AC ver. DC Motors

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physis

Senior Member
I'm watching a cooking show and they're testing electric mixers. A big point is made that "this one has a "DC" motor" and we asked some "experts" and they said that DC motors have more power than AC motors.

I think the only parameters would be size and eficiency. I know that DC motor's gonna need a big hot rectifier.

I don't guess three phase is a consideration.

Any experts agree or disagree with the TV experts?
 

physis

Senior Member
Re: AC ver. DC Motors

I've come to the conclusion that there's a secret panel that makes sure that nothing truthful ever makes it to the television.
 

coulter

Senior Member
Re: AC ver. DC Motors

The following comments are based on supposition, innuendo, statistical samples of one, and twice relayed, unverified, third party information. As such, it may be no worse that normal television programming standards.

Originally posted by physis:
I know that DC motor's gonna need a big hot rectifier.
Shouldn't be too hot. Say 3A FLA on the mixer (We have a Kitchen Aid that pulls 2.5A - I think it is a big mixer for household stuff). Figuring a 1.4V drop for a full wave bridge, that's only 4.2W - not a lot of heat.


Originally posted by physis:
I don't guess three phase is a consideration.
I've seen a couple, but they were fastened in place equipment in commercial kitchens.


Originally posted by physis:
Any experts agree or disagree with the TV experts?
I don't know any experts on television grade mixer motors.


Originally posted by iwire:
I believe everything I see on TV.
Originally posted by physis:
I've come to the conclusion that there's a secret panel that makes sure that nothing truthful ever makes it to the television.
When it comes to rating household grade mixer motors, I would go with Iwire.

But as far as this secret panel, I don't think they need one. I think it comes natural from the attitude that news isn't journalism, its entertainment with ratings.


carl
 

physis

Senior Member
Re: AC ver. DC Motors

If I remember right trains do as much as 28,000 horsepower. That's almost 20.1 million watts at 100% efficiency.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: AC ver. DC Motors

Originally posted by physis:
If I remember right trains do as much as 28,000 horsepower. That's almost 20.1 million watts at 100% efficiency.
Might want to re-image that protien computer :D The work horse of locomotives is a GM FP59 which has a V-12 3200 hp diesel engine to drive the generator to turn the 4 wheel motors. There is also an additional V-12 diesel motor called the "head end motor" to supply electrical to the rest of the train like HVAC, lights, pumps, etc.
 

rattus

Senior Member
Re: AC ver. DC Motors

Originally posted by physis:
If I remember right trains do as much as 28,000 horsepower. That's almost 20.1 million watts at 100% efficiency.
Sam, where did you get that info? The Twilight Zone? First you have to burn the diesel oil to crank the generator, and that is theoretically 50% efficiency max. Then there are the inefficiencies in the generator and motor. 100%? Not today. Better than steam though, I think.

The universal motor is widely used in applicances and power tools. It will run on DC very nicely. Now they may have gone to a permanent magnet DC motor to save a few pennies or for better speed control. But, I see no great need for DC motors in kitchen appliances.
 

physis

Senior Member
Re: AC ver. DC Motors

I guess I don't member right. :D

That's 746 watts per horsepower Rattus. A 100% efficient motor will give you 1 horsepower for 746 watts.

Edit: See, 20 megawatts is too much.
Edit: Man, you can't get away with anything here. Whatever it is, someone's gonna know it.

[ March 27, 2005, 12:57 AM: Message edited by: physis ]
 

hurk27

Senior Member
Re: AC ver. DC Motors

I see no great need for DC motors in kitchen appliances
I do.
PM DC motors have come way down in price and cost to manufacture Thank's to over seas cost of manufacturing :D

When I was first trying to find an optional way to power my equipment without lugging a generator around I tried 10 deep cycle battery's connected in series to provide 120 volts DC. It worked real good for my saw, drill, and reciprocal saw but they had no speed control and only worked with the trigger all the way in. :D
Now I use inverters with output transformers. :D

Sam The battery's are not in the trunk!!! there behind my seat. :D

My van dosen't have a trunk! :roll:

[ March 27, 2005, 01:38 AM: Message edited by: hurk27 ]
 

charlie

Senior Member
Location
Indianapolis
Re: AC ver. DC Motors

Dereck, it is interesting that they call it the head end and the guys in communications also use the same term to describe the source for the fiber. :D
 

rattus

Senior Member
Re: AC ver. DC Motors

Sam, where do you buy these 100% efficient motors? I want one!

Hurk, as for the need for DC motors, I mean the universal motor has worked just fine, but there is always a need to cut the cost of manufacturing especially if that includes size reduction and improved performance.

It is quite possible that PM motors of a given size are more powerful than the universal motor, but I would not think they produce enough torque for some applications, say a Sawzall or drill motor. But, I am guessing now.
 

hurk27

Senior Member
Re: AC ver. DC Motors

By Rattus: I would not think they produce enough torque for some applications, say a Sawzall or drill motor. But, I am guessing now.
Think about the motors in a cordless drill, sawzall. and there only 12 to 18 volt now think if these motors were design to run on 120 volts? :D
 

physis

Senior Member
Re: AC ver. DC Motors

Wayne, wasn't it a vega or something with the way too much transmitting power? :cool:

I remember your van description too, also cool.
 

physis

Senior Member
Re: AC ver. DC Motors

It must have been 2800 HP I was told those engines do. When I asked the engineer I got that from (electrical, not railroad, we worked on some RR stuff, had a set of their radios) why they don't use more (it's a guy thing :D ) he said that they'd just spin the tires.

GM FP59 which has a V-12 3200 hp diesel engine
Dereck, a couple of these would be perfect for a big enough boat. I figure 100 or 150 nauts for a 50 or 60 footer. Better reenforce the hull. Any idea how much they weigh and cost?
 

rattus

Senior Member
Re: AC ver. DC Motors

Hurk, are you sure your cordless drill uses a PM motor? It is my understanding that the PM motor is in effect shunt wound--without the winding. Guess I will have to check out my Makita.

As for designing a motor to run on 120Vdc, it would still be limited by copper and iron loss. The current draw would be less which allows for smaller wire and more of it.

They are marvelous little things whatever.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Re: AC ver. DC Motors

Do all DC motors still have brushes? That has always been the big downside to DC motors. I'll bet that food processor barely makes it to the 90 day warranty!!

And the 4.2 watts mentioned earlier is a lot of heat for a small electronic component. I'll bet that our DC mixer only draws a quarter of that 2.5 amps that the kitchen aid draws!!!
 

spsnyder

Senior Member
Re: AC ver. DC Motors

Much higher rpm's are attainable from DC motors. Maybe that's a big advantage for a blender.
 
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