30KV circuit Noise - Page 1
Forum section: electronics / projects

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: August 12, 2015, 01:55:13 pm
content: Hi everyoneI design and prototyped an flame igniter circuit that generate 30KV between the secondary of a HV transformer and GND.I have an arc on the ignition flame sensor but i have a lot of noise everywhere on the circuit it sometime reset the MCU but they don't most of the time. And it's visible on the scope in every point of the circuit.Every instrument connected to the board act crazy when the igniter start arcing i even got flashing black screen on my labtop ( connected with a serial port to the board )Am not sure where should i start to minimise this noise.

author: TerraHertz
author_rank: Super Contributor
timestamp: August 12, 2015, 03:29:44 pm
content: Quote from: hamdi.tn on August 12, 2015, 01:55:13 pmThis kind of analysis requires seeing the actual setup, both mechanical and circuit, otherwise it's unlikely suggestions will be useful.Incidentally, I'm pretty sure you have a typo in "I have an arc on the ignition flame sensor but i have a lot of noise everywhere". Did you mean "I have ashieldon the ignition..."I presume by 'igniter circuit' you mean you're driving the transformer primary with something other than mains AC? (I ask because a large oil burner of mine just applies mains to the ignition arc transformer. No electronics.)

author: fivefish
author_rank: Frequent Contributor
timestamp: August 12, 2015, 04:07:21 pm
content: That's not noise anymore... that's a big Electro Static Discharge.There are several tricks to prevent your MCU from resetting caused by the ESD. Basically, you need to protect your input and output pins going to the MCU. This may involve a combination of series resistors, diodes or zener, or ESD suppressors. Probably need to shield the whole MCU/PCB inside a metal case.See this article too.http://www.digikey.com/en/articles/techzone/2012/apr/protecting-inputs-in-digital-electronicsFor my personal testing, I rig up a barbecue/grill lighter (drained the lighter fluid, and attached ground wire via alligator clip, and exposed the tip) and discharge it at different points of my PCB and/or case. You can then test if the protection you added was effective or lessened the ESD problem.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: August 13, 2015, 06:40:42 pm
content: Quote from: TerraHertz on August 12, 2015, 03:29:44 pmAm sure, but i can't put the circuit or schematics online, sorry for thatbut will put some diagram or fragment of schematic to explain.Quotewhat i mean is the ignition circuit work fine, and nop there no shielding what so ever.Quoteit is an main AC transformer, the MCU is activating it with an opto-triac.the secondary of the transformer is connected to the flame sensor and the second pin to a FID circuit, and this one is connected to some OP'amp and the ADCwill post some detail about that.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: August 13, 2015, 06:54:08 pm
content: Quote from: fivefish on August 12, 2015, 04:07:21 pmam not sure if metal case will help, since the secondary of the transformer is connected to some electronic on the board.however i noticed that the MCU stop resetting once i moved away ground wire connected to the flame ignition electrode from the board and twisted with the other flame ignition electrode wire going out of the transformer.for now it's not resetting any more.It's not the a final thing am just doing test on the bench, not mounted on the final product.

author: holko
author_rank: Contributor
timestamp: August 13, 2015, 07:01:03 pm
content: I suspect the fault coming from one of these things, followed with a possible solution:1. EMI noise from the supply, does the ignition coil and the µC share same supply?- A reasonable solution is to make a RC or LC based RFC (Radio Frequency Choke)2. EMI/EMF noise induced into the reset pin on the µC. Is this connected further to more circuitry?- Tie it down with an R/RC or directly to rail if it is not further used.3. µC is not adequately shielded or too close to the ignition coil and reacts on EMF induced noise.- Shielding helps.Another thing that is worth looking into is snubberizing the coil so it won't kick back so much noise.-holko

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: August 13, 2015, 08:02:15 pm
content: Quote from: holko on August 13, 2015, 07:01:03 pm1- They share a "ground" connexion2- an RC is already connected to reset pin3- The uc and the coil are in opposite edge of the board so lot of space (maximum) and lot of ground between them and a lot of via to help minimize ground impedance.4- igniter have a snubber circuit on primary

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: August 13, 2015, 08:04:33 pm
content: little something to clear a part of it

author: MagicSmoker
author_rank: Super Contributor
timestamp: August 13, 2015, 08:13:00 pm
content: Quote from: hamdi.tn on August 13, 2015, 08:02:15 pmThen lower the pullup resistor and/or increase the value of the shunt capacitor. I've used 3k3 and 10nF successfully.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: August 13, 2015, 08:14:44 pm
content: Quote from: MagicSmoker on August 13, 2015, 08:13:00 pmOn my to do list

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 13, 2015, 08:24:30 pm
content: Bear in mind that the risetime of a spark discharge is of the order of nanoseconds, so the inductance of even a short wire is significant when it comes to grounding etc. Minimising loop area of the discharge path is an important first step.

author: eneuro
author_rank: Super Contributor
timestamp: August 13, 2015, 08:47:46 pm
content: Quote from: hamdi.tn on August 13, 2015, 06:40:42 pmMaybe a photo with ruler to see the size of elements used and have some vision how its is connected mechanicalyHV stuff is always interesting, but probably I'd rather put any electronics inside a few milimiter in thickness steelhttps://en.wikipedia.org/wiki/Faraday_cageand fiber optic (eg. cheap plastic) to control this thing from.... another faraday cage like Tesla below in his lab

author: GreyWoolfe
author_rank: Unknown
timestamp: August 13, 2015, 08:59:14 pm
content: Now, THAT'S how to light a BBQ!

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: August 13, 2015, 09:17:35 pm
content: Sorry Tesla , this is all i have

author: eneuro
author_rank: Super Contributor
timestamp: August 13, 2015, 10:17:01 pm
content: How did you determined it is 30kV? It looks like 10mm-15mm spark or so...Anyway, I do not know howto to do such effect (probably Tesla coil and grounding wires above?) but this is what I'd like to have in my gardenIt should be good to kill all bloody moskitos in the garden, but probably extreme high voltages, since it looks like 1 meter sparks?Are there somekind of grounding above tesla coil to achieve such amazing effect?

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: August 13, 2015, 10:47:22 pm
content: i didn't measure it , an other guy in an other lab tested ignition transformer only, with a huge probe and he said to me that it deliver 30KV. i don't have the proper equipment to confirm that.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 14, 2015, 05:41:05 am
content: 30kV is about right for some older automotive type ignition transformers. Some ignition transformers used on modern engines can go as high as 60kV in order to reliably ignite leaner mixtures for better fuel economy.It's also true that following the ignition pulse with a smaller "probing" waveform can make for a very economical way to sense the cylinder pressure and how long the power stroke lasts, which is then used to optimize ignition timing. Don't know if there's any production car using that technique, but it's definitely going to be one of the tricks the automakers will turn to in order to keep up with competition from EVs.

author: TerraHertz
author_rank: Super Contributor
timestamp: August 14, 2015, 07:20:26 am
content: Quote from: hamdi.tn on August 13, 2015, 08:04:33 pmBy clamping the direct return line from the spark gap to both the chassis and PCB grounds, via D26 and RV2, you're guaranteed to inject the HF spark noise into the PCB ground.Try something like this instead:I see from your pic of the spark gap, that the low side is directly screwed to the metal framework. So you should do all the heavy duty clamping of the hot return to the same thing - the chassis. Then tap off the signal you want via a high impedance (R1 resistors) to the PCB. Have a lower impedance low-pass filtered connection (L1, R17) between chassis ground and PCB ground.In my diagram R1 is two or more resistors in series, since metal film resistors tend to go open circuit if stressed by high voltages. Spread the stress.R1 is just to limit current to the later diode clamps on your ADC. Also for a small amount of low pass filtering with R1/C1, if needed, to cut off the very high freq. spikes that get past the heavy duty clamping.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: August 14, 2015, 10:39:26 pm
content: Awesomewill try that thanks