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1. 06:05 AM - Re: Re: Z8 Ground Power test switch (Noel Loveys)
2. 02:37 PM - Re: Z8 Ground Power test switch (user9253)
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Subject: | Re: Z8 Ground Power test switch |
Cessna uses a relay at the battery box to prevent reverse polarity form an
incorrectly wired ground source. If the polarity of the ground plug is
reverse the relay won't close so there is no chance of a reverse polarity
between the aircraft battery and the ground source. It's a nice simple
system which does however depend on the relay operating and not welding
itself closed. It would be simple to install a ground power indicator on
the panel so you won't try to take off trailing a ground power supply.
Noel
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of jonlaury
Sent: October 9, 2010 9:14 PM
Subject: AeroElectric-List: Re: Z8 Ground Power test switch
Bob,
> (Is it Jon or John??
It's actually John. I've had the email moniker for 20+ years from when ATT
would only allow 8 letters. It was for both me and my wife so we shortened
my name to 'jon' and Laurie's name to 'laury'. When email came into common
use, my wife got her own address and I stuck with this one.
Once again, you're flooding light on my little dilemma. I like your elegant
3 pos switch (w/appropriate indicator lights) and 2pole contactor idea. Do
you know a source for a 2 pole 12vdc 200-300 amp contactor? I didn't pull
anything up from Google in a quick search.
The simplest solution is to have stand alone contactors. I can use all my
existing switches, wiring, (FW pass throughs are sealed up), and the
contactor that's mounted for the GPJ. I would just get a Bosch type 40/60
amp ice cube relay w/neg spike suppression (Beuler makes several), for the
stby alternator. I will probably go this route as it is the simplest,
smallest and most economical solution.
Thank you again for trying to keep me from frying myself :) .
John
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=315233#315233
Message 2
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Subject: | Re: Z8 Ground Power test switch |
I agree with Bob McCallum about the danger of reverse polarity with the aux alternator connected in parallel with the ground power. The two circuits can be isolated with an inexpensive relay like this: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=255-1830-ND or available at auto parts stores.
Bob N will correct me if I am wrong, but I believe that Z-8 is a work in progress
and has not been finalized. Is the 9024 module available yet?
Rather than design your own circuit based on Z-8, I suggest that you use one of
Bob N's proven circuits like Z-12 or Z-13/8. Those have an endurance bus, which
in my opinion, offer more options and thus safety in case something goes
wrong with the electrical system.
Having a ground power receptacle might make it convenient to get your engine
started in case you run the battery down by leaving the master switch on. But
then you will be tempted to take off with an uncharged battery. And there is
the danger of damage to your expensive electronics from reversed polarity or
high voltage caused by someone with inexperience or absent mindedness. Adding
more weight and complexity will increase the odds of something going wrong.
If you are determined to design your own circuit, see the modifications that I
made to simplify it and to remove the parallel circuit around the OV circuit
breaker.
http://lh3.ggpht.com/_9Rmupq9lpCs/TLItnxSlz0I/AAAAAAAAAFU/_adRmhLnQag/s800/z8_188-a.jpg
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=315277#315277
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