USB Power Line down / up for USB Ventilator


Advanced Member
Oct 18, 2009

I have a raspberry pi, and I want to use it to controll an usb ventilator ( I have my reasons for it :p ).

As far as I understand it, it has no driver but just starts when it gets power.

I have read you can't disable the usb power lines on the raspberry pi, just the data lines. And that you can use an USB hub to archieve it, but I am not sure if the HUB is strong enough to power the ventilator (5V, 500 ma). The standard says USB Bus powered hub must not power Highpower devices but I am not sure if the manufacturers obey the standard.

Would the Pandora be able to power its usb power lines down? So the ventilator would stop and start if I like it? If yes, are there still cheap broken Pandoras (i need no screen, just somesthing the starts a ventilator via scripts)?
Can I just switch the Power and the Data lanes cables?  Does the data lane cables have enough Volt and Amperes to power the ventilator?
Well you can switch the power lane on/off on the Pandora. The data lane stays active so far i know, so it is the exact opposite to what you said about the PI. 
No offense, but is there a reason this question about the Pandora is in the Pyra General Talk?

-God Ginrai
Well I want to power a ventilator, if it is a bit slower, it is ok :) .
If the fan draws too much current, the Pi's power supply might cut out. It might be possible to make it run slower with less current by adding an extra resistor in series, depending what type of motor it has.

Facebook is watching me: it's now showing me adverts for that fan :(
Thank you for your advice, will it destroy the PI or the suplly if the power suply cut out? Or will just turn off?
Get a darlington array chip. I love these things! They allow you to drive high current/voltage devices without worrying about destroying your controller. Worst case scenario, the $2 array chip melts down.
The Pi has a polyfuse on the power input, which is supposed to recover itself after it trips. But it's meant for emergencies, and probably not very healthy for the system.

Whether using a FET or a Darlington, you still need to power it with something that can supply enough current. Using a second 5V supply might be a good idea here.
Ok guys, I am getting more and more confused by this electrical stuff. I decided to avoid gpio wiring, since it could damage the PI if it happens to often, like you said. So lets use the USB Port, avoid soldering^^.

I wanted to buy one of these:

And controll it via USB (I have experience with micro controllers, uart and atmega assembler, so it is fine). I wanted to wire the ventilator power lane to the relay NO power lane (and wasn't sure where to put the ground lane).

Now I see:

It is fully powered by the USB port.

4 SPDT Relay channels - selectable by user:

  • JQC-3FC/T73 DC5V (7A / 250VAC, 10A / 125VAC, 12A / 120VAC, 10A / 28VDC)
  • RAS-05-15 (10A / 250VAC, 15A / 120VAC, 15A / 24VDC)

Is this even possible? This is far more power then the USB port provides (and the ventilator could take). Is this correct? Is it an error? I can't power the ventilator with it right?

Can it provide the power constantly? Or will it shut down after X seconds? Sorry for knowing so little about electricity and thank you very very much for your time and knowledge.
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Those ratings are the maximum power you can pump through the relays - power you provide separately, not from the USB side.

To wire it up you'd want to wire +V to C, then wire the positive line of the fan to NO, and the negative line to your power supply 0V - so that from the +V output it forms a loop going through first the relay then the fan before going back to 0V.

That doesn't give you any power control though other than on and off. I don't think you really want to use relays for what you want.
The Pi's USB ports are not fully powered either. They are normally limited to 140mA each, and if you bypass those polyfuses (as a lot of people did), they are limited by the Pi's power supply just the same as taking power from the 5V pin. So even forgetting about control, you couldn't actually run the fan from a Pi USB port.

I think you need a controller board with a separate 5V power supply (whether a ready-made product or something you built yourself).

That relay board would probably do the job, but it's a bit expensive/overkill, and you still need the additional power supply. EDIT: Nope, looks like the software for it is x86 only. The Android demo video actually has the Android device loading PHP pages over Wifi (and those PHP programs are running on an x86 machine on the other end of the USB cable, just outside of the shot).
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Thank you for your answers. At least I understand, that there is no magic involved which makes 10A / 28V out of 0.5A / 5V :) .

So my last question is: do you know a ready to go controller board which can provide 500 ma/ 5V for the ventilator? And has a usb port to be controlled by the pi (and best a powered on/off one for the ventilator)? I2C would be ok too, but I try to avoid soldering.
EDIT: Nope, looks like the software for it is x86 only. The Android demo video actually has the Android device loading PHP pages over Wifi (and those PHP programs are running on an x86 machine on the other end of the USB cable, just outside of the shot).
Oh ok, I thought it was Java. And there is a free python implementation of it too:
The official software is Java, but looks like it depends on proprietary drivers (it even says on Linux you have to unload the default (open-source) driver before running their program). But as you pointed out, the free Python one would probably be fine - it does use the open-source driver.

Somebody has installed libftdi on Raspberry Pi:
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Can I put a 5V / 500ma power source (not controll, this is done via PI) into the relay (lets say an usb cable from a battery with (500ma / 5V) and create a power lane with  5V / 500ma output?
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