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Variable speed motors on dual motor dryers, need understanding

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Posted: Wed Mar 17th, 2010 10:19 pm

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rick_dryerbox
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I understand that a version of the Sears Kenmore Elite and Whirlpool Cabrio dryers can have two motors, one drives the drum rotation and a separate motor drives the air blower. The blower apparently is variable speed and automatically ramps up to a pretty high speed near the end of the drying cycle. Does anyone know why or what benefit this is providing? Also, how popular this concept is in other manufacturer models?

I’ve been working on the firmware code for the LintAlert dryer safety alarm, and this variable speed issue in some dryer models creates a challenge in the LintAlert firmware code as it initially monitors the back pressure in the dryers’ exhaust system. Any variation in the speed would skew the results.

Thanks for any assistance.

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Posted: Wed Mar 17th, 2010 11:31 pm

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TroyAC
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The harmony (GE) dryer has this same set up. I know that this type of system is able to have longer vent systems. I have changed a few of these motors out, including my own. It will quit drying when the motor does not reach a set RPM speed. As far as the full advantage, I really dont know if there is one that jusitfies all the extra parts. Though dispite being a GE, the harmony set has held up pretty good in our house with 4 kids.

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Posted: Wed Mar 17th, 2010 11:44 pm

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rick_dryerbox wrote: ... LintAlert dryer safety alarm ...probbaly not needed on the GE Harmony (made by LG)

The addition of a dedicated blower motor enables the dryer to alter fan speed whenever necessary to optimize air flow.

The blower motor is a DC, variable speed motor capable of operating at different speeds in response to changing air temperature and venting impedances.

The dryer uses dual thermistors to monitor incoming air temperature as well as the air temperature leaving the drum.

The sensors work together with the variable heater and blower to provide consistent even heat.

This enables the dryer to respond quickly to temperature changes and ensure proper air flow to optimize drying effectiveness.

This capability greatly increases drying performance and efficiency.

Normal blower speed will vary (1100 - 2700 rpm) depending on installation and venting conditions.

Below 1000 rpm, the dryer control turns the heater off.

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Posted: Thu Mar 18th, 2010 11:17 pm

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rick_dryerbox
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Thanks Reg...

Boy, how do you know so much about this one unit. Could it be assumed that startup on any setting likely uses a "norm" or consistant rpm and not until some event would it alter the speed.

Do you have one of these units, or have worked on them. What other manufactureres offer a variable speed exhaust motor.

Would like to learn as much as I could about the entire cycle as it relates to rpm adjustments throughout the cycle, and how different knob settings effect the rpm's as well. Thanks very much.

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Posted: Thu Mar 18th, 2010 11:39 pm

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appl.tech.29501
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i have worked on a few of these and the blower rpmm's will increase as the mperature does but doesnt vary a whole lot once normal operating temps are reached (140-170 F). Whirlpool also has a dryer with this system that they manufacture for sears.

I personally dont like these systems at all, I do understand the reasoning behind them as far as efficiency. however, they are no more efficient than the standard dryer system if the venting is not properly done.

But unfortunately we will be seeing more and more of these...there not going anywhere...you can thank the Gubment for that.

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Posted: Fri Mar 19th, 2010 12:05 am

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rick_dryerbox
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appl.tech.29501 wrote: i have worked on a few of these and the blower rpmm's will increase as the mperature does but doesnt vary a whole lot once normal operating temps are reached (140-170 F). Whirlpool also has a dryer with this system that they manufacture for sears.

I personally dont like these systems at all, I do understand the reasoning behind them as far as efficiency. however, they are no more efficient than the standard dryer system if the venting is not properly done.

But unfortunately we will be seeing more and more of these...there not going anywhere...you can thank the Gubment for that.

Thanks Zenzoid, ... my desire is to dial in the firmware code on our LintAlert device to also work with these variable speed dryers. Knowing why and when they ramp up or down would help me in determining the best time to "calibrate" and how often to monitor.

From your reply, it sounds like initially the unit starts up at a low rpm, and as temp increases, so does the rpm, likely within the first 60 seconds it might be at max rpm and perhaps hold that.

My instructions could be such that calibration should be done at a paticular setting, if this setting was providing the max rpm, perhahps its airfluff.

Can you take a moment and watch my technical video on the LintAlert. Your comments would be appreciated. We had someone with subject dryer model calibrate and at the cool down portion of the cycle, it ramped up and triggered the final alarm stage, likely a 50 % increase in back pressure from the initial calibration.

Thanks again.

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Posted: Fri Mar 19th, 2010 12:09 am

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rick_dryerbox
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http://www.lintalert.com/technicalvideo.htm
Forgot link to technical video

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Posted: Fri Mar 19th, 2010 12:10 am

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appl.tech.29501
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post a link and i will be glad to watch it.

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Posted: Fri Mar 19th, 2010 01:04 am

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RegUS_PatOff
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my previous message was from the GE Harmony service manual

It looks like it's self monitoring and Dryers in the future will also likely be self monitoring also.

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Posted: Mon Mar 22nd, 2010 05:44 pm

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rick_dryerbox
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Troy, Reg, and Appl, gotta say I appreciate your assistance with these unusual dryers. Each of your replies were helpful.

I'm still on a mission to confirm "when" there is vatiation to the blower motor speed. Or if I could confirm with someone that startup rpm's are always consistent, and its not until such event or time that variations can occur.

This way, I could code my LIntAlert to only look at the first x seconds to get or do a pressure reading from the exhaust conduit. ie, if we only looked at the first 12-15 seconds of the initial startup, and this period proved to always be at a paticular speed, no matter what type of drying cycle that was selected, then we could safely display the slow progression of lint build-up over a 1-3 year period.

In summary, if any of you could experiment with your dryer, and confirm the startup rpm on the blower side is consistent no matter what type cycle, and some feel for when it does ramp up or down, this would be great to know. I am willing to pay you for your time, donate to your beer fund, or send along a LintAlert.

Thanks again, looking forward to any replies and findings.

Rick in FL

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Posted: Mon Mar 22nd, 2010 07:45 pm

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RegUS_PatOff
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just wondering, why would anyone buy a LintAlert if the Dryer monitors itself ?

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Posted: Mon Mar 22nd, 2010 08:02 pm

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rick_dryerbox
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RegUS_PatOff wrote: just wondering, why would anyone buy a LintAlert if the Dryer monitors itself ?

Gosh, that is a good question. I am speculating that you mean, why would someone buy a LintAlert if they own a dual motor dryer, or do you mean the LG version that has some sort of built in lint build up alarm.

I think the only dryer that offers some sort of notification of lint buildup is one or a few of the LG versions, right. But having dual motors does not provide any monitoring feedback.

My current needs are to learn what is happening with the variations in motor speed... mostly at what point does it change, and is it always the same motor speed during the first 20 seconds of any of the various cycle startups.

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