How can i Measure load current 0 - 20A (Off Topic)

[BOB_SANTANA]

Hi All

Just need some pointers on how to measure load current
i am looking for something that can convert my current to voltage then i
can then scale it to 0-5v dc for my Pic.
any pointers would be very much appreciated

Bob
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BOB_Santana

[SherpaDoug]

Two quick questions:
1) Is the current DC or AC?
2) Does this current run in a conductor that the PIC can use as ground?

If the current is AC you can use a "current transformer" to drive a load resistor and get a good input for the PIC A/D.

If the current is DC you need either a "shunt resistor" and an amplifier, or a "hall effect" sensor.
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The search for better is endless. Instead simply find very good and get the job done.

[BOB_SANTANA]

Hi SherpaDoug

The current is AC and the supply would be mains 230V
any example would be helpful

Bob
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BOB_Santana

[SherpaDoug]

This item from Digi-Key comes immediatly to mind:

http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=196&M=AC-1025

The figure at the bottom of the datasheet shows that if you put 25A though the hole you get 2.5VAC across a 100 Ohm load resistor (or very close to 5V across 200 Ohms, check the graphs). If your PIC knows when the power line zero crossing is you can pick the right part of the power line cycle to measure. Othewise add a "zero crossing detector" or an analog rectifier.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[libor]

I used Hall-effect current sensors for a similar problem with a PIC.
Look at these here e.g: Allegro Micro Hall-effect sensors can be used for both AC and DC currents, giving you the same galvanic isolation as a transformer.

[Guest]

Thanks Guys for the advice
i am ordering some parts and would keep you updated

Bob

[jfk1965]

Check out Farnell electronic components they have many devices to suit your needs in the sensor section.

JFK