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 shdesignsPowered By Infinite Improbabilty DrivePremium
join:2000-12-01
Stone Mountain, GA | reply to brushless
Re: Is this a brushless motor? said by brushless : quote:
It looks like it, but since most AC motors are brushless this is to be expected.
by most what exactly do you mean? at least more than 50% of AC motors are brushless.? In the tools department, one that I am quite familiar with, most are brushed, in fact, I would say 99% of the AC tool motors are brushed. I also work with HVAC systems and they are brushed... in my field I encounter them. I don't take them apart but I can tell just by them having 3 wires. Common and 1 and 2nd speed. A brushless motor requires a controller to change speeds. Look at a typical home A/C. The condensor, compressor and blower fan are all brushless AC induction motors.
Small hand tools tend to have brushed motors especially where speed control is needed. Large tools have induction motors (table saws, compressors etc.)
The induction motor as you have shown are probably the most common. They tend to run fixed speeds but some fan motors have multiple taps for speeds. No controller is needed.
quote:
also, brush motors tend to run cooler!. i don't know why you think they run hotter.
they may seem to run hotter to you but in actuality, what you feel is hotter, is only the windings. While the stator runs cool (i.e. bearing run cool) since there is no heat transfer from stator to rotor. quote:
The real question, is what is the OP concerned with, and why, regarding dishwasher motors? Lifespan? Electrical characteristics? Heat? GFCI? AFCI?
1- over all efficiency and longevity. 2- Brushless motors are typically 85–90% efficient
Plus I do have an admiration for brushless technology, I guess that is the geek in me  .
on monday, I will take a part some motors at work. AC units and dishwashers to see if they are brushed or not. i'm guessing they are brushed.
--
Scott Henion
Embedded Systems Consultant,
SHDesigns home - DIY Welder | |
| quote:
I think you ar confusing induction motors with brushless DC motors. Most induction motors like you have shown are 60-80% efficient.
The 3-phase induction motor has efficiency over 85% at nominal speed.
The single-phase induction motor has lower due the lack of 2 phases.
And I know the difference between AC and DC motors:) | | |
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 whizkid3Premium,MVM
join:2002-02-21
Queens, NY
kudos:9
1 edit | said by Simonuthiner:The 3-phase induction motor has efficiency over 85% at nominal speed. Agreed. But most 3-phase induction motors produced today have a much better efficiency.
Old NEMA MG-1 motor standards for 'Design B' motors (the type used in most applications), from 1 to 200 hp, required most motors to have an efficiency of over 90% with a load of 50% to 100%. The efficiency 'sweet spot' is 75% of rated load. Manufacturers and importers were required by law to meet this efficiency standard since 1997 via the Energy Policy Act (EPA) of 1992.
More efficient motors, called NEMA Premium Efficiency Levels were available with efficiencies from about 1% to 4% higher. Since 2010, the 1992 EPA requires all 1hp to 200hp motors sold or imported into the US must meet the premium efficiency requirements, making their efficiencies over the same range from about 92% to 95% efficient. Similar requirements are also in force for larger motors, and types other than NEMA 'Design B'. The full-load efficiencies are available in NEMA MG-1 table 12-12. Note that the efficiency improves below 100%, hitting its peak at about 75% of rated load (see the graph above). Smaller motors, and single-phase motors tend to have lower efficiencies, with most still over 85% at their operating load in a good design. See table 12-12 here:
»www.nema.org/stds/complimentary-···mium.pdf
Here is a good primer, 'Motor Efficiency, Selection and Management' from the CEE:
»www.cee1.org/ind/motrs/CEEMotorGuidebook.pdf
Single-phase motors smaller than 1hp don't come close to this level of efficiency. Then again, relatively speaking, they don't use much energy to begin with.
VFDs are great for improving the efficiency and speed control of motors. However, you don't find them on smaller motors, because the cost in comparison to the energy savings, is not worth it. For motors that are run at a single speed, its a lot less costly to select a motor at peak efficiency than to use a VFD. Primarily, VFDs are used where the motors must adjust speed over a wide range to meet their load demands. This in turn allows a high efficiency over its operating range. I seriously doubt one is going to find a VFD in a dishwasher, when there are other less costly techniques that can be used and there is little reason to operate the motor over a wide speed range. Likewise, motors that operate on VFDs have no need for additional wires, contrary to the thoughts expressed by the OP. The additional wires are likely for either the starting circuit or speed control. | |
| Here are the schematics of the motor in picture...
and this is the schematics of a motor with two wires...
so based on this, which motor is more efficient? | |
 leiboldPremium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:6
 ·SONIC.NET
| said by brushless :so based on this, which motor is more efficient?
That is impossible to tell from the schematic. The first dishwasher changes the spin direction of the motor for the wash and drain cycles. The second dishwasher has the motor rotating in the same direction all the time and uses a drain valve/solenoid to change from washing to draining.
--
Got some spare cpu cycles ? Join Team Helix or Team Starfire! | |
| quote:
The first dishwasher changes the spin direction of the motor for the wash and drain cycles. The second dishwasher has the motor rotating in the same direction all the time and uses a drain valve/solenoid to change from washing to draining.
you are correct about the solenoid... all I see is lines in the schematics (though I know how to read HAVC schematics).. i'm guessing the solenoid in the schematics is the 40 ohm coil.... here is a pic of the two wire motor I pulled out from my cell phone....
just by motor outer reappearance, I can gather an opinion that the 4 wire motor is more efficient for the following reasons...
1- it is smaller
2- it has less frame.. i.e. more heat dissipation = longer life.. (the other is more canned = short life span)
3- benefits of being more open frame is that one can get access to the bearing for maintenance. The canned frame in the two wire is welded. no maintenance require when it fails, just throw it away.... or buy a new dishwasher.
Further, wouldn't it be more efficient to eliminate a solenoid than to change the motor direction?
Also, for some reason, this dishwasher makes less noise and the washing cycles sound heavy duty. By that I mean that the noise the water inside splashing is way louder than on the two wire motor. To me that translates to better "scrubbing". | |
leiboldPremium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:6 Reviews:
·SONIC.NET
| I agree with you on the the fact that better airflow through the motor reduces heat and that will improve life expectancy of the motor. I also agree that the main noise coming from a dishwasher should be the water splashing inside and not a whiny motor.
I still couldn't tell motor efficiency from a picture of the motor or a schematic without detailed specifications.
The counter argument would be that the more enclosed two wire motor is more efficient which results in less heat loss while the reversible motor must have wider openings for cooling since it is less efficient. However it is all speculation until you measure the electric power consumption of each motor while in use and relate it to the amount of water pumped.
From the point of system complexity and manufacturing cost there is probably no big difference between the two designs. Personally I like the reversible motor design better.
--
Got some spare cpu cycles ? Join Team Helix or Team Starfire! | |
| quote:
I still couldn't tell motor efficiency from a picture of the motor or a schematic without detailed specifications.
yeah I know is hard to tell just by schematics. it is also hard to tell when looking at them in person... why? I speak from experience. I will mention two that I have encountered more than one..
1- the fan in the two wire motor is metal and tends to get loose. The bad part is that it is inside the motor... so there is no way to repair the fan (epoxy it back, for example). Even though the motor might still be good. for this reason a lone, it makes the motor useless because when it runs it sounds like a rattle snake on drugs. no one wants to hear that.
2- the front bearing on the two wire motor is impossible to get access to. If the front bearings just happens to just need a little lubrication, one cannot do that... I know from experience in this. I tried it but there is no way to get to it. And it could not just need a little lubrication but some fine sanding too... but one does not have access to it, so bad front bearing = whole motor to trash.
On the other hand, the other motor will not suffer from this since both, the cooling fan and the bearings, have easy access. Just by that alone gives it efficient points in my book. The cooling fan looks more beefy on the 4 wire motor too. And even if it comes loose for some reason, it can be epoxied back with not much effort.
Ok, lets look at it this way... with both motors being equality inefficient, does a solenoid valve makes the whole unit less efficient or more?
quote:
The counter argument would be that the more enclosed two wire motor is more efficient which results in less heat loss while the reversible motor must have wider openings for cooling since it is less efficient. However it is all speculation until you measure the electric power consumption of each motor while in use and relate it to the amount of water pumped.
yes I understand the speculating part, but what I don't understand is how is maintaining heat inside a motor more (less heat loss) efficient since the motor fan attached to the rotor is there to fan out the heat.
From what I understand, a brushed motor gets mainly hot at the coils (rotor) and dissipates from there. A brushless motor gets hot at the stator (coils) and dissipates from there. The bottom line, the goal is to dissipate heat and not maintain heat inside the motor. so i don't understand why you would say less heat loss is good.
quote:
From the point of system complexity and manufacturing cost there is probably no big difference between the two designs. Personally I like the reversible motor design better.
you are probably correct. but I am mainly focusing on my wallet and not the companies
even though both motors might cost the same, I gain more benefit from one than the other. Ease of fixing is also calculated in the efficiency equation in my book, but that is just my opinion, thanks for the enlighten. | |
leiboldPremium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:6 Reviews:
·SONIC.NET
| said by brushless :The bottom line, the goal is to dissipate heat and not maintain heat inside the motor. so i don't understand why you would say less heat loss is good. Basic physics tells us that the difference between the electrical energy that we put into the motor and the mechanical work performed are losses (electrical resistance of the wires, mechanical friction in bearings, etc.) that turn into heat.
While getting rid of the heat inside the motor is good, even better (and far more economical) is when the motor is so efficient that it doesn't produce much heat in the first place.
--
Got some spare cpu cycles ? Join Team Helix or Team Starfire! | |
| quote:
Basic physics tells us that the difference between the electrical energy that we put into the motor and the mechanical work performed are losses (electrical resistance of the wires, mechanical friction in bearings, etc.) that turn into heat.
yes understood. But lets not forget that the main point is that heat is motor's enemy... and so is to an intel i7 2600K CPU. They both need cooling to maintain longevity and stability or for them to even work. If you run your CPU at 90C, yes it will work but it won't last you that long. Or if you run it with out cooling, you Pcwon't even boot up due to it heating up and shutting down. Heat principals apply similarly to AC/DC motors. Even to your own body outside in the heat... your sweat is your AC unit.
Back to electric motors, heat on DC motors kills/weakens the magnets, for one. Also, heat can evaporate the lubricants... which weakens the bearings... which makes the motor less efficient over time.
An open frame motor is more efficient to me just for that reason alone. I am sure that it would even due fine with a smaller fan than a fully canned motor has.
quote:
While getting rid of the heat inside the motor is good, even better (and far more economical) is when the motor is so efficient that it doesn't produce much heat in the first place.
if it's a motor with bearings that require grease, the motor needs to get hot enough to melt the grease to lubricate the bearings. But yeah, I agree.
Thanks anyways, my conclusion over all is that this washing machine is more efficient over the others for various reasons.
1- open frame motor.
2- new model and it is expensive. (most things new are more efficient than 4 years ago)
3- easy access to motor if it needs maintenance.
4- heavy duty wash cycles. (more scrubbing per cycle)
5- no solenoid valve.
Sometimes we have to go with our logic, and I believe this is one of those times.
Thanks everyone for the info. | |
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