over-voltage on universal motor
over-voltage on universal motor
(OP)
Hi. I am trying to source a universal motor for a prototype- with very little luck.
I need 240V, 1/2 hP
I have found a 1/4 hP, 115V. If I double the supplied voltage, any guesses whether I will destroy the motor?
I am running this in cold water, so cooling will be plentiful.
(We have successfully done this with BLDC motors, but I'm unsure about the construction of universals)
thanks
I need 240V, 1/2 hP
I have found a 1/4 hP, 115V. If I double the supplied voltage, any guesses whether I will destroy the motor?
I am running this in cold water, so cooling will be plentiful.
(We have successfully done this with BLDC motors, but I'm unsure about the construction of universals)
thanks





RE: over-voltage on universal motor
Aso, running it under water is just dumb. At least if you allow water to get into the motor.
Why not get a motor that is suitable instead of trying hopeless "solutions"?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: over-voltage on universal motor
RE: over-voltage on universal motor
Running a motor underwater is neither dumb, nor unique. Contrary to that, it is actually ideal, as water has a much better cooling capacity that air. Sure, it is fair to say letting water *into* a motor is dumb!
the reason for the interest in universal motors is that the power to weight ratio is high, and motor drivers are not required (and cost is low- more on that later). In subsea vehicles, size and weight are both premiums.
As I mentioned in the original post, typically we use BLDC motors. This project is for a scientist and the budget is limited, so we are trying to improvise and give a cost effective solution. And, he can use free labor (grad-student) to change brushes every 300 hours.
thanks again
RE: over-voltage on universal motor
If you look into a universal motor, you will see a collector and brushes. All of these things are connected to voltage and bringing them into contact with water is the dumbest thing you can do to such a motor.
If you do not believe me - just go try it! But beware of the dangers involved.
A six or twelve volt motor might work, but definitely not a 240 V motor.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: over-voltage on universal motor
Believe me, a waterproof housing that incorporates a shaft seal is not a problem to design, fabricate or assemble. that was not my question here- I am well versed in marinizing both custom and COTS equipment.
The question was simply about a piece of equipment that I am not overly familiar with- universal motors.
So, thanks for your initial input: doubling the voltage/speed of a universal is likely to cause problems.
have a nice weekend.
RE: over-voltage on universal motor
RE: over-voltage on universal motor
Bill
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"Why not the best?"
Jimmy Carter
RE: over-voltage on universal motor
RE: over-voltage on universal motor
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If we learn from our mistakes I'm getting a great education!
RE: over-voltage on universal motor
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: over-voltage on universal motor
The "universal" in the name means universal in the respect that they can be used on AC and DC. They are, in effect, small series wound DC motors with a laminated core, so they can also work with AC.
But half-wave is one of the worst waveforms you can select for them. The peak voltage will not be reduced and the current crest factor will be really bad. All that while you still won't get any more power out of it.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: over-voltage on universal motor
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(2B)+(2B)' ?
RE: over-voltage on universal motor
They may have encountered applications similar to yours.
RE: over-voltage on universal motor
I know them very well, did consulting work for them just a few weeks ago.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: over-voltage on universal motor
I would like to know any experience/s, anecdotal or factual re how bad a half-wave rectifier feeding a "universal" motor is. I bet that type of motor doesn't care if it is fed DC, AC, or a mix of both. Been there, done that, and that setup worked: the job was done (need to run a power tool rated at 115V with the only supply available was 240VAC). Any wild reaction is accepted.
RE: over-voltage on universal motor
The motor will run on all occasions. But half-wave AC is the worst commutator killer. Ever.
I'll be back with a report. May take a few hours. Patience!
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: over-voltage on universal motor
Read here: ht
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: over-voltage on universal motor
Yours
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: over-voltage on universal motor
One more question: did you add a free-wheeling diode across the rectifier output/ parallel with the universal motor when you did your experiment? Because if you did, you won't see that much arcing, IMO.
RE: over-voltage on universal motor
You can see the reason if you study the voltage (black) trace. As you can see, theres a small negative excursion at the end of each voltage half-wave. That is where a free-wheeling diode would conduct and the energy at that point is very low. So, it wouldn't affect the arcing much.
Also, the inductivity of a universal motor is quite low. You can see that if you study voltage and current phase relatioship - the angle is quite small. That is best seen in the AC recording.
A free-wheeling diode across a highly inductive load would be another thing and it would reduce arcing across an external breaker. In a universal motor, the "breaker" is in the commutator, between the two active commutator bars and the brush and an external diode doesn't influence the goings-on there very much.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.