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I am doing a DIY three phase AC motor power generation project. I can understand the basics of electronics, and also understand how the wires are wired in a single phase rectifier. However, for three phase, I am unable to understand from any of the videos or documentation on how to do the wiring.

I am planning to buy something like this rectifier.

I get from the circuit diagram that the DC positive output is on the bottom left of the product image and the bottom right is the negative. I also get that the three live wires need to be connected on the other side.

My confusion is how the neutral of stator gets connected to the bridge rectifier, or is this not necessary? My stator looks like this image.

Smart Drive Stator

In the Stator the coil winding goes clockwise starting from the pin marked '110C1' and all three phase coils end at the small dark rectangle to the the right of the pin. Earlier, I just tested power generation by connecting my multimeter to one of the live phase pins and the neutral to the single joining of all phases.

Is there no neutral required, since when one phase is live, the others are not?

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    \$\begingroup\$ You leave the neutral open. Power flows between the live wires through the neutral point. The neutral connection would only be needed if you had unbalanced load on the generator which could only happen when one of the rectifier diodes is broken. \$\endgroup\$ – Janka Feb 13 '17 at 16:32
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The answer depends somewhat on what you intend with the AC and DC voltages afterwards, but one option is to ignore the Neutral line if you only want the DC output:

enter image description here

It would appear you have a 'Y' wired stator, so (if all you want is the DC output) you can safely ignore the Neutral.

All three phases are active all the time in a conventional generator. In your variant (which looks to be based on a washing machine motor) it depends on the configuration of the rotor magnets and stator coils.

I assume you are have already read things like this.

Additional: I'm not sure what you may have done with your motor windings, there are many projects where they are re-configured to get different voltage/current options. The table below shows the options tried at this Uni for different applications. In many cases the voltage output for the (usually with series connected pole windings) motor is too high at gas engine speeds so they get wired in parallel to reduce the voltage and increase the current capability.

enter image description here

I'd be tempted (and this is just my opinion) to wire the motor (series pole windings) as a Delta output configuration which will reduce the voltage ( this would reduce the voltage by (Y-phase-to-phase / 1.7) ) and increase the current capability (reduced phase to phase winding resistance) when gas engine driven.
And since the pole windings are stationary you could always bring them out individually and connect them into various configurations to test out your available voltage/current options at engine speed.

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  • \$\begingroup\$ Yes you are right. My motor is similar to the F&P and has a one large star winded stator. I tried connecting the neutral on my multimeter to one of the other two live input, and this time I was able to get more power out of it as opposed to when I had it connected to the last neutral on the motor. Would this mean that as a generator, this motor only have one or two live wires at any time? \$\endgroup\$ – Shahid Thaika Feb 13 '17 at 18:03
  • \$\begingroup\$ I'm not sure I understand what you did. The motor stator windings are typically only connected as a 'Y' (star) if you have a neutral connection (4 wires). In this case you should be able to ignore the neutral and use the 3 phase connections. If you use the neutral then you can create a ground with +ve and -ve supplies though with less voltage of course. If you connected neutral to any phase output you are shorting out one phase.... that's not a good thing to do! \$\endgroup\$ – Jack Creasey Feb 13 '17 at 19:36
  • \$\begingroup\$ What I meant to say was, earlier I connected the red wire of my multimeter to the first live wire pins and the black wire of the multimeter to the centre of the Y wiring... in other words where the three phases meet. When I connected the black to the third live wire pin, I got a higher volt generation reading while spinning the rotor. \$\endgroup\$ – Shahid Thaika Feb 13 '17 at 19:56
  • \$\begingroup\$ In a Y configuration, if you measure the voltage phase to phase, then this voltage will be 1.7 times what you measure phase to neutral (center of star). This is a result of the way voltages with differing phase relationships are added. The power you can supply with the generator is limited by the voltage, the current and the winding resistance (which causes voltage droop). Depending on the wire size of your particular winding tells you the maximum current that can flow in a winding. This is an absolute, beyond that you will overheat the windings. \$\endgroup\$ – Jack Creasey Feb 13 '17 at 20:33

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