# Delta Rockwell band saw motor will not start



## Janderso (Jul 14, 2020)

I am so incompetent when it comes to electric motors but I think this is a no-brainer.
I bought this beautiful Delta-Rockwell 14" metal/wood band saw off Facebook Marketplace yesterday.
When I went to look at it I knew I had found something special. It's very clean and has seen little use.
The seller told me it runs but you need to give it some help. Sure enough, spin the blade pulleys and off she goes.
This morning I found this 216-259 mfd start capacitor burnt out, smelly and I have no change when I touch my Fluke T5-1000 to the leads. I get 0L.
I found one from Graingers I just hope UPS will get it to me.

Question,
Why do they continue to use these capacitors? They don't last. Is there a brand that will last the life of the motor?


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## kb58 (Jul 14, 2020)

Short answer: no.
Longer answer: Yes, but it would cost a lot more and be bigger.

BTW, any good capacitor will always read "OL" on an ohmmeter because of how capacitors are constructed. There will be an initial inrush of current, but after that, zero conduction. An ohmmeter is only good for checking for shorts.


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## silence dogood (Jul 14, 2020)

A capacitor is basically made of two metal plates separated by an insulator.  Won't go to much into detail, but a cap can store electricity and then release it when necessary.  The problem is the insulator which is also called a dielectric.  To get a capacitor that can hold a charge big enough to start an electric motor would be the size of a room.  So a special dielectric is made that works so well the capacitor can be made much smaller.  Unfortunately, this dielectric is a form of paste that can over time dry out or degrade.  That is why I always recommend to get the newest caps on the market, they even have a shelf life.. Maybe with more development on these new aeogel capacitors, the problem will be solved.


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## markba633csi (Jul 14, 2020)

Jeff: Not sure if you did this but you should reverse the leads of your meter a couple times when using the resistance range of the meter to test.
You should see the meter swing towards zero ohms then climb towards infinity each time you swap leads as the cap charges/discharges.  This test won't detect changes in cap value, only open or shorted caps. A quicky test. Old fashioned needle style analog meters are great for this.
The way these caps are constructed they only last a few years for what they cost.  The older US made units would sometimes go for decades.
Newer import caps seem to fail more frequently. From the looks of it yours had leaked/failed after many years of use.
-Mark


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## SLK001 (Jul 14, 2020)

Janderso said:


> Question,
> Why do they continue to use these capacitors? They don't last. Is there a brand that will last the life of the motor?



It's a start capacitor - it changes the field angle enough to get the motor running, then it is switched out of the circuit.  You can tell that it is a start cap, because you could "push start" the motor by hand.  Having a start capacitor makes the motor smaller, because you don't have to have a separate start winding - the main winding is doing double duty.  A good analogy is a car transmission.  To get a car rolling, you use a low gear (ie, have a start capacitor).  To run a car efficiently, you use a high gear.  A motor is wound for "high gear" and uses a start capacitor (low gear) to get the motor running fast enough to shift into high gear.


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## Janderso (Jul 14, 2020)

markba633csi said:


> Jeff: Not sure if you did this but you should reverse the leads of your meter a couple times when using the resistance range of the meter to test.
> You should see the meter swing towards zero ohms then climb towards infinity each time you swap leads as the cap charges/discharges.  This test won't detect changes in cap value, only open or shorted caps. A quicky test. Old fashioned needle style analog meters are great for this.
> The way these caps are constructed they only last a few years for what they cost.  The older US made units would sometimes go for decades.
> Newer import caps seem to fail more frequently. From the looks of it yours had leaked/failed after many years of use.
> -Mark


Mark,
I didn't know my Fluke wouldn't test a capacitor. I see they make specific products to test these things.
How about a visual.
This thing is toast. It stinks to high heaven too.


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## kb58 (Jul 14, 2020)

Right, so no need for testing.


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## Janderso (Jul 14, 2020)

kb58 said:


> Right, so no need for testing.


I still wanted to verify but it seems I don't have the correct device.
I learned that much.


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## kb58 (Jul 14, 2020)

Even if it had tested fine, no way one with that sort of damage should be used. Too much risk of shorting or starting a fire.


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## darkzero (Jul 14, 2020)

A bit of repeating but no, capacitors won't last "forever", they eventually dry out). Of course some are made better than others & may last longer.

Mark already said it but if you use the OHM function, the resistance will climb then eventually show open (OL). Reverse the leads & it will repeat. But this doesn't actually tell you the cap's reading.

Not sure what model Fluke you have but some MMs have a capacitance function. On my Fluke this is the symbol  
	

	
	
		
		

		
			





.   Sometimes it may be in blue meaning it's an alternate function & you have to press the blue button to switch to that function.

I've had good luck with Grainger's Dayton brand caps. Start cap on my mill blew only a yr old. Wanted to fix it ASAP cause I was in the middle of something so I picked one up from Grangier next morning. Well I replaced the Run cap too just for the heck of it. They were made in China but it's been 7 yrs now trouble free.

EDIT: Oh & in the future, if you are going to measure a pretty good/large size cap, be sure to discharge it first.


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## benmychree (Jul 14, 2020)

One of my all too many possessions is a capacitor analyzer, but yours is quite beyond its use; probably Grainger is the place to get a new one, or if there is a motor shop in town, they would likely have one; hopefully, the MFD value is still legible.
The analyzer was a gift from a guy that I used to work for, who had to sell/give away everything that he owned when he lost his shop and storage venue.


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## benmychree (Jul 14, 2020)

kb58 said:


> Even if it had tested fine, no way one with that sort of damage should be used. Too much risk of shorting or starting a fire.


That one definitely had the smoke let out of it!


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## Janderso (Jul 14, 2020)

benmychree said:


> hopefully, the MFD value is still legible.


Fortunately yes, 216-259 MFD.


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## Ulma Doctor (Jul 14, 2020)

An oil flled capacitor will have the longest life span


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## Ulma Doctor (Jul 14, 2020)

SLK001 said:


> Having a start capacitor makes the motor smaller, because you don't have to have a separate start winding - the main winding is doing double duty.


Not true
T5, and T8 is the start windings on most single phase capacitor start motors you will run across


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## benmychree (Jul 14, 2020)

Ulma Doctor said:


> An oil flled capacitor will have the longest life span


I have never seen an oil filled capacitor used for motor starting, only running.


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## Janderso (Jul 14, 2020)

How do you know if they are oil filled?
This one had goo in it. It was all over the cover and the capacitor.


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## benmychree (Jul 14, 2020)

Oil filled caps have an all metal, sealed case, and are more oval shaped, start caps usually have a round black plastic case with Micarta end cap with a blowout disc near the terminals; yours is a bit different, having an aluminum shell with a cardboard sleeve around it.  I have never (previous to this one) seen one blow out like that in the picture, usually they just quit working, or blow some smoke/fire out the bursting disc, which yours did not have, the whole end was a bursting disc!


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## MikeInOr (Jul 14, 2020)

Janderso said:


> Fortunately yes, 216-259 MFD.



You do not need to get a new capacitor with an exact 216-259MFD rating.  Any capacitor around 180MFD to 300MFD with the same or higher voltage rating will do the job just fine.  The bigger the capacitor (more MFD) the quicker the motor will come up to speed but the more amps it will draw while doing so.  A MFD range is given (216 - 259) because the actual MFD will change based on load, voltage and temperature... so starting capacitors generally don't have a single fixed MFD value that they are rated at.

Or replace the motor with a 3 phase motor and a VFD and get rid of the starting capacitor all together while gaining greater control over the speed of the saw.  (I would just buy a new capacitor!)


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## Janderso (Jul 14, 2020)

MikeInOr said:


> (I would just buy a new capacitor!)


I have one coming from Grainger. It's shipped but let's hope UPS can deliver.


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## markba633csi (Jul 14, 2020)

There may be some motors that use the run windings for starting but it's rare to see that. Most made from the 50s onward using a start capacitor
have 2 run and 1 start winding.  Some are called split-phase; they don't have start capacitor, only a centrifugal switch. They work well in applications where high starting torque is not required.
I went for years without any type of capacitor meter, but recently bought one of those little imported circuit board units that runs off a 9v battery.
It measures caps, inductors and semiconductors with pretty good accuracy and only cost around 7 bucks. Highly recommended, and I'm a tightwad when it comes to buying test gear
Here it is:








						LCR-T4 ESR Meter Transistor Tester Diode Triode Capacitance SCR Inductance M328 714890585287 | eBay
					

Inductors, capacitors, diodes, dual diode, mos, transistor, SCR, the regulator, LED tube, ESR. diode (including double diode), thyristor, transistor, resistor and capacitor and other components. 3:Can detect the transistor, MOSFET protection diode amplification coefficient.



					www.ebay.com
				




-Mark


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## Ulma Doctor (Jul 14, 2020)

My simpson meter is great for testing capacitors.
you can watch the cap charge up and then watch the needle drop
a bad cap won't charge, the needle won't swing


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## Ulma Doctor (Jul 14, 2020)

benmychree said:


> I have never seen an oil filled capacitor used for motor starting, only running.


they get pricey as you get larger in value, but they do indeed exist


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## Janderso (Jul 14, 2020)

MikeInOr said:


> You do not need to get a new capacitor with an exact 216-259MFD rating. Any capacitor around 180MFD to 300MFD with the same or higher voltage rating will do the job just fine


Just for kicks I went down to Ace Hardware in town.
They actually had one capacitor in stock. The value was, 124-149uf. I understand uf and mfd are the same thing?
Based on what you said, I don't think Ace is gonna help me.


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## MikeInOr (Jul 14, 2020)

Janderso said:


> Just for kicks I went down to Ace Hardware in town.
> They actually had one capacitor in stock. The value was, 124-149uf. I understand uf and mfd are the same thing?
> Based on what you said, I don't think Ace is gonna help me.



uF is microfared,  mF is millifarad which equals 1,000 uf.

If they are both starting capacitors that doesn't sound quite right.  Most starting caps I have used are within 100% to 300% or so of each other across a very wide range of motors.  They generally won't be different by a factor of more that 1000.  Can you post a pic of the writing on the old capacitor?


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## Ulma Doctor (Jul 14, 2020)

I have seen Microfarads expressed as mf on older capacitors.
Don’t confuse with milli-farad


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## MikeInOr (Jul 14, 2020)

Ulma Doctor said:


> I have seen Microfarads expressed as mf on older capacitors.
> Don’t confuse with milli-farad



Yes, microfared for a starting capacitor makes much more sense to me!  I had actually posted that the substitution looked good to me until I looked it up to make sure.

WIKIpedia:
For most applications, the farad is an impractically large unit of capacitance. Most electrical and electronic applications are covered by the following SI prefixes:


1 mF (millifarad, one thousandth (10−3) of a farad) = 1000 μF = 1000000 nF
1 μF (microfarad, one millionth (10−6) of a farad) = 0.000 001 F = 1000 nF = 1000000 pF
1 nF (nanofarad, one billionth (10−9) of a farad) = 0.001 μF = 1000 pF
1 pF (picofarad, one trillionth (10−12) of a farad)


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## kb58 (Jul 14, 2020)

Oh microfarads is what you need for sure. Another tip off for the right part is size. If a vendor tries handing you one that's 5x bigger or 10x smaller than the old one, nope.


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## Janderso (Jul 18, 2020)

Well shoot.
I replaced the start capacitor and it just hums, tries to decide which direction to turn then goes to full speed. This takes a couple seconds. One time it turns clockwise, the next counter clockwise.
Now what?
I replaced it with an identical start capacitor.


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## CluelessNewB (Jul 18, 2020)

Check your connections.   Did maybe a wire slip out from under a wire nut?  It could also be dirty or pitted starting contacts.


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## kb58 (Jul 18, 2020)

What you're describing is that the motor isn't seeing the capacitor. Could be miswired, a bad connection, or the capacitor has too small a value.


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## Bi11Hudson (Jul 18, 2020)

An "expert" must be taken as the individual sounds that make up the word. "Ex" being a has been. And "Spert" being a drip under pressure. Further, I am not an expert, having never finished grammar school. Never went to high school but worked in the "industrial" electrical field fo well over 50 years.

That said, my experience leads me to the following disertation on the subject:

First off: "microfarad" is a common reference for capacitors, as are nano and pico farads. Milli-farads was not used until *very* recently, the last ten years or so. I use the symbol "u" to represent the Greek "mu" or "micro". Most "electrolytic" capacitors use "mF" or "uF" to refer to capacity. I have never seem a "milli-farad" designation. A capacitor of such capacity is normally refered to as 47,000 uF or mF. It is not labeled as 47 milli-farads. The use of 1 to 50 Farads (or larger spans) is *very* recent and usually for low voltage capacitors, 5 volts or so. It is an accepted fact that as voltage rating goes up, size also increases. When space permits, voltage rating is at least double, usually more, in linear power supplies.

In addition to this, there are "non polarized" electrolytics that allow the use on A-C. The 47,000 uF mentioned above is polarity sensitive and usually explodes on reverse polarity. Such filter capacitors must never be used on A-C or reverse polarity. They make great voltage stabilizers on D-C but must never be used on A-C. I have some non-polarized electrolytics on hand, of 300 uF or so and 480 volts AC. They are the size of an oil can.

Second: Motor capacitors are *non-polarized electrolytics*. Their purpose is to assist in altering the start winding so that there is an effective phase shift in the secondary winding. This phase shift is what allows the motor to start. Essentially a two phase motor. Not as strong as a three phase, but usable. There are motors that run the "start" winding continously, forming a second "phase". They are usually used on fans and similar light loads. They are called "split phase" motors. I do use one on a table saw, but it stalls much easier than a regular single phase motor.

I offer http://www.hudsontelcom.com/uploads/ShopElex.pdf as a text on the application of motors. It is limited, but gives insight into the phase shifting. Be advised, it has been shortened to exclude running three phase motors on single phase and generating 120-208 volts from an automotive alternator. But is still near fifty pages in length.

Electrical is a deep subject and I have barely broken the ice on the surface of the subject. Electronics and the components for it are a whole different subject. They should not be confused. Modern VFDs to run three phase motors from single phase power are quite a boon to especially hobbyists. But running three phase motors from single phase has been done since before World War One. It is not new technology. Only the VFDs use new (20 odd years) technology and their key is the variable speed. Motors run at a "fixed" speed based on the power line frequency. There are exceptions, but as a rule they are not used on machine tools because speed is not very stable. Hence, the "Variable Frequency Drives" of modern technology.

.


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## Ulma Doctor (Jul 18, 2020)

the centrifugal start switch may no be functioning or there is a problem in the start winding

this short video may help out...


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