Results 27 to 39 of 41
07-01-2012, 09:16 PM #27
hey thanks again timebuilder- and thanks for the semi-constructive criticism from jersey shore.
07-01-2012, 10:51 PM #28
Bury your nose in reading wiring diagrams and the manufacturers literature. You'll be way ahead of the average tech.Local 597 Service Fitter
Metal Trade Journeyman
PAY ME NOW OR PAY ME LATER
It was working when I left...
07-02-2012, 02:01 PM #29
These days it is just not good enough to issue some equipment commands from your laptop, you have to know why and understand what you are doing. Just my
07-03-2012, 06:38 AM #30
I sort of don't really understand what you're asking, so let me ramble on based on what I think....
In AC circuit, the power usage is determined by V * A * PF.
If we're talking about machinery PF is determined by cos phi where phi is the amount of phase shift. Pure capacitor is +90deg, pure inductor is -90.
Suppose you have something that has a PF of 0.5. Line voltage is 200v (for the sake of calculation) and current is 10A. Power is 1kW.
Under ideal conditions a 1kW load at 200v draws 5A. At PF of 0.5, it draws 10A and 2kVA. The wiring still needs to accommodate 10A. Transformers will also incur the same amount of loss as powering a 10A load.
In residential, you're only billed for kWh.
In large comm & indust, if your facility used 15,000kWh but you averaged 0.75 PF, you will get surcharged for inefficient utilization of distribution asset and losses incurred in transformers.
For the most part, industries heavily make use of big motors and as such, the cos phi is mostly lagging. Therefore, facilities add parallel capacitor to create "counter force" to bring the power factor closer to 1.0 to avoid getting penalized by the poco.
You could think of poor power factor as in fuel injected cars that puts a lot of fuel back to the tank through return tube. You're only using what the engine is burning, but the fuel that goes back to the tank is using up the pump capacity.
07-03-2012, 07:08 AM #31
I think the OP needs to understand the "why" of a capacitive circuit seeing current leading voltage, and an inductive circuit seeing current LAGGING voltage.
Once he has that idea, were can discuss the nuances of demand metering.
07-03-2012, 08:13 AM #32Regular Guest
- Join Date
- Jun 2010
Yes, not really sure what you are looking for. I'll offer the following and we can go from there.
With capacitors....current leads voltage because current must flow through the plates of the capacitor before a voltage can be developed. With inductors....when current first flows it causes a feild to be built up. The polarity of this field opposes the current flow. This opposition means the generated voltage will appear first and it will oppose the current....so the voltage leads the current.
A suggestion....when I wanted to understand some of this better....and knowing I wasn't willing to go back to school for years.....I took up a hobby, building (tube based) audio equipment. It was a big help, a lot of fun, and allowed me to understand what decent music reproduction equipment sounds like. Here is a post I made on inductors on an audio forum. Maybe it will answer some questions too.
"It is possible to show that the flow of current through a conductor is accompanied by mangnetic effects. In other words, the current sets up a magnetic field. Work, which requires power, is done in setting up this field. Since power is used there must be a voltage drop during the time the feild is storing energy. This voltage drop has nothing to do with resistance. Instead it is the result of an opposing voltage induced into the circuit while the feild is building up to it's final value. When the feild becomes constant the induced EMF disappears.
Now what does this have to do with a choke restricing current flow?
Since the induced emf opposes the the emf of the source it tends to prevent the current from rapidly changing in the circuit. The amplitude of the induced emf is proportional to the rate in which the current is changing and to a constant that we call inductance. So when the circuit tries to draw more current work is being done against the induced emf by storing energy in the magnetic feild and when the current is decreasing the stored energy in the feild is returned to the circuit.
So it might be more correct to say a choke keeps the current constant since it can supply energy as well as oppose the flow of it.
Addtionaly eddy currents and hystersis come into play especially when the choke is an input choke. The AC voltage will set up a current flow in the iron core of our choke. Such currents flow through the resistance of the core and thus cause heating. Also since the iron tends to resist a change in magnetic state the AC current, which is changing polarity, is forced to supply energy to overcome this. Both of these are are an energy loss that are effected by the frequency.
I will not bore you with reactance as you seem to have that well in hand.
In closing I will recap by saying that chokes maintain better regulation by tending to keep the instanteous current draw the same and that chokes used in input service have the extra chore of dealing with large eddy current and hystersis loss. They will be subjected to much rougher live than the lucky choke who has a cap before him
07-03-2012, 01:28 PM #33
Out of high school I got into a A and P school and from there into Avionics.
Did hobby building because I was never satisfied with just looking at a circuit board without knowing exactly what was going on.
Built everything from switching DC power supplies to signal generators, 7 segment LED driver displays and EEPROM flashing and reprograming modules.
Old tech but tubes are older sti and they're fascinating. The predecessor to transistors and proof to unedecated conspiracy theorist that we didnt reverse engineer some flying saucer and come up with an IPad
Its just fundamematally the manipulation of electrons.
It is also a completely diffdrent animal than what s tech is going to experience on a daily basis. ELI and ICE may be applicable to power distrubition as far as we're concerned.
Electronix deals with changes in frequency which alters overall impedance. Its a bit simpler when dealing with your average AC unit.
07-03-2012, 01:32 PM #34Regular Guest
- Join Date
- Jun 2010
Yup, probably get a lot more out of refrigeration cycle/P-h diagram than understanding reactive circuit behavior.
07-03-2012, 02:49 PM #35
If I may offer a recommendation:
Resist the urge to think too deeply into these processes at first and focus on simple things to make the system work i.e. do I have power? is this a load or control problem? how is the charge? are things clean? how is airflow? etc. I'm sure you already do most of these things and more. I was really guilty of over thinking things when I started out too. It's very easy to do.
I was told by a mentor of mine the guy never had an HVAC class, but grew up from 5 years old in the trade. If you run into a problem you cannot solve then start doing maintenance on the system. I scoffed at this initially, "Too simple" I thought but used it when a machine was kicking my butt one time, and it worked. I'm not sure if it takes your mind out of the loop that is preventing you from seeing what is wrong, or if it helps you find obvious things you tend to overlook but it has worked for me a lot.
Now to my real recommendationnce you are truly comfortable troubleshooting in the field, and if you are still wondering "why" all the time start taking courses in HVAC design.When I came to a point where the engineers and the seasoned techs could not answer my questions I did two things that really helped. I went to Ferris State University (great online program) and studied HVAC/R design, and I joined ASHRAE. These two things are the reason that 99% of my "why" questions have been answered.
As for psychrometric charts I have used psychrometric charts a lot, but it is more applicable to design and advanced troubleshooting of processes where the conditioned space parameters are critical than residential HVAC.
You can get into power factor eventually if you if you want to but you'll most likely not use that in troubleshooting HVAC (I never have) more so in industrial settings as discussed above. Likely you'd be part of an energy management team and HVAC/R would just be one of your focus areas.
If you like design and decide pursue that you'll be 10X better than the average designer because you've contorted yourself into a unit and sliced up your knuckles on the coil because some clown did not put the AHU far enough from the wall or blocked the door from opening right with poorly designed piping.
In the mean time read contractor magazine and other trade journals to broaden your knowledge, try to attend the Dallas AHR Expo in January '13 and get every bit of info that interests you, and read it. Last and most importantly start to determine the area you want to specialize in. I have been very lucky to have been exposed to almost every type of system that you can possibly work on. I realized that I have definite strengths and weaknesses and likes and dislikes after working on such a variety of equipment. Find the niche you are good at and really enjoy and concentrate on that and you'll find greater satisfaction that trying to learn it all.
Most of all maintain your hunger for learning. Don't listen to the naysayers that criticize you for being curious, and because they cannot answer your questions.
The guys here are telling you the truth about this one understanding this is difficult and not necessary to get a malfunctioning system running. Keep in mind this is a business and there are limitations of what you can do because of that (another restraint I am lucky to be less subject to than most).
I wish you the best in your future endeavors, good luck with HVAC.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."
07-03-2012, 05:03 PM #36Professional Member
- Join Date
- Jun 2010
all but one of those kids from jersay shore are actuqlly from jersey.. and hes from south jersey .. which is like the differencefrom n. korea to s. korea..
jersey rocks so much it really sucks... we are all in a big rush to go nowhere...
id say only 5 percent are in a rush to go fistpump.
07-03-2012, 06:02 PM #37Regular Guest
- Join Date
- Jun 2012
I come from a history of Induction Melting. Before I had any knowledge beyond the basics of electrical theory and physics I could diagnose problems just as quick and many times quicker than the EE's and electricians assigned to get them going. Having researched and gone through formal education I am no more capable than I was before at repairing a work coil or power supply, although I can design and build one if I were incline to do so now.
A fine example of this: I was a young melt supervisor. We had smart, experienced tech's working on a inoperable furnace. We were running the crap out of the furnace next to it. 12 megawatts going through one alone mind you. I smelled burning wood in the power supply room. I alerted every single person that would or should know any cause of this. Engineers, techs, the manufacturer rep was even there that day. I was a tad worried of the possible cause behind this, all said that there was no wood used for insulation any where on these power supplies or furnaces. I finally let it go after 20 minutes of arguing, 5 minutes later BOOM! One of the 4 bus bars from the supply to the coil lead had blown apart. These were hefty water cooled bus bars, big bus bars. One coolant flow path had become restricted. The soldered copper piping on the bar melted down. Moral of the story, think logically not complicated.
07-03-2012, 10:06 PM #38
LOL- LOVE the fact that there is a slight deviation towards jersey shore now in this post....gotta laugh, right boys?
Anyways, thanks again for the encouragement as well as the info from both Russ 57 and hvacbear- Russ57- KILLER opening description going into voltage lag and lead, VERY digestible for me.
07-04-2012, 09:51 AM #39Professional Member
- Join Date
- Feb 2007
- Central NJ
1) don't live anywhere near the jersey shore. i'm closer to philadelphia than the shore. and i'm not italian or a guido, that bs is everything about human society that i'm against. new jersey, as small as it is, is more diverse from north, central, south, east and west than most other states in america. but if you choose to be willfully ignorant....
2)the point i was trying to make was how tiring it gets coming on this site and having people who work in the same "industry" knock others because some don't work on certain types of equipment that guys like you have just been given the opportunity to. i mean, we come here to share information with others since maybe 1% of us know 100% of every HVAC/Refrigeration system out in the field, not bash each other because of their employment circumstance.
i get your point regarding "filter changers", guys who have zero desire to do anything but. there are a couple guys at the company i work for that should thank the gods their still employed. and really, none of those types of people are aware of this site anyhow because they don't do any research in their free time.
i can only surmise that you have the luxury of living at home,rent free and therefore can pick and choose your form of employment without having to worry about bills, mortgage or children to feed in this poor economy. just as you assumed i was from the "jersey shore".....You have to pay your due's before you pay the rent!