How to use a usb 5volt and transform it to 12volts.

[rambow70]

I want to be able to use any wall charger or computer usb to power a fan for an idea I have. Usb's sadly only use 5volts. I even considered 9volt batteries but those just seem too out of date and a hassle for people to buy. I was wondering what is a small, cheap, streamline way to transform amperage to voltage from a usb? Or in other words just make the usb put out 12volts without modifying the female usb port from the computer/wall charger. The fans I am using are 25mm 12v .08A DC current and 1.1watt.

Would something like this be my answer?
**broken link removed**

It would be nice if I could get something more streamline and less bulky, my next challenge will be packaging that thing.

Anyways I am new here so sorry if I broke any rules, nice to meet all of you and thank you for any help! There is what I have so far, so if I need to splice anything in there let me know. 5v is was too weak for what I want it to do, 9v was better but I know 12 volts should get me there.

Edit: Or are these possibly any power bricks that you could plug into the wall that supply male usb ports with 12v instead of 5v?

 

[D.A.(Tony)Stewart]

That wont work.




To be Universally compatible due to the un-negotiated current limit is 0.75W or 150mA.


When you boost output voltage 250% then the input load current must increase at least 250% .

i.e. 1.2W@5V=240mA , unfortunately USB1 limits current to around 160mA until negotiated for 500mA max, USB3 will permit 900mA negotiated. Then powered Hubs can be used or up to 100W in future.

https://www.usb.org/developers/powerdelivery/PD_1.0_Introduction.pdf

 

[BradtheRad]

To answer the question of this thread from a theoretical standpoint...

Here is a simulation showing how a boost converter could step up 5V to 12V at 57 mA. That is about the best you could do, if you must draw less than 150 mA from the USB port.

 

[rambow70]

To answer the question of this thread from a theoretical standpoint...

Here is a simulation showing how a boost converter could step up 5V to 12V at 57 mA. That is about the best you could do, if you must draw less than 150 mA from the USB port.

The thing on ebay says it can boost 5v to 12 with .8amps. I do not think the usb makes that kind of amperage nor will the fan need that much so it won't draw it, the power it does not need?

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That wont work.




To be Universally compatible due to the un-negotiated current limit is 0.75W or 150mA.


When you boost output voltage 250% then the input load current must increase at least 250% .

i.e. 1.2W@5V=240mA , unfortunately USB1 limits current to around 160mA until negotiated for 500mA max, USB3 will permit 900mA negotiated. Then powered Hubs can be used or up to 100W in future.

https://www.usb.org/developers/powerdelivery/PD_1.0_Introduction.pdf

All my fan needs is .08amps and 12v so if usb makes 240mA why can that not be converted into voltage? If there is a loss in amperage when transforming it I'm sure .24 could be lowered to .08 easily?

 

[FlapJack]

This is the simple explanation.

When you convert from one power source to another you compare power, power = watts.
Watts = amps x volts.

You have a USB port that will only give you 150mA without a negotiated output. This means that you can only have 150mA without having a microprocessor talk to the USB port and request more current. If more current is available it will then give it to you.

You are talking about using a simple DC to DC converter that has no ability to communicate with the USB port, so you will only get 150mA.

150mA (milli amp) = .15A

Watts = amps x volts

.15A x 5v = .75 Watts

You have a 12v fan that needs .08A current.

.08A x 12v = .96 Watts, you are short .96W - .75W = .21 Watts, and this is assuming 100% conversion efficiency. The cheap junk on Ebay may be as low as 70%.

 

[BradtheRad]

Sorry, not knowing how USB protocol works, I can't say what is possible or impossible.

About the best I can do is mention how USB hard drives used to come with two cables, to plug into two USB ports. One carried data. The other powered the drive. Why not use one cable to do the job? Because a single USB port does not provide sufficient power. The limit I've heard is 0.5A.

I don't know whether it has always been part of the protocol, for the port that powered the drive to require negotiation, before it would provide up to 0.5A.

 

[rambow70]

This is the simple explanation.

When you convert from one power source to another you compare power, power = watts.
Watts = amps x volts.

You have a USB port that will only give you 150mA without a negotiated output. This means that you can only have 150mA without having a microprocessor talk to the USB port and request more current. If more current is available it will then give it to you.

You are talking about using a simple DC to DC converter that has no ability to communicate with the USB port, so you will only get 150mA.

150mA (milli amp) = .15A

Watts = amps x volts

.15A x 5v = .75 Watts

You have a 12v fan that needs .08A current.

.08A x 12v = .96 Watts, you are short .96W - .75W = .21 Watts, and this is assuming 100% conversion efficiency. The cheap junk on Ebay may be as low as 70%.

What if I used a 9 volt battery instead. Could I transform the voltage with one of those dc to dc converters? Alkaline 9volt battaries put out 565mAh at 9 volts. So a 9 volt battery can put out 5 watts. If I go Lithium 9volt it says they put out 1200mAh and 9.6volts, putting out 10.8 watts. Would this be a good solution?

 

[FvM]

Alkaline 9volt battaries put out 565mAh at 9 volts. So a 9 volt battery can put out 5 watts.

Nope. Learn about the difference between mA and mAh. https://en.wikipedia.org/wiki/Ampere-hour
And see a typical discharge charateristic of a 9V Alkaline block:

 

[D.A.(Tony)Stewart]

The thing on ebay says it can boost 5v to 12 with .8amps. I do not think the usb makes that kind of amperage nor will the fan need that much so it won't draw it, the power it does not need?

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All my fan needs is .08amps and 12v so if usb makes 240mA why can that not be converted into voltage? If there is a loss in amperage when transforming it I'm sure .24 could be lowered to .08 easily?

It must be a smart USB target to request more than 150mA default max current. This is true for all USB 1,2,3 . Using a 5V fan that requires 1.2W will barely turn at 50% and will likely cutout by current limiter.

 

[rambow70]

Nope. Learn about the difference between mA and mAh. https://en.wikipedia.org/wiki/Ampere-hour
And see a typical discharge charateristic of a 9V Alkaline block:

So I do not fully understand the graph. If I use a 9volt Alkaline battery that puts out 565mAh what is the real wattage and mA? So the fan to the ebay dc to dc step booster converter to the 9v battery wont give the fan the 1.1W it needs at 12v and .08A?

It must be a smart USB target to request more than 150mA default max current. This is true for all USB 1,2,3 . Using a 5V fan that requires 1.2W will barely turn at 50% and will likely cutout by current limiter.

I am starting to abandon the usb idea all together. I am now exploring the Alkaline 9volt battery with the dc to dc converter.

What I got from another source "a 9 volt battery will store 580 mA hours. This means .58 ampres at 9 volts for 1 hour, So... 5.22 watt hours, or 18.8 KJ"