Pierre, I've been watching this thread with interest and would like to help you find a solution to your problem. I suspect that the drive is not defective but maybe programmed less than optimal.
My first question about the data: Are you sure the winding drum is 6 inch circumference? Is it possibly 6 inch diameter?
Second question: You have 200 lbs you need to lower in a fixed period of time. Can you give us the distance traveled and the amount of time to make that move?
Third: Do you have a means of displaying or monitoring the DC bus voltage while lowering the load? If yes, can you tell us what the voltage is doing when the motor starts to oscillate?
Finally, just an observation. I suspect that you are bumping up against some kind of braking capacity limit. I say this because, as you increase descending speed, you also increase the braking hp. It seems that a limit is reached around 15hz and the oscillations begin.
Please advise above requested data.
We are going there tonight for a try. This system works once a day. Goes down.... rotates for 3 minutes, then goes back up. The End.
Its really 6 inches cir. every turn the cable goes down 6 inches.
200 pounds going down 40 feet in 15 seconds. Thats what they want anyway... it might not be what the system can give them... its about 180 feet per minutes... 42 HZ ...
What the DC buss is doing while oscillating load... I will check this during our tests tonight.
''limit is reached around 15hz and the oscillations begin.'' Hard to tell... If we run this below 10 HZ... it slip to the floor BOOM!. With the resistors, we have not checked which is the failure limit. We only know that we need to go to 15 HZ fast... we tried a 30 seconds accel going up and it failed... no on DC Buss overvoltage... the load just slipped back down... we hit the EM switch hence cannot give any good data on what happened. We only know that we did not have a DC OV alarm.
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Tonight we will boost the Torq to 15% and switch its control mode to sensorless vector. We will do an auto-tune on the drive prior to testing the SV control.
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I have to mention that this system was sized by a major companie. The 2 HP was there idea. It was to be sufficent. But us we have notice that going UP at 15 HZ... we see 4 Amps... the motor should be pulling no more than 2.85
This is not a perfect setuyp but the limitation in siz and space was very hard to accomodate.
Yes we stress the motor but we do it only 30 seconds a day... the rest of the time it can sleep