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Gigavac GV200QA humming, buzzing noise

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Hey,

another questions regarding the contactor of my EV-build.
I used the Netgain Hyper9 system with the SME ACX1 inverter.
So there is the main contactor GV200QA. As soon the inverter is powered and has gone through self checks it activates the contactor.
But it makes a really "loud" humming noise as soon as activated.
I can control the pich of the noise when changing the frequency in the program, also the volume if I turn down the holding voltage. But if I turn it down to much the contactor loses connection when there are vibrations in the vehicle.
The other one (GV200MAB) I used controlled by the Orion 2 BMS doesn't make such noise.

Is it right, that the noise is normal due to the low frequency PWM given by the inverter?
Didn't hear such noise in other EV builds so wondering if this could be an issue.

Hope for your thoughts on this.
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So today I reprogrammed all parameters to check if they are set 100% right.
Then put in the capacitor but this doesn't work. The inverter falls into Error mode and says "contactor open/short".
Tested it with a 60V 100µF capacitor, it was the only one with that specs to fit in my selection.
So the only way will be to turn down the frequency to 120Hz and try to mount it in a isolating way.
That can happen due to additional capacitance delaying the contactor closing. Controllers usually have a programmable value as to how long they'll wait for contactor to close, you could try to bump up that value.
 

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Lower duty cycle forms a secondary frequency...
Any square-pulse signal, including PWM at any non-trivial duty cycle (i.e. other than 0% or 100%), produces a horrible range of frequencies; the duty cycle will change that spectrum, but it will never just be the PWM pulse frequency. If the duty cycle is unchanging (as the contactor drive is while the holding level is applied), the extra frequencies should only be harmonics (multiples of the pulse frequency), not lower... but multiples of anything between 125 Hz and 1 kHz are annoying; it is almost as if the controller designer chose this range for maximum irritation.

Let's say we want to have 12v holding voltage from a 48v (nominal) pack. That's the 25% the voltage, and we achieve it by using 25% duty cycle of the output. Now we have a 400Hz PWM driver, which means out of 400 possible pulses, it needs to put out every 4th pulse in order to maintain 25% duty cycle. If we write it like a binary number, it would look like this :

1 0 0 0 1 0 0 0 1 0 0 0 0 <--- 400 times every second. I don't think that sub millisecond gap would affect audibility of the signal.
That would be something like "pulse count modulation", not pulse-width modulation (PWM). PWM at 25% and 400 Hz means 400 pulses per second (so 25 ms per pulse cycle), with each pulse being 25% of the pulse cycle duration (so 6.25 ms on, 18.75 ms off). Changing the output of a PWM signal changes the duty cycle, not the frequency of pulses or the number of pulses. A constant PWM output (for a constant holding voltage in this case) means a continuing series of identical pulses, not a pattern of pulses with the number missing related to the desired output value because it's not binary coded, which the point of pulse width modulation as distinct from pulse code modulation.


The example binary string above could be considered 100 Hz PWM @25% duty cycle with only five possible output levels (0%, 25%, 50%, 75%, 100%)... but that's exceptionally crude.
 
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