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

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.

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.

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

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

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

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

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

MichaelG.

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

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

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

Dynamo generators will motor, when connected to a DC supply and supply DC output. Alternator generators will not motor and produce an alternating output. They are all generators but either DC or AC.

Dynamos are, therefore ‘driven motors’ (look at the name). Obviously designed to generate rather than motor, but basically of the same form. They have commutators and need brush gear whereas the alternator generator has slip-rings and brushes. Remember, too, that commutator motors will operate with either a DC or AC supply.

As far as I am aware, all dynamos are armature-wound (for the output), but alternators may be armature- or stator-wound for the output. Vehicle alternators are all stator-wound, these days. Most alternating generators, which are required for a DC output, are three phase (or more) machines which will deliver a DC output (after rectification) with much less ripple than possible with a single phase output.

Armature wound alternators are less common these days but have certain advantages over stator wound versions. Weight is not usually one of those as the frame is often basically a rolled steel magnet, but starting inductive loads is a definite advantage over the stator-wound offerings with electronic voltage regulation.

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The advert clearly mentions slip rings … therefore there must be something[s] playing the role of brushes.

Did you watch the little video, Dave ?

MichaelG