Ed,
I think the objective is to keep from having a wire-induced fire when you get a short to ground. If the insulation rubs and a short develops, you want a fuse/breaker sized to pop before the wire melts and causes a fire.

If the equipment has an internal problem, the fuse/breaker isn't going to help save it.
Bill Schertz
KIS Cruiser # 4045
----- Original Message ----- From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, October 20, 2006 5:12 PM
Subject: [FlyRotary] Fuse Ratings for Wiring??

One thing  I have never really understood  regarding  fuses (or CB for that matter) is  - why you would use a fuse/CB with the rating set to protect the wire!!!   If you have a system operating off a power wire, it is highly likely that the wire will flow much more current than the system requires by quite a bit.  So if you select a fuse or CB rating that protects the equipment then automatically it will protect the wire.

 However, if you select the rating to protect the wire, the system could easily fry and the fuse or CB might never trigger.  Just one of those things (wire size) that everybody uses as a guide for selecting the ratings (Fuse/CB) and yet, it has never made sense to me (and still does not) {:>)

I guess IF you put more system load  that used more current than a wire was rated for then a fuse sized for the system would not protect the wire which could over heat.  But, that is simply a bad wiring decision in selecting too small a wire in the first place. I guess the rational is better the system fry than the wire - but not certain I buy it.

I don't really lose sleep over this one - but, I do wonder from time to time about things we come to accept {:>)


Ed




----- Original Message ----- From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, October 20, 2006 5:47 PM
Subject: [FlyRotary] Re: Injector Switches !!! was Re: Powering fuel injectors

Welcome, Greg.

Yes, there are arguments pro and con about fuses and CB - its about the only thing I disagreed with Bob Nuckolls about {:>).  Probably influenced by my years flying military aircraft - where CB are everywhere and fuses no where {:>)

In any case, glad you are now aware of the "disable" switch function regarding doubling the fuel flow through on pair of injectors when the other is turned off.  You can fly easily on one pair - provided it is doing double duty with the fuel flow.

Ed

Thanks for that Ed,  I am using the EC2 but I hadn't gone through the install of it thoroughly yet and wasn't aware of that mode.  I'll make sure that it's done now.

I follow what you're saying about breakers instead of fuses and I have to agree,  but following the Bob Nuckolls school of wiring means that the fuses/breakers should be no more than 6" to a foot from the power source (battery) and the batteries are behind the rear baggage area and no where near the panel.  The argument for the fuses to be near the source of electric power is also valid considering the fuses are there to protect the wiring.

Greg

Hi Greg,

Looks like a good electrical system over all.      However, I would not feel comfortable with fuses in my critical system power line. But, I see that you are routing two power sources to each switch of your critical system which means if one fuse blows due to a transit spike, the other one, hopefully, will not.  Again, this is my own personal bias against fuses in critical systems - there are arguments to the contrary for sure.

One thing I did notice, is looking at your injector power switches, I am not certain if these are meant to be the same as Tracy Crook's Injector disable switches.  If they are (and they may not be), I do not see the connection that automatically grounds the "cold Start" mode in the EC2 when either injector pair are disabled (turned off).

 This may be a detail just not shown on the drawing - but it is crucially important.  If the injector power switch does not have the "cold start" grounding provision, then if you ever switch off one of the injector pairs, your fuel flow will drop approx by 1/2 half.  The reason is that (with Tracy's recommended switch set up) when you turn off one pair of injectors , that automatically grounds the "cold start" pin which causes the EC2 to double the duration of the PW (Pulse Width) signal to the remaining injector pair.  This in turn doubles the amount of fuel from the active pair of injectors.  If the "cold start" is not activated (by automatic grounding of the cold start pin through a DPDT switch) when an injector pair is switched off,  then the PW signal does NOT double and the fuel flow through the one injector pair will only be 1/2 of what the engine needs.


Ed

Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.dmack.net/mazda/index.html

----- Original Message ----- From: "Greg@itmack" <greg@itmack.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, October 20, 2006 3:33 AM
Subject: [FlyRotary] Re: Powering fuel injectors

I'm trying to keep the number of switched down as well,  I attached a pdf
with my schematic which is a work in progress for your review.

I have noted that a lot of builders reduce a lot of this complexity by just
hanging everything off 1 or 2 fuses which is fine until a fuse blows and
then everything stops.

Greg RV8 down under

I am using Z-19 from the Aeroelectric Connection as a guide for wiring
my plane.  I would like to power the injectors from the battery buss.
Looking at Z-19, do I need to install a complete switch and diode system
for the injectors like is done for the fuel pump and ECU, or can I tie
on to the fuel pump OR the ECU system after either the switch (add a
separate diode) or after one of the diodes?
There will be the two DPDT switches to disable the primary and secondary
injectors after this connection.
My panel is becoming somewhat switch festooned and I would like to keep
more switches to a minimum.
How have you guys accomplished this?

Thanks.
Bill B


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