Single Phase Capacitor Sizing 165n13

Single phase capacitor sizing 21/03/2011 by Lemau 13 Comments

When install a motor using capacitor for starting or running methods,we must sizing the rated of capacitor suitable with motor to get correct starting torque and avoid winding from overheating and can cause a damage. This is basically a question of motor design.There is no straightforward regular relationship between capacitance and the motor size in kW. When replacing these capacitors, the capacitance value and voltage should be taken from the manufacturer’s plate on the motor or from the old capacitor.This must be correct within ±5% and is sometimes stipulated down to a fraction of a μF.The choice of a running capacitor is even more limited than with a starting capacitor.

How to sizing the starting capacitor? 1) A rule of thumb has been developed over the years to help simplify this process. To select the correct capacitance value, start with 30 to 50μF/kW and adjust the value as required, while measuring motor performance. We also can use this basic formula to calculate capacitor sizing :

2) Determine the voltage rating for capacitor.

When we select the voltage rated for capacitor,we must know the value of our power supply.For safety purpose,multiply the voltage of power supply with 30%.Factors that affect the selection of the proper voltage rating of the capacitor include: • Voltage de-rating factor • Safety agency requirements. • Reliability requirements • Maximum operating temperature • Space available

How to sizing the running capacitor? When selecting motor run capacitors all of the required parameters above need to be identified in an organized process. that, not only are the physical and basic electrical requirements important.

But the type of dielectric material and the metallization technique should be examined.The wrong choice here can have adverse effects on the overall performance of the capacitors.Please refer to motor nameplate or supplier or manufacture to get a accurate value of capacitor.Safety First - See more at: http://www.electricneutron.com/electric-motor/single-phase-capacitor-sizing/#sthash.2uIVJEqN.dpuf

http://www.temcoindustrialpower.com/

Overview

A start capacitor is used to briefly shift phase on a start winding in a single phase electric motor to create an increase in torque. Start capacitors possess a very large capacitance value for their size and voltage rating. As a result, they are only intended for intermittent duty. Because of this, start capacitors will fail after being left energized for too long due to a faulty starting circuit on a motor.

Start vs. Run Capacitors Start capacitors give a large capacitance value necessary for motor starting for a very short (seconds long) period of time. They are only intermittent duty and will fail catastrophically if energized too long. Run capacitors are used for continuous voltage and current control to a motor's windings and are therefore continuous duty. They are generally of a much lower capacitance value.

Are start and run capacitors interchangeable? Yes and no. In unusual circumstances, a run capacitor could be used as a start capacitor, but the values available are much lower than the values usually available for dedicated start capacitors. The capacitance and voltage ratings would have to match the original start capacitor specification. A startcapacitor can not ever be used as a run capacitor, because it could not handle current continuously (only a couple of seconds). View our video tutorial below to learn the differences between start and run capacitors.

What is a resistor and do I need one? Most replacement start capacitors will not include a resistor. You can check the condition of the old one by checking the resistance value, or just replace it with a new one. This should read somewhere around 10-20k Ohms and around 2 watts. The resistors are usually either soldered or crimped to the terminals. The purpose of the resistor is to bleed off residual voltage in the capacitor after it has been disconnected from the circuit after motor start up. Not all start capacitors will use one, as there are other ways to accomplish this. The important part is if your original capacitor had one, you'll need to replace it on the new capacitor. Learn how to install a bleed down resistor on your start cap.

Troubleshooting How do I know if my start capacitor is bad?

Most electric start motor capacitor failures are one of two types:

"The Start Cap blew its guts out!" This is what we call catastrophic failure. It is usually caused by an electric motor's starting circuit being engaged too long for the intermittent duty rating of a start cap. The top of the start cap has literally

been blown off, and the insides have been partially or fully ejected. Similarly but not quite as dramatic, a start cap may just exhibit a ruptured pressure relief blister. In either case, it's easy to tell that the start cap is in need of replacement.

My motor is slow to start. Is my start capacitor bad? The answer to this question is maybe. Your start capacitor may have lost its capacitance rating due to wear and age, or you may have other non-capacitor related issues that have to do with other motor components.

Specifications

Most start capacitor applications use a rating of 50-1200 uf capacitance and voltages of 110/125, 165, 220/250 and 330 VAC. They are also usually always 50 and 60 Hz rated. Case designs are typically round and cast in black phenolic or Bakelite materials. Terminations are usually ¼" push on terminals with two terminals per connection post.

Voltage Select a capacitor with a voltage rating at or above the original capacitor. If you're using a 370 volt capacitor, a 370 or 440 volt one will work. The 440 volt unit will actually last longer. A capacitor will have a marked voltage indicating the acetable peak voltage, not operational voltage. Capacitance Select a capacitor with a capacitance value (given in MFD, uf or microfarad) that is equal to the original capacitor. Do not deviate from the original value, as it sets the operational characteristics of the motor.

Frequency (Hz) Select a capacitor with the Hz rating of the original. Nearly all replacement capacitors will be labeled 50/60. Connection terminal style Nearly every capacitor will use a ¼" flag style push-on connector. The next question is, "How many terminals per terminal post are needed for the application motor?" Most start capacitors have two terminals per post, and most run capacitors will have either 3 or 4 terminals per post. that your selected capacitor has at least the number of connection terminals per connection post as the original motor capacitor. Case shape Nearly all start capacitors have a round case. Round run capacitors are by far the most common, but many motors still use oval designs. Electrically speaking, there is no difference. Fit is the only question here. If space in the mounting box is not limited, the case style does not matter. Case size Just like case shape, overall size makes no difference electrically. Select a capacitor that will fit within the space provided. Back to Top

Product Selection

110/125 VAC Capacitanc 1 Piece Price e w/ Shipping Value

5 Piece Price w/ Shipping


108-130

SC0005 SC0006 SC0007 $8.63 view » $29.16 view » $46.56 view » You Save $13.99 You Save $39.74

161-193


189-227


200-240

SC0089 SC0090 SC0091 $54.32view » $8.63 view » $31.55 view » You Save $11.60 You Save $31.98

216-259


233-280


270-324


324-389


340-408


378-454

SC0029

SC0030 $37.59 view »

SC0031 $57.95 view »

$9.93 view » You Save $12.06 You Save $41.35 400-480


460-552

SC0035 SC0036 SC0037 $11.04 view » $42.28 view » $66.84 view » You Save $12.92 You Save $43.5+

540-648


590-708


708-850


829-995


1000-1200


220/250 VAC Capacitanc 1 Piece Price e w/ Shipping Value



59-71


64-77


72-86


88-106


108-130


124-149

SC0068 SC0069 $10.86 view » $41.52 view »

SC0070 $65.40 view »

You Save $12.78 You Save $43.20 145-174


161-193


189-227


216-259


340-408


430-516

SC0001 SC0002 SC0003 $20.37 view » $67.61 view » $120.67 view » You Save $34.24 You Save $83.03 SC0004 - 25 Lot $347.60 view » You Save $161.64

630-750


165V Capacitance 1 Piece Price Value w/ Shipping



124-149

SC0092 SC0093 $8.53 view » $40.14 view » You Save $2.51

SC0094 $62.63 view » You Save $22.67

189-227


SC0097 $60.14 view » You Save $31.96

400-480


330V Capacitance 1 Piece Price Value w/ Shipping



88-106


135-162


SC0106 $99.93 view » You Save $24.67

Overview A run capacitor is used to continuously adjust current or phase shift to a motor's windings in an effort to optimise the motor's torque and efficiency performance. Because it is designed for continuous duty, it has a much lower failure rate than a start capacitor.

Dual Run vs. Run Capacitors The dual run capacitor design's only advantage is that it comes in a small package with only 3 connections. Aside from this, here is no other difference between run and dual run capacitors. If there is enough space for mounting, using two separate run capacitors in place of your original dual run capacitor is acceptable. They generally have connections marked "C" for "common", "H" or "Herm" for "Hermetic Compressor" and "F" for "Fan." They will also have two different capacitor ratings for the two different parts. See our guide on dual run capacitors for more details.

Start vs. Run Capacitors Start capacitors give a large capacitance value necessary for motor starting for a very short (seconds long) period of time. They are only intermittent duty and will fail catastrophically if energized too long. Run capacitors are used for continuous voltage and current control to a motor's windings and are therefore continuous duty. They are generally of a much lower capacitance value.

Are start and run capacitors interchangeable? In unusual circumstances, a run capacitor could be used as a start capacitor, but the values available for them are much lower than the values usually available for dedicated start capacitors. The capacitance and voltage ratings would have to match the original start capacitor specification. A start capacitor can never be used as a run capacitor, because it could not handle current continuously (only a couple of seconds).

View our video tutorial below to learn the differences between start and run capacitors.

Back to Top

Specifications Most run capacitor applications use a rating of 2.5-100 uf (microfarads) capacitance and voltages of 370 or 440 VAC. They are also usually always 50 and 60 Hz rated. Case designs are round or oval, most commonly using either a steel or aluminum shell and cap. Terminations are usually ¼" push on terminals with 2-4 terminals per connection post.

Voltage: Select a capacitor with a voltage rating at or above the original capacitor. If you're using a 370 volt capacitor, a 370 or 440 volt capacitor will work, though the 440 volt unit will actually last longer. A run capacitor will have a marked voltage indicating peak voltage acceptable - not operational voltage.

Capacitance: Select a capacitor with a capacitance value (given in MFD, uf or microfarad) that is equal to the original capacitor. Do not deviate from the original value, as it sets the operational characteristics of the motor. Hz: Select a capacitor with the Hz rating of the original. Nearly all tun vapacitors will be labeled 50/60. Case Style: Round or Oval? Round Run Capacitors are by far the most common, but many motors still use oval designs. Electrically speaking, there is no difference. Fit is the only question here. If space in the mounting box is not limited, the case style does not matter. Overall Size: Just like case style, overall size makes no difference electrically. Select a capacitor that will fit within the space provided. Terminal Type: Most run capacitor terminal designs include 1-4 ¼" push on tab and will have either 3 or 4 tabs. Just make sure you have enough tabs per connection post to make the connections you need.

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Run Capacitor Product Selection

Round, 370 VAC Capacitanc e Value (uf)

1 Piece w/ Shipping

5 Lot w/ Shipping RC0021 $25.02 view » You Save $5.98

10 Lot w/ Shipping

60 Lot w/ Shipping

5

RC0006 $6.20 view »

RC0036 $47.60 view » You Save $14.40

10

RC0007 RC0022 RC0037 $11.92 view » $36.10 view » $50.20 view » You Save $23.50 You Save $69

15

RC0008 $7.50 view »

RC0023 $35 view » You Save $2.50

RC0038 $52.16 view » You Save $22.84

20

RC0009 $7.8 view »

RC0024 $37.61 view » You Save $2.39

RC0039 $53.16 view » You Save $26.84

25

RC0010 $7.40 view »

RC0025 $28.89 view » You Save $8.11

RC0040 $55.43 view » You Save $18.57

30

RC0011 $7.89 view »

RC0026 $34.95 view » You Save $4.50

RC0041 $60.90 view » You Save $18

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35

RC0012

RC0027

RC0042

-

-

$9.60 view »

$40.29 view » You Save $7.71

$58.05 view » You Save $37.95

40

RC0013 $8.50 view »


RC0043 $72.28 view » You Save $12.72

45

RC0014 $9.15 view »


RC0044 $61.38 view » You Save $30.12

50

RC0015 $9.35 view »


RC0045 RC0046 $55.05 view » $375 view » You Save $38.45 You Save $186

Round, 370-440 VAC Capacitanc e Value (uf)

1 Piece w/ Shipping

5 Lot w/ Shipping

10 Lot w/ Shipping

25 Lot w/ Shipping

50 Lot w/ Shipping

5

RC0047 RC0053 $6.37 view » $12.35 view » You Save $19.50

40


RC0092 RC0093 RC0094 RC0095 $47.53 view » $105.73 view » $193.03 view » $363.75 view » You Save $14.90 You Save $50.75 You Save $120.50 You Save $264

100

RC0096

RC0098 $86.33 view »

RC0097 $47.53 view »

RC0059 RC0074 $48.75 view » $92.5 view » You Save $110.50 You Save $226

100 Lot w/ Shipping

RC0099 $169.75 view »

RC0100 $290.03 view »

RC0079 $156 view » You Save $481

RC0101 $532.53 view »

$15.04 view » You Save $28.50 You Save $66

You Save $212.50 You Save $476

You Save $1001

Oval, 370-440 VAC Capacitanc 1 Piece e w/ Shipping Value (uf)

5 Lot w/ Shipping

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25 Lot w/ Shipping

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5


-

RC0075 $92.5 view » You Save $226


7.5


RC0061 RC0071 RC0076 $27.50 view » $56.50 view » $104 view » You Save $28.50 You Save $83.50 You Save $176


10


RC0062 RC0072 $31.10 view » $62.25 view » You Save $50.90 You Save $142.75

RC0077 $115.50 view » You Save $294.50


15


RC0086 RC0087 RC0088 $43.65 view » $86.33 view » $154.23 view » You Save $9.90 You Save $48.25 You Save $115.50

RC0089 $290.03 view » You Save $250

50


RC0064 RC0073 $59.95 view » $129.95 view » You Save $43.55 You Save


RC0060 $48.75 view » You Save $110.50

RC0078 $249 view » You Save

$118.80

$248.50

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Troubleshooting When is it time to replace a run capacitor?

As a general rule of thumb, a run capacitor will far out-last the same motor's start capacitor. A run motor capacitor will wear down differently, making them a bit more complicated when trying to determine if it needs to be replaced.

When a run capacitor begins to perform outside the allowable range,it is usually indicated by a dropping of the rated capacitance value. For most standard motors, a run capacitor will have a "tolerance" specified describing how close to the rated capacitance value that the actual value may be. This will be usually +/- 5% to 10%. For most motors, as long as the actual value is is within the 10% mark of the rated value, you're in good shape. If the capacitance drops outside of this range, the capacitor should be replaced.

Due to a defect in a capacitor's construction or a non-capacitor related motor issue, a run capacitor will sometimes bulge from internal pressure. For most modern run capacitor designs, this will open the circuit, disconnecting the internal spiral membrane as a protective measure to prevent the capacitor from popping.

The test in this case is simple: if its bulging, time to replace. If you measure no continuity across the terminals, it is also time to replace.

View the video below on how to replace a run capacitor in an air conditioning unit.

Causes of Failure Depending on how close the run capacitor is to its design life, there may be multiple factors that determine why a run capacitor has failed.

Time - All capacitors have a design life. Several factors may be interchanged or combined to increase or reduce the life of a run capacitor, but once the design life is exceeded, the internals may begin to more rapidly decay and drop in performance. Simply put, a failure may occur because the capacitor is "just old."

Heat - Exceeding the design limit of operating temperature can have a big effect on run capacitor life expectancy. In general, motors that are operated in hot environments or with little ventilation will experience a dramatically reduced

lifespan on their run capacitor. The same can be caused by radiated heat from a generally hot running motor, causing the capacitor to run hot. If you can keep your run capacitor cool, it will last a lot longer.

Current - Motor failure causes the capacitor to be overloaded. This scenario is less commonly noticed, as it would usually be accompanied by a partial or complete failure of the motor. The motor is overloaded or has a failure in the windings, causing the current to climb. This can have an effect on the capacitor.

Voltage - This single factor can have an exponential effect in shortening design life. A run capacitor will have a marked voltage rating that should not be exceeded. Let's use 440 volts as an example. At 450 volts, the life may be reduced by 20%. At 460 volts, the life may be reduced by 50%. At 470 volts, there is a 75% life reduction, and so on. The same can be applied in reverse to help increase life by using a capacitor with a voltage rating significantly higher then needed, although to a less dramatic degree.

Capacitor Lifespan The mid point for a good quality aftermarket run capacitor (one that didn't come with your motor) would be 30,000 to 60,000 running hours. Factory-installed run capacitors sometimes have a designed lifespan that is much lower. In highly competitive industries where every part can have a significant impact on cost, or where a motor's intended use would likely be intermittent and infrequent, a lower grade of run capacitor may be selected with a design life of as little as 1000

hours. Additionally, all of the factors from the section above (run capacitor causes of failure) may dramatically modify the reasonable expected life of a run capacitor.

Overview

Dual run capacitors are commonly used in HVAC (heating, ventilation, and air conditioning) units. Dual capacitors have three terminals, unlike regular run capacitors, which have only two. Electrically, they are the same as run capacitors that have two terminals. Using a dual run capacitor allows you to save space if you have a small mounting area. The terminals are also clearly marked, making it easy to hook it up to the different components of your air conditioner.

Dual capacitors usually have connections marked "C" for "common," "H" or "HERM" for the hermetic compressor, and "F" or "FAN" for the fan in an HVAC unit. They also have two different capacitance ratings (for exampple, 35/5 uf). The larger value is always connected to the compressor (35 uf in the example), while the smaller value will always be connected to the fan (in this case, 5 uf).

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Specifications Below is a list of specifications that must be taken into consideration when selecting a new capacitor.

Capacitance Make sure the capacitance of your new capacitor is the same as that of the one you're replacing. Voltage Dual capacitors are usually rated for 370V or 440V. Use a capacitor that has the same or higher voltage as your system voltage. Never select one that has a lower voltage rating than your system voltage. Frequency Most capacitors will be rated for both 50 and 60 Hz. Oval vs. Round Case Style As long as the capacitance, voltage, and frequency of your capacitor is right for your application, the shape of the capacitor does not matter as long as it can fit within the provided mounting space in your motor or air conditioning unit. Terminal Type Most capacitor terminals include one to four ¼" push on tabs. Most have 3 to 4 tabs, so make sure you have enough tabs per connection post to make the connections you need.

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Video - Replacing a Dual Run Capacitor

View our video tutorial on how to diagnose problems with your air conditioning unit and how to replace the run capacitors in it. For a more in-depth look at troubleshooting, check out our Troubleshooting Guide.

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Product Selection

1 piece prices include shipping. All lots have free shipping!

Dual Run Capacitor Selection Chart Capacitance (uf)

1 Piece

35/5

RC0102 » $7.57

RC0103 » RC0104 » RC0105 » RC0106 » RC0107 » $29.10 $53.35 $105.73 $193.03 $363.75 Save $9 Save $48 Save $165 Save $360 Save $750

40/5

RC0108 » $7.61

RC0109 » RC0110 » RC0111 » RC0112 » RC0113 » $28.62 $55.29 $107.67 $193.03 $367.63 Save $9.75 Save $49 Save $166 Save $363 Save $755

45/5

RC0115 » RC0116 » RC0117 » RC0118 » RC0119 » RC0114 » $29.05 $54.27 $126.05 $241.53 $435.53 $8.58 Save Save Save $191 Save $412 Save $855 $14.30 $58.55

50/5

RC0120 » $8.92

60/5

RC0126 » RC0127 » RC0128 » RC0129 » RC0130 » RC0131 »

5 Lot

10 Lot

25 Lot

50 Lot

100 Lot

RC0121 » RC0122 » RC0123 » RC0124 » RC0125 » $31.04 $59.17 $134.83 $260.93 $445.23 Save $14 Save $60 Save $198 Save $428 Save $888

$9.55

70/5

$33.95 Save $14.25

$63.05 Save $63.50

$140.65 $266.75 $464.63 Save $211 Save $457 Save $950

RC0133 » RC0134 » RC0137 » RC0135 » RC0136 » RC0132 » $37.83 $66.93 $474.33 $144.53 $270.63 $10.95 Save Save Save Save $243 Save $525 $17.45 $73.90 $1090

Overview

A start capacitor resistor (also called a "bleed down resistor") is used to bleed off residual voltage in a start capacitor after it has removed from a motor circuit after start up. Not all start caps use resistors, as there are other ways to accomplish the task of reducing residual voltage in a capacitor.

What is important to note is that if the capacitor you are replacing had a bleed down resistor, then you will need to replace the resistor in your new start capacitor. You can either check to see if the old resistor is still good, or you can replace it with

a new one. The resistance value should read somewhere between 10 to 20k Ohms and around 2 watts. Resistors are usually crimped or soldered to the start capacitor's terminals.

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Specifications & Product Selection Use for start capacitors:

Voltage: up to 330V Capacitance: up to 1200 uf Mounting type: Solder Resistor body diameter: 0.1255 in. Resistor body length: Overall length (including leads): 2.363 in. Lead length: 1 in. per side Lead diameter: 0.19 in.

View our selection of start capacitor resistors. All prices listed have free shipping included. Quantity

Part Number

Price

1

SCR001 »

$3.95

5

SCR002 »

$4.95

10

SCR003 »

$6

25

SCR004 »

$9

50

SCR005 »

$15

100

SCR006 »

$25

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Replacing a Resistor

Most start capacitors do not have a resistor. But if you need to replace a start capacitor that does have one, you'll need to use a resistor on the new capacitor as well. You can either see if the old resistor is still good, or just use a new one.

View our video tutorial on how to install a start capacitor bleed down resistor.

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