# How to make a device which is "Reverse solenoid"

Nidum
Gold Member
One of the main problems with linear generators is that for a large part of the forward and reverse stroke very little power is generated . Generation is velocity dependent and with SHM only middle third or so of each stroke is likely to do anything useful .

In the early days of the power industry there were a few 'beam engine' generators . Steam cylinder one end and big coil with plunger magnet the other end . Some early electric motors worked this way as well - big coil and magnet plunger at one end and crankshaft at the other end .

There have been many proposed uses for linear generators over the years most of which have disappeared . The only application I know of which seems to have been reasonably successful is in tethered bobbing buoy wave power generators .

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Merlin3189
Homework Helper
Gold Member
One of the main problems with linear generators is that for a large part of the forward and reverse stroke very little power is generated . Generation is velocity dependent and with SHM only middle third or so of each stroke is likely to do anything useful .
I wonder if this was also true of a simple single (or bi-) phase rotary generator? Only two peaks per revolution.
By adding more poles you got more peaks per revolution, but still peaks and nulls . By going to 3 phase those peaks overlap.

And does this matter?
For the torch, I assume, the AC is rectified and smoothed by a capacitor or battery/cell and used to power a DC driver for a LED. It may actually be better to have peaks of high voltage rather than a continuous low voltage, as these can be more efficiently rectified.

How efficiently input energy is converted to electrical energy, what average power can be achieved, how well the generator fits the source of energy and costs are all important considerations.
Your wave generator may suit this type of generator because linear oscillating motion may be easier to derive from waves, than rotary motion.
The linear generator torch may be less efficient than a rotary generator turned by a handle, but it can be operated by one hand and maybe it will charge without any special attention from the natural motion of walking.

I carry no torch for linear generators, but they may well have niche applications. So the interesting engineering questions arise about how to make them as good as we can.

Baluncore
2019 Award
Perhaps instead of one large sliding magnet in one long coil, it would be better to have a series of short magnets sliding between a toothed stator and a series of coils?
That is how it is done in free piston alternators. A stack of magnets moves with the piston in a ceramic cylinder. Many coils, (with 1/3 the pitch of the magnets), are wound around the cylinder and connected as three phase power for rectification and battery charging.

I remember an interview with Eric Laithwaite in the 1970s. He said human powered flight was impossible.

Baluncore