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Topic: ACS 754-200A-Bus bar shunt (Read 1 time)previous topic - next topic

sam_cqdx

Oct 20, 2011, 05:44 pm
Hi need some advice ,have a ACS 754 200A current sensor(hall) would like to measure up to +-200A dc but dont know if i will need some sort of current shunt in conjunction with the current sensor as i dont think the current sensor will be able to handle all the current on the bus bar ,i have seen images of the ACS being incorporated into a bus bar ( current divider ) but have no specs on the actual bus bar shunt or dimensions as i dont want the sensors current terminals burning off due do some high current short used in the crowbar protection circuit ..figure 4 is what im talking about ...

www.allegromicro.com/en/Products/Design/an/AN295045.pdf

I have sent a mail to allegro regarding the current divider ,but no reply from there side maybe someone can shed some light on this idea..

Many thanks

pekkaa

#1
Oct 20, 2011, 06:43 pm
If think that the application note you attached very clearly says that you need a current divider configuration only if you want to measure currents above 200A. So if you are going to measure currents at max +-200A, you don't need a current divider configuration. If you thought of some kind of shunt resistor configuration, I don't think that's how the sensor operates.

sam_cqdx

#2
Oct 20, 2011, 06:53 pm
Not so much a shunt resistor but the part of the bus bar that does not have a notch in it what would the dimensions be as the smaller the area on the bar is the more current will flow through the sensor and not the copper bus bar .

pekkaa

#3
Oct 20, 2011, 07:32 pm
The application note didn't give any formula how to calculate how much of the current flows through the sensor and how much flows through the bus bar if you use the divider configuration. I'll say it depends on the ratio of the sensor's conductor resistance (spec says ~ 100uOhm) and the resistance of the part of the bus bar that passes the sensor. But if you are measuring currents below 200A, you don't need the divider configuration at all.

May I ask what are you doing that involves currents up to 200A? At any voltage, that's awful lot of power. You better be a professional when you deal with currents that high, and know better than to trust any advise you get from anonymous persons from the Internet forums, including anything I just wrote.

sam_cqdx

#4
Oct 20, 2011, 07:50 pm
True so true,well pekka a dc power supply ...the main thing is that the protection in the circuit (SCR -crowbar) actually monitors  dc voltage when the output  goes over the set voltage it shorts the supplies positive and neg rail together to protect the equipment that is connected to the supply before the pass transistors (example  2n3861 if i remember right ).Inline with the Scr is a dc circuit breaker that disconnects the dc if the pass transistors go short due to various things , what i dont want is for minimal current to flow through the current sensor and thus degrading the current flow to pass transistors thats if the current sensor is placed after the SCR but before the pass transistors ,another solution is to put it on the output line but then again i dont want the supply to short out the sensor ,there is current limiting on the pass transistors ......

Hope this sheds light on the question

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