choosing "affordable" test equipment (lcr meters, etc)

[amberwolf]

there is a bit of discussion scattered around the forum about good test equipment, mostly multimeters of various types, some about oscilloscopes.

but very little about *affordable* lcr meters, which are extremely helpful in determining motor characteristics to set them up in various controllers requiring inductance and resistance measurements. (iirc the lebowski will determine these itself, but some like the sfoc5 by incememed don't, and it'd be good to have a reference to go from in case there are problems with the autodetection of a controller, as i will likely test more than just the present motors i have on the trike...).


i'm actually looking to buy one now, for this and other purposes, but i have a *very* low budget, in the sub-$100 range if possible, as i am already budgeting about $400 for a pair of lebowski brains and a pair of honda ima inverters, and assorted bits of connection hardware and the like that i'll need for them (and am hoping to not spend all of that, either). i have *some* leeway at the moment, as for now my job is protected at work from hours cuts due to the covid19 business impact, and it's letting me save back a bit more than usual, but that could change in the next months or more, so i don't want to spend anything i don't have to (well, i never do, but...).


there are lots of really cheap ($10-$30) bare-board "lcr meters" out there, but none of them appear to be able to measure down to the single-and-double-digit uh (microhenry) inductance range, or similar milliohm ranges, at least not with any accuracy, which is what's needed for this specific purpose. plus, with a bare board not in a case, i'd have to build a case for it or else end up destroying it somehow (i am a klutz, at best).


so in the search for decent "affordable" units, i've poked around a bit and found this article (trustworthiness unknown):
https://nerdtechy.com/best-lcr-meter
which lists these as good ones in the $40 to $230 range:

https://www.amazon.com/5000-Handheld-LCR-Meter-accessories/dp/B00S298KJO/ref=as_li_ss_tl?ie=UTF8&linkCode=sl1&tag=nerdtechy-20&linkId=06ce9af73fd2acbe796d8ee8b3e3db01&language=en_US

https://www.amazon.com/Extech-380193-Passive-Component-Meter/dp/B00023RTYU/ref=as_li_ss_tl?ie=UTF8&linkCode=sl1&tag=nerdtechy-20&linkId=1e926dedea540684618dfed514ddd5fc&language=en_US

https://www.amazon.com/Proster-Capacitance-Inductance-Resistance-Self-discharge/dp/B071WNNYQT/ref=as_li_ss_tl?ie=UTF8&linkCode=sl1&tag=nerdtechy-20&linkId=8fb28c7352cf4e164a58b460183b6e3e&language=en_US

the extech has what seems like a lot more features, but i only *need* the ability to simply measure the very low inductance and resistance of motors and such; capacitance measuring would be useful in various situations. all the spiffy features like connection to a computer, or storing readings, etc., are probably things i wouldn't use.

my main concerns are more accurately measuring the lowest possible resistances and inductances.

the proster seems pretty basic, and is more like my budget range, but i'm not sure it will measure low enough, accurately enough.



now...i'm sure there's other lcr meters out there, possibly in the sub-$100 range, that i could use for this purpose (and hopefully a lot more things, like troubleshooting controllers, wiring, transformers, motors, etc), that i haven't run across, or simply don't know enough to look for. (a google search of "lcr meter" brings up much more than i have been able to digest in several weeks or more of poking around ).

so i'm hoping for some experienced pointers in this direction.



as a side note, i already have a basic isolation tester, so that function isn't needed in the lcr meter. but unfortunately because it's designed to test for *high* resistances *between* motor phases / etc, it won't do for testing the *low* resistanced *of* the motor phases (or the other properties needed).

 

[john61ct]

cheap to try
https://www.wish.com/product/5afe52bd77f5b51cccc8a077


https://www.wish.com/product/5b8911bb19374d6a57546e2f

 

[amberwolf]

Unfortunatley those two, like most of the cheap ones, aren't capable of sufficiently low resistance measurements. The resolution only goes down to about 100milliohm increments, which won't allow accurate measurements of motor resistance, which are generally in the range of that increment itself. Additionally, I don't see that those will do the 4-wire kelvin connections, which are apparently important when you get down to very low ranges like this, for accuracy.


The only other response I got, from Kiwifiat via email in our Lebowski discussions, recommended the DER EE DE5000, and so since I was wanting to have something in hand to do work with on this week-and-a-half time-off-work I take this time every year, I went with that, and have it in hand at this moment.

It was more than I really wanted to spend, but as is often true, you pay for what you get, and it does have the measurement capabilities I need, though I'm still reading the PDF English manual to learn how to use it, as it is a bit complex. (the printed manual is in Japanese).

For those interested in extreme detail, this is a teardown and discussion of the DE5000
https://www.eevblog.com/forum/testgear/der-ee-de-5000-unboxing-and-teardown/

and as it does have a serial interface for pc connection, there is also opensource software to talk to it (if you choose not to buy the OEM kit for that, as it doesn't come with it in the common versions available for the $100-ish price range).
https://sigrok.org/wiki/DER_EE_DE-5000
and some printable holders for a USB-IR converter (though lacking in any detail on how to wire it)
https://www.thingiverse.com/thing:2551379
https://www.thingiverse.com/thing:1589728
this thread describes another method
https://www.eevblog.com/forum/testgear/is-the-de-5000-software-useful/

I don't have any need (at least for now) for a PC connection, as everything I can use it for right now is just static single-property measurements.

(though the ability to display both the inductance and resistance of a motor phase pair at the same time is useful).

 

[amberwolf]

So I've been trying to learn how to use the DE5000 LCR meter, and it seems easy enough, for the most part, though I don't know / understand yet what all the properties of things it can measure actually are, or what they might be useful for.

As a test, I thought I'd try it out on something that *should* have known inductance and resistance properties, a QS205 50h v3 5T. That should have, according to QSmotors, 300uH phase-to-phase inductance, and 64.90milliohms phase-to-phase resistance.

also available as text from here, as 330uH instead of 300:
https://endless-sphere.com/forums/viewtopic.php?f=31&t=65972&p=1250076

RPM Voltage Winding Kv Inductance mΩ
300 48 17*7T 6.25 / /
350 48 20*6T 7.29 449uH 66.60
400 48 22*5T+ 8.33 / /
650 72 24*5T 9.03 330uH 64.90
765 72 28*4T 10.63 / 55.50
820 72 30*4T 11.39 / 48.50
956 72 33*4T- 13.28 / /
1100 72 40*3T 15.42 106uH 16.60

But this meter says it's 97.8uH Y-G, 99.2uH G-B, 97.7uH B-Y, for inductance.

Resistance I'm not sure. There are four possible measurements it shows as the secondary when doing inductance, which are:
ESR in ohms
phase angle (theta symbol) in degrees
D (forgot what this is)
Q

So the following are the sets of values given that match with the inductance measurements above, in the order listed just above:
Y-G
0.03ohms
87.0degrees
0.050 (D)
19.80 (Q)

G-B
0.03ohms
87.1degrees
0.048 (D)
20.4 (Q)

B-Y
0.03ohms
87.1degrees
0.050 (D)
19.99 (Q)

I don't know which is the resistance; none matches the QSmotor data.

Setting explicitly to resistance for the main measurement, I get 0.031ohms for all three phase combinations.


I made sure to do the "calibration" (open/short leads) procedure first, so this should be an accurate measurement, if the meter itself is accurate.

Also, all measurements were made with the stator not in the motor, to be sure the magnets would not affect the readings.


So the question is, is my measurement right, or is QSmotors' ?

 

[amberwolf]

It's not quite good enough to check shunts, resolution is too low. But I tested some anyway. Grin shunts (the ones for the CA-SA model) measure consistent 4milliohm, when they are actually supposed to be 1.000. But this also includes the resistance of the wires (12g?) out of the shunt casing, which are almost 3" long on each side, so about 6" of that wire total on either end of the shunt.

Then I checked the Crystalyte HSR3548 hubmotor, first with the stator in the rotor, and then with it pulled out. There is a large difference between the two sets of readings, most especially that one phase will read very differently from the others with the rotor magnets in place, but all are about equal with the stator separate. All the readings are significantly lower with the magnets in place vs with just the bare stator.

Still in rotor:
GB: 146.1uH 0.12ohm
GY: 170.2uH 0.12ohm
YB: 145.1uH 0.11ohm

Bare stator:
GB: 189.4uH 0.10ohm
GY: 192.0uH 0.11ohm
YB: 192.8uH 0.12ohm


I also checked a few more motors, three "9C" types. One is a bare stator from an old Goldenmotor "1000w" hub. Another is a complete 9C from Ebikekit, so the magnets are affecting the readings, making them lower than actual. A third is a stator with covers but no rotor from AmpedBikes. I don't know the winding pattern on any of them; I probably have them documented in the CrazyBike2 thread somewhere if I go dig for them, as they were all used on there at one point or another.


GM1000w:
GY: 464.1uH 0.21ohm
GB: 461.1uH 0.21ohm
YB: 462.3uH 0.21ohm

EBK 9C:
GB: 491.8uH 0.32ohm
GY: 427.7uH 0.32ohm
YB: 511.4uH 0.33ohm

AB 9C:
GY: 562.9uH 0.35ohm
GB: 555.8uH 0.34ohm
YB: 552.7uH 0.34ohm




I also checked a random large capacitor I had out of what used to be a hefty power supply of some type, and the reading of 991uF is very close to it's marked value of 1000uF. It gives an ESR of 0.03ohms; I dont' know if that is right or not.


Measured the small burner off an electric stove, gets 4.4uH and 36.1ohm.

 

[amberwolf]

Photo dump of the pics taken during the above measurements: