---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Wed 05/12/04: 10 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:07 AM - Re: What's all this load dump stuff anyway? (echristley@nc.rr.com) 2. 07:26 AM - LASAR Ignition Wiring (ronald jagels) 3. 08:05 AM - Re: OVP and Load Dump (Troy Scott) 4. 08:09 AM - Re: What's all this load dump stuff anyway? (Wallace Enga) 5. 08:43 AM - Re: What's all this load dump stuff anyway? (Robert L. Nuckolls, III) 6. 09:50 AM - RG142 (Eric M. Jones) 7. 09:54 AM - Single Ground (David Schaefer) 8. 11:17 AM - Re: RG142 (LarryRobertHelming) 9. 04:20 PM - For Bob Nuckolls () 10. 10:13 PM - Re: OVP and Load Dump (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 06:07:00 AM PST US From: echristley@nc.rr.com Subject: Re: AeroElectric-List: What's all this load dump stuff anyway? --> AeroElectric-List message posted by: echristley@nc.rr.com > But now imagine that you have turned on your 1000W sound system > ensuring that the alternator is being called on to deliver maximum > power. Assume you turn off the sound system, i.e. "dump the load," > so that the bus voltage starts to rise. The VR reduces the current > in the field but it takes a finite amount of time for the magnetic > field in the armature to change to the new value. In the mean time > the bus voltage continues to rise. This sudden, momentary over > voltage can cause damage to electrical components. The OVP circuit > won't help as the VR has already turned down the current in the field. > > Excellent explanation Brian, but I'd like to add the image that makes it blatantly clear to me. Imagine you're trying to open a door. Really stubborn door. You push with everything you have, and even call in me, Bob and several others from this list. We are all sweating and grunting to get the door open. Suddenly, and without warning, your wife, who is more intelligent than all the rest of us combined, turns the door knob. The resulting explosive release of force can be referred to as a load dump. ________________________________ Message 2 _____________________________________ Time: 07:26:58 AM PST US From: "ronald jagels" Subject: AeroElectric-List: LASAR Ignition Wiring --> AeroElectric-List message posted by: "ronald jagels" Building an RV-8A with battery in the rear, LASAR electronic ignition and planning to use Z-13 as a starting point for electrical systems. The LASAR installation instructions I pulled off the internet apply to a backfit on existing aircraft and indicate use of the conventional O-L-R-Both-Start switch. Power is feed to the LASAR control box and then distributed to the MAG backups with blue wire to the left MAG P lead and green wire to the right MAG P lead. Question - has anyone wired the LASAR ignition using 2-3 switches as described by Bob in the AeroElectric Connection Book? If so how did you wire it? ________________________________ Message 3 _____________________________________ Time: 08:05:47 AM PST US From: "Troy Scott" Subject: Re: AeroElectric-List: OVP and Load Dump --> AeroElectric-List message posted by: "Troy Scott" Wallace, Thanks for your response. Actually, I do understand the difference in alternator regulator OVP and an OV event caused by Load Dump. I just believe that a device advertised to have "over voltage protection" should include features that provide for common possibilities like Load Dump, which IS a short duration high-voltage-on-the-bus event. The B&C regulator is a separate box with wires going to and coming from it. Would it be a big deal to add the $.49 part and a few wires which would connect to the proper places to absorb a Load Dump? With this and maybe a few other features, maybe then you could legitimately call it a complete OVP system. And it doesn't matter if everybody else makes OVP systems without these features. We're supposed to be better that everybody else, right? Regards, Troy tscott1217@bellsouth.net ________________________________ Message 4 _____________________________________ Time: 08:09:10 AM PST US From: Wallace Enga Subject: Re: AeroElectric-List: What's all this load dump stuff anyway? --> AeroElectric-List message posted by: Wallace Enga Brian, Great explanation on this mysterious electron producer. The one paragraph below, I might quibble with you on, is regarding alternators with Internal Voltage Regulators. These do not have the "classic field wire", but rather a control wire. Cutting off power to this lead may not shut the alternator down in all situations. That is the reason for the addition of a "B Lead" Disconnect Contactor, along with it's Load Dump issues when inadvertently opened. Wally Enga At 12:02 AM 5/12/04 -0400, you wrote: >--> AeroElectric-List message posted by: Brian Lloyd > > >Bob over-voltage protection circuit discovers this high voltage long >before it is dangerous to the devices on the bus. It cuts off all power >to the field thus turning off the alternator. Now you limp home on the >juice left in the battery. No worries. ________________________________ Message 5 _____________________________________ Time: 08:43:18 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Re: What's all this load dump stuff anyway? --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" At 12:48 AM 5/12/2004 -0500, you wrote: >--> AeroElectric-List message posted by: "Jerzy Krasinski" > > > > >............... But now imagine that you have turned on your 1000W sound >system ensuring that the alternator is being called on to deliver maximum >power. Assume you turn off the sound system, i.e. "dump the load," so that >the bus voltage starts to rise. The VR reduces the current in the field but >it takes a finite amount of time for the magnetic field in the armature to >change to the new value. In the mean time the bus voltage continues to >rise. This sudden, momentary over voltage can cause damage to electrical >components. The OVP circuit won't help as the VR has already turned down >the current in the field. > > > > > > Brian Lloyd > > > > >It depends what OVP circuit. A proper OVP circuit is a fast and brutally >acting device capable to sink a lot of current from the bus whenever it >detects a voltage increase above the norm. In other words it is a device >momentarily increasing the load on the bus, absorbing all the excess current >caused by the load dump. It absorbs as much current as needed to keep the >bus voltage only slightly increased above the norm, far away from damaging >voltages. In the mean time the regulator can reduce the field current so >the voltage on the bus goes back to normal. That reduces the current through >the OVP device which goes idle and the system continues to work in a >standard way. >Jerzy We're stirring two separate events together in the same pot and blurring sharp distinctions between the two along with consideration of practical remedies. Over Voltage Protection addresses a condition that was largely ignored until alternators were installed on aircraft. It's precipitated by a failure of the voltage regulator failure and the engine driven power source begins pushing an otherwise normal system voltage upward. This is a gross failure of a control device where potential energy available to damage system components is measured in Killowatt-Seconds and the event will proceed with no practical bound on time unless automatic protection (or pilot intervention) steps in to shut off the failed alternator. Voltage settings and time versus voltage operating characteristics have been studied and defined over the past 40 years or so and the result is a large field of offerings in over-voltage relays and, in the AeroElectric case, crowbar OV protection modules. The "load dump" phenomenon is described by simple dynamics of an alternator and it's companion regulator to respond to sudden reduction in load. It doesn't require a 'failure' to initiate the event. A simple operation of the alternator control switch on a Figure Z-24 OV protection system or operation of the battery master in a Bonanza while the alternator is carrying a substantial load is all it takes. This phenomenon is a relative low energy perhaps less than 100 watt-seconds and is self terminating. The classic OV Protection system was not designed for nor should it be expected to deal with this event. The technology of choice is an adaptation of zener voltage regulator diodes especially crafted to provide a temporary but rather robust LOAD to the alternator during the tens of milliseconds that it takes to recover from a sudden drop on demand for its formidable output capabilities. This class of zener is commonly referred to as a TVS or transient voltage suppressor. It's a device rated to soak up large (1500 Watts or more) surges of energy for short (less than 100 milliseconds) periods of time. Load dump is a RARE event in normal operation. Certified aircraft have not been fitted with prophylactic measures because it is so rare. This topic has been stirred numerous times here on the List and elsewhere over the past 5 years or so. It was not until Van's Aircraft noted that flipping the alternator control switch in an aircraft wired per Figure Z-24 might produce a load-dump event (that could damage the alternator only) that the topic bubbled to the surface again. The debate is not whether a load-dump event can happen. We know and accept that its occurs under specific conditions that have become less rare because one can accidently produce the event by flipping switches under otherwise "normal" conditions. The conversation is not so much a debate but a desire to understand and confirm recommendations already circulating throughout the automotive industry for RATING the TVS device. It may well be that a suitable device will surface in the form of this critter: http://www.aeroelectric.com/Mfgr_Data/MR2535L-D.pdf They cost about $3 in low quantity and are installed by simply attaching to the back of the alternator. One wire to the b-lead terminal, other to ground. I've oft cited the value of "repeatable experiments" as the foundation for good engineering decisions. TVS devices come in hundreds of part numbers of which perhaps 20-30 parts are best suited to our task. There's much published literature from the automotive industry that suggests the part cited above will do the trick for 99% of the installations common to OBAM light aircraft. In fact, if any of you are especially concerned about load dump transients, you could acquire one of these critters and install it this afternoon and be 99% assured of having fabricated a firewall against a .001% event. Incidental to the outcome of the proposed repeatable experiments are real debates as to the need for clamping off load-dump transients at voltage levels far below values common in Spam cans. DO-160 cites 40 volt withstand levels for products intended to serve in 14 volt aircraft. Many suppliers to the OBAM community are ignorant of or choose to ignore this simple and easily accommodated recommendation. They offer devices advertised with 20-30 volt limits. Some folk suggest it is in the consumer's best interests to accommodate these products with extra-ordinary efforts found no where else in the aircraft (or automotive) industry. From the perspective of a designer with feet in both buckets, I've suggested that we'll better serve the OBAM aircraft community by insisting potential suppliers educate themselves on the simple techniques proven effective in thousands of products intended for a certified world. OV protection and load dump protection are separate tasks with different requirements. The risks for not installing protection are well documented and not very debatable. I have every expectation that experiments currently proposed will not offer new and startling discoveries . . . the numbers gleaned will allow us to confirm a choice of devices for a well understood task. It's going to be something akin to deciding whether a piece of equipment is held to the airframe with #6 hardware . . . or would #8 be better? There is useful debate to be conducted on how we view ourselves as champions and practitioners of leading edge technology. I prefer to take advantage of 5 decades of knowledge base on electrical system performance upon which we will build an ever expanding leading edge. I don't find it useful and cannot recommend that we step back from the best-we-know-how-to-do just to accommodate the new kids on the block. Let's help them join us at the leading edge instead of spending time and dollars to craft a system especially friendly to sub-standard products. In the hypotheticals I cited yesterday, it would be like putting low compression jugs on an engine to accommodate Nuckolls' cheap 75 octane fuel or drilling half again more holes to install wing attach bolts so one can use hardware store grade 5 fasteners. No doubt some will choose to be accommodating and that's fine too. This is, after all, an OBAM aircraft community. If accommodation does not compromise safety, then I'll be the last to get really excited about anyone's CONSIDERED decisions on configuring their aircraft. I won't recommend accommodation when it's easy to avoid and when the effort is beneficial to the OBAM aircraft community as a whole. This I will happily debate any time . . . it's my job. Bob . . . ________________________________ Message 6 _____________________________________ Time: 09:50:44 AM PST US From: "Eric M. Jones" Subject: AeroElectric-List: RG142 --> AeroElectric-List message posted by: "Eric M. Jones" If RG142 is the only coax that is used in an airplane--about how much is used per airplane? (Now please don't say it depends...). I am trying to find out how much weight can be saved by changing to something else, and if RG142 ONLY can be used for everything coaxial. Offline is best: Email: emjones@charter.net Regards, Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge MA 01550-2705 Phone (508) 764-2072 ________________________________ Message 7 _____________________________________ Time: 09:54:51 AM PST US From: "David Schaefer" Subject: AeroElectric-List: Single Ground --> AeroElectric-List message posted by: "David Schaefer" Bob .. I need your thoughts on a problem I've run up against. I've followed your single ground specifications to a tee. All my grounds are run to the single B&C ground block. However, I have an issue. I have a 'pre-made' harness with 8 power and 8 ground connections all on very short leads coming out of the main cable bundle. All have ring terminals on them. I've cut off the power side ring terminals and replace them with fast-ons to connect to my fuse block. However, I can't decide what to do with the ground side. Do I cut them off and splice longer wires (3') onto the leads to get back across the plane to the ground block? OR can I put the ring terminals on a single bolt and run one larger wire back to the block? OR do I put a couple of bolt-studs by the fuse blocks and ground the ring terminals to the firewall? Will the splices 'degrade' the ground? I'll look forward to your input. Regards DWS ________________________________ Message 8 _____________________________________ Time: 11:17:55 AM PST US From: "LarryRobertHelming" Subject: Re: AeroElectric-List: RG142 --> AeroElectric-List message posted by: "LarryRobertHelming" If you locate your antennas only in the wing tips it will take considerable more coax than if you locate them in the belly of the plane. * AND* How many antennas will you have? (Now please don't say it depends...). Your answer will not *depend* on anything but your own desires. Indiana Larry ----- Original Message ----- From: "Eric M. Jones" Subject: AeroElectric-List: RG142 > --> AeroElectric-List message posted by: "Eric M. Jones" > > If RG142 is the only coax that is used in an airplane--about how much is > used per airplane? (Now please don't say it depends...). I am trying to find > out how much weight can be saved by changing to something else, and if > RG142 ONLY can be used for everything coaxial. > > Offline is best: > Email: emjones@charter.net > > Regards, > Eric M. Jones > www.PerihelionDesign.com > 113 Brentwood Drive > Southbridge MA 01550-2705 > Phone (508) 764-2072 > > ________________________________ Message 9 _____________________________________ Time: 04:20:43 PM PST US From: Subject: AeroElectric-List: For Bob Nuckolls --> AeroElectric-List message posted by: Bob-- I've been following the load dump thread with some interest, for the plane I'm building and the one I fly. I have had a Beech C33A for 15 years and put about 2000 hours on it. It has a 70A alt. and plenty of equip. to load it up. In all this time I had no idea until this issue came up on the Connection that there was the potential to trash 10s of thousands of dollars of avionics and other equip. There is nothing in the POH about this. In fact the POH says that in the event of an overvoltage condition, [which would be indicated by an O-V warning light], batt and alt switch "off momentarily, then on [this resets the overvoltage relay]". As I understand it this in itself could generate a load dump if the batt were switched off slightly ahead of the alt.. Am I correct? Seems strange that the issue of load dump and operation of the master sw was not included in the POH. Are you aware of any reason for the omission other than that pilots rarely feel the urge to turn off the master while in flight or when on the ground with the engine running? Jim Kaser ________________________________ Message 10 ____________________________________ Time: 10:13:28 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: OVP and Load Dump --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" At 10:02 AM 5/13/2004 -0500, you wrote: >--> AeroElectric-List message posted by: "Troy Scott" > > >Wallace, > >Thanks for your response. Actually, I do understand the difference in >alternator regulator OVP and an OV event caused by Load Dump. I just >believe that a device advertised to have "over voltage protection" should >include features that provide for common possibilities like Load Dump, which >IS a short duration high-voltage-on-the-bus event. The B&C regulator is a >separate box with wires going to and coming from it. Would it be a big deal >to add the $.49 part and a few wires which would connect to the proper >places to absorb a Load Dump? With this and maybe a few other features, >maybe then you could legitimately call it a complete OVP system. And it >doesn't matter if everybody else makes OVP systems without these features. >We're supposed to be better that everybody else, right? The LR3 regulator wires to the ship's systems with 20 and 22 awg wires of variable length. The best place to install a TVS is as close to the source (alternator b-lead) as practical with shortest lengths of wire. When the TVS is finally sized, the recommended location would not be inside the LR-3 regulator but right on the back of the alternator. This will allow a single recommended installation to cover all manner of load-dump event in both externally regulated and internally regulated machines wired per Z-24. Bob . . .