X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 23 Jan 2009 17:47:10 -0500 Message-ID: X-Original-Return-Path: Received: from QMTA01.westchester.pa.mail.comcast.net ([76.96.62.16] verified) by logan.com (CommuniGate Pro SMTP 5.2.11) with ESMTP id 3438500 for lml@lancaironline.net; Thu, 22 Jan 2009 10:15:19 -0500 Received-SPF: pass receiver=logan.com; client-ip=76.96.62.16; envelope-from=jabeluttrell@comcast.net Received: from OMTA01.westchester.pa.mail.comcast.net ([76.96.62.11]) by QMTA01.westchester.pa.mail.comcast.net with comcast id 6b3f1b0050EZKEL51fEMBx; Thu, 22 Jan 2009 15:14:21 +0000 Received: from JabesComputer ([174.48.39.73]) by OMTA01.westchester.pa.mail.comcast.net with comcast id 6fEb1b00F1ahy5a3MfEdb6; Thu, 22 Jan 2009 15:14:42 +0000 X-Original-Message-ID: From: "Jabe Luttrell" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: Alternator Load Dumping and Voltage Spike X-Original-Date: Thu, 22 Jan 2009 10:14:30 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0130_01C97C7A.370DDEC0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5512 This is a multi-part message in MIME format. ------=_NextPart_000_0130_01C97C7A.370DDEC0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Alternator Load Dumping and Voltage SpikeHi Jeff, If you're trying to squelch load dump transients there are a few things = to consider: 1. The transient seeks to maintain the power your load was drawing just = before it was shut off; the higher the initial power load the higher the = transient, 2. The voltage generated during the transient will be ain indirect = function of the remaining load; the greater the remaining load the = smaller the transient. 3. 12vdc systems will have lower peak voltages (~60vdc max) than 24vdc = systems (~90vdc max) 4. Load dump transients are relatively long, many milliseconds rather = than microseconds. 5. To absorb the transient with transorbs or TVS's requires big = components or lots of them ($$). 6. To absorm the transient with capacitors requires big capacitors (F = not microF). 7. Failure of your suppression devices will cause complete loss of the = electrical system. 8. The best absorber is a battery and tight, clean connections. 9. High voltage dropout of the alternator will protect against load dump = and regulator failure. 10. Robust connection between the alternator and the battery with as few = components and connections between them as possible is the best = protection. 11. An old battery, short on acid level, can act as a open between the = battery and alternator and lead to a load dump transient. 12. As an alternative approach to protect a sensitive load, you can use = a three terminal linear voltage regulator (LDO type); e.g. 7812. It = will be non-regulating most of the time until the transient occurs then = it will prevent the transient from reaching the load. One for each load = will be cheaper than the necessary transorb. The regulator will need = heat sinking because the dropout voltage x the load current will be = dissipated continually. Also the devices have a grounded substrate which = eliminates any special treatment when affixing them to structure = directly. Place them on the load side of the circuit breaker. Jabe Luttrell ----- Original Message -----=20 From: F. Barry Knotts=20 To: lml@lancaironline.net=20 Sent: Thursday, January 22, 2009 9:17 AM Subject: [LML] Re: Alternator Load Dumping and Voltage Spike Jeffrey Liegner, MD wrote:=20 I recently experienced a sudden failure of my PS Engineering = intercom during the take off roll,=20 Very interesting and timely post. I have been having a similar = experience. My LIV-P has been eating avionics. In 100 hours I've lost the PS = Engineering audio panel, AOA computer, encoding altimeter, one headset, = and my electronic trim controller board (Precise Flight)...The loss of = trim was particularly troublesome, it went out during decent and just = before I needed to shoot an ILS...fortunately to a high ceiling. I have also discovered a nasty power surge that occurs only when I = shut off the low boost pump and then only on some occasions. My first = impression was that I might have a big back EMF surge. There's no = obvious surge when I have the high boost on, though, but I've only = attempted that on the ground at idle or slightly above. I have a couple TranZorb devices on their way from Digi-Key. I'm = concerned that they may not be nearly beefy enough to withstand the = surges that seem to be going through my avionics. And exactly where do = I put them? Across the leads to the fuel pump? Any thoughts about how the chase down this intermittent gremlin? LIV-P, Conti TSIO-550, 24V 100 Amp alternator with full size battery, = reserved and isolated backup 24V 100 Amp alternator and full size = battery. Barry Knotts ------=_NextPart_000_0130_01C97C7A.370DDEC0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Alternator Load Dumping and Voltage Spike
Hi Jeff,
 
If you're trying to squelch load dump = transients=20 there are a few things to consider:
 
1. The transient seeks to maintain = the power=20 your load was drawing just before it was shut off; the higher the = initial power=20 load the higher the transient,
 
2. The voltage generated during the = transient will=20 be ain indirect function of the remaining load; the greater the = remaining=20 load the smaller the transient.
 
3. 12vdc systems will have lower peak = voltages=20 (~60vdc max) than 24vdc systems (~90vdc max)
 
4. Load dump transients are relatively = long, many=20 milliseconds rather than microseconds.
 
5. To absorb the transient with = transorbs or TVS's=20 requires big components or lots of them ($$).
 
6. To absorm the transient with = capacitors requires=20 big capacitors (F not microF).
 
7. Failure of your suppression devices = will cause=20 complete loss of the electrical system.
 
8. The best absorber is a battery and = tight, clean=20 connections.
 
9. High voltage dropout of the = alternator will=20 protect against load dump and regulator failure.
 
10. Robust connection between the = alternator and=20 the battery with as few components and connections between them as = possible is=20 the best protection.
 
11. An old battery, short on acid = level, can act as=20 a open between the battery and alternator and lead to a load dump=20 transient.
 
12. As an alternative approach to = protect a=20 sensitive load, you can use a three terminal linear voltage regulator = (LDO=20 type); e.g. 7812.  It will be non-regulating most of the time until = the=20 transient occurs then it will prevent the transient from reaching the=20 load.  One for each load will be cheaper than the necessary = transorb. =20 The regulator will need heat sinking because the dropout voltage x the = load=20 current will be dissipated continually. Also the devices have a grounded = substrate which eliminates any special treatment when affixing them to = structure=20 directly.  Place them on the load side of the circuit=20 breaker.
 
Jabe Luttrell
 
 
----- Original Message -----
From:=20 F. Barry Knotts
Sent: Thursday, January 22, = 2009 9:17=20 AM
Subject: [LML] Re: Alternator = Load=20 Dumping and Voltage Spike


Jeffrey Liegner, MD wrote:=20
I recently experienced a sudden failure of my PS Engineering = intercom=20 during the take off roll,

Very interesting = and timely=20 post.  I have been having a similar experience.

My LIV-P = has been=20 eating avionics.  In 100 hours I've lost the PS Engineering audio = panel,=20 AOA computer, encoding altimeter, one headset, and my electronic trim=20 controller board (Precise Flight)...The loss of trim was particularly=20 troublesome, it went out during decent and just before I needed to = shoot an=20 ILS...fortunately to a high ceiling.

I have also discovered a = nasty=20 power surge that occurs only when I shut off the low boost pump and = then only=20 on some occasions.  My first impression was that I might have a = big back=20 EMF surge.  There's no obvious surge when I have the high boost = on,=20 though, but I've only attempted that on the ground at idle or slightly = above.

I have a couple TranZorb devices on their way from=20 Digi-Key.  I'm concerned that they may not be nearly beefy enough = to=20 withstand the surges that seem to be going through my avionics.  = And=20 exactly where do I put them?  Across the leads to the fuel=20 pump?

Any thoughts about how the chase down this intermittent=20 gremlin?

LIV-P, Conti TSIO-550, 24V 100 Amp alternator with = full size=20 battery, reserved and isolated backup 24V 100 Amp alternator and full = size=20 battery.

Barry Knotts


------=_NextPart_000_0130_01C97C7A.370DDEC0--