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).
It's the yellow one in this photo.
-Garry
I would check the battery first. My meter started reading crazy all over the place and it was the very old battery. Worked much better after I swapped in a new 9V...
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!
Ok, thanks guys. I'll try changing the battery and report back. I don't even think the battery in it is that old either.
-Garry
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.
Only if the resistors are statistically independent. Does not apply if your resistors came from the same batch where their values will be highly correlated.
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!)
-Garry
I've been watching that one too, but I don't think it's ever on sale. In fact, they have RAISED the price...
When I first posted on this one (https://budgetlightforum.com/t/-/3603), it was only $40, now it $45! In the meantime, get one of the cheap red ones they giveaway for free with a coupon...
http://www.harborfreight.com/7-function-multimeter-98025.html
I do have two of the cheap red ones. Back when I got my first KD C8 I found the cheap red HF one to be crap for current measurements. .
I'm about to just use a 20% off coupon on that meter and get it at regular price. $36 for it still isn't bad.
-Garry
I just got a nice 2nd DMM from FastTech: uni-t-ut50b - higher end than my older UNI-T one, same great features. UNI-T's are known low resistance.
interested ? its an 8062A model. With leads
Don't think so, but thanks for the offer.
-Garry
Hi,
I can’t really see the image in detail, but can you set the range of current on your meter? Have you tried setting it to a range that’s higher and see what happens?
Jim
I always use the 20A setting.
-Garry
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.
The UNI-T UT61E is know to have a high burden voltage in the A ranges (i.e .high resistance).
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...
A high end Fluke is not necessary good. The problem is usual the x00uA and x00mA range on auto ranging meters.
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.