Using solid state relay to drive ignition coil - Page 1
Forum section: electronics / beginners

author: altnergy
author_rank: Newbie
timestamp: January 10, 2024, 04:02:51 am
content: I know there are a gazillion ways to drive an ignition coil.I have an experiment that will help me a lot if I drive it with the SSR.I AM ALREADY 99% THERE IN MY GOAL!So far I have success in driving the coil with a solid state relay and obtaining a spark from a spark plug. HOORAY!Next step is I want to boost the power going to the ignition coil. I was thinking perhaps it is possible to place a Darlington Transistor between the output of the SSR and the input to the coil.ALL creative thoughts AND DIAGRAM solutions are desired.God bless and be well!

author: inse
author_rank: Super Contributor
timestamp: January 10, 2024, 05:36:01 am
content: What kind of interesting experiment could it be?SSRs are familiar to me for mains switching applications, are you driving the coil with AC or DC?One of the things I do professionally has to do with IGBTs for ignition coil control.The driver is in principle the most simple circuit you can imagine.A 5V rectangular pulse drives the IGBT via a 1k resistor, depending on the requirements a shunt might be used for current monitoring.We select the IGBT for switching behavior and clamping voltage.The IGBTs have to withstand roughly 30A and up to 450V.How would a Darlington transistor help to improve your SSR circuit?

author: liaifat85
author_rank: Regular Contributor
timestamp: January 10, 2024, 10:34:16 am
content: You have to choose the appropriate resistor values based on the specifications of your SSR and Darlington transistor. You also may need to add protection diodes across the coil to prevent voltage spikes.

author: CaptDon
author_rank: Super Contributor
timestamp: January 10, 2024, 09:18:22 pm
content: Driving an IGBT with a 1K series resistor?You must drive that wave to a large negative voltage to get a sharp cutoff from the IGBT??? 1K driving all that gate capacitance? The gate signal probably looks more sine than square with that much resistance. 10 to 47 ohms is more typical. SSR driving an ignition coil? How does the SSR not self destruct? The flyback voltage alone on the primary side should kill it and SSR's are generally slow as hell. Sounds like a poor driver for an ignition coil. And a poor building block as the heart of a more advanced system. Wow, just wow!

author: Bud
author_rank: Super Contributor
timestamp: January 10, 2024, 09:53:18 pm
content: There is nothing wrong with the described setup when it is provided by a poster with an appropriate nickname.

author: inse
author_rank: Super Contributor
timestamp: January 10, 2024, 09:57:29 pm
content: If you will excuse me, Capt Don, but what is your basis for the statement on the required gate drive?What I mentioned is backed up by maybe millions of combustion engines for decades, that’s the standard IGBT gate driver design: 5V and 1k resistor.

author: Benta
author_rank: Super Contributor
timestamp: January 10, 2024, 10:10:09 pm
content: Just ignore CaptDon, I do. Trolls and Iceland fit somehow.

author: CaptDon
author_rank: Super Contributor
timestamp: January 10, 2024, 10:14:06 pm
content: I'd like to see a plot of say a 0 to 5 volts back to 0 volt 10 millisecond pulse driving the 1K resistor and then show me a real time scope plot of the actual gate drive signal taken from a real E.C.U. and also the SIM plot of the same signal with 1K series resistance and include the gate capacitance. What is the gate capacitance of a substantial IGBT rated to drive an ignition coil? I would have guessed around 1000pf anyway. Somehow that combination of resistance and capacitance seems way to slow to get a good sharp cutoff required for maximum spark energy. Unless you have a diode across that resistor to pull the charge out of the IGBT and a substantial Push-Pull current driver to get the gate charge in and out of that IGBT quickly. 1K ohm doesn't say 'quick' to me. I've done Bosch and Hoerbiger ECU's. Our gate resistors were much smaller.

author: CaptDon
author_rank: Super Contributor
timestamp: January 10, 2024, 10:17:24 pm
content: Benta, you can do the plots in my above post. Don't they seem a bit slow to you for an ignition circuit. Don't you agree using an SSR driving something else is just stupid? Easier to build a correct drive circuit to drive the 'something else' don't you think? Trolls, Yup, We got 'em.

author: inse
author_rank: Super Contributor
timestamp: January 10, 2024, 10:21:22 pm
content: I work at a competitor, and here it’s done like this.I won’t share any further details.After all there’s no update from Altnergy, so topic closed

author: CaptDon
author_rank: Super Contributor
timestamp: January 10, 2024, 10:22:46 pm
content: Actually, I thought my first post was dead on. Just adding my experience with 4400HP diesels which get converted to spark ignition for landfill well head methane gas. I've done some ignition circuits in my time including V8 circle track race engines. I have a tiny bit of ignition circuit experience. Benta, I told you to put me on your ignore list, you're way to easy.

author: Whales
author_rank: Super Contributor
timestamp: January 10, 2024, 10:54:07 pm
content: Welcome to the forum altnergy.QuoteCan you provide photos of what you have assembled and a full circuit diagram, including the part numbers that you are current using?The suggestions I make depend on the exact type of coil (some are flyback) that you are using, the size of your SSR, your method of controlling it and your method of powering it. All of these details matter, a photo and a circuit diagram are the easiest ways of answering lots of potential questions."Boosting the power" might not be possible without higher drive voltages (and might not be in the interests of the longevity of the coil). Some systems provide multiple sparks in very quick succession instead.

author: langwadt
author_rank: Super Contributor
timestamp: January 10, 2024, 11:44:56 pm
content: Quote from: CaptDon on January 10, 2024, 10:14:06 pmlook at a data sheet for an ignition IGBT, all the specs are with a 1k Rghttps://docs.rs-online.com/6958/0900766b813c081c.pdf

author: CaptDon
author_rank: Super Contributor
timestamp: January 11, 2024, 12:56:45 am
content: Looks like they are getting some respectable times even with 1K series resistor. Looking at the spec sheet I see the zener clamp and also what would appear to be a Baker Clamp circuit internal to the device which keeps it out of hard saturation to get a faster turn off. We have used physically bigger IGBT devices with large gate capacitance and much lower value series resistor along with a diode facing the gate driver circuit to get faster turn off. With the turn off diode in the gate drive circuit we did not go with a Baker Clamp circuit internal or external to the IGBT. Our big units max out at 950 RPM so we have lots of time for Multi-Spark-Discharge through pumped resonance on each combustion cycle for the methane powered units. The diesels get multi-injection events (pilot injection followed by power injections). The hardest obstacle to overcome, getting good efficiency at lower combustion temperatures to keep the tree huggers happy.

author: langwadt
author_rank: Super Contributor
timestamp: January 11, 2024, 01:34:12 am
content: Quote from: CaptDon on January 11, 2024, 12:56:45 amit's not a baker clamp, it's a voltage clamp to dissipate the energy and protect the coil from overvoltage if for some reason, like a broken plug wire, the spark doesn't fire. Similar to an avalanche rated FET

author: altnergy
author_rank: Newbie
timestamp: January 11, 2024, 02:27:08 am
content: WOWZA!I Am currently using DC SS relay by the way. BUT I believe that what you are doing with the IGBT could work better for me.I want an easier way to power this Multiwave Oscillator. (Google Lakhovsky MWO) if you are unfamiliar and intersested in that machine. Otherwise these attached diagrams should suffice.In diagram MWO PS1 is the original tried and true design using a FORD model T tremblor coil. Frequency was limited to about 200HzIn MWO PS2 was an updated version from decades ago using a Oil Filled automobile coil driven by Darlington transistor and associated 555 etc. Frequency of 1500Hz max was ALL that was ever desired, and still is.I want to avoid working with the 555 raw chips and associated components as much as possible, and just build more modular for ease.The PWM is able to drive the SSR at the desired frequency range I want of @200Hz to 1500Hz. But the coil spark is very small. Other than THAT everything is Exactly NICE!So I thought a Darlington that was used in the MWO PS2 drawing would help increase the spark.However I find what you are saying quite intriguing.Perhaps what you are doing will work instead! I don't mind switching to using IGBT. I want to know more and much appreciate your help!God bless and be well!

author: CaptDon
author_rank: Super Contributor
timestamp: January 11, 2024, 03:39:21 am
content: I guess the diode below the avalanche diode is in fact facing the wrong way to be a Baker Clamp! I see when the collector voltage rises above the avalanche it enhances the gate and causes the collector to pull toward the emitter limiting the spike voltage, at least from the schematic representation. Indeed in a Baker Clamp the diode cathode goes toward the collector for NPN devices. I didn't think about the direction it faced, I am so used to seeing Baker Clamps in high speed switches using transistors. Not so much with FET devices. My bad.

author: langwadt
author_rank: Super Contributor
timestamp: January 11, 2024, 02:45:46 pm
content: Quote from: altnergy on January 11, 2024, 02:27:08 amahh, pointless quackery nonsense

author: CaptDon
author_rank: Super Contributor
timestamp: January 11, 2024, 03:07:34 pm
content: Take notice the 1K resistor is used in a test circuit which will normalize (to an extent) the differences in gate charge storage from part to part allowing a sensible set of Tr / Tf parameters to be established which translates to "The devices Shall conform to the manufacturers published specifications when tested in conjunction with the published test circuit". Someone saw that 1K in the test diagram and 'Went with it'. That is not specified as a design value for an external series gate resistor. The manufacturer touts "An internal gate resistor". In fact the internal 10K to 30K gate to emitter resistor forms a voltage divider reducing available drive level after the 1K external series resistor. I still think a Senior Fellow reviewing that gate drive circuit would insist on a lower value or at least a diode and series 100 ohm resistor placed in parallel to the 1K to pull the gate charge out of the IGBT more quickly reducing turn off time, possibly increasing spark power (be it voltage or current or both) and increasing spark timing accuracy by reducing the variance in turn off delay formed by differences in gate capacitance from device to device. Company 'X' designed their E.C.U. with the 1K in place and company 'Y' and 'Z' copy catted the design by reverse engineering. Our timing is 1 part in 18,000 per engine revolution or 1 part in 36,000 per engine cycle.

author: langwadt
author_rank: Super Contributor
timestamp: January 11, 2024, 03:23:39 pm
content: Quote from: CaptDon on January 11, 2024, 03:07:34 pmbut why? it doesn't matter

author: gnif
author_rank: Unknown
timestamp: January 11, 2024, 09:04:36 pm
content: OP has reported and complained about this discussion and stated they will go elsewhere for "the other 1%". LockingFeel free to start a separate thread about the 1K resistor gate thingy