Showmans Engine

Hi All

I need help for the last 10 years I have been building a 2 in Fowler and Burrell Showmans engine but I come to the part that to me and most of the trade is a black art The Dynamo .

I have 2 twelve volt car dynamos that I think will work but how would you wire these up and can they go in either direction will a resistance have to be fitted as the speed will be variable , I have asked at shows and every one seems lost as to my question , or is there a better way forward .

The trade sell end plate castings they look good any help would be great (scrumpy)

Try and seek out an old style car repairer/ autoelectrician who remembers times before the alternator. Not all that long ago. Or what about the vintage car enthusiasts who always seem to be at the same shows as the traction engine chaps. Sorry, can't help with the complicated stuff though.

Mick

Have a look at this thread on Traction Talk Forum, you will need to register to view.

Its by a guy who built a MJ Eng 2" Burrell Showmans and he details the setup

If you also use the advanced search on that forum to look for "dynamo" in teh miniatures section you will get a lot more info.

Lucas 12V dynamo also fits the MJ outer casting with a bit of tweaking.

Edited By JasonB on 03/08/2013 08:32:05

Be clear about whether you have a dynamo or a more modern alternator. A dynamo will produce a variable voltage depending on load and speed in it's native state because the regulator device is external for them (a special sort of relay). An alternator has the regulator built in.

A dynamo is just an electric motor run in reverse but not a permanent magnet variety. Therfore it has field coils for the magnets which have to be fed with current. (old timers may remember the Tycol model boat motors).

The field coils can be in series or parallel with the rotor winding and the dynamo generates its own current to feed them. In a dynamo they are in parallel but not connected directly - the wire goes via that regualtor. In a simple system the regulator can be replaced by a resistor which you would find by experiment for the speed and load you intend to run. Experiment by rigging it on your lathe to provide a variable speed drive.

Dynamos do have a preferred direction - imagine it fitted to a car- and will not work well in reverse. Check the brushes as they probably need replacement and will then give variable results until bedded in.

I have some limited knowledge of dynamos from older motorcycles. The Lucas and Miller dynamos are 3" diameter by 6" long and much smaller than car versions and so might be better for your model. You could hide them in a larger casing that replicated the traditional showmans dynamo frame.

They will produce 12v and 60 watts or more at 3,000 RPM. There are earlier (1930 - 1950) types with three wires and inbuilt regulators that I suspect are direction sensitive - these are not so useful. The post 1950 type usually have two connections: 1) an output (output can be configured positive or negative by quickly polarising the residual magnetism and reversing the field wiring), and 2) a field energising connection. Both grounds (earths) for these connections are common and connected to the main body. The field energising input must be fed the correct variable voltage to regulate the output. Nowadays we use small electronic regulators.

Many electrical generating devices (e.g. a magneto) are optimised for direction of rotation but it is the view that this type of electromechanically regulated dynamo will work in either direction, however the field windings will have to be switched internally.

The dynamos and regulators are commonly available from several supplies to the classic motorcycle market. They would be able to tell you which direction of rotation it is set for. You also find them on eBay.

If you want something that looks authentic measuring about 3" you could try making this:

http://www.modelsteamenginesuk.com/acatalog/Electrical_Generation.html

In Model Engineer, starting 17th March 1989, a series called "Going Electric" will tell all about using automotive generators, but I would look for something smaller, a good size motor is one from a battery drill, or you'll find a good one in an old H-P Ink Jet printer. These motors can be diguised in a false casing. Ian S C

The artical is actually about using the generator as a motor.