HP logic

[ptonsparky]

As a rule of thumb, I’ve estimated undersized motors by the current they are now pulling. Everything else being equal. The 5 hp that is pulling 10 amps and overloaded @ 480 could be replaced with a 7.5 or a 10. Reasonable or not?

 

[petersonra]

As long as the load can take it.

Engineers size things based on what little information they get upfront and it generally seems like this often ends up with things being undersized.

However, I would want to pass the decision to up size such a motor to someone competent to make that decision, rather than just replacing it. There might be something else going on like a seized bearing.

 

[Cow]

I do the same.

It is pulling a given amount of current for the work being performed.

In response to the above poster, a lot of what I see is ag related. Farmers taking their best guess at making something work, and sometimes falling short of the mark. No engineering here, just farmers making it work.

 

[ptonsparky]

This is a new install and the company supplying the product to be moved is going to change the mixture so it isn't quite so sticky. Hoping the 5 or 7.5 will work. I think auger suppliers always think dry corn in this area of the country.

 

[gar]

191025-1100

ptonsparky:

Do an Internet search with
induction motor peak efficiency
75% migjt be a good spot. Cjeck the specific motor specs.

.

 

[ptonsparky]

As long as the load can take it.

Engineers size things based on what little information they get upfront and it generally seems like this often ends up with things being undersized.

However, I would want to pass the decision to up size such a motor to someone competent to make that decision, rather than just replacing it. There might be something else going on like a seized bearing.

Turns out there was no engineering, or so it seems. There is product buildup on the auger. New product blend is supposed to help.

 

[junkhound]

No engineering - does not augur well for any project.

Sorry for bad pun, could not help myself.

 

[kwired]

This is a new install and the company supplying the product to be moved is going to change the mixture so it isn't quite so sticky. Hoping the 5 or 7.5 will work. I think auger suppliers always think dry corn in this area of the country.

Probably somewhat common for you as well to put a meter on certain items so the operator can adjust flow accordingly. I put a meter on a leg once (new installation) Owner of the place happened to be there to witness one of the first few trucks that got unloaded, we had gates set so leg was pulling all we wanted it to pull and owner said "we need to be able to unload faster than that".

Wanted to reply well then you should have gotten equipment rated for higher rating, this is what this can handle within it's design. I bet next bigger leg took a pretty good price jump and he probably balked at that.

 

[Jraef]

One issue I’ve noticed is that decades ago, motor Service Factor was identified as being a time-limited amount of overload capability. Some time over 20 years ago, that changed to remove any specific mention of time, allowing people to believe that continuous overloading is acceptable, ie a 10HP motor with a 1.15SF can be loaded to 11.5HP continuously. I have never bought into that concept, but OEMs certainly have. I believe they are the ones who lobbied for the change.

 

[ptonsparky]

One issue I’ve noticed is that decades ago, motor Service Factor was identified as being a time-limited amount of overload capability. Some time over 20 years ago, that changed to remove any specific mention of time, allowing people to believe that continuous overloading is acceptable, ie a 10HP motor with a 1.15SF can be loaded to 11.5HP continuously. I have never bought into that concept, but OEMs certainly have. I believe they are the ones who lobbied for the change.

My area pump installer says they are encouraged to design into the SFA.

 

[Jraef]

My area pump installer says they are encouraged to design into the SFA.

Yep, I believe it. When I worked for an equipment mfr years ago, they bought their pumps without motors and we picked out the motors based on required flow at required head to get BHP, then added 10% and rounded up to the nearest standard motor size to be safe, then used a 1.15SF motor. Those days are long long gone.