Measure current using a microcontroller PIC

[hussain_kiet]

Re: measure ac current microcontroller

yes shunt method can work for 8 -10A but you have to increase the wattage of your shunt
P = I*I x R => 10 * 10 * 0.1 = 10 Watts
so your shunt should be off 10 Watt for 0.1 ohms @ 10A

 

[nsaspook]

Re: measure ac current microcontroller

You can use a simple open-loop hall sensor that directly interfaces with the PIC ADC.
amploc current sensors
I've used them in a solar energy monitoring system.
DSCN2020 | Flickr - Photo Sharing!
DSCN1998 | Flickr - Photo Sharing!

 

[shreyas_patel21]

thanks hussain_kiet

but if high current load is of very low resistance then the voltage will be dropped through shunt resistor??

for example if load is of 1 or 2 ohms then for 0.1ohm shunt, for 5V output 450mv will be dropped across shunt. is it true?

 

[hussain_kiet]

thanks hussain_kiet

but if high current load is of very low resistance then the voltage will be dropped through shunt resistor??

for example if load is of 1 or 2 ohms then for 0.1ohm shunt, for 5V output 450mv will be dropped across shunt. is it true?

in that case you can parallel two or three of them so that the voltage drop will be decreased and the power requirment of each shunt will also be lesser....
else there are shunts available in the milli ohm range...

 

[horace1]

I have sucessfully used a LTC6101 current sense amplifier connected to ADC input of a PIC24
LTC6101 - High Voltage, High-Side Current Sense Amplifier in SOT-23 - Linear Technology

 

[shreyas_patel21]

thank you hussain_kiet ,

will calibration required in current measured by shunt method?

 

[hussain_kiet]

it depends upon your application how much critical is your current sensing...
if your shunts are precise then you may ignore calibration..
but if you want to calibrate then make sure that the calibrating equipment is precise enough...

 

[jimmy_tag]

Re: how to measure current easily microcontroller

Just put a Switch ,where windows close
If the window is Closed the switch is Pressed...
Your pic just only need to check the Switch Status to Check if motor stopped or no.

Regards
Cortex

Simply Right answer..!! []

 

[shreyas_patel21]

for 1V 8A the load resistor is of 0.125ohms and now for 0.1 ohm shunt resistor almost half of the voltage will be dropped in shunt resistor is there any solution for this?

 

[horace1]

in the LTC6101 application note
http://cds.linear.com/docs/Design Note/dn374f.pdf

a shunt of 0.01ohm produces an output voltage of 4.99V at 10Amp which would be a voltage drop of 0.1v across the shunt

 

[hussain_kiet]

for 1V 8A the load resistor is of 0.125ohms and now for 0.1 ohm shunt resistor almost half of the voltage will be dropped in shunt resistor is there any solution for this?

since your voltage is very low therefore your shunt will also effect the load current so should select a shunt in milli ohms
and calculate your load current in presence of shunt.
eg. for a shunt of 0.01 ohm your total resitance will be 0.01 + .125 = 0.135 ohm
hence I = V/R => 1/.135 => 7.407 A which is less than 8A
so select a shunt resistance such that your load current remains 8A...

 

[mdorian]

Are you using relays to reverse the motor? If you're using a semiconductor driver to run the motor then the shunt solution is useless since there is no ground point as reference. If you can , use the limiting switches and two diodes , is the simplest solution, see the attached picture. More than that , think what can happen if your program has a bug or the control circuit gets burned and is continuously running the motor? It can start a fire in your car.

 

[horace1]

mdorian makes a good point in that if the controller logic or hardware failed your motor could run continuously.
when controlling a ram in one of our projects, in addition to the current sensor (up to 20amps), there was a temperature sensitive trip in the supply line. Any problem it would trip cutting the supply to the ram and also send a signal to the microcontroller which informed the operator to check the system and reset the trip.