Project of the Month Winner
- Mar 23, 2014
- Reaction score
- Gold Coast, Australia
This may seem a strange title for a thread, let me explain. A lot of us here spend a good portion of our time making small engines, steam, internal combustion or whatever, and on completion would like to see the thing do a bit of work after all the effort of construction. It also provides a riposte to the inevitable “....yes, but what does it do?” question from those around us.
The most obvious solution to putting a small engine to work is to have it generate electricity, generally low voltage DC and watch the wonder in small eyes as lamps flicker and glow into life. The problem is finding suitable small DC generators that can fulfil the need and yet still look to be part of model making.
One solution is to use small series universal motors that power most plug in power tools. These are readily found used and are cheap. I had an old 240 volt AC Ryobi trimmer router that had broken it’s plastic guide plate and was hence useless (no spare parts) but the motor was still in good shape. I stripped it down, retrieved the armature, field carcass and brush holders and, because this was going to be driven by a model of a Victorian era steam engine, rebuilt it so that it looked as antique as I could make it. Now, here is the really good thing about series universal motors, they will generate low voltage DC, which is safe, if the field coils are arranged to be wired in parallel with the armature rather than series. This is now termed a Shunt wound generator. (I will post the circuit diagrams later if there is enough interest.) I separately excite the fields with low voltage DC as this allows me to control the output very precisely, however they can be made to self excite. Interestingly they will also run happily as a DC shunt wound motor and as can be seen in the video. At 32VDC the motor spins to around 2000 rpm which I think is pretty impressive. Perhaps I’m easily impressed but I thought this was worth sharing. Cheers, Peter.