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Dryer dry time and 240/120VAC

micabay

1,976 views

Today's customer was complaint: Dryer taking too long to dry.
blogentry-82846-0-91809500-1439502238_th
Here in the states, our homes are typically wired for 240/120VAC. Some are 208/120VAC systems but that is for another day/story.
The heater in this Samsung Dryer is 9.5 ohms.
Pictured above, the dryer was found hooked up incorrectly, with L1 and Neutral being hooked up backwards when the movers installed the new dryer cord. Which means the heater element was only getting 120 Volts rather than 240 Volts as it was designed.

 

What does this mean for our poor drying complain? The heater in this Samsung Dryer is 9.5 ohms. The heater was supplied with 120 VAC (incorrectly).
9.5 ohms @ 120VAC =1516 Watts.
Now if the dryer was hooked up correctly, blogentry-82846-0-04947400-1439502257_th the heater would be getting 240 VAC.
9.5 ohms @ 240VAC= 6063 Watts. Watts is power output or heat. 1516/6063=.25 or 25% of normal output wattage.....

 

Dryer taking too long to dry. Her quote when describing the problem: "I have to run the dryer about 4 times to get a fully dry load."

 

The best part about this story, the manufacture color codes the wires from the dryer to match the dryer cords. Just in case there is any confusion, they have also attached a pretty picture. blogentry-82846-0-38007600-1439502270_th

 

Bonus Question: What would have happen if you hooked up the cord incorrectly with L2 and N switched?
blogentry-82846-0-44893800-1439506026_th




11 Comments


Smashycomman

Posted

If I'm not mistaken, you'd fry the main control board by putting 240vac through it, yes?

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1st off, I'm glad nobody died here... the whole chassis was hot before your fix and had somebody completed the circuit via ground they'd be bitten. 

 

Lucky for them they didn't switch L2 and N otherwise they'd be buying a new board.

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I think acfixer is right. I didn't know what the other problem would be until I read acfixerdudes reponses, but it makes sense to me. The polarity to the board was switched.  But that must have not effected the board or they would not have been able to dry at all.  Which make sense now that I think about because the digital components are powered via the transfomer.  Corrected? 

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1st off, I'm glad nobody died here... the whole chassis was hot before your fix and had somebody completed the circuit via ground they'd be bitten.

The chassis was not hot. The bonding jumper is directly connected to the Neurtral wire of the dryer. It would have tripped the breaker almost instantly if this was hooked up for a three wire cord rather than the four they needed for their home.

These folks had been using this dryer like this for four months, before they called me because it wouldn't start, broken belt.

On older, timer controlled dryers, the contacts in the timer would handle the higher voltage long enough to fry the motor. On this computer controlled model, it likely would have fried this board. We may never know. Unless anyone has computer controlled dryer they would be willing to donate to science?

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Samurai Appliance Repair Man

Posted

If L2 and N were switched, you would have been putting 240vac across the transformer, motor relay contacts, light bulb, and motor.

 

The motor relay is probably rated at 240vac anyway but, even if it weren't, the worst that would've happened would be that the relay contacts would have burnt.

 

The transformer primary may be affected by the higher voltage but the bigger effect would be the higher secondary voltages which may take out the on-board rectifier.  

 

The light bulb would glow very bright for a few moments and then burn out. But this would've been a secondary concerns to the primary one which is that the motor would have 240 V AC across it.

So the real bonus question becomes: What happens to a motor that's rated for an operating voltage of 120 V AC that has 240 V AC applied to it?

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And it Burns, Burns Burns that ring of voltage...

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Here Now Tech

Posted

Would it short the Overload Protector?

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micabay

Posted (edited)

22 minutes ago, Here Now Tech said:

Would it short the Overload Protector?

Short? No.  The motor would rotate faster, until the overload heats up, opening the circuit.  Trip may be a more appropriate term than short.

Edited by micabay

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hathawayrepair

Posted

On 5/1/2016 at 3:27 PM, micabay said:

Short? No.  The motor would rotate faster, until the overload heats up, opening the circuit.  Trip may be a more appropriate term than short.

Had a service call for an older Whirlpool dryer w/timer, L2 and N crossed.  Drum tumbled super fast for about 5 seconds and then overload would trip.

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