Current clamp variation

Ted Technician Berwick, Nova Scotia Posted   Latest  

I was checking for a parasitic draw on a Honda Odyssey when I noticed that just by turning my current clamp 90 degrees I got a fairly significant change in the milliamp reading, just turning it or taking it off and repositioning it 90 degrees gave the same result, anyone have a theory on this?

The I’ve had this clamp for about 10 years and have used it frequently for finding draws but have never noticed this before, I have another low amp clamp that I use with the scope but never thought to try it and see if I got the same result.

Maybe when I get a free minute I’ll do a comparison...

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Interesting
Albin Diagnostician
Leavenworth, Washington
Albin Default
 

A current probe is just a big antenna that picks up the magnetic field that is surrounding the wire that is carrying current. Do oyou have a different current probe to try your test with?

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Ted Technician
Berwick, Nova Scotia
Ted Default
 

Yes I do, when I get a minute free at the shop I'll re-do the test with both clamps and post the results here.

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Jj Technician
Quincy, Massachusetts
Jj Default
 

I'm pretty sure it has something to do with the hall effect sensor in the clamp portion. It's the reason you want to make sure you know where the body of the clamp is going to rest when you let go of it before you zero it out. Say you zero the clamp, put it on the cable, let it go and it slides along the fender or something to a different position. That could mess with your reading a good bit…

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Olle Instructor
Albert Lea, Minnesota
Olle Default
 

There is always a magnetic field around us. When you reposition the clamp, the sensor sees a magnetic field of a different strength. Zero the amp clamp close to and in the orientation you intend to use it in.

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Ted Technician
Berwick, Nova Scotia
Ted Default
 

Yes, we do exist in a giant magnetic field. My question would be how do I know which millamp reading is accurate? As you can see by the pictures the range of difference is equal to what would be considered the maximum allowable draw on most cars (old 50mA draw rule of thumb). Short of disconnecting the battery cable and putting a meter in series (intrusive test and generally agreed to be a last…

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Rex Technical Support Specialist
Alliance, Ohio
Rex Default
 

Recently I came across some directions on zeroing that said to put the jaws parrelel to the wire being measured then zero. Had never seen that before. Seems to help. Maybe it's always been like that and I missed it. Doing that does seem to help.

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Ted Technician
Berwick, Nova Scotia
Ted Default
 

Couldn't hurt to try for sure...

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

You can also clamp your probe around the load and zero it. Now take the probe off and see what is the difference.

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Ted Technician
Berwick, Nova Scotia
Ted Default
 

Never thought of that....good suggestion Albin

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Dennis Owner/Technician
Plymouth, Michigan
Dennis Default
 

In and ideal world that might help sometimes its hard to get the freekin clamp on and the jaws closed all the way.

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Jj Technician
Quincy, Massachusetts
Jj Default
   

The most accurate reading will be the one you get when you zero the clamp and ensure the orientation doesn't change. As little movement as possible after zeroing is what will give you the most reliable reading. Edit: Here is a video that talks a little bit about this. He makes some changes to the meter, but for some reason doesn't really show what he does and I can't seem to find the procedure…

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

I'm glad you explained this JJ. I am always a little befuddled by how much my reading could change and I was never holding the clamp right next to where I was about to use it, when I zeroed it. Mystery solved.

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Jj Technician
Quincy, Massachusetts
Jj Default
 

Yeah, it can skew your reading by a surprising amount. I have that same meter that's in the video i posted, but I haven't worked up the courage to mess with the trimmer pot he talks about to reduce that effect and "align" the meter for fear of messing it up and adjusting it way out of alignment.

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Danny Technician
Losangeles, California
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I don't think any of the modifications the YouTuber is making to the probe impacts how it reads in relationship to the position of the circuit it's testing. He's making it respond faster, and he made it output a waveform. That probe wasn't built to output a signal. I have that particular DMM/Current Clamp, and as long as you keep the orientation to the wire being tested stationary, it works fine…

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Tom Owner/Technician
Boise, Idaho
Tom Default
 

This is the method I use. I get next the circuit and zero, sometimes repeatedly. Then re-zero often​.​There is a huge magnetic feild all around us we have to compensate for...

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default
 

Well I dont have a scientific answer but ill give it a shot. The best way to test that clamp would be to put an DMM in series with the negative cable and then check the clamp against the meter. My experience with handheld clamps or clamps that connect to a scope is I have hard time trusting them under like 200 milliamps. Also I really need to get a milliamps clamp. I bet it would work much…

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Ray Diagnostician
North York, Ontario
Ray Default
 

I use 2 amp probes at the same time and if both probes are measuring exactly the same, then I'm confident of the amp draw reading.

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Dan Owner/Technician
Ingleside, Texas
Dan Default
 

... My sharp eye detects a SECOND large black lead coming offa that negative battery clamp...maybe that has something to do with it?...Dan H. ...South Texas...

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Dennis Owner/Technician
Plymouth, Michigan
Dennis Default
 

Dan you beat me to it.

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Ted Technician
Berwick, Nova Scotia
Ted Default
 

Good eye Dan but the other cable goes to the starter and it had 0mA on it no matter how I placed the clamp...feel free to keep playing though, lol

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Hollis Technician
Boulder, Colorado
Hollis Default
 

I gave up using an inductive amp clamp for battery draws / drains especially in the milliamp range, got tired of Zeroing and not trusting my meter, values changing, ect. I use this method. static​.​nhtsa​.​gov/odi/tsbs/2014…​.​pdf

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Ted Technician
Berwick, Nova Scotia
Ted Default
 

Thanks Hollis, I agree that this way is probably the most accurate and on older cars I don’t mind using this method but some newer cars really don’t like having the battery disconnected unless you enjoy spending an hour relearning crap , these are the ones that I prefer to use the current clamp on

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Hollis Technician
Boulder, Colorado
Hollis Default
 

I use a memory saver before disconnecting the battery.

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Hollis Technician
Boulder, Colorado
Hollis Default
 

Time is money :O) I've got the Amprobe LH41A, it's a little more stable if you want to spend the money. amazon​.​com/Amprobe-LH41A… And I've got the ESI-687, it performs like yours. Good meter. aeswave​.​com/Low-Current-Pr…

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David Owner/Technician
St. Albert, Alberta
David Default
 

Speaking to DC current, we must remember that the magnetic field around the wire is actively rotating around the wire and it moves in a specific direction. So the amp clamp is using that to make a reading. If you are moving the clamp, the reading will not be accurate at all. If you do not zero the meter each time you before you enter the field around the wire and then close the clamp you will…

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Rudy Technician
Montebello, California
Rudy Default
 

Others have sufficiently chimed in as to why it changes,Ill add that the quality of the clamp comes into play as well. It looks like youre using a ES clamp or some other Chinese variation, yes? I used one for years,but I hated how it would drift(even if it wasn't physically moved) and have found that better quality clamps drift much less and are generally more reliable. (My current fave is…

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Angelo Instructor
St. Louis, Missouri
Angelo Default
 

I sort of like working with the "pushbutton zero" amp clamp more then the "trim pot" amp clamp because they all seem to drift and I hate messing with the "trim pot" which is seemingly more painstaking.

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Ted Technician
Berwick, Nova Scotia
Ted Default
 

I agree, my high current clamp has a dial and it’s a bit of a pain, the only good thing is when checking starter circuits a couple amps this way or that doesn’t make any difference.

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Ted Technician
Berwick, Nova Scotia
Ted Default
 

The clamp in the picture is actually a General Technologies Corp current clamp, built in Canada no less, my other low amp clamp (for scope use)is the same one sold by .AESwave, PDI I think is the manufacturer.

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Ted Technician
Berwick, Nova Scotia
Ted Delay
 

Still haven’t had time to do any testing, hopefully after the holidays if things slow down a bit

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