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1. 01:33 PM - Re: SDS CPI-2 Circuit Protection Question (Charlie England)
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| Subject: | Re: SDS CPI-2 Circuit Protection Question |
Well, this is obviously my 'Duhh' moment. I thought we were talking
about the full SDS engine control system. A 15 A feed just for ignition
coils threw me a curve.
My apologies to everyone involved for hammering on the injection issue.
Charlie
On 9/28/2021 4:24 PM, David Carter wrote:
> Let's also recall that the CPI-2 is an ignition-only product. It does
> not provide fuel injection. The PC680 would run much longer powering
> just a dual CPI-2 & minimal other loads. That said, I have two
> alternators & a single battery (Z101 architecture) in my CPI-2
> equipped plane. As long as there is gas to power the engine, the
> ignition should have electrons. The redundantly-powered engine bus
> supplies both the primary & backup power feeds to both CPI-2 ECUs &
> coils.
>
>
> ---
> David Carter
> david@carter.net <mailto:david@carter.net>
>
>
> On Tue, Sep 28, 2021 at 2:40 PM Charlie England <ceengland7@gmail.com
> <mailto:ceengland7@gmail.com>> wrote:
>
> On 9/28/2021 12:21 PM, Robert L. Nuckolls, III wrote:
>>>> 2. My requirement in my system for a separate engine bus, as
>>>> stated in other posts, has nothing to do with noise, or
>>>> resistance, or impedance. It's an *operational* requirement for
>>>> me, to keep fundamental engine control isolated from
>>>> fundamental airframe electrical control. 'Mag switches'
>>>> independent of the airframe 'Master switch'. The goal is to
>>>> mimic as closely as possible the emergency procedures we were
>>>> all trained to follow when we suspect an electrical issue in
>>>> flight. The dedicated bus also eliminates multiple potential
>>>> failure points in the supply path to the engine which are not
>>>> in the loop in traditional a/c systems (master switch, master
>>>> contactor, etc).
>>
>> I am mystified by incorporation of a backup battery with
>> this system. Are we confessing to an inability to craft
>> a failure tolerant electrical supply to a DUAL electronic
>> ignition system?
>>
>> Will the engine run on ONE of the two systems? If
>> your engine driven supply is compromised, is there
>> sufficient standby power generation to sustain
>> flight? This means your design STARTS with a
>> load analysis of what items are included on the
>> plan-b actions list.
>>
>> This was the kind of thinking from which the endurance
>> bus was crafted about 30 years ago. Question: how much
>> WELL MAINTAINED BATTERY is needed to keep the airplane
>> comfortably airborne for a period of time equal to or
>> greater than design goals?
>>
>> I had builders crafting systems in LongEz ships
>> that would exhaust a full tank of fuel during
>> battery only operations.
>>
>> Your design goals are your own but the tools
>> for achieving them are ancient protocol. Know
>> your energy budget then provide sources to equal
>> or exceed that budget as determined by
>> analysis on the bench and confirmed by
>> demonstration in the air.
>>
>> If you've got more than one battery on board,
>> you're overlooking something. If you have two
>> engine driven power sources, will the smaller
>> of the two sustain cruising flight while holding
>> the battery in reserve for descent and approach
>> to landing? If you're worrying about multiple
>> failures of critical items, what are the failure
>> modes and what are probabilities of loosing
>> two such devices during the consumption of one
>> tank of fuel?
>>
>> The elegant system architecture achieves design
>> goals with a minimum of hardware, cockpit controls,
>> weight, cost, etc.
>>
>> Thought problem: Z101 style engine bus. Triple
>> energy source (60 + 30 alternators) and a
>> well maintained battery sized to be determined.
>> Engine bus energy supplied by two delivery pathways.
>> All functional engine loads supplied by the bus.
>> No standby battery.
>>
>> Failure of what system feature would put this
>> system at risk for unplanned arrival with the
>> dirt? What are the limiting factors for achieving
>> design goals (endurance) after having experienced
>> the failure?
>>
>> I am concerned with talk of 'noise' in this
>> ignition/fuel system? Exactly what has been
>> demonstrated as a noise problem? Is the source
>> identified? What appliances are victims of this
>> 'noise'? What is being done to bring the
>> antagonist into a neighborly coexistence with
>> all players in the electrical sandbox?
>>
> Uh, not that I disagree with most of what you wrote, but you
> quoted my response to the OP, not his posts. :-) I did *speculate*
> on several different possible reasons that SDS recommended
> separate feeders for the ECU vs coils and/or injectors.
>
> I do think you need to remember that this:
>
> /I had builders crafting systems in LongEz ships//
> // that would exhaust a full tank of fuel during//
> // battery only operations.
>
> /only applies to mags, or electronic ignition-only systems. The
> combo of electronic ignition, electronic injectors, and high
> current fuel pump means that a PC680 equivalent battery is good
> for about 40 minutes, as long as all other airframe electrical
> loads are minimal. If there are 5-10 amps of unshed panel loads
> (not unusual these days), battery-only operation could be as short
> as 15-20 minutes.
>
> Automotive style injection changes the battery-only operation
> equations by a bunch.
>
> Thanks,
>
> Charlie
> /
> /
>
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