I've now confirmed that my multimeter is reading too high. Thin leads, thick leads, doesn't matter. A week or so ago I was getting 1.68A on high on a 4xAMC 1.4A Nanjg driver and this morning I was getting 3.35A on an 8xAMC 2.8A Nanjg 105c driver. I've heard of getting low readings, but why are mine too high? Could it be the battery in the meter?
Has anyone else experienced this? Voltage measurements seem ok (I think, but now I wonder).
Think I've seen the smae thing on my DMM with batteries getting low. If it's anything like my light meter, it drives me nuts! When the battery starts getting low, it reads a little high, than as it degrades, the readings get higher and higher till it's obvious! Had me tricked sometimes - think'n, wow! My mods are sure working miracles!
against a known voltage (a good car battery without surface charge should read 12.8 v) in series with a known resistance (cheap, good power resistors from Hosfelt or others). 3A or so shouldn’t change the voltage much. In this case you’re looking for big errors so you don’t need a lot of precision with the V and the R.
A bunch of cheap 5% resistors in parallel or series will give you higher precision at less cost than a single precision resistor, according to the Root Sum Square formula for combining tolerances.
A voltage reference IC that you can run off a 9v battery with a resistor is less than a buck.
If you compare the readings of several meters you will get lesser certainty that your meter is good or bad than if you use a reference.
OK, tried a brand new battery (Rayovac alkaline). That's not the problem. Checked voltage of the battery I took out (Duracell) - 9.53v and voltage of new Rayovac - 9.76v (both measured on another cheap meter known for being off a bit - usually measures 0.03v lower than I expect for a Li-Ion. Checked currents with the new battery and still reading high - 3.46A on a 2.8A Nanjg driver.
So now what? Perhaps it's just time to get a new meter! (I'm waiting for that darn meter at Harbor Freight to go on sale! I'm beginning to think it never will!)
That’s a nice one. I prefer the 20A setting to be unfused anyway; generally lower resistance. My Metex M-3800 is 0.025 Ohms including my homemade stubby leads that I can solder onto drivers for current testing.
I also like having a power button, so you do not have to wear out the dial contacts just to turn off the meter.
Ohhh - I got the 33D for about $15 and it's been doing great and a "super tech" @work has a few and said the low resistance is about the same as his high end Fluke. Hhhmm, didn't thoroughly run/test the 50B for amp readings yet, have to check it out this evening...
I’m not sure about the meters you have but have you had any of them calibrated? I’m not sure what it might cost to get done as my Dad does mine.
Working as a linesman so many people say their incoming voltage is high or low because their sparky mate checked it with their meter, but that meter has never been calibrated so it’s only useful for checking if there is a voltage or not.
A flat battery stole a couple of hours of my life hunting for a fault that didn’t exist because the battery was flat enough to ruin my day but not enough to trigger the low battery alarm.