Problem with XL609

[Spacecommand]

Hello,
I am using the XL6009 converter to step up the 5 volts from usb to the 12v which my fans need to work properly. But I came up with a problem: after wondering about the low rpm of the fans I found out that the voltage coming from the usb cable is at 2,4 volts and not 5 as planned. I used my lab bench power supply to check it out but the same issue appeared. However after I increased the current from the necessary 900 mA to over 2 amps the voltage jumped up to 5 volts and the currents dropped back to under 900 mA. Just to be sure the converter is not defect I tried to use another one but experienced the same problem. When I apply the 12 V directly after the converter everything works just fine, so it got to be the converter causing this problem.
I hope anybody can help me to solve this and thanks for the effort.

 

[davenn]

When I apply the 12 V directly after the converter everything works just fine, so it got to be the converter causing this problem.
I hope anybody can help me to solve this and thanks for the effort.

the probability is that you are trying to draw more current than what the USB port can supply

 

[Spacecommand]

I use an external usb hub which provides over 1 amp and th necessary current which i calculated is around 700 mA. Also it did not work witth my power supply under a level of 2 amps

 

[davenn]

Also it did not work witth my power supply under a level of 2 amps

and there is your biggest hint and backs up what I said

Also you will find most motors require a higher start current to get them spinning than when running in normal operation

Also, you have given zero info on the motor type and specs used for these fams

Dave

 

[Spacecommand]

I use 2 basic DC fans with each one draining 120 mA at 12 V which leads to 1,44 watts per fan.
The fans start to spin evenat low current levels but they don't reach the speed they are supposed to have because of the low incoming volate.