---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 04/23/07: 11 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:56 AM - Re: PM ALTERNATOR- REGULATOR CHOICE (Ken) 2. 07:43 AM - Re: PM ALTERNATOR AC OUTPUT (Robert L. Nuckolls, III) 3. 08:31 AM - Re: PM ALTERNATOR- REGULATOR CHOICE (Robert L. Nuckolls, III) 4. 08:33 AM - Re: PM ALTERNATOR- REGULATOR CHOICE (Robert L. Nuckolls, III) 5. 09:26 AM - Re: PM ALTERNATOR SPIKE PROTECTION (NOT) (Robert L. Nuckolls, III) 6. 10:28 AM - Re: Relay and capacitor info needed () 7. 02:52 PM - Re: PM ALTERNATOR- REGULATOR CHOICE (Peter Harris) 8. 03:03 PM - Re: PM ALTERNATOR- REGULATOR CHOICE (Gilles Thesee) 9. 03:36 PM - Re: PM ALTERNATOR- REGULATOR CHOICE (Peter H) 10. 04:13 PM - Re: PM ALTERNATOR SPIKE PROTECTION (NOT) (Peter Harris) 11. 05:24 PM - Re: PM ALTERNATOR CHOICE OF REGULATOR (Peter Harris) ________________________________ Message 1 _____________________________________ Time: 05:56:37 AM PST US From: Ken Subject: Re: AeroElectric-List: PM ALTERNATOR- REGULATOR CHOICE Peter I'm not sure why you want a regulator that will start up without a battery? It sounds like you do have a battery present. Do you know for sure that your regulator will not start without a battery present? No the Ford regulators will not work with a PM alternator. THey are for wound field alternators. Wound field alternators have a field connection and circuit breaker that supples current to the field winding. No such thing with a PM alternator as the field magnetism is provided by Permanent Magnets. If you intend to use the B&C over voltage module with a PM alternator you do need a disconnect relay for the module so the module can disconnect the alternator. I use a $3. automotive relay to break an AC line from the alternator to the regulator/rectifier. A diode or transorb is incapable of protecting your system from a runaway regulator so you need the relay if that is a concern. Arguably a transorb might provide some protection from a momentary spike but we have no real evidence to support the existance of such momentary spikes. Don't get overly concerned about your momentary16 DC volt measurement. Your bad connection could explain everything. I am pretty confident that it was not caused by a misbehaving regulator. I use over voltage protection because I run electronic fuel injection and ignition and it is not difficult or expensive to add. Some guys use it because they have expensive avionics or just because they want to. Some guys don't feel the need for it. The AC volatage will normally be well above 14 volts at all times so that is normal. Ken Peter Harris wrote: > >Ken apologies I should have read the Z files first. I have a condenser >connected that way as in Z16. I think I need a different regulator that does >not need excitation from the battery. Bob Nucholls refers to the generic >Ford type regulator, do you know if this is OK for the PM alternator >application? >Peter > > ________________________________ Message 2 _____________________________________ Time: 07:43:07 AM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: PM ALTERNATOR AC OUTPUT At 04:13 PM 4/23/2007 +1000, you wrote: > > >Gilles >Apologies I have found B and C and ordered the OVM. How essential do you >consider the alternator relay? And where to buy as I did not see at B&C ? >Thanks for your trouble, The S704-1 IS a B&C part number. They offer the ov crowbar ov module, capacitor, relay and installation hardware at: http://www.bandc.biz/PmOVdesc.html Bob. . . ________________________________ Message 3 _____________________________________ Time: 08:31:17 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: PM ALTERNATOR- REGULATOR CHOICE At 08:52 AM 4/23/2007 -0400, you wrote: > >Peter > >I'm not sure why you want a regulator that will start up without a >battery? It sounds like you do have a battery present. Do you know for >sure that your regulator will not start without a battery present? Why would one NOT want an alternator that will run without a battery. Generators did this from day-one and we had to give that feature up when generators got replaced by alternators in the 60's. Alternators on the Bonanza and Barons have self excited for decades and the company touts this as a desirable feature. A few months ago we did an exercise to figure out how to make an SD-8 come up without assistance from a battery. This is generally considered a good thing to do and it can be done. Bob . . . ---------------------------------------- ( IF one aspires to be "world class", ) ( what ever you do must be exercised ) ( EVERY day . . . ) ( R. L. Nuckolls III ) ---------------------------------------- ________________________________ Message 4 _____________________________________ Time: 08:33:18 AM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: PM ALTERNATOR- REGULATOR CHOICE At 04:35 PM 4/23/2007 +1000, you wrote: > > >Ken apologies I should have read the Z files first. I have a condenser >connected that way as in Z16. I think I need a different regulator that does >not need excitation from the battery. Bob Nucholls refers to the generic >Ford type regulator, do you know if this is OK for the PM alternator >application? Read the archives and check out Z-25. This pot was stirred several months ago. Bob . . . ________________________________ Message 5 _____________________________________ Time: 09:26:52 AM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: PM ALTERNATOR SPIKE PROTECTION (NOT) At 10:50 AM 4/23/2007 +1000, you wrote: > > >Ken thanks for the lead to Bob's advice on spike protection. Re your >comments about the use of a capacitor is this connected across the two AC >output leads from the stator? >I have been told to just fit a diode from the regulator output to B+ for >spike protection but this would not enable isolation of battery from >regulator? >Thanks >Peter The capacitor is not for "spike protection". The single phase PM alternators are exceedingly noisy without at least a battery on line and the noise can be further reduced by addition of a capacitor. Further, if you'd like for your SD-8 or similar alternator to come up self-excited and run well without a battery, you'd be well advised to install at least the 22,000 uF capacitor and the resistors described in Figure Z-25 Revision L on page 27 of . . . http://www.aeroelectric.com/articles/Rev11/AppZ_R11J.pdf It would be pretty cool if we could eliminate the word "spike" from the vernacular of speaking of airplane electrical systems. The word has morphed into a dozen different meanings on the part of some speakers . . . and most are regarded as evil. The word is then picked up by the neophyte student of electrical systems and whacked about like a shuttlecock in a badminton game with each speaker believing that he's speaking with some level of understanding and each speaker having a different vision of what's being discussed. Sounds like Congress! The ONLY instance where our electrical systems are likely to experience a true "spike" (see definition in chapter on over voltage) is during the opening of coil on a relay or contactor. The spike CAN be exceedingly spectacular. See: http://www.aeroelectric.com/Pictures/Curves/Cole-Hersee_without_Diode.gif but (1) even if ignored, the ONLY potential victim of such spikes is the SWITCH THAT CONTROLS the relay or contactor. The spike DOES NOT propagate out onto the system. Even if it did, it's of such low energy content that a .10 uF capacitor across the bus or the +14v input to an appliance would wash it completely. See: http://www.aeroelectric.com/Pictures/Curves/CH_Bus_Noise_w_0p1_Cap.gif (2) by adding the diode or other spike suppression process, we can give the controlling switch some relief that results in a longer service life for the switch. See: http://www.aeroelectric.com/Pictures/Curves/CH_w_1n5400.gif http://www.aeroelectric.com/Pictures/Curves/CH_w_2x18v_Transorbs.gif http://www.aeroelectric.com/Pictures/Curves/CH_w_120_Ohm.gif ALL OTHER FORMS of bus voltage perturbation come from instabilities of one kind or another in the alternator system and are not properly called "spikes." Regulator stability problems manifest themselves as small "surges" or "dynamic instabilities excited by transient loads". These are low energy, non threatening things as well. The guy we need to take note of is the "over-voltage" condition promulgated by the uncontrolled, full-bore output of the engine driven power source that pushes bus voltage toward the moon until it's brought under control by some means crafted for that purpose. Know that the capacitor in a PM alternator system is just there for smoothing the considerable ripple voltage that exists on a full wave, single phase rectified power output typical of the SD-8. I did some comparative noise studies on an SD-8 some years ago and compiled this data: http://www.aeroelectric.com/Pictures/Curves/SD-8_Noise_Data.pdf Note that with a 10KuF cap (of unknown quality) the noise under most conditions was under 700 mv pk-pk except when the battery was disconnected on page 5. Further tests with a brand new 47KuF capacitor brought the noise levels down nicely even with a battery off line as shown on page 7. Yeah, I know those traces look kinda "spikey" but let's not speak of them in that matter. The voltages plotted are the normal and expected performance characteristics of the system under study and none of the traces should cause an sense of evil or foreboding that seems to bubble up every time folks start worrying about "spikes". A few months ago we studied and solved the problem of getting the SD-8 to come up self-excited. This is where the resistors and rectifier were added to Z-25. At some later time and under a different discussion topic, we considered moving the control relay to the AC side of the PM alternator's regulator as shown on the current revision of Z-16. However, this is a case of not having your cake and eating it too. Moving the control relay to the AC side of the regulator kills our ability to come alive self excited. We'll have to throw the pot back on the stove to see if we can achieve both qualities from a single architecture. Bob . . . ________________________________ Message 6 _____________________________________ Time: 10:28:46 AM PST US Subject: Re: AeroElectric-List: Relay and capacitor info needed From: Hello Bob I think my questions may have gotten lost during your sojourne: Thx. for the reply. There remains unanswered questions if you don't mind, I will note below with **** >>Have a few questions (4) about relays and capacitors to be used on my 914 >>Rotax powered Europa: >> >>1) If I use a B+C S704-1 "Sealed" relay for OVP to open and close a yellow >>output wire of the internal generator (mounted on engine side of >>firewall), are the chances good it will not blow apart if I choose to wave >>soar up to 35K with long wings? How about at 18K with intercooled motor >>running hard and temp of relay gets up to 212F? > > Use the relay to do AC switching instead of DC switching . . . **** The yellow output wire of the Rotax generator is AC. My question has to do with the internal pressure of the relay blowing apart the sealed container like a bag of potato chips that will explode at altitude. Do you think this relay can take the internal pressure of 35K or 18K at 212F without exploding? >>2) If I use a Bosh 75 amp "Vented" SPST relay #75251 from >>www.waytekwire.com on the engine side of the firewall used in parallel >>with the B+C for OVP to disconnect the 22K uF capacitor from my E-Bus. >>Should the service life be reasonable on a vented relay on the engine side >>of the firewall on an airplane stored for the most part in a unheated tin >>hangar? It has a small slit to allow it to vent. (On my design, if >>capacitor shorted it would draw down the E-Bus with no way to sever short >>without 2nd relay. My design addresses failure of battery (opened or dead) >>when attempting in flight restart after soaring) > > Why not wire your PM alternator like Z-16 and leave the capacitor > across the battery all the time? **** If running on E-Bus, having a leaking capacitor that can not be disconnected will defeat much which I desire in my design. I am not using a Battery contactor, but a Flaming River switch, and turning it off will not sever the capacitor from the E-Bus. I am willing to accept the extra complexity to have this extra relay that will disconnect the capacitor when Rotax generator is turned off either by generator switch or OV. This is in addition to opening the AC with S704-1 relay. Yes kinda like wearing suspenders and a belt, but it will accomplish what I desire. My question is do you think this vented 75 amp relay will provide reasonable service living on the engine side of the firewall with regard to condensation causing problems (corrosion/contamination ingress) and or any other problems that can be associated with a vented relay? >>3) When turning on and off the internal generator, the 75 amp Bosh relay >>will be used to charge up the 22K uF capacitor. Can this relay most like >>give good service charging up the capacitor at least once per flight? >>Could the B+C S704-1 "Sealed" relay most like take the abuse of charging >>up the capacitor at least once per flight and be used in place of the Bosh >>75 amp? (Bosh weighs in at 3.1 oz and has dual contacts) > > If you're wired per the latest control philosophies for PM > alternators, the capacitor charges through the battery contactor > which won't be particularly stressed by this activity. The > act of charging the capacitor using the output of the alternator > is current limited by the alternator's dynamics. No inrush > concerns here. **** I am not precise following the latest control philosophies for PM alternators. I addressed concerns in my design to allow operations from total loss battery/s for extended soaring, failure of main battery if it occurred during an inflight restart after soaring, once motor running on a failed main battery I can get Rotax generator on line to power E-Bus, if smoke from electric, I can shut down everything and have a fuel pump running autonomous in seconds. I want to use either a 75 amp Bosh Relay or a B+C S704-1 to disconnect DC side from Generator. Do you think the 75 amp relay will hold up charging the 22K uF capacitor at least once per flight? Do you think a B+C S704-1 relay will hold up charging the 22K uF capacitor at least once per flight? Again this relay will be the tool used to make a connection and charge the capacitor. >>4) I want to use for pitch trim small "Sealed" Osram 12v 5a relays from >>Digikey pn G6B 2214P US DC12, are the chances good it will not blow apart >>if I choose to wave soar up to 35K with long wings? Will be mounted in >>cockpit. > > What kind of trim motors? You're probably fine with MAC/RayAllen > actuators. You could easily go all solid state with these duties > and eliminate the worries entirely. You're not going to "blow them > apart" . . . the risk is that at reduced pressures, the arcing > that inevitably forms between spreading contacts is more severe > and you get reduced service life. I've not tested open relays at > these altitudes . . . our mil-spec products are sealed. **** It is a Ray Allen, I forget the exact model but it is the smallest one with a indicator. Question is again about blowing them apart because the internal pressure is higher than the outside pressure at altitude. I doubt design had in mind aircraft use??? Do you think there is a good chance that they will not blow apart? Thx. Sincerely Ron Parigoris ________________________________ Message 7 _____________________________________ Time: 02:52:16 PM PST US From: "Peter Harris" Subject: RE: AeroElectric-List: PM ALTERNATOR- REGULATOR CHOICE Thanks Ken. I am interested in the possibility of using the alternator as a dual source for power supply as shown in page Z11 (if I read it correctly) . Basically two diodes back to back , alternator feed one side, battery feed the other side and dual source power out from the centre tap. I am preparing to install EFI in a Jabiru J3300. I will need to study how to load the alternator when the battery is off line. I have ordered the OVM crowbar and now sourced an alternator relay, but also need to find the right regulator for the job. The Jab regulator will not work if the battery is disconnected. The question about running the PM alternator with battery off line is covered on page Z 10 note 20 which warns that some regulators will not start without battery connected. Still learning and thanks for the insight. Peter -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Ken Sent: Monday, 23 April 2007 10:53 PM Subject: Re: AeroElectric-List: PM ALTERNATOR- REGULATOR CHOICE Peter I'm not sure why you want a regulator that will start up without a battery? It sounds like you do have a battery present. Do you know for sure that your regulator will not start without a battery present? No the Ford regulators will not work with a PM alternator. THey are for wound field alternators. Wound field alternators have a field connection and circuit breaker that supples current to the field winding. No such thing with a PM alternator as the field magnetism is provided by Permanent Magnets. If you intend to use the B&C over voltage module with a PM alternator you do need a disconnect relay for the module so the module can disconnect the alternator. I use a $3. automotive relay to break an AC line from the alternator to the regulator/rectifier. A diode or transorb is incapable of protecting your system from a runaway regulator so you need the relay if that is a concern. Arguably a transorb might provide some protection from a momentary spike but we have no real evidence to support the existance of such momentary spikes. Don't get overly concerned about your momentary16 DC volt measurement. Your bad connection could explain everything. I am pretty confident that it was not caused by a misbehaving regulator. I use over voltage protection because I run electronic fuel injection and ignition and it is not difficult or expensive to add. Some guys use it because they have expensive avionics or just because they want to. Some guys don't feel the need for it. The AC volatage will normally be well above 14 volts at all times so that is normal. Ken Peter Harris wrote: > >Ken apologies I should have read the Z files first. I have a condenser >connected that way as in Z16. I think I need a different regulator that does >not need excitation from the battery. Bob Nucholls refers to the generic >Ford type regulator, do you know if this is OK for the PM alternator >application? >Peter > > ________________________________ Message 8 _____________________________________ Time: 03:03:53 PM PST US From: Gilles Thesee Subject: Re: AeroElectric-List: PM ALTERNATOR- REGULATOR CHOICE Peter Harris a crit : > but also need to find the right regulator > for the job. The Jab regulator will not work if the battery is disconnected. > The question about running the PM alternator with battery off line is > covered on page Z 10 note 20 which warns that some regulators will not start > without battery connected. Peter, Have you considered the Schicke GR6 ? http://www.schicke-electronic.de/dgr3tech.htm Same as the GR4 I installed some years ago, but with better heat rejection capability. We bench tested it, and it starts to life even with no voltage applied to the sense wire. I did not test it with no load at all. There was always a battery or capacitor to load it. Regards, Gilles http://contrails.free.fr ________________________________ Message 9 _____________________________________ Time: 03:36:14 PM PST US Subject: AeroElectric-List: Re: PM ALTERNATOR- REGULATOR CHOICE From: "Peter H" Thanks Bob I have now a better understanding of Z25, and Gilles. I am a bit handicapped for the Schicke as I am based here in Queensland OZ and do not speak German but I will keep it in mind and it is good to get a first hand recommendation. I will be pleased to find another alternative recommendation. Thanks I appreciate the good advice on this list Peter Read this topic online here: http://forums.matronics.com/viewtopic.php?p=108735#108735 ________________________________ Message 10 ____________________________________ Time: 04:13:16 PM PST US From: "Peter Harris" Subject: RE: AeroElectric-List: PM ALTERNATOR SPIKE PROTECTION (NOT) Bob I got a spike which destroyed my electronic ignition module when my alternator CB popped. I was running a half baked circuit with no proper protection, hence my journey into your excellent and informative Appendix Z. I have ordered the OVM and now digging deeper. Can you recommend a regulator rectifier for the Jabiru, one that can be started like Z25 without a battery? Thanks Peter H -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: Tuesday, 24 April 2007 1:34 AM Subject: RE: AeroElectric-List: PM ALTERNATOR SPIKE PROTECTION (NOT) At 10:50 AM 4/23/2007 +1000, you wrote: > > >Ken thanks for the lead to Bob's advice on spike protection. Re your >comments about the use of a capacitor is this connected across the two AC >output leads from the stator? >I have been told to just fit a diode from the regulator output to B+ for >spike protection but this would not enable isolation of battery from >regulator? >Thanks >Peter The capacitor is not for "spike protection". The single phase PM alternators are exceedingly noisy without at least a battery on line and the noise can be further reduced by addition of a capacitor. Further, if you'd like for your SD-8 or similar alternator to come up self-excited and run well without a battery, you'd be well advised to install at least the 22,000 uF capacitor and the resistors described in Figure Z-25 Revision L on page 27 of . . . http://www.aeroelectric.com/articles/Rev11/AppZ_R11J.pdf It would be pretty cool if we could eliminate the word "spike" from the vernacular of speaking of airplane electrical systems. The word has morphed into a dozen different meanings on the part of some speakers . . . and most are regarded as evil. The word is then picked up by the neophyte student of electrical systems and whacked about like a shuttlecock in a badminton game with each speaker believing that he's speaking with some level of understanding and each speaker having a different vision of what's being discussed. Sounds like Congress! The ONLY instance where our electrical systems are likely to experience a true "spike" (see definition in chapter on over voltage) is during the opening of coil on a relay or contactor. The spike CAN be exceedingly spectacular. See: http://www.aeroelectric.com/Pictures/Curves/Cole-Hersee_without_Diode.gif but (1) even if ignored, the ONLY potential victim of such spikes is the SWITCH THAT CONTROLS the relay or contactor. The spike DOES NOT propagate out onto the system. Even if it did, it's of such low energy content that a .10 uF capacitor across the bus or the +14v input to an appliance would wash it completely. See: http://www.aeroelectric.com/Pictures/Curves/CH_Bus_Noise_w_0p1_Cap.gif (2) by adding the diode or other spike suppression process, we can give the controlling switch some relief that results in a longer service life for the switch. See: http://www.aeroelectric.com/Pictures/Curves/CH_w_1n5400.gif http://www.aeroelectric.com/Pictures/Curves/CH_w_2x18v_Transorbs.gif http://www.aeroelectric.com/Pictures/Curves/CH_w_120_Ohm.gif ALL OTHER FORMS of bus voltage perturbation come from instabilities of one kind or another in the alternator system and are not properly called "spikes." Regulator stability problems manifest themselves as small "surges" or "dynamic instabilities excited by transient loads". These are low energy, non threatening things as well. The guy we need to take note of is the "over-voltage" condition promulgated by the uncontrolled, full-bore output of the engine driven power source that pushes bus voltage toward the moon until it's brought under control by some means crafted for that purpose. Know that the capacitor in a PM alternator system is just there for smoothing the considerable ripple voltage that exists on a full wave, single phase rectified power output typical of the SD-8. I did some comparative noise studies on an SD-8 some years ago and compiled this data: http://www.aeroelectric.com/Pictures/Curves/SD-8_Noise_Data.pdf Note that with a 10KuF cap (of unknown quality) the noise under most conditions was under 700 mv pk-pk except when the battery was disconnected on page 5. Further tests with a brand new 47KuF capacitor brought the noise levels down nicely even with a battery off line as shown on page 7. Yeah, I know those traces look kinda "spikey" but let's not speak of them in that matter. The voltages plotted are the normal and expected performance characteristics of the system under study and none of the traces should cause an sense of evil or foreboding that seems to bubble up every time folks start worrying about "spikes". A few months ago we studied and solved the problem of getting the SD-8 to come up self-excited. This is where the resistors and rectifier were added to Z-25. At some later time and under a different discussion topic, we considered moving the control relay to the AC side of the PM alternator's regulator as shown on the current revision of Z-16. However, this is a case of not having your cake and eating it too. Moving the control relay to the AC side of the regulator kills our ability to come alive self excited. We'll have to throw the pot back on the stove to see if we can achieve both qualities from a single architecture. Bob . . . ________________________________ Message 11 ____________________________________ Time: 05:24:48 PM PST US From: "Peter Harris" Subject: RE: AeroElectric-List: PM ALTERNATOR CHOICE OF REGULATOR Bob your page Z10 note 20 warns that some regulators must have B+ connected to operate and my Jabiru regulator seems to be that way. Would it be reasonable to expect the Z25 circuit to enable the Jabiru regulator to run without a battery? (It is a solid state shunt type and looks like the PMR1-14 but has two leads out for B+)I read also that the PMR1-14 also requires battery connection but does Z25 overcome the problem for that unit? Thanks Peter H -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Peter Harris Sent: Tuesday, 24 April 2007 9:11 AM Subject: RE: AeroElectric-List: PM ALTERNATOR SPIKE PROTECTION (NOT) Bob I got a spike which destroyed my electronic ignition module when my alternator CB popped. I was running a half baked circuit with no proper protection, hence my journey into your excellent and informative Appendix Z. I have ordered the OVM and now digging deeper. Can you recommend a regulator rectifier for the Jabiru, one that can be started like Z25 without a battery? Thanks Peter H -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: Tuesday, 24 April 2007 1:34 AM Subject: RE: AeroElectric-List: PM ALTERNATOR SPIKE PROTECTION (NOT) At 10:50 AM 4/23/2007 +1000, you wrote: > > >Ken thanks for the lead to Bob's advice on spike protection. Re your >comments about the use of a capacitor is this connected across the two AC >output leads from the stator? >I have been told to just fit a diode from the regulator output to B+ for >spike protection but this would not enable isolation of battery from >regulator? >Thanks >Peter The capacitor is not for "spike protection". The single phase PM alternators are exceedingly noisy without at least a battery on line and the noise can be further reduced by addition of a capacitor. Further, if you'd like for your SD-8 or similar alternator to come up self-excited and run well without a battery, you'd be well advised to install at least the 22,000 uF capacitor and the resistors described in Figure Z-25 Revision L on page 27 of . . . http://www.aeroelectric.com/articles/Rev11/AppZ_R11J.pdf It would be pretty cool if we could eliminate the word "spike" from the vernacular of speaking of airplane electrical systems. The word has morphed into a dozen different meanings on the part of some speakers . . . and most are regarded as evil. The word is then picked up by the neophyte student of electrical systems and whacked about like a shuttlecock in a badminton game with each speaker believing that he's speaking with some level of understanding and each speaker having a different vision of what's being discussed. Sounds like Congress! The ONLY instance where our electrical systems are likely to experience a true "spike" (see definition in chapter on over voltage) is during the opening of coil on a relay or contactor. The spike CAN be exceedingly spectacular. See: http://www.aeroelectric.com/Pictures/Curves/Cole-Hersee_without_Diode.gif but (1) even if ignored, the ONLY potential victim of such spikes is the SWITCH THAT CONTROLS the relay or contactor. The spike DOES NOT propagate out onto the system. Even if it did, it's of such low energy content that a .10 uF capacitor across the bus or the +14v input to an appliance would wash it completely. See: http://www.aeroelectric.com/Pictures/Curves/CH_Bus_Noise_w_0p1_Cap.gif (2) by adding the diode or other spike suppression process, we can give the controlling switch some relief that results in a longer service life for the switch. See: http://www.aeroelectric.com/Pictures/Curves/CH_w_1n5400.gif http://www.aeroelectric.com/Pictures/Curves/CH_w_2x18v_Transorbs.gif http://www.aeroelectric.com/Pictures/Curves/CH_w_120_Ohm.gif ALL OTHER FORMS of bus voltage perturbation come from instabilities of one kind or another in the alternator system and are not properly called "spikes." Regulator stability problems manifest themselves as small "surges" or "dynamic instabilities excited by transient loads". These are low energy, non threatening things as well. The guy we need to take note of is the "over-voltage" condition promulgated by the uncontrolled, full-bore output of the engine driven power source that pushes bus voltage toward the moon until it's brought under control by some means crafted for that purpose. Know that the capacitor in a PM alternator system is just there for smoothing the considerable ripple voltage that exists on a full wave, single phase rectified power output typical of the SD-8. I did some comparative noise studies on an SD-8 some years ago and compiled this data: http://www.aeroelectric.com/Pictures/Curves/SD-8_Noise_Data.pdf Note that with a 10KuF cap (of unknown quality) the noise under most conditions was under 700 mv pk-pk except when the battery was disconnected on page 5. Further tests with a brand new 47KuF capacitor brought the noise levels down nicely even with a battery off line as shown on page 7. Yeah, I know those traces look kinda "spikey" but let's not speak of them in that matter. The voltages plotted are the normal and expected performance characteristics of the system under study and none of the traces should cause an sense of evil or foreboding that seems to bubble up every time folks start worrying about "spikes". A few months ago we studied and solved the problem of getting the SD-8 to come up self-excited. This is where the resistors and rectifier were added to Z-25. At some later time and under a different discussion topic, we considered moving the control relay to the AC side of the PM alternator's regulator as shown on the current revision of Z-16. However, this is a case of not having your cake and eating it too. Moving the control relay to the AC side of the regulator kills our ability to come alive self excited. We'll have to throw the pot back on the stove to see if we can achieve both qualities from a single architecture. 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