Speedfrog Posted March 14, 2023 Share Posted March 14, 2023 Mini and micro relays have different form factors with different pin layout and are not interchangeable. Resistors and diodes have the same basic fonction, resistors are more durable and the preferred choice in automotive applications. 2 Link to comment Share on other sites More sharing options...
audiomick Posted March 14, 2023 Share Posted March 14, 2023 Thanks. In the meantime I had a look at this again: https://www.e-hack.de/der-grosse-kfz-relais-ratgeber/ which actually answers both question. Nevertheless, it's good to have the information here, I reckon. 14 minutes ago, Speedfrog said: Resistors and diodes have the same basic fonction, resistors are more durable and the preferred choice in automotive applications. That document says the same thing. It goes on to explain that the function is to damp the Voltage peak that is generated by the collapsing magnetic field in the coil when the activating current is turned off. Resistors don't work as well for that, but don't care which way round the activating current is connected, i.e. if the positive is on contact 85 or on 86, because a resistor doesn't care which way the current flows through it. A diode does, so if it is a relay with a diode, it has to be ensured that the +12V that activates the switching coil is connected to 86 (and 85 to earth / battery minus). The reason for damping the voltage peak is to protect any sensitive electronics that might be controlling the activating current, so not really an issue when the activating current is being controlled by a mechanical switch. 1 Link to comment Share on other sites More sharing options...
docc Posted March 14, 2023 Author Share Posted March 14, 2023 I have ordered four of the Picker Components relays from onlinecomponents. $10US each with the shipping and taxes(tariffs). I'll sacrifice one to compare construction to the OMRON G8HE and the CIT. I am especially interested in the bulk of heat sink and the mounting /location of the resistor. One of these will go into Position #1 of my early Sport. This uses the weaker N.C. contact in this "load shedding" start relay to carry all of the load to Relay#2 from a 15 amp fuse. One of the reasons a relay rated 10 amps/ NC is not ideal for this location. The Picker relay has the highest rated NC contacts I have seen at 25 amps. Good find, @Speedfrog! Link to comment Share on other sites More sharing options...
Speedfrog Posted March 14, 2023 Share Posted March 14, 2023 Good heavens @docc, you draw faster than your shadow! I had meant to post earlier that I found a cheaper source for the PC 782 relays: https://www.digikey.com/en/products/detail/picker-components/PC782-1C-12S-R-X/12352866 Sorry I couldn’t catch you in time before you pulled the trigger. I’m thinking of changing my screen name to “Slowtoad”... It’s all for a worthy cause though, I’ll be curious to hear what you find out.. 1 1 Link to comment Share on other sites More sharing options...
Speedfrog Posted March 14, 2023 Share Posted March 14, 2023 @audiomick That’s correct, when the voltage is removed and a relay is the de-energized, the magnetic field sudden collapse can result in a voltage surge in the opposite direction. A diode will offer a better protection to sensitive electronic circuitry upstream of the relay. In that light, I wonder if relay #5 controlled by the ECU wouldn’t benefit from having a diode protected relay to safeguard it from voltage spikes?? Link to comment Share on other sites More sharing options...
docc Posted March 14, 2023 Author Share Posted March 14, 2023 29 minutes ago, Speedfrog said: Good heavens @docc, you draw faster than your shadow! I had meant to post earlier that I found a cheaper source for the PC 782 relays: https://www.digikey.com/en/products/detail/picker-components/PC782-1C-12S-R-X/12352866 Sorry I couldn’t catch you in time before you pulled the trigger. I’m thinking of changing my screen name to “Slowtoad”... It’s all for a worthy cause though, I’ll be curious to hear what you find out.. Ah, it seems DigiKey is 1/3 the cost, depending on shipping and tariffs. I also recall that DigiKey has a European distribution center. I have added the DigiKey link to the "Answered" post as an update along with the datasheet linking directly to Picker Components. 24 minutes ago, Speedfrog said: @audiomick That’s correct, when the voltage is removed and a relay is the de-energized, the magnetic field sudden collapse can result in a voltage surge in the opposite direction. A diode will offer a better protection to sensitive electronic circuitry upstream of the relay. In that light, I wonder if relay #5 controlled by the ECU wouldn’t benefit from having a diode protected relay to safeguard it from voltage spikes?? I see that Relay#5 supplies power to pull in the ECU (#4) Relay, but can we say it is "controlled by" the ECU? I seems if we seek to protect "sensitive electronics" we would want a diode in Relay #4 to protect the ECU (?) Link to comment Share on other sites More sharing options...
Speedfrog Posted March 14, 2023 Share Posted March 14, 2023 Looking at the electrical schematic, relay #4 supplies power to the ECU and in turn the ECU triggers(control?) relay #5 to power ignition, injectors & fuel pump. Note that relay #4 is already protected by an external diode. Dang, we need @Kiwi_Roy in-fused science to bring us the light! 1 Link to comment Share on other sites More sharing options...
docc Posted March 14, 2023 Author Share Posted March 14, 2023 2 hours ago, Speedfrog said: Looking at the electrical schematic, relay #4 supplies power to the ECU and in turn the ECU triggers(control?) relay #5 to power ignition, injectors & fuel pump. Note that relay #4 is already protected by an external diode. Dang, we need @Kiwi_Roy in-fused science to bring us the light! I would venture that Relay#5 is "pulled in" or turned on by the Ignition Switch/Run Switch through Fuse#2 (no "sensitive electronics"); Relay #5 then "pulls in"/ turns on Relay #4 that puts power to the ECU; The ECU then triggers/controls the coils and injectors directly without going through any of the relay system. Check my work . . . edit - @Speedfrog has this corrected in the very next post. Link to comment Share on other sites More sharing options...
Speedfrog Posted March 14, 2023 Share Posted March 14, 2023 @doccYou are right when you say: On 3/14/2023 at 2:47 PM, docc said: The ECU then triggers/controls the coils and injectors directly without going through any of the relay system. But with all due respect, I think you got the energizing of the relays arse about. Let us look at the schematic and those 2 relays in question, we agree that the top one #49, is the ECU relay(#4) and the bottom one #46 is the EFI relay(#5). For reference, Relay pin/terminal identification: 85 Relay Coil Negative - 86 Relay Coil Positive - 87 Common Contact - 30 Feed/ Line In Positive _ The ECU relay #4 gets triggered(pin 86) from the ignition switch via the kill switch. _ The EFI relay #5 gets triggered(pin 86) from the ECU pin #19 Fuse #2 is only protecting the EFI circuit from +12V feed coming from the battery. I don't pretend to be 100% correct but that's what I see. 1 1 Link to comment Share on other sites More sharing options...
docc Posted March 14, 2023 Author Share Posted March 14, 2023 43 minutes ago, Speedfrog said: @doccYou are right when you say: But with all due respect, I think you got the energizing of the relays arse about. Let us look at the schematic and those 2 relays in question, we agree that the top one #49, is the ECU relay(#4) and the bottom one #46 is the EFI relay(#5). For reference, Relay pin/terminal identification: 85 Relay Coil Negative - 86 Relay Coil Positive - 87 Common Contact - 30 Feed/ Line In Positive _ The ECU relay #4 gets triggered(pin 86) from the ignition switch via the kill switch. _ The EFI relay #5 gets triggered(pin 86) from the ECU pin #19 Fuse #2 is only protecting the EFI circuit from +12V feed coming from the battery. I don't pretend to be correct but that's what I see. Yes indeed, @Speedfrog, you are absolutely correct in this. I stand corrected having remembered this wrongly and having failed to look at my references before posting. Welldone, sir, and thank you for your diligence! About those beers I owe ya . . . 1 Link to comment Share on other sites More sharing options...
Speedfrog Posted March 15, 2023 Share Posted March 15, 2023 That leaves us with the question, would a diode protected relay be beneficiary in position #5 in insuring no voltage spike do any damage to the ECU?? 1 Link to comment Share on other sites More sharing options...
Speedfrog Posted March 15, 2023 Share Posted March 15, 2023 3 minutes ago, Speedfrog said: That leaves us with the question, would a diode protected relay be beneficiary in position #5 in insuring no voltage spike do any damage to the ECU?? I think it is cheap insurance and that’s what I’ll do. Those Picker relays come in both flavors Link to comment Share on other sites More sharing options...
docc Posted March 15, 2023 Author Share Posted March 15, 2023 I admit I do not understand from where the voltage spike would be coming from and across what terminals of the relay the diode would block it. Link to comment Share on other sites More sharing options...
activpop Posted March 15, 2023 Share Posted March 15, 2023 I'm sure this has been asked, but I'm a new guy. You can have different but comparable relays on the same block, right? Link to comment Share on other sites More sharing options...
Speedfrog Posted March 15, 2023 Share Posted March 15, 2023 27 minutes ago, activpop said: I'm sure this has been asked, but I'm a new guy. You can have different but comparable relays on the same block, right? As long as they are micro relays... the only requisite is that relay #1 (#23 on the schematic) has to be SPDT where all the others are SPST. The physical difference is SPDT has 5 pins and SPST has 4 pins. A SPDT (5 pins) can be fitted in all positions, but a SPST will not function in position #1. 3 1 Link to comment Share on other sites More sharing options...
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