Bump

What voltage is the Loco motor? If it's 12 or 24V an engine driving a car / lorry alternator would be a better idea than a mains generator and transformer arrangment. A major limitation with mains generators is the need to keep the engine revs constant tto keep the correct frequency, this is not efficent. If using a vehicle alternator the engine can run at it's optimum revs as he AC frequence does not matter as it's turned to DC. This i what the modern "inverter" generators do, they generate "frequency wild" AC, convert to DC and then chop it up into AC at 50 (60) Hz.

If you use a vehicle alternator you could remove the regulator, connect the motor to the alternator output and control power and speed by varying the field of the alternator. Depending on the motor and if it has a governor you might have to provide some throttle control to that too.

Separate enge and alternator gives layout flexibility too.

Robert G8RPI.

A bit far to go to Hereford S M E at Broomy Hill, (At least you'd be approaching from the Ross side of town ) for help or advice, and to run?

Howard

As above, do stick to a 24 volt alternator, if that is the voltage you are choosing. Nobody has been electrocuted by a 24V DC supply – as far as I know!

Every voltage conversion loses energy. Many modern generators are a) rated for maximum output at 0.8 power factor (so kVA, not kW) and b) not many have a continuous output at the advertised maximum.

There are PMGs (Permanent Magnet Generators) out there that could be direct coupled to an engine, but a couple of belts and a pair of pulleys should not present too much hardship to engineer? Electronics controlling the engine speed should not be too difficult to arrange.

At the very least, go for a 110V generator if you must…

If you want to be a bit different you could have a three phase motor, which would be smaller than a single phase of the same power. You would supply it with a VFD (AC motor control) which would be supplied from the Generator. The downside of this sort of arrangement is that everything is high voltage. The nice side is that everything is available off the shelf.

John

Part 8 is in issue 4621, but I think most of the stuff you are asking about is in parts 6 & 7 in 4618 and 4619. The parts seem to be consecutive.

Neil

One post mentions Hydraulic drive motors. A petrol engine driving a pump to drive the wheels, foolproof. No electricity, no danger wow.

I'm not impressed by single-phase electric motors for this application. Compared with other types they have too many limitations: for traction their low torque (turning power) and difficult speed control are killers, on top of that they run bumpy with relatively poor efficiency. A DC Motor, Brushless or 3-phase motor will be much more satisfactory. As these and suitable controllers are all readily available I don't see any advantage in single-phase, only pitfalls.

Andy's problem is how best to match the output of an off-the-shelf 240VAC generator to a motor. Now that VFDs are affordable, I'd be inclined towards a 3-phase motor – reasonable torque, efficient and VFDs do a good job of speed control. However, even though it will easily out-perform a single phase motor my main concern would be a 3-phase motor's ability to shift a heavy load from a standing start. This is why IC engines need a flywheel, clutch and gearbox.

Indirect electric drive, for example when a generator charges a battery, which in turn powers a DC motor is a good compromise. The battery provides a high-current source which is good at satisfying peak demand during starting and acceleration.

These peak demands don't last long. Once an indirect drive vehicle is moving, the generator tops up the battery and then powers the wheels via the battery. Having a storage system deal with peaks means the generator can be sized to meet average demand, which is considerably less than the start-up demand. Get the sums right and the battery can also be quite small because it only works hard during starting. An interesting development in Hybrid Vehicles is the use of super-capacitors rather than batteries. Although a super-capacitor holds less energy than a chemical battery, it charges and discharges much faster at almost 100% efficiency. This makes super-capacitors attractive for stop-start operation and regenerative braking.

Dave