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
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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