Mar 24, 2009, 10:02 AM
Registered User
United States, OH, Eaton
Joined May 2006
1,144 Posts
Discussion
Help identifying motor

I bought this "bell" motor at a swap meet. I'm trying to determine the aproximate KV so I have an idea of what it might be used for. The website didn't help much because the motors aren't shown from behind. Any help is appreciated.

Chris

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 Mar 24, 2009, 06:42 PM Registered User Chattanooga, Tennessee, United States Joined May 2003 27,208 Posts Do you have a tach? Put a couple of of black Sharpie patches on the bell, shine a flashlight at the edge of the bell, run it up on any voltage you wish, measure the rpm.... divide rpm by voltage and that will give you "raw Kv".
 Mar 25, 2009, 01:19 AM Registered User Joined Nov 2008 213 Posts It looks very much like a towerpro 2408-21. But go with Dr Kiwi's test to prove it.
 Mar 27, 2009, 05:13 PM Registered User United States, OH, Eaton Joined May 2006 1,144 Posts OK, I don't have a tach but I can read the frequency in HZ and voltage while turning with a drill. I found that I can get the voltage and RPM and use the formula Kv = ((RPM/ volt) / 1.41) / 0.95 if I know the RPM. My question is, how do I convert HZ to RPM. It gives pulses on 2 out of 3 cogs of the motor (6 out of 9 poles) so would it be (Freq/6)60=RPM? If so, that's very close to the spec of the drill. It does have the correct number of poles and magnets to be a 2408-21 motor. Chris
 Mar 28, 2009, 03:46 AM Registered User Joined Nov 2008 213 Posts I don't think your drill test is going to tell you much. A lot of motors from the same manufactures just have a diffferent number of turns to vary the Kv so turning them with a drill would give the same Hz from each but the Kv's would be different. Just as a reference a 2408 is 23.9mm outside of poles and 6.4mm deep. They have an 8mm dia mount.
 Mar 28, 2009, 04:36 AM Registered User East Anglia, UK Joined Sep 2002 29,709 Posts Don't worry about its KV..just fire it up ion a 6x4 first, on 3s. and go up till you get to about 12A or so. That's a reasonable max for something like that.
Mar 28, 2009, 08:38 AM
Registered User
United States, OH, Eaton
Joined May 2006
1,144 Posts
Quote:
 Originally Posted by GeorgeM I don't think your drill test is going to tell you much. A lot of motors from the same manufactures just have a diffferent number of turns to vary the Kv so turning them with a drill would give the same Hz from each but the Kv's would be different. Just as a reference a 2408 is 23.9mm outside of poles and 6.4mm deep. They have an 8mm dia mount.
Right, but a different number of turns will give you a different voltage output at a given speed. It's on THIS PAGE about winding your own motors. I think I'll just take it to the shop sometime where there is a vice, a tach, and lots of other stuff that measures.

Chris
 Mar 29, 2009, 08:33 PM Registered User Joined Nov 2008 213 Posts I guess the formual from that page may give you a very rough idea but you still need to know what max current draw is for that motor before you decide what to use it for.
 Mar 30, 2009, 08:40 PM Registered User United States, OH, Eaton Joined May 2006 1,144 Posts Mystery solved Mystery solved. I took the motor in to the shop today and did 2 tests. For the first test, I ran it up to full speed, tached it, and measured the voltage. I came up with 13636rpm / 9.35V = 1458KV. For the second test, I checked the Speed of the drill, then turned the motor with it. The tached speed of the drill was 1260 RPM. The voltage on one phase was .63 at a frequency of 128 Hz. Using my former calculation of (128 Hz * 60)/6 = 1280 RPM. Very close. From the formula HERE Kv = ((1260/ .63) / 1.41) / 0.95 = 1493 KV. Both answers are reasonably close so I'm going to say it's equivalent to aTower pro 2408-21 . Chris