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quantity motor cost 4

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dpenney

Electrical
Jun 15, 2003
11
I am developing a prototype for what I hope to be an OEM application that involves motion control with constant reversing and variable speed (only about 1/4HP required).

I definitely want to use an electric motor (as opposed to pnuematic, hydraulic, etc.) and it seems like a 3-phase induction motor with a regenerative VFD will be best suited for reliability (no brushes) and cost (so I thought).

But after checking some prices for off-the-shelf, they are much more than I expected. I had originally thought that given the cost of power tools (I understand these use brushed universal motors) as low as $10, I expected to be able to buy what I wanted for $30 or less. I can't find any single quantities for less than $80 and assuming that quantity buying would bring that down 25%, $60 would make my intended product too expensive...

My questions:
1) Am I in the right ball park for 3-phase induction motor costs?
2) If so, why are induction motors so much more expensive than universal motors? They both have no magnets and I understand quality insulation, etc., but 8X worth?
3) Am I missing some obvious electric motor solution that I should be considering?

Thanks,
Dan


 
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dpenney,
There are a couple of problems here.
1) You will not find a "regenerative" VFD for a small 3 phase motor like that. If you need braking, you can add dynamic (resistive) braking but it will generate heat. The VFD alone will be more that that target price, even in large quantities. Consider 4 quadrant DC for that size of load and application (regeneration implies braking). Manufacturers of treadmills, grocery store checkout stands, moving signs etc. still use DC because 4 quadrant operation under 2HP is still far cheaper to do with DC that AC, regardless of volume.

2) Even if you don't need true 4 quadrant operation, off-the-shelf 3 phase motors will still probably never get into your price range for the motor, there is just not enough volume for them to deal with. But more and more appliance manufacturers are going to 3 ph AC motors and inverters for things like washing machines and dryers, so from an OEM standpoint you may be able to get a lot closer, you just may need to think outside of the box as far as suppliers. Who have you gone to so far?



"Venditori de oleum-vipera non vigere excordis populi"


 
Hi jraef, thank you for your response.

>>Who have you gone to so far?

I basically just typed "electric motor," induction motor," etc., into search engines and clicked on many of the resulting links. Baldor and Leeson were two that come to mind since their motors were carried by many distributor sites. Seems like the best of those (as far as my search went) was which had the lowest prices BY FAR for small quantities. Prices there made my app look feasible again.

Your comments are very helpful. To respond:
1) I was planning to make the inverter from scratch, including regeneration features and controlling it with a PIC microcontroller. Unless my plan is not realistic, this approach seems to come in cheaper than a DC motor solution, based on my web findings that they are 50-100% more expensive than AC induction with the equivalent HP.

My app will need to do a lot of stopping, starting, reversing, hence the need for regeneration.

2) So instead of off-the-shelf, I should try to use the same motor as a large-volume application such as a specific washer/dryer?

Hate to be lazy, but what does the Latin phrase translate to?
 
The motor suppliers you started with are in the industrial marketplace, your need is closer to robotics. Try Bodine or Oriental Motor and Franklin EMPD for small AC motors, or search again adding the terms "fractional polyphase".

You may find it difficult to build your own regen AC drive. How were you thinking of regenerating? With VFDs you need an active front end instead of a simple bridge rectifier, so essentially you need two back-to-back VFDs (other than not needing to duplicate the DC section). I seriously doubt that you can build them yourself for less than what you can buy them for from established manufacturers spitting them out by the thousands each day. All you would save is their profit margin, but you would loose than and more in lower component volume. Then there is the labor cost factor, unless you are already in India or some other low cost production environment. Good luck.

"Venditori de oleum-vipera non vigere excordis populi"


 
PS
The latin phrase is "Snake Oil sellers can't thrive without an ignorant populace"

"Venditori de oleum-vipera non vigere excordis populi"


 
I had hit Bodine before ( but they didn't have prices on the web, so I moved on since I guessed that meant too expensive. Based on your recommendation, I just sent in the request for info. I checked out Oriental (expensive) and Franklin (outrageous!).

I expect you are right about the difficulty of the regen drive. I was planning to use 3 power MOSFET PCHs and 3 NCHs to drive the motor, which seems common (practical) and fairly inexpensive. But then I designed a more complex power supply circuit to feed it that will dump excess energy back to the single-phase source. This may be where I'm fooling myself as far as actual usage but it seems to work in simulation. Parts-only cost is around $25. At this point I think I will build one up and see how it performs, unless you suggest some obvious consideration I'm missing (I realize that may be difficult without seeing the circuit)...
 
dpenney,

I have been through this many times and I have learned several things;

First. Never fall in love with your first idea! Re-iteration and stepwise improvement is the key to a good design. Sometimes "Back to the drawing board" for a total redesign is needed.

Second. What you think is important may not be important at all. And there is usually somthing that you have overlooked that is very important.

Third. Review power requirements. You are usually an order of magnitude above or below actual need. Intermittent loads can be many times higher than rated power - a fact that can be used to reduce size and cost.

Four. Make an evaluation of all available technologies. Not just those that you are familiar with. I would look at FHP LV DC, steppers, single-phase asynchronous, thyristor DC in addition to frequency inverters and three-phase asynchronous and I would not be surprised if 24 V DC (Bosch etc) turns out to be the better solution.

Five. Standard components are OK for small volumes. Custom components can't be beaten when you get above 10 000 units. The limit can be much lower, lower than you think.

Six. Never let list prices guide you. The negotiated price for an OEM customer can be as low as 1/3 or 1/4 of list price.

Seven. Test the design in real life before deciding to go for that design. Look out for things like positioning error, cycle times, heat build-up, interference, life.

Eight. Power saving is usually not an issue in applications like these. Regeneration will not save you much. Losses will usually eat up the available energy and not much will be returned to the mains.
 
Hi shogsgurra, thank you for the excellent lessons learned list. Especially useful is #6 in answering many questions for me.

Regarding #8, power savings is not a critical concern, I believe regen (or dynamic braking, or something similar) is required in order to prevent excessive heat generation from the constant stopping and reversing (although I think dynamic braking really just allows me to locate the heat dissipation to the spot of my choosing). However, you indicate losses will probably prevent effective regen. I assume that would be because the motor is so small? Because it seems that at some point a large enough motor develops enough energy to make the switching losses neglible when trying to shunt it back to the mains.
 
Comment on skogsgurra (Electrical) Apr 3, 2004 marked ///\\Six. Never let list prices guide you. The negotiated price for an OEM customer can be as low as 1/3 or 1/4 of list price.
///How do you negotiate the internet purchases when there is no option for such things as 1/3 or 1/4 of the list price?\\\
 
Suggestion to dpenney (Electrical) Apr 3, 2004 marked ///\\Regarding #8, power savings is not a critical concern, I believe regen (or dynamic braking, or something similar) is required in order to prevent excessive heat generation from the constant stopping and reversing (although I think dynamic braking really just allows me to locate the heat dissipation to the spot of my choosing).
///Agree.\\ However, you indicate losses will probably prevent effective regen. I assume that would be because the motor is so small? Because it seems that at some point a large enough motor develops enough energy to make the switching losses neglible when trying to shunt it back to the mains.
///Please, notice that the inexpensive solution is sought; however, the preferences such as regenerative (Active Front End (AFE)) drives are about 60% more expensive than non-regenerative ones.\\\
 
Comment on the original posting marked ///\\2) If so, why are induction motors so much more expensive than universal motors? They both have no magnets and I understand quality insulation, etc., but 8X worth?
///Have you visited:
and type Motors: Electric under Product or Service, which will return 494 companies to approach to for the best solution
and compare prices with
and type Motors: Universal under Product or Service, which will return 41 companies to approach to for the best solution

The price difference between the universal motors and the induction motors should not be that high
 
jb,

I do not understand the meaning of your comment:
///How do you negotiate the internet purchases when there is no option for such things as 1/3 or 1/4 of the list price?\\
How are you thinking there?
 
Comment on the previous posting: I am thinking there very simply. I visit an internet side and click on an item that is then put into a cart without any chance to negotiate the price. There is some credit card needed, and that is about all. Actually, I am surprised that this option was not addressed since many purchases are being made like that. What about internet auctions where there are not list prices at all?
 
jb,

I understand now. But the situation is somewhat different from what you think. Dpenney says that it is about an OEM application.

So it is obviously about industrial development and the purchasing process is not exactly what you are envisioning. The normal routine is to find three or four reliable vendors and ask them for their best offers. The quotations are then compared and the vendors evaluated. Then, there are a few weeks (or months) where things like quantities, prices, guarantees, delivery times and so on are discussed. It is a give-and-take situation which ends in a written agreement about all these things.

For a typical product with a market life of between five and ten years, this negotiation takes place once a year. It is a long-time committment.

List prices are given one off and are consumer prices. You need not be a big contractor to have 40 or 50 percent off the list prices. If you are an OEM, it is not unusual to have 60 or 70 percent reduction.

I think that you are thinking hobbyist activities. The industrial "real world" rules are something else. I think that you should not be surprised that the internet shop cart was not mentioned. Nor the auctions. They are fine for personal needs, but totally wrong if you are in manufacturing.
 
Comment on the previous posting marked ///\skogsgurra (Electrical) Apr 4, 2004
jb,
I understand now. But the situation is somewhat different from what you think. Dpenney says that it is about an OEM application.
So it is obviously about industrial development and the purchasing process is not exactly what you are envisioning. The normal routine is to find three or four reliable vendors and ask them for their best offers.
///What if these reliable Vendors have internet sites where you have to fill out a form just like anyone else. There may or may not be "a wholesale price" for OEM or Contractors and the "a retail price" for the rest of consumers. However, there may be field called "Quantity". This is where the OEM or Contractor has the edge since they can buy many pieces instead of one or two what average consumer buys. Have you ever bought software? How much was there for one license and for many, say 100 or 1000 licenses?\\ The quotations are then compared and the vendors evaluated.
///Or web site prices, unless you are addressing items like nuclear power plants, e.g. General Electric, Westinghouse, ABB, etc.\\ Then, there are a few weeks (or months) where things like quantities, prices, guarantees, delivery times and so on are discussed.
///This tends to be more and more shifted to web sites.\\ It is a give-and-take situation which ends in a written agreement about all these things.
///Things are also somewhat changing with the global competition.\\For a typical product with a market life of between five and ten years, this negotiation takes place once a year.
///Are you referring to Nuclear Power Plants?\\It is a long-time committment.
///It really is\\List prices are given one off and are consumer prices. You need not be a big contractor to have 40 or 50 percent off the list prices.
///Yes, agree. There are huge sales and discounts in many places.\\ If you are an OEM, it is not unusual to have 60 or 70 percent reduction.
///Apparently, OEM buys more than other customers.\\I think that you are thinking hobbyist activities.
///I got an impression that you work in the nuclear industry.\\ The industrial "real world" rules are something else. I think that you should not be surprised that the internet shop cart was not mentioned. Nor the auctions. They are fine for personal needs, but totally wrong if you are in manufacturing.
///Not quite. I see questions on some website who one is. Have you visited lately:
etc.?\\
 
Brush type DC motors and controls are much cheaper than AC. One thing you might want to check is if the potential customer will accept brush DC motors. More and more of the larger corps. will not allow brush type DC motors in their plants due to the maintenance/down time cost.

Is there anyway you can reduce the HP requirement? Often times a counter weight or spring/mechanical assist somewhere in the cycle is cheaper than a larger motor when doing volume.

Barry1961
 
Hi Barry1961,
I don't think that a brush motor is appropriate for my app, but thank you for the suggestion. After some modification of my original design, I think I will be OK with the expected quantity costs of AC induction motors. We'll see...
 
Dpenney:
You may want stepper motor. Can you tell the specs?
How much can you tell me about the project and yourself?




<nbucska@pcperipherals.com>
 
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