# Current Sensing Stage



## TheSGC (Nov 15, 2007)

Get a Hall Effect sensor. It's isolated and real simple to use and doesn't require and special components.


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## JRP3 (Mar 7, 2008)

I've been looking into a hall effect ammeter for around 600 amps but haven't found anything applicable. Any links?


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## WSJ (Sep 18, 2008)

The BB Series Hall effect current sensors accurately measure
DC and AC currents and provide electrical isolation between
the output of the sensor and the current carrying conductor.
The response time can be improved with a faster op amp.

http://www.sypris.com/filemanager/library/BB150_300_600.pdf


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## TheSGC (Nov 15, 2007)

JRP3 said:


> I've been looking into a hall effect ammeter for around 600 amps but haven't found anything applicable. Any links?


Here is the one that is used on the PakTrakr: http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMsxh6GsALyYlEtzRzbBeJe%2b5fbG3zJD2zM=

I have two of these and working on putting them in my custom BMS I am working on.


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## JRP3 (Mar 7, 2008)

TheSGC said:


> Here is the one that is used on the PakTrakr: http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMsxh6GsALyYlEtzRzbBeJe%2b5fbG3zJD2zM=
> 
> I have two of these and working on putting them in my custom BMS I am working on.


I saw the PakTrakr unit but the opening looks too small for 2/0 cable, and though they show a copper bar that fits through it, one of the benefits of using a hall effect is you avoid the 2 extra connections of a shunt. I was also hoping for a complete package with sensor and gauge.
The Sypris unit looks large enough but I'd have to build a sealed mounting enclosure for it. Maybe there is no off the shelf item that will do what I want.


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## Dennis (Feb 25, 2008)

> Hello,
> 
> I have a problem of performing current sensing, as I'm not sure to what device should I use for it. The problem is that expected current rating should go up to 450A, but it is also expected to be much lower during cruising speeds. Should I go with some kind of IC, op-amps, current sense transformer, or even something else that I'm not aware of.
> Any input is greatly appreciated as I'm trying to keep this thing fairly affordable.
> ...



I built a 50 AMP bike speed controller and I used 1/2 of a LM193 (other half is used for PWM) comparator that compares a very stable voltage of 50mV against what my current sense resistor shows on its Kelvin leads (the resistor has 4 terminals) when current flows through it. The downside of course is some power is lost as heat when using resistors as current sense elements.


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## Fujiyama1 (Oct 8, 2009)

Hi, current limiting i think is the wrong term, in the circuits i have seen , the current sensing just reduces the on time for the output stage PWM, i think correct me if iam wrong , should call it power limiting using the time domain, i was thinking of using feedback from the motor output shaft speed to ensure the duty cycle is capped across the zero to low speed range, I dont think batteries can react that quick to high current in the nS duration due to there resistance and induction (inc wiring) , whilst capacitors can go bang if subjected to this treatment, if batteries reacted that quick we wouldnt need capacitors I think
please reply with your views
Barry
Currently building my own controller 60vmax 1000 amps max


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## Fujiyama1 (Oct 8, 2009)

*Re: Current Sensing using other methods*

Hi guys, another thought, the idea of PWM is to reduce volt drop from the system eliminating wasted power, so dont use a resistive current sensor , use a hall type, but ensure the frequency response is high enough for switching of the PWM rise times nS , and off cause the output of these device will not give you an accurate reading as it is not a dc current you are measuring but a square wave made up of a infinite amount of high frequency sine wave components of different phases and magnitudes, this will change of cause when the duty cycle changes, In industry we get around this using a true rms meter but these a expensive and ahve a sample time which will slow down the feedback response, I have considered several designs but could not guarantee to limit the current accurately to say 400 amps within milliseconds, whilst with a known duty cycle and battery voltage and motor (impedence) resistance I think you could calculate the max on peroid of the waveform for a given motor speed with some added safety margin
Barry


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