Alan B said:
It will give you a value which may be useful, but probably not comparable to the specifications test conditions, (one thing you'll probably want to figure out is at what test current). For the spec sheet they probably do it at fairly significant current, and a cheap meter probably does not. As was already covered, 5V on the gate is not a good value to use. If you want to compare to the data sheet you have to use the same values they did.
I just glanced at the AOT290L datasheet, and they give the test circuits as I mentioned before. No need to ask for them. You already have them.
You are probably dead on...if the tester runs a mosfet at 200mA and more than 5 volts I would be surprised. BUT is this limited test "good enough"?
This is the test schematic for Rds presented in the AOT datasheet. RL would be a watt meter and shunt to show circuit amperage. Rg can be a 1k resistor and doesn't really matter what the value is. Vdd isn't stated in this schematic, but in the one above it looks to be about 12 volts. Vgs also was shown at about 12 volts. Feed the mosfet gate a 12 volt trap wave and watch the voltage drop across source to drain on an o-scope. Do a little math to calculate Rds and you have Rds the "real" way. If this produces similar results to a component tester that does Rds...then this setup is irrelevant since the component tester is producing "good enough" test measurements.
1. I bet egregious mosfets are going to be off the mark regardless of the voltage and current they are run at. IE: An inexpensive component tester capable of Rds at a minimum ought to find those components easily and quickly.
2. A "simple" rig that's essentially the above schematic will provide the "real" test set up. I have everything needed to make that happen.
My hope is that the "quicky check" with the component tester does will result in the same information as actually testing the "real" way produces. OR at least is close enough that it doesn't matter very much to need further testing. My theory is that there is a level of mosfet testing that is "good enough" and that cheap a component tester will provide that. We will see! I do understand finding matched mosfets...hence my level of mosfet testing that I have already been doing. How close to "perfectly matched" is good enough? I guess that depends on the person and their expectations. Will a $30 component tester purchased on ebay provide "good enough" results? My suspicion is that it will, but the proof is testing a mosfet with a component tester and then comparing those results with what the test rig produces. If the results are similar and therefore "good enough" then a mosfet testing rig is a mute point.
I don't know this for a fact, but I suspect that most controller manufacturers assume that the mosfets they bought from whatever supplier are all good and at most, put them through a very quick test to make sure they turn on and off correctly. Beyond that, they put them in a controller and test the controller as a complete unit. If it runs a motor and passes the various system tests they do, then the mosfets are considered "good enough". It's only people like me that might want another level of precision in finding the best pairing of mosfets.
Since no one has provided any actual demonstrations of such work...only opinions, I'm suspicious that they have not done any testing at all. In that case, opinions about what is or isn't going to work to produce "good enough" test results are purely supposition and probably not based on actual experience. I'm not imputing anything, just stating my observations and suspicions. It seems that my basic testing with a component tester and a few steps beyond that are far more than anyone else typically does. Assuming mosfets are "in spec" and NOT testing them in any way at all seems highly probable in most cases. At least I do some basic testing. Which is more than anyone else has shown demonstrable results for. LOL!
When I say, that the AOT290's I have received don't match spec or vary widely, it's because I've done actual testing of those mosfets. This is infinitely more than anything that anyone else has presented, since no one else has presented anything at all...just opinions. I have actual testing on my side. What does anyone else have? Nothing, zero, nada, just opinions and suppositions!
I have a thread that I started recently. It's far from done yet and I have hardly put any content in it. It's almost entirely place holders at the moment. See below. I intend to put a post in there about mosfet testing. The results from various ebay component testers and a "real" test set up all on the same mosfet will be presented. THAT will settle this and then people can nit pick or state opinions all they want, but the test results will be the actual facts. I don't know when I will get to the mosfet testing specifically, but hopefully sooner rather than later. I'll wait at least until I have the component tester I just bought.
"Random tools and EV related projects"
https://endless-sphere.com/forums/viewtopic.php?f=10&t=91589&p=1337793#p1337793