Fisher and Paykel Smart Drive Motors

 

 

The Fisher and Paykel Smart drive washing machine uses an electronically controlled brushless motor which, after rewiring, can function as an effective three phase permanent magnet alternator to charge a low voltage (12-48 volt) battery bank. They can be setup to do this at a relatively low rotational speed, making them suitable for a wind or water turbine.

 

A smart drive stator with the windings cut ready for rewiring.

 

Warning: A smart drive motor is capable of generating dangerously high voltages (200+ volts), especially before being rewired and without a load connected. Anything you do is at your own risk, and I can take no responsibility for anyone who uses the information on these pages.

I have a few smart drive motors that I recovered from dead washing machines; it seems the electronics in the machines often fail before anything goes mechanically wrong, and this sometimes results in the whole machine being dumped. Getting the motor out is easy once you have the right tools and know where to start. I plan to add photos and details on doing this soon.

There a few components in the control modules that are worth saving, such as the MOSFET transistors; so far all the ones I've recovered have worked fine. Depending on the machine there are usually various other parts too, such as relays and high wattage resistors.

Now although a smartdrive motor will generate electricity in it's factory form, the voltage is too high (for charging a low voltage battery bank) and the current very low due the combined resistance of the windings, as each phase is wired in series.

To get good output you will need to rewire the windings. How this is done depends on (a) the number of turns and size of wire in the windings of the smartdrive motor you have, and (b) the voltage of the battery bank or load you intend to drive.

From the factory, smart drive motors are three phase, each phase consisting of 14 coils wired in series, for a total of 42. Every third coil around the perimeter is part of the same phase. The resulting six connections (two from each phase) are then wired in Star, giving three terminals.

This is where rewiring comes in.

 

A smart drive stator part way through rewiring, the first phase is just completed.

 

If you have the model of smart drive motor that has the thickest windings (and therefore the least number of turns) then there is a simple way to rewire it which can give good results for not much effort. Take out the bridging link that joins three of the six output terminals (which creates the star wiring configuration). Then establish which pairs of terminals are the three windings by testing with and ohm meter. Then connect each winding to a bridge rectifier. Then connect the DC output of your three bridge rectifiers together in parallel.

If you have one of the smart drive motors with thinner windings, or you want to get more power at a higher rotational speed, the coils can be disconnected from their original series wiring and reconnected in parallel. The smart drive motor will now need to spin significantly faster to reach charging voltage for a battery bank (14 or 28 volts depending on the setup) but when it does the output current will be greater. For a compromise you can cut every second connection, giving seven pairs of coils. The pairs are in series with each other, and all the pairs are then wired in parallel. This is most likely to suit a small windmill.

Either way you will (hopefully) end up with two connections for each phase(group of 14 coils). With these three pairs of wires, you have some more options.

First, and in my opinion best, option is to connect each phase to its own bridge rectifier (or diode rectifier arrangement, same thing) and then connect the (pulsating) DC outputs of the rectifiers in parallel. This way the voltage is the same as any one of the phases by itself, but there is three times the current capacity.

Note the three DC outputs from the rectifiers cannot be connected in series to get three times the voltage, because the DC voltage is pulsating as the alternator turns, and each output pulsates out of time with the other two. With big enough filter capacitors this might work, but I haven't tried it yet myself.

The other two options are star and delta connections. As far as I know, a delta connection would give the same output as the individually rectified setup, but with the small advantage of less diode volt drop.

 

More info coming soon.

 

Star reduces efficiency because it is putting two phases in series (any two at any given moment), which are out of phase, meaning you don't get double the voltage. Therfore you don't get full output that your alternator is capable of, which you could get in the individually rectified configuration. However it can be a simple solution to bring the voltage up to a useful level, for example to reach charging voltage for a battery bank at a given rotational speed. Wiring in star increases voltage by a factor of about 1.7, with the phase difference being the reason it is not doubled.

 

Then there is the bank of batteries being charged. Because the voltage of a permanent magnet alternator varies with its rotational speed, and the speed is likely to vary a lot with a wind or water turbine, charging a battery bank is usually the best option, giving a steady power supply independant of the generators.

You now have a fairly consistant output voltage, stored electricity while the turbine is not running, and a load on the turbine to prevent overspeeding damage. The only other thing that is required is a charge controller, to prevent the battery bank being overcharged. Here is a good one.

 

More info and picture to come

 

 

Links:
Comprehensive page by Micheal Lawley including graphs of his output data - Getting Smart with a Smart Drive
A company here in NZ that sells smart drive motors and related parts - EcoInnovation
Search this site for information about smart drive experiments - Fieldlines

 

Last Updated: January 2008