Capacitor – How frequently . . .
alanplanesaw
| Posted in Power Tools and Machinery on
I have a Jet dust collector. DC1200, I think.
Anywho. The motor has a capacitor. I just had to replace it. Does anyone know how frequently can I turn the thing (the dust collector) on and off in an hour? Does turning it on and off affect the capacitor or the motor?
Is there such a thing as turning off and on more than so many times an hour such that it does damage to the capacitor?
Just a thought that for some reason I thought I should ask.
Thanks,
Alan – planesaw
Edited 8/23/2008 11:37 pm ET by Planesaw
Replies
Alan,
I can't give you any answers based on theory, but I regularly turn my dust collector on and off - on every time I turn on by table saw, bandsaw, planer, or chop saw and off ever time time I turn the tools off. I bought my Jet 1HP dust collector used over a year ago and no problems so far.
Chris @ www.flairwoodwork.spaces.live.com
- Success is not the key to happines. Happiness is the key to success. If you love what you are doing, you will be successful. - Albert Schweitzer
Alan,
I was down at the IWF on Friday and stopped by the Onida booth. IIRC, there was a label on one of their dust collectors that said no more that 6 cycles per hour, but it was one of their 5-10hp DC units.
I would contact Jet's technical department and ask them to be sure.
I do know that a motor running a dust collector is running at almost full power, and it takes a lot of juice going through the capacitor to get it going.
-Kevin
I have a shop full of machines that rely on capacitors to start. My shop is my livelyhood. I have had no failures in 6 years. If it is a mission critical piece of equipment for you and there are no local sources then I would recommend stocking a spare.
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You can't wait for inspiration. You have to go after it with a club. Jack London
Alan, John White addressed this issue some time ago. I wasn't able to find the thread, but if you're a subscriber here you could ask in the "Experts" section, or just find his name here at Knots and send him an email.
The gist of it was it's probably better not to turn the DC on/off/on/off frequently (e.g., with every cut, the way I used to). He gave the reasoning, sorry I can't remember.
I could not find Johns article either. I let mine run and shut all blast gates between operations. Closed gates means minimum current draw on the system and my motor does not have to engage the high current start winding or the capacitor when I am ready for more dust collection.
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You can't wait for inspiration. You have to go after it with a club. Jack London
don,
I would think that closing the gates, starving the blower for air would make it work harder. But I'm no engineer. Could you explain?
I had a capacitor fail on my duct collector moter a few years back. Replaced it, and that one went south too, like immediately. The third one, I had an electrician friend have a look before firing it up. Turns out the circuit breaker was bad. We deduced this was the problem, when fire came out the entrance panel...
Ray
Ray,
DC blowers do the most work when there is a high differential between the suction and discharge. Closing the gate reduces the differential to near zero, so the motor is under the least load.Don
Hi Ray;
No air to move = no work to do = minimum power draw. Seems kinda counterintuitive but you can verify it with a clamp on ammeter. The collector is working hardest with all gates open.
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You can't wait for inspiration. You have to go after it with a club. Jack London
Don,
Does this apply to the Jet DC 1200? No air to pull = reduced workload on motor?
Alan - planesaw
Yup.
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You can't wait for inspiration. You have to go after it with a club. Jack London
Ray,
One "fires up " one's Indian. One does not fire up pesky dustandstatic collectors and other finicky single phase items -one gently flips a switch, with trepidation in some cases...And one leaves them running because oft repeated cycles heat up those capacitors and use power.(Just checking).Philip Marcou
philip,
After a feller sees fire coming out the box on the wall, it's easy to imagine tiny flaming electrons chasing one another thru the wires.
Ray
All manufacturers should be forced to adapt motors and capacitors that only produce the "cold sparks" that come off ceramic BS guides by one company. Then you could turn it on and off as often as you like. That's the American Way. ha.. ha... ha..ha..ha..
Sarge..
Only piece of equipment I had fail in the new shop (or the old for that matter) is/was my DC. (a Delta unit) it was about a month old and it started having issues starting then it starting popping breakers and then it just died. Took it in they fixed it right up and it has been good to go the last 2 years.
As for the close blast gates, I don't get that. If you close the gate it will be trying to create a vacuum and pulling what ever air it can get into it, When you do this it sounds like it is going made. I would think that at that point it would do just the opposite. I was always under the impression from everything I have read that when you have the freest airflow the system is under the least load, but as you restrict the airflow it works harder. So if you opened all the gates (and if you want to go nuts, take off the filter/bag) it would put the least load on the unit. But I am not an expert. If I think about this I may ask some of the so called experts in a couple weeks at the tool displays at the expo.
Doug
You got me on opening and closing the blast gates, Doug. I eliminated all that by placing my cyclone central and direct hook-up to the 4 major machines I use it for. My single line has no ports between the cyclone and the machine I have it hooked to and that run of 6" flex pipe is around 16" feet with no reduction at all. I made the standard machine ports 6".
But... I don't know but think as you and Ray.. but "I don't know" is the key phrase here on my part.
BTW... was it you that ask me to check the Laguna Platinum TS at IWF? I lost my notebook a the Show with who ask what even though I was able to see all that ask me to look for something for them.
Regards...
Sarge..
Not me, I have a shop full of tools, and cant afford / justify replacing them. (Alas I bought them a few months before SC hit the stores)
Only thing I am looking for is something to make sharpening simpler / faster.
But speaking of the show is there anyplace to see a webpage about all the new stuff introduced at the show by all the companies (vs each companies web site)
Doug M.
Sarge;
Maybe Bill Penz explains it better than I can.
"If you open the ports or change the blower, you need to test your unit. Dust collectors use impeller blowers that work the hardest when they push the most air. If allowed wide open air access with a big impeller, most blowers would quickly push so much air that the motor would draw too many amps and either cut out if protected from overheating or burn up, so dust collector makers limit port and impeller sizes. They also use less efficient heavy steel impellers that are self-cleaning and can stand some heavy pounding. If you closed the intake and tested with your amp meter, you would find your unit is loafing! Yep, in spite of the noise these things take it easy when they are not working and should be left on instead of being constantly turned on and off. Surprisingly enough, adding a cyclone and lots of ducting reduces the airflow until the motor is barely working. It astounds me that so many when finding that their units are not "sucking" enough, want to run out and buy a bigger motor. If it is barely using the horsepower available what does adding more horsepower do when the bigger motor turns at the same speed except waste your money and electricity? On the other hand, opening all up wide especially with a bigger impeller can draw enough amps to quickly burn up a motor. You need to carefully check your final system with an amp meter while all blast gates are open fully to ensure you do not draw too many amps."
Relevant section of his website is here.
Paragraph 7.
BTW the price of that hopper fed screw gun was about $7k base price and around $11K the way I needed it set up when I checked a couple of years ago.
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You can't wait for inspiration. You have to go after it with a club. Jack London
Removing all restrictions from your system such as the filters and inlet restrictor could possibly result in burning up your motor due to overload.
It is easy to verify, just get out your ammeter and see for yourself.
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You can't wait for inspiration. You have to go after it with a club. Jack London
Ya got me to wondering, so..I have an Oneida system and went to their site. From the horses mouth so to speak:"question Can I run my dust collector with no or minimal ductwork off the inlet?
Under 5hp OAS systems should not draw excessive amperage even with no ductwork attached to the inlet. 5Hp and larger systems are designed for industrial applications and require ductwork and should be properly sized."I still cannot get my head around the claim that closing all the gates creates less work for the motor. Oh well.Cheers,Peter
Better life through Zoodles and poutine...
"I still cannot get my head around the claim that closing all the gates creates less work for the motor."
Think of a fan (which is what a dust collector is, after all) operating in a vacuum. No resistance to the blades & no air to move, so the motor just purrs along like it was not attached to anything. In a DC, if all the inlets are closed, the fan creates a partial vacuum and since there's not much air to move (i.e., work to do), the load is less. That's why the motor runs faster, not slower, when you plug the intake on a DC or a shop vac. Less load = higher RPMs.
Mike HennessyPittsburgh, PA
Mike,I think your explanation, among all the others, is the one that allows anyone who thinks the fan motor is "working harder, trying to suck air" against closed gates, to understand that exactly the opposite is happening.When the gates are closed, the impeller is running in a vacuum and the blades have no air "resistance" to push against. With no resistance to its rotation, the motor speeds up. It's not working harder, it's just free running. It just SOUNDS like it's working harder because it makes more noise, and especially if some small amount of air is shrieking in past the gates, which after all, are not perfectly air tight. Lots of noise, but minimal load on the motor. It is almost the same as though no impeller is attached to the shaft. In which case the motor would run at its highest speed and draw the least current. Of course, there would also be almost no noise and the motor would finally SOUND unloaded.The more air that's let in to the impeller area, the more resistance the blades must push against. THEN the motor works harder. To carry that condition further, think of the blades as flat paddles, with no aerodynamic design, pushing air molecules. In that poorly-designed DC, the motor will turn still more slowly, drawing more current. It will SOUND quieter, giving the impression that it is running easier, because it is running slower, but it is burning up.Carrying that example to the ultimate, think of the air as being extremely dense so that the impeller can barely turn, or imagine slowing and stopping the motor by grabbing the shaft with a braking device - same thing. The motor coils will melt.No air in the impeller assembly = no load on the blades = same as no impeller attached to shaft = motor loafing at high speed.Lots of air in the impeller assembly = motor under increased load = draws more current, ultimately burning up if the impeller is poorly designed.Lots of people actually have practical experience with this whole situation because hair dryers are so prevalent. Let the intake grill of a hair dryer get blocked because it has sucked a towel against itself and almost everyone instinctively yanks the obstruction away, fearing the thing is self-destructing. Hearing the fan scream at high speed, the natural reaction is that the fan, having "detected" extra resistance to air flow is somehow "working harder" to pull air through the blocked intake. Nope, it's impeller is free-running in a partial vacuum and is perfectly safe that way. There IS extra resistance, it's to the air coming in the intake, but that's all.It's important to remember that none of these conditions exist if the impeller is not in its shroud. That changes everything.Then, the fan 1. Can't ever experience a vacuum and 2. Doesn't ever meet anywhere near the air resistance because air molecules can escape in all directions. I think most people who are having a problem grasping the principles involved in a DC are thinking in terms of a fan not in a shroud.For an unshrouded fan, the equivalent conditions would be:1. (same as gates closed on DC) Fan blades "feathered" so they are parallel to the direction of rotation = no air gets moved = no load = same as no blades attached to the shaft = motor loafs and runs at high speed.2. (same as gates open on DC) Fan blades turned at right angle to direction of rotation = some (but non-optimal) air movement = maximum load = slow speed = high current draw. I don't think anyone has trouble with this model.Rich
Edited 8/25/2008 9:38 pm ET by Rich14
That's my general understanding from what I have read. Though I don't know the sceintific why's of all of it.. I just use mine as directed by the manufacturer. I do not turn mine on-off over 4 times in an hour as reccomended. I doubt I will take the filters off to test the theory as mine seems to work very well with the filters on it. :>)
Regards...
Sarge..
The capacitor is only used to start the motor, as soon as the motor comes up to speed, a centrifugal clutch kicks it out of the circuit. I used to maintain an industrial system that started, ran for about a minute, stopped, reversed, ran for a minute & repeated the cycle 24/7, it was always under full load. We used to replace the capacitor every 90 days for "insurance". They would usually fail within 6 months. I have a 2-hp air compressor in my shop and have replaced the capacitor once in over 20 years. The lifespan is dependent on the number of "starts" and the mechanical load at start.
Thanks Ray. The problem is Jet's capacitors cost about $38 plus shipping. I could not find one like it at Grainger or any other large company like it.
Alan
btw: I am not an electrician. I can change out a light switch or a wall socket, even did the capacitor, but what I put in was exactly like what I took out.
If there was a brand or model number marking on the replacement you may be able to source it elsewhere.
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You can't wait for inspiration. You have to go after it with a club. Jack London
Apart from the capacitors you need to consider the motor itself. When a motor is running at full speed it generates a "back emf", ie it generates a reverse current to what is turning it. Consequently, while spinning up, it draws a much larger current and this heats up the windings.Part of an electric motor's spec defines the number of starts per hour it can handle. From experience I've noted that some motors have no problem with 50 -60 starts per hour while others seriously overheat with 10. (All were rated at 6).
Well, you did it right. When in doubt, go with the original. When the one in my air compressor went bad, I took the old one to an electrical supply house and had them match it. Wasn't cheap there either :-(
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