Drives Consolidation

We use powerflex 700 ac drives on just about everything here and have a range of sizes. I would like to start reducing the amount of drive sizes that we use meaning if the application calls for a 1/2,1,3,5 HP i would just like to use a 5 hp and stock 1 drive vs 4.

My question is where are the break points in this and why? When is a drive too oversized or too big? is it okay to run a 1/2 hp motor on a 5 hp drive? What about in the higher hp ranges? I have read many articles online that say not to oversize the drive too much but gives no more data on how to determine how much is too much.

Iam trying to apply this only on our fractional to 50 hp drives primarily

Here is a list of pflex 700 drives with the curent and hp ratings we use some of all of them.I just want to consolidate as much as possible

For Example from my attachment 0.5 hp to 7.5 hp are the same frame so can i use a 7.5 hp to run a 0.5 motor and be okay?

Any loss of efficiency?

The Plc Kid said:

We use powerflex 700 ac drives on just about everything here and have a range of sizes. I would like to start reducing the amount of drive sizes that we use meaning if the application calls for a 1/2,1,3,5 HP i would just like to use a 5 hp and stock 1 drive vs 4.

My question is where are the break points in this and why? When is a drive too oversized or too big? is it okay to run a 1/2 hp motor on a 5 hp drive? What about in the higher hp ranges? I have read many articles online that say not to oversize the drive too much but gives no more data on how to determine how much is too much.

Iam trying to apply this only on our fractional to 50 hp drives primarily

Here is a list of pflex 700 drives with the curent and hp ratings we use some of all of them.I just want to consolidate as much as possible

For Example from my attachment 0.5 hp to 7.5 hp are the same frame so can i use a 7.5 hp to run a 0.5 motor and be okay?

Any loss of efficiency?

Click to expand...

Kid

I think this is a good idea. I think your approach needs some refining.

I would use double or maybe triple size VFD to gain savings ie I would use a 1 or maybe 2 HP VFD assuming you can set parameters for smaller motor.

I think any loss of drive efficiency from oversizing (factor of 2 oversize) will be possibly offset by savings in real estate. This consideration may just work out to a drop in the bucket.

You need to figure space saving dollars vs increased unit cost dollars and see where the curves cross.

I think you should look at how many motors you have in each size ie HP. If you have only one 1/2 HP then use oversize
if you have 100 then it may be better to carry 3 to 5 spares.

The other thing is what is lost production cost - it may be cheaper to replace a 200 dollar drive with a 500 to get back up and running.

Another major consideration is how many have you replaced in 3 to 5 years?

For sure I do not thing there is a magic canned answer - it is a plant specific question and also depends on how and where they want to spend money.

Maybe another way to summarize what I am trying to say is it is a cost of doing business versus delivered benefit. MAybe it is left hand dollars vs right hand dollars but the dollars still come out of the big budget ie product sold and PAID for.

Dan Bentler

Kid, it makes a difference if you are using these drives in open loop V/Hz or sensorless vector mode.

In V/Hz, you can probably go 10/1 oversize but be sure the drive software has limits wide enough so you can set the motor data and current limits low enough for the smallest motor. You absolutely must set the correct motor nameplate data in the drive or the wheels fall off everything else.

In sensorless vector, you need to find out what the lowest vector detection current is for the drives you intend to use. This will set the oversize limit along with the software parameter setting limits. You may need to consult AB for the detection current limit.

This detection current is used to derive an abundance of motor performance data and, if too small, the drive looses its ability to operate in vector mode and the accuracy and control simply go away.

Thanks Guys

Dan our stores manager just wants to standardize and reduce parts and so do i the price between the drive sizes is nothing compared to the benefits of having fewer spare but still retain full coverage. We use the rockwell spares program here and the way that works is that rockwell will store whatever inventory you want in your plant 1 million,2,3 at a fee of 1% of list on an annual basis.They come in quarterly to inventory the parts and you are only billed for the parts when you use them and your warranty starts when you use them plus there is a ruge discount on repairs and exchanges with this program.

But it still takes up space and costs money so if we can have one drive that works in more applications it comes out to our advantage.


Dick

Thanks for your reply i will get this info from ab as all our drive applications are sensorless vector or encoder feedback with 1024 ppr encoders. We have no v/hz / scalar setups.

I knew there was a gotcha on this but i did not understand the dynamics. As always you made it simple enough for us young'uns to understand.

Thanks Guys

I believe that if you are running a motor less than 1/3 of the drive rateing, you should use a seperate overload device between the drive and the motor. This was true on some older drives, like AB 160's.