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Back EMF

http://www.google.com/search?hl=en&q=%22back+emf%22

As a fix, or as another diagnostic tool, before you apply power, if you can spin the saw blade in the direction of normal rotation just a few RPMs, this will take some of the kick out of the startup surge.

Do not qualify for a Darwin Award. If you do not fully understand what is below, don't do it.

With this marginal saw, possibly putting the tip of a phillips screw driver blade into the hole that all these blades have, and giving it a shove, may be enough.

A safer but more inconvenient way is to spin up the blade with a drill motor, 3/8" drive socket and drill-chuck/socket adaptor. The socket mates with the saw bolt head.

You are looking for the minimum RPMs to prevent the breaker from tripping, most or all of the time.


BTW, I'm just about "out of cards to play."
At this point I'd decide on the most likely cause and pursue that cause.
For the money riding on this, it's almost worth it to rent additional test equipment to trace the cause.

Or, if you can get past the Marketing People at Hitachi, a Hitachi Application Engineer will probably help you (at risk to his job). This problem and its solution is probably common knowledge on the factory floor at Hitachi.
Try to do this by phone. If the main Hitachi number ends in a number like 8000 or 6000 or something, try dialing 8001 or 8002 to get to speak to an ordinary person. Then ask for "the Application Engineer that you were just talking to."

That's how I got to talk to a person at the IRS who actually helped me. Do not underestimate the arrogance of large organizations.

Or, tell Hitachi you have a question on the Technical Service Bulletin that is out on this problem. Or the (hidden) warranty on this problem.

Getting your foot in the door may also work with e-mail. Address it to something like [email protected]

I had a slime-ball Auto Dealership deny that there was a problem with their cars' headlights burning out, but he did say that there were aftermarket solutions to this (problem which he never admitted was widespread in some of his cars).
Hitachi may admit to a similar solution if they don't want to lose face but still want to help you.

The more knowledgeable you sound, the less likely they will give you BS. Probably all Public Relation Types don't want to risk being caught in a deception. The appearance of credibility is all they have.
And you can always say that you will run their answer past someone knowledgeable who chooses to remain unidentified (this Forum!!!).
 

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made a measurement on my saw

If your saw is like mine, you'll need a breaker that can stand 60A for .0083 seconds; maybe even 90A.
The trip curves will show what the breaker can stand.

You are supposed to already have that much capacity.

Sounds like a bad breaker.

The reason your saw trips the breaker only occasionally is maybe because you happened to turn it on when the AC waveform was at its peak of ~170v. This might happen 1 or 2 times for every 4 times you turn it on.

Please post back with what you finally did on this.:)
 

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Discussion Starter #43
If your saw is like mine, you'll need a breaker that can stand 60A for .0083 seconds; maybe even 90A.
The trip curves will show what the breaker can stand.

You are supposed to already have that much capacity.

Sounds like a bad breaker.

The reason your saw trips the breaker only occasionally is maybe because you happened to turn it on when the AC waveform was at its peak of ~170v. This might happen 1 or 2 times for every 4 times you turn it on.

Please post back with what you finally did on this.:)
Yoyizit & everyone else invloved;

I wanted to post back on this topic with some results and Thank everyone again for all the imput.

I went over to my dad's yesterday and did some testing. He had been out of town for days and that delayed the testing.

I pluged the saw into the extension cord, and I put a digital meter into the same outlet that the cord is pluged into. The voltage droped from 120(sometimes reads 121) to 114 when the saw was started / run. The saw did NOT trip the breaker during our testing while it was connected to the extension cord.

The saw pluged into one of the circuits on one of the outlets that is close to the panel, where it trips the breaker, reads 120 to 121 regular voltage. Then it only every drops to 116 at the lowest when the saw is run - This is the connection where the breaker will trip.

So from the testing we have done, it appears that using the extension cord (about 40') causes enough voltage drop to prevent nusiance triping.

While this does not necessarly 100% solve the mystery, it does offer an easy solution to the problem.

My dad and I appricate all the information, and he is greatful that a easy solution was arived at, nice and easy - use an extension cord.

Some day I will get a better meter and be able to take some more accurate readings. However for now the mystery will remain, and I will be happy that there is a easy solution.

Thanks again,
Jamie
 

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I pluged the saw into the extension cord, and I put a digital meter into the same outlet that the cord is pluged into. The voltage droped from 120(sometimes reads 121) to 114 when the saw was started / run. The saw did NOT trip the breaker during our testing while it was connected to the extension cord.

The saw pluged into one of the circuits on one of the outlets that is close to the panel, where it trips the breaker, reads 120 to 121 regular voltage. Then it only every drops to 116 at the lowest when the saw is run - This is the connection where the breaker will trip.

So from the testing we have done, it appears that using the extension cord (about 40') causes enough voltage drop to prevent nusiance triping.
What gauge extension cord? It will be stamped on the insulation.

If you cut wood with this cord in place, it should be at least as heavy as your manual recommends for a cord of this length, so you don't shorten the life of the motor.
 
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