Posted by daestrom on June 1, 2009, 9:43 pm
>>
>>
>> Gordon wrote:
>>
>> >
>> > > So, is the diode breaking down and conductong in both directions when
>> > > the voltage exceeds the PIV? That would explain why it is putting a
>> > > load on the alternator. I would have expected that from a zener
>> > > diode
>> > > but I thought a typical rectifier diode would simply burn out and
>> > > become open if overloaded.
>> > >
>> >
>> > Yes, when the PIV is reached, the diode will conduct in the
>> > reverse direction. Not completely tho, there will be a
>> > voltage drop on the diode roughly equal to the PIV. It
>> > will be acting like a zener.
>>
>> Actually usually an avalanche breakdown diode but commonly misunderstood.
>>
>> Diodes in series is *dumb*.
> I'm not sure why you are saying that--the diodes are not really in series
> in
> this 3-phase rectification circuit. I merely used "series" do describe
> how
> the diodes were connected in a way that most people could easily
> understand
> without seeing a schematic. It's basically a bridge rectifier circuit
> plus
> another half of a bridge.
Commonly referred to as a three-phase full-wave rectifier.
daestrom
Posted by Ulysses on June 2, 2009, 1:53 pm
> >
> >>
> >>
> >> Gordon wrote:
> >>
> >> >
> >> > > So, is the diode breaking down and conductong in both directions
when
> >> > > the voltage exceeds the PIV? That would explain why it is putting
a
> >> > > load on the alternator. I would have expected that from a zener
> >> > > diode
> >> > > but I thought a typical rectifier diode would simply burn out and
> >> > > become open if overloaded.
> >> > >
> >> >
> >> > Yes, when the PIV is reached, the diode will conduct in the
> >> > reverse direction. Not completely tho, there will be a
> >> > voltage drop on the diode roughly equal to the PIV. It
> >> > will be acting like a zener.
> >>
> >> Actually usually an avalanche breakdown diode but commonly
misunderstood.
> >>
> >> Diodes in series is *dumb*.
> >
> > I'm not sure why you are saying that--the diodes are not really in
series
> > in
> > this 3-phase rectification circuit. I merely used "series" do describe
> > how
> > the diodes were connected in a way that most people could easily
> > understand
> > without seeing a schematic. It's basically a bridge rectifier circuit
> > plus
> > another half of a bridge.
> >
> Commonly referred to as a three-phase full-wave rectifier.
Ah. Thanks. I figured it had to be called something.
> daestrom
Posted by Eeyore on May 30, 2009, 7:12 pm
Ulysses wrote:
> I'm not sure what the rating is on the diodes I'm using but I seem to recall
it was
> around 450 volts.
If you had 600V on the cap, I'd be looking at at least double that for safe use.
Graham
--
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my
email address
Posted by Eeyore on May 30, 2009, 7:10 pm
Ulysses wrote:
> Hi guys. I attached the coils and rotor (the entire PMA) from a Honda
> eu2000 generator to a 4 HP engine--direct drive, just like it originally was
> on it's original engine. This is a 3-phase alternator in a Y configuration
> so I connected two diodes in series to each output
Bad idea. You need to 'voltage share' to avoid avalanche breakdown with equal
value resistors across each diode of a value compatible with leakage current.
Use appropriately rated diodes instead as determined by running the generator
with a light resistive load.
That's probably your only problem.
Graham
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>>
>> Gordon wrote:
>>
>> >
>> > > So, is the diode breaking down and conductong in both directions when
>> > > the voltage exceeds the PIV? That would explain why it is putting a
>> > > load on the alternator. I would have expected that from a zener
>> > > diode
>> > > but I thought a typical rectifier diode would simply burn out and
>> > > become open if overloaded.
>> > >
>> >
>> > Yes, when the PIV is reached, the diode will conduct in the
>> > reverse direction. Not completely tho, there will be a
>> > voltage drop on the diode roughly equal to the PIV. It
>> > will be acting like a zener.
>>
>> Actually usually an avalanche breakdown diode but commonly misunderstood.
>>
>> Diodes in series is *dumb*.
> I'm not sure why you are saying that--the diodes are not really in series
> in
> this 3-phase rectification circuit. I merely used "series" do describe
> how
> the diodes were connected in a way that most people could easily
> understand
> without seeing a schematic. It's basically a bridge rectifier circuit
> plus
> another half of a bridge.