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

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stevez

 

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

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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:

http://www.jaycar.com.au/productView...Max=&SUBCATID=

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)

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Every little bit counts! It works with money, and it works with electronics!

 

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?

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Every little bit counts! It works with money, and it works with electronics!

 

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.

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Every little bit counts! It works with money, and it works with electronics!

 

You can get current sensors from LEM.

Try Googling or looking in RS components, Farnell, CPC, Jaycar etc.

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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.

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Every little bit counts! It works with money, and it works with electronics!

 

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.

 

Could you possible use Current Sense Resistors?

 

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.

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Every little bit counts! It works with money, and it works with electronics!