# Circular saw burned out in 15 seconds



## TWheels (May 26, 2006)

Although I cannot find the thread right now, someone posted the idea that we were all purists, doing *everything* with routers, ripping, crosscutting, etc. Until a few weeks ago I was such a purist. My power tool collection included a jigsaw that had lost the ability to set cuts at 90°, a power drill, a dremel 300 series, and my router. In the interest of trying to get several projects done by mid August, I finally bought a circular saw, an Hitachi 7 1/4 inch model. After studying the instruction manual, and overcoming my spouse's fears about it, I finally tried to use it. I plugged it in, turned in on birefly, turned it off to adjust the cut, turned it back on and started the cut, and within a few seconds, it stopped and smoke was coming out of it. It felt noticeably warm to the touch. I did notify Hitachi and they are sending me a new one, so high praise for how Hitachi handled my situation.

Did I do something wrong? Does anyone need more information to diagnose the problem or did I simply obtain a defective saw?

Thanks very much


----------



## curiousgeorge (Nov 6, 2006)

Tom, it sounds like a defective saw. I do have a couple of questions... were you using an extension chord with the saw and, if so, what gauge was it? The reason I asked is if you were using say a 50ft 14ga. extension it could have caused the motor to overheat and burn up. People don't realize that a tool pulls a lot of power and you need to use no less than a 12ga. extension to handle the load.


----------



## Woodnut65 (Oct 11, 2004)

Hi Tom, what type of power did you plug into? Since this forum is available in other countries, we may not be talking the same AC power. I assume you plugged into 110 volt, 15 amp circuit, which is standard in the US. If that is the case, it sounds like a bad tool. A long extension cord with wire that is 14 gauge or less would cause the saw to run at lower voltage, due to voltage lost to resistance in the wire. But that would have taken more time. I suggest that you try the new saw without a blade in it, and with it plugged into the outlet directly. After it runs for several minutes, unplug it put the blade in it and try cutting some wood with it. Hope this helps Woodnut65


----------



## AxlMyk (Jun 13, 2006)

Since he lives in Illinois, I assume it's 120v 60hz.
A long, undersized extension cord, or the saw is bad.


----------



## TWheels (May 26, 2006)

I was using the same extension cord that I use with my Makita 3612C router, and there has never been a problem with it. The extension cord is the heaviest gauge I could find. 

Thanks for the suggestions. I will look into the extension cord issue, and when I get the new saw I will try it first plugged directly into the same outlet that the extension cord is normally plugged.


----------



## harrysin (Jan 15, 2007)

Tom, I presume that it is a portable saw as distinct from a saw table, if so what type of material were you cutting and were you using it freehand as distinct from following a straight edge/s. Most often when cutting a large panel I do it freehand then clean-up the edge with my 3612C against an Aluminium straight edge.


----------



## TWheels (May 26, 2006)

Harry, it was a portable saw that I was trying to use to follow a straight edge. I was trying to cut an UMHW guide. I cannot imagine that UMHW would be more difficult to cut than pine.


----------



## bobj3 (Jan 17, 2006)

HI mftha

" within a few seconds " " defective saw " 
I would let it go as a defective saw, They are going to replace with a new one so no big deal.. 
But if you have the same error on the replacement WELL then I would do some back trackong on the power cords etc.and the way you are using the saw..

They do make tools at 5:00 on a Friday  (speed kills)


=========





mftha said:


> Although I cannot find the thread right now, someone posted the idea that we were all purists, doing *everything* with routers, ripping, crosscutting, etc. Until a few weeks ago I was such a purist. My power tool collection included a jigsaw that had lost the ability to set cuts at 90°, a power drill, a dremel 300 series, and my router. In the interest of trying to get several projects done by mid August, I finally bought a circular saw, an Hitachi 7 1/4 inch model. After studying the instruction manual, and overcoming my spouse's fears about it, I finally tried to use it. I plugged it in, turned in on birefly, turned it off to adjust the cut, turned it back on and started the cut, and within a few seconds, it stopped and smoke was coming out of it. It felt noticeably warm to the touch. I did notify Hitachi and they are sending me a new one, so high praise for how Hitachi handled my situation.
> 
> Did I do something wrong? Does anyone need more information to diagnose the problem or did I simply obtain a defective saw?
> 
> Thanks very much


----------



## harrysin (Jan 15, 2007)

I suppose that it would be insulting to ask if the blade was the correct way round..........duck for cover.


----------



## TWheels (May 26, 2006)

harrysin said:


> I suppose that it would be insulting to ask if the blade was the correct way round..........duck for cover.


Harry, Duck!

The blade was already inserted when I obtained the saw. It appeared to me to be correctly oriented, and according to the manual it was.

The extension cord is a 14 gauge. Unless there is someplace where I live that I do not know about, there are no 12 gauge extension cords available here, and one online store came back with a "did you mean 14 gsuge", and nothing showed up on other web sites except Amazon.

What confuses me is that this extension cord is the same one I have used with my router (Makita 3612C) for two or three years and there has never been a problem. The cord is rated for the amount of current.

I do give credence to the explanation suggested by Bobj3


----------



## harrysin (Jan 15, 2007)

Tom, totally forget about the extension cord, this could NOT have caused the problem. I know that I'm dicing with death here but, are you using 220 volts, which wouldn't be unusual for a big machine like the Makita 3612C router, if this be the case, is the Hitachi saw rated at 110 volts? I won't duck for cover over this one Tom!


----------



## bobj3 (Jan 17, 2006)

HI Harry

In the USA the 220volt drop cords are real BIG ,20amp,30amp,50amp (50amp are about 3/4" OD cord size..) not to say anything about the spec.plugs ends on the drop cords.

Almost imposable to plug in a 110volt tool into one of them.or the other way around..


http://en.wikipedia.org/wiki/Domestic_AC_power_plugs_and_sockets#Polarized_plugs

========


----------



## harrysin (Jan 15, 2007)

My point Bj. was that if a 3 1/4" hp router works just fine, then the saw certainly will.


----------



## bobj3 (Jan 17, 2006)

Hi Harry

He is in the states,,, West Central,Ill. USA if I recall ,I have many 3 1/4 HP routers and they are ALL 120 volts 15amp., most people in the states don't have 220 volt outlets in the shop...maybe one for a table saw,welder or a air compressor but that's it.. the norn.

===========


============


----------



## TWheels (May 26, 2006)

My Makita 3612C is built for 110 V. In my day job I do use equipment that requires 220 V, and the plugs and outlets are so different that it would be impossible to plug a 110 V instrument into a 220V outlet or 220V into 110V. So Harry, your suggestion this time does not explain the problem. Bobj3 is right.

FYI Harry, I am a pacifist, conscientious objector during one of those wars (Viet Nam) that has no doubt set in motion what recently caused Her Majesty to revoke our grant of independence, opponent of every military action in which the U.S. has been involved since then, etc. (For Hamlin's benefit, let me state that I do fully support our troops however, and think we do not do nearly enough for them while on active duty or as veterans.) I would defend my family with the minimal force necessary to be successful. Yes, I was picked on and bullied in elementary school. There is absolutely no way I would every knowingly take any action for which you should duck.


----------



## BrianS (Nov 7, 2004)

mftha said:


> The extension cord is a 14 gauge. Unless there is someplace where I live that I do not know about, there are no 12 gauge extension cords available here, and one online store came back with a "did you mean 14 gsuge", and nothing showed up on other web sites except Amazon.


Tom, they are available, I've got 2 of them. Mine were home made ones, but commercially I think they are available as contractors cords. This is one I found after a quick search: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96709

Brian


----------



## TWheels (May 26, 2006)

Thanks Brian. While the consensus and expert opinion (Harry, Bobj3, Axlmyk, Woodnut65) is that the problem is not the extension cord, I still will obtain a 12 gauge because I believe it is always wise to have more capacity than one anticipates using.


----------



## bobj3 (Jan 17, 2006)

HI Tom

If you want a 12 gauge drop cable just stop by HD/Lowers/Ace Hardware and pickup some cable and make your own cheap,,,they have reels and reels of cable and the ends you will need..

But I would suggest you make them 25ft long that should do it for a shop drop cord, you can always make two of them....I would also suggest you put a 4 gang box on one end..
can't have to many outlets 

===========


----------



## Hamlin (Dec 25, 2005)

Hi Tom,

I had some similar happen to me several yrs ago when I first bought my Milwakee Zawsaw, turned out, a wire came loose on the switch, fact. default. Cost me $30 to get fixed. Took it to a local repair shop. (Didn't have time to fix it myself).

I usually make my own extension cords, I use 8 to 10gauge wire. Yes, it's overkill but, have yet to fry any power tools.

Regards,


----------



## harrysin (Jan 15, 2007)

At the risk of really having to duck for cover may I respectfully suggest that the USA not only comes into the 21st century by going fully metric but also goes to at least 220 volts (we have 240), that way your cables won't act as heaters because as our old friend Mr. Ohm discovered, doubling the volts halves the amps, hence lighter and cooler cables!
I'll prepare a white flag just in case I'll need it to re-enter the forum.


----------



## bobj3 (Jan 17, 2006)

Hi Harry

Boy would that be a night mare  ,,,,I think the USA would go bankrupt for sure paying the bill for that update.. LOL LOL LOL 

=========


----------



## TWheels (May 26, 2006)

Harry, when Her Majesty implements her decision to rescind our grant of independence, what impact will that have on our electrical grid? Will we be rewiring and need all new appliances etc (or a large number of transformers)? Now there would be an economic stimulus, especially if the electricity is generated from wind, solar, etc. and not by burning fossil fuels.


----------



## TWheels (May 26, 2006)

I now have a major cleanup problem: removing egg from my face and everything else. Thanks for all the great advice in this thread. I do now have a 12 gauge 25 ft (7.6 m) extension cord. I received the new circular saw from Hitachi, and followed Woodnut65's advice, although I did not remove the blade, for fear of making Harry's question a self-fulfilling prophecy. I plugged in the saw directly to the outlet, squeezed the trigger on the saw and……nothing! The circuit breaker had tripped. Apparently there is nothing else of any importance on that circuit. When I reset the breaker, and tried the saw again, IT WORKED. There was a slight odor of smoke, but my guess is that was the brushes. I then tried the one I had declared to be burned out. It works! Of all the obvious things to overlook! But if it is rated for 15 amps why would a 20 amp circuit breaker have tripped?


----------



## curiousgeorge (Nov 6, 2006)

That's funny, if not a little embarrassing.  But, we all have the habit of overlooking the obvious thinking it has to be more technical than a tripped breaker.



> But if it is rated for 15 amps why would a 20 amp circuit breaker have tripped?


Any number of reasons... Old (weak) breaker, saw blade got jammed causing a power surge, external line surge, a short circuit.... You name it.


----------



## harrysin (Jan 15, 2007)

"But if it is rated for 15 amps why would a 20 amp circuit breaker have tripped?"

You may not be aware Tom that the start-up current of a motor is about six times the running current and this must be taken into account when choosing a circuit breaker for a motor circuit. It is not uncommon for circuit breakers to occasionally trip for no obvious reason.


----------



## rwyoung (Aug 3, 2008)

When an AC motor starts, it draws MUCH more than its rated nominal load current. If the motor was defective, blade jammed, etc it can easily draw much more than the 40A (takes about double current for a few seconds to pop). The 14 gauge extension cable would just act like a dropping resistor in line with the motor. A dead short in the motor (or a stalled/jammed motor) at the end of a resistor is still sufficient to blow a breaker.

Most "small" residential breakers (those without leakage current detection abilities) operate on the ferromagnetic principle. As the breaker heats up from current draw, it changes the magnetic properties of a small part inside the "catch". Loose enough of the magnetic properties and it will pop. There are other features for arc quenching and a mechanical snap-action to hold things open.

These things aren't exactly manufactured to aerospace tolerance, probably 10% or even 20% tolerance so a 13A load at the end of a long run of Romex could blow a 15A breaker "for no obvious" reason as the breaker heats up.


----------



## Thrifty Tool Guy (Aug 23, 2007)

Harry,

Relative to your comments about 220V and the metric system.........I think we're already there. At the pole (i.e., transformer), we receive 220-240V 60-Hz power to our houses. For safety reasons, we split that to 110V for small appliances and lights. However, you have a point relative to the Joule losses in our homes. But, if you're going to pick on our joule losses, I'll expect you to apologize for the generation inefficiency of 50-Hz power. What an unforgivable travesty in these days of global warming.

Now, the metric system. Believe it, or not, outside of the construction and agricultural equipment businesses, most US production is metric or metric compatible (i.e., american cars). IMHO, we've made the conversion, but our politicians like to grandstand on dead issues. "Save America......Measure in Inches!" or "You'll only take my yardstick from my cold, dead hands" 

TTG


----------



## jerrymayfield (Sep 25, 2004)

The nominal voltage in this country has been 240 vac for over thirty years. I was in the electrical business for over forty years as an electrician,a contractor and an electrical engineer and I find many of these responses very inventive.

Regards

Jerry


----------



## harrysin (Jan 15, 2007)

TTG,
"For safety reasons"

Wow, that makes it sound like we have people being electrocuted day in day out, not so.
As for the frequency, well there's little difference in transformer size between 50 and 60 Hz, now if we went to 600 Hz as I think aircraft do or used to use, than that would be different.
Jerry, what country do you live in? What specifically do you find to be inventive in the above posts?


----------



## Thrifty Tool Guy (Aug 23, 2007)

Harry,

Well, Europe had Tesla and the US had Edison. Standards evolve and are definitely result of politics. In the end, claims of safety are always the last refuge.

However, you are on the bottom of the earth and live in a country primarily populated by sheep. No doubt your concept of safety is a bit different than ours. Just like the toilets, ours flow down, while yours flush up.

Best wishes and thanks for being a good sport.

TTG


----------



## harrysin (Jan 15, 2007)

"while yours flush up."

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


----------



## malb (Sep 15, 2008)

Thrifty Tool Guy said:


> However, you are on the bottom of the earth and live in a country primarily populated by sheep. No doubt your concept of safety is a bit different than ours. Just like the toilets, ours flow down, while yours flush up.
> TTG


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.


----------



## harrysin (Jan 15, 2007)

Malb,I won't agree with all you said for fear of upsetting any Kiwi members who live here in Australia, but having been retired since 2000 I bless the day that I decided to pay into a private retirement fund, without it I doubt that I would be able to keep up with my hobbies and would certainly be living a totally different lifestyle.


----------



## Thrifty Tool Guy (Aug 23, 2007)

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 (Oct 14, 2008)

mftha said:


> Harry, Duck!
> 
> The blade was already inserted when I obtained the saw. It appeared to me to be correctly oriented, and according to the manual it was.
> 
> ...


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 (Oct 14, 2008)

Thrifty Tool Guy said:


> Harry,
> 
> Relative to your comments about 220V and the metric system.........I think we're already there. At the pole (i.e., transformer), we receive 220-240V 60-Hz power to our houses. For safety reasons, we split that to 110V for small appliances and lights. However, you have a point relative to the Joule losses in our homes.
> TTG


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 (Aug 7, 2008)

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 (Oct 14, 2008)

Microsuffer said:


> 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.


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/electric_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/Publications/maglev/inductionmotors.pdf
http://books.google.com/books?id=k2...hl=en&sa=X&oi=book_result&resnum=12&ct=result
http://books.google.com/books?id=a9...hl=en&sa=X&oi=book_result&resnum=14&ct=result
I found information on some very large induction motors.


----------



## Microsuffer (Aug 7, 2008)

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_g...ield-keywords=12-guage+extension+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 (Dec 25, 2005)

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. 



> The circuit breaker had tripped. Apparently there is nothing else of any importance on that circuit. When I reset the breaker, and tried the saw again, IT WORKED.


----------



## Microsuffer (Aug 7, 2008)

Ha! I hadn't been following closely for a while so I missed the breaker fix comment. Also, while I've never thrown a breaker by binding the blade, I did get my 12-guage extension cord using my CS while working on an addition to my house some years back. That popped the breaker solid. Still using the two cords...and the saw. Does that let me in the club?


----------



## johncs (Oct 14, 2008)

Microsuffer said:


> 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."
> 
> <snip>


The fact that anyone says "thus and so" does not make 'thus and so" the truth. The para you cite has no explanation and no reference. However, the question occurs later in the article.


I took up the question with John Storey, the author of one of the articles I mentioned. He's given permission for me to quote him to you.


> The statement "Under voltage fries induction motors pretty well" is a curious one. I have heard this before(!), but I have never seen any evidence for it, nor a good explanation. Maybe it is just an urban myth. However, it's also just possible that it's true, for the following reason. With most motors, as you increase the load and hence slow the motor down, the torque increases. In the case of a permanent magnet motor (or a series wound motor, or a "universal" motor), the torque is maximum when the motor is stalled. So, if for some reason the motor was running under-voltage and hence turning slower, it would nevertheless produce all the torque it needed to keep spinning. However, some induction motors (but not all - it depends on the design of the rotor) achieve maximum torque when running close to their maximum speed, and the torque they produce at lower speeds (including stalled) is much lower. Such a motor might, if fed from a voltage that was too low, be unable to produce enough torque to get properly up to speed, and would stagger along at a lower speed drawing a lot of current and eventually "fry".



From your wikipedia article, I see the turning speed is a function of the supply frequency (as produced by accompanying electronics, not necessarily the supply), but not the supply voltage and not the supply current.

If the frequency supplied says "run at 1200 rpm," but I have some bloody big Stilsons attached to the axle and hold it so it cannot turn at all, then it will draw all the current the resistive (does impedance matter here?) circuit will allow and likely the smoke will get out.

When the motor is first turned on, this is roughly the situation, and it draws up to nine times its full load current. Ordinarily, the motor immediately starts turning and the situation is alleviated.

If there's no load and the voltage is reduced, I don't see a problem, the motor won't want any more current anyway.

If the motor is under significant load and the voltage is reduced, then I suppose it might try to draw more current (P=VA), if has fewer volts it wants more amps.

An electrician in another forum noted that fuses are to protect the infrastructure, not the load, so I guess the motor might fry itself.



Given the number of power outages I've heard California has suffered in the recent past, if this is a real problem, I'd expect to have hard of significant large failures. Maybe Arnie getting stuck in a lift[1] or something
[1] Elevator to those on the wrong side of the Pacific.


----------



## AxlMyk (Jun 13, 2006)

johncs said:


> [1] Elevator to those on the wrong side of the Pacific.


In 1853, E. Graves Otis sold his first "Life-Saving Steam Elevator".
http://www.otisworldwide.com/d31-timeline.html

Hmm. I believe we are on the correct side of the Pacific/World.


----------

