Well..since I don't have a 4 wire low ohm meter, how would connecting 2 test leads to the same exact place on the shunt somehow produce different results? 2 test leads or one connected to the exact same place are electrically identical. I'll probably replace the alligator clips for better ones. It's just getting a good bite that makes the difference here and causes the losses.madin88 wrote: ↑Dec 18, 2017 12:50 pm"where is the problem if it does not have 4-wire resistance measurement"
Well, now you know
Contact resistance from 2 sets of alligator clips is going to be less than one set of clips. Same for good clips vs cheap ones. Two sets of clips are going to be attached to the part side by side. Assuming equally good connections, the resistance difference between the 2 side by side alligator clips is going to be negligibly different. If it was say 1 ohm different, then that's going top badly skew the measured result and invalidate any measurement. The chances of current separation between side by side alligator clips is also equally negligible. I would think that contact resistance can be zeroed out just by clipping the 2 leads together and zeroing the meter. Then, whatever you get when attached to a component should be all component resistance. 2 or 4 wires shouldn't make a difference since 2 wires electrically in parallel is going to be the same as a single wire.Alan B wrote: ↑Dec 19, 2017 2:08 amPutting the excitation current and the reading currents through the same contact point causes the meter to be unable to differentiate the contact resistance from the shunt resistance, so it cannot accurately measure low values of target resistance. Four wire meters separate these two currents, and by using a very high impedance amplifier on the voltage readout they make the contact resistances disappear from the measurement.
ElectricGod wrote: ↑Dec 20, 2017 4:24 pmAnyone with a 4 wire meter...
Please do a test for me for comparison. Take a length of solid copper wire, a shunt, a 6-32 screw, leg to tab on a transistor...whatever you easily have on hand. Connect it to your meter. Don't cram the clips into the object under test, just clip them on. Measure the results. Now shift your leads around. Do you consistently get the same resistance? My suspicion is that you don't. My suspicion is that a 4 wire or 2 wire meter is going to suffer from contact resistance variations equally. And especially so at these low resistance levels.
Better alligator clips won't help much because the difference still would be way to high for comparing Rds on of mosfets.ElectricGod wrote: ↑Dec 20, 2017 4:24 pmNotice how I expose anything I discover. For example, depending on how the meter is connected to the shunt, I get different readings on the meter. It may be that better alligator clips significantly reduce this issue. I have some on order and they will be in my hands come January. I have no ego to protect and as I've said from the beginning...the results will be the results. I was also able to measure .005 ohms like my precision shunt is valued at. The picture when I took it shows .012 ohms, but just a second before, I was looking at .005 ohms after zeroing the meter.
Of course anything I post that I find will get used as "proof" that I'm doing something wrong whether it is or isn't wrong.
Why do a test if you're already certain what the result will be? You're free to spend your time learning things on your own that are already common knowledge, but it's not surprising that no one else feels the need to do these experiments.
I didn't do the test because I don't have a 4-wire meter and I don't plan to buy one right now because I don't think I need it.
Well... 4 wire meter purchased for comparison purposes and a couple sets of decent grade gold plated kelvin clips purchased for the 2 wire meter. We will see what happens soon enough! If the 4 wire meter blows the socks off the 2 wire meter...fantastic...if it doesn't...fantastic. The results will be the results. That's infinitely more than anyone else can say.Addy wrote: ↑Dec 21, 2017 3:00 pmI didn't do the test because I don't have a 4-wire meter and I don't plan to buy one right now because I don't think I need it.
On the same note, you could do some reading and gain some understanding of these concepts instead of yakking on about how you're the only one testing and everyone else must be lazy.
Seems like you're more interested in conjecture than technical discussion.ElectricGod wrote: Now we all know why you don't ever test anything...you can't test...plain and simple. You have no choice but to take what you read on faith. And that's perfectly OK...just say so. Why was that so hard? There was quite literally nothing to hide except for the fact that you can't prove anything you say with actual testing. I on the other hand can test and can back up what I say with real live testing. Good god man! What a waste of time posturing and pretending when honesty was the best approach!
Well, I can see why you don't bother learning the theory.ElectricGod wrote: I never worked a day in the field because I discovered I liked computers so much more and hated all the math an EE needs.
I'll comment on this one thing...Addy wrote: ↑Dec 21, 2017 4:17 pmSeems like you're more interested in conjecture than technical discussion.ElectricGod wrote: Now we all know why you don't ever test anything...you can't test...plain and simple. You have no choice but to take what you read on faith. And that's perfectly OK...just say so. Why was that so hard? There was quite literally nothing to hide except for the fact that you can't prove anything you say with actual testing. I on the other hand can test and can back up what I say with real live testing. Good god man! What a waste of time posturing and pretending when honesty was the best approach!
I'd rather trust theory from reputable sources, than the postings of some guy on the internet who doesn't understand the limitations of his testing.
Fortunately for me, I'm not worried if you trust my tests or not. I trust them. Beyond that, if I help others, great. If people get in the way of that, than shame on them.Addy wrote: ↑Dec 21, 2017 4:34 pmI'd rather trust theory from reputable sources, than the postings of some guy on the internet who doesn't understand the limitations of his testing.
You are publishing your test results in an open forum, writing statements that AOT290 FET's have big abnormalities.
I fed the gate with 10VElectricGod wrote: ↑Dec 22, 2017 6:00 pmIn your resistance test, what voltage are you feeding the gate? I would be curious to find out why the digikey mosfets are under Rds spec. I'm not complaining...less resistance is a good thing. And why the one from the controller was dead on typical spec. Variations do occur and if you had three mosfets and one was significantly different than the other 2, then it's also possible for that difference to swing the other way as well. Like I have said in the past.
I guess this would only make sense regarding the first versions as far as i could see?Once you are happy that the controller is running well make some changes to it.