Equally respectfully - "dumping to ground" is not dumping, but
connection to the negative DC output terminal.
I attach a little OpenOffice drawing that hopefully clarifies (I hope
that works).
Regards,
Jan
On 1/20/2014 11:21 PM, Greg Fuchs wrote:
>
> Respectfully, I believe that the circuit configuration that you are thinking
> of is incorrect, Jan de Jong.
>
> The SCR's do EXACTLY 'dump' the AC output DIRECTLY to ground.
> When one end of the thyristor connects to the alternating current output of
> the coil, and the other end to ground...then that is all they can do but
> short the AC output to ground. It is not acting as a PWM-like device at all,
> simply a grounding device. Call it a direct-connect.
>
> You mention heat. The direct-connect method is the best way to deal with the
> heat. The forward voltage drop of the 'dumping' device is low, and the
> current does not need to go through the diodes at all, which are
> bypassed...hence your lowest heat output.
>
> Since the 'dumping device' connects the alternator output directly to
> ground, without going through the diode, what is the power dissipated? While
> in the dumping mode, lets say the current to dump was 10 amps(I'll use your
> generously supplied information, so I don't have to look up specs) it would
> be 1.1V * 10 amps. That's it. 11 watts. That is much better than the 18
> Watts in your configuration.
>
>> (
>> a failure mode for the Ducati device is reportedly the loss of continuity
> of a diode pill attachment through thermal >cycling; fitting external
> parallel diodes has been proposed as a solution; replacing the whole device
> seems more
>> sensible
>> )
> Well, maybe so! However, if the failure mode is a loss in continuity, that
> would mean the diodes are opening. That would also mean that connecting the
> external diodes to the regulator would bring it back to life!
>
> Regards,
> Greg
>
>
> -----Original Message-----
> From: owner-europa-list-server@matronics.com
> [mailto:owner-europa-list-server@matronics.com] On Behalf Of Jan de Jong
> Sent: Monday, January 20, 2014 7:40 AM
> To: europa-list@matronics.com
> Subject: Re: Europa-List: Re: Ducati rectifier/regulators
>
>
> Re two-phase bridge rectifier/regulator.
> The 2 thyristors in the rectifier bridge do not short the AC input or "dump"
> anything.
> On the contrary, they disconnect the DC output from the AC input when the
> output voltage threatens to exceed the set voltage.
> All output current passes through one branch of one diode and one thyristor
> in series half the time and through the other identical branch also half the
> time.
> Heat development is proportional to the output current and the voltage drop
> across a branch.
> Voltage drops increase somewhat with current, so heat development increases
> more than linearly with output current.
> In the Ducati device the diode is reportedly a MR2510 pill (typically 0.75V
> at 10A, 0.8V at 20A), the thyristor can be a 2N6504 (typically 1.1V at 10A,
> 1.3V at 20A).
> So at 10A the two branches of the bridge are each expected to generate
> 0.5 x (7.5 + 11) = 9.25W (total 18.5W) of heat.
> And at 20A the two branches of the bridge are each expected to generate
> 0.5 x (16 + 26) = 21W (total 42W) of heat.
>
> (
> a failure mode for the Ducati device is reportedly the loss of continuity of
> a diode pill attachment through thermal cycling; fitting external parallel
> diodes has been proposed as a solution; replacing the whole device seems
> more sensible
> )
>
> Cheers,
> Jan de Jong
>
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