Hi all, I have a Uni-T UT210E clamp meter. For this project I have a battery pack, and a bank of LEDs. Two heavy wires run between the battery pack and the LED bank, a positive and negative. I will be measuring Amperage with the clamp meter on the 100A setting
Should I be clamping the meter on the Negative wire running from the pack to the LEDs, or on the Positive lead returning from the LED bank to the batteries?
Will which direction the meter is facing effect the accuracy of the results? Or will it just read with a - symbol if I get it backward.
Voltage questions:
I am going to use a separate DMM with a regular set of leads to measure voltage UNDER LOAD at the same time.
For this does it make any difference at all where I tie into the system? Or can I just grab any positive and negative point in the loop with my leads?
The accepted way is measuring off the groud (-) wire on the load side. Some might correct me on that, but that’s how I do it. If you get the direction wrong, it shows (-) on the reading, but in my experience that doesnt affect accuracy.
Depends what you want to measure, voltage at the battery terminal, or voltage at the led, voltage at the led will be lower because of the voltage drop in the wires (resistance), if you want to see how the battery behaves under load then measure at the battery.
For this part it does seem to make a difference. Clamping on the negative cable I get a 6.25% higher reading vs when I clamp the positive. I would have thought clamping anywhere in the closed loop would be the same, but it doesn’t appear so in this case.
Okay, I think I have this cleared up now. I did some controlled testing (heavy wires, regulated output etc) and found that there were two key factors about using this meter.
The direction of flow does seem to effect accuracy with this meter. For example flowing in the correct direction I could repeatedly measure 1.94 amps. Stop, clear the meter and then get 1.93 or something very similar when Clamped to the negative side. Reversing flow would cause it to drop a few percent to like 1.84. When clamping on the Positive side, direction of flow makes a much more dramatic and repeatable difference. On on the + side with the meter zeroed and direction of flow correct I get 1.94 amps. With the flow reversed It read 1.63 amps. So a 19.01% difference.
Zeroing the meter. The instructions for this product say to clear the meter more than once if it doesn’t zero the first time. On the 2 amp setting it will never stay at zero if the meter is moving, but on the 20 amp setting its pretty stable. Even if the meter does default back to zero after taking a measurement I’ve decided its good practice to hit that button, but the only way I’ve seen a noticeable effect is if the meter is showing some positive number.
Thank you all so much. I appreciate everyone who chimed in. I knew I could count on you guys!
As for point 2, that’s to be expected. If it fidgets by, say, 2 units, that’s 20% on a 0-10 scale, but only 2% on a 0-100 scale.
That’s why a lot of those clampmeters are AC only (ie, don’t bother trying to measure unchanging DC), or are only made to measure huge currents.
It’s measuring microscopic bits of magnetism that are about on-par with Earth’s magnetic field. Clamping it closed should “close the circuit” but it often doesn’t.
what might be going on is, you are changing the clamp
it really needs to be zeroed before you move it, if you move the clamp you should zero it again. because its position etc has a big effect on what it reads.
