Circular saw burned out in 15 seconds

harrysin

"while yours flush up."

Is THAT why I've always got a wet bum?

__________________
Harry



Nothing but heaven itself is better than a friend who is really a friend. - Plautus

malb

Sorry, but in your comments about sheep, you are confusing us Aussies with our near neighbours the Kiwis from New Zealand.

Australia is primarily populated by Kiwis from New Zealand who come her because it is much easier to live on our welfare system than theirs. Next is working Aussies paying taxes to support the social welfare system. Then there is working age Aussies living on the social welfare system because thats how their parents raised them. And finally, there are the senior Citizens who did eveything for Australia through a fifty year working life on the promise that the country would care for them when they reached retirement. They are the ones who get the lousy deal from the social welfare system.

And I am a working Aussie, not a senior citizen or social welfare recipient.

Thrifty Tool Guy

Harry,

Let me tell'ya about these 401(k) things we have in America. You put the money in and hope for a return before the bank/brokerage fails.

TTG

johncs

Seems to me the extension cord issue is a red herring. If it's too long, it will dissipate too much power and the saw may consequently lack power.

I don't see it overheating, that would occur if you fed it too many volts, not too few.

Harry might not remember this, but Western Australia used to run on 250VAC, to overcome excessive line drop (akin to a too-thin extension cord). Irecall dropping in on the SEC in Busselton in 1965, where I was shown a graph of the voltage supplied to the town for the past 24 hours. It was consistently over 260VAC.

In the 70s (I think), some TV sets expired, presumably because of too many volts and the SEC found itself compensating consumers.

I reiterate, I don't think a too-light extension cord will cause this kind of problem.

johncs

I don't hear of many people being electrocuted by domestic power transmission lines take someone occasionally.

OTOH I'm not keen on the idea of a power supply fused to allow 40 amps, that sounds like a fire hazard to me.

Microsuffer

Under voltage fries induction motors pretty well. They are fairly quiet and typically found in drill presses and table saws. Universals, which are generally found in drills and circular saws run slower with lower voltage, but don't tend to be harmed by it. They are quite noisey.

johncs

I've done some googling to try to find a reference to support your argument that low voltage can harm an induction motor, but haven't been able to. If you can find some evidence, I'd like to see it.

I did find lots of interesting reading, including:
http://www.phys.unsw.edu.au/hsc/hsc/...ic_motors.html (but ignore the black wire)
http://www.ece.villanova.edu/~singh/ece8830/88303a.ppt This very quickly descened into maths beyond my comprehension
http://eece.ksu.edu/~starret/589/man/I.html "It is not uncommon for such motors to be in daily use for more than half a century, with the only maintenance being a new set of bearings every ten years or so."
http://www.dot.state.co.us/Publicati...tionmotors.pdf
http://books.google.com/books?id=k22...m=12&ct=result
http://books.google.com/books?id=a98...m=14&ct=result
I found information on some very large induction motors.

__________________
John

Microsuffer

Check http://en.wikipedia.org/wiki/Under-voltage_(brownout) with the following statement in the section on "Effects of a Brown Out".

"AC Induction and three phase motors will draw more current to compensate for the decreased voltage, which may lead to overheating and damage of the insulation on the motor's field windings."

However, I agree that the cord is likely a red-herring. My suspicions would be at a) binding of the blade in a cut (easy to do), or b) a bearing that died early. If the blade still turns freely, then the bearing is eliminated.

As to a heavier cord, a quck search for a "12-guage extension cord" on Amazon returned 2 hits - http://www.amazon.com/s/ref=nb_ss_gw...n+cord&x=0&y=0 and any good hardware store will have them under the label of "heavy duty".

If OP's cord is old, then it might have a compromised connection at one or the other end. It happens. Inspect closely. However, if it still runs a similar motor load without problems then I think we can safely ignore the cord.

Hamlin

Hi,

While a "brown out" is just as hard on an electric motor as too high voltage. I believe you 2 have missed the part that Tom has found the problem.

__________________
Ken

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