Problems with a Motor Burning-up

properly size the motor for the application. perhaps 1/2hp is not enough to turn the blower at that speed. The blower can have virtually 0 resistance due to bearings (and feel like there are no restrictions when turning by hand), but when the RPM's are increased, it moves more air, creating more resistance. I would simply get a more powerful motor to do the job if it were my situation.

Customer had comment that since the hood wasn't pulling enough, some one changed the pulley that the motor moves to a smaller one to get greater speed and thus more pull (cubic feet per minute).

If that's what happened (as opposed to customer thinking it might have happened, it's difficult to tell from your #5 - who's "some one"?) why didn't you say it in the OP?

That's almost certainly the reason for the burnout - if you increase fan speed it's going to draw more power and unless you've done some checks there's no reason to think an existing motor will cope.

Cheers.......Codey

How about replacing the pulley to a bigger one??

My first suspect would be your duty cycle. Many motors this size and price have fairly short duty cycles, something like 30 minutes every hour and a half. Do you have that info on your motor? What is your duty cycle?

The next suspect would be the overhang load you're putting on the bearings. Using the motor for a tensioner isn't the slickest approach in the world.

Finally, I'd look at the free air available around the motor.

good suggestions, mine is more the "part changer" approach, with a brute force mentality. duty cycle is deffinately a factor to consider, and the side bearing load from the hanging motor deffinately wont help, (putting in a heavier motor will only create more side load). And the free air around the motor is something that haden't even entered my thoughts, but its oftentimes the culprit. GA

Yeah, maybe he is seeing too much load at rated rpm. Good point. An ammeter reading + tach would be of great benefit. A GA back at ya!

Have not checked amp going to the unit because of the typical customer answer that the unit had been working fine. Will test to see if it is within specs.

I would check the amp draw from the motor, when working at full capacity. compare your results with the specs from the manufacturer. the thermal overload is tripping from (my guess) either not enough airflow for proper motor cooling, or the motor is simply working too hard and is pulling more amperage than it is rated for. Check the current, compare to the specs and get back to us

This blower pulls from an 10 inch dia vertical duct that when it reaches the ceiling (where the blower in question is located) it enters the blower from a horizontal position and the blower wheel expells it through a vertical 10 inch dia chimmney to the enviroment.

If you restrict the incoming air--The load on the motor will decrease.

I have set air intakes on blowers using an amp meter and restricting the air to meet Full Load Amps. If unrestricted and no overload protection, you can burn motors up with air movers--Not sure if water pumps are the same, but I found this kind of interesting.

Good luck and Happy T.

It looks like most of the bases have been covered, assuring that the motor is being supplied the specified voltage, and the amp draw is not excessive. One other possibility that would exist with a single phase motor of that size is if the capacitor is defective, or of the wrong value. I don't know whether you replace the capacitor when you replace the motor but it's cheap insurance anytime you replace a motor.

You didn't mention whether this was a new installation, or a fan that had been running for a period and had just experienced a failure.

I have no doubt the amp draw is excessive. My recommended remote test procedure. 1. Assure the motor is being supplied the correct voltage.

2. Check the amp draw of the motor with the belt off, it should be considerably below 7.8 amps. If it is install the belt and check the amp draw again I'm sure you will find it is exceeding 7.8 amps.

If so they amp draw can be reduced by installing a larger pulley on the squirrel Cage shaft, or a smaller one on the motor. Most of these fans come with an adjustable shiv on the motor, in that case open the shiv to reduce the amp draw. Just a footnote dayton does make mistakes but generally they're pretty good about matching motors to fans.

A second method to reduce the amp draw is to restrict the inlet to the fan with a damper and adjusts to full load amps.

If you found the amp draw to be high on the motor without the belt, you either have a bad capacitor, incorrect supply voltage, or the whole mess is wired wrong.

Whatever you do don't trust the wiring of the guy before you. The fastest money I ever made about $100 for three or four minutes work was putting an amp meter on an direct drive condenser fan motor, it is almost a idiot proof part to be replaced (almost). It turned out the homeowner (I was doing this is a quick favor for a friend) had been replacing one motor a season for several years, it was a multi-voltage motor the original technician had selected the correct wire for the supply voltage, and then rather than capping the other two wires he connected them together, which was incorrect, everybody else did the same.

When I put an amp meter on it the motor it was pulling almost twice its full load rated amperage, the amazed homeowner said nobody had ever done that before, after scratching my head for 30 seconds I saw the mistake and simply cut the two wires that were connected together . My fee was going to be a can of Coca-Cola or a beer, I couldn't stop them from shoving $100 bill in the pocket he explained that he spent close to $1000 over the last three or four years trying keep his air-conditioning running and watched every service man replaced and wire the motor and never put a meter on it.

As suggested before it looks like either the motor capacity or the belt tension is inadequate. The motors are designed to take a certain side load so you need to apply belt tension as otherwise you would get belt slippage and overheating of the motor as a consequence (!). Don't forget that some(?) motors automatically switch of when overheated to protect them from burning out, however, it might then already be too late for the bearings. This is a common problem with for example alternators. So it could be that you need to contact the motor supplier and have him tell you what the recommended belt tension should be for your application. Allowing the motor to "hang" in the belt is very unsavoury as the belt load becomes (even more) variable with changing speeds and you might have problems with the system dynamics, you might however get away with it if the motor is considerably overspecified. To conclude, both over- and under- tensioning will cause problems so match the required tension (load) to the motor and application.

Exhaust hood fans many times are B.I fans. (backward inclined) From experience I have seen these fans set up running backwards. They move a small amount of air backwards but will overamp and cycle on overload.

Happy Thanksgiving

Greetings and Happy Thanksgiving.

If this has been running for a long time and then started this problem you might look into the bearings or bushings of whatever the motor is driving.

I have had mechanisms that seemed just fine when you turned them over by hand but the shaft or the bearing but usually the bushing was worn and wouldn't stand higher speeds. The frustrating thing is that sometimes these problems are not enough to make a squeal or a vibration. Wiggle both ends of the part driven and see if you can feel any wobble to your wiggle. If you have an infrared point and shoot thermometer start up the motor and point and shoot at the bearings or bushings to see if you have any heat building up.

go back to your own words and ask yourself how fast you will be able to move with two 12" blocks tied to each foot or hand.

the motor is if as you related allowed to hang on the belt will have that effect.

ibefore you tear the fan away from the cieling replace sheet metal ducting pulleys or whatever may i suggest you use a belt tension gage to determine how tight the pressure on the pulley endbell bearing is?

second consider putting in at the least a belt tensioner made up out of a guy wire tensioner and cables or something along that line. what size is the blower unit itself, the idea of bearings bushings etc have to be considered as does how paralell the drive pullet and belt are to the driven pulley, by experience 75% of motor burn outs ive seen came from misaligned pulleys. the next step you might consider and if space and budget permit put a idler pillow block between the motor and the scirroco.

'da ber

Hi Barfnagler

There's nothing wrong in principle with using the weight of the motor to provide belt tension. It's common practice on e.g. some Roots blowers. Has the advantage of being self-adjusting. Of course it has to designed that way.

Cheers.....Codey

I helped maintain fans for multiple hood setups for 3 different labs in plants for years.All advice so far is good.I would also check out the following if you have found nothing so far.What was the original motor,pulley and fan setup?Many of these hoods have sealed and heat resistant motors due to explosive or corrosive fumes and heat.I looked up this motor.This motor is a common open fan motor.Is anything harmful getting to it to affect it?Is it the wrong motor in the wrong place.It could very well be a time bomb just waiting for the right conditions to take a life or just burn the place down.This may be a very serious thing if the wrong vapor is in the hood.Just because it is there does not even mean that it is installed correctly or is the correct installation for the job.

Also check out any possible changes in use of or habits of the users.A new employ on the night shift with their OWN way of doing things has often caused much trouble and expense for long periods before discovery.To find people that will LIE about their operation of equipment is common.I once found a lab employ grilling steaks under the hood at night.She believed in soaking the charcoal in vast amounts of starter before lighting.Someone had shown her how to disconnect the alarms and auto smothering system.Guys were doing it too.All lied.None saw any wrong or danger even though many solvents were kept and used in this lab and hood.My"Lab-Nerd" friends and us "Neanderthal Stone-Smiths" as they called me often think completely different about such things!

You have a "Witch Hunt" going on here.When all else fails,a little VOODOO and a lot of prayer often helped me make it through the job!Good luck,Alfred

Some blowers will be overwhelmed without any control on the air supplied to it. Restrict the amount of air to it(sometimes it doesn't take much). I have already posted this (and it has been covered in a previous thread), but found this out the hard way.

Here's a the link to the thread--

http://cr4.globalspec.com/thread/28648#comment300466

eqiserv,

Have you confirmed the required motor HP/RPM/SF?

Have you confirmed the supply voltage?

Have you confirmed the motor rotation? CW or CCW?

Don't forget a new belt.

Has the owner cleaned the grease filters lately?

The modified sheave on the motor needs to be returned to original.The factory designed the blower to work with that sheave.

Good luck and don't get hurt.

SM