Been looking at the Bosch 4000 contractor table saw. It claims 4.4 peak HP but that is more than a Unisaw or most other cabinet saws which didn’t seem feasible.
Looking at the specs it says 15 Amp @ 120 V. Going back to my old high school physics, I recall that power= voltage * amperage. So 15A saw generates 1800 Watts.
Now 1HP = 750W, so 1800W = 2.2HP. How can they claim 4.4 ‘peak’ HP? That would be a draw of 30A and would surely pop the breaker.
Anyone care to shed some light on Bosch’s claims?
Wally
Replies
Yep, that's when it "peaked" and popped.
No specific answer, other than the one you yourself provided. However, it is educational to read the saw's reviews on Amazon.com. Look up Bosch 4000 and Bosch 4000-07 (and does anyone know why the model with the folding stand is cheaper than the saw by itself?).
LINK
That is a universal motor (I think) and they don't have NEMA ratingss.
So they are often tested with a unlimited source of current (and smoke).
Acctually that is a CONCERSATIVE RATING compared to some on the shop vacs.
Did you say, 'lawsuit'?
Maybe we all can get a sawblade and an extension cord while the shysters get millions.
"I was glad that when everything finally hit the fan I was holed up in a little beer joint in Robstown, Texas called the El Gato Negro."
That peak HP is exactly that - the current peaks at start-up because the motor has to overcome friction and inertia when you turn it on. The reason the breaker doesn't pop is because this is instantaneous. When the saw gets turned on the current peaks, then very quickly drops to its operating current, which is closer to the 15 A number. Even at 15 A you won't get 2 hp out of it because of the efficiency of the motor. You'll be lucky to get around 1 under load, since single-phase motors are not as efficient as three-phase.
So if the saw does develop 4.4 hp, it's when the motor is accelerating to its operating speed, well before you take wood to the blade, and at best you'll get about 1 hp out of it during actual use (cutting), depending on the motor efficiency - 4.4 is a garbage number spewed forth by marketing, and has no application to the actual use of the saw.
Hopefully that makes sense, maybe someone who deals with motors regularly can explain it better.
I've always assumed that those bullsh*t high horsepower numbers were based on taking into account the inertia of the machine or any other capacity for energy storage that it may have. That certainly goes for air compressors with tanks- they often quote a horsepower rating which is quite impossible based on the motor alone, but you can instantaneously get at least four times the air flow out of the tank than the compressor itself puts out if you're only demanding it for short periods. I figured the shop vac powers were determined on the same basis.
The recent FWW article had it right: for power tools you should ignore these spurious power figures and just look at amps or watts. For air compressors it's the flowrate they can generate AND the pressure that flow is determined at (i.e. is that actual cfm at 100 psig, or is it standard cfm at atmospheric pressure?)
> I've always assumed that those bullsh*t high horsepower numbers were based on taking into account the inertia of the machine or any other capacity for energy storage that it may have.
That is correct. It's the instantaneous HP with the saw up to full speed when the first tooth touches the wood. That inertial energy is used up quickly -- I'd guess in less that a revolution of the blade -- and you're back down to the real continuous power for the rest of the cut. To convert advertised HP to real HP, you have to divide by something in the range of 10 to 25.
-- J.S.
I don't think that is it at all.That would not work for shop vac's.I have heard a couple of different methods. All of the possible.One is based on starting current x voltage. One is locked rotor current x voltagee. In both of those cases there is no real work being done so no real horspower beign developed.That last one and the most "meaningful" is to connect to an unlimited current source and load it up.That will give you true HP numbers, under the circumstance, but not useful in real world.
This 'peak hp' is just what Sears used years ago to sell it's tools.
It's the start up hp rating of a tool not under load. They would say 'Develops 2 1/4 hp' advertising one of their saws. All with a slight bit of truth but useless for knowing what you really have.
Better to know quality by reading comparisons such as FHB does. At least then you know how a tool handles underload on an equal testing basis.
I appreciate FHB very much for their efforts in comparitive testing. My only dissapointment is they don't test tools to destruction. You know real field 'bad carpenter' habits.
Test
1. Surviving out in the rain and snow and ice.( see Pro-decks frozen mitre saw picture here)
2. Backing into saw with delivery truck or fellow worker,( another post here about this)
3. Late night going home tired truck toss load up and overnight forget to put up thief test
4. Fellow worker 'I don't like your pretty tools' envy abuse test
5. Flying out of my truck at 65mph because I forgot to tie it down test
and so on...You get the idea Real Test for Real Tools
Those are some good tests. Also add the apprentice test - change blades with pliers and/or hammer, load up until blade is smoking and wood is golden brown, etc.
Thanks all for the replies. I figured it had to be some kinda crap like that. I long since figured that checking amps was the way to go, but wondered where those suspicious HP figures came from. Same concept as stereo manufacturers who quote 'peak music power output' watts that are 10-15 times the amp's actual RMS/channel numbers. Marketing.
Wally
Lignum est bonum.
How about some DIYer tests, like the "wife gets pissed at you telling her what to do and drops favourite cordless drill on floor from ladder height" case impact resistance test? Or the "loan to dumb*ss relative" survival test- that's a popular one!
There ya go! I like the relative test so much I'm actually testing two tools now.
regardless of "marketing magic numbers" the saw is wonderful
i've been using it for a couple of months trimming custom homes, i have the folding stand and outfeed and side extensions
i retired my 8" makita and roussou (sp)? table after seeing the new prices for the roussou stand
the bosch is quite a bit larger and heavier than the mak, but it really feels like a shop saw well worth the money.
my 2 cents
mike
off the back of the truck at 10 mph when it is 5 degrees out shatter test.
(GC told me plastic tool boxes make big mess with this one.)
Gravel and drywall dust in motor vents test. Lignum est bonum.
-just heard someone talking about a sawdust fire in their table saw motor.... smoked the whole thing.
> -just heard someone talking about a sawdust fire in their table saw motor.... smoked the whole thing.
Today table saw motors are usually TEFC = Totally Enclosed Fan Cooled. That's what the new one on my Unisaw is. The original one from before WWII was the old "bullet" motor, totally enclosed, but no fan. I remember warming my hands on it when I was a little kid.
Was this a case of someone putting the wrong kind of motor on the saw, or did it happen with a properly enclosed motor?
-- J.S.
coulda been a drip proof...
a Sears kinda special....
A TEFC motor will pull fines into it's self thru the electrical hook up to the motor..
down hill from there...
pay attention to all details...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
Im going to look for it, but to the best of my recollection it was like Imerc stated. The motor was enclosed, current date wise, but there was some sort of hole that the sawdust got sucked into, and packed the motor up.
But - none of you mentioned the magic words "Soft Start." What does that mean? I are an electrickul injunear, and I haven't the foggiest idea. Probably postdates my education - lessee, now - my diploma says something about a degree in "Natural & Experimental Philosophy."Don - REAL old FartThe GlassMasterworks - If it scratches, I etch it!
Soft start is that it slowly comes to speed, it doesnt have that old time jerk that your circ saw did, or router. The one that feels like you are shooting a pistol when you pull the trigger.
Edited 1/11/2005 6:33 pm ET by zendo
My guess is that they have triac and the instead of a ressistive control on a delay trigger (like a light dimmer) they have a cap and charging resister so that it slowly ramps up.
For the quick and dirty crash course come turn on my old PC 690 router. Then put it down and squeeze the trigger on my new Bosch D handle router. For all the BS hype with promoting tools, soft start is actually a feature that makes a very noticeable difference.
Diesel: Since the only soft start tool I have is a Bosch Table saw, have never been able to observe how it starts up. Yes, I know that jolt when you start up hand tools. My old Craftsman router really wants to twist itself out of your hand when it kicks off. The reaction I like is the gyroscope reaction when you try to rotate a drill or the like perpendicular to its motor axis. You really have to be prepared or it goes all over the place. Really tough on the wrist of the unprepared.Thanks, all for telling me what soft start is. I don't think I can really see or hear the difference in startup for my TS.DonThe GlassMasterworks - If it scratches, I etch it!
My Skil wormer has a nice twist when if fires up...
But back to the Bosch, it's a sweet peice. Highly recommended, regardless of what the goofy marketing people say. Who reads that stuff anyway?Jake Gulick
[email protected]
CarriageHouse Design
Black Rock, CT
here is a list of some formulas: http://home.grics.net/sfi/formulas.htm
Or some more interesting info http://www.mcintoshengineering.com/Hard%20Rock%20Handbook/Rules%20of%20Thumb/electrical.htm
And here is another: http://www.infomine.com/SearchMiningRule.asp?FID=23
It appears that peak hp may be defined somewhere unknown at the moment but generally speaking peak power is very close to 2x continuous power.