Hello everyone. They handed me a plate of a Split Surrey (I don't know the model yet) since the internal fan was going up and down, even stopping for several seconds. Then I asked to give me the engine too. The engine has 3 power cables, plus three tachometer cables per Hall effect. When the system starts working on my work table, I see that the engine (loose and without mechanical problems) starts well and after a few seconds it starts to lose speed, stops due to lack of tension, and after another few seconds it starts again slowly. And so on continuously. Connecting the oscilloscope I see that: [list] [*] The tachometer signal reaches the mic well. [*] The voltage in the motor is sinusoidal (50Hz) and ranges between 220Vac and 100Vac. (Hence the drop in speed and stop) [*] The pulse that reaches the optocoupler that connects the PWM of the micro with the power sector is fixed (420ns) without changing as soon as the speed changes. [*] I have already changed the offset / start capacitor twice. (1.5uF x 400V polyester, I did not get class X2 as the original) [/list] What could be the cause of this problem? Why doesn't the mic compensate for the pulse width when it detects that the speed drops? I hope you can give me some clue to continue with my research. Thank you all for reading my post. Regards, Bruno.

It is a problem of motor power. PWM pulses are limited to small variations in speed, but if the power varies 100%, that is not going to be corrected with PWM pulses. On the other hand, PWM circuits do not vary in frequency, it is normal to be kept at 420ns, which varies in these circuits, is the width, and therefore the duration, of the positive and negative semi cycles. Find out what is the cause so that the motor supply is varying from 110V to 220V and you will see how you solve the problem. Greetings.