How to modify a clamp meter to read lower amps

Thread Starter

Jinno

Joined Aug 4, 2020
4
Hi all,

My clamp meter has 2 ranges, 200A and 1000A which I want to modify to be able to read currents from small home appliances, e.g. desk fans, kitchen mixers. But because of its large range it's useful only for measuring large appliances that consume 1amp and higher.

So to be able to read something in the range of a few milliamps to a max of say 10 amps I'm thinking of adding more windings to the clamp. I haven't opened it yet so I have no idea how many turns it has or how many turns would fit in the case.

Disregarding the physical size for the sake of discussion, if for example it has 100 turns and I add 100 times more wires will it read 100 times less?

So for the 200A range I want to change to 2A, and 1000A to 10A will it work?
 

neonstrobe

Joined May 15, 2009
143
A few problems here.
Think through what the current transformer is doing, then consider how many turns you need.
The magnetic effect of 1 turn of wire is "not much". If you want to read lower currents, you'll need more turns on the main (primary) winding, although with an amp clamp it generally only has 1 turn effectively.
Many DMMs might measure 10A without needing a clamp. Could be cheaper solution
 

crutschow

Joined Mar 14, 2008
27,170
Trying to modify innards of the clamp is problematic.

You can however, increase the sensitivity by running more wires through the clamp's opening in a loop from the item you are trying to measure.
For example 100 turns would increase the sensitivity by roughly 100 time.
The question would be how large a wire could you thread through the opening to get the desired turns (how big is the opening?), and would its resistance then significantly lower the voltage to the load?
You could add a plug and socket to the added wire so it would be easy to connect between the main's outlet and the load.
 

rsjsouza

Joined Apr 21, 2014
309
Whatever @crutschow mentioned.

To determine the number of turns (either 10 or 100), you need to take into consideration the resolution of your clamp as well.

In other words, the power consumption of desk fans, desk lights, etc. is usually less than 1A. If your clamp has 2000 counts, the 200A range would give a resolution of 0.1A (100mA). Using 10 turns of 18 or 20AWG wire would be enough to improve this resolution to 10mA without having too much wire that could cause a significant drop in voltage. This arrangement would be suitable for currents of up to 20A (in the 200A range).

Using 100 turns it becomes quite excessive due to the mechanical arrangement and voltage dropout. This would be suitable for currents up to 2A (in the 200A range). However, at that level you are better served by a handheld DMM and its current ranges.
 

neonstrobe

Joined May 15, 2009
143
Well, that's what I meant by "primary winding"- the wire through the amp clamp needing more turns, not adding turns to the amp clamp internally.
 

Alec_t

Joined Sep 17, 2013
12,060
Assuming the meter is of the type having a current transformer, increasing the transformer's burden resistor value would increase the meter sensitivity.
 

bassbindevil

Joined Jan 23, 2014
158
An "energy monitor" gizmo like the Kill-A-Watt is useful for that kind of thing. It'll read voltage, current, watts, power factor, and line frequency, plus record power consumption. The price has crept up since I got mine, but the no-name copies may be good enough.
 
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