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Old 10-18-2018, 09:03 PM   #1
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1990 29' Excella
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Furnace blower motor RPMs modified... is faster ok?


I found a form - fit - function replacement blower motor for my Suburban NT-30k furnace. (original no longer avail)

All except the rpms. The new one is 33% faster. I thought that this would be fine, but now I am thinking the fire box running cooler could cause water vapor to not be totally ejected from the fire box?

I have read about corrosive problems that need special design considerations in high efficiency furnaces.
Would these things happen in my case?

Am I thinking correctly or worrying too much?
I dont want to have a rusted hole in the firebox halfway through the winter.

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Old 10-18-2018, 09:26 PM   #2
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A resistor will slow the motor down, as will a potentiometer. Reducing voltage to reduce motor speed is an accepted method. Just make sure the method used is rated for the current used.
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Old 10-18-2018, 09:49 PM   #3
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1990 29' Excella
baltimore , Maryland
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Yes, I think reducing the RPMs is the best solution too.

Going to need several power resistors. Have to drop 4 volts and 60 watts to get supply voltage and RPMs down by 33%. That is if Vsupply and RPMs are linear.
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Old 10-18-2018, 11:34 PM   #4
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A more efficient way would be a PWM adjustable speed control.
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Old 10-18-2018, 11:54 PM   #5
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1990 29' Excella
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Yes, I have heard about using PWM.

What would this circuit look like?
Its got to take some heat.
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