When ripping lots of boards on the tablesaw the motor gets hot after about 15 minutes so I shut it down and let it cool off before ripping some more.
Question………how hot should you let the motor get before cooling it off.
Saw is a Sears contractor model; cuts great; Freud sharp carbide rip blade; doesnt bog down; belt doesn’t slip; sawdust blockage is not a factor.
The motor gets hot enough to be uncomfortable to the touch but it wont burn you.
I’ve noticed that it runs cooler longer with a dado blade.
On long ripping jobs I’d like to run the saw for hours at a time.
Any similar experiences??
Replies
How much sawdust is in/on the motor? Also, how long is your extension cord? Don't use one if you can avoid it. If you must, make sure it's a lot heavier than the one on the saw. 11 ga will work for a smaller saw. How hot is the plug when you shut it off? If it's hot, the cord may be too small or too long. Neither of which is good. Rather than use an extension cord, get a really heavy one and replace the original power cord by cutting the new one to length and installing it as a hardwired cord. Your saw should be happier and you won't need to replace your motor. If you have the option of wiring the motor for 220V, do that.
Sawdust gets blown out at the end of each use.
2 things I did forget and these are whoppers..............the saw is 60 hertz and the current here is 50 hertz; also on extension cords, I couldnt quite reach the shop from the house with one cord, a 100 footer so I added one, a 50 footer............so now we have 150 feet.
The plug gets warm; not hot; and the cord gets slightly warm.
The shop is wired for 110/220 50 hertz but is not connected to the grid yet; things are slow in the tropics.
Thanks for the input.
The 50 Hz part is less of a problem than the 150' of extension cords. The cord has resistance and the voltage drops the farther it goes out. The Power formula is P=IE and if the voltage (E) drops, the current (I) goes up if the motor is trying to develop the same power as it it were connected to normal voltage. More current = more heat. Is there any way you can get heavier cords? I'm actually surprised the circuit breaker or fuse hasn't popped while you were using it. I tried to run my pancake compressor on an extension cord and the breaker popped every time it turned on.
"I cut this piece four times and it's still too short."
I'll be in the USA in May; pick up some heavier wire.
Supply here is 127v 50 cycles 2 wire; 220ish also 2 wire is available at additional cost.
The tablesaw is mobile so it can be moved closer to the power source and eliminate 50 feet of extension cord.
The extension cords are 2 wire, orange, no markings.
Hopefully be on the grid soon.
My compressor wont run either on the cords; pressure goes to about 20 psi then the fuse blows.
2 wires with or without a separate ground? Where are you?
"I cut this piece four times and it's still too short."
2 wires no ground; hot and a neutral only.
Location..........Bonaire, Netherlands Antilles, Dutch Caribbean.
This might seem like a Banana Republic question..................in order to get a heavier extension cord could you use 2 cords side by side; one is the hot and the other is the neutral; cut both ends off both of them and splice all the wires together in each individual cord then connect them individually to the terminals of new plugs??
I know it would probably be a lot cheaper to buy a heavier cord BUT things cost 3 to 4 times what they do in the US and I have several extension cords.
You could do that, or use each in the normal way and tie the hots together and the neutrals together. Same current carrying ability, but theoretically, they twist the wires for a reason, which is usually to reject outside noise (twisted pair is great for common mode noise rejection). On a saw, noise isn't really an issue.
"I cut this piece four times and it's still too short."
The hot and neutral wires together reduce induction heating. Noise resistance is irrelevant in this application. It's worth buying the heavy extension cord. It's safer, cheaper than a cheap cord and a new motor, and you'll most likely find lots of other uses for it.Pete
Edited 3/19/2006 11:36 am ET by PeteBradley
Thanks Pete,
I'll be in the USA in May; long shopping list and extension chords are on the list.
Highfigh has nailed it-particularly the part about the plug itself being hot.
I think that if the motor is too hot to keep your hand on for any length of time something is wrong, such as mechanical or electrical overloading, and the end is nigh.
Thanks Philip,
Presently working on the cord length and guage.
Shop will be on the power co. grid soon.
Some of these motors have built in thermal protection and will trip off when they become overheated. Is there a reset button anywhere? If it has thermal protection and it's not tripping out, I think you're OK. It's normal to be too warm to hold your hand on, because their operating temperature is pretty high. Check your nameplate, it's probably class "B" insulation which would be in a temperature range too warm to be comfortable for your hand. If you're not bogging down the motor or stalling it, it's probably OK to keep it running.
My guess on the dado cuts is, that most dado's are short cuts and the rip cuts are long so the amount of actual "working time"is longer, allowing more time for the motor to reach it's full load operating temperature.
I hope this was helpful.
Motor is indeed class B insulation; code H ???; 25 degrees C; 120/240; frame 56 and it has a red reset button.
My dado cuts are much shallower; less load on the motor than ripping??
Sorry for the delay.
"code H ???"
"Code" is also sometimes written "kVA Code". It is used to calculate the locked-rotor or inrush current range, and will give the correct value at either voltage if dual-voltage. I don't want to type out the whole table of values, but you can Google on kVA Code and get a site like this one http://www.motorsanddrives.com/cowern/motorterms6.html which give the values. They're also in the NEC.
Try converting the kVA Code letter on your motor - you'd be surprised how much current it actually draws when you flick the switch.
Edit: I should add that the general rule for running an induction motor on a different frequency than the nameplate frequency is to keep the volts-to-hertz ratio the same, so if you're running a 60Hz motor on 50Hz, you should reduce the voltage to 83% of the nameplate value. If you don't, you essentially have an overvoltage condition, which will cause heating almost as much as an undervoltage condition. That would be a big contributor to overheating, though I would not consider too hot to hold your hand on to be overheated (see my previous post).
And as mentioned before, it's generally not recommended to use a single-phase motor on a frequency other than nameplate - the V/Hz ratio stuff really is better applied to 3-phase, since they don't have start and/or run capacitors, and centrifugal switches.
Be seeing you...
Edited 3/30/2006 11:22 pm ET by TKanzler
Thank you TK,
Lots of homework for me to do and I just found this sweet spot on the reef where the fish are biting.
While dado cuts do put a pretty fair load on the motor, most dado cuts are short (like cutting a dado for shelves in a cabinet) and give the motor time to cool between cuts. Also the motor will cool down to normal operating temperature faster if it is allowed to run unloaded for a minute or two, because of the cooling fins on the rotor. If it is not tripping the reset, it probably is not overheating.
PS I worked in a motor repair shop for 34 years.
Taking what burly oak said one step further, even Class A insulation is 105ºC rated (Class B is 130ºC, Class F is 155ºC, and Class H is 180ºC). Water boils at 100ºC, just for reference. So a motor with Class A insulation operating continuously at rated load in 104ºF air (typical rated ambient - look at the nameplate) could have hot spots in its windings reaching 221ºF. If it has a TEFC frame, it likely has Class B insulation, and since all the heat loss is through the outside skin of the frame, it will run hot to the touch.
That doesn't mean the outside of the frame will reach that temperature, because it won't, but it gives you an idea what kind of temps are actually involved. It's also possible the manufacturer used a higher class insulation to pack more hp into a smaller package than the NEMA standard requires. I've seen ventilated NEMA 56 motors with Class H insulation, allowing higher hp for it's size.
I would, however, be concerned about that very long run of cord, for reasons others have given. I would not shut it off to cool, though - I'd just let it run with no load, since that will bring the temerature down faster. The motor is made to run continuously under full load, so getting hot isn't necessarily a problem, and running under no load keeps the cooling air moving while adding very little heat (low current due to low/no load).
If you want something to compare your motor to, find an attic fan, furnace blower, water pump, pool pump, something that runs for long periods of time under load, and put your hand on it. Even a vented motor is going to be too hot to keep your hand on.
Be seeing you...
You are on the right track by fixing the electrical supply problem. I'll add something that could buy you some time. Use a low tooth count ripping blade. Maybe 20 or 30 teeth. The cuts wont look very nice but the motor will not be as taxed.
Mike
Thin kerf wouldn't do any harm either.My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
good point, are there 30 tooth thin kerf blades out there? I suppose forrest has them, what about some of the more value brands?
Mike
The original Forrest WoodWorker II is being discontinued and they have reduced the price. Too bad I don't need another one. Maybe they're doing the same with the rip blade.
"I cut this piece four times and it's still too short."
Not to start another thread BUT.... what's this about Forrest Woodworker II being discontinued? I've used a LOT of blades in the past but nothing has compared to Forrest...well may be the Tenryu has been pretty close or even a tie....I hate to see them stop making such a great blade that's been around for sooo long....what gives?
They're replacing it with what they think is a better blade. It was on sale at the WoodWorkers Show for $79 when I was there. A moment of silence, please. I don't remember what was different about the new blade, though. It's probably on their website.
"I cut this piece four times and it's still too short."
Thank You for getting back to me....
Steve
Thank You for getting back to me....I appreciate it.
Steve
S.K.: You have three problems:
1: 50hz will overheat a 60hz motor
2: Long cords not sufficiently heavy will cause voltage drop=extra heat. A well made extension cord (good quality plug and connector properly installed)of proper gauge is no different then wire in the wall.
3: Using your hand to test temperature, use an instrument. Read the nameplate for temperature rise then get the ambient reading and compare the two.
Duke the electrician
The Bill of Rights
December 15 1791
NRA Endowment Member
LEAA Life Member
CRPA Member
Duke, I need a good book on basic electricity; understand 50 hz runs slower than 60 so motors run hotter. Also if 50 hz is less efficient than 60 why do so many countries use 50?
This is probably not the forum for electricity for dummies but thanks for the input.
My dad once made an extension cable/ cord?? from romex 2-#12's; wasn't too flexible but seemed to do the job. Wire in the wall or wire on the floor.
50 Hz isn't significantly less efficient, but 60 Hz motors trying to run on 50 Hz current are less efficient because they aren't designed to run on the lower frequency. A second problem, in addition to the overheating, is that the 60 Hz motor will run slower at 50 Hz and the centrifugal starter switch won't cut out at the proper time, further stressing the motor.
John White, Shop Manager, Fine Woodworking Magazine
Thank you John,
We are 50 miles offshore from Venezuela which has 60 hz.
Bonaire is a Dutch island; Holland is 50 hz.
OK guys; what size extension cord do I need to reach Caracas??
Skid: Motors will run at their proper speed at the design frequency. A good book that covers most everything about electricity is "Electricity 1-7". It starts out with the real basics of electron theory and goes on. Proably available used from abebooks.com. or others. Romex is not for extension cords as the solid wire will crack and the insulation isn't made to flex. Don't know why some countries use 50hz but way back 25hz was used; you could see the flicker in incandescent bulbs, so I hear. This is the formula for motor speed if you want to play;
Srpm = 120 x F P
Kenneth Duke Masters
The Bill of Rights
December 15 1791
NRA Endowment Member
LEAA Life Member
CRPA Member
I don't know, but I suspect Henry Warren of Telechron Clock fame might have had something to do with the US adopting 60 Hz. IIRC those clocks used a synchronous motor designed to deliver whatever speed was required to drive the second hand at 1 revolution/minute. They might literally operate at 1 rpm, I don't know. Before Henry, AC power frequency was delivered about like time was delivered before the railroads, LOL.
Why 50 Hz?
Ed: I am not running 50hz anything, I was just answering someone's questions on the subject. Can you imagine the havoc that would ensue if our 60hz power was not steady. I can just hear all the a/c motors speeding up and slowing down and who knows what else. Fortunately utilities keep the grid within a cycle or less of 60hz, for the most part.
DukeKenneth Duke Masters
The Bill of Rights
December 15 1791
NRA Endowment Member
LEAA Life Member
CRPA Member
Duke,
Your book reference is on my USA shopping list; thanks.
Using romex for an extension cord was just a thought; perish it!
Skid: That book will serve you well for understanding electricity. I have a piece of a REAL extension cord, I'll try and post a picture later. DukeKenneth Duke Masters
The Bill of Rights
December 15 1791
NRA Endowment Member
LEAA Life Member
CRPA Member
Thank you Duke,
Your book reference is 7 volumes by Harry Mileaf and is still available.
7 volumes??
No TV for a long while methinks.
Looking forward to the pic.
I have the version with all 7 in one, fairly heafty, volume; probably a better way to go if it is available. DukeKenneth Duke Masters
The Bill of Rights
December 15 1791
NRA Endowment Member
LEAA Life Member
CRPA Member
Duke I ordered a 2nd edition hardcover used copy; 7 volumes all in one book for $35; new copies are $93; thanks for the info.
Skid: Here is the jumbo cord, a short piece but you'll get the idea. The technical description is 500/3 and it is rated up to 2000 volts, weights 36lb/ft and probably cost today about $50-60/ft. I actually never worked with this monster but got the sample from my wire distributor. I gave a piece of the original sample to my stereo store salesman so when costumers had a hard time choosing a speaker wire he would pull out this stuff and end the discussion. Standard pencil and six inch ruler for scale.
DukeKenneth Duke Masters
The Bill of Rights
December 15 1791
NRA Endowment Member
LEAA Life Member
CRPA Member
Impressive speaker wire Duke; reminds me of the transatlantic cable.
Great pictures!!
"1: 50hz will overheat a 60hz motor"
When I first read you were running on 50 Hz I reached for my hat from long ago, and tried to remember my converstion with Vern re designing electrical stuff so that it works on both 50 & 60 Hz. IIRC he said that, in general, things run hotter on 50Hz because:
The motor runs slower (17%)
The current goes up the same amount (17%)
The cooling is less because the motor is running slower
Depending up the quality of the motor its life will be shortened.
Remember that HEAT DESTROYS.....everything. Period. Working in my shop one day, I had a job that I was pretty sure was going to burn up my old Hitachi table saw. I had to rip about 25 white oak planks in a tight timeframe. I rigged the intake of my Delta dust collector (AP400) to the exposed ####-end of the motor and moved more air than that little impeller could ever hope to! It took two blades, but the motor stayed ice cold.
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