show off a steam engine, efficiency is hardly likely to be an issue!

Edited By John Haine on 07/02/2021 10:47:02

At the risk of inciting semantic outrage ...

The ‘Stuart Dynamo’ is an AC Generator:

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**LINK**

https://youtu.be/qOZGZ__3vi8

So the brushes are in contact with slip-rings, and therefore most unlikely to be damaged by reversing the direction of rotation.

MichaelG.

Is it a DYNAMO ? A/c current, slip rings - dynamo or alternator ???

Oops, I should have read the previous post from Michael!

Edited By Speedy Builder5 on 09/02/2021 07:05:35

My best guess is that the word ‘alternator’ was coined for the emerging Motor Industry, to conveniently distinguish AC dynamos from DC dynamos ... but I don’t know by whom.

Alternating Current Generator

Here’s some more info about the Stuart machine : **LINK**

http://www.stuartturnersteam.com/Machines/Bottone/Bottone.html

MichaelG.

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Edit: __ I haven’t yet found a freely downloadable copy of Bottone’s little book, but :

https://www.si.edu/object/siris_sil_243390

and

https://www.nature.com/articles/031052a0

.

UPDATE:

https://ia800205.us.archive.org/26/items/dynamohowmadehow00bottrich/dynamohowmadehow00bottrich.pdf

Edited By Michael Gilligan on 09/02/2021 08:04:35

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A bad guess ^^^ it appears: **LINK**

https://en.wikipedia.org/wiki/Alternator#History

MichaelG.

Excuse the outrage but Stuarts also made two DC ones, which Dave may have been thinking of as Br had not shown which one he had at the time. One was small and intended to be run from the S50 and 10 series models, the other older one was more like Br's in looks

You don’t need to be excused, Jason ... You are a Moderator

‘though I’m not sure why you felt the need to post a link to a page I had already referenced.

MichaelG.

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Note: The semantic outrage that I risked was that initially expressed by Speedy Builder5

... but of course he then read my post, and got the point.

Edited By Michael Gilligan on 09/02/2021 09:28:53

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AC can be easily be rectified by fitting a simple bridge rectifier to give DC ! Noel

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Just out of curiosity does it have brushes at all? Is it really a Magneto, i.e. the armature spins a permanent magnet rather than an electromagnet powered by slip rings? The warning about not removing the armature without bridging it suggests a permanent magnet to me. Doesn't matter: Magneto or slip ring alternator, it should generate rotated in either direction.

Etymology is interesting. From the Greek word for force δύναμη. Dynamo appeared in 1882 as a contraction of Dynamo-machine, itself a contraction of Dynamo-electric-machine which dates to 1862.

Current electricity was originally called dynamic electricity and we still call the other sort Static Electricity.

There's nothing in the dictionary to suggest a dynamo produces DC rather than AC, so I guess the distinction between Alternator (AC) and Dynamo (DC) is technical English and came later.

Dave

Edited By SillyOldDuffer on 09/02/2021 13:25:55