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Non-contact detection of Current/Voltage in a single Automotive wire

Thread starter #1
Hi all,

Looking for a solution to detect 12V on a single wire without splicing directly into the conductor. The wire will typically be running incandescent lamps ranging from about 1~5Amps current draw. I'm only looking to detect a discrete ON/OFF, based on when the lamps are operating or not.

I've considered Hall effect IC sensors, though I'm not sure if the small magnetic field created by the wire would be sufficient for detecting reliably and repeatably.

I've seen some neat looking clipping arrangements in diagnostic tools that read CAN bus twisted pairs:

https://blog.vboxautomotive.co.uk/2...ehicle-can-bus-without-a-physical-connection/

Again I'm not sure if this can be translated to a reliable detection.

Some other requirements:

- Low cost solution
- Reliable, unaffected by EMC or noise from neighbouring wires (Assume the wire will be part of a bundle of wires in a harness)
- Small as possible
- Signal or sense wire can be fed back into an ECU

Any constructive feedback or suggestions welcome.

Thanks

Tom
 

picbits

Well-Known Member
#2
A hall effect DC clamp should do the job. Any interference can be easily filtered out by an RC network and 1A+ of current will give you a reasonable margin of signal to noise anyway with a half decent clamp. We use them a lot at work on engines without too much of an issue.
 

MikeMl

Well-Known Member
Most Helpful Member
#3
How about a photodetector looking at the lamp?
 
Thread starter #4
A hall effect DC clamp should do the job. Any interference can be easily filtered out by an RC network and 1A+ of current will give you a reasonable margin of signal to noise anyway with a half decent clamp. We use them a lot at work on engines without too much of an issue.
Thanks, good to know it is a possibility. I imagine you are using a measurement or diagnostic tool for this? What's the approximate size of the clamp? I'd like to see if there's a feasible design solution that can be scaled up to a production level.

How about a photodetector looking at the lamp?
Interesting you mention Mike, not long ago we had another application where we needed to determine the state of the Hi-Beam on a vehicle without being able to patch into the harness. This was raised as a possible solution.

For this application I'd be looking to attach/clamp onto the main body harness in the rear luggage compartment area (or elsewhere inside the cabin).

-Tom
 

picbits

Well-Known Member
#5
Thanks, good to know it is a possibility. I imagine you are using a measurement or diagnostic tool for this? What's the approximate size of the clamp? I'd like to see if there's a feasible design solution that can be scaled up to a production level.
We make our own - we were using Fluke clamp meters at £300 a time but they were getting melted / burned / soaked / covered in oil so I designed an alternative - I can't say too much about them but most of the info is out there for DIY clamp meters. Try and use ferrite cores if you can - they are quite brittle but if that isn't an issue then you'll get a better output with fewer issues.
 
Thread starter #6
We make our own - we were using Fluke clamp meters at £300 a time but they were getting melted / burned / soaked / covered in oil so I designed an alternative - I can't say too much about them but most of the info is out there for DIY clamp meters. Try and use ferrite cores if you can - they are quite brittle but if that isn't an issue then you'll get a better output with fewer issues.
Thanks, I'll take a look and see what can be done. I'll post something up if I have any luck with it.

Cheers -Tom
 

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