DC power source to an AC appliance

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  #1  
Old 08-30-04, 09:47 PM
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Location: Lake Hamilton FL
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Question DC power source to an AC appliance

Here in Central FL we were hit by hurricane Charley on Aug 13th. I was one of the lucky ones and I was without power until Aug 30th. Some are still without. THANK YOU VERY MUCH TO THE UTILITIES PERSONNEL AND PUBLIC SERVICE WORKERS/VOLUNTEERS!!!!! I DO NOT HAVE THE WORDS TO PROPERLY THANK YOU FOR YOUR TIRELESS EFFORTS TO HELP YOUR NEIGHBORS AND STRANGERS ALIKE. I CAN NEVER PROPERLY REPAY YOU FOR YOUR EFFORTS. THANK YOU AGAIN!! Onto the question..In short, my neighbor tried to finish a load of laundry by connecting his clothes washer to a 12 volt, deep cycle trolling motor battery. Now the washer will not function. What kind of damage will this type of connection do to the washer? Could there be an inline fuse that has blown? Could the wiring harness be melted? Could the motor itself sustain damage? I am completely illiterate when it comes to electricity. Any input would be welcome.
 
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  #2  
Old 08-31-04, 05:07 AM
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Location: Oregon
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In short, yes to all of the above.
An appliance will be designed to operate at 120V _AC_, or alternating current. This means that the voltage is constantly changing from + to -. The battery is much lower voltage (only 12V), but also _DC_ or direct current. This means that there is a constant steady voltage coming out of the battery.

There are many components in a washer that depend upon the constant change of the applied voltage. In particular, the _motor_ almost certainly requires the constantly changing voltage to restrict the current flow through the motor, and if you apply a steady voltage to it, lots of current will flow potentially burning up the windings. Even though the voltage is much lower, the motor doesn't limit direct current nearly as much as it limits alternating current.

Additionally, and electronic controls will depend upon semiconductor switches (SCRs) that can only switch alternating current. In going from + to -, with AC there are times when the voltage is exactly _0_, and the semiconductor switches depend upon these 0s. Older washers have mechanical switches, so this won't be a problem.

Once you have excess uncontrolled current flow, anything can happen, from motor windings burning out, to switch contacts burning out, to wires melting, to fuses blowing.

-Jon
 
  #3  
Old 08-31-04, 05:56 AM
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I hope he didn't connect t direct to the 12volts, but tried to use an inverter. In either case the washer is probably fried. I suspect the inverter was not large enough to handle the motor load and caused a low voltage situation. This could have seriously damaged the control ciruits.
 
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