Table Saw soft start - Router Forums
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post #1 of 14 (permalink) Old 03-23-2012, 02:18 PM Thread Starter
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Default Table Saw soft start

Hello guys
Is there a guy, (kinda Terminator or Rambo) able to give me the schematic of a motor soft-start of 1500 W.

I am searching since about 4000 years (yes i began my research when we went out of Egypt to find the Promise Land) and I never found such a schematic.

So knowing that American guys are the world's best guys, I came here and posted my small message, hoping that you will be able to help me.

Have a good day
Margeloc
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post #2 of 14 (permalink) Old 03-24-2012, 08:51 PM
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Assuming it is an induction(capacitor start) motor, you really can't soft start it.
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post #3 of 14 (permalink) Old 03-25-2012, 02:39 PM
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You can't soft start a single phase induction motor like those typically used in table saws. These motors have starting capacitors and a centrifugal switch to switch the capacitors in and out of the circuit at about 1/2 of the motor's operating speed and this will prevent the successful installation of a soft start circuit, but you could replace the motor with an equivalent 3 phase motor and use a solid state motor controller to run it from single phase power. These controllers will allow you to soft start, brake, and vary the speed of the 3 phase motor. The only issue with them is when running the motor under heavy loads at slower speeds because the motor fan doesn't turn fast enough to cool the motor properly. Commercial installations have separately powered fan motors built into the motor housings to keep the main motor cool when it's running no matter what speed it is running at.

If you have one of the smaller saws with a brush type AC/DC motor you may be able to install a soft start board from a large 3 hp router. I have never tried to do this, but it would seem to be possible.

Central North Carolina
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post #4 of 14 (permalink) Old 03-26-2012, 09:28 AM Thread Starter
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Hello guys
So glad to see your answers, because my problem is rather an "orphan problem" (like the orphan diseases).
First of all i want to thank you for the time you've lost for me.
Unhappily, I know what is a three phases motor, or a capacitor motor (capacitor starter with centrifugal switch or permanent capacitor) but my motor is an universal.
For you to be sure of that, I will give you three reasons.

First of all, the " more expensive one" model of Ryobi is soft-start equipped.
Second the motor is brushes equipped (coals)
Third, I already tried with a simple manual gradator and it works fine, i can start the motor as softly as I want.(not too low though, because the motor "snarls")
Unhappily, this is manual, and I can't, (each time i run my saw) turn the gradator knob, besides, at the stop moment, the gradator would remains at its maximum, so that's an impossible thing.
In fact, I am searching a schematic for making a "drive ramp" for the triac, a ramp which should cut the total sinus at the beginning then the more and more later.
And that is what I can't find all over the net, though I swear I searched for months.
So if you can help me, don't hesitate to give me an idea, electronical or mechanical,the target beeing to make my saw more calm and not bounding like a horse when i start it.(and above all such a brutish start is not good for the exit sprockets)

(I apologize, I surely used wrong technical words , but it tried to do my best)

Have a good day

Margeloc
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post #5 of 14 (permalink) Old 03-26-2012, 10:42 AM
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I don't know of any "ready made" controller that you could use other than possibly one of the soft start circuit boards from a large router. These would get you the soft start and some speed control, but would not have braking capability.

A brush type motor becomes a poor quality generator when it is turning without being supplied with power, so some hand tools have used this to create a braking effect by shorting the input leads of the motor, sometimes through a low value resistor, to cause the braking effect. The power switch closes this braking circuit when the power switch is turned off and opens it when the switch is turned on, before the power is fed to the motor.

If your motor already has a soft start circuit, it is not recommended that you put any other type of controller ahead of it because doing this can damage the soft start/speed control electronics of your power tool.

Central North Carolina
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post #6 of 14 (permalink) Old 03-26-2012, 11:16 AM
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"So if you can help me, don't hesitate to give me an idea, electronical or mechanical,the target beeing to make my saw more calm and not bounding like a horse when i start it.(and above all such a brutish start is not good for the exit sprockets)"
Are you saying it is a Ryobi?
If everything is in alignment, and running freely, I'm having difficulty understanding why the initial torque is causing such a violent reaction? Is this a common problem with small portable saws?
My (much heavier) Delta Contractor saw starts up effortlessly...wouldn't ripple a cup of coffee.
Is it possible the problem is mechanical rather than an electrical design flaw?
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post #7 of 14 (permalink) Old 03-26-2012, 02:26 PM Thread Starter
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Ok DaninVan
I first have to tell that I am French, and above all from South of France, a country where ALL the fishes that we fish are at least 6 feets long....
So, my Ryobi (not portable but on bench) does not really leaps like a young goat but all my other electrical tools are soft-started, so finally
i have to avow that the initial shock is above all "anti mechanical" for my sensitive ear.
And more, the saw owns two staggered sprockets (to use the more of the blade diameter) and I am sure that these sprockets don't appreciate the shock.
But yes, you're right , it is not a "tsunami".

I own a chipper for boughs, which starts like a feather descending from the sky,(the start-up takes 3 seconds) and I would like to have the same effect on my Table Saw (1500W).
Ok, if you prefer, we will say it's a fantasy...but i would accomplish this one...

Thanks for your intervention.
(now i will try your idea about a coffee cup..but you didn't say how much sugars ?)
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post #8 of 14 (permalink) Old 03-26-2012, 02:51 PM
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"...where ALL the fishes that we fish are at least 6 feets long..."
So what you're saying is that you have to throw them back because they're undersize?
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post #9 of 14 (permalink) Old 03-26-2012, 02:57 PM
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Michel, all kidding aside, I'm still thinking there may be a mechanical issue, ie loose setscrew, too much backlash in the drivetrain, worn bearings(?), etc.
Try taking the drive belt off completely, and start the motor. Does it still "buck"? At least now you know it's the motor in isolation, or the drivetrain, that's causing the problem.
Cheers,
-Dan
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post #10 of 14 (permalink) Old 03-27-2012, 06:50 AM Thread Starter
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Hello Dan
Thanks for your advices.
Though the saw is totally new, and you maybe will think that I am lunatic, but the normal start (original) is however displeasing .
You know it is a small saw, i mean 1500 w, and there is no belt, only the blade attached to the motor with 2 internal sprockets in way to shift the axis on the motor's side.
So very simple.
I really think there is no mechanical problem, and i tried the motor without even the blade, all is normal.
Maybe the problem is in my head but I don't like the motors starting brutally.

I think i will contacvt Ryobi and ask for buying the soft-start that equips on their bigger saws.
But you know that all the spares parts are always so expensives, (if you buy a car only in spares part, you will pay ten times its global sell price)this is why I hoped to make a soft start by myself, because i tried, and a simple light gradator makes exactly what I want.
But it works manually, and I would like to make it automatic.
Anyway thanks for your interventions, i will wait more, and maybe someone (electronician) will help me, because, between us..... how could I cut the six feet long fishes that I fish everyday if my saw doesnt work as I wish ???

Cheers
Michel.
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