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1. 09:10 AM - Re: What makes diode get warm (Eric Schlanser)
2. 06:16 PM - Re: What makes diode get warm (Robert L. Nuckolls, III)
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Subject: | What makes diode get warm |
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Which Z diagram would it look like without the E buss?
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Eric
Time: 01:18:06 PM PST US
From: "plaurence" <peterlaurence6@gmail.com>
Subject: RE: AeroElectric-List: What makes diode get warm
Mike,
If you have a second alternator, and using B&C's regulators, you really
don't need the E buss.
Peter
//mail.yahoo.com
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Subject: | Re: What makes diode get warm |
At 01:06 PM 10/27/2009, you wrote:
>
>I have the B&C diode on the heat sink (smaller one). I was bench
>testing things to make sure the flow was correct, I just took the
>breaker panel and hooked up power to the main bus then the
>E-bus. The diode did not heat up at all, the flow was in the
>correct direction. I hooked up power to the E-bus and the diode did
>prevent current to the main bus, the main would only read 0.4 volts
>which I assume is normal. With this set up the diode again did not
>heat up. I then hooked up one of the 50W MR16 landing light bulbs
>to a CB thinking maybe I needed a load, again the diode did not heat up.
Perhaps it did . . . just not enough for you to perceive it
by feeling. Was your e-bus alternate feed switch OPEN
during the test. If so, then the normal feed path diode
would have been carrying all the e-bus loads and it would
warm up.
Why a diode on a heat-sink? How large are your anticipated
e-bus loads? The diode-bridge rectifier mounted on a metal
airframe surface is good for 10+ amps. Schottky diodes
are a bit better yet. I've tested this guy to 20A
http://aeroelectric.com/Catalog/AEC/9001/IM9001-700A.pdf
when mounted on a surface .062" thick with no additional
heat sinking.
>So what make the diode heat up, is it more load on the system or is
>it when there is power going to both buses, as when you have the
>master on and the E-bus alternate feed on at the same time.
If the alternate feedpath switch is closed, then the
normal feed-path is bypassed and the diode will carry
no current . . . nor will it warm up.
>With both buses getting power the diode is getting power from both
>sides. I hear you can fly around this way but not sure I will, my
>plan now is the have my E-bus alternate feed under a guarded switch
>that stay off when guarded. When the E-bus gets power from the main
>via the diode there is a slight voltage drop . . .
and is the time when it dissipates a few watts of power
and will warm up. The degree of temperature rise depends
on mass and configuration of the heat sink.
> . . . the the E-bus alternate feed was on the flow from the
> battery to the E-bus would win out and supply the E-bus since the
> voltage from the main is lower. . . .
The main bus voltage isn't 'lower' but a voltage drop
in the normal feed path becomes insignificant when
the alternate feed path bypasses the diode.
> So would this meeting of currents be what heats up the diode? As
> far as flying around with the E-bus alternate feed on I don't see
> the need with my system I have a standby alternator.
How about being able to fire up the comm radio for
ATIS and clearance delivery before starting the engine?
THIS is the time that the alternate feed path
is also tested.
> Once I am using standby power then I might consider turning the
> alternate feed on for automatic switching in case the standby
> alternator then quit. Thank for the help.
The purpose of the alternate feed path switch is to
allow battery only operations without having a battery
contactor closed. You didn't mention which, if any
of the Z-figures you based your system. If you're
running Z-12, then having the switch "pre-closed"
offers no degree of automation. I'll suggest you do
a site search on "e-bus" at aeroelectric.com and
review the conversation about how the e-bus came into
being and what it's all about. There's about 30
hits that should offer some insight.
Over the past 15 or so years, folks have tended to
overload the e-bus and/or lost track of the
e-bus design goals. It may well be that your
design goals are served by not having an e-bus.
It's a strong probability that your normal feed-path
diode assembly is oversized.
Bob . . .
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