ac versus dc motors

[Mick@itc]

Hi all. Am interested to understand the differences between Ac electric motors and dc motors. Apart from one runs on Avon and the other dc, what are the differences and why would you pick one over the other?
Thanks
Mick

[WestVanHan]

Avon?

You may think I'm a jerk and that's OK.....but why should someone spend 20 minutes typing stuff you can look up?

[FMS]

Provide more details on the application / role of these motors.

[CatBuilder]

Avon = He typed it in from an Android phone. I don't know how many times my online words have been screwed up by those phones.

Definitely the details and application would be helpful to comment.

So far all we can say is...

http://en.wikipedia.org/wiki/Electric_motor

[Mick@itc]

Originally Posted by CatBuilder

Avon = He typed it in from an Android phone. I don't know how many times my online words have been screwed up by those phones.

Definitely the details and application would be helpful to comment.

So far all we can say is...

http://en.wikipedia.org/wiki/Electric_motor

avon....avon..!!! yes i can see an electric motor running on a cosmetic brand!! yes android got me.

ok more info. i am still researching the practicality of a hybrid system on my 55 foot cat. catbuilder, you have been here I know. so the motors are for propulsion, around 18kw.

what i have found so far is that the dc motor has a controller of sorts that pulses the dc to mimic ac...at least that is my understanding. so the difference to me is an extra piece of kit in the form of those controller. i also note that there are people sprouting that one is better than the other in scattered comments in many threads. what i would like to do is try to get all the relevant facts in one thread and get opinions directly in one easy to find, properly titled spot.

Thanks for your info in advance.

Mick

[Submarine Tom]

Other than don't waste your time, money and effort is:

Go to endlesssphere.com and see if there isn't a way you can make it work for your particular application.

Best of luck.

Use the force.

-Tom

P.S. What on earth (pun!) was "avon" supposed to mean?

[CDK]

Originally Posted by Mick@itc

what i have found so far is that the dc motor has a controller of sorts that pulses the dc to mimic ac...at least that is my understanding.

You understood wrong.
The process is PWM (Pulse Width Modulation) and is used to control a DC motor without wasting power by converting it into heat. Power is switched on and off very quickly, the ratio between on and off determines how much power is fed to the motor.

The choice between an AC or DC motor depends on two factors, the available power source and the required level of control. If the source is DC, it would be foolish to convert it and use an AC motor because that creates unnecessary losses and complexity.
If the source is AC, an AC motor is used unless precise control at minimal cost is required. Cheap washing machines have AC motors that can run at 2 or 3 speeds, if variable speed is required, a DC motor with controller is used.

[Mick@itc]

Originally Posted by Submarine Tom

Other than don't waste your time, money and effort is:

Go to endlesssphere.com and see if there isn't a way you can make it work for your particular application.

Best of luck.

Use the force.

-Tom

P.S. What on earth (pun!) was "avon" supposed to mean?

Auto correct decided that AC was avon. There is a brand of cosmetics called avon. Gotta love technology and the problem between the screen and the chair!!

[Mick@itc]

Originally Posted by Submarine Tom

Other than don't waste your time, money and effort is:

Go to endlesssphere.com and see if there isn't a way you can make it work for your particular application.

Best of luck.

Use the force.

-Tom

P.S. What on earth (pun!) was "avon" supposed to mean?

Auto correct decided that AC was avon. There is a brand of cosmetics called avon. Gotta love technology and the problem between the screen and the chair!!

[Mick@itc]

Originally Posted by CDK

You understood wrong.
The process is PWM (Pulse Width Modulation) and is used to control a DC motor without wasting power by converting it into heat. Power is switched on and off very quickly, the ratio between on and off determines how much power is fed to the motor.

The choice between an AC or DC motor depends on two factors, the available power source and the required level of control. If the source is DC, it would be foolish to convert it and use an AC motor because that creates unnecessary losses and complexity.
If the source is AC, an AC motor is used unless precise control at minimal cost is required. Cheap washing machines have AC motors that can run at 2 or 3 speeds, if variable speed is required, a DC motor with controller is used.

Ok so for boating we will need varying control for maneuvering and have dc current from batteries so DC is the way to go in marine propulsion. Am I reading that right?

Went on to endless-sphere and to be honest I cant find any comparison of the two motors pros and cons. Are there any cable size, relative locations to worry about with dc versus ac?. Thanks for your help.

Regards
Mick

[michael pierzga]

Brushed DC motors are expensive and require big expensive copper cables to supply the low volt dc.

In the end you have to consider the application.

[CatBuilder]

Mick: I struggled through the same thing you're going through.

What I found was that it was probably best to use proven, reliable, off the shelf technology. This meant 3 phase AC generators, 3 phase motor controllers and 3 phase AC motors.

Added benefit to a catamaran is there is less weight involved in the cabling

Added benefit to anyone is that those systems are used in regular industrial applications all over the world and are readily available everywhere for a reasonable price.

The reason I didn't choose electric propulsion is that I just couldn't find any propulsion system that weighed less than a pair of outboards (+/- 450 lbs for the entire system - motor to prop).

I stopped looking at electric propulsion once I saw that the generators plus motors was a ridiculous weight.

[mydauphin]

Originally Posted by Mick@itc

Auto correct decided that AC was avon. There is a brand of cosmetics called avon. Gotta love technology and the problem between the screen and the chair!!

I wonder if Avon paid goggle for this feature...

[mydauphin]

Originally Posted by CatBuilder

Mick: I struggled through the same thing you're going through.

What I found was that it was probably best to use proven, reliable, off the shelf technology. This meant 3 phase AC generators, 3 phase motor controllers and 3 phase AC motors.

Added benefit to a catamaran is there is less weight involved in the cabling

Added benefit to anyone is that those systems are used in regular industrial applications all over the world and are readily available everywhere for a reasonable price.

The reason I didn't choose electric propulsion is that I just couldn't find any propulsion system that weighed less than a pair of outboards (+/- 450 lbs for the entire system - motor to prop).

I stopped looking at electric propulsion once I saw that the generators plus motors was a ridiculous weight.

An of course it will all die sooner than later when it get corroded or humidity finds its way in. We are not there yet. Only for military ships and cruise ships, and you see what happens to them. Any failure and they become useless.

[CatBuilder]

Originally Posted by mydauphin

An of course it will all die sooner than later when it get corroded or humidity finds its way in. We are not there yet. Only for military ships and cruise ships, and you see what happens to them. Any failure and they become useless.

Humidity? Corrosion? I'm not sure what kind of boat you have, but at 70 ft, everything in there should be dry as a bone.

Does any of your stuff actually corrode? I've never had any problem with corrosion of things inside my boat, since my first boat - a 23' trailer sailer.

In any event, they make motors that are certified for operation fully submersed in salt water.

Like most things in life, you just have to know what you are doing to get it to work. Not really a big deal. They use motors like this all the time in environments filled with acid gas, etc...

That's why I suggest AC motors. They are proven in harsh industrial applications and commonly used there.