From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Over-voltage protection/alternator failure
Date: Sat, 4 Jan 2025 07:49:07 +0800
References: <list-3773526@lancaironline.net>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-3773526@lancaironline.net>
Message-Id: <2CF56A1F-C75D-4CEE-B637-3D2C2018638E@gmail.com>


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Hi Finn

Really appreciate your reflections and design ideas.
I had graded the risk of my smallish ~45amp alternator going HV as low, =
and had =E2=80=98assumed' that in such an event the 40Ah battery bank =
and ~20amp system load would ballast the system voltage for some time =
(minutes) before a critical engine failure was imminent.
My engine monitor will let me know =E2=80=98audibly=E2=80=99  as soon as =
the system voltage exceeds 15 volts.

=E2=80=98Assumptions=E2=80=99 right! I hadn=E2=80=99t got real =
confirmation of the real voltage/current over time in such an event.

The truth is I have always struggled to get a handle on how a three wire =
automotive alternator works electrically.
The 'Sense', I thought was simply the feedback for the regulator which I =
have from memory via a 5 amp fuse to the engine buss.=20
But what is this =E2=80=98lamp/field=E2=80=99 wire??=20
In mine it=E2=80=99s not connected, and again I =E2=80=98assumed=E2=80=99 =
that as my idle is ~1900 rpm this was spinning enough to excite the =
system and self sustain the magnetic field at that point.
Perhaps I ought diode feed this from the Engine Buss?

I understood that because of the above characteristic once these =
alternators were generating power you couldn=E2=80=99t turn them off by =
de energising a =E2=80=98field=E2=80=99 etc. wire and therefore your =
plan to disconnect its output/ B terminal is required.

I=E2=80=99m thinking that in your circuit, when your Over Voltage relay =
is de-energised by the OVP popping the CB, like disconnecting an =
alternator from its battery, (at high RPM, not simply idle) might damage =
the alternator diodes/regulator though this is an acceptable outcome if =
it keeps the engine running in a critical situation.

What I would like to know in order to make an realistic risk assessment =
is:
1. How these alternators actually work electrically=20
2. What a High Voltage on the B lead will do over time.
	A. In the immediate mSec of an event and
	B Over the next 5 minutes

How is your RV4?
I hope you can get back in the air soon.

Thanks again for the reflections.

Steve Izett


> On 3 Jan 2025, at 11:35=E2=80=AFam, Finn Lassen =
finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote:
>=20
> And this is the way I should have done it!
>=20
> The error I made (powering the overvoltage relay and alternator field =
via the 5A breaker that is pulled to  ground when OVP unit triggers) is =
what caused total power loss when battery failed  open.
>=20
> With an internally regulated alternator it needs to power itself after =
startup even when disconnected from battery. Because in case  of a OVP =
nuisance trip, the alternator will continue producing power. The =
33,000uF (or bigger) cap on the B+ terminal should ensure sufficiently =
clean (low ripple and noise) to power itself and the engine electronics =
is case of no battery (disconnected or failed open).  (Size it for your =
engine bus current draw, desired alternator RPM range and maximum ripple =
you can tolerate. C =3D I / (RPM/60*3*2*Vpp) --- three-phase =
bridge-rectified alternator. I my case 10 amps, 3,000 RPM and 1V =
peak-peak ripple ~ 0.033 or 33,000uF.
>=20
> You should probably have a way to monitor the voltage on the B+ =
terminal to ensure the OVP didn't trip on a real alternator runaway, =
before trying to reset the 5A breaker. (BTW, a 1A breaker should suffice =
-- it's only powering the overvoltage relay).
>=20
> Now I'm undecided whether to add a backup battery or not.
>=20
> Finn
>=20
> <Battery-AlternatorMin.png>--
> Homepage:  http://www.flyrotary.com/
> Archive and UnSub:   =
http://mail.lancaironline.net:81/lists/flyrotary/List.html


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<html><head><meta http-equiv=3D"content-type" content=3D"text/html; =
charset=3Dutf-8"></head><body style=3D"overflow-wrap: break-word; =
-webkit-nbsp-mode: space; line-break: after-white-space;">Hi =
Finn<div><br></div><div>Really appreciate your reflections and design =
ideas.</div><div>I had graded the risk of my smallish ~45amp alternator =
going HV as low, and had =E2=80=98assumed' that in such an event the =
40Ah battery bank and ~20amp system load would ballast the system =
voltage for some time (minutes) before a critical engine failure was =
imminent.</div><div>My engine monitor will let me know =E2=80=98audibly=E2=
=80=99 &nbsp;as soon as the system voltage exceeds 15 =
volts.</div><div><br></div><div>=E2=80=98Assumptions=E2=80=99 right! I =
hadn=E2=80=99t got real confirmation of the real voltage/current over =
time in such an event.</div><div><br></div><div>The truth is I have =
always struggled to get a handle on how a three wire automotive =
alternator works electrically.</div><div>The 'Sense', I thought was =
simply the feedback for the regulator which I have from memory via a 5 =
amp fuse to the engine buss.&nbsp;</div><div>But what is this =
=E2=80=98lamp/field=E2=80=99 wire??&nbsp;</div><div>In mine it=E2=80=99s =
not connected, and again I =E2=80=98assumed=E2=80=99 that as my idle is =
~1900 rpm this was spinning enough to excite the system and self sustain =
the magnetic field at that point.</div><div>Perhaps I ought diode feed =
this from the Engine Buss?</div><div><br></div><div>I understood that =
because of the above characteristic once these alternators were =
generating power you couldn=E2=80=99t turn them off by de energising a =
=E2=80=98field=E2=80=99 etc. wire and therefore your plan to disconnect =
its output/ B terminal is required.</div><div><br></div><div>I=E2=80=99m =
thinking that in your circuit, when your Over Voltage relay is =
de-energised by the OVP popping the CB, like disconnecting an alternator =
from its battery, (at high RPM, not simply idle) might damage the =
alternator diodes/regulator though this is an acceptable outcome if it =
keeps the engine running in a critical =
situation.</div><div><br></div><div>What I would like to know in order =
to make an realistic risk assessment is:</div><div>1. How these =
alternators actually work electrically&nbsp;</div><div>2. What a High =
Voltage on the B lead will do over time.</div><div><span =
class=3D"Apple-tab-span" style=3D"white-space:pre">	</span>A. In the =
immediate mSec of an event and</div><div><span class=3D"Apple-tab-span" =
style=3D"white-space:pre">	</span>B Over the next 5 =
minutes</div><div><br></div><div>How is your RV4?</div><div>I hope you =
can get back in the air soon.</div><div><br></div><div>Thanks again for =
the reflections.</div><div><br></div><div>Steve =
Izett</div><div><br></div><div><br></div><div><br></div><div><br></div><di=
v><br></div><div><br></div><div><br></div><div><br></div><div><br></div><d=
iv><br></div><div><br></div><div><br =
id=3D"lineBreakAtBeginningOfMessage"><div><br><blockquote =
type=3D"cite"><div>On 3 Jan 2025, at 11:35=E2=80=AFam, Finn Lassen =
finn.lassen@verizon.net &lt;flyrotary@lancaironline.net&gt; =
wrote:</div><br class=3D"Apple-interchange-newline"><div>

 =20
    <meta http-equiv=3D"Content-Type" content=3D"text/html; =
charset=3DUTF-8">
 =20
  <div><p>And this is the way I should have done it!</p><p>The error I =
made (powering the overvoltage relay <i>and</i>
      alternator field via the 5A breaker that is pulled to&nbsp; ground =
when
      OVP unit triggers) is what caused total power loss when battery
      failed&nbsp; open.</p><p>With an internally regulated alternator =
it needs to power itself
      after startup even when disconnected from battery. Because in
      case&nbsp; of a OVP nuisance trip, the alternator will continue
      producing power. The 33,000uF (or bigger) cap on the B+ terminal
      should ensure sufficiently clean (low ripple and noise) to power
      itself and the engine electronics is case of no battery
      (disconnected or failed open).&nbsp; (Size it for your engine bus
      current draw, desired alternator RPM range and maximum ripple you
      can tolerate. C =3D I / (RPM/60*3*2*Vpp) --- three-phase
      bridge-rectified alternator. I my case 10 amps, 3,000 RPM and 1V
      peak-peak ripple ~ 0.033 or 33,000uF.<br>
    </p><p>You should probably have a way to monitor the voltage on the =
B+
      terminal to ensure the OVP didn't trip on a real alternator
      runaway, before trying to reset the 5A breaker. (BTW, a 1A breaker
      should suffice -- it's only powering the overvoltage =
relay).</p><p>Now I'm undecided whether to add a backup battery or =
not.<br>
    </p><p>Finn<br>
    </p>
  </div>

<span =
id=3D"cid:B4943BAA-A228-4D1B-93DA-5CF4EBA4DBA4">&lt;Battery-AlternatorMin.=
png&gt;</span>--<br>Homepage: &nbsp;http://www.flyrotary.com/<br>Archive =
and UnSub: =
&nbsp;&nbsp;http://mail.lancaironline.net:81/lists/flyrotary/List.html<br>=
</div></blockquote></div><br></div></body></html>=

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