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From the picture that you posted, it looks like you made a disk shaped plate to fit on the back of the motor to mount it. Is that disk blocking off the cooling vents at the back end of the motor? If so, that's your problem.
Fred
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I have replaced my Taig Micro Lathe II's motor from the Marathon Electric 1/4HP 1725RPM stock model to a new Marathon Electric 1/5HP 3250RPM.
With the stock motor I could take max cuts of 0.005 and if I pushed the feed to max the motor would start slowing down.
With the 1/5HP the motor is half the size but I swear its three times as powerful I actually tried to stall it and it would not let me! I can now take 0.015 cuts in AL and get a great surface finish and I plowed 0.050/pass and destroyed a 0.5in brass bar in a few passes and while the surface finish is not so wonderful a pass of 0.003 and it was nice and shiny again!
I was using cheep chinese indexable tools from KMS Auto ($5 for the 1/4in tool holder and $1/HSS insert) and im very pleased with my results especialy given the fact the motor cost a whole $30. I'm going to pick up a few more of these that's for sure.
The main problem is with normal use keeping cuts below 0.015 the motor does get quite hot and im worried about it, destroying that brass rod made is very hot indeed in a matter of minuets. I have been thinking of putting a plastic fan on the back and wrap some sheet metal around the motor as a duct but I'm not sure that will be enough. I want to keep it as low cost as possible but could pick up an old heater core from the wreckers for $10
What do you guys recommend I do to keep this motor within its temp range??
Motor is rated:
Max ambient Temp 40c Insulation Class B1 (130c)
From the picture that you posted, it looks like you made a disk shaped plate to fit on the back of the motor to mount it. Is that disk blocking off the cooling vents at the back end of the motor? If so, that's your problem.
Fred
[URL="http://www.pure-geometry.com/"]Pure Geometry LLC[/URL]
Vertical Lathe tool holders and more.
And no matter how it seems, a 1/5hp motor WILL be less powerful than a 1/4hp!
The 1/4 will have 'x' torque at 1725rpm, by doubling the rpm the new motor will have less than half the 'x' torque!
You're maybe getting better cuts as the cutter is operating at a more benificial speed?
NOT NECESSARILY! Motor power rating is commonly inaccurate. Some manufacturers in China will copy a motor with little testing and put whatever numbers on it they want. Also, if the motor was actually tested, you have no idea what conditions the motor was in when the rating was achieved. The motor market is a numbers game, he who has the biggest numbers, wins. So some manufacturers will find ways to fudge (or downright lie) to get higher numbers.Originally Posted by kawazuki
It is possible the 1/4 hp motor was fudged more than your 1/5 hp motor.
In regard to cooling, you want to let as much air THROUGH the motor as possible. Do not cover any vents!
"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." Antoine de Saint-Exupery (1900 - 1944)
A servo motor typically has a fairly flat torque curve, from maximum at stall up to the max rated rpm.
The correct way to test the HP value is to use a Dynamometer.
Al.
CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
Hey all, thanks for the replies.
TXFred: That plate is the stock 48N face mount. I might take it off and remove some material and make it spoked like a wheel so a fan can get the air moving through it.
kawazuki: I agree that at 1725 the 1/4 will have 1/4HP and the 1/5 will have like 1/10HP but I am using a step pulley to keep the stock going at the same rated speed for the cutter. So if I keep the spindle going 1200RPM the 1/4HP motor is putting out say 0.35HP as its geared at 0.7 (1200/1725) while the 1/5 is a much higher gear ratio at 0.35 and effectivly 0.57HP
HawkJET: I agree that chinese motors are horribly rated. I have a "700W 12V PMDC Motor" that at full power I can stop with my fingers.. real letdown. But these are Marathon Electric motors and their used in everything. 90% of the air handling units we put on builds use them. I hope their up to par on their lables.
Al_The_Man: I might pop into my old college and see if they will let me borrow a dyno as our motors class had one on every bench. Well it was a dc motor with a variable load and readout but it was just as accurate as the older guys.
As for cooling is a fan really going to be the best option? I don't think a water jacket will be all that useful and would be quite difficult to machine but I could put on a peltier I was thinking...
It's definitely the cheapest option. Adding a fan is easy. If it doesn't work, then try something more complex and costly.
I wouldn't do too much without contacting the manufacturer. If these motors are as good as you say, then overheating sounds abnormal. It's possible your motor is just defective.
Fred
[URL="http://www.pure-geometry.com/"]Pure Geometry LLC[/URL]
Vertical Lathe tool holders and more.
Well I know size is a big factor as well. The 1/4HP is vary large and god quite warm with heavy use but nothing to worry about. The 1/5HP is about a third the size and has the same 40c ambient and class B insulation rating but is very compact.
Marathon Electric says these motors are $138 new to buy so i'm going to go into town tonight or tomorrow and pick up another one to keep on hand as a spare.
I'm going to take the casing off this one and I'm hoping the field coils are in a harness or around a core that way I could get good air movement over everything. Ill post some pictures if I get it apart.
if you add a TEC it has to be very strong. you will need a dedicated power supply for it and a watercooling loop to cool the peltier. a cheaper solution would be submerging the evaporator of a window ac in a cooler and chilling water then using the chilled water to chill the motor. Get a thermocouple on it to get a temperature reating
This seems to be much ado about nothing! Just allow the vents that are already in the motor to do their job! If you are covering any vents, uncover them. If the motor is rated properly, it has been designed to cool with all the vents unobstructed. If you are not overloading the motor, it should be just fine. If you need to get additional cooling, add a forced air fan.
Many motors are designed to run hot. using your hand as a thermometer is not reliable.
"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." Antoine de Saint-Exupery (1900 - 1944)
I'm working on getting a proper temp probe but I have nothing currently. I can't even find an old glass thermostat around the house...
If a motor is rated for 130deg (Class B) is that its absolute maximum temperature or its rated temperature?
also keep in mind that when you put your hand on anything warmer then 60c your body will react "HOT GET HAND OFF" so often you think its way hotter then it really is... past 60c you can't really detect how hot something is...
cheers
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