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Would it be safe to use one of the USB ports on my Cerbo X to power a small 80mm fan to cool an electrical component during hot summer days oce t reaches a preset temperature . The fan would be 5 volts and comes with a USB plug attached at less than 52watts . My concern is that it might damage or overheat the Cerbo if running for several hours .
No, it’s not a good idea to try.
The Cerbo GX USB ports are only intended for connecting supported accessories.
Far better to run a dedicated fan at battery voltage, or a dedicated USB power supply from battery voltage.
You can run that through the cerbo gx relay for control though.
Thanks Guy , its these types of issues that i wish i had a 12 volt system as fans come in either 5 or 12 volts and my actual voltage is mostly around 29 volts .
There are cheap adjustable DCDC buck converter for up to 60V to any voltage you need: 2.5V, 3.3V, 5.1V, 6V, 9V, 12V...
As you only want to run a small-ish USB fan or 12V PC fan, they can manage this easily.
fun fact: the Cerbo itself uses a small buck converter inside as power supply to be able to be hooked up to a broad range of voltages.
At 12V-24V, we've had very good service from these cheap and nasties: https://www.amazon.com/Maxmoral-Converter-Adjustable-Step-Down-Regulator/dp/B07MKQXNWG
I did wonder if these thigs would work but worried about heat as it would be inside a very small enclosed space with no ventilation to dissipate heat ,
If i am to use something to provide different voltages to my systems 28.2 volts at the temperature i would require the fan to cut in then i have other fan voltage options , 5 , 12 24 volt fans are all readily available , unfortunately the 24 volt ones show a maximum operating voltage of 27.6 , juts a bit to low to connect directly to my system which would have been the perfect option .
I’m a total noob with electronics but I wired a pair of computer fans off my 48v batteries through a dc 24v converter. The relay worked but the fans moved for a half second, stopped, and smelled. Pretty sure they’re dead. What did I do wrong? Too many amps get to the fans? I read somewhere else someone was using an additional relay. I basically followed the attached. 
