Problems with a Surface Grinder

Was that grinder also available with a variable-speed DC motor? That could explain the reference to the brushes.
 
Look at all the education you are getting, Randy! :)
 
Yeah, I think I just learned; if it ain't broke don't fix it. 8^)
I don't know if a variable speed was an option. I kind of doubt it; as it was a low end Enco. There may have been one available from the factory though.
My ammeter arrived today. Hopefully I will get to try it out tomorrow.

Randy
 
SOOT (Sort of on topic) user tip for clamp on ammeters:

Since they operate on the principle of induction, they read a current induced in the laminated iron made up by the clamp. These meters typically have a rather high minimum measurable current. It is possible to "trick" the meter into reading lower currents, into the milliamp range. Simply take the wire (remember, only one of the leads of the motor or DUT) and instead of just clamping the meter around it, wind up 10 loops into the clamp of the meter. This increases the account induced in the clamp by a factor of ten. Just remember to divide the reading by 10 to get the actual current.
 
Being a total Noob to the clamp on ammeter, that is a great tip. I sure didn't see THAT tip in the instructions.

I am hoping to get to it tomorrow. I had required husbandly duties to perform today 8^(

Tony, do have any ball park idea of what kind of amp range I should be seeing on each wire of a 3 phase 1.1 KW motor?
I am presuming 1/3 of the stated name plate amp draw and relatively equal???

Randy
 
The current rating on the motor plate isn't all three added up. It's what you can expect to see on each wire at full load. When you're just running at idle, the current will be somewhat less. You should only see the plate value when it's running at full rated horsepower.
 
Power calculations get pretty involved at times. Your 1.1 KW motor works out to 1.5 HP. You won't see the 8 amps at idle, as Hawkeye points out. In fact, if you calculate back from 8 amps, you have a larger motor. Why? Something called power factor. Look at it as efficiency. If the motor never put out any heat, only rotary motion, it's Pf would be 1 (or 100%). No such motor exists yet. Good motors are 85-90% I believe. Plus, if you stall the motor, you get a whole new set of numbers called FLR amps, for fully locked rotor. This will be quite high, and one you hope to never see. Under no load, you should see less than the 8 amps on the plate. That 8 amp figure is with the Pf considered, and loaded to 1.5 HP. I'd guess (and it's only a guess) that you'd see 3-4 amps on each leg.
 
Well I finally got some time to play with the surface grinder. I checked each leg on the motor:
L1- 1.2 amps W1
L2- 3.3 amps V1
L3- 3.5 amps U1

So what do you think? It doesn't say too much to me.

A new mechanical problem has raised its head. The motor and spindle are connected by a coupler. The coupler is 2 cast iron disks each with 2 large tabs. The tabs on the opposing disks interlock with lots of clearance. The disks and tabs are enclosed in a relatively sealed cavity. When disassembling the coupling it seemed to be packed with a substance that looks like a mixture of saw dust and asphalt. I tried to simulate it with silicon sealer. Now that I have it all together; when I start up or shut down the motor I get a considerable amount clacking. I presume it is the tabs slapping against on another. Any ideas on what I could use as a cushioning medium?

Randy
 
I suspect that the low reading on the W1 wire is due to the RPC. As several members have pointed out, you can only expect about 2/3 of the rated power from an RPC setup. Power is, crudely put, Amps times Volts. Lower amps and/or lower volts = lower power.

The sawdust mixture could be what age does to a rubber insert. Consider replacing the whole coupler. A thick section of silicone sealer can take a week to cure completely. If it's still too soft, it could allow the prongs to prang. Here's a weird idea. Try mixing the silicone with - wait for it - sawdust. The filler may stiffen it enough. Allow plenty of time for it to cure. It does so by reacting with air. The thicker the section, the longer it takes for the reaction.
 
Most of your run-of-the-mill RTV silicones are not going to work there. Get with a power transmission supplier for a coupling. They will need the shaft sizes and horsepower transferred as well as the anticipated RPM.

Enco might or might not be any help on this. I'd go straight to Applied Technologies or someone like them.
 
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