What type of motor do these use?

[earthling177]

Induction motors are asynchronous motors -- they run *close* to the speed they'd run if they were *synchronous* motors, but not the same.

For example, a 2-pole synchronous motor runs at precisely 3600 rpm at 60 Hz. A 4-pole sync motor runs at 1800 rpm.

Contrast that with 3450 rpm and 1725 rpm, which are (common) speeds under load for a 2-pole asynchronous (induction) motor and a 4-pole one.

Synchronous motors (particularly vey large [over 10HP] ones) usually cannot self start, particularly under load -- several different ways have been used over the years, like disconnecting the load with clutches, using an auxiliary starter motor, or, more recently, building a self-starting motor (typically induction) that disconnects as the speed gets near synchronous speed and turns the motor into a synchronous motor.

Induction motors are asynchronous because they depend on having a spinning magnetic field to generate the current in the rotor.

There isn't a very good reason to use a synchronous motor, which costs more (usually) to build than other kinds if you are not making use of the main advantage of such motors, which is very precise speed. If you just need variable speeds, there are many cheaper ways to achieve it.

 

[tolivac]

Self start synchronous motors use auxillary windings on the rotor to make it start like an induction motor.As it reaches 75% speed-the field current is applied and then the motor runs as a synchronous one.Small synchronous motors are expensive-those below 10 hp-esp those under 1hp.They are used where the speed is critical.Induction motors won't maintain speed when used for purposes where speed is critical.Induction motors won't reach synchronous speed because of the magnetic "slip" in their design.Yes,older design synchronous motors used "pony motors" for starting.

 

[tolivac]

Another addition for LARGE Synchronous motors-yes they are more efficient than induction and have greater breakdown torque.A bonus-they can be used as a power factor correction device-adjust the DC to overexcite the rotating field and you have a variable power factor correction device.If you see a large cylindrical horizontal object at a substation-it is an enclosed synchronous motor that the power company can start and adjust if the power factor goes out of tolerance.The motor does not drive a mechanical load.It is enclosed in a hydrogen,nitrogen,or SF6 filled container.Modern synchronous motors are brushless-they use a rotating secondary transformer winding on the rotor along with a rotating rectifier assembly.The primary is stationary.This same system is used with synchronous power generators-the one we have works this way.Cat 3816.

 

[Chetlaham]

All excellent and very educational replies!

Spot on about induction motors never being truly synchronous due to the slip and need for a spinning field to generate a counter field in the rotor. Immediately reminded me of this video:



One advantage to Whirlpool's motors (at least the DW drain pumps) is that they appear to not have any type of rotor seal, ie the rotor is housed in water and the stator slips over the plastic housing.

 

[Chetlaham]

Well

I knew it was to good to be true But just as fascinated. Seems like this motor has an entire algorithm to determine the speed based on load, and it seems to give up without load.

 

[combo52]

Amusing Video

But this guy should stick to wood working, he made so many incorrect assumptions about how this motor works and why that I won't even start to address them, in the end all he really manged to do was destroy a good DW.

 

Thanks for posting Chet, it was amusing to watch while I ate lunch.

 

[Chetlaham]

How it works

I know it might not seem worth it, but can you explain them at least? I am even more clueless as the guy lol. Especially the function of the circuit board.

I do agree about the DW though, that looked like a really good model, and at 1 year old he would have had a new DW possibly for pennies on the dollar.

 

[johnb300m]

With all his incorrect statements (which I don't know, tell us John!) at least he seems to have a very efficient blower motor until the bearings roast!

 

[tolivac]

Interesting-----WHY go thru all of that trouble when inexpensive blowers are already available?Yes,he should stick to woodworking--incidently its UNSAFE to have the child roaming around your shop while you are working!To many ways for the kid to get hurt on all of the sharp equipment in a woodshop!How are you going to keep an eye on the little girl while you work?The motor from the DW doesn't work like the synchronous motors I have dealt with.

 

[combo52]

Amusing Video

Hi Rex, yes indeed why go through all that trouble to build a blower, I hope he has a sprinkler system in that work shop, these DW pump motors are not continuous duty they will overheat and hopefully shut off, if not and a plastic motor lubricated with oil attached to a wooden fan assembly, well lets just say it would be a waste of time to apply for UL approval label, LOL.

 

It was a fun video to watch and it is fun to watch the creative spirit at work, but I don't think I would bother taking a video of a project like this and putting it on line. Now I will admit that when I was 12 or 13 I built a wooden refrigerator using the sealed refrigeration from a 50s Westinghouse ref, I think I realized after I got it all framed together that it was a silly idea and did not complete it.

 

As Rex mentioned there are so many good blowers that can be had for about nothing, I would take one out of a high end WP or maybe a Samsung Dryer that has a variable speed blower with a separate motor, these move a lot of air and are designed to work with flammable lint so they should be well suited for sawdust.

 

[Chetlaham]

Control board

Is the control board to stop the motor with no water or to achieve direction?

 

[henene4]

Probably current sensing for some form of load sensing.

 

[combo52]

Control board is to start motor and keep it running with the least amount of power consumption, and to make it run in the correct direction.

 

[tolivac]

I obtained a good blower for nothing when a TV station replaced their RCA transmitter with a new one. I repaired the old one they scrapped-spent a lot of time on it.So--when it was replaced they let me salvage stuff from it.Got some of the tubes-I collect transmitting tubes.Then I got the blower that cooled the diplexer assembly-this combines the outputs of the sound transmitter with the visual one-this was an analog Tx.The blower is a heavy cast iron fancase-1/3 hp 120/240V motor.The fan is cast aluminum.I have it in my goodies pile with thpoughts of using it as a dust collector fan.Price---FREE!
I wonder and hope this man only runs his homemade fan only when he is in the shop.Yes,don't think that plastic motor will last long with plastic on plastic with no water "lubrication".Oil can soften the plastic or even dissolve it!Same with grease-you could try silicone grease.Oh on that transmitter-the double sided blower-two fans and fancases on one motor-this cooled the visual driver and PA was a 480V 3ph motor at 7Hp.Left it because I couldn't use it.The poor transmitter looked kinda sad on the curb-dumpted like an old washer or dishwasher.Later scrappers took the rest.Was purchased in the 80's.

 

[johnb300m]

pond pumps indeed.........

Upon thinking about this more, and watching that video.......
I hope many on here go watch that video a 2nd time, maybe three times.

I can't count how many times people were arguing in threads about when these little "puny pond pumps" were put in dishwashers, and everyone was crowing about cheap and weak they were.

Did you see the video?
That thing was running at full 3400-3600 rpm whether unloaded or very heavily loaded with a WOOD impeller pushing 6in dia.
That's a ton of drag for a little 55w motor.
And in some instances it was overdrawing to maintain speed.
The torque on that thing must be pretty good.
That's how you get your good water pressure from a dinky "pond pump."

 

[tolivac]

The "pond Pump" is now delivering air suction and pressure now.Would like to see some CFM and air pressure readings on that repurposed dishwasher motor now a blower motor.Yes,guess for 55W its doing pretty good.Just wait until the motor gets full of sanding dust and sawdust!