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Old Mar 24, 2009, 10:02 AM
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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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Old Mar 24, 2009, 06:42 PM
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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".
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Old Mar 25, 2009, 01:19 AM
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It looks very much like a towerpro 2408-21.
But go with Dr Kiwi's test to prove it.
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Old Mar 27, 2009, 05:13 PM
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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
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Old Mar 28, 2009, 03:46 AM
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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.
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Old Mar 28, 2009, 04:36 AM
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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.
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Old Mar 28, 2009, 08:38 AM
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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
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Old Mar 29, 2009, 08:33 PM
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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.
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Old Mar 30, 2009, 08:40 PM
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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
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