LOAD RPM

[kwired]

Interesting geometric tidbit: Some people feel intuitively that smaller objects should pack better. But in fact if the shape is unchanged objects of any uniform size will have the same packing fraction (ratio of occupied space to total space.)
Milled corn can have a higher density than shelled corn for three reasons.
1. The shape of milled corn particles allows tighter packing than shelled corn particles.
2. Milled corn contains a mixture of particle sizes, allowing the smaller ones to fit into the voids between the larger pieces.
3. Milled cord particles are softer and so can be packed tighter because the touching parts can compress to allow closer packing.

Fourth factor is moisture content of the corn and can effect shelled corn or ground/milled corn.
Some processes may have a desired moisture level and it won't vary much in the supply, some processes it could vary.

 

[ptonsparky]

I caught them before they changed speeds on anything. They eventually agreed there was a problem where I suspected.

I’m Inclined to think they need more than what they are going to do, but it’s a start.

The owner has now told me he wants to add liquid to the process. Ah, No.

 

[winnie]

The owner has now told me he wants to add liquid to the process. Ah, No.

Why not? The owner simply needs to write the spec in the comment line on a large enough check

 

[ptonsparky]

Today was demonstration day. I was as blunt and strait forward as I could be when the millwrights finally showed up with their fix, that didn’t help much, if any.

What we‘ve done with control works, but it opened another can of worms that needs to be dealt with on a temporary basis.

 

[ptonsparky]

Get a more sophisticated OL relay that looks at kW in addition to current. kW is always going to reflect true motor shaft loading, it doesn't vary with line voltage fluctuations like current does. Uncouple the motor, read the kW, that's your "Broken Shaft" threshold point. Couple it to the transmission but remove the belt, read the kW and that's your "Broken Belt" threshold. Couple it to the auger, run it unloaded, read the kW, that's your "Unloaded Auger" threshold point.

I know you have suggested a product you have used in the past. Would you send me a link or list it here again?
Thank you.

 

[petersonra]

We called those “as-built drawings”.

Electricians around here don't believe in following the drawings anyway. They just wire it up however they please and then when it doesn't work it's an engineering problem.

 

[paulengr]

You can use RPM to calculate load approximately but it’s not very accurate. The motor RPM at full load will be on the name plate. It is slightly less than synchronous which would be 3600, 1809, 1200, 900, 600…depending on the number of poles. Subtract both the actual speed measured and the full load number from synchronous then divide to get a percent load. It is reasonably linear up to about 200% of load but there are so many errors it’s just a guess. Using kw is more accurate and even better is looking at a frequency spectrum of the current and looking at the pole pass harmonic but that’s very advanced.

But beyond that if they are set up correctly you have two protection devices: overcurrent and overload. If it’s overloaded it’s mechanical. If overcurrent trips it’s electrical, in general. For such a simple device motors have a lot of ways they can fail.

A couple days ago we had a 7.5 HP tank agitator. FLA was 12.5 A. On startup it jumped right up to 96 A and held for 10 seconds until the overload relay tripped. The agitator had no build up on it. I did run a full blown LCR test on the motor (Megger, resistance, inductance) and found nothing wrong. Typically in a short situation you will be at 10x FLA or more. It pulls normal locked rotor until the motor gets above the peak torque point at around 75-80% if full speed before it drops down to normal. So 96 A is around 8x FLA. So no leaks to ground or anything like that so looks very mechanical. As a follow up the gearbox was full of water, pieces of gear teeth, etc.

It can be hard to definitively tell if you have a mechanical or electrical issue. There are things that can go wrong that can fool you into misdiagnosis. So check everything you can every time and let the data determine the troubleshooting path. Don’t just make assumptions. As an example if you repeatedly reset a eutectic overload (common with screw conveyors) it will gradually lose solder over time and eventually trip early. This one can be frustrating to find.

 

[xptpcrewx]

I have augers that I monitor the RPM. Priority is no rotation, then drive belt slippage. The overloads are very good at detection of LRA so that is not an issue.
What reduction in RPM should I expect from an unloaded motor to fully loaded? My suspicion is none, but I can set a percentage.
One auger is sheave reduction only the others are sheave to gear reduction.

Nameplate RPM is the full load RPM at the nameplate voltage. As far an no load RPM, you can reference the torque/speed curves...