Extract 12 V from USB port

Question

I wish to drive a 12 V stepper motor with a USB port as the source of power. However, the USB port only outputs only 5 V. This will obviously not work.

I had thought up of several ways to overcome this.

1. Chain multiple USB ports in serial to bump up the voltage.
2. Use some sort of circuit ("booster") to increase the 5 V to 12 V

I have tried searching this issue online, however, I have seen very differing answers. Some people say that using 2 USB ports in series will create a short circuit, while other people say that this will work and is the basis of Y cables. Could someone clarify and suggest the best option to increase a 5 V supply to 12 V?

Answer 1

Y cables put the power connections of the USB port in parallel and allow you to get more current.

You cannot put the power connections of two USB ports in series. This will cause a short circuit.

You could use a boost converter to get 12V from 5V.

You are limited to the power available, though.

USB is limited (with exceptions) to 0.5A at 5V. That's 2.5W.

If you boost the 5V to 12, the available current goes down. The power stays the same, but the voltage goes up. Therefor, the current has to go down. At 12V, you would have less than 200mA. I doubt that is enough to power your motor.

Answer 2

You'd be much better off powering the motor with a 12V power supply and designing some type of interface circuit to control it via the USB port. But it doesn't sound like you have the level of knowledge designed to build something like that.

Answer 3

I think the best option for you would be to use a Boost Converter (There are many available and with example circuits in the datasheet).

Make sure you know :- Current Requirements Noise Requirements (if any)

If you dont feel confident enough to design and build a 12V boost converter then go to Ebay there are many cheap options availbale which work of the shelf.

Answer 4

There are companies that make USB to 12 volt adapters. Here's one example I got from a quick search. https://www.amazon.com/Cigarette-Lighter-Socket-Female-Converter/dp/B07J2JPWFD/ref=asc_df_B07J2JPWFD/

This provides 10 watts maximum, and that's about all you can expect from a USB port. There's ample USB power bricks that are rated to supply 12 watts but I suspect you are trying to get this power from a USB port on a computer. With the trend for people using USB to power devices I've seen USB ports getting "amped up", some supplying 12 watts like the power bricks so many people use to charge up their cell phones and tablet computers. As an example Apple has been doing this since they introduced their USB 2.0 iPods. Most computer makers though allow at most 7.5 watts from their USB ports before some over current protection kicks in, with lower maximum power ratings also possible.

Trying to connect multiple USB ports together to get more voltage or current is playing with fire. This would be especially so for putting USB ports in series to get more voltage, the ports almost certainly share a ground and connecting the ground of one USB port to the +5V of another USB port is just going to short circuit the power supply. The most likely result is the computer shutting down to protect itself. Another possible result is smoke coming out of something.

There are Y-cables out there that will take power from two USB ports to get around this power limit on USB ports but this violates the USB spec and so can have unpredictable results. Unpredictable as in you could see smoke come out of something. It's certainly possible to get power safely from multiple USB ports but this will not be cheap or easy.

It's not "obvious" to me that a 12 volt motor cannot be run from a 5 volt supply. Running motors at voltages lower than their rated voltage is practically routine. How your motor would respond depends on how it's built. Running it on 5 volts could let some smoke out. Simply running the motor on 5 volts may be an option.

Check the power consumption of the motor. If it's under 10 watts then you might be able to buy or build a booster circuit that supplies 12 volts from a single USB port. Check the USB port to see if it is able to supply enough power for your motor. If you need to boost the voltage then the USB port needs to supply enough power to make the motor happy and make up for losses in the booster circuit.

Rather than trying to combine the power from multiple USB ports see if you can't split the load. It's been a while since I had to work on motors at university but I can recall that there can be more than one magnetic coil in the motor. Perhaps you could power the separate coils from separate USB ports.

I would highly discourage combining the power from multiple USB ports, again that's playing with fire.

Answer 5

It is a simple matter to convert 5V to 12V. But you have to know how much current you will need, as well as how much ripple you can tolerate and etc.

If for example you only need 800mA at 12V, you might try an LTC3122, but no guarantees. For one thing it still depends on how much current your USB port can supply. Read the datasheet, and follow the recommended layout very closely. I have used this family for a few designs, they work well for me.

You can look at some more choices on the Analog website under "internal switch boost regulators", or on the TI website under "buck converters (internal switch)".

Answer 6

You cannot connect USB ports in series for higher voltage, as their power supplies are not isolated by specifications. You would only cause a short.

You can use a boost converter to "boost" the voltage from 5 V to 12 V. USB ports have a current limit of 500 mA. Some specialized specifications can deliver more, but higher current limit needs to be requested from the port, so you'd need an USB interface chip.

Some connect USB ports in parallel with a Y-cable to get 500 mA per port, resulting in higher number, but the voltage cannot be increased. Connecting ports in parallel might also cause a short, if the ports are not internally being powered from the same supply.

USB Type C or power delivery will provide enough power, but the voltage needs to be brought down with a step down converter. Compliant ports aren't as easy to find though. And as said, you need an interface chip to negotiate the voltage and current.