Thread Number: 61948  /  Tag: Modern Dryers
What Determines a Dryers Spin Rate?
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Post# 845798   10/14/2015 at 11:13 (3,088 days old) by stricklybojack (South Hams Devon UK)        

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Today i was at the laundromat watching my towels stuck to the sides of the dryer thinking i wish the machine had a rheostat adjustable speed control
so i could dial down the spin a little and get those towels to drop at or near the 12 o'clock postion of rotation.
When they finally dryed enough they started to drop as i would like for more drying action.
So please chime in all you real and would be thermodynamic engineers and blow some hot air on this subject for us, thx.





Post# 845801 , Reply# 1   10/14/2015 at 11:22 (3,088 days old) by DADoES (TX, U.S. of A.)        

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Related factors are drum diameter and baffle design, and possibly airflow rate.


Post# 845810 , Reply# 2   10/14/2015 at 12:45 (3,088 days old) by jerrod6 (Southeastern Pennsylvania)        

I wonder about weight.  I have never had a wet towel stuck to the dryer drum but have had wet lightweight undershirts initially stick to the drum  when there was only one or two items being dried.  In this case there was nothing to move them off of the drum so they spun around stuck to it until they were dried enough to fall off, and even then there was not a lot of tumbling going on----justs riding against the drum...so perhaps it is load size, weight, and moisture content as well. 


Post# 845811 , Reply# 3   10/14/2015 at 12:46 (3,088 days old) by henene4 (Heidenheim a.d. Brenz (Germany))        

Most dryers should have tumbling rates that (should) do exactly that 11/12 to 4/5 tumbling.

However, its hard to get the proper speed for any load.

You see, most dryer motors are not speed controlled per se. They are designed to give a certain output speed at a certain line frequency. Saves a whole lot on electronics (whole lot in developer standards, aka now where near 50 bucks probably). And further, you can probably optimise the motor to run at max efficency at that certain Hz number.

Onwards, most fabrics don't need special treatment tumbling wise to survive a drying in a tumbler (more on that later).
Bur, drying is a pretty random thing. Tumbling patterns of loads are incredibly complex. A load can be the exact same and tumble 100% differently. Some loads are lighter, thus not sticking to the drum as easy, others have items that are somewhat less airy, thus getting kind of "blown up".
So, manufacturers take an average speed to get most loads tumbling as good as possible.

Now, some could say "Why don't they add a sensing feature?"
Well, some did, kind of. I know that Miele and Electrolux both have sensing procedures, not for drum speed, but for reversing.
A load that becomes tangeled either rolls or drops as a bunch. No matter which configuration, anytime they hit a baffle, the motor has a sudden load peak, thus, if one would plot the power draw over time, there would be serious spikes noticeable. The electronic monitors those spikes and, if they get to big, they trigger a reversing cycle.
Now, why is sensing for speed not done? Well, my guess would be the randomnes of loads.
To put it extreme: You could have 100 pairs of thin socks in your dryer. Per se, they are light and tumble well. But a simple weight sensing cycle would say "Heavy load, slow down!". Thus, they'd roll and not dry well. On a mixed load, depending on sensing, the load would seperate in a bunch of clothing sticking on the wall and the rest tumbling.
Further, a 3D-sensor used for example on Panasonic washers (which watches the drum for sudden movement during wash in correlation to motor load) can't apply neither as the drum is rigged mounted.
So, sensing would most likely only lead to even more disturbance (at least, by my logic).

Anyway, some try to get arround this. Newest example in the EU: WPs hollow lifters, guiding air from the back of the drum through the lifters out of holes into the drum in a 90° angle to the regular air flow.


Sidenote: Electroluxes heatpump dryers here in Europe use actually up to 2 Inverters. One controlls the heatpump power on the A+++ models, the other drum speed.
Why? They usually stick to the same regime of speeds as a normal dryer. But there are exceptions:
On a night mode (only TOL models), they slow down to reduce noise.
During initial sensing, they slow down to max the sensor contact.
The wool cycle speeds the drum up to get the drying flat effect by fixing items to the wall.
The silk cycle tumbles verry slowly to reduce creases and wear.
There are probaly more varriants, but these are the few I know for sure.


Post# 845816 , Reply# 4   10/14/2015 at 13:00 (3,088 days old) by Stricklybojack (South Hams Devon UK)        

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You sir know a lot about dryers, thx Henrik.


Post# 845818 , Reply# 5   10/14/2015 at 13:03 (3,088 days old) by henene4 (Heidenheim a.d. Brenz (Germany))        

Most of that is just combination of what companys brag about they do have. AKA years of Google, YouTube and this site.

Post# 845864 , Reply# 6   10/14/2015 at 20:34 (3,087 days old) by Launderess (Quiet Please, There´s a Lady on Stage)        

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During several debates over operating a 50hz washer or dryer on 60hz (and vice versa) IIRC the upshot was motor speed for DC types depended upon frequency more than AC. Also things depended upon if the machine in question had any sort of speed controller.


Post# 845889 , Reply# 7   10/15/2015 at 00:09 (3,087 days old) by kb0nes (Burnsville, MN)        

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Every once and a while I think that it would be neat to modify a dryer to have a variable tumble speed.

With a dryer like one of the traditional Whirlpool designs it would be as simple as cutting off the rear motor shaft then mounting a small motor in front of the existing motor solely to turn the drum. Drive that motor with a small variable frequency AC inverter and tumble speed would be easily varied. With a belt tensioner redesign the drum could also be reversible.

Initially I figured the speed could just be manually adjustable to set where it works best. But since we have easy electronic speed control, why not ramp the speed up and down to break up balling resonances during the cycle? It would also be possible to add an ultrasonic sensor to actually "observe" the tumbling action and make the speed interactive! Once you add some smarts then its only software to really make a machine adapt to conditions.


Post# 845909 , Reply# 8   10/15/2015 at 04:04 (3,087 days old) by richnz (New Zealand)        

Would the dryer need to speed up or slow down as the load dried?

I think to have the machine adjust automatically falls into the too-hard for too-little return basket.

For instance 1 kg of towels would behave differently to 1kg of face-cloths.
I cannot imagine how residual moisture after spinning affects the way items tumble.

As for how a machine could distinguish between a load that had balled vs an overly full dryer. Well short of some sort of computer vision system.


Oh kinda related. I saw a YT video relating to AEG's dryer which dries woolen items. The item clings to the drum as opposed to tumbling.


Maybe a manually controlled dryer.
A window for the user to check the tumbling and two knobs. One for speed of rotation and the other for temperature.


Post# 845969 , Reply# 9   10/15/2015 at 17:33 (3,087 days old) by kb0nes (Burnsville, MN)        

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Rich,

Please bear in mind that my concept only amounts to spitballing ideas.

But if the hardware were added to allow for a variable tumble speed, then it would be silly to not make the system fully adaptive. Most all modern appliances have a computer in them now which allows for versatility and adaptability. Its just a matter of programming once we ditch the simple mechanical timer for something that runs code.

What I was envisioning was rudimentary form of computer vision, although it would probably be ultrasonic or infrared. It would be pretty simple to see that laundry items were falling independently in the drum rather then balled up for instance.

Since the system could be adaptive the speed could change depending on if the load were wet or dry or based on the articles in the load.

I'm sure it will never become a commercial product, I haven't a clue if it could aid drying efficiency which it would have to do to be cost effective. But if I ever find some free time, I may have one of these ;)


Post# 845974 , Reply# 10   10/15/2015 at 18:49 (3,087 days old) by Combo52 (50 Year Repair Tech Beltsville,Md)        
Dryer tumble speeds

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Historically only whirlpool in the 70s had a variable speed tumble on their dryers and Frigidaire also built a two speed motor on a few dryers in the late 60s. For 90% of drying variable tumble would be of little use but for certain loads that tend to ball up or stick to the drum it could be a real breakthrough.

 

Phil's ideas of having some sort of optical sensor to actually detect problems and correct them are good I've thought about this a lot myself. It would also be easy to do with today's technology.

 

I see absolutely no benefit in a reverse tumble on a full sized dryer, a dryer can be better designed if it runs and just One Direction. We have proven that very well in the US we have by far the best performing fastest dryers in the world. And none of our dryers reverse to do this. There were only ever to full-size dryers in the US that reversed tumbled the Philco from the late 60s and 90s Frigidaire built dryer. Neither were the least bit successful and had no benefit over the dryers but did not reverse.

 

My friend Bob in Cleveland and I took a 1974 whirlpool gas dryer with variable tumble and added a window to it. We also wired it so the light will stay on and it was really a marvelous dryer because you could watch the clothes tumble and you could find just the right tumble speed and pattern quite easily. In addition this dryer had a variable thermostat like a range has with a close cycling tolerance and a dual input gas burner that went up to 30,000 BTUs probably one of the best dryers we've ever used.


Post# 845979 , Reply# 11   10/15/2015 at 19:38 (3,087 days old) by stricklybojack (South Hams Devon UK)        
Yes!

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That what i'm talkin' about!
And when i say that i mean what John(Combo52) is talkin' about :)


Post# 845991 , Reply# 12   10/15/2015 at 21:41 (3,086 days old) by powerfin64 (Yakima, Washington)        
Variable speed whirlpool

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I own one of the whirlpool variable speed dryers. As john says, it is from the 70's. Mine is a 3 speed. small loads(slow),(medium) normal sized loads, Heavy large loads(fast)
Each speed is for a specific type of load to be dried.
Small loads- Delicates, knits, blouses.
Medium loads- towels,shirts, jeans, diapers.
Large loads- Quilts, sheets, bedspreads.
I haven't used mine in a while but I know it works, it is fun, plus it has a florescent light that lights up the cycle dial!


Post# 845992 , Reply# 13   10/15/2015 at 21:47 (3,086 days old) by powerfin64 (Yakima, Washington)        
Variable speed whirlpool

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I own one of the whirlpool variable speed dryers. As john says, it is from the 70's. Mine is a 3 speed. small loads(slow),(medium) normal sized loads, Heavy large loads(fast)
Each speed is for a specific type of load to be dried.
Small loads- Delicates, knits, blouses.
Medium loads- towels,shirts, jeans, diapers.
Large loads- Quilts, sheets, bedspreads.
I haven't used mine in a while but I know it works, it is fun, plus it has a florescent light that lights up the cycle dial!


Post# 845993 , Reply# 14   10/15/2015 at 21:52 (3,086 days old) by powerfin64 (Yakima, Washington)        
I got a error code when I tried to post, Robert

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"unable to connect/too many connections"

Post# 846154 , Reply# 15   10/17/2015 at 01:00 (3,085 days old) by henene4 (Heidenheim a.d. Brenz (Germany))        
Reversing

Quite useless on full size dryers, quite beneficial if done right on a compact\EU model.

Post# 846207 , Reply# 16   10/17/2015 at 12:29 (3,085 days old) by marky_mark (From Liverpool. Now living in Palm Springs and Dublin)        

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My experience has been that American dryers do seem to ball up certain types of bedding quite badly/quickly/frequently just as with Euro dryers.  I haven't found that the larger tumbler alleviates the problem.

 

Of course, I don't know if reversing would solve the problem.  But my observations do tend to suggest that it would perhaps lessen or solve the problem, particularly if smart-reverse technology were employed as discussed in the comments above.

 

My current Miele T1 heat pump dryer only reverses for 10 seconds every 5 minutes and it balls some bedding quite badly.  It has no form of adaptive/intelligent reverse and it's driving me crazy.  Miele say they are aware of the issue with these dryers and I had a tech out to update the software.  Still not happy whatsoever.  Another update is expected.


Post# 846225 , Reply# 17   10/17/2015 at 13:54 (3,085 days old) by marky_mark (From Liverpool. Now living in Palm Springs and Dublin)        

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I have also found that the American dryers I've used couldn't seem to cope with drying a single item (or a couple of lightweight items) because the tumbler rotated too fast and the items got stuck to the sides.  The result is wet patches and a lot of creasing.  All Euro dryers I've used could cope with a single item.

 

American dryers win hands down in terms of size and brute force (speed).  Euro dryers typically have heating elements of 2500 Watts and gas dryers made by White Knight in the UK have a 3000-Watt gas burner.  Whereas American electric dryers typically have elements of around 5500 Watts and gas dryers often have burners somewhere around 6500 Watts.  But I've found that other aspects of their design are not exactly cutting edge.  Overall I still think an American gas dryer is a sound choice though.



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