---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 11/20/14: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:25 AM - Re: Solid State Master Relay (user9253) 2. 07:10 AM - Re: Re: Solid State Master Relay (Robert L. Nuckolls, III) 3. 04:35 PM - Re: Solid State Master Relay (Justin Jones) 4. 07:29 PM - Re: Solid State Master Relay (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 06:25:46 AM PST US Subject: AeroElectric-List: Re: Solid State Master Relay From: "user9253" The specs for the solid state relay state, > Internal diode protection for inductive load > switching I am curious as to how this protection works. Any inductive induced current will flow in the SAME direction as normal current. Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=434167#434167 ________________________________ Message 2 _____________________________________ Time: 07:10:33 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Solid State Master Relay At 08:24 2014-11-20, you wrote: > >The specs for the solid state relay state, > > > Internal diode protection for inductive load > > switching > >I am curious as to how this protection works. Any inductive induced >current will flow in the SAME direction as normal current. http://aeroelectric.com/Pictures/Curves/Relay-Contactor_Performance/Cole-Hersee_without_Diode.gif They're talking about limiting any potential effects for having SWITCHED an inductive load to an OFF state. Here they're speaking to protection of the contactor as a switch and assuming that unlike legacy practice for protecting battery master and starter contactor switches, the installer would use the device to manage an inductive load that is not also surrounded with coil suppression. Bob . . . ________________________________ Message 3 _____________________________________ Time: 04:35:11 PM PST US From: Justin Jones Subject: Re: AeroElectric-List: Solid State Master Relay Apologies for not responding sooner. I am currently deployed. The relay failures that I have experienced were on Cessna aircraft and both were the factory installed part numbers. One was a rental aircraft (172) and one was my own aircraft (182). The 182 relay failed after 500 hours of use. The failures can and do happen, although they are rare. I have over 3,300 hours of flight time in everything from small aircraft to C-130s. I have had numerous electrical emergencies on certified aircraft and 3 of them were due to failed relays (not master relays). The C-130 has a set of =9CK=9D relays that switch the AC busses and they are notorious for giving crews issues. There has been some talk of testing zero switching SSRs to see if some of the failure rates can be reduced. The cost is higher, but SSRs have rated cycles of 100,000 to 500,000 cycles. This outlasts legacy mechanical relays by far. They haven=99 t been proven for 50+ years, but if we don=99t start testing them, they will never be proven. I don=99t expect to put 100,000 cycles on my system, but if it works as advertised, I should never have to replace the relay. The relay heat sink has to be able to dissipate the heat that 300A of continuous usage would generate. I can=99t think of a situation where the battery would last long enough for heat to be an issue with this relay. If it is, the aluminum heat sink should be able to handle it. Living and operating the aircraft in Alaska will help with this as well. I can weigh it when I get home, but I do remember thinking that this is much lighter that I initially thought. I believe it is on par with other 12V master relays. I am building a Bushcaddy L164 for off airport operations in Alaska. One reason I would like to use the SSR master relay is to experiment with it and test it. I am interested to see if it is a viable option to replace the legacy relays. If so, failed relays may become a thing of the past. The reason for the installation of the remotely operated battery disconnect switch would be to stop a running battery in the unlikely event that the relay sticks and starter contacts weld together. Skytec has a webpage about this and has explained it. The gentleman in the article installed a starter run-on light modification that simply lights an LED when the starter is receiving power. This will tell you if the starter relay has stuck closed. The gentleman in the article has installed an Eaton starter relay. It should be noted that he has a 28V system. http://www.skytecair.com/Cessna_Solenoids.htm Justin > On Nov 19, 2014, at 4:01 PM, Jeff Luckey wrote: > > Justin, > > I'm curious about the decision process that lead to selecting the solid-state relay. I see some down side: > > 1. Cost - that relay is 4 or 5 times the price of an equivalent mechanical device > 2. Power dissipation - That's a pretty hefty heat-sink. How much power does it need to dissipate > 3. I wonder if it is heavier that a mechanical - I didn't see a weight spec. > 4. "Proven technology" - How much track record is there for this device? (I compare this against the standard Master relays with a 50+ year history.) > > This is the Master Relay I'm using (I like it because it's lightweight, small, low coil current, & reasonable cost): > http://tinyurl.com/nb72gal > > Re wiring starter directly: > That's what I'm doing in my RV-7. Battery to start-assist solenoid to starter. BobN just made a post in the last couple of days re this topic and I concur w/ his thoughts. Basically a hung start-assist solenoid is such a rare event that I don't worry about it. > > A couple of questions: > 1. Which airplane are you building? > 2. Tell us about your master relay failures. What aircraft? which relay/contactor? > > > Please understand that my intent is not to be critical but rather to understand how you reached your conclusions. (I might learn something.) > > > -Jeff > > > > On Wednesday, November 19, 2014 2:16 PM, Justin Jones wrote: > > > I purchased the following solid state master relay to use in my project. It is designed to be used as an ambulance master relay. > > http://www.waytekwire.com/item/44407/300-AMP-SOLID-STATE-BATTERY/ > > I am wondering what the typical inrush and cranking amperage is to the Skytec starters for the Lycoming IO-360. I am contemplating wiring the starter from the battery, through the relay and to the starter rather than connecting it thru the Battery Master Switch. It would seem that limiting the high amounts of current that the starter draws would prolong the already long life of these solid state devices. The maximum rating for this relay is 500A for one second. Over the years, I have experienced numerous master relay failures, and I am anxious to try this out. The link to the data sheet is below. > > http://www.waytekwire.com/datasheet/44407.pdf > > > One other option I considered is to wire the starter from the battery, to a manual disconnect (such as one in the links below), then through the starter relay, thence the starter. One could attach a push-pull cable or rod to the armature of this switch, and easily disconnect the battery from the starter while sitting in the cockpit in the unlikely event of the starter contacts getting welded together, or the starter relay fails closed. This switch should probably be located as close to the battery as possible. > > http://www.jegs.com/i/Flaming+River/898/FR1006/10002/-1 > http://www.jegs.com/i/Flaming+River/898/FR1003-1/10002/-1 > http://www.jegs.com/i/Moroso/710/74105/10002/-1 > http://www.jegs.com/i/Unisteer/668/8070030/10002/-1 > http://www.jegs.com/i/Unisteer/668/8070040/10002/-1 > > > > Thoughts are welcome > > Justin > > > > > > > > ________________________________ Message 4 _____________________________________ Time: 07:29:59 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Solid State Master Relay At 18:33 2014-11-20, you wrote: Apologies for not responding sooner. I am currently deployed. The relay failures that I have experienced were on Cessna aircraft and both were the factory installed part numbers. One was a rental aircraft (172) and one was my own aircraft (182). The 182 relay failed after 500 hours of use. The failures can and do happen, although they are rare. I have over 3,300 hours of flight time in everything from small aircraft to C-130s. I have had numerous electrical emergencies on certified aircraft and 3 of them were due to failed relays (not master relays). The C-130 has a set of =9CK=9D relays that switch the AC busses and they are notorious for giving crews issues. There has been some talk of testing zero switching SSRs to see if some of the failure rates can be reduced. Certainly, alternative parts with higher degrees of robustness can improve the MTBF numbers in any system. But quite often, it's less expensive, simpler and lighter to design for failure tolerance. For example, all of the Z-figures featuring and Endurance Bus combined with well maintained batteries can make the loss of the battery relay no more than a maintenance event. The cost is higher, but SSRs have rated cycles of 100,000 to 500,000 cycles. This outlasts legacy mechanical relays by far. They haven=99t been proven for 50+ years, but if we don=99t start testing them, they will never be proven. I don=99t expect to put 100,000 cycles on my system, but if it works as advertised, I should never have to replace the relay. If that is the design goal, by all means. Suggest you verify that it's not just a battery isolation relay but truly capable of bidirectional conduction (charge and discharge). The relay heat sink has to be able to dissipate the heat that 300A of continuous usage would generate. I can=99t think of a situation where the battery would last long enough for heat to be an issue with this relay. If it is, the aluminum heat sink should be able to handle it. Living and operating the aircraft in Alaska will help with this as well. I can weigh it when I get home, but I do remember thinking that this is much lighter that I initially thought. I believe it is on par with other 12V master relays. Good . . . I am building a Bushcaddy L164 for off airport operations in Alaska. Wheeled or floats? One reason I would like to use the SSR master relay is to experiment with it and test it. I am interested to see if it is a viable option to replace the legacy relays. If so, failed relays may become a thing of the past. It may well be. Suggest you use it in conjunction with an architecture that includes a Plan-B that tolerates loss of battery contactor . . . contactors can fail to close for reasons other than failure of contactor itself. The reason for the installation of the remotely operated battery disconnect switch would be to stop a running battery in the unlikely event that the relay sticks and starter contacts weld together. Skytec has a webpage about this and has explained it. The gentleman in the article installed a starter run-on light modification that simply lights an LED when the starter is receiving power. This will tell you if the starter relay has stuck closed. The gentleman in the article has installed an Eaton starter relay. It should be noted that he has a 28V system. http://www.skytecair.com/Cessna_Solenoids.htm Quoting from the article: Why pick on Cessna? Can't this happen to any similarly configured aircraft? This absolutely could (and occasionally does) happen to any/all brands of aircraft. However, we see this occur far more often with Cessna aircraft because of the type (architecture) of relay Cessna specified for use as a starter contactor in production of their aircraft. The RBM/Stancore/Cole-Hersee 'beer barrel' contactors have often been cited for an elevated failure rate. But one mechanic I talked with some years ago admitted that numbers of Cessnas running through his shop were about as great as all the other brands combined. He wasn't sure that Cessna was experiencing a FAILURE RATE significantly higher than other brands. A data point he offered was the fact that poorly maintained batteries were the greatest threat to the health of any contactor . . . with the 'beer barrel' style being the most vulnerable. Tentative and or chattering closures when a soggy battery is loaded by the starter places all contactors a higher risk for sticking. Wrong Part - By Design? Observing the parts manual for most Cessna aircraft, you will note the same part number used to describe both the starter contactor as well as the master switch relay (master contactor). Really? I'll have to check on that tomorrow. I've got some work to do in the EMC lab at Cessna in the morning I'll get into a computer and dig through some service manuals. I recall writing about the DIFFERENCES between intermittent duty and continuous duty contactors for service as battery and starter control . . . but don't recall the specific models. I'll check the drawings. For instance, one of our customers, Willie Zeiger who flies a beautiful Cessna 185 out of Anchorage Alaska, notes in a letter to the factory, "Both relays are rated for continuous duty and are good for both the master relay and starter relay." However, the duty of each of these functions (starter contactor vs. master relay) are quite different and, as such, should (and in other makes of aircraft DO) require different types of relays. I cannot dispute anyone's observations for having found a battery contactor installed in place of a starter contactor but I'm skeptical that the parts catalog calls it out. The difference between them is well understood. Further, they're the same price to the OEM. Any notion that such a condition exists by design is suspect. I'll check. Bob . . . ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.