# Multiple 3 phase Rectifiers on alternator's ???



## janmarsh (Jan 13, 2009)

Would be grateful for expert advice on the following :

I am completing the convertion of a permanent magnet AC servo motor to a 3 phase alternator. It is very possible the output will certainly excede 150amps.

On ebay, Item number: 280339457212 is a diode bridge rectifier, 150amp 800v 3phase. Is it reasonable for me to think such unit's could be placed in parallel to cope with larger output ?


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## major (Apr 4, 2008)

janmarsh said:


> On ebay, Item number: 280339457212 is a diode bridge rectifier, 150amp 800v 3phase. Is it reasonable for me to think such unit's could be placed in parallel to cope with larger output ?


Hi jan,

I've seen plenty of high power industrial VFDs use parallel diodes to rectify incoming 3 phase. So I think the answer is yes, parallel diodes work.

Regards,

major


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## janmarsh (Jan 13, 2009)

Many thanks Major !


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## janmarsh (Jan 13, 2009)

Would be grateful for further expert advice.

I am now converting my third AC Servo Motor to three phase Alternator. The stator of this one has 36 poles, rotor is 4 pole permanent magnet.

I am wanting high amps/low voltage so have opted for Delta configuration.

Each phase, having twelve coils will be configured 6 series pairs.

My question is this: "If I then connect the series pairs to eachother in parallel, am I going to find myself with heat problems", or will amperage output simply be gained at lower R.P.M. without undue heating occuring ? 

Many thanks.


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## major (Apr 4, 2008)

janmarsh said:


> Would be grateful for further expert advice.
> 
> I am now converting my third AC Servo Motor to three phase Alternator. The stator of this one has 36 poles, rotor is 4 pole permanent magnet.
> 
> ...


Hi jan,

I'd say you're o.k. thermally if you keep the individual coil currents the same. Then going from the series connection to six path parallel, gives you six times the output current and one sixth the voltage, providing the same RPM and torque input.


Regards,

major


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## janmarsh (Jan 13, 2009)

major, As ever......... Many thanks again for your advice.


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## COS (Dec 23, 2008)

I don't know if this iss too lat but you SHOULD isolate each output of your bridge rectifier with a high current/voltage diode so output from one rectifier will not leak into the the other. Theoretically it shouldn't but a couple of cheap diodes will be worth the safety of the bridge rectifiers.
Runninf the bridge rectifiers will work but protect them. Also, consider using a high current inductor in series to filter ripple voltage to a minimum and a shunting cap to eliminate the ripple. This will give you a smoother DC voltage.
________
Mature live


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## janmarsh (Jan 13, 2009)

Certainly not too late COS. I shall definately make note of your reply. Thankyou.


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