Professional Member
Hey guys,
I recently got a position with a pretty awesome company. Ill be able to finally start putting all of the stuff I learned in school into place in the real world because I'll be working with a crew of refrigeration mechanics on refrigeration equipment instead of just being an air cundishnin guy- LOL
No offense intended to anyone out there, HVAC has been good to me so far throughout my apprenticeship and I have learned a lot, but let's face it; most guys who work on roof tops for a living don't even know what a subcooling valve is or the difference between a current relay or a potential relay- I know this because that was me except for the few weeks in school when I tried to absorb as much as possible.
All that being said, I guess I should get to to the point of this thread- understanding inductive and capacative loads. So, I can understand pretty well on a graph or chart that the voltage leads by 90* in a purely inductive circuit, the current leads by 90* in a purely capacative, and that in a purely resistive circuit they're in phase..........but what the hell does this mean in the real world? Maybe a better way to ask this question would be, "What kind of resources can ANYONE recommend for helping a guy to understand vectors and impedance and capacitance outside of black and white friggin charts in a text book. I can run the calculations and size my caps and figure out power factors etc, etc..........but I have always seemed to have a disconnect between seeing it on paper, which I think i can grasp relatively easily, and seeing it in a mechanical room or with the motor in front of me.
I think most of you senior techs can understand now why I felt the need to post my recent career change details at the beginning of this thread now: you basically need not even care about this stuff if you're just changing out oem parts on rooftops all day long between flipping filters.
Again, anyone who knows of some good resources via a good electrical website or even a good RSES book or publication (Im a proud and participating member).......please feel free to hook a young dumb apprentice up!
Thanks for all the help guys.......stay tuned for more questions from a hopeful young fridgie.
God Speed, Jim. We'll miss you - 2-26-23
Not a good way to get help. Comparing many of our members here, to your limited knowledge and time in the trade.No offense intended to anyone out there, HVAC has been good to me so far throughout my apprenticeship and I have learned a lot, but let's face it; most guys who work on roof tops for a living don't even know what a subcooling valve is or the difference between a current relay or a potential relay-
AOP Committee/Professional Member*
Apparently, you have not worked with the right HVAC guys.
And probably, not with the right HVAC company.
"Changing OEM parts all day."
You were fortunate if you had an expereinced tech to identify and order the OEM parts. I have seen SO many hacked systems where someone was forced into using a non-OEM motor, where the factory part had non-NEMA dimensions, like the Carrier blower motor with the extended length shaft. I say "forced into" because many commercial accounts will dictate what parts will be used, and/or what they are willing to pay for those parts.
"Flipping filters."
This reminds me of the service brokerage in-house techs that get sent out to do PMs. Anything beyond a filter is beyond their abilities. And often, those little arrows showing the direction of airflow are overlooked. The upside is that these guys get in over their heads quickly, and give guys like me an opportunity to look like heroes.
I like refrigeration. In may ways, the vapor cycle is more of your focus, and interpreting values is more critical because losses like food are involved. However, commercial HVAC is often just as complicated and vexing as refrigeration.
You just were not there long enough or in the right situation to appreciate the challenges of the comfort side.
[Avatar photo from a Florida training accident. Everyone walked away.]
2 Tim 3:16-17
RSES CMS, HVAC Electrical Specialist
Member, IAEI
AOP Forum Rules:
Professional Member*
how to win friends & influence peopleOriginally Posted by beenthere
It`s better to be silent and thought the fool; than speak and remove all doubt.
AOP Committee/Professional Member*
Yep.how to win friends & influence people
He needs two things:
1) The Dale course, (http://www.westegg.com/unmaintained/carnegie/dcc.html)
and
2) the Forrest Mims book.
http://www.amazon.com/Getting-Starte.../dp/0945053282
[Avatar photo from a Florida training accident. Everyone walked away.]
2 Tim 3:16-17
RSES CMS, HVAC Electrical Specialist
Member, IAEI
AOP Forum Rules:
Professional Member*
He also needs a spell checker for his title. Capacative???
Doug
Regular Guest
inductance=creation of voltage through changes of magnetic flux
reasearch electromagnetism.
inductance and capacitance work against each other in an ac circuit. when current lags voltage it is being restricted. For example, a very crude example: a motor creates back electromotive force that pushes current in the opposite direction of the way it is supposed to go. The capacitor stores energy to counter act this. This is just one example.
visit this site.
http://www.daviddarling.info/encyclo..._and_lead.html
Professional Member*
I can already see..
The more you know
The bigger your head will be.
Looking down at every technician.
Be humble my friend
Professional Member*
Occupation
Refrigeration mechanic Apprentice, recently left HVAC to be a real refrigeration mechanic
Yep he's just a know it all kid.
Professional Member*
the difference between refrigeration & air conditioning = 10 degrees
Professional Member*
Electromagnetic and inductance theory is not for the faint of heart. Unless you want your brain to explode just learn the basics for the trade. Capacitors resist a change in voltage, inductors resist a change in current.
Luckily someone much smarter has figured out that motor made of a number of coils wrapped in a certain diameter circle pushing a piece of steel made of more coils of wire needs a 7uF capacitor.
Professional Member
honestly guys- No offense intended whatsoever and if coming across as arrogant or as having what we refer to here in BC as "the refrigeration walk" then I most sincerely and humbly apologize to all.
As timebuilder said, I should have been more specific and said the RIGHT HVAC company. I've had several peers from other companies as well as mentors who have spent their careers in HVAC and have a very impressive understanding and well rounded perspective to many things not found in the more 'purely-refrigerative' areas of the trade (for lack of a better term).
Apologies to all and many thanks for the great links as well
Professional Member
hey awesome example- believe it or not, that 'crude' little example of yours actualy put a few critical pieces of the puzzle together for me-LOL
Professional Member
I hear you loud and clear brother- but having more than the basic understanding is what I believe is one of the components that helps to create the difference between a guy who knows what the right part is and WHY the right part is what it is.
Professional Member*
I believe that too. If you know the process behind something you can do any job better than just throwing parts at it. I graduated from OK state an EE but i don't think knowing why that motor needs a 7uF and not a 5uF make be a better motor diagnostician.Good luck in your studies!
Professional Member
The Dale Carnegie book How to Win Friends and Influence People has the potential to change your life. I would venture to say that it will make you more successful in HVAC/R than knowing how the magnetic lines of flux in a motor winding affect something you'll rarely ever measure anyway.
That is not to say that you should not seek out an answer to your question. Just realize one is wisdom the other is knowledge.
Good luck.
Quote
“Engineers like to solve problems. If there are no problems handily available, they will create their own." Scott Adams
"We can't solve problems by using the same kind of thinking we used when we created them."
Albert Einstein
Regular Guest
It goes so much more in depth than that though. A lot of electrical engineers (I didn't say all) would not be able to remember the physics behind all of this unless they use it every single day. I know I had a better understanding of it a few years ago. Use it or lose it...
Professional Member*
Although it's important to have a thorough understanding of the principles of electricity and how individual components effect the operation and power quality of a circuit it's not knowledge that you're going to be using in the field as a tech.
I use to be into electronic hobby building and avionics so the study of components in both AC and DC circuits actually interest me to a great deal.
In response to your first post the effects of capacitance and inductance on a AC circuit as far as you should be concerned relate to over all power quality.
Power quality can be expressed as that circuits power factor which is a ratio of real power to apparent power. It's a measure of the efficiency of the power in a circuit and is expressed on a scale of 0 to 1.
Real power is the power that actually performs work and apparent power is the effect of resistance, inductance and reactance in the circuit.
Both capacitors and inductors store energy. Capacitors store it in their electric field and inductors store it in their magnetic field. The combinations of these two elements in a circuit with resistance add up to that circuits total reactance. Also note that capacitance and inductance change with frequency.
Since frequency is constant ( 60 hz ) it's not an issue in typical linear power distribution.
So in purely resistive linear circuit the current and voltage waveforms are in synch and your power factor is very close to 1.0
It's at it's most efficient. Once you start adding inductance, ( motors, relays, lamp ballast, etc ) and capacitance ( DC power supplies in computers and servers, and wire and cable have some capacitance ) you start lowering the power factor and that circuits efficiency and start adjusting the phase angle of current to voltage ( Voltage will Lead Current ) which will increase overall power consumption.
Most buildings and especially industrial sites have a large inductive loads. ( big motors) and may require the addition of capacitor banks to correct the low power factor or pay a penalty to the utility company.
You might see a capacitve bank sitting next to a pump motor or next to a service panel that feeds a number of electric motors. They're trying to increase their power factor.
Capacitors and inductors in DC circuits have a variety of uses and unless your planning on getting into component level trouble shooting on circuit boards you don't need to waste time studying their many applications.
Professional Member
If I was to continue in my career with only troubleshooting units of say 10 tons or smaller and basically be able to say "yup, change the board" or "yup, add a hard start kit" then for sure I would agree with your summarization of the importance of this type of stuff.
The fault I have made in my apprenticeship thus far, and what I am trying to correct, is by listening to those who have said "just get a general understanding because you won't need to know that in the field".
This perspective towards understanding only a portion of what I have been taught in school has been literally CRIPPLING when it comes to being able to apply a skill-set and knowledge-base from one type of equipment onto something different.
The best technicians I have known and still know, and ALL of the mentors and live resources I turn to have extensive knowledge of not only electrical theory but also of refrigeration theory and refrigerant properties- characteristics that are FAR from common amongst most techs I have met here in B.C.
The limited exposure I have had to larger scale refrigeration equipment tells me that when the day comes that I get called out to a plate style cooler system for a dairy tank with 50K of milk in it or to a 70 ton chiller system for a 40 story tower, I sure as HELL be a lot better on my theory than what would consist of a general understanding.
I know that I probably come across to MANY as a young cocky know it all little $#!T but please believe me when I say that with every piece of knowledge I learn, read, see, or am taught comes with about 10 pieces that I feel anxious about until I learn (and no, I don't need to do the math on that equation to realize it's impossibility- LOL)
But enough ranting for now- I'm probably overdue for a good punch in the teeth right about now anyways!
Professional Member*
Your post is a good example of how experience or lack of affects our perceptions of what's important and practical.
The example you used of voltage and current waveforms leading or lagging was explained ( did you read my entire post? ) in context to our industry. If you want to pursue their characteristics as applied to DC theory GO BACK to school. Or rather enroll in a school that focus' on electronics. ( hope your smart because it's an entirely different animal than simple AC power distribution.)
I've been in the industry for almost twenty years and have worked on everything from large kilo-ton centrifugal chillers to small 5 ton package units.
My knowledge of electrical theory as applied to our industry and electronics is pretty extensive. Do I know everything ? No, I do possess some humility.
That said I have yet to pull out my pocket note book and work through the electrical mathematic principles of a 100 ton air cooled chiller for purposes of trouble shooting.
Understand the engineering aspect of the machine and the sight where it's located where worked out by people most likely more knowledgeable than yourself far before you arrived.
As a tech I'm under obvious time constraints and it's my responsibility to quickly narrow down the offending component or issue causing the issue and repair it using correct service techniques without cutting corners and get to my next service call.
If it's going to take a day or two to order in parts then let the customer know and then hit the road.
What's important is understanding the specific functions of the specific type of equipment you're working on. Also a thorough understanding of the components and principles of refrigeration in general.
IF you walk up on a 70 ton chiller that's off on high pressure do you need to know how to figure for total inductance ( XL = 2πfL ) ? Are you going to be wasting time connecting a oscilloscope and watching sinusoidal waveforms shoot across a screen ? No you need to be focused on the problem at hand.
Nothing wrong with having a good base of education but because of your experience level you don't know what information is going to be useful to you.
When guys who have been in the field for 20 years tell you what you need to focus on why would you question that ?
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