440 370 vac b capacitor

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Understanding & Selecting Capacitors

The motor may be the heart of any HVAC system, but it is useless without quality capacitors which, like a car battery, keep the motor and the system running properly. How much do you understand about the capacitors’ critical function in the HVAC system?

This article will help you understand some of the industry standards set for capacitor quality, safety, and performance and will give you insight into selecting capacitors on-the-job.

What Capacitors Do

Almost every motor is furnished with either a start capacitor, a run capacitor, or both.

The start capacitor is connected into the motor’s electrical circuit at rest. It gives the motor an initial “push” on start-up, briefly increasing its starting torque and allowing the motor to be cycled on and off quickly. A typical start capacitor rating ranges from 25 µF up to 1,400 µF and 110 Vac to 330 Vac.

Once the motor reaches a specific speed, the start capacitor is disconnected from the winding circuit by a switch (or relay). If the motor drops below that speed, the capacitor will be switched back into the electrical circuit to bring the motor to the speed required.

Designed for continuous duty, the run capacitor always remains energized and connected in the motor’s electrical circuit. A typical run capacitor rating ranges from 2 µF to 80 µF and is either rated at 370 Vac or 440 Vac.

A properly sized run capacitor will increase the efficiency of the motor operation by providing the proper “phase angle” between voltage and current to create the rotational electrical field needed by the motor.

Proper Fitting/Substitution of Capacitors

How important is it to match the capacitance rating specified by the motor? In short, it’s very important -- even critical. In order to ensure the proper motor operation that the manufacturer designed it for, and to prevent damage to the motor, always use the exact same nominal rating of capacitance specified by the motor nameplate. 

There is always a tolerance level on the microfarad (µF) rating. A typical tolerance on the capacitance of a motor run capacitor for HVAC applications is +/-6%. With this being said, that means that a 40 µF capacitor can rate from 37.6 to 42.4 µF and still be considered a passing capacitor.

When engineers design motors, they take into consideration this type of tolerance range. They specify the nominal (40 µF) rating along with a tolerance (+/-6%) to make sure that if the capacitor is to be replaced, the motor will provide the same performance that it was designed for. 

Given the explanation above for the tolerance ranges, it is not suggested to use a 35 µF in place of a 40 µF. 

40 µF ±6% = 37.6 to 42.4 µF     35 µF ±6% = 32.9 to 37.1 µF

As you can see, the high side of the 35 µF capacitance tolerance (37.1 µF) does not meet the low side of the capacitance tolerance of the 40 µF (37.6 µF) capacitor you are trying to replace it with. This also is the same for 5 µF and the 4 µF capacitors. 

5 µF ±6% = 4.7 to 5.3 µF                 4 µF ±6% = 3.76 to 4.24 µF 

Using improperly sized capacitors can have a variety of detrimental effects on the motor. If the capacitor’s µF rating is less than the motor was designed for, the motor winding current will be too high. If the capacitor’s µF rating is higher than the motor was designed for, the motor winding current will be too low. Either scenario can lead to one or more of the following:

  • Reduced motor speeds   
    • reduces system airflow/cooling   
    • increases system noise 
  • Temperature increase   
    • causes bearing wear and lubrication loss   
    • results in insulation breakdown   
    • increases noise 
  • Lower motor efficiency   
    • increases energy consumption   
    • reduces system and motor life 
  • Improper equipment operation   
    • results in improper cycling   
    • increased noise   
    • stresses other components 

Motors are designed with a specific, nominal rating and tolerance.

If anything is outside that rating, the motor will run either faster or slower. Either way, the end result will be that the machine will not work properly, and the motor, capacitor, or any other component in the machine will receive additional stress that will cause damage, make noise, and require repair. 

There have also been questions about what voltage to use when replacing capacitors. The rule of thumb is to always use greater than or equal to the voltage rating that is required by the motor. The voltage required is always stated on the motor name plate. NEVER use a lower voltage than required because it lowers the life of the capacitor exponentially. Using a lower voltage rated capacitor will not damage the system, but it will accelerate the capacitor’s end of life. 

The voltage rating is the working voltage for the capacitor to reach 60,000 applied hours. If the heating or air conditioning unit increases voltage to the capacitor (for example: the capacitor is rated for 370 Vac, and is seeing 440 Vac from the unit), then the life of the capacitor will be lowered significantly. On the reverse side, if the heating or air conditioning unit is decreasing the voltage to the capacitor (for example: the capacitor is rated for 440 Vac, but is seeing 370 Vac from the unit), then the life of the capacitor is increased. 

Even though a capacitor is an inexpensive component, installing the wrong size can have a dramatic impact on an entire system! 

Industry Standards 

So the question is, how does one know which capacitor has the quality and reliability that the motor manufacturers require without having to place capacitors in the actual HVAC unit for years and years and see if they perform? 

There are various tools to ensure good capacitor quality and those are electrical and mechanical tests outlined in several capacitor industry standards. For long term reliability, the main and only tool is Highly Accelerated Life Testing (HALT). Many industry standards are out in the marketplace today, the main ones being: 

  • Tecumseh H-115 
  • IEC-60252-1 
  • EIA-456-A 

Increasing demand for quality capacitors has been seen in the marketplace over the past several years. It seems that many manufacturers have cut corners on material quality and manufacturing processes so that, even though capacitors test well off the shelf, they don’t last more than 6 to 12 months in the field. Obviously, with cheaper materials and the elimination of some manufacturing processes, capacitor price has dropped to very low levels. Hand-in-hand with these lower prices, the market has also seen capacitors with extremely low field life. 

The keys to a quality capacitor, aside from using quality materials in production, are the capacitor design, quality control systems, and performance testing throughout the production process in order to manufacture a capacitor that will pass the HALT testing. Most if not all capacitors will test the same off the shelf, but over the life of the capacitor, you will see drastic changes from one supplier to the next. This is where the industry standards come into play. 

Tecumseh H-115 

The Tecumseh H-115 was one of the first attempts at standardizing testing criteria for film capacitors. This standard was and still is mainly used in the U.S. and only applies to capacitor motor run applications. This standard includes a reliability test with two acceleration factors that include applied voltage and applied temperature. 

Testing Conditions: 

  • Number of Capacitors Tested: 12 units 
  • Applied Voltage: 126% of rated voltage 
  • Applied Temperature: 80ºC (motor run capacitor is typically rated at 70ºC) 
  • Test Time (Hours): 500 hours 
  • Life Simulation (Hours): 60,000 hours 

Considered Failures:

  • Microfarad (µF) Loss: greater than 5% 
  • Dissipation Factor Gain: Does not discuss 
  • Failures Allowed: 1 unit out of 12 units 

IEC-60252-1 

The IEC-60252-1, created by the International Electrotechnical Commission (IEC), was and still is mainly used in Europe and Asia Pacific. As did the Tecumseh H-115, this standard also only applies to capacitor motor run applications. This standard uses only one acceleration factor (applied voltage) for the reliability test. 

In this standard, different class ratings specify different field life for capacitors. The different class ratings depend on the amount of test hours that a capacitor goes through. 

  • Class A specifies an applied life of 30,000 hours 
  • Class B specifies an applied life of 10,000 hours 
  • Class C specifies an applied life of 3,000 hours 
  • Class D specifies an applied life of 1,000 hours 

This article focuses only on the Class B specification of the IEC-60252-1 standard. 

Testing Conditions for Class B specification:

  • Number of Capacitors Tested: Does not specify 
  • Applied Voltage: 125% of rated voltage 
  • Applied Temperature: 70ºC (motor run capacitor is typically rated at 70ºC) 
  • Test Time (Hours): 2,000 hours 
  • Life Simulation (Hours): 10,000 hours 

Considered Failures: 

  • Microfarad (µF) Loss: greater than 3% 
  • Dissipation Factor Gain: Does not discuss 
  • Failures Allowed: To be determined between customer and supplier 

EIA-456-A 

The EIA-456-A, created by the Electronics Industries Alliance (EIA), was and still is mainly used in the U.S. The EIA took both of the above mentioned standards and improved on them by publishing an all-encompassing standard for metallized film capacitors for ac applications.

It not only covers motor run applications, but also includes the capacitors used in high intensity discharge lighting applications and general purpose applications such as power supplies and power factor correction banks. 

Testing Conditions: 

  • Number of Capacitors Tested: 12 units 
  • Applied Voltage: 125% of rated voltage 
  • Applied Temperature: +10ºC over rated max operating temperature 
  • Test Time (Hours): 2,000 hours 
  • Life Simulation (Hours): 60,000 hours 

Considered Failures: 

  • Microfarad (µF) Loss: greater than 3% 
  • Dissipation Factor Gain: greater than 0.15% 
  • Failures Allowed: To be determined between customer and supplier 

When comparing these three standards, the EIA-456-A is the toughest and most thorough. It is also the basis for many, if not most, of the HVAC original equipment manufacturers (OEM) reliability standards for capacitors. 

Many capacitor manufacturers state that they have a 60,000 hour capacitor, but the real question is which test has been applied to their products? There is a four times factor differential when comparing the Tecumseh H-115 (500 hours of test time) versus the EIA-456-A (2,000 hours of test time). 

Since the testing conditions of both the Tecumseh H-115 and the EIA-456-A are the same, one can see that 500 test hours on the EIA-456-A scale is equal to roughly 15,000 applied hours (refer to Table 5). The Tecumseh H-115 applied hours is very similar to the IEC-60252-1 Class B standard of 10,000 applied hours. 

In the U.S., the standard is 5,000 estimated applied hours; thus, you can assume that the EIA-456-A standard, which specifies 60,000 applied hours for a capacitor, estimates that a capacitor will last roughly 10 to 12 years, while the Tecumseh H-115 estimates that a capacitor will last only 2 to 3 years since it compares to 15,000 applied hours instead of the 60,000 hours. 

Are You Getting What You Paid For? 

This has been a lot of detail, but hopefully it has given you a better understanding of capacitor ratings and standards used in the HVAC industry. 

The key thing to remember is that all capacitors are going to test well out of the box, but it’s the lifespan of the capacitor that matters. The recommendation is to do your homework before purchasing capacitor products. This can save you money and headaches down the road. 

Question the manufacturers about how their products compare to the EIA-456-A industry standard. Do not be afraid to ask the manufacturers for their capabilities for reliability testing. Any reputable manufacturer will be able to discuss this with you. From this, you will be able to assess the quality of the capacitor product yourself. Saving a few dollars on capacitors may end up costing you hundreds in the long run, so it is important that you understand what you are getting. 

Reprinted with permission by RSES Journal

Sours: https://www.ien.com/product-development/article/20850180/understanding-selecting-capacitors

5 Capacitor Facts You Should Know

One of the most common parts to fail on a single-phase HVAC system is a run capacitor, so much so that we sometimes refer to junior techs as “capacitor changers.” While capacitors may be easy to diagnose and replace, here are some things many techs may not know.

Capacitors Don’t “Boost” the Voltage 

A capacitor is a device that stores a differential charge on opposing metal plates. While capacitors can be used in circuits that boost voltage, they don’t actually increase voltage themselves. We often see higher voltage across a capacitor than the line voltage, but this is due to the Back EMF (Counter electromotive force) generated by the motor, not the capacitor.

Current Doesn’t Flow Through the Capacitor, Just in and Out of It 

Techs notice that the one side of power is connected to the C terminal or the side opposite the run winding. Many techs imagine that this power “feeds” into the terminal, gets boosted or shifted, and then enters the compressor or motor through the other side. While that may make sense, it isn’t actually how a capacitor works.

A typical HVAC run capacitor is just two long sheets of thin metal, insulated with an insulation barrier of very thin plastic and immersed in an oil to help dissipate heat. Just like the primary and secondary of a transformer the two sheets of metal never actually touch, but electrons do gather and discharge with every cycle of the alternating current.  For example, the electrons that gather on the “C” side of the capacitor never go “through” the plastic insulation barrier over to the “Herm” or “Fan” side. The two forces simply attract and release in and out of the capacitor on the same side they entered.

The Higher the Capacitance, the Higher the Current on the Start Winding 

On a properly wired PSC (permanent split capacitor) motor, the only way the start winding can have any current move through is if the capacitor stores and discharges. The higher the MFD of the capacitor, the greater the stored energy and the greater the start winding amperage. If the capacitor is completely failed with zero capacitance, it is the same as having an open start winding. Next time you find a failed run capacitor (with no start capacitor), read the amperage on the start winding with a clamp to see what I mean.

This is why oversizing a capacitor can quickly cause damage to a compressor. By increasing the current on the start winding the compressor start winding will be much more prone to early failure.

The Voltage Rating is What it Can Handle, Not What it Will Produce

Many techs think they must replace a 370v capacitor with a 370v capacitor. The voltage rating displays the “not to exceed” rating, which means you can replace a 370v with a 440v but you cannot replace a 440v with a 370v. This misconception is so common that many capacitor manufactures began stamping 440v capacitors with 370/440v just to eliminate confusion.

You Can Test a Capacitor While the Unit is Running

You simply measure the current (amps) of the motor start winding coming off of the capacitor and multiply it times 2652 (on 60hz power 3183 on 50hz power) and then divide that number by the voltage you measure across the capacitor. 

Publication date: 6/10/2019

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Sours: https://www.achrnews.com/articles/141390-capacitor-facts-you-should-know
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PowerWell 40 + 5 MFD uf 370 VAC or 440 Volt Dual Run Round Capacitor PW-40/5/R for Condenser Straight Cool or Heat Pump Air Conditioner 40/5 Micro Farad

A capacitor is an electric component that temporarily stores an electrical charge. A dual "run capacitor" supports two electric motors, such as a fan motor and a compressor. Round dual run capacitors are used to start and run the unit more efficient. It saves space by combining two physical capacitors into one case. The dual capacitor has three terminals labeled "C", "FAN", and "HERM", which stand for the *C*ommon, Fan, and *HERM*etically sealed compressor.

Dual capacitors come in a variety of sizes, depending on the capacitance (µF = MFD = micro farad), such as 60 plus 5 µF, and also the voltage. A 440 volt capacitor can be used in place of a 370 volt, as it is build better, but the 370 can’t be used in place of a 440 volt. It will work for a while and will fail prematurely, as exceeding the capacitor's rated voltage will cause the dielectric to break down and the capacitor to short out. Same as an electric wire- 600V rated wire is better than 300V one .The capacitance(µF or MFD or micro farad) must be the same or stay within 10%+ or 5%- of its original value . Example: 40 µF cap can be substituted by 38 - 44 MFD with the same or better voltage ratings capacitor.

If your fan is working but compressor not, or the capacitor is bulged on top most likely your capacitor is defective. Round capacitor can be used to substitute oval shape one with the same MFD AND Volt specs.

You will ask “Why I need a Cap that is rated 440V in my A/C?”

Answer: You need to realize that a motor is an inductive device. When the supply voltage is applied to the motor run winding, the voltage across the start winding will be increased to a higher voltage value. A motor acts like a transformer with the run winding acting as the primary and the start winding acting as the secondary. This is why the capacitor has a much higher voltage rating than the 230 being the supply voltage.

If a Capacitor is not EIA-456-A approved means it is NOT approved for USA market.

Sours: https://www.amazon.com/PowerWell-Capacitor-Condenser-Straight-Conditioner/dp/B072HM7Z27
Motor or Compressor Won’t Run? Capacitor Test, Troubleshooting

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Vac capacitor b 370 440

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Don't Just Change The Run Capacitor

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