LCR meter help
 

I am looking at picking up a LCR meter to test some brushless motors. I've heard that some of the meters won't work because they can't measure in the ranges needed. Does anyone know what the ranges are and what a good meter on the cheaper side would be?
Thanks!

I use the DM4070. It can be found on eBay for around $40.
This is the same one that was used by John Tag from eXpress Motorsports

Works great.

Thank you

The DM4070 accuracy is insufficient for stator resistance.

MMS is a very good meter. Can find a used one for $65-75 usually. Bit over a hundred new.

http://www.racersmeasurementsystems....stem-MMS-2.htm

ROAR Spec 25.5 motor: Only three slot "Y" wound stators are permitted. No delta wound or slot less stators are allowed. Only circular (round) pure copper magnet wire permitted. The three slotted stator must be wound with 25.5 turns of two strands of wire with a maximum diameter of .643mm per slot. The minimum resistance between any 2 phases of the motor (AB, AC, BC), when measured at 25C with an Instek GOM 802 milliohm meter, will be no less than 101 milliohms. The stator stack length must be a minimum of 19.7mm and a maximum of 21.0mm. Only 12.3 mm diameter rotors will be permitted in 25.5 Spec motors and the diameter must measure 12.30 +/-.05 mm. The rotor magnet length must be between a minimum of 25.0mm and a maximum of 26.0mm, not including any balancing material."

buy the one ROAR uses or says to use....

Only $830 thru Amazon! :lol: Definitely not on the cheaper side.

The OP asked about an LCR meter. So far most of our comments have been directed only at the resistance measurement.

A handheld meter to measure inductance and capacitance isn't too expensive, as illustrated by the DM4070 suggested by imprsme.

The resistance measurement is a little more challenging. The GOM802 goes for $510 (which is what I paid): http://www.testequipmentdepot.com/in...er-gom-802.htm
The GOM801H is less accurate, but probably still useful, and costs $340: http://www.testequipmentdepot.com/in...r-gom-801h.htm

The MMS suggested by Andy is quite popular, but I have never seen any published accuracy specs for it (which doesn't matter if one is just comparing one stator to another, using the same meter).

There is a Chinese meter for about $65 on Ebay, as whitrzac mentioned in one of my threads on the subject. I don't know of anyone who has used it.

And finally, the cheapest way to get accurate resistance measurements is covered in this thread:
http://www.rctech.net/forum/radio-el...l#post14329133

From what I've seem, most motors are being measured using the resistance mode. (hence the MMS is popular). Also switching to Kelvin clips on the MMS meter made a huge difference in readings. More stable and assuming more accurate.

Yes, it is absolutely necessary to use a four-wire (Kelvin) connection to get the required accuracy.

As a general rule, a meter using only two wires for resistance measurement is a dead giveaway that it won't do what we need.

Electric noob here, how is this done? If I decide to get the MMS.

Is resistance a more important measurement then inductance and capacitance for brushless motors? I remember reading somewhere that said to get a LCR meter. I can't find the link anymore, oh course.

Yes.

The MMS has two wires going to each alligator clip, but the wires connect together at the clip. You'll need to arrange a pair of contacts for each clip, with each wire having its own contact. The contacts then touch the connection tab on the motor, but never each other.

I'm sure there are several good ways kluge this, though I have never done so myself.

To give you a better idea of the concept, here is one of the Kelvin-connection alligator clips on my Instek meter. (The hex nut is just for illustration.):

http://i1191.photobucket.com/albums/...psqzruyxx3.jpg

You can also just use one alligator clip per wire (four total), but it's a pain getting them on the motor tabs without touching each other.

I wish ROAR had published other spec motor rules with the amount of detail the 25.5 rule has. :)

I'll take that as a compliment!

Let's keep our fingers crossed that the rules for the other winds will be updated soon.