lml@lancaironline.net Mailing List Archive

<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << 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.