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# fan speed and Voltage4

## fan speed and Voltage

(OP)
Hi there,
Second doubt.
I have learned that the rotational speed depends by the number of poles and frequency only.
Why then a fan connected in delta and star connection has a different speed, even though it is the same fan and fed at the same frequency ?
I admit it is a basic question.
Could anybody suggest me a link or a book to buy in order to clarify these doubts ?
thanks !

### RE: fan speed and Voltage

Less Volts per turn and less torque when running on the star connection. The speed slips further down the slip curve.
Some fan motors are fairly high slip motors and there will be more of a difference with the start connection than with a standard motor.
Many loads cannot be speed reduced this way without damaging the motor, but the torque fall-off with fans and centrifugal pumps is very forgiving of low voltages.

Bill
--------------------
"Why not the best?"
Jimmy Carter

### RE: fan speed and Voltage

Voltage Control is very common for FHP motors with fan loads. A simple Triac is used for speed Control.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

### RE: fan speed and Voltage

#### Quote (PaulLag)

I have learned that the rotational speed depends by the number of poles and frequency only.

... and slip ( in case of fan).

Speed regulation of single-phase fans.

### RE: fan speed and Voltage

There are certain types of motors that are capable of having two speeds by switching the number of poles when the connection is changed from delta to star. Search 'Dahlander' motor for information about the most common type of two speed, one winding motor. A 'PAM' (pole amplitude modulation) motor is a second, less common, type.

### RE: fan speed and Voltage

(OP)
Hi

This has been absolutely useful.

I have some more question, hoping not to steal time.

1) I understand that there is a square relationship between tension variation and torque variation.
Please, which is the formula that relates this two parameters ?

2)
please, would you be so kind to recommend me some literature concerning the topic of tension, connection as the previous part
Unfortunately I can't find any reference in cowern papers

3) please, I would like to understand following topic.

Let's assume I have a fan labeled @ 400/3/50.

let's suppose I vary the tension.
I understand the current will increase - if the tension decreases - or decrease, if the tension increases.
In one case there is the problem of excess of current, in the other to saturated the magnet, if I have understood correctly

if I vary the frequency, what will happen ?

Why are some fans labeled not only 400/3/50 but also 400/3/60 and 460/3/60 ?

Thanks !

### RE: fan speed and Voltage

#### Quote:

1) I understand that there is a square relationship between tension variation and torque variation.
Please, which is the formula that relates this two parameters ?
T(V) = T(V0) *(V/V0)^2
where w is speed and V is voltage and 0 is the reference condition, usually rated condition.

To predict change in operating point, you'd also need to predict intersection with the fan curve which is often T(w) = T(w0)*(w/w0)^2 excluding the very low speed portion of the curve. Typically you'd do that graphically.

But I'm making an ASSUMPTION that voltage is the only thing changing, not the number of poles which rhatcher has pointed out. It's worth to doublecheck, did you check the nameplate? Or perhaps did you measure the speeds in the two configurations?

=====================================
(2B)+(2B)' ?

### RE: fan speed and Voltage

#### Quote (PaulLag)

let's suppose I vary the tension.
I understand the current will increase - if the tension decreases - or decrease, if the tension increases.

I can't agree. The current will decrease - if the voltage decreases, in case of fan application.

You don't have to change the number of poles or frequency in order to change the rotational speed of fan. You can change the slip only as I already wrote.
It is not allowed to exceed the rated voltage.
If you change the frequency (or number of poles) you will change the synchronous speed and consequently the rotational speed of the fan.
If you change the slip ( changing the voltage) the synchronous speed remains the same, but the rotational speed of the fan changes.
Read again a nice explanation from waross (19 Feb).

### RE: fan speed and Voltage

zlatkodo - Sorry, but I can't agree with your posts. Posting about varying the speed via voltage on special high slip capable single phase fan motor has no relevance when talking about a standard 3-phase induction motor. The OP mentioned wye vs delta in the first post which makes it clear that this isn't a single phase application, hence it won't be a special high slip capable single phase fan motor.

Lets just look at an example using more realistic typical 3-phase motor data. Start with this data.
At 100% speed the fan requires rated motor torque.
At 50% speed and rated voltage, the motor produces 100% torque and draws 500% current.

So, you want to run this fan at 50% speed. The required fan torque = 100% motor rated torque * (0.5/1.0)^2 = 25% motor rated torque

Now, at 50% speed, the motor started at 100% rated torque with rated voltage, and we need to reduce this torque to 25%. Well, the motor torque is the ratio of the current reduction squared. So, we need to reduce the current to 50%, since 100% torque x 0.5^2 = 25% toque. The problem is that the motor started out drawing 500% current, so reducing the current by 50% only drops the current to 250%. That's a big problem. The motor will quickly overheat and fail if you attempt to operate it at these conditions. You simply can't vary the speed of a standard induction motor via a voltage reduction alone.

### RE: fan speed and Voltage

(OP)
Hello everybody

In a second hand, I just got back to one of my first questions, that were: could you recommend me a suitable literature or web reference where these topics are presented ?
I mean, there are lots of books about electrical motors, nonetheless I was not able to find one about these specific topics.

Is audel the right one ?
are there others ?

Many thanks !

### RE: fan speed and Voltage

Hi, PaulLag,

I can not recommend a particular book that will answer your specific question, because this is part of the basic theory of electrical machines.
Try to find something about the power, torque and slip depending on various types of loads (constant torque vs constant power and specially variable torque application).

LionelHutz:

Everything I wrote in the last post refers to the three-phase fan motors. And not just to fan motors.
The same principle is widely used as a three-speed, three-phase winding of circulating heating pumps.
Note, this is the same kind of load.
This is achieved by adding the turns ( less or more) in each phase winding for middle and low speed, which is equivalent to voltage reducing.
Otherwise, how could you explain this case of three-speed motor ( see the nameplate photo below)?
Obviously, it is 2 pole, 50 Hz, three-phase winding for each of three speeds.
The number of poles and frequency is the same for each speed, but the slip is not.
As you can see Amps decreases with adding the turns ( ie. reducing the volts per turn).

More at:
Overhaul-of-heating-pumps

### RE: fan speed and Voltage

#### Quote (zlatkodo)

Otherwise, how could you explain this case of three-speed motor

Very simply, if the motor speed can be significantly varied by varying the voltage then it's a specially designed motor, PERIOD!

Voltage reduction for speed control DOES NOT work on standard SQIM's. Claiming that since it works with a specially built motor that it'll work for any motor is idiotic. Claiming that the motor can be speed controlled via voltage just because the OP posted that it's a fan application is also idiotic.

Going back to the first post, I expect the delta and star connection mentioned ACTUALLY changes the poles of the motor because it's a 2-speed motor. BOTH a star-delta motor starter and a Dahlander motor use 3 contactors. If you didn't know what to look for then you wouldn't know the difference.

### RE: fan speed and Voltage

LionelHutz
There is no need for harsh words.
You better try to learn something that is obviously new for you . I would be glad if I inspired you to do that.
Or , you think you already know everything ?

The first question ( and my answer too) is related to three phase FAN motor.

#### Quote (PaulLag)

Why then a fan connected in delta and star connection has a different speed, even though it is the same fan and fed at the same frequency ?
An answer is so simple: because of change in slip caused by change of voltage, PERIOD.

#### Quote (LionelHutz)

I expect the delta and star connection mentioned ACTUALLY changes the poles of the motor because it's a 2-speed motor.
There is no need for two speed Dahlander motor for mentioned application. This is a winding with one number of poles, designed for delta connection at rated voltage.
You do not have to agree with me, but I expect arguments, not any aggressive attitude.

Tech Support in Winding Design and Rewind

### RE: fan speed and Voltage

Zlatkodo
The speed for an asynchronous motor is given by number of pole pairs and frequency. There is also a small load dependancy so that more load creates more slip.

For a normal motor, the slip is small, simply because slip represents losses and you do not want losses in a normal system. That is why high-efficiency motors are used. They have very low slip.

For certain low power applications and where load torque is speed dependent (torque proportional to speed squared) it is common to use simple voltage control of the motors. Kitchen fans and such appplications come to mind. They are usually FHP motors and the losses at half speed, where torque is around 25% of nominal torque, is tolerable if compared to the losses in a VFD.

These truths were valid for many years, but it will probably change when (constant) losses in the auxiliary Control system gets lower or when matrix inverters are being introduced also in the lower power ranges. But, for the time being, these truths are still valid.

To sum up:
Normal ASIM's speed is almost purely frequency dependent and can not be speed controlled with voltage change. That is why VFD:s are used.
Small and special built ASIM:s (high rotor resistance, high and load dependent slip) *can* be speed controlled via voltage (and load) change.

I can very well understand that your opponents get angry when you deny these well-known facts. It is you that need to learn basics before you try to educate others.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

### RE: fan speed and Voltage

I do not want to repeat the same thing over and over again.
I think my explanation is sufficient and I do not care whether someone's vanity is affected or not. It is not my problem if someone rejects something he don't know anything about.

#### Quote (PaulLag)

Why then a fan connected in delta and star connection has a different speed, even though it is the same fan and fed at the same frequency ?

which confirms that the fan has different speeds at different voltages ie. at Y and D connection . Quite enough.
Quote any of my statements to be inaccurate.
The photo below shows an external wiring from the terminal box of similar fan motor: high speed in Delta and low speed in Wye ( not Dahlander, YY-D connection).

The only thing more dangerous than ignorance is arrogance. (Albert Einstein)

### RE: fan speed and Voltage

zlatkodo - You are the one that has no clue what you are posting about. Your posts are misleading. PERIOD.

Gunner is EXTREMELY knowledgeable about motors. I've been working with induction motors for a long time too. For me it's not vanity, but rather annoyance at seeing such poor information being posted as fact and leading the person asking the original questions completely astray. Your explanations only work on very small motors specifically designed to allow high slip operation. Standard 3-phase induction motors WILL NOT operate that way.

My example was based on REAL motor data for a 75hp motor that I was looking at yesterday. This REAL motor would ABSOLUTELY require 250% current to run a fan at 50% speed.

I gave rhatcher the star because what appears to be a star-delta motor starter is most likely controlling a Dahlander motor. It's the most plausible answer based on the question.

PaulLag - There is a simple reason that you don't find information on reducing voltage to reduce speed when researching industrial standard induction motors - It can't be done.

### RE: fan speed and Voltage

LionelHutz

I do not want to be so rude as you are and I'm glad to inspire you to search little bit more on this topic:

#### Quote (LionelHutz)

Your explanations only work on very small motors specifically designed to allow high slip operation.
You begin to realize what it is about. It is OK for beginning. It is a big advance for you. Just keep continue.
It is a proof that my post is not useless.
By the way, I am talking about three phase fan that is connected in Delta connection for high speed and Wye connection for low speed, because, that was an initial question.
Also, looking at the picture above ( example of external wiring for this type of connection) , it is clear to everyone (even to beginner), it can not be Dahlander winding. You are wrong again and your advice is misleading.

Tech Support in Motor Rewind

I am patient with lack of knowledge but not with those who are proud of it. (TZ)

### RE: fan speed and Voltage

I am saving this thread for two puposes:
1. It shows how someone, who thinks that he knows a subject without understanding it, sometimes acts.
2. To remind myself not to behave like this if I ever find myself in a similar situation.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

### RE: fan speed and Voltage

zlatkodo - You keep claiming we know nothing and you understand all, so prove yourself right. Post detailed data on a typical standard (not Dahlander) 100hp or 75kW SCIM that can be speed controlled via voltage reduction. Post the nameplate data, speed vs torque and speed vs current curves and then explain using the data how the speed can be successfully reduced to say 80% and 60% speed by simply reducing the applied voltage. Use a typical squared type variable torque fan load that applies rated load to the motor shaft at rated motor speed. If you actually know what you are talking about and what you are claiming is true then this is an easy task for you.

PaulLag - Why don't you post details of your motor so everyone knows what motor you are actually dealing with?

### RE: fan speed and Voltage

Read again my two posts from 8 March. No need to repeat.

### RE: fan speed and Voltage

Pretty much what I expected. "It works" but I can't prove it.

### RE: fan speed and Voltage

Do you expect that I will teach you something more, after your inappropriate reactions?
Certainly, I will not.
The proof is already in initial question.

#### Quote (PaulLag)

Why then a fan connected in delta and star connection has a different speed, even though it is the same fan and fed at the same frequency ?
I may have a difficulties with English language but I'm sure, PaulLag is not asking " is this possible?" but " why it is possible?".
But, it seems, you can't realize that it is possible?
Your stubborn assertion is: it is about Dahlander winding not D/Y connection. OK. I hope someone will give you a "star" for this.

Quote any of my statements to be inaccurate.
None.

### RE: fan speed and Voltage

OK, I'm just going to throw together a little data to show why you can not speed control standard induction motors via applied voltage.

Attached is the data from literally the first 75hp motor data that I found. Nothing cherry picked here. I just grabbed the data from the first 460V premium efficiency motor that came up in the list. I put the full-voltage curve data into EXCEL and then calculated what the torque and current would be if the motor was star connected instead of delta. I also plotted the torque curve for a typical fan. This image is the results.

So, the motor will run at a speed where the load torque and motor torque cross. In star, this occurs at approximately 75% speed. So, next look at the star current curve at 75% speed to determine the current. The curve shows the current is approximately 200%. You can't continually run a motor at 200% of it's rated current without burning it out. This clearly illustrates that any claims about running a standard induction motor at a reduced voltage to vary the speed are wrong. It also illustrates to the OP why he didn't find information on doing so.

#### Quote (zlatkodo)

I can't agree. The current will decrease - if the voltage decreases, in case of fan application.

Will this do as a quote of something you posted that is wrong?

#### Quote (zlatkodo)

You don't have to change the number of poles or frequency in order to change the rotational speed of fan. You can change the slip only as I already wrote.

### RE: fan speed and Voltage

Friends:
I am unhappy to see this dissention between professionals whom I respect.
I am also a little confused as to the possibility of using reduced voltage to control the speed of a fan.
There have been requests to identify a specific motor that is suitable for speed control by reduced voltage.
I started searching the web for answers and now I may be a little more confused.
What I found:
Disclaimer; None of the information that I have found so far identified a specific motor.
I looked for speed/current curves for star delta starters on the star connection.
The results were all over the map.
One chart indicated that the starting current dropped to 100% at 37.5% speed. The motor was not identified and this is probably not typical. This motor may have been a good candidate for control by reduced voltage if it is available.
Some charts indicated that the slip curve on the star connection was almost identical to the curve on the delta connection. Such a motor may not be suitable for reduced voltage control. However I am not convinced of the accuracy of the curves.
I found a number of charts indicating that the current on the star connection dropped to 100% at about 90% of synchronous speed.
Then I came across this web site. I have no opinion as to the credibility of the site.
Variable voltage
The speed of small squirrel cage induction motors for applications such as driving fans, may be changed by reducing the line voltage. This reduces the torque available to the load which reduces the speed. (Figure below)

Variable voltage controls induction motor speed.

#### Quote (OP)

Why then a fan connected in delta and star connection has a different speed, even though it is the same fan and fed at the same frequency ?
Can speed on an induction motor be controlled by dropping the voltage?
With some loads such as fans, some motors may be speed controlled by dropping the voltage.
Is this done in practice?
For very small fan motors, yes.
For larger motors, eg 1 HP and larger, given the several hundred years of cumulative experience of the responders, myself included, who have not seen this done in practice, probably not. A damper is much cheaper than a star delta starter.
If I was to implement this method of control, I would probably use design "D" motors. The inherent high slip of a design "D" motor may make it the most suitable motor for this control method.
The Cowern Papers give torque/speed curves for various designs of induction motors.
See .pdf page 7
Remember the cube law for fan HP.
At reduced speed the required torque is also reduced.
Will I ever use voltage reduction to control the speed of an integral HP fan?
Probably not.
A damper or stepped control of multiple fans is so much cheaper.
The motor may have to be oversized at full speed use to allow reduced speed use.
Also there would be no danger of a failed motor being replaced with an unsuitable motor.
Is this a good idea? NO
Now let's be friends again.
The first round is on me in Pat's Pub.

Bill
--------------------
"Why not the best?"
Jimmy Carter

### RE: fan speed and Voltage

Bill - the graph you posted is rather useless without the 100%V current vs speed curve. It's easy to show that a reduction in voltage will reduce the torque which causes more slip and a slower operating speed. But, you can't ignore current since it's not a valid operating mode when the corresponding current will be too high. The motor basically has to be designed to have a suitable current vs speed characteristic (the curve is low), which also causes the motor to have a low power factor and poor efficiency. It's why using slip for speed control is generally only seen in packaged fractional HP applications. The motor is specific to the application it's packaged with.

### RE: fan speed and Voltage

Yes, Bill. SMALL single phase asynchronous motors can - and are - speed controlled by changing the voltage. It has been done for a long time and part of my bread and butter in the eighties and nineties came from designing controllers for such applications. I dug a couple of them out from my garden shed and attach a few pictures. There is also a picture on a circulation pump for heating. All of these motors are very low power and that is what I said in my 19 Feb 17 18:10 answer. The rated Power is from 4 W to 60 W, which is a typical range for this kind of motors.

Zlatko falsely says that ANY asynchronous motor can be controlled that way, which is completely incorrect. I would not even try a 1 HP motor and Zlatko says he can control a 75 HP motor. Which is utterly wrong. To be successful, the rotor resistance needs to be high so that there is a monotone and increasing slip as voltage decreases. Such motors cannot be had and are, hence, not possible to control the way Zlatko says.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

### RE: fan speed and Voltage

Lionel and Gunnar;
Lionel, I had not seen your latest post when I posted. That is the curve set that I was looking for.
May I take advantage of your help with two more questions gentlemen?
1> With the same load, if the motor was upsized to 150%, would that allow the motor to drive the fan at about 55% speed and 100% or less current? I do realize that at this point we will be using a 150 HP motor to drive a load of around 20 HP at the lower speed.
Not very smart but will it work?
2> A premium efficiency motor may be my last choice. I am wondering about the use of a design "D" motor with it's higher slip at higher speeds.
a> Would a design "D" motor work with less than 100% stator current on a star connection?
b> If a design "D" motor will work with acceptable stator current on the star connection, is there a danger of overheating the rotor?
Thank you for your time gentlemen.
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

### RE: fan speed and Voltage

Bill, the rotor losses will be extreme. At 55% and 20 HP output, you will have somewhere like 12 kW rotor losses. Add the very high losses in the stator winding and see the motor go up in smoke.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

### RE: fan speed and Voltage

Bill,

#1 - Not star connected. Start with the curves I posted then drop the load curve to 67% (this reduction is the same as upsizing the motor by 1.5 times). The star torque curve will now intersect this new load curve past the breakdown torque peak closer to full speed. So, the speed will only drop around 1-2%. The problem with oversizing and attempting to use a star connection to reduce speed is that the torque is still so high that the motor almost reaches rated speed.

#2a - You might be able to find some motor that would work, but I expect you'll only be capable of proving a case where the speed drops a couple of percentage without overloading the motor.

#2b - I would expect that any time you cause more slip then rated that there is a danger of overheating the rotor. If rated current is going into the motor with significantly less then rated torque coming out, you end up with that extra current heating the rotor instead.

No matter what motor, when connected in star vs the normal delta for running, you can only slide back the curves to the speed where the delta current goes over 175%. Once below that speed, the motor will draw over rated current no matter what load is connected. This is why. In delta when 100% current goes into the motor only 58% of that current flows in each of the delta connected coils. So, the motor is actually only capable of operating at 58% of the rated current continually when connected in star. You simply have to look at 6-lead motor data to see that this current ratio is true - the higher voltage rated star connection will have less current. The ratio of delta to star current is 33% and 58% divided by 33% is 175%. So, the speed where 175% current occurs on the "delta" graph is the lowest speed you could potentially operate at when you attempt to run the motor at the delta voltage, but star connected instead of delta connected.

Overall, I don't really feel like creating a bunch of different scenario graphs trying to prove that something which is never done in practice might just possibly work in theory under one perfect set of circumstances.

### RE: fan speed and Voltage

LinelHutz,
Regarding the both quotes.
I will repeat my post from 8. Mar.

#### Quote (Zlatkodo)

I am talking about three phase fan that is connected in Delta connection for high speed and Wye connection for low speed, because, that was an initial question.
Also, looking at the picture above ( example of external wiring for this type of connection) , it is clear to everyone (even to beginner), it can not be Dahlander winding.

That means , if this fan is connected to high speed in Delta 400 V then you can connect it to low speed by connection to Wye or keep the Delta connection and decrease the voltage from 400 to 230 V ( line to line). And the Amps will decrease for sure.
And it's clear, you can change the rpm with the same Hz and poles, by changing the slip.

Whether or not this kind of design has a limitation?
Yes, as many others.
Mostly, the limitations are related to rpm range to be regulated.
Any reasonable person would not expect the regulation of rpm from 0 to 100%.
For example the reduction of speed of 2-pole fan motor below the 1500 rpm (at 50 Hz) it is not reasonable too.
Even the high speed of these fans must be designed with slightly higher slip then usual etc....
Regarding the "special" , "standard" , "normal or abnormal" motor , "small or large HP" .
Yes, it is special design as many others. One way to do that is already described:

#### Quote (Zlatkodo)

This is achieved by adding the turns ( less or more) in each phase winding for middle and low speed, which is equivalent to voltage reducing.
There are other ways too. For example, three speeds of such a fan can be obtained by changing the stator connection from 2Delta to 2Wye and to 1Delta (same number of poles and Hz).
A very similar way is used at triple rated motors, (but for same rpm) in order to increase the efficiency in case of low loads, as well as reconnection from delta to star if the any motor for general application is loaded too low, again in order to increase the efficiency.

Whether or not the rotor is "special"?
Could be, as could be in many other designs.
Regarding the HP.
Is there any particular reason that something valid for "small" three-phase motors is not valid for "large" motors?
What could be a conclusion of all above mentioned?
In some cases of 3phase fan or pump applications, the VFD for speed regulation is not needed at all, if the rpm range is suitable for simple and low cost voltage regulation,
despite the recommendation of some VFD experts.
Skogsgurra

#### Quote (Skogsgurra)

Zlatko says he can control a 75 HP motor
This claim sounds arrogant and it is not mine. Not my style. Where did you read it?

### RE: fan speed and Voltage

Zlatko, you say that any size motor can be voltage controlled and, since Lionel chose a 75 HP motor for his example (8 Mar 17 18:36) - and you said that you had nothing to add - I used that size for my example.

I can tell you that you are getting famous in certain quarters. You are the topic of quite a few coffe-break conversations and you are not contributing positively to the good name of Nikola Tesla's countrymen. Please accept practical results and solutions and forget about extrapolating into absurdity. Tesla did and, as you know, he wasn't very successful in his later Days.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

### RE: fan speed and Voltage

Your picture of the connections doesn't prove anything about what happens with the motor until you post full details on that motor.

As for the rest. I really have no idea what the actual point of your rambling is except I caught this part - "Is there any particular reason that something valid for "small" three-phase motors is not valid for "large" motors?" It seems this is the conclusion of your ramblings and you're attempting (again) to claim that what works on little specialty motors will work on larger motors. I posted real life data that illustrates why it doesn't work on large motors, not just some random claims that it shouldn't. If you think it does work on large motors then post real life examples of it being used. You have to include ALL data related to the motor and load to do this, not some random picture of who knows what exactly, like that connection diagram.

Also note that voltage control generally won't even work on standard small motors. The motor has to be a special design. The curves of a standard 1/2hp or 1hp squirrel cage induction motor look very similar to the 75hp motor curves and would run into the same issue with the current being too high if you attempted to use slip to run at a lower speed.

### RE: fan speed and Voltage

I answered a question from the initial post.
You disagree and insist that this is a Dahlander winding.
OK.
Thanks to both self-declared experts on all their disqualifications and insults .
It is quite sufficient to evaluate their knowledge.

Regarding the Tesla: unfortunately, only the birth country and similar last name is common to us. Not a knowledge.
I would be very happy if I had at least 10% of his knowledge and ideas.

Tech Support in Winding Design and Motor Repair

### RE: fan speed and Voltage

Circling back to the OP (Hi Paul, I hope you've found this entertaining, at the very least).

I think I can offer two book recommendations that would help the OP with his questions. I have had the same ones answered by these books. One is still in print and one is old and out of print but I still know of no substitute:

Austin Hughes, Electric Motors and Drives

Excellent writing, illustrations very clear, math is essential but limited to only what supports the reader's understanding.

Robert Rosenberg, Electric Motor Repair

Essential techniques in motor repair, built upon solid foundation of how electric motors are made and operated. Covers every sort of electric motor I can think of. The "solid-state" control sections are hopelessly out of date so indulge your inner historian.

Now, something has gone haywire at Amazon and their used book sellers, because the prices are pretty wonky for the Rosenberg book. I bought my used 2nd edition copy 10 years ago for about 40 bucks US and there's no reason for the price to rocket upwards now. It is strangely possible, now that the internet links everything to everything and big data can process associations between such disparate websites as Amazon's used book resellers to a book recommendation on Eng-Tips (which I have done a dozen times since reading Rosenberg's book) and boost the price accordingly, but that my be my personal paranoia. It should still be possible to get a copy of Rosenberg's unique book for 50USD, just maybe not from Amazon bloodsuckers. It is worth looking for.

STF

### RE: fan speed and Voltage

(OP)
Hello everybody
First I do apologize if my question was unclear so that I generated this discussion.
Just to put things straight my question was referring to electrical motors utilized in fans as for example

(see the ac fans)
If you see AC fans can
- Be connected in delta and wye
- Can work at different tensions (ex 400/3/50 or 400/3/60 or 460/3/60)

in a second hand this enforces the topic for me to increase my knowledge on topic, so, many thanks SparWeb, I will certainly take into consideration these two literature references.
I would like to thank all for having shown me how deep and extended is the subject.
Once more, please accept my excuses if a non-precise question has generated this discussion.
Thanks

### RE: fan speed and Voltage

PaulLag,
Short conclusion:
- here it is not about Dahlander winding, at all, but about the motor that is connected to Y for low speed and D for high speed.
- Regarding the above-mentioned limitation to single-phase, FPIM (fractional power induction motors): you can find on the link above a list of manufacturer's voltage regulators for 3ph fan motors. Some among them are 40 Amps at 50 Hz (note that is not VFD, but only voltage regulator). It is hard to be a "fractional power home appliance"!!!!

Tech Support for Rewind Shops

### RE: fan speed and Voltage

LOL, have to come back after 2 months to make more claims? The fan motors in the documents found by following the link are all small HP, very high slip and very low efficiency motors specifically designed so they could be speed controlled. There was not a single fan with a high efficiency, low slip motor like you'd find in any standard industrial motor catalog. As for the current ratings of the speed controllers. In this day and age with conservation and high electricity prices being the normal, would you actually want a 10hp or 15hp motor that is only 50% efficient operating in your facility?

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