Why Do Capacitors Fail? (It’s not why you think)
HTML-код
- Опубликовано: 5 июл 2018
- You may have asked "Why do capacitors fail?" and come across many theories as to what causes run capacitors to fail so often. In this video, we review how a run capacitor works and some of the potential causes of failure.
One theory is that a high amp draw on the motor causes compressors to fail. Another is that systems with low charge or dirty condenser coils cause capacitors to fail prematurely. However, it looks like capacitors have a fixed amount of current that can go in and out of them, and they're more independent than a lot of us realize.
A run capacitor is like a pressure tank for electrons forced into it; it constantly stores and releases electrons 60 times per second (60 Hz). However, at some point, it can no longer store any more electrons.
The C side typically connects to the run side of the circuit, and herm typically connects to the start winding. Electrons have to move in and out of the capacitor for there to be voltage between C and the start winding. However, there is no connection between the C and herm sides of the capacitor, so electrons can't move between terminals. A capacitor essentially adds a 90-degree phase shift to correct the inductive phase shift of the motor, so it helps the motor run in the correct direction.
Capacitors have a capacitance rating (in microfarads). The amount of electrons that can go in and out of the capacitor (as well as the amperage) is dictated by that capacitance. However, setups that include a potential relay and start capacitor(s) will increase the electron capacity, and that type of setup may draw higher amps briefly. Without that setup, the amperage on start and run will be the same. The only way to get higher amperage on the start winding is to have higher voltage and higher capacitance.
The ambient temperature can affect life expectancy, as sustained higher ambient temperatures can make run capacitors fail prematurely. Capacitors have oil to keep them cool, so they are a bit sensitive to heat. High-voltage surges (transients) can also decrease the life of the compressor, as bridging across the plates can cause premature failure. High voltage, high amperage, and poor capacitor manufacturing are mostly to blame for run capacitor failure.
We show all of this in action with a few field tests, including reading inrush amps on the start winding (0) and then the run winding (60). According to our results, the motor behavior on startup doesn't affect the amount of electrons a capacitor can hold; even back EMF doesn't affect startup conditions. We also include a guide for testing a run capacitor under load, which you can find here: hvacrschool.com/wp-content/up....
Overall, we can ensure that capacitors reach their life expectancy by minimizing the probability of transients (such as with surge suppressors like thermally protected metal oxide varistors), keeping the capacitor cool, properly installing the capacitor with tight connections, and using well-made capacitors.
AMRAD: www.americanradionic.com/
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/
I learned more in 36 minutes than I did in the last 10 years.
That's when you know you are a slave and we are only made smart enough to work and not question.
jamie Webb or some people look for knowledge and others just blame everyone else for their lack of knowledge instead of trying to learn
Slamming a schroll like that can kill them. Dont teach stuff like that.
Indeed, this channel is incredibly informative.
That makes YOU a shit bag. Work harder you'll stink less.
It caused me physical pain to hear that compressor short cycling like that, great vid keep up the good work
Agreed - that was tough...
I caught myself biting my finger nails
Same here!! I once had a bad mechanical thermostat that did that sometimes and it was making that awful sound, now I know that it was running backwards. It did actually blow the start capacitor. The only time I've ever blown a start capacitor. Hard to think that it's a coincidence.
Cringe for sure
@@castirondude single phase compressor running backwards?
Run capacitors fail so often, especially in hotter climates for one simple reason, the capacitors you get today are poorly made. They are insulated and cooled internally as cheaply as possible, even the ones installed in units from the factory.
@@CactusBobsPlace In NY I just replaced mine after 25 years when the fan needed replaced for the first time, the other unit still has the original cap.
Amrad capacitors are guaranteed for 5 years... I match my labor to their caps for good reason... the "el-cheapo" caps MIGHT last 2 summers... two service calls (let alone el cheapo) pay for ONE service call with an installed AMRAD... I put my name on an AMRAD for 10 years... I don't warranty them for that long... but I know AMRAD to last for ABOUT 15 years... YES, THEY ARE THAT GOOD!
The main cause is not cheap production, its the environmentalists. The chemicals to produce more reliable capacitors have been forbidden about 20 years ago, thats when the quality went downhill.
@@joskevermeulen9275 I disagree... amrad makes capacitors that last.... everything else, pretty much, does not.
@@joskevermeulen9275 No, it's cheap products. The Chinese caps are the worst. They are tiny compared to, say, US-made GE caps (back when GE owned the plant and made them here). Capacitors generate heat during operation, and that heat has to be dissipated. also, a smaller capacitor is made by using thinner aluminum deposition (which means higher internal resistance) and thinner polymer separator (which has higher loss). Combine all these cost saving "features" and you inevitably have a capacitor with a shorter life.
Brilliant demonstration! For anybody who is interested, there is an explanatory article showing the math more completely, written by Bryan Orr in AC news, titled "Testing the Run Capacitor While the System is Running", found with Google. Basically the 2652 comes from Xc=(1/(2*pi*f*C)), with 2652 in microfarads = 10^6/(2*pi*f). f is assumed 60 Hz. So, Xc = 2652/C, in microfarads. Plug that into Ohm's law E=I*Xc and rearrange to isolate C. So, C=2652*I/E. Remember that the start cap is only in the circuit for a short time at each start, so this measures only the run capacitor quality. For the brief episode when both are in the circuit, the capacitance for the two parallel lines is additive.
Older caps also were double the size to current day units, it's all a money grab now a days, but it keeps me employed so I'm not complaining
You must be young, that was the transitional period when PCB capaciters were eliminated from availability. The new non PCB caps were large until they got the design correct.
The older larger caps were always paper caps, and as such had a (sometimes poorly defined) limited life span. Modern caps are often polypropylene and "should" last longer. Of course, they don't always last longer in practice as it's fully possible to underrate them as well. They might even be more prone to heat damage than a properly manufactured (very expensive) paper capacitor.
@@mjouwbuis bingo in California caps last 5-10 years on new units, I've worked on 40+ year old carriers with factory caps still in them haha
Thumbs up, lot of good info there. That short cycling part was killing me too!
Love your podcasts and videos! Lot's of material and information in short period. I listen and watch over and over again to absorb the information. Was thrilled to discover your android app and have been using it the last couple days just for the capacitor in circuit tests. Makes very quick work of the formulas and nice you've included percentages in the results. Replaced 2 bad caps in 2 days and was actually surprised to find both new caps just slightly outside the 6% margin.
These videos/podcasts are pure gold, thank you brian orr for all that u do for the industry.
I always look at rated voltage on a cap. If a higher rated voltage capacitor is in stock, we use them as the capacitance is only affected by back EMF, so a higher rated (sometimes 440V) voltage capacitor can "help out" in areas where voltage is inconsistent. A 220V rated capacitor can fail with spikes/lightning in area as stated. Good work Bryan!
yep exactly! Some ppl confuse voltage rating and capacitance.
The untold capacitor spec is internal *impedence*... larger caps have a lower impedance and higher voltage rating
Great lesson. I don't care how long if be doing this business there's always something to learn . I've been here for 50 years everyday there's a new idea or approach to things I've been doing for years. Thank you
Hey this is a great video, I started listening to your podcast before following your youtube channel, I like that this video felt as if I was in the field getting hands on training! keep them coming, thank you!
I'm an HVAC Contractor in the Metro Phoenix area. I've got units 2-3 years old with dead caps under warranty and we literally just experienced the hottest June in history and I emptied out multiple 5 gallon buckets of dead caps over the last 5-6 weeks. They are poorly made and 117 degrees plus, sustained over time fucks em' up. EXTREME HEAT kills them.
Extreme crap quality does that too.
Lived in Phoenix for decades. People don't understand just how fast caps die in that area. HVAC, Pool pump motors, car batteries, car belts, tires, etc. The heat just destroys everything. They won't even warranty tires for much over half the original warranty.
I would think that it may be likely that 117 temps ambient could end up 150 degrees under the cover if direct sunlight is bearing down on it. Possibly something to cast a shadow on the unit might help a little bit. Also 140 degree air inside the cabinet is going to affect the cap temp too.
I work in the phoenix area as well go with the turbo200 caps they do great and havent seen any fail, they also come with a 5 yr warranty
I found some made by AMRAD, all USA made capacitors.
Very good review of capacitance with a hands on example. Excellent!
Awesome video. Thank you for posting Bryan. Job well done !
23:23 into the video One of my experience out in the field was a surge right after a thunderstorm I've had a few replacement because of that. Coming from my perspective it was because high voltage like you stated!. I recommend to install a 'Surge Protector'. I explained what it could do and how it works they insisted so went ahead and installed it for them.
Thanks, very instructive video. My choice would be to always use a 440 Volt capacitor as long as there is physical space to accommodate it. It is worth any extra expense. The other thing is to check carefully that all connections are clean and tight. Check terminals on the capacitor, but also check the contactor and any terminal blocks. Failing connections in various locations could increase motor back EMF, causing higher voltage across the capacitor.
you forgot - CHEAP CHINESE PARTS, AND LOOSE TERMINAL CONNECTORS, AND LIZARDS
*Ha!, ha! So right. Floridians agree on that!*
Really great video! Thanks Bryan!
This is so good, I'll have to watch it again. Much thanks.
Really great information! Every HVAC tech should watch this.
Best video on the subject. EVER!
BTW, I always use caps with a dielectric strength of 440v vs. 377v. I suspect they're more robust in handling those pesky transients.
it's good to have extra margin around the limits
Yes, the 440v is better suited for voltage spikes, or low loading conditions.
I've seen in desert areas where the contractor put in a relatively cheapcompressor where the capacitors that fail rated to 40C in an area where it can be constantly above 45C (114F). These need to be replaced but a Cap rated to 70C (158F) to minimize it's failing.
Very informative. In my experience totaline seems to have the highest fail rate among manufactures. Ever since carrier started using them I noticed a big increase in failures
Nice video man. I got info from it ,thanks. It was helpful.
Regarding surge suppression we need to keep in mind that MOVs degrade over time due to the number of surges and their amplitude. You can have an MOV that looks perfectly fine but is no longer providing surge suppression.
More than once I've also seen them fail in a dangerous way, where the MOV was conducting enough to make it heat up and catch fire while not drawing enough current to blow the fuse. For this reason I do not use any MOV based surge protectors that have a plastic housing, I've seen power strips that completely melted down and we had a UPS at work catch fire about 15 years ago.
@@James1095 It's true, as the voltage rises across an MOV, the resistance drops proportionately. It can easily reach a point where the amount of current through the MOV will get hot, catch fire and or blow apart.
Much obliged for a comprehensive explanation of running caps. I have chastised my various HVAC Techs for replacing them (mostly as a revenue increaser) when, in fact that was unlikely the problem. The 'American made' recommendation is most appropriate!
Hey.. that first cap is mine! I forgot I submitted this lol. Great video, watching it again.
Old Caps were much bigger in the earlier years (50's-70's) so they held more oil to keep them cooler. Ambient heat is the number one cause of failed capacitors here. Some condensers (Ruud for example) have the capacitor in the fans airflow- you'll notice these last longer.
Pay attention to periodic potential start relays sticking.
The reason those old caps were bigger is because they used paper as the separators between the foil plates. When they went to polymer separators, they were able to make them smaller. Then they went to metallized polypropylene, making them smaller yet. But, there was a limit to how small they could be made and still have long life and good surge capacity. When you start making them as small as the import caps, there's no way they can be expected to last.
Also the chemicals caused cancer too lol like asbestos. Anything good is bad for us
I have a 1990's Rudd 2 1/2 ton with capacitors that mount into cutouts in the contactor connection box, and the cases, except for the top connections, are in the cooling airflow. Luckily, I found properly sized US made caps to replace them with, along with a new Eaton contactor.
On the Texas Gulf Coast lightning "caused" power surges are common. I lost thousands of dollars in appliances and electronics; but I solved the problem 8 years ago. I installed an Eaton CHSPT2ULTRA surge protector on the load center. It has a surge current rating of 108 kA. Since then I have not lost anything. Best $200 I ever spent. It wont protect from a direct lightning strike like I had when 6ft of the chimney trim was blown off (nothing will do that); but it should protect for almost anything from the electrical lines.
You failed to consider what happens if a compressor's connections are loose.
Consider what happens when a motor (inductor) is running with loose connections. A sudden disconnect on an inductive circuit causes voltage spikes of unlimited voltage- like your car's spark plug coil. So, age, but primarily voltage spikes resulting from bad compressor connections (or fan) cause most capacitor failures. The spikes violate the capacitor's dielectric material resulting in a short, intense heat, and then an explosion.
Check for good electrical connections at the compressor and at all connecting points in the system- the number one preventive measure! I've seen it many times.
That's something you don't hear often. Actually never. Thanks
Yeah every-time I see a failed cap, the compressor spade terminals or OF terminals are loose. I squeeze them down a little after I change the caps.
My A/C unit was actually eating run caps so I decided to check all of the wire connections. I found one of the ears was broken on a female spade connector that was connected to the low voltage coil on the contactor. Once I fixed that connector, I never had to replace another run capacitor on the condensing unit until the compressor died 10 years later. The really amazing thing is that the condenser fan motor was made by GE and it ran for almost 28 years without failure. I would oil the sleeve motor bearings every Spring.
I just replaced a cap and found a loose spade terminal. A loose terminal will cause it to overheat and burn the terminal and spade connector, wire, leaving a crispy mess and possibly a damaged compressor. Always make sure those spade terminals aren't loose.
Move to Phoenix and you'll add to your statement.
This is amazing. I had not clue that so much is taking place in these things.
The good part is, I'm a carpenter....being clueless is fine. tHanks for this great video! Love it
ha, being clueless is one thing, but in your career, being glueless, is another!
@@Dwayne_Green Well said! I need to stick to these videos....
Very good class my friend. I'm going to make my coworkers watch this style vids u have so they can explain to the cust easier and so they know for there own good lol.
What are you going to do tie them down and force them to watch. Customers are not interested in why parts fail. They just want to know how much it cost to replace.
1 out of 10 customers are helicopter want to know exactly what happened capacitor failure explain spot on mini batteries units.👍✌️💪🙏
@johnd4348 you would be surprised.
Very good explanation, buy one thing I am sure about is those Caps from the old units from the 70's like a GE ....those caps lasted 15 or more years.
GE makes good stuff.
Except the new GE Zoneline PTAC units. Circuit boards go bad on about 25% in first two years.
A very informative video! Thanks for sharing.
Okay yeah I'm on 29:58 and yes that what happened to me not that long ago ... Great you mentioned that!!!!. Right on man I stayed till the end didn't know if it was gonna be mentioned or not but had to come back say it, You really have saved me a bunch of effort and money. I'm not new to this but I surely am true to this game !!!!.
Excellent Video.
Capacitors are one of the few components used in the HVAC industry that have actually gotten cheaper in the last 40 years. Some of this is due to materials used but a large part is because I could not find a manufacturer that still does testing on production lots (I had a reason at the time). It's simply cheaper to give you a new capacitor than run production lot tests.
The number of capacitors that I've found outside tolerance straight out of the box in the last 10 - 15 years is a lot more than you might think.
C H I N A, as in made in.
My next door neighbor has been in refrigeration for over 40 years. There were still US manufactured capacitors that contained PCBs when he started. They rarely failed... He still sees some old equipment during changeouts where the capacitor is still good. The pressure from Wall Street on HVAC manufacturers to maximize profits has driven them to "sell their souls" and purchase crappy off-shore components. My neighbor ONLY uses US made capacitors for replacement because he hates call-backs. Sadly, it's getting more difficult to source quality US made components... If you care about your customer, try to source US made 440V capacitors - ensure that all connections are clean, no burnt wires - and secure the capacitor properly (no duct tape)!
The main reason that run caps fail is primarily the printing on the label. 30 -40 years ago it was quite uncommon for them to fail. I've found caps out of the box that were out of the 15% rule of thumb. The most problem caps have printing on the label reading "PRC" and thats a big problem
Made from chinesium or mexinesium .
@@freespirit1975 made by a factory staffed by both Chinese and Mexicans. People think it's a food place. Company name ....ElChinco
My compressor Ran backwards all day. My wife ignored my advice and didn’t turn it off. It was hot as heck when I got home. I let it cool for an hour and turned it back on. It was fine and worked. The unit was already 10 years old so I called my friend and got an estimate for a new one figuring the compressor was going to die. That was in 2014. It’s still fine and runs perfectly. I’m in south Florida so it runs 12 months out of the year.
Top shelf education dude, many thanks.
Keep in mind that the capacitor is also a chemical based component and over time they can actually dry out which causes the capacitor value to fall over time to the point that eventually the motor startup will fail.
I think that is what is happening to my 50 HP 3 phase converter (from single) I bought the unit with 33 50 up capacitors to start 50 HP. not enough now it won't start. trying to learn to fix it myself.
@@bradjunes1610 Do you have a meter to check the caps with? If you suspect the caps but don't have a meter you can always keep your fingers crossed and just swap them out.
Great info. Thanks for sharing.
All I can say is wow. It was very intuitive. I've been in the field for over 25 years and learned a lot on this video, but with that said the old capacitors that had PCB in them and a resistor on the terminals lasted for decades or never failed before the unit rotted out. These days it's two years on a new unit 50% of the time. So
The purpose of resistor to bleed off residual voltage in the capacitor after been disconnected from the circuit after motor start up.
PCBs, or polychlorinated biphenyls, are highly toxic industrial compounds. They pose serious health risks…
Many reasons.. surging grid volts is a biG one, no lead in the steel, or solder, the aluminum is low grade... here in FL, it's most often after lightning storms.. surge protector helps 50% of the time..
@@globedimmer8286 That's what I'm saying. It helps bleeding off the cap reducing it overheating and popping and as far as the PCB's.., I'd rather have one of them in a landfill compared to the 10 that haved popped open off a single system in a landfill.
Excellent tutorial👍
Thanks for this great video!
I am of the opinion that bigger is better. Some old air conditioners had huge capacitors. I don't think I have ever seen one fail. Great video
DoctorT327 you nailed it. Those big run capacitors were made with pcbs and made in the USA, both of which no longer happen. They would fail, but it was rare.
That was outstanding, increase my knowledge in half hour!!
Thanks for the valuable information...much appreciated
As voltage goes up amperage goes down. The same is true in reverse. It must balance. If it does not balance heat is formed. If you have bad connections or BURNT CONTACTS which is the number one reason for capacitor failures, you will have voltage drop and heat formed. Heat is the root cause of capacitor failures. That is why very old large heavy oil filled Capacitors did not fail. They could disperse heat. Amperage draw increases heat which is a byproduct of electrical current. I spent 30 years of repairing and fixing electromechanical systems and equipment. From window units to 500 ton chillers in industrial sites. It all comes down to basics . I have held 50 year old capacitors in my hands that are just as good 50 years later as the day they were made and I have taken out bad ones that are less than a year old. Build quality is the greatest factor.
Excellent video! Those of you with thumbs down, just don't understand the principles of electricity. My question is how much coffee did you drink before you did this video?
Really well done video! I’m an EE, but no experience with motors and capacitors. This all makes perfect sense, and thanks for the tip on AmRad! I followed the link to their site and learned about their Turbo 200 universal run caps. With a total of 6 HVAC units between two houses, I love the idea of being able to cover all of them with just one cap! (Only thing is, I assume the diameter will be larger than some of the standard caps, so I may have to fiddle with the mounting.) Besides the convenience, I love that they’re US-made.
Turbo200 3x-4x more costly than standard run cap & cost has to be passed on to customer= too expensive! Great versatility in a pinch, then can go back & install correct rated cap
@@matthewclifford5824 *Wisdom*
I've seen extremely old capacitors last longer than the new ones
They were not built in China. Caps 30 years ago would last 10 or more. They ones now last about 3 to 4 yrs. I check them routinely and their weak after only 2 years.. Not bad, just weak. I just replace them every 3 years on routine maintence . Replacing them is cheap insurance and may save a compressor.
Daniel Roig Should've been under Carrier's 5 year warranty
Daniel Roig With Carrier it depends on the year it was made
The old capacitors had PCB oil.
After 2010-11 it's a 10 year warranty
Wow!!! great video. You were killing me with that short cycling.
Sacrifices for science 😉
short cycling is a good test for starter efficiency in worst case scenario.
Best starter being a "SOFT STARTER" that ramps up current instead of down from 5x locked rotor spike!
(figure that the rotor magnetic core needs to get charged to be polarized before stator windings electro-magnetic force can orient the rotor spin direction)
Here's one for you. Our system has a filter at the air handler which we wanted to replace. The unit was on and I was pulling on the sheet metal door to remove it and guess what was in there? A safety switch on the door so as I was pulling the door and jogging it to remove it, the safety switch as turning off then on the system vs. the squirrel cage fan. That action grounded out the compressor ! Sometimes the safety stuff shouldn't be when professionals who know what they are doing are faced with these surprises. There was no label or information on the panel to advise of this feature. Cost me big on that one.
As a service technician, I've noticed some summers are capacitor hungry... some summers are fuse hungry... something tells me, the failure of capacitors OR fuses, is due to supplied power...
Very good theory to applied. Most caps fail because the dielectric material breaks down, accelerated by surge / strikes. Temperature is a factor, however, I haven't seen any research for long term with monitor of spikes/surge. The use of a properly sized MG set will take care of any line problems.
I live in South Carolina. I service thousands of roof top units. On an average day the ambient temperature on a tar and gravel roof will be about 145 degrees Fahrenheit. On a hot day where the air temperature is 95 degrees+ I’ve seen the roof temperature up to 160 degrees. I will always use capacitors rated at 440v. And if I have unit that is in a bad location where it has poor air flow or is next to and hood fan from a kitchen I will add a hard start. That may seem like overkill but it works every time.
Worked on a Fedders unit a couple of weeks back. Still had original cap. Manufactured 1977. Pretty sure it was a PCB filled cap.
I don't think new techs even know PCB oils used back in the day for cooling.
I haven't seen one of those old Fedders since the early 80's. We had a Fedders unit on our house in 1972 and the compressor probably died because my parents never had the unit serviced.
New to your channel. I've lived in AZ for over 15 years and this seems to make them fail every 2 to 3 years. My house is worse I believe because when they built the home they put the A/C on the ground and the A/C unit is getting blasted by the sun at the hottest time of the day. Great video! My A/C buddy just got me a new Cap and its a AM Rad. The one that failed is Genteq from Amazon from 2016.
Tripin feld jobes explain mistackinreso expals ok
I have studied electronics in depth in high school, trade school, and in college. Your explanations of the factors causing capacitors to fail was never mentioned. We analyzed inductive & capacitive reactance. Counter or back emf (voltage) was not discussed either. This analysis applied to actual compressor winding circuits helped to clarify many issues for me. Thank you.
I wonder if excessive vibration can also lead to internal breakdown for capacitors.
I started adding some kind of start assist. It seems to have helped. I have had customers when looking at the history. I see run caps replaced every couple of years. I added a start assist and it's been 5 years so far. They are out in the country where surges are common.
I ended up installing a hard start kit (with the potential relay) in my A/C condensing unit and I installed a whole house surge protector in the power panel. I am thinking about adding another surge suppressor with brownout protection in my A/C disconnect to further protect my condensing unit. Over the years, I have lost a furnace blower motor to a power surge and lightning strikes have destroyed at least one of my TV's.
Wow you know your stuff!!
Great video!
Capacitors fail for several reasons, mostly heat and the surge cycling over time, basically because capacitors are not built to last as they once were, using inferior materials to keep production costs down. If a capacitor has been replaced in the past, if could very well be the original was replaced with a less reputable product. The voltage rating of a capacitor: is the amount of voltage a capacitor can handle on "peek demand", not what the unit runs at. The unit may run on 220-240v but the start up demand is much higher, sometimes peeking at 290v. The mfd is the charge/discharge rate of capacitor, the lower the mfd rating is, the higher charge/discharge rate. Always try to match the mfd and voltage as close as you can, if not, always go with the higher voltage rating and or a smaller mfd rating but don't make drastic mfd changes. When you are replacing a capacitor, take into consideration the age of the unit, how old is the cap and is there rust or powder present on the cap. Capacitors dry out with age, and you will get swelling, a liquid dripping or a fine powder forming on the capacitor, or an outright exploded capacitor. The powder is the dielectric drying out due to over use or just plain crappy dielectric, the liquid present is also the dielectric leaking due to expansion, the swelling is due to the dielectrics reaction with inferior materials used inside the capacitor in production, an exploded cap tells you there is too much voltage demand on the capacitor and you may want to consider a higher voltage rating when replacing it. If you replace a cap 40mfd @ 250v with the same, it will perform "as designed", you can also safely replace that same capacitor with one rated for higher voltage (40mfd @ 350 or 450v)m and it will perform as designed or better due to the higher voltage handling capability, manufacturers use absolute ratings for cost and effective production. What I mean is, higher voltage rated capacitors are going to cost more and will perform just as well and also have a longer life, but that cost may be prohibitive to the production costs, therefore manufacturers will go with the less expensive unit to save on cost. If you have a high rate of failure on this system, you may want to consider upping the voltage capacity of the capacitor, but match the mfd rating. The reason for this is due to the draw surge in electron demand on startup, the unit may now be demanding a higher capacity due to age and wear. If a unit is not maintained properly, it's demand will increase and cause a higher demand in startup voltage. As things get older the voltage demand increases, wearing of parts, lack of maintenance and whatnot. Also if the compressor HAS been replaced but the capacitor has not, the compressor and capacitor are not matched. The compressor may be a direct replacement but the physics demands may have changed. Therefore the voltage demand on startup may not be the same rating, and the capacitor voltage rating needs to match the demand. The way to figure this out is if the compressor seems to be sluggish when starting, then you know you need to lower the mfd for a faster start rate. If the compressor starts and stops a couple times or seems hesitant, it could be the mfd rate is too low and needs to be increased to allow the compressor to get a good start rate. The lower the number MFD the faster the start rate. As an example: 50 MFD will start the motor faster than a 70MFD because it takes less time to recharge the capacitor. I hope this helps. (43 years experience)
"50 MFD will start the motor faster than a 70MFD because it takes less time to recharge the capacitor" If that were true, adding a start kit, 389-524 mfd, it would further slow the compressor start, but in real life, it actually speeds up the compressor start, according to the manufacture. Even so, there is no reasonable field way to time the compressor sta, maybe in a lab....
The higher the mfd # the faster it will
Start..but it has to match the A/c
Compressor's requirements very close
Great, thank you for all the information.
Bryan, Excellent, in depth presentation. Would you consider doing an explanation of the use of a run capacitor as a crankcase heater? Is it a practical use of the run capacitor for this application? Thanks !
aliso 82 yep that video is coming soon
Run Capacitor Tunes the Sign Wave... Right. Kinda like a tune up on an engine. Makes the motor run smoother with less running amps at rated speed weather cking amps on comm or run. Full circuit is made from comm to runn ie:230vac line 1 and line 2 supply voltage. Very interesting in depth post.
Great video. Maybe they should be strapped to suction line with a heat sink material :) I remember when they were about as big as motorcycle batteries. They didn't fail hardly ever.
Love the thumbnail with the turbo cap. 20 years in and I have yet to see a turbo go bad.
Good information learn a lot about the capacitor thank you..
How to run a compressor backwards, Also cheap capacitors fail more often. Good work guys nice safety glasses.
That is a solid compressor. Nice electron pressure tank.
Brilliant explanation
< HVAC School explanation > is well thought out, suitable for the general public.
Curious if there are people there that understand the physics of the circuit shown,
when the momentary greater Start current, hence larger input electrical power Energy, is required to move the motor from 0 to up to rated rpm.
My original run capacitor just lasted 21 years. I estimate I run the A/C for 500 hours each year, though, so that is only 10,500 hours -- far less than the 60,000-hour alleged design life. It was mounted with the connections pointing downward, so I assume this is what you mean by "upside down". Maybe it would last longer if I flip it around, but it seems like water could possibly collect on top. Nice job on the video!
I think you should also think about a chattering main contactor. It's impossible to change current instantaneously across an inductor... like a motor. Some insanely high voltages can be produced if your motor contactor is having intermittent contact and there is no resistor to drain the potential infinite voltages. These (discharging winding) spikes could easily damage a run capacitor if there is no other place for them to go. When you see a burned and pitted contactor, most likely the run cap has had a bad day in that situation. If there is no suppression between motor legs on the load side of the contactor this could be another factor. The same effect makes tennis racket bug zappers produce 2750 volts from two AA batteries.
Sir Ver that’s right change the batteries in that t-stat that works only off the battery voltage to operate that contactor !
Good comments like these help me get through all the dumb ones.
All the more reason to change a pitted contactor, too.
Thank you Brian! I really appreciate what you doing.
I changed bunch of capacitors lately and ask myself "what HFAC happening"?
It was heat wave in New Jersey temperature get around 90 Fahrenheit. That's the answer.
I will check voltage surging.
Bacical fuding playin tocking failing not me lon lot jobe filing why ??
In Portland Oregon, I replaced a lot of capacitors each summer. They typically run between 238 and 245 volts to most residential units with bad capacitors. When measuring across the two capacitor terminals while the compressor is running, I normally get between 400 and 426 volts, depending on the capacitor size, with the larger modern high efficiency units with huge capacitors running even higher than typical. A 4 ton system with a 65 Mfd capacitor is around 425 volts across the two terminals. Sometimes I see a 370 volt capacitor in the systems.
You must use the 440 volt capacitors in Oregon, where the running voltage is normally very high. 370 volts will not survive very long.
When I worked at a University, the main building had 67 water source heat pumps running at 208 volts, and I rarely ever had a capacitor fail in that building. But other buildings with 480 volts, or the residential units for student housing had capacitor losses.
Great info. Bryan. Thanks for all your work.
Capacitors, as they age, can develop series resistance (ESR), causing them to heat during use. Also, one should note that if the capacitor is not properly correcting for the inductive load (i.e. high amps, motor failing, wrong capacitor value), the voltage will be higher than the normal line voltage (back emf), and cause the capacitor to fail more quickly.
Nathan, so...could one then use a multi-value capacitor and a power factor meter or some other tester to dial in a "better" capacitor value for older systems or to compensate for wear/deviation from design?
@@douglasmontgomery6315 In fact, YES!
You had some useful info at the end, but you could cut the repetition and reduce the video time by 2/3 without losing one bit of information. Who cares what some people think? Tell what is correct.
100% correct.thanks for the video.
Awesome vid!!!
The basic problem is that the legacy American infrastructure does not provide 3-phase power to homes, because 100 years ago nobody expected us to be consuming $100s/month to power multi-horsepower rotating machinery (A/C compressors) all day long. This is a huge long-term waste and inefficiency. The capacitors are just a poor compromise to synthesize a second phase; it would be far better to just receive the three phases that the utility has nearby. But that would require an investment. ECM essentially converts single-phase to multi-phase, but the conversion is always significantly inefficient, and the converters are expensive, short-lived, and not ruggedly reliable, with costly maintenance.
@@devnull7550 Small world greetings, Dev! You're welcome.
In my 40+ year old a/c I have the original dual run capacitor. One that is oval, 11" tall and has a ground spade, too. The unit also came stock with what is called a starter capacitor in the circuit. Though even with the starter capacitor exploded(I don't know when !, I just found a few days ago when I was doing a pre-run inspection)the unit still ran well last year in this condition ! I am replacing the starter capacitor before I attempt to run it...as a matter of fact USPS informed delivery says that it is out for delivery and I should have it today !!!
spend a little on maintenance parts to save a lot on not replacing with a new short-lived unit.
Check your Starter Circuit that fried the cap... the day your compressor fails to start because of bad starter maybe one of its last days due to locked rotor high currents toasting old winding insulation.
Little homework is worth your time... AC disconnect be your friend 👍🏻
The start relay could be bad, too. It's always safest to replace both at the same time.
an added note to those that fail to mount the run caps properly. These caps need that metal mounting strap as a heat since to dissipate the heat from the can to the surroundings. Failure of most electrical components is heat and moisture. I was wondering what effect using a higher or lower uf cap would have on a fan and compressor. These hard starts seem to work on out of warranty units to get em a few more years of life. How is this accomplished?
It's a little bit more complicated than that but I gave you an up vote because you were mostly right
Techs that don’t know capacitors, how they work or why they fail, are probably the same ones that charge by beer can cold and tell homeowners they need a new compressor and not just a cap. Very good video but every field tech should definitely already know all this.
For a capacitor, by definition I = C x dv/dt so if you are getting large changes of voltage in a short period of time, then current will increase. The easiest way to get a high dv/dt is to connect and disconnect an inductive load, e.g. a motor. These high voltage spikes are very short, so you will never see them on your meter, but you would see it on a peak detector or an oscilloscope. It's this peak voltage that occurs for only a very short period of time that kills a capacitor, not the average voltage.
Of course heating and line voltage spikes will also cause premature failures...
Actually, you get a higher back EMF from an underloaded motor that can cause premature failures, too.
My God Man!! You are worth more money!! Damn Good Job!! Thanks
Learned at lot on caps, 😃😃😃 Thanks
Very good 👍🏻
Great video
Run caps fail by building up internal pressure caused by heat from having high *current* combined with high *resistance* ie. impedence.
Parasitic heat generated by caps:
P = R x I2
The current being squared make caps particularly sensitive to it when internal impedence rise during aging.
Good caps are known as "LOW ESR": Equivalent Serial Resistance which grants them long service life.
Nothing magic: low-quality either builds repeat business or kills business like too many American iconic names
😂
OUT OF PHASE [23:00] : "Cap sends back"... nothing!
The cap supplied voltage and drawn current is what is out of phase.
I had one of those clear plastic shake lights. It was very bright for a long time of use. So I put it in the jocky box in the car for a light that I thought would be better than a battery powered alkaline battery light. Well years later when I pulled it out after changing vehicles it was no longer brilliant but like an old first Gen shake light. I am thinking of cutting it apart and changing the capacitor.
Eli the ice man.... Inductance . Voltage leads current while current lags voltage vs capacitance current leads voltage while voltage lags current.. great video
Eli - voltage leads current in an inductive circuit. Ice - current leads voltage in a capacitive circuit. The L in eli is inductive, C in ice, is capacitive.
That's been a long time since I learned that.
Yes when we had that heat wave a few weeks ago I replaced several condensing motors all 2 find out it needs a cap as well and what took it out was a dirty condensing coil short cycled off on high head but I replaced 1 everyday that week
One thing I have noticed on Franklin submersible pumps, their CSCR control boxes have a 23uf run cap and a 108 start cap. I have tested some after 20 years of hard service and the caps were still good. The run cap is a gray plastic and I can't find them anywhere, or at 23uf. {On edit they are Aeromet, see link above} AMRAD has a 20uf US made one which I suppose is close enough. The start cap is BMI 108-120 US made and available. Anyway, point being that you can design a system that doesn't blow caps every 2 years.
The capacitor is kind of like two very large old-fashioned wire TV antennae that are folded and inter meshed with one-another, but never touching anywhere inside the container. Thus, they should have no possible way of conducting direct current inside them unless they develop a short circuit of some sort, called "leakage", which is bad news. They can also burn out and no longer conduct anything, which is a far safer way to fail. What they do is charge up the two interleaved antenna wires with a charge, on side being positive and the other negative, allowing them to soak up a rather large, for the size of the device, electrical voltage across the tiny internal gaps. How much current and voltage they handle defines their capacitance. To get a flow of power across the gap, you need AC current, since moving one side of the wires will move the other side like many tiny magnets on rollers next to one-another along each internal wire. The capacitance and voltage requirements on a capacitor tells you haw much charge can be stored inside (it can be large enough to kill you in some designs!) and how fast the frequency has to be that is being conducted to get certain amounts of power to go through the capacitor. Low capacitance devices need higher frequency AC to get enough flow, while large capacitance devices have a lot of "surface area" inside and can work at lower frequencies -- in electronic devices this controls what frequencies are allowed through various circuits and is what allows most of these things (smart phones, for example) to work. Storing charge to give a higher kick to a circuit, as being discussed in this video is the other major use.
Not sure if this applies to HVAC capacitors, but one of things we do in electronics is to measure the ESR of electrolytic capacitors to get an indication of it's health. If we see a capacitor with a higher than normal ESR, then we know that it's on it's way out. A capacitor with high ESR will run hotter, which in turn shortens its life. Also if we see a capacitor reading higher than it's rated capacitance, then that could be an indication that it is becoming electrically leaky and it's probably time to start thinking about replacing it. In electronics we generally consider Japanese and American capacitors to be the best for quality and life expectancy. Not sure if you can Japanese Rubycon HVAC capacitors?
after a few thousands cycles of the contactor the silver contacts become worn and arc, and the arcing induces voltage spikes that exceed the capacitors rated voltage and it pops, replace the contactor and capacitor at the same time
Excellent video! Especially the demo showing the compressor running backwards- didn't know that could happen because of short-cycling. I was also surprised and intrigued to see higher than line voltage across the windings due to EMF. I was actually watching this video to assist me with troubleshooting a valve actuator utilizing a PSC motor which is blowing fuses. At the beginning of the video, you show lots of pictures of catastrophically failed caps. Is this how you normally find them in the failed state? What I mean is do you also find compressors with problems due to bad run capacitors which show NO outward signs of failure on the capacitor? What will a compressor do when its run capacitor is degraded? What I mean is, suppose the 45 MFD run capacitor is now only a 10 MFD capacitor. What happens?
I also enjoyed your demo of attaching the capacitor directly across line voltage. I have to admit, I was expecting them to go poof. Amrad capacitors- I'll remember that.
I have been doing commercial A/C and refrigeration service for almost 30 years. I have found capacitors that were bad without showing any outward signs of failure. So, it's always best to check them.
Degraded capacitors can cause motors to overheat, or even not start. A 45 degraded to 10, probably would not start under any kind of load.
Vrey good welcome iliked all shring teckanl feld vrey vrey good