Today's Message Index:
----------------------
1. 09:10 AM - Re: IVO Prop current limiter (kfav8r)
2. 05:49 PM - Re: Overvoltage event (non-lithium battery) (John Keen)
3. 07:02 PM - Re: Re: IVO Prop current limiter (Robert L. Nuckolls, III)
4. 09:35 PM - Re: Re: IVO Prop current limiter (Mike)
Message 1
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| Subject: | Re: IVO Prop current limiter |
It's been awhile, but thought I'd post my latest results with this circuit.
I finally have the engine running on my Kitfox, with the medium IVOProp and the
limiter circuit.
With the engine off, the prop changes pitch in both directions, mostly without
premature cutoff from the limiter. I measured the current to the prop motor, with
readings between about 3 Amps and 9 Amps, depending on the state of the prop
pitch.
With the engine (912ULS) running, at any RPM setting, the limiter cuts off prop
power almost immediately. I think this is what Mike Welch described some time
ago. There is a small amount of pitch adjustment with each switch engagement
before current is cut off, shown by small RPM changes.
I've not yet measured the current to the prop with the engine running, but will
attempt that.
Doug
--------
Doug
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=468933#468933
Message 2
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| Subject: | Re: Overvoltage event (non-lithium battery) |
This may be a naive question but is there any reason why then I can't use on
e master switch to turn on both the battery and alternator?
If I turn my master off and e-bus on I would then be on battery-only operati
on.
John Keen
0412 141 833
> On 2 May 2017, at 11:59, Robert L. Nuckolls, III <nuckolls.bob@aeroelectri
c.com> wrote:
>
> At 04:48 PM 5/1/2017, you wrote:
om>
>>
>> I had what is suspected as being an overvoltage event take out my nav rad
io recently.
>>
>> Here's the platform data:
>> Continental IO550
>> 24v electrical system
>> VPX Power Distribution system
>> Stock 50a alternator w/B&C LR3C-24 voltage regulator
>> SD20 backup alternator w/B&C LS-1A voltage regulator
>> Val Avionics NAV2KR nav radio
>>
>> The other day I got a circuit fault alarm on the nav radio circuit when I
hit the avionics master. When I switched to the screen to get details, it s
howed "short circuit". Powered cycled the circuit and the fault returned. We
nt to troubleshoot once I got home and found no fault in the wiring. Sent th
e radio back to Val and got a call that the overvoltage protection circuit w
as blown. That it would have taken 50+ volts to cause that. Talked with the
m for a while about what could have caused the OV and the only thing they co
uld think of after describing how I operate was powering on the alternator A
FTER engine start.
>>
>> I was told (and have since done) to start on battery only then after the e
ngine was running, turn on the alternator. And I never turn on the avionics
until the alternator is on.
>>
>> Then I threw the scenario to the VPX guys. They don't know what could ha
ve caused an OV event to take out the nav radio (and only the nav radio. All
other devices are fine). But they agreed with Val that the alternator shoul
d be on during engine start. And that the VPX has overvoltage protection bu
t only when the alternator is on.
>>
>> So I guess my question is: Have I been starting planes the wrong way for t
he past 20 years? Should the alternator be on during engine start?
>
> It doesn't matter. Waazayyy back when, the exemplar generator
> regulator had three principal components. Three relay-looking
> devices were configured (1) to prevent the back-feed of battery
> voltage into the generator (making it run like a motor), (2) an
> output current limiter to prevent smoking the armature wires
> due to overload and (3) a voltage regulator.
>
>
>
>
>
> Unlike the generators of yesteryear, an alternator is
> inherently current limited by its magnetics. This feature,
> combined with the diode array (converts stator winding
> AC voltage in to battery friendly DC) means that CURRENT
> LIMIT and reverse current cuttouts are not necessary.
>
>
>
> The key phrase in the foregoing narrative is CURRENT
> LIMITING. Whether you're speaking of generators or alternators,
> there is a finite limit to the current they can supply.
> That current level is only a small fraction greater than
> the nameplate rating of the machine.
>
> Wwwaaay back when, the avionics master switch was
> perceived to be a prophylactic against 'spike generated
> by starters'. In years since, DO160/Mil-STD-704 design
> verification guided the appliance designer in the
> simple task of making their product immune to any
> voltage excursions one might expect from the ship's
> DC power system. Over those same years, I've had
> occasion to attach data acquisition systems to dozens
> of airplanes. Like the elusive 'snipe', no matter how
> close I looked or longingly I called . . . no such
> critter ever emerged.
>
> A question I've asked dozens of appliance engineers
> goes something like this: "Under what conditions of
> normal or inadvertent abnormal management of the aircraft's
> power system will bus voltage exceed catastrophic
> failure limits for your product?"
>
> The real answer should be "none". In 50 years
> of working with alternators, starter generators
> and batteries both in the lab and in aircraft,
> I've never had the slightest concerns for turning
> batteries and alternators on/off in any order.
> An alternator coming on after the engine is started
> may deliver a small overshoot . . . usually less than
> 1 volt due to regulation dynamics. But in no way
> can it push the bus to levels suggested by your
> radio guy.
>
> Another set of questions to ask: "How much current
> do you need to push into a battery to elevate the
> 28v bus to say, 50 volts?" The answer is:
> "hundreds of amps for an EXTENDED period of time . . .
> like tens of seconds."
>
> The next question: "How does an alternator rated
> at 60 amps produce such an event?" The answer is:
> "It can't".
>
> If the ov protection system built into the radio
> was damaged, I hypothesize a design or manufacturing
> flaw. I'd be willing to help them sort it out . . .
>
>
> Bob . . .
Message 3
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| Subject: | Re: IVO Prop current limiter |
At 11:09 AM 5/3/2017, you wrote:
>
>It's been awhile, but thought I'd post my latest results with this circuit.
>
>I finally have the engine running on my Kitfox, with the medium
>IVOProp and the limiter circuit.
>
>With the engine off, the prop changes pitch in both directions,
>mostly without premature cutoff from the limiter. I measured the
>current to the prop motor, with readings between about 3 Amps and 9
>Amps, depending on the state of the prop pitch.
>
>With the engine (912ULS) running, at any RPM setting, the limiter
>cuts off prop power almost immediately. I think this is what Mike
>Welch described some time ago. There is a small amount of pitch
>adjustment with each switch engagement before current is cut off,
>shown by small RPM changes.
>
>I've not yet measured the current to the prop with the engine
>running, but will attempt that.
That idea goes back a ways . . . we started talking
about it early 2011 I think . . .
The 0.1/0.2 paralleled resistors in the source of Q114
offers a current limit on the order of 9 amps.
If the system is 'twitchy' with the engine
running, I'm wondering if we're not getting come
noise into the latch-loop Q103-R106-D110-Q115-
D109-R105.
How is the circuit constructed? Can you post
some pix?
Bob . . .
Message 4
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| Subject: | Re: IVO Prop current limiter |
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