Thread Number: 90768  /  Tag: Modern Automatic Washers
How do VMW detect unbalanced loads?
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Post# 1152677   6/28/2022 at 01:35 (666 days old) by Chetlaham (United States)        

chetlaham's profile picture
How do VMWs know a load has become unbalanced during spin when they have no position sensors or tub displacement switches?

Here is an example at 56:54 where the washer makes two attempts at spin and then aborts shift to rinse:












Post# 1152695 , Reply# 1   6/28/2022 at 07:07 (666 days old) by combo52 (50 Year Repair Tech Beltsville,Md)        

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Electrical load on motor,

\

Just like every FL washer built today.

 

Computers are wonderful.

 

John L.


Post# 1152697 , Reply# 2   6/28/2022 at 07:21 (666 days old) by Pierreandreply4 (St-Bruno de montarville (province of quebec) canada)        
abount unblance load

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i have a vmw maytag topload and very bulky items must be wash with other items to keep load balance in spring i tryed to wash a bathtub floor carpet even do i place it well when first spin came went off-balance

Post# 1152713 , Reply# 3   6/28/2022 at 10:45 (666 days old) by ea56 (Cotati, Calif.)        

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My Roper RTW4516 has never yet aborted a spin cycle. In fact this past Sunday I washed the bathroom rug that is in front of the sink by itself. It went into the first spin before the rinse cycle with no hitches.

Then when it started the final spin after the rinse cycle I heard two bangs from being unbalanced and I was all ready to run upstairs to rebalance the load, but before I could even stand up the machine had corrected itself and went into a high speed spin with no further banging or noise. I believe it has a spin balance ring around the top of the tub to help keep loads balanced.

This machine performs just like the TLís that I had in the 70ís, 80ís and 90ís. It may not last forever but Iím sure gonna enjoy its trouble free service just as long as it does last. I NEVER have to babysit this machine!

Eddie




This post was last edited 06/28/2022 at 11:14
Post# 1152730 , Reply# 4   6/28/2022 at 14:32 (666 days old) by Chetlaham (United States)        

chetlaham's profile picture
What does the current draw of an unbalanced load look like? Is it just consistently greater in magnitude or does the unbalance also show up as oscillations in the sine wave?


Also how does the control board sample the current? Is there a low impedance resistor in series with the motor circuit that measures the voltage drop across it to calculate current draw?

Fascinating stuff.


Post# 1152731 , Reply# 5   6/28/2022 at 14:40 (665 days old) by Pierreandreply4 (St-Bruno de montarville (province of quebec) canada)        

pierreandreply4's profile picture
on my washer when load is unbalance it shows sensing on the display


Post# 1152741 , Reply# 6   6/28/2022 at 15:46 (665 days old) by henene4 (Heidenheim a.d. Brenz (Germany))        

On a FL, an OOB load will create a varying current draw.
On a TL, since the load won't go against gravity during one part of a drum rotation and with it during the other, the current will be consistently higher for a given load.

But, once the machine reaches a certain rpm, since the load weight won't matter (it already has a certain needed inertia, keeping it at a certain speed dosen't really need much different energy input depending on load weight) it will probably just go depending on total current draw and not actual variation in current draw.

A TL like a VMW also isn't the same kind of suspension as a FL - it's really just free floating and not dampened per se.
As long as it can spin up, the actual amount of unbalance dosen't matter, it just swings freely.



So, a FL will probably just look at maximum current draw secondarily and mainly check what the difference between maximum and minimum of the current draw is.

A TL will check if maximum current draw isn't exceeded until a certain rpm is reached, and once that is reached, it will just check if current draw is below a certain level.



Current sensing is usually done with a shunt resistor and with a known voltage across it.

It is done at several points for several functions in several specific ways - most kinds of power supplies from USB power supplies you use to charge your phone to what supplies the processors in these appliances all kind of rely on such stuff.

For example, certain components only start conducting once a certain voltage is applied.
So once a certain current runs through a certain resistance a certain volatge is seen across that resistance which in turn means these components then start conducting and thus switch other components.



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