I’m a mechanical engineer, working on large petrochemical rotating equipment. My good friend Sean is an architect. I thought maybe he could help me out on a little issue. The email exchange sort of went like this:
Michael: The motor I’m buying is 5105 amps. Do you have a good source for a circuit breaker? The voltage is 12,000v at the motor terminals.
If you’re an engineer / architect / tech of some sort, that’s a fun question. If you’re not, that was greek. Here’s some examples to put those in perspective:
- 60 watt household light bulb: 0.5 amps at 120v
- refinery motor: 5105 amps at 12,000v.
Sean: Are you buidling a hydroelectric plant to power this motor?
Fun Exercise: How many “D” size batteries would be required to run this motor and how long would this last?
Dang it, Sean’s putting me to work. First, I’ll need to find out what a “D” cell battery is good for. I’m going to have to ignore that whole “single phase DC power” versus “three phase AC power” for this exercise.
Michael: Nah. I just plug it in. I use an extension cord if I have to. Supplying the power is Electrical’s problem.
A D cell battery is 1.5v and rated for 18 amp-hours. I’d need (12000/1.5) = 8000 “D” batteries lined up end to end, and they’d last just under 13 seconds. I’d need 284 columns of 8000 batteries, or 2.272 million “D” cell batteries to make it last an hour. I’ll suggest it, but I don’t think Electrical will like this solution. I’ll stop by Kroger on the way home.
I checked, by the way. Kroger only had about 30 “D” cell batteries available.
Chasing the Wind 
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