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Re: Europa-List: Re: Ducati rectifier/regulators

Subject: Re: Europa-List: Re: Ducati rectifier/regulators
From: Jan de Jong <jandejong@casema.nl>
Date: Mon, 20 Jan 2014 16:40:25

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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