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Massive EMI issues

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da075:

--- Quote from: Andreas on June 01, 2020, 04:58:03 am ---Hello,

2) the main problem is that aluminium oxidizes and so gives no good contact between the layers. Assuming the EMI source is the motor and leaves the motor housing by the wires you might want to short it back to the motor housing before it spreads over your whole cirquit. So with a better conducting material you might have luck by contacting the shield back to the motor housing (and or to the metal plate below the PCBs). Yes there are EMI-Shields for this purpose but they are not cheap.

1) a 10-100nF capacitor across the terminals might help somewhat. But it is also possible that the H-bridge cannot handle capacitive loads. You need a path back to the motor housing. So additional to the 10-100nF across the pins you need 2 * 1-10 nF from the pins to the motor housing to prevent the EMI getting from the motor to the motor supply lines. Another possibility to prevent leaving the EMI from the motor housing would be adding some inductivity 10-470uH or EMI-Ferrites into the supply lines close to the motor pins.

3) This will most probably not help as there are already some capacitors. What I would try is a 1-10nF capacitor between reset and ground pin of the processor (shortest possible connection).

with best regards

Andreas

--- End quote ---

Did you rule out reasons other than EMI? EMI may not be the main culprit. if not, make sure that the AC adapter is capable of delivering what it is rated at. so check the voltage at the output and see if it is dropping when the motors are turning, and see how much current is being drawn. also check if your system vibrates when the motors are running, you might want to ensure that all wiring remains well connected.

floobydust:
H-bridge MDD10A is rated 20kHz max. and you are running it at 62.5kHz, did you check this is going to work without shoot-through currents generating high level EMI?  :o

As I mentioned, you can be accidentally generating a lot of EMI in hardware or software and instead of a shielding goose chase, I always start with getting the generated EMI low as possible. I know the foil gives sorta a fix but it's not going to be reliable and there will be drama at higher motor currents. It's just showing there is a relationship between the motor and encoder wiring. The motor wiring is terrible, using low current 22AWG wire and JST connectors running alongside the encoder signals- not a good design to begin with.

Without a scope it's pure guessing if the EMI source is the PWM carrier or the motor brushes or on the power supply. The susceptible EMI receiver may be the encoder and MCU inputs. Without any test equipment, you're going to have to guess and try things.

Capacitors at the motor are best to deal with EMI from the brushes. It's just three say 22nF parts soldered in free air right at the motor's terminals. For ferrite clamp-on cores, put either the two motor wires or the five encoder wires inside and clip together, as a common-mode filter for RF frequencies.  It's just one bead, not along the entire cable run.

bob91343:
Too many replies, so I only browsed.  However EMI comes in two flavors, conducted and radiated.  And it you have it, the source may be external or internal.

So it needs to be categorized.  If a device is amplifying a signal then its input must be well defined.  Ground is not ground because it's different everywhere and should never be relied upon to conduct signals or power.  All need separate returns.

If the problem is radiated, shielding can help.  A good approach is to run power leads in pairs, hot and return, twisted, and inside a shield that is connected to a frame at one point only.

Sometimes slipping a ferrite core over a cable can make a big difference.  My experience with bypass capacitors has been poor to mixed.

If you have EMI, is it a steady signal or just transient?  You need to learn more about it in order to suppress it.

OM222O:

--- Quote from: floobydust on June 01, 2020, 06:28:33 pm ---H-bridge MDD10A is rated 20kHz max. and you are running it at 62.5kHz, did you check this is going to work without shoot-through currents generating high level EMI?  :o

As I mentioned, you can be accidentally generating a lot of EMI in hardware or software and instead of a shielding goose chase, I always start with getting the generated EMI low as possible. I know the foil gives sorta a fix but it's not going to be reliable and there will be drama at higher motor currents. It's just showing there is a relationship between the motor and encoder wiring. The motor wiring is terrible, using low current 22AWG wire and JST connectors running alongside the encoder signals- not a good design to begin with.

Without a scope it's pure guessing if the EMI source is the PWM carrier or the motor brushes or on the power supply. The susceptible EMI receiver may be the encoder and MCU inputs. Without any test equipment, you're going to have to guess and try things.

Capacitors at the motor are best to deal with EMI from the brushes. It's just three say 22nF parts soldered in free air right at the motor's terminals. For ferrite clamp-on cores, put either the two motor wires or the five encoder wires inside and clip together, as a common-mode filter for RF frequencies.  It's just one bead, not along the entire cable run.

--- End quote ---

I should probably RTFM but it never occurred to me that an H bridge has a "maximum frequency", at least not down in the tens of kilohertz range at least. For future iteration I most likely will switch to an H bridge which I designed myself, as well as a teensy 3.6 so I can just use one micro for the entire motion controller. For now reducing the PWM down to 7.8KHz (Arduino has no inbetween, it's either 62.5K or 7.8K because the prescaler is just weird like that), Shielding the power lines in aluminized mylar + using ferrite beads (4 encoder wires separately and one over the shielded power lines for good measure) seems to have stabilized everything and like others mentioned, without proper testing equipment (university is closed due to human malware) I can't really pinpoint the source of the EMI to try and correct for that.


--- Quote from: floobydust on June 01, 2020, 06:28:33 pm ---The motor wiring is terrible, using low current 22AWG wire and JST connectors running alongside the encoder signals- not a good design to begin with.

--- End quote ---
And yes, I definitely agree the design is quiet horrible but unfortunately I really don't have another option as the entire robot was designed based on  these specific motors and wheels which came as a set and for the time being I just have to make things work in a pinch.

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