I was just kidding about doing a 20A test with it. I don't have the Lexan-protected safe box to do testing like you do...I'll probably keep this meter in a mA ranges max.
Too late to back out now.
Direct Current
20A +/-1.5%+3, res 10mA
Max measuring voltage drop: measuring range 20A is 200mV
Max input current: 20A (no more than 10 seconds)
Overload protection: 20A/250V fuse
For AC, is basically the same except
Max input current: 10A (no more than 15 seconds)
Think that's a 20A 250V glass fuse in there? I don't have another meter that claims 20A and my bench supply is good for 6A.
But I think I can get us a constant 20A and the Brymen can read 20A with a pretty low drop. Wonder what current that little baby shunt will open up at.
As for frequency at 500mV, 1V and 5V the best I could do stably was 10MHz. After that is sometimes would show the higher frequency briefly before going to all 0's - up to 20MHz then, nothing.
The manual has a CAUTION about auto range only in frequency mode. I wonder if they won't switch to the low range. Did you try both the mv and volts functions? Same results?