Testing motor speed?

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Old 02-08-11, 07:47 PM
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Testing motor speed?

Hello again,

I would like to know if there is an easy (and cheap) way to test that an oil pump motor is running at its rated rpm? Also, are there any cool tricks to check if a coupler is slipping? Just wanted to know. Learning with every repair.
 
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Old 02-09-11, 04:08 AM
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pump

you could chec the amperage draw on the motor,this is not a definitive answer,but it will give you a quick indication of what is happening. check the motor nameplate amperage rating,then use your amprobe at the motor lead. amperage should be close to what the nameplate is. I would suspect that if the amperage is low or very low,the coupler may be loose or just spinning.
 
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Old 02-09-11, 04:54 PM
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The best way I've found to check for a slipping coupling is a visual inspection & by twisting the end caps in opposite directions. For the visual part, look at the shaft sockets on the end caps. Slippage will be pretty evident.
If you want to get real froggy you can remove the pump, leave the coupler on the motor end, hold the fan, & twist the coupler. Next install the coupler on the pump end & get hold of the pump shaft with a small pair of vice grips, hold the shaft, & twist the coupler. If it slips, it goes.

BTW, I still haven't found that exploded view of the Suntec pump.
 
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Old 02-16-11, 09:09 PM
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Thanks

I just wanted to know if there was a tool like an automotive timing light that lets you check actual rpm. On the rare occasion I have to replace a coupler, I put a chalk mark on the end I can see through the air bands. Doesn't tell me the speed, but lets me know it's spinning.

Don't sweat the Suntec pump diagram Grady. I took the one I replaced apart and couldn't find anything wrong. I expected something simple like a broken o-ring, (there are none), or worn gears.

Sorry for the tardiness of my reply. Thanks again.
 
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Old 02-17-11, 08:48 PM
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There are stobes for measuring speed but I've not a clue as to where to get one. There are also contact tachs but again, where to get one?

I just found the Suntec book yesterday but it didn't have the diagram in it as I thought. I know I've seen one somewhere. Now you've got me on a mission.
 
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Old 02-18-11, 09:33 PM
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Contact tachs

I remember them! Basically, just an adjustable wire and tube. Set the wire to a certain length, touch it to the motor, and see if it vibrates, right? A scale on the handle measured rpm. (?)

Don't sweat the diagram. I think I have one somewhere too; just can't find it. In other words, don't , just
 
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Old 02-19-11, 06:20 PM
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The contact tach I had in mind has a rubber wheel which rides on the motor shaft. One type had various wheels & cups to fit over the end of a shaft. I remember using a wire type on a lawn mower engine. As I recall you turned the center hub, adjusting the wire length until the vibration stopped or stayed between two marks. That was a LONG time ago & the memory is a bit foggy. I appreciate the
 
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Old 02-19-11, 06:40 PM
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How much do you want to spend? I have a Monarch phototach that I bought ten or fifteen years ago for I think around $100. It looks like the new and improved model is going for about $350 now. Doing a search I found that the least expensive phototach is going for about $160.

I did have a Stewart Warner hand-held (mechanical) contact tach but it "froze up" and so I had to junk it. I also have a "revolution counter" (contact) that I bought from Sears some forty years ago or so that you had to use in conjunction with a watch.

Okay, I just checked Harbor Freight and they have both a contact and a non-contact digital tach for $30 and $40 respectively. I can't attest to either the accuracy or durability.

Contact Tachometer

Non-contact Tachometer
 
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Old 02-19-11, 06:48 PM
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Thanks Furd. That contact tach is very much like the one I remember using except it's digital. As I recall you put the cone end on the end of the motor shaft. Most larger motors have a dimple in the center of the shaft end presumably either from being turned on a lathe or for centering of a pulley puller.
 
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Old 02-19-11, 08:55 PM
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You're welcome! Yes, there is a cone-shaped rubber tip that you use when the shaft has a center hole and a tapered cup when the shaft does not have a center hole.
 
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Old 02-20-11, 09:01 PM
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Thanks to all

HF comes to the rescue again. I should have looked there first, before posting. Thanks Furd, for the links. And Grady, yes that tach I was referring to was one I saw used to adjust idle speed on a lawn mower many, many years ago.
 
 

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