sarathy
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Using Raspberry pi with high current motor

Thu Aug 14, 2014 5:49 am

Hi,
I have pi model B.
I am going to use it to drive 12v 10a servo drive.
i2c communication is used to run the drive.
According to the data sheet of the drive it is said that both grounds(pi-ground & drive-ground) must be connected commonly.
So is it advisable to connect the ground commonly like picture attached below?
or i have to attach a diode or resistor in the ground line?
Attachments
CIRCUIT FOR RASPI FORUM.jpg
This is the Circuit.
CIRCUIT FOR RASPI FORUM.jpg (55.31 KiB) Viewed 1053 times
Last edited by sarathy on Thu Aug 14, 2014 7:40 am, edited 1 time in total.

rgrbic
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Re: Using Raspberry pi with high current motor

Thu Aug 14, 2014 6:20 am

Not enough information about the drive and there is no picture below. But generally speaking yes, you should connect Pi ground with driver electronics ground.
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joan
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Re: Using Raspberry pi with high current motor

Thu Aug 14, 2014 7:46 am

sarathy wrote:Hi,
I have pi model B.
I am going to use it to drive 12v 10a servo drive.
i2c communication is used to run the drive.
According to the data sheet of the drive it is said that both grounds(pi-ground & drive-ground) must be connected commonly.
So is it advisable to connect the ground commonly like picture attached below?
or i have to attach a diode or resistor in the ground line?
Make sure your I2C device doesn't have any pull-ups. The Pi has I2c pull-ups to 3.3v. It's not safe to have other I2C pull-ups to a higher voltage.

sarathy
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Joined: Wed Apr 23, 2014 11:38 am
Location: CHENNAI

Re: Using Raspberry pi with high current motor

Thu Aug 14, 2014 7:57 am

rgrbic wrote:Not enough information about the drive and there is no picture below. But generally speaking yes, you should connect Pi ground with driver electronics ground.
by connecting this ground will it make any disturbance to pi? because this drive will handle 10a current max.

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joan
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Location: UK

Re: Using Raspberry pi with high current motor

Thu Aug 14, 2014 8:48 am

It will not work if you do not connect ground. There will be no circuit for the SDA/SCL signals.

hampi
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Re: Using Raspberry pi with high current motor

Thu Aug 14, 2014 1:57 pm

sarathy wrote:...or i have to attach a diode or resistor in the ground line?
If the resistor is small enough about 100 ohms or less should work and you will get some protection from induced voltages on motor power supply lines. You could use level shifting FETs on SCL and SDA too. Does the RPi have a separate power supply or it gets the power from the same +12 V source?

This seems to work for me, but is of course much smaller driver around 1 amp

https://github.com/oh7bf/RasPiHBridge

Ravenous
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Location: UK

Re: Using Raspberry pi with high current motor

Thu Aug 14, 2014 4:46 pm

I would suggest you try and separate your power supplies a bit more:

Do "Star earthing" - that is, take all the earths from one central point. The battery's 0V connector could connect to one central connection somewhere on the machine, and you connect to it the motor driver's earth and the raspi's keeping a reasonable separation between them. So any big return currents from the motor driver more directly to battery negative.

The +V connection could split in two in the same way, with a thick wire to the motor driver, and a thin wire to whatever produces your +5V supply for the raspi. (You don't do this if the raspi is being powered by a separate power supply, but its 0V can still be connected as above)

I'm not an expert in heavy DC currents like yours, but a wiring arrangement like this will at least reduce some of the voltage variations to the raspi, caused by voltage drops in the wiring etc.

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