How to limit USB port current?

[Javid.zare.s]

Hi guy
I wanna describe it as simple as possible
My usb sdcard reader gets very hot when connecting to any usb source and even hotter when i use it with otg cable on android.
So i wanna limit the current to prevent burning my new card reader.
What im thinking is a resistor btw the positive input and the chip.so lower current goes into the chip which results less heat
Since normally the input is around 0.7 - 0.9 mah i decided to choose 6-7 ohm resistor (R=V/I)

Is it the correct choice for resistor?

 

[KlausST]

Hi,

Buy a new card reader.
If it gets hot then there is something wrong.

Klaus

 

[Javid.zare.s]

Hi,

Buy a new card reader.
If it gets hot then there is something wrong.

Klaus

I do have another one also another type but only this model supports otg
Im pretty sure it gets hot because chinese keep the design minimalistic and as cheap as possible

 

[ads-ee]

it gets hot because chinese keep the design minimalistic and as cheap as possible

As the saying goes you get what you pay for.

The question you need to ask yourself is...do you buy a cheap card reader that overdraws current on a standard USB port risking damage to your expensive laptop...or buy a better made card reader that doesn't do that.

Adding a resistor isn't going to do squat, it will probably result in more current draw due to lower voltage on any DC-DC converter for 3.3V, 2.5V, or 1.8V that is in the card reader. (Maybe that cheap chinese product uses 5V parts so it gets hot).

- - - Updated - - -

Since normally the input is around 0.7 - 0.9 mah i decided to choose 6-7 ohm resistor (R=V/I)

What kind of measurement is that 0.7 to 0.9 mah
that is not a current measurement.

And if you meant 0.9mA then the power dissipation on 5V (USB) is only 4.5mW, which won't be "hot".

 

[Javid.zare.s]

As the saying goes you get what you pay for.

The question you need to ask yourself is...do you buy a cheap card reader that overdraws current on a standard USB port risking damage to your expensive laptop...or buy a better made card reader that doesn't do that.

Adding a resistor isn't going to do squat, it will probably result in more current draw due to lower voltage on any DC-DC converter for 3.3V, 2.5V, or 1.8V that is in the card reader. (Maybe that cheap chinese product uses 5V parts so it gets hot).

- - - Updated - - -



What kind of measurement is that 0.7 to 0.9 mah
that is not a current measurement.

And if you meant 0.9mA then the power dissipation on 5V (USB) is only 4.5mW, which won't be "hot".

Its very hot to the touch i believe itll burn my microsd or it self soon
For me its more like a challange to improve the circuit , if i use a resistor itll absorb most of the current and heat or the input current will be limited? Or az you sqid itll raise

 

[ads-ee]

There is something wrong with that microsd reader if it gets that hot.

What does that reader require a USB3.0 with 1A of current or a charging port current that is even higher? I could see it getting toasty if it's pulling 1.5A off the 5V USB power, but that means the reader is a very bad design.

Does the silly thing have a motor in it to spin the microsd around like a HDD ;-)

 

[Javid.zare.s]

There is something wrong with that microsd reader if it gets that hot.

What does that reader require a USB3.0 with 1A of current or a charging port current that is even higher? I could see it getting toasty if it's pulling 1.5A off the 5V USB power, but that means the reader is a very bad design.

Does the silly thing have a motor in it to spin the microsd around like a HDD ;-)

Loool thats a great ideaa���� that would be mesmerizing like figet spinner toys
Usb2 , i need some time to measure current
I think you are probably right , since my pc is very old it cant deliver much power and its alot cooler comparing to phone's otg , definetly this colud be true pc usb output is 2.5watts since my blackberry port goes up to 5 or more watts
I should measure asap tnx , ill mention you after mesurment������

 

[Javid.zare.s]

Txt

ive measured and found out its only consuming 40miliamp when standby and up to 80 miliamp when in use ��(almost same on pc and my phone)
It wasn't expected at all , im totally confused how that amount of heat is generated

 

[KlausST]

Hi,

Either there is something wrong with your heat measurement or with your current measurement.

Klaus

 

[Javid.zare.s]

Hi,

Either there is something wrong with your heat measurement or with your current measurement.

Klaus

Hi this is how i placed multimeter"A" refers to current mesuring mode)

 

[Pjdd]

I use card readers regularly to transfer files from digital cameras and mobile phones. I have several card readers, some of which are cheap Chinese products. One of them cost the equivalent of about 10 US cents with free shipping from China! They work as well as the branded ones like Transcend. The only difference I've noticed is that the cheap ones tend to die in one to three years of regular use, but none of them heats up excessively.

I agree with the others in that a series resistor is not the solution. I too like tinkering and finding unconventional solutions, but these should be based on a sound knowledge of the principles involved, especially when there's a risk of damaging expensive devices. Your proposed approach is not advisable.