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I think I see what's happening.

You seem to be changing the frequency instead of the duty cycle.

You need to fire the contactor at 100% duty cycle, then back the duty cycle off a few dozen percent after a hundred or two milliseconds. The contactor SHOULD NOT be opening and closing. If it is, your duty cycle is too low in the power save portion of the cycle.
I don't think that's correct. I was going through a bunch of that stuff with a Curtis 1236 controller recently. Contactor is driven via one of the PWM outputs, where duty cycle is used to adjust the output voltage to the coil. So like my battery nominal is about 50V, contactor has a 24V coil, so duty cycle is set for 50% for basically putting half the battery voltage to the coil. Then there is the second parameter for adjusting hold voltage in a similar fashion. THEN, on top of that, all PWM outputs on Curtis have an output frequency adjustment within a certain range. Changing that parameter has no effect on the duty cycle itself, just really how that duty cycle is achieved.

Looks like the OP made up his mind though, so I will refrain from further input :D
 

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Thanks for making my point....
😘

The "hold voltage parameter" is not correctly set
Okay, I think I caught up with your idea now. Lower duty cycle forms a secondary frequency, like 25Hz for 25%, which may be audible. That is plausible, but if one wants to utilize the economizer, capacitor is still the way to fix it. I think the reason PWM outputs in these things aren't smoothened by caps is because caps need to be picked for each load, which isn't known ahead of time.

Hold on, I wrote nonsense about 25Hz... need to think for a moment :D

Okay, so I think this last idea is swill wrong, and my first thought was correct.

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.
 

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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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