Iron Core Losses - Hysteresis and Eddy Currents

[safe]

This guy spent his whole life studying this stuff and it's still a mystery in some ways even today:

http://www.energyscience.org.uk/le/le18.htm

The bottom line is that there are losses that produce heat and they are difficult to get a handle on because they are not attributes of the motor that most people publish. (or possibly even know) It seems that the thinner the laminations of iron that you use in building the motor (and the design) the lower your eddy currents turn out to be. "Whatever" your eddy current charactoristics are when the voltage rises the eddy currents increase with the square of voltage, so at some point things go to hell really fast!

Does the DC motor have the same issues with eddy currents as the AC motor?

What do people know about this very specific area?

If the eddy currents are very low to begin with then you might not even notice them until the voltage hits a level that allows the curve to come into view. Once the curve becomes apparent then you're screwed because you can't raise the voltage past that point or the losses will be extreme. A while ago there was a brushless motor that had higher efficiency at 36 volts than at 48 volts and one wonders if this was the cause... :?

 

[safe]

If you read that article he proposes a theory that says that the "extra" eddy current energy that is measured in real life situations is the bizarre result of heat producing it's own electric current. You end up with a turbocharger like situation where eddy currents create heat, which then produce additional currents, and so on. (follow the link again at the bottom of this page)

http://www.energyscience.org.uk/le/le18.htm

The guys theory might be wrong, but it's interesting to see how he thinks... :wink:

 

[The7]

Does the DC motor have the same issues with eddy currents as the AC motor?

The simple answer is YES.

All DC motors (brushed and brushless) as well as AC motors undergo alternating magnetic flux in the iron core path.
The rate of alternating flux is the frequency.
In most ebike motors the frequency is from 200Hz to 400 Hz at top-speed.
This frequency is direct proportional to the rpm of the motor.
Iron core loss will occur in any iron core subjecting to alternating magnetic flux.

 

[safe]

Iron core loss will occur in any iron core subjecting to alternating magnetic flux.

But the laminations of the core reduce the eddy current losses (so I've come to understand). There's no easy way to know how the core will react to voltage. There are no formulas that tell us what the "baseline" eddy current sensitivity is and so we have no way (except to experiment) to discover at what voltage the eddy current losses intersect with the motor's performance.

We know that the eddy current losses are as a square of voltage, but we don't know the scale on which we are working. The hysteresis losses are apparently a constant, so that should not be a big deal.

Only trial and error can educate us on our specific motors...

 

[TylerDurden]

Only trial and error can educate us on our specific motors...

Now you're getting warm...

:lol:

 

[The7]

Iron core loss will occur in any iron core subjecting to alternating magnetic flux.

But the laminations of the core reduce the eddy current losses (so I've come to understand). There's no easy way to know how the core will react to voltage. There are no formulas that tell us what the "baseline" eddy current sensitivity is and so we have no way (except to experiment) to discover at what voltage the eddy current losses intersect with the motor's performance.

We know that the eddy current losses are as a square of voltage, but we don't know the scale on which we are working. The hysteresis losses are apparently a constant, so that should not be a big deal.

Only trial and error can educate us on our specific motors...

We did such experiments for iron core transformers in tecnical college/university.
Now, your turn on motors if you like.

 

[safe]

We did such experiments for iron core transformers in technical college/university.
Now, your turn on motors if you like.

You see my point right?

We won't know if the eddy current losses are significant until we try overvolting and see what happens. It might turn out that the eddy current losses don't become significant until you get up to 72 volts on a normally 36 volt motor. If you were to go to only 48 volts the eddy currents and hysteresis might be reasonably insignificant.

There have been people who have taken 24 volt 400 watt Kollmorgan motors and overvolted them to 72 volts with great success.

At some point we know that eddy currents will play a major part in bringing down the high voltage / high rpm efficiency of a motor, but we just can't know (in advance) if it's within the voltage range that we are most likely to be operating within...

 

[TylerDurden]

There have been people who have taken 24 volt 400 watt Kollmorgan motors and overvolted them to 72 volts with great success.

For example???

 

[safe]

For example???

There was a guy on YouTube that did this. He said that after a year his motor was still running fine. I have no idea what the link might be. Sorry.

 

[fechter]

Knoxie reported the rotor flies apart somewhere around 60v. Perhaps this person was lucky and got a better glue job or a better run of magnets.

It looks like you could add some super glue around the magnet to fill in the gaps in the original glue job. This should increase the max RPM.

 

[monster]

Safe you really need to lable your X and Y axis. i never know WTF you are on about. you should never assume people know.

its all good stuff tho

 

[fechter]

Safe you really need to lable your X and Y axis. i never know WTF you are on about. you should never assume people know.

its all good stuff tho

I've suggested that also. It's one of the reasons he catches so much flak from some of the members.

 

[cadstarsucks]

Safe you really need to lable your X and Y axis. i never know WTF you are on about. you should never assume people know.

its all good stuff tho

I've suggested that also. It's one of the reasons he catches so much flak from some of the members.

It is not his graph...if you follow his link it is described, but the units are not easily applied.

Dan

 

[TylerDurden]

The link is to a free-energy crackpot... go figure.

 

[cadstarsucks]

The link is to a free-energy crackpot... go figure.

Perhaps, but the one I posted earlier is not:

http://endless-sphere.com/forums/download.php?id=3852

Dan

 

[TylerDurden]

Yes. I read the paper. Is a full study with data published?

 

[cadstarsucks]

Yes. I read the paper. Is a full study with data published?

Might well be...if you can afford $100 or a membership to the IEEE

He has a bunch of stuff on his site:
http://energy.ece.uiuc.edu/chapman/publications.htm

Dan