Balancing the Breaker Box

It will be a ground unless it's a four pin outlet. It's still not safe. A better, but still not great, solution would be to hardwire the two heaters in series with a single 240V plug.

Reply to
krw
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I'm wrong even though I never claimed what my friend claimed? I had never heard it before and didn't know, that's why I asked here. It is amazing that you can become a professional engineer with such a reading comprehension problem. It's also amazing that you parallel an actual electrical measurement, high leg current, with moon phase and price of soybeans. Maybe you claim your P.E. because you passed physical education class? Giving you the benefit of the doubt, you should know if meters ran based off of the high leg then balancing would let you use all the power you were being charged for. That is completely different than moon phase, price of soybeans, or carrying a black rock in your pocket. I suppose you think fixing a leak in a gas tank to save fuel would be like a 100mpg miracle carburetor too. Go back to the gumball machine and get your doctorate.

RogerN

Reply to
RogerN

Motors, inductive loads, voltage leads current, capacitors, current leads voltage. Is a switching power supply more like a capacitive load or inductive load? I'm curious, I installed a 10HP variable frequency drive on my retrofitted CNC lathe. I ran the motor at idle and the drive showed 13A, but a meter only measured 5A on the line side. I have heard that the reason for this is that the drive handles the power factor problem, drawing closer to true power from the supply. If I understand correctly, a VFD is sort of like a 3 phase SMPS with the motor being the inductors in the circuit. Just wondering how this affects my household power factor versus other motors running from the line.

Also, before using solid state drives to get 3 phase from single phase, I used an old 10HP 3 phase motor to make my own rotary phase converter. I ran

240V into two of the legs and am able to run my shop from L1, L2, and the 3rd leg of the running motor. I use a single phase motor to spin the 3 phase motor up and then switch on the power. This thing drew a lot of amps until I installed some motor run capacitors to balance out the voltages. I don't have drives for all of my machines yet but I do for the ones I use the most, they seem to be a real nice way of running 3 phase equipment from single phase.

RogerN

Reply to
RogerN

Neither. It's a harmonic load. ;-) Uncorrected it has a very crappy current waveform.

A fully loaded motor should have a PF pretty close to unity. What any particular VFD does to it is anyone's guess. I suggest you buy a "Kill-A-Watt" or "PowerAngel", or some such. These things are about $25 and will report V, A, VA, W, PF, F, kWH, and H (did I leave anything out?). You can then play with various loads to get a feel for what they're about.

Reply to
krw

If the heaters are the same wattage and are run at the same time, it will work. It's not really advisable, but it isn't likely to cause any real problems. Some clothes dryer receptacles have a neutral so that's a better idea. Yeah ground and neutral go to the same place, but the ground really shouldn't be used to carry current.

Reply to
James Sweet

In a sense they do, since as a meter ages, lubrication tends to dry up, and mechanical components wear so they do tend to slow down with age. The new meters are not really "faster", they are correct, and the aged meters often turn a bit slower than they should. It's only an issue when an old meter gets replaced with a new one and the customer notices a sudden increase.

Modern fully electronic meters eliminate this of course.

Reply to
James Sweet

This thread has been so full of rubbish, some of it true, some of false, most of it by people trying to show what the know, and mostly succeding in proving they know very little.

You are too buried in the crap to see that Charles, like me has got fed up with the trash and is making appropriate sarcastic remarks.

Grow up! You or your friend or whoever was wrong in the begining and all this crap has only gone on to prove that, but will you give up Oh No!.

John G.

Reply to
John G

Lubrication? They have magnetic bearings and the moving parts are degreased, not lubricated.

Very very rare to find one slow. Oh, and in most states in the US, IF, big IF, you pull the old meter and it tests slow (every removed meter is tested), then the customer gets back billed for 2 to 3 years of unpaid usage. Check the public service regulations. If the meter is fast, they get a credit for 2 to 3 years overcharge. It is extremely rare.

Charles Perry P.E.

Reply to
Charles Perry

But Ma, He started it! :-) I said long ago that I believe what they have been telling me here, that the meter measures true power and not high leg power X 2. But the idea is valid that if they measured high leg power X 2 then you could save some money by balancing the load. Others pointed out that it would be illegal to charge based on high leg power but a little fine print would probably take care of the legalities. I have a better understanding of utility power meters now, and agree that they are not basing the power on the high leg. But yet I'm accused of arguing that I believe the power meter measures based on high leg power. I don't believe that but I questioned it based on what a friend heard. It's BS, no problem, I gave that up about as soon as the replies came in.

RogerN

Reply to
RogerN

Yeah, I wouldn't use the ground as a neutral. About the only way I would proceed that way is a complete rewiring of the heaters (oil filled radiators) so that both 600W elements were in series and both 900W elements were in series, and all with proper fusing / breakers for each pair of elements.

RogerN

Reply to
RogerN
Ï "Charles Perry" Ýãñáøå óôï ìÞíõìá news: snipped-for-privacy@mid.individual.net...

I thought they had jewelled bearings, like an expensive watch. It's not likely that with age they drift. However, I've read that with the advent of nuclear power stations engineers thought that electricity would be so cheap it wouldn't need to be metered. That was before 3 mile island or Chernobyl, obviously.

Reply to
Tzortzakakis Dimitrios

Thanks for the info. I found the Kill-A-Watt at Newegg for $20, plan to order one next order.

RogerN

Reply to
RogerN

(you're too kind :-)

I understand that the 'true' measure of power is instantaneous V * instantaneous I and that that can simplify to simpler terms in certain specific situations (such as DC or sine waveforms).

I guess I just can't 'wrap my head around' the meter responding to instantaneous V*I when the magnetic field from the potential coil is delayed nearly 90 degrees from V.

The only way I can make sense of it is if the eddy currents in the disk are highly inductive (much like they are in a conventional single-phase induction motor near stalled conditions). If the eddy currents lag the air-gap flux by nearly 90 electrical degrees, I can see a torque developed proportional to real power.

But the lag in eddy current would mean the torque pulse also is delayed. That would mean that a 'peak' of instantaneous power (peak V and I for a resistive load) creates a 'peak' of torque a quarter of a cycle later when the instantaneous power has actually dipped to zero. And that momentary zero instantaneous power that occurs when V and I are zero-crossing is not 'sensed' by the disk until another quarter cycle when the eddy currents in the disk are zero-crossing and developed torque is momentarily zero.

I know that for revenue purposes, the meter's response to harmonics caused by non-linear loads is acceptable enough, but with both the inductance of the potential coil and the disk, I can't help but wonder just how accurate they can be with large loads of this type. Seems the currents induced in the disk by a non-sine current through the current coil would not be a perfect match and thus not perfectly accurate.

daestrom

Reply to
daestrom

Reply to
<dhky

Yes, yes, I'm familiar with two phase motors and the 'shift' of the flux. But since the disk is not ferromagnetic, that alone doesn't create a torque (i.e. it's not a reluctance motor). So we have to have an eddy current induced in the disk (a 'rotor current') and to my mind it's the interaction of that eddy current with the magnetic field that produces a torque. Much like the current in the squirrel cage of a conventional single-phase motor.

A disk that was composed of numerous 'pie slices' insulated from one another would not work. Right?

R/X near 1 would certainly work, but an R/X near infinity might not (i.e. there has to be some inductance). With the eddy currents exactly in phase with one winding's flux, the currents would decay before the other winding's flux increased very much. I see your point about R/X near unity, after all as you said class D motors have some of the best starting torques and that is how they achieve this.

Well without getting into 'gawdoffal' calculations, it just seems that if the eddy currents in the disk lag behind the flux that produces them (i.e. the disk has some inductance) then the torque pulses would seem to lag behind the instantaneous power 'pulses' that occur at twice line frequency.

So I wonder how close the disk is operating near 'synchronous speed'. Where I think the synchronous speed in this case is function of mechanical shift between current and voltage coils (i.e. the equivalent 'number of poles' arranged around the rotor). But also the phase shift between current in the two coils (which of course depends on connected load and R/X of potential coil). That is, the time shift between the flux of one pole and the other.

If the maximum power to be registered is anywhere near a fraction of this 'sync speed', then you effectively have a significant variation in slip of the rotor. Of course some motors have a pretty flat torque curve at the lower end of speed when starting and for a given applied voltage/current, that's what we want here. So that torque produced is

*not* a function of %slip but only the measured power. Or variations in %slip are tiny because the 'sync speed' is so much higher than expected speed of the rotor.

(ouch, my head's starting to hurt ;-) )

All of the references I've found on the matter seem to say that the potential coil does have a low R/X so that magnetic flux is nearly 90 lagging from applied voltage. If it's something 'in between', wouldn't that give you some calibration issues? For example, if R/X is 1 in the voltage coil, then a connected load with a current lagging by 45 degrees would be exactly in-phase with the voltage coil's current. No torque produced but the customer is getting power (at 0.707 pf)

daestrom

Reply to
daestrom

I have an Ohaus balance beam type of scale, and also a reloading scale that have a sheet aluminum flat tip, the tip runs between two magnets. Somehow the magnets produce a drag and dampen the scale. Is this effect related to how the motor in the meter works?

RogerN

Reply to
RogerN

---------- I'm not even considering a ferromagnetic disk - and a good example of an unbalanced two phase motor is an drag cup control motor. A beer can stuck on a nail in a rotating field will run as a motor. All that is needed is a conductor and a component of the stator field that "shifts". (A paper clip will also rotate- done both)

Reply to
<dhky

Don Do you have any more information on the second book by White and Wilson? I used AddAll and found quite a few copies of the book by Krause at very reasonable prices but did not find any thing on the second book. Thanks Dave Foreman

Reply to
Dave Foreman

Oops. Correction:

It is White & Woodson (of MIT), "Electromechanical Energy Conversion"Wiley 1959, Lib. of Congress No. 59-5874 It is the original book that covers machines from a generalized basis and is quite mathematical , by page 30 it has covered electromagnetic force production basics and is starting on the Hamiltonian. The developments go on to general basic models which can be used, depending on the restraints applied, to represent any machine. Years ago, Westinghouse capitalized on this to make a generalized lab machine set where, depending on connections could be a DC machine, a 2 phase induction machine, a synchronous machine, etc-- unfortunately is was atypical and somewhat inferior machine in any configuration but did illustrate the theory. Amazon lists one copy at $165 -it's not worth that! Krause,, while sticking to more conventional machines is probably a better bet.

Reply to
<dhky

Thanks Don Dave Foreman

Reply to
Dave Foreman

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