From: RWolf99@aol.com
Message-ID: <5e.e912.26d80a56@aol.com>
Date: Fri, 25 Aug 2000 13:43:50 EDT
Subject: Circuit Breakers for Hydraulic Pump Relays
To: lancair.list@olsusa.com
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
          <<  Lancair Builders' Mail List  >>
          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> 
>>
Is there really a need for a circuit breaker for the hydraulic pump relays on 
a 320/360?  Let me explain....

I'm using the EXP2 bus from Control Vision (NOT Vision Microsystems) for my 
power distribution system.  This device uses polyswitches instead of circuit 
breakers and has a 40 amp capacity.  The hydraulic pump itself will not be on 
this device, and will instead be connected via a stand-alone 50 amp breaker.  
Further, Control Vision recommends that pitot heat not be connected to their 
device, and that a stand-alone circuit breaker be used for that as well.  I 
could connect the pump relays to either the EXP2 bus or to a stand-alone 
breaker, but for the following aesthetic reason I want to connect it to the 
EXP2 bus.  

The aesthetic problem is that the EXP2 bus indicator module only leaves room 
for 4 circuit breakers on the tilted 360 electrical sub panel.  (I could 
always put another breaker elsewhere, I suppose, but it would look weird...)  
I'd like to use these for a 50 amp hydraulic pump breaker, a 40 amp breaker 
for the EXP2 bus itself, a smaller one (20 amps?) for pitot heat, and an even 
smaller one for electric trim (in case of a runaway trim -- I'd catch it 
before it went hard over and pull the breaker....maybe).

I know I need to protect the wiring to the pump relays, and this is what the 
EXP2 bus provides.  However, I'd plan on connecting the pump relays to a 
circuit that is always active when the master switch is on.  This means that 
I will have no means of turning off power to the flap relays in flight, short 
of turning off the master switch.

I don't see a real problem here.  To do a manual gear deployment test I would 
pull the 50 amp pump breaker, but a relay will be powered on as soon as I use 
the hydraulic bypass (dump) valve.  So what?  It's an intermittent-duty 
relay, but is this a problem?  (I have the Bosch relays recommended by Bill 
Rumburg and others.  I THINK it's an intermittent duty relay but I'm not 
sure.)  How long would the relays have to be powered on before I run into a 
problem?  In a real emergency where I have to disconnect the pump for some 
reason (like, it won't shut off) would I really need to pull the relay 
breaker?

A final thought.  I can give up the breaker on the electric trim system in 
favor of the pump relay.  What's the likelihood of actually catching a 
runaway trim and pulling the breaker before you're already at full trim?  How 
likely is the trim system to fail hard-over?  Most importantly, is the 
320/360 controllable with full trim?  (I suspect I'm opening a Pandora's box 
here.  Dive on in, guys!)

Thanks in advance.

- Rob Wolf
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
LML website:   http://www.olsusa.com/Users/Mkaye/maillist.html
LML Builders' Bookstore:   http://www.buildersbooks.com/lancair

Please send your photos and drawings to marvkaye@olsusa.com.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>