Ed Anderson
Joined: 10 Jan 2006
Posts: 475
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 Posted: Sat Jul 04, 2009 1:40 pm Post subject: DP3T switch? Switch wiring conundrum |
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Hi Mark,
From one of your messages, I understand you stated you simply do not have room for the two switch set up. While as indicated in the manual, you can indeed go flying without a disable switch, I think you will find that the benefits of the two switch system is worth additional effort. In event you do have a problem with one bank of injectors or the other, you can disable or turn them off and continue running more or less normally on the remaining bank.
Here is what may not be apparent, the two switch system does more than just turn on/off one of the other set of injectors (if that was all it did you could accomplish the same thing by just having a power switch for each bank) , it also grounds the EC’s “Cold Start” function. When that is grounded it automatically doubles the pulse duration to your injectors. True one bank is now disabled, so it does not turn on, but the other bank has its flow rated doubled.
So without it, if you turn off one set, then the same pulse duration is now being sent to half as many injectors, therefore your fuel flow is cut in half – meaning you are going to have to reach very quickly for that mixture control and crank it up to full rich. I do not recall, but I think the mixture control will only vary your flow by perhaps 25% (I could be wrong about this), so you may have difficulty getting the initial fuel flow back by mixture along – at the very least you are going to have to be messing with your mixture control during a period when things might be a bit stressful..
However, if you do have the two switch set up wired as recommended, the when you switch off on bank of injectors, it will AUTOMATICALLY double the pulse duration to the remaining bank of injectors thereby giving you close to your original fuel flow (provided of course your single bank of injectors are large enough to provide 75-100% of the total fuel flow you need). In my rotary installation (which has four rather large injectors in two banks), I have found the fuel flow easily provided more than adequate power on only one bank.
Also, the disable feature can be great for trouble shooting injectors or installation – not to mention that when you turn off /disable the injectors, there is no fuel being pumped into the engine as it winds down.
If you truly can not find a way to place two DPDT switches – then a DP3T switch might (I have not looked at it to see) provide a way to combine it into one switch, but as several have mentioned, then that becomes a single point of failure.
Decisions, decisions, decisions – not to mention compromises and alternatives and redundancy all makes this a somewhat challenging endeavor.
Good luck.
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson(at)carolina.rr.com
http://www.andersonee.com
http://www.dmack.net/mazda/index.html
http://www.flyrotary.com/
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.rotaryaviation.com/Rotorhead%20Truth.htm[url=http://www.dmack.net/mazda/index.html][/url]
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Mark R. Supinski
Sent: Friday, July 03, 2009 11:55 PM
To: aeroelectric-list(at)matronics.com
Subject: Switch wiring conundrum
Hello everyone-
I've been wracking my brain trying to figure out a way to control my EFI injectors using a single 2-XX switch. I can't find a way to do what I want to do (perhaps there is no way).
Here's what I'm trying to accomplish:
I have 2 banks of injectors. I need to be able to wire them such that I have a single 3 position switch (Primary - Both - Secondary). That part is easy enough using a 2-10. Here's the added trick: whenever Both is not selected, I need to tie a certain line on the EFI to ground. (This lets the EFI know one bank is offline & it automatically doubles the fuel flow through the remaining bank.)
The suggested implementation from the EFI manufacturer is to wire each bank to a 2-3. One side of 2-3 control whether the bank gets power, the other side controls whether the EFI line ties to ground. When an injector bank has failed, the pilot is "guessing" which bank to take offline. If he guesses right, the engine smooths out & all is well for a no-sweat landing. If he guesses wrong, the engine runs off & he must quickly restore power to the bank he just turned off & remove power from the "other" bank. Using two separate switches for this seems like a recipe for frantically flipping switches to try to get the engine back on if the pilot guesses wrong. My idea is that if it is a single pri-both-sec switch, it is much easier to simply reverse the position of the single switch you already have a hold of should the guess be wrong.
Hopefully someone is cleverer than I am and can figure out how to do this without requiring 2 switches! Or, at least I can find out it is impossible & I can resign myself to having two switches.
Thanks,
Mark
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_________________
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com |
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