Invertor 48V /220V

[Jane]

The invertor has  2 air fans that start only  when quite a high electricity consumption is needed . Otherwise the fans are  quiet. It worked that way for about 2 years. Now,however, the  fans work all the time.

On the enclosed pictures you can  see   a   region   where fans are connected. It seems quite simple. Anyone knows the principle , how the  fans are controlled?
Thank you

[Kwakerman]

Looks like you have a temperature sensor attached to the heatsink (first picture top heatsink).  Might be for overtenp protection or fan control (or both).  Suggest you try and find a circuit drag for it.

[Jane]

Thank you for the reply.
Can you please mark in the picture where do you think there is the sensor?

[voltsandjolts]

It's here:

[johansen]

the traces on the board run all the way to it.

looks like the fans get power from a rectifier and aux turns on the transformer.

[Vovk_Z]

Yes, fans get power from a main transformer. The higher load the higher FAN voltage. But there possibly is BJT transistor which controls swit hing on and off of a FAN. And possibly it became shorted.

[coromonadalix]

yep i would have said the same thing,  come from the main ac voltage then rectified as DC, a crude way to make them work ... and they are 2 wires only ...

the thermal sensor should be used in the main controller section