Something interesting...about BT3100

[eezlock]

I went into Home Depo's website a few minutes ago....I found out that
they DO advertise the Ryobi BT3100 aluminum tablesaw as being a
[3 hp]beltdriven saw....just to satisfy all that are interested and really wanted to know the hp of their saws, like other companies advertise theirs!
eezlock

[Wood_workur]

well, most 3 hp routser draw about the same abount of amps, so I'd think its true, but something has 1.5 hp written all over this motor.

[vaking]

Ryobi web site advertises it as 15Amp belt-driven saw. Neither Ryobi web site nor BT3100 manual provide the HP rating, just repeat the 15Amps.
From the physics perspective any appliance plugged into the 120V 15Amp circuit is limited to 1800 Watts or about 2.4HP and that is under the the most ideal conditions, real output is always less. Anybody who claims to have a 3HP tool with the regular 2 or 3 prong plug at the end is lying (make that "taking liberties with definitions"). Any appliance that really produces 3HP must consume more current and is designed to be plugged into a more powerfull circuit, at least 20 Amps. Electrical code in US requires that such appliance must have a different plug (one leg turned sideways), so you cannot plug this appliance into regular outlet. The 20 amp receptacle will accept both regular plug and a 20 Amp plug - it will have a T-type opening for one of the prongs.
Here is a link:
http://www.sweetwater.com/expert-cen.../d--01/09/2001

[Knottscott]

well, most 3 hp routser draw about the same abount of amps, so I'd think its true, but something has 1.5 hp written all over this motor.

You'll find a real 3hp motor in a standard PM66 or General 350 cabinet saw. Most routers that claim 3hp will do so only when struck by lightening..... Even a constant ~ 1.5hp would be pushing it. They'd likely never run again if they really hit 3hp. My shop vac claims 6.25hp! Some of the portable jobsite saws with a similar motor to the BT are claiming 4.4hp. Sales 101 - "if you're going to fudge the numbers, say it with confidence and put decimal point on the end."

The claims are misleading and unfortunate...but the consumer machinery industry is not the only industry to make "ambitious" claims. How about a 500 watt car amplifier for $29.95 at one of those traveling weekend sales?

[JimD]

I think HP ratings on universal motors are pretty bad although I would agree that a 500W car amp is ridiculous (40+amps?). Universal motors torque is a function of their rpm. At their highest rpm, they make the least torque. At zero rpm, they make the maximum torque. The "3hp" rating is the highest torque at the highest rpm. The motor will never do this (or maybe only instantaneously do it). You cannot so easily do this trickery with synchronous motors. They stall as soon as the rpm decreases so they will really make their stall torque at their rated rpm. For that reason and the fact that synchronous motors have higher effiency, a 15 amp synchronous motor will do more work than a 15 amp universal motor.

Jim

Jim

[drumpriest]

The computer industry loves to do this with your power supply rating, in watts. I had a "400 watt" power supply when I last upgraded my graphics card. (3d graphics programming is my job)

I blew the PS and fried a drive due to insufficient power. I now have an Antec "trupower", 550 watt supply, which can actually deliver that amount of power. They did a test and only the Antec came up to the power it claimed.

Same in every industry, the numbers are meaningless. The bt, however, is somewhat underpowered when compared to contractor or cabinet saws. This is not an issue for stock in the sub 1" thick range, but I get nervous any time that I rip a hardwood piece over 5/4 in size.

[dwolsten]

You cannot so easily do this trickery with synchronous motors. They stall as soon as the rpm decreases so they will really make their stall torque at their rated rpm. For that reason and the fact that synchronous motors have higher effiency, a 15 amp synchronous motor will do more work than a 15 amp universal motor.

Synchronous motors? Are you sure you don't mean induction motors? Synchronous motors are only used in power plants, very large industrial machinery, etc., not in power tools. The problem with synchronous motors is they aren't variable-speed; they will not run at all at any speed other than the speed which is synchronous with the power-line frequency. This means (interestingly enough) you can't plug them in and turn them on, because they simply won't run, unless the shaft is already turning at the synchronous speed. Because of this, they require a second motor (usually induction) as a "starter motor" to bring them up to synchronous speed before they actually work.

You're probably thinking of an induction motor, which is commonly used in large power tools. It requires no starter motor, and can start itself. However, it never actually reaches synchronous speed, as it always has a little (~3%) "slip".

I think you'd have an extremely hard time finding a synchronous motor that uses only 15A. 15,000A is probably closer to a reasonable number.

[dwolsten]

The computer industry loves to do this with your power supply rating, in watts. I had a "400 watt" power supply when I last upgraded my graphics card. (3d graphics programming is my job)

I blew the PS and fried a drive due to insufficient power. I now have an Antec "trupower", 550 watt supply, which can actually deliver that amount of power. They did a test and only the Antec came up to the power it claimed.

Most of the cheap power supplies (and some of the expensive ones too) are over-rated like this. They also output very poor-quality power (lots of ripple, voltage too low, voltage sags under load, etc.). A good power supply can make a big difference in how well your computer runs and for how long, but unfortunately most people just look at price. Read the reviews where they do real load testing on power supplies before buying one.

Seasonic and PC Power & Cooling also make high-quality supplies which can deliver their rated power (sustained), and which have higher-than-average efficiency. Seasonic in particular is noted as making highly efficient supplies, around 85%. This can make a big difference in your power bill over a year if you use your computer a lot or leave it on all the time.

Cheap power supplies also don't have many protection features the nice ones have. If your PS actually sustained damage because you put an excessive load on it, it was a piece of crap. A quality PS will detect an overload condition and simply shut down.

Using "numbers marketing" isn't confined to power supplies in PCs; for a while, Intel was trying to sell processors based solely on their clockspeed, even though their CPUs actually did less work per clock cycle than AMD's. Even worse, high clockspeeds cause higher power consumption, so not only was an Intel machine slower overall than a similar AMD, it was hotter and used more power as well. Luckily, now that their stock has plummetted they've finally realized people won't be fooled any more and they're coming out with some quality designs.