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Topic: Current measurement on positive or negative side? (Read 1 time) previous topic - next topic

Current measurement on positive or negative side?

Hi,
I´m going to use this sensor: ACS758ECB-200U-PFF-T (http://www.allegromicro.com/~/Media/Files/Datasheets/ACS758-Datasheet.ashx), and I was wondering if it makes any difference if I place the sensor on the positive or negative side of my motor (130 amp dc). If I could place on the negative side, it would allow for much shorter sensor wires. Thanks :)
Planned setup is: Battery positive --- motor --- current sensor --- contactor --- mosfets --- battery ground

Riva

I think the sensor is designed for AC power supplies only and your trying to use it with a DC motor.

jonisonvespaa

no it measures ac or dc, im sure it would work both ways, test it both ways

Riva


no it measures ac or dc, im sure it would work both ways, test it both ways

Thanks for point that out. Once I read the text instead of just looking at the pictures I see it.  :smiley-red:

MaJiG

I don't think that the position of the current sensor matters as long as it is in series with the motor. I might place it between ground and the rest of the motor circuit.

Veco

Look up Kirchhoff's current law, Current will be the same whatever side you put the sensor, assuming it doesn't branch off at some point. Make sure you put it in series!

Thank You, I thought so, but it's nice to be sure. I'll probably need to read up on my electrical basics :)

jonisonvespaa

#7
Feb 14, 2013, 04:02 pm Last Edit: Feb 14, 2013, 06:19 pm by jonisonvespaa Reason: 1
bloody hell 130a dc be careful with that, i used to work on lifts with very big dc generators scary stuff.

Docedison

#8
Feb 14, 2013, 09:11 pm Last Edit: Feb 14, 2013, 09:19 pm by Docedison Reason: 1
I realize it is counter intuitive But I'd place the sensor in the high side of the motor... because of the possibility of a failure in the power connections to the sensor or the sensor proper. If low side sensing fails then you  have full supply voltage on the ground leads.. If high side sensing fails you have no power to the motor, much easier to troubleshoot and much safer to work around. This is one of the reasons why switching grounds is not wise unless it is an absolute last resort -- do-able but inadvisable. Supplies may be switched but it is Always a last resort to switch or sense ground in any high voltage control circuit.
The Allegro ACS series current sensors have a 2KV isolation barrier between sense and sensed conductors so there should be no issues of that nature in using the sensor in the high side of the motor power circuit.

Bob
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

There is little risk of personal injury, as the system is only 24 volts. But I see your points about troubleshooting and also it makes sense to not have permanent power on ground leads. I will have to find the best compromise between physical layout, possible interference and safety. Thank you.

HugoPT

Quote
of my motor (130 amp dc)

Quote
as the system is only 24 volts


Does I understand this well? You have a motor that "eat" 130 amps @ 24V :smiley-eek-blue: :smiley-eek-blue:
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Chagrin


Does I understand this well? You have a motor that "eat" 130 amps @ 24V :smiley-eek-blue: :smiley-eek-blue:

If I were to wager a guess I'd say "hydraulic power pack" like jonisonvespaa described. Common on snow plow trucks or dump trailers.

jonisonvespaa

130 amps 24v

what sort of motor is that? im guessing some sort of automotive starter or alternator maby?

afremont

Since the sensor is not actually carrying any current, it's not going to have any affect on safety either way in my opinion.  It's a hall sensor, meaning it magnetically measures the current in the wire, so circuit isolation is very high.

Is this for some kind of RC car?
Experience, it's what you get when you were expecting something else.

jonisonvespaa


Since the sensor is not actually carrying any current, it's not going to have any affect on safety either way in my opinion.  It's a hall sensor, meaning it magnetically measures the current in the wire, so circuit isolation is very high.

Is this for some kind of RC car?


current does flow through the sensor, on pins 4 and 5 -  ip+ and ip-

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