Building a dynamo/generator into your design for power - any experience?

I am working on a design (weather sensing) whereby I have a fixed shaft and on that shaft is a platter that spins. There will be some sensing electronics and a RF transceiver mounted that must operate. The original consideration was to use batteries to power this, however I was thinking it would be possible to design in a dynamo/generator which would save introducing parts that require frequent replacement.

I was thinking that if a permanent magnet were installed in the shaft such that the magnet is in the center of the platter (i.e. the magnet passes through the center of the platter), then some coils could be mounted on the platter in a ring around the shaft/magnet, and as the platter rotated I would get pulses of current in the coils, which could then be rectified and smoothed the charge a rechargeable battery to keep everything running.

Does that sound reasonable? Does anyone have any experience on the realities of generator design? I have no idea where to start with the calculations on how powerful the magnet would need to be, how close the coils must be, or how thick and how many turns of wire would be necessary to generate the power needed. The circuit runs on 5V and I can calculate the maximum speed that the platter can rotate at, but beyond that I am not sure where to go, hence I am here.

Any input?

Reply to
fastturbovette
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It is a reasonable idea, but it would be simpler not to reinvent the wheel. Why not just mount the platter on a permanent magnet DC motor housing, and fix the shaft to the stationary part. Then the armature terminals will rotate with the platter and provide power.

Reply to
John Popelish

That'd work, if the platter spins fast enough to produce usable EMF.

Another approach would be to transfer via a "rotary transformer", one side of which is stationary. See, e.g.,

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This can be done very compactly with a pair of ferrite pot cores. You can scrounge excitation electronics free from a burned-out compact fluorescent bulb -- they have electronic ballast elex built into the base that converts 117VAC 60 Hz to about 30 KHz.

Reply to
Don Foreman

I had thought of that, however I do not think it would be possible. The shaft must be 3/4 diameter and the shaft must be supported at either end. That would dictate a pretty beefy motor and also it must be quite strong to hold up to relatively high wind speeds. "de-coupling" the support shaft and connecting to a motor shaft on either end would pose a problem structurally, so I thought I'd see if anyone has any experience or pointers in designing such?

Reply to
fastturbovette

You could couple the shaft to the motor with a belt or cable.

Why not use a rechargeable battery and a solar panel? You might be able to hack one of those rechargeable garden lights to do what you want.

Reply to
Homer J Simpson

Your choice of how to solve this problem will have a lot to do with how much electrical energy (i.e. power) is required for the circuitry on the platter. A second consideration to take into account is the range of rotational speed that the platter is expected to work within. And lastly is there a dwell time between when the rotation is within operable range and when it is not in range of expected operation where power is still required.

It sounds like your application is a wind generator monitor of some sort. I expect that there will be periods of no rotation at all that could go on for some time. Do you need to have platter power during this time....and if you use rechargable batteries can they hold up through the worst case of low to no rotation.

As with any project there are many variables to consider. If this were my project I would consider a system where I used a low power design for everything on the platter. I would then couple the necessary power from fixed shaft to the rotating platter through a concentric transformer mechanism where one winding rotates with respect to the other. I would then drive the fixed side coil with a power driver at some reasonably high frequency (KHz to 10's KHz range comes to mind) and then rectify off the rotating coil to get power up on the platter. The fixed coil driver side can be powered off the normal wind generator output if there is available wind and can be powered off a static power source or the power grid in cases where the wind is slow or non-existent.

This scheme will eliminate the wide range speed and poor efficiency at low speeds of a direct generator approach.

- mkaras

Reply to
mkaras

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