# Electronics 115v from 125v???

Discussion in 'Modding' started by PetDMC, 9 Jul 2003.

1. ### PetDMCWhat's a Dremel?

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hi guys,

i need some help with this, i have a blower motor (AO Smith) and its meant to run at 115v but my main supply is 125v. the problem i'm have is that the motor starts to get hot (50*C+) i have a dimmer on it but it still gets hot.

now what kind of resistor should i get?

Motor spec:
1/20 HP, 1PH, 115V, 60Hz, 2.45A
1550 RPM, CWLE, TP, INS, CL "B", speed two

thanks

2. ### SmilodonThe Antagonist

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well... on the mains power you can have up to +/-10% of the voltage... (umm.. was that sentence well-formulated???)

this means that if your supply is 110volts you can have 11volts more or less.. (99 to 121 volts)

this goes for the motor aswell... that means that your motor gets 4 volts more than it REALLY can take... but in this case i really don't think it matters...

electric motors do get hot... it's normal...

if you should have a resistor on that thing you would need a pretty large one... should handle about 800watts... that is 3200 normal resistors...

i'm no expert in this field... so if anyone want to shoot me.. go ahead..

3. ### cpemmaEcky thump

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The resistor needs to drop 10v at 2.45A, so only 24.5W (bang you're shot ).

Value will be 10/2.45 = 4R. I'd be tempted to try 3 x 12R in parallel, and use at least 15W for each to cope with the higher starting current.

They'll get stinking hot so mount them where the air can get round them but nobody can touch the leads (125v hurts)

Don't expect the motor to run cool at 115v, I agree with Smilodon there.

4. ### SmilodonThe Antagonist

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umm.. yeah.. i always mix that up... anyway.. the motor itself draws abour 800W (730W=1HP plus some loss)

some of that is given out as heat... (20% IIRC)so you have a little oven there...

same with monitors... people keep complaining about that they ute so much power... but ALL the power is given off as heat so... and this heat heats your house... duh: )

5. ### PetDMCWhat's a Dremel?

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holly crap

i'll just slap on some heatsinks

6. ### SmilodonThe Antagonist

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well... heat isn't as harmful to a electric motor as it is to a CPU...

7. ### AmorphusWhat's a Dremel?

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if this is AC you could use a transformer, too. could probably pick one up at a local electronics shop (prolly not Radioshack)

8. ### viridiusWhat's a Dremel?

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Just slap an inductor in there and use the reactance. No significant loss from heating.

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