current clamp/measuring device?

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bunghole

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does anyone have any ideas, diagrams for ways to measure current (preferably without interrupting the line). i was thinking of one of those hall effect sensors, with the core (ferrite?) around the line. i want to use it to drive a 20 led bargraph display (using two LM3914's) and create an analog display, with the leds around it, and current measured on the front, and i can also calibrate it to work. sorry about the crappy picture, it's a stretch of an ammeter cut from another picture, but just give the general idea. it would be good as well if there was a schematic for a 2-3 digit led numerical display ammeter

ta
 

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THat's what fluke meters do. You can buy cores just for that I think. I forget who makes some. Tamura maybe?
 
Consider that the wires/conductors to/from have some resistance and however small that resistance and current there is a voltage drop. If the circuit of interest operates at a relatively safe voltage you might consider sampling between the end of a conductor. An example might be in an automobile - wire from battery to starting motor does see a significant drop. You'd need to run some tests initially to determine voltage drop vs current
 
in this (my) case, the meter (leds) are on a panel, and the core measuring the current is in a separate place (where the measured wire is), like the picture i posted. it's always there or 'permanent', not like a measure this-measure that or temporary application
 
I've built a few current meters for some prototypes (0-50 amps and a 0-300 amps).

I used the clip on ferrite filters you can buy for a couple of quid. They come in two halves with a plastic shroud which clips together.

I then ground out a small square flat on one of the edges and epoxied an Allegro hall effect sensor in place. You need a sensitive linear type.

This will measure current flowing either way - the hall effect sensor gives out 2.5 volts with no current flow through the cable and varies up or down depending on the current direction and current draw.

I only had a supply that would give me a maximum of 10 amps but over that range it was suprisingly linear with around 1% error maximum.

A whole current clamp can be built for around £5/$10
 
the largest ferrite filter i can get will be alright, but i'm not sure about the hall sensor. i used this in a speedo, but not sure if it will work:

**broken link removed**

or i have one from rs components (stock no. 307-446) i found in the bottom of an old files box (might've been there since 1993-1997)
 
The hall sensor you got from Jaycar should be ok. I used the ones from Allegro and they were great - this one looks similar.

The ferrites I used were the ones that Rapid Electronics had on clearance (the long squarish ones) as they weren't ROHS compliant.
 
as long as it's a UGN3503U, it sould be okay to use for this purpose, as it's the same part found at Jaycar, i would assume. doeas to clamp have to fit 'snuggly' around the cable, like for 6mm diameter cable i use a 6mm ferrite, or can i use one 12mm ferrite for all size cable 12mm and below?
 
The ones I played around with had 1.5mm cable going through a 6mm hole so there was plenty of slack around the core.

Best thing to do is to have a play with it - its only a 5-10 minute job to mock something up.
 
and mock something up i shall, turn something easily over AU$500 into less than AU$30! many thanks to all for this.
 
You can get current sensors from LEM.

Try Googling or looking in RS components, Farnell, CPC, Jaycar etc.
 
i work part-time in an electrical warehouse, so if there is anything suitable, i can probably order it through the warehouse. i don't really want anything fancy, just something like what picbits has made will do for this. i just need it to measure current withdrawal for an electric traction motor (DC). thanks anyway.
 
You can buy commercial clamp meters that measure DC as well as AC for £50-£100

Just make sure it will measure DC current with the clamp as a lot of the cheaper ones only measure AC current.
 
picbits said:
You can buy commercial clamp meters that measure DC as well as AC for £50-£100

Just make sure it will measure DC current with the clamp as a lot of the cheaper ones only measure AC current.
Click to expand...

that around AU$100-200 for me and not really worth it for what i need it for. 1% error i can deal with.

i'm also not familiar with current sense resistors.
 
bunghole said:
i'm also not familiar with current sense resistors.
Click to expand...

If you are willing to insert something into the circuit, like a current sense resistor, you may also want to look at the Allegro ACS75x series of Hall devices. I have been using the ACS754xCB-100 (100 AMP) and like its ease and stability.

John
 
I guess it all just depends on how much current you want to measure. But a current sense resistor goes inline, and you measure the voltage drop across the resistor. The resistors are very low resistance, down to 0.001 ohms I believe.
 
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