AC/DC HARM?

[Roger Borg]

If an ebayer tested a true dc fan (not a laminated stator universal brush motor) on ac, what are the implications?

From a recent post:

Michael Rathberger

Posted November 5

Russ taught me, and generally speaking, an AC brush motor will have a laminated stator and a DC will have an iron core. If a laminated coil you could probably run it on DC but a solid iron stator is DC only. As David said, his runs faster on DC. I've run all brass Westinghouse fans marked AC on reduced 50-60v DC and they seem to run nicely

 

[Russ Huber]

2 hours ago, Roger Borg said:

If an ebayer tested a true dc fan (not a laminated stator universal brush motor) on ac, what are the implications?

From a recent post:

Michael Rathberger

Posted November 5

Russ taught me, and generally speaking, an AC brush motor will have a laminated stator and a DC will have an iron core. If a laminated coil you could probably run it on DC but a solid iron stator is DC only. As David said, his runs faster on DC. I've run all brass Westinghouse fans marked AC on reduced 50-60v DC and they seem to run nicely

 

The implications are the result of the seller running alternating current into a cast field DC motor and the results of that are the choice you make with the seller. Most importantly it has nothing to do with this Russ guy and Michael Rathberger, or the post exchange on Nov. 5th.

Edited December 2, 2024 by Russ Huber

[Nicholas Denney]

Nothing bad about AC into cast iron DC fans. It's DC into electrical steel AC fans that can do some damage.

[Roger Borg]

4 hours ago, Nicholas Denney said:

Nothing bad about AC into cast iron DC fans. It's DC into electrical steel AC fans that can do some damage.

Ok, gotcha, I was under the impression the reverse was true.

Either way, what kind of damage could be expected? And can damage result immediately (mere seconds), or after a longer duration (minutes)?

Thanks...

[Roger Borg]

9 hours ago, Russ Huber said:

The implications are the result of the seller running alternating current into a cast field DC motor and the results of that are the choice you make with the seller. Most importantly it has nothing to do with this Russ guy and Michael Rathberger, or the post exchange on Nov. 5th.

Okie dokie, I'll take that as a pass on the question. Thanks anyway...

[David Allen]

22 minutes ago, Roger Borg said:

If an ebayer tested a true dc fan (not a laminated stator universal brush motor) on ac, what are the implications?

Roger, the issues are many when it comes to running a DC motor with AC power. The simple answer is that (with nameplate voltage) it will not do damage "in seconds" but the fan will likely not run very fast if at all. If allowed to remain energized, there can be heating of the solid field coil cores over a period of many minutes, but that would take a lot longer than it takes to see that the motor isn't running properly. 

If the eBay seller claims they powered it on and it ran slow, or hummed but didn't run then likely it has nothing wrong with it. However, if they claim it sparked or smoked or popped then likely the motor has deteriorated wiring and short circuits and the failure was unrelated to the use of AC. 

[Roger Borg]

2 minutes ago, David Allen said:

Roger, the issues are many when it comes to running a DC motor with AC power. The simple answer is that (with nameplate voltage) it will not do damage "in seconds" but the fan will likely not run very fast if at all. If allowed to remain energized, there can be heating of the solid field coil cores over a period of many minutes, but that would take a lot longer than it takes to see that the motor isn't running properly. 

If the eBay seller claims they powered it on and it ran slow, or hummed but didn't run then likely it has nothing wrong with it. However, if they claim it sparked or smoked or popped then likely the motor has deteriorated wiring and short circuits and the failure was unrelated to the use of AC. 

Thank you David.

Story I received was it was powered briefly and the motor "did not work".

Hard to trust if a seller would acknowledge it sparked, so trying to determine the downside attributed to all possibilities. 

My DC experience is minimal, as is apparent, so please excuse the learning curve. If the stator consists of solid field coils, then any damaged wiring would likely reside in the commutator? Would the field magnets misshape with (extended) heat? Could damage also extend to the commutator and/or brushes? I expect these may be unanswerable and different in all situations, but more than anything else, just trying to pinpoint worst case issues.

Thanks again...

[David Allen]

10 minutes ago, Roger Borg said:

Thank you David.

Story I received was it was powered briefly and the motor "did not work".

Hard to trust if a seller would acknowledge it sparked, so trying to determine the downside attributed to all possibilities. 

My DC experience is minimal, as is apparent, so please excuse the learning curve. If the stator consists of solid field coils, then any damaged wiring would likely reside in the commutator? Would the field magnets misshape with (extended) heat? Could damage also extend to the commutator and/or brushes? I expect these may be unanswerable and different in all situations, but more than anything else, just trying to pinpoint worst case issues.

Thanks again...

DC motors are typically more complex than their AC counterparts. If the motor sparked it could be from anywhere that the wiring was touching and shorting out because the insulation was gone. It was reckless to power on any old motor like this without testing it and using a current limiter or other means to safely test it. If the seller did that he probably has no experience with this type of thing. 

If it is a solid pole design, the solid cast iron pole pieces will get hot from the AC magnetic field. They will not warp but the winding coil around them could burn out. This would take a very long time before anything like this happened, if it happened at all.  Inductive reactance typically limits the AC current which will pass through a DC motor to a very low level, but not always and not always evenly limited through each part of the motor. 

If the seller claims the motor didn't work, your safest bet is to treat it as a non-working motor and make an offer on it as such. Trying to go into detail with some of these sellers only serves to get them to raise the price. Many are not the sharpest tool in the shed. 

[Roger Borg]

17 minutes ago, David Allen said:

DC motors are typically more complex than their AC counterparts. If the motor sparked it could be from anywhere that the wiring was touching and shorting out because the insulation was gone. It was reckless to power on any old motor like this without testing it and using a current limiter or other means to safely test it. If the seller did that he probably has no experience with this type of thing. 

If it is a solid pole design, the solid cast iron pole pieces will get hot from the AC magnetic field. They will not warp but the winding coil around them could burn out. This would take a very long time before anything like this happened, if it happened at all.  Inductive reactance typically limits the AC current which will pass through a DC motor to a very low level, but not always and not always evenly limited through each part of the motor. 

If the seller claims the motor didn't work, your safest bet is to treat it as a non-working motor and make an offer on it as such. Trying to go into detail with some of these sellers only serves to get them to raise the price. Many are not the sharpest tool in the shed. 

Well said, appreciate the response. All the best...

[Russ Huber]

3 hours ago, Roger Borg said:

Okie dokie, I'll take that as a pass on the question. Thanks anyway...

I didn't pass on the question, Roger. What the seller claimed they did with the motor, and what the seller actually did with the motor could be two different things. You would then have to go by your own choice and gut instincts.

[Roger Borg]

15 minutes ago, Russ Huber said:

I didn't pass on the question, Roger. What the seller claimed they did with the motor, and what the seller actually did with the motor could be two different things. You would then have to go by your own choice and gut instincts.

Of course, that is baked in, and I understand that aspect of the equation.

My query was aimed more at enlarging my knowledge of DC motors, and better understanding their functionality, in tandem with the associated concern of pre-troublshooting the actions of a sloppy seller.

Thank you for clarifying...

[Russ Huber]

15 hours ago, Roger Borg said:

If an ebayer tested a true dc fan (not a laminated stator universal brush motor) on ac, what are the implications?

20 minutes ago, Roger Borg said:

My query was aimed more at enlarging my knowledge of DC motors, and better understanding their functionality,

 

Please include your query in your first post in the future for better results. However, any gained knowledge received is still not going to change what the seller actually did energizing the motor. Good luck.

[Roger Borg]

9 minutes ago, Russ Huber said:

Please include your query in your first post in the future for better results. However, any gained knowledge received is still not going to change what the seller actually did energizing the motor. Good luck.

Fair enough. I figured context beats out on semantics, but stand corrected. I will do my best to be more precise next time.

Thanks for the well wishes, until next time, take care...

[George Durbin]

5 hours ago, David Allen said:

Roger, the issues are many when it comes to running a DC motor with AC power. The simple answer is that (with nameplate voltage) it will not do damage "in seconds" but the fan will likely not run very fast if at all. If allowed to remain energized, there can be heating of the solid field coil cores over a period of many minutes, but that would take a lot longer than it takes to see that the motor isn't running properly. 

If the eBay seller claims they powered it on and it ran slow, or hummed but didn't run then likely it has nothing wrong with it. However, if they claim it sparked or smoked or popped then likely the motor has deteriorated wiring and short circuits and the failure was unrelated to the use of AC. 

No damage for a little burst of power but...  It's like the "NFL"   NOT FOR LONG!

[David Allen]

7 hours ago, George Durbin said:

No damage for a little burst of power but...  It's like the "NFL"   NOT FOR LONG!

Exactly! A short test enough to know it isn't working wouldn't ruin it but then common sense has to come into play to turn it off when things aren't working. And common sense is.... well.... uncommon these days.

[George Durbin]

21 minutes ago, David Allen said:

Exactly! A short test enough to know it isn't working wouldn't ruin it but then common sense has to come into play to turn it off when things aren't working. And common sense is.... well.... uncommon these days.

Right before they go up in smoke they make this cool growling sound!

Don't ask me how i know! 😅🤣😂

[Nicholas Denney]

I had a power supply running an AC fan and it was mistakenly switched to DC. The fan ground to a halt and made a LOUD roaring sound in the motor, and tripped the breaker before I could correct. The fan still worked after but that clearly was not kind to it. 

If you run solid iron DC motors on AC, they will just run weakly. There's no excessive heating or anything of the sort.

 

You can perhaps think about it this way. AC into DC is injecting a moving field into a stationary field machine, therefore the stationary field machine doesn't utilize the moving field efficiently. Conversely, DC into AC is injecting a stationary field into a moving field machine. It results in an electromagnetic tug-of-war between poles. 

Edited December 3, 2024 by Nicholas Denney

[Russ Huber]

55 minutes ago, Nicholas Denney said:

If you run solid iron DC motors on AC, they will just run weakly. There's no excessive heating or anything of the sort.

So, what do AC eddy currents create more of in a DC iron core as opposed to a laminated core besides poor motor function?

Edited December 3, 2024 by Russ Huber

[George Durbin]

10 hours ago, Russ Huber said:

So, what do AC eddy currents create more of in a DC iron core as opposed to a laminated core besides poor motor function?

Lots of heat...

[Jim Kovar]

Eddy current in a solid core
compared to laminated.

 

A hydraulic analogy...

[Russ Huber]

In a DC motor with a cast iron core, AC eddy currents would have a significant negative effect, causing increased heat generation within the core due to the changing magnetic field, leading to reduced efficiency in the motor as the energy lost to eddy currents is not converted into usable power; this is why most DC motor cores are made of laminated steel to minimize eddy current losses.

[Chris Campbell]

20 minutes ago, Russ Huber said:

In a DC motor with a cast iron core, AC eddy currents would have a significant negative effect, causing increased heat generation within the core due to the changing magnetic field, leading to reduced efficiency in the motor as the energy lost to eddy currents is not converted into usable power; this is why most DC motor cores are made of laminated steel to minimize eddy current losses.

Aside from a Jandus that can be wired DC or AC I have never owned a laminated steel DC. 
 

What motors are DC only and have laminated steel? 

[Russ Huber]

43 minutes ago, Chris Campbell said:

What motors are DC only and have laminated steel? 

Stamp Steel Westinghouse DC models, and models to follow.  All the GE late 19th and early 20th century DC ceiling fans had laminated stators, and for that matter, I don't know of a GE DC desk or ceiling fan that didn't have a laminated stator. 

[Steve Rockwell]

     GE did experiment, but I believe that's as far as it went.

   The photo does not display the interior (experimental) parts, it's merely a typical fan photo of this model...

                                                

[Russ Huber]

30 volt Railway stamped steel Westy DC.