Researching the history/compatibility of 120v DC/AC utility power

Discussion in 'General Electronics Chat' started by DMahalko, Jun 24, 2012.

  1. DMahalko

    Thread Starter Senior Member

    Oct 5, 2008
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    I guess I will put this in a new thread. Probably should be in Projects forum.

    I'm a Wikipedia technology hobbyist. I have been researching the history of electric power for a couple of years, and I'm getting to know a fair bit about the history of 120v DC and 120v AC back when both were in use in 1880.

    I'm a contributor to lots of technical articles that discuss the history of electricity:

    The whole 120v "nominal" AC business appears to be to allow the people of 1880 to use 120v DC interchangeably with AC , which was the mainstream Edison power source originally. DC from lead acid batteries isn't 120v but up to 136-140v when charging. Haven't found a specific cite for that yet but it appears to be the reasoning for nominal AC...

    ,

    I am looking for a high amperage (call it 16 amp, since that is the continuous rating for a standard 80% 20A circuit breaker) voltage stabilized 120v DC power source to test out modern device compatability with DC.

    • Any modern resistive device will work fine with 120v DC, such as incandescent lamps, non-electronic coffee pots, resistive-heat kitchen stoves, cookers.

    • Induction and synchronous motors will likely just burn up. Or they may just sit there and do nothing and survive 120v DC without damage. Dunno. Let's find out, shall we?

    • Ballasted fluorescents are a mystery. If the starter can get a high-voltage spark off through the induction coil, it may be possible to sustain the arc at 120v DC, using the inductor as a resistor.

    • 120v AC "universal motors" will run on 120v DC just fine, which is any motor with a commutator and brushes. (120v AC/DC is why they're called universal motors in the first place) There's a huge amount of these made yet, inside variable-speed rheostat-controlled devices like blenders and power tools. They're also in most vacuum cleaners, where the motor runs as fast as possible limited only by the physical load.

    • Switched mode supplies are a whole different ball game, didn't exist until after vacuum tubes were invented. Some may work fine on 120v DC and some won't work at all. It depends on where or if they have internal isolation transformers. If it's on the front end during rectifying, nothing will happen. If they rectify to DC and then produce their own AC before it hits the isolation transformer, a switched mode will work fine on 120v DC.

    Probably most commercial switched mode devices can run on 120v DC even if the nameplate says AC only. Likely includes many compact fluorescents, 120v LED fixtures, many new "high efficiency" compact wall wart chargers.

    We're at a point that we throw away so much electronics every year that I don't really care about putting some old obsolete electronics on the sacrificial altar of historical testing and research.

    ,

    As far as safety goes. Well. I'll isolate the input if you want but there is no point. 120v DC @ 16A is as dangerous as 120v AC @ 16A, and it has to be treated with the same respect as any AC line source.

    The wiring and fusing is identical to 120v AC. Which oddly, seems to be intentional since the NEC got started when 120v DC and AC were being used, so the code was apparently designed to apply to either one.

    Generally, the NEC doesn't make any distinction between AC/DC, all they care about is voltages, though they focus on RMS AC and not peak AC which is also odd for a technical guide. Once again appears to be due to 120v DC.

    Fusing and breakers between 120v RMS AC and 120v DC are the same.

    Grounding didn't exist when 120v DC was still popular, but may be a rather good idea if the point of this is to test AC devices to the point of potential destruction. It looks like pick a side and ground it, and do that consistently everywhere. I choose negative.

    General wiring fusing/breakers are to protect the wiring, not the individual device. It's up to the device to provide its own fuse if the manufacturer thinks it needs one, and many induction and synchronous motors don't use fuses at all. Tsk tsk. That may be a smoky problem at 120v DC.

    ,

    One way or another, I am going to proceed. The stupid way is to buy 10 deep cycle 12v "marine" batteries. Put them in parallel and charge them at 12v, then disconnect and restring them in series and test with 120v, then disconnect and recharge in parallel at 12v again afterward.

    Batteries would be a waste of money because they are going to go bad in a few short years, and it's going to be an annoying hassle to have to constantly rewire the string to recharge them, and dealing with the risk of miswiring when switching between 12v charge/ 120v operate modes.

    Plus the hydrogen gas emitted when charging. And the fact that large lead-acids have enough potential current to output 120v at 100 amps or more if a short occurs. I would put 20A circuit breakers between each one to protect against that, if this is the route I am forced to go to do this inexpensively.

    An electronic regulated high-amperage 120v DC power supply would be far simpler, though I'm not looking to blow $1000 on a professional scientific grade power supply for this hobby project.

    ,

    It may be possible to run photovoltaic home power systems straight off 120v DC without an inverter, and for off-grid homes to just use 120v DC directly from what appear to be standard-wired 120v AC wiring and breaker panels in their home rather than building out a weird and nonstandard 12v/24v/48v DC power system.

    120v DC battery power as a utility voltage in a home has the advantage that you don't need to waste energy keeping the sinewave going in the walls, even if nothing is drawing power. When all loads turn off, the flow stops and there's no inverter power drain.

    120v DC has the potential to be much more energy efficient and less expensive to install for off-grid homes, since you also don't need huge heavy gauge wiring for large low-voltage DC loads. Just use the regular gauge and type used with normal 120v AC circuits.

    If at some point in the future the homeowner would want to go from 120v DC to on-grid AC, it's a simple matter to disconnect the batteries and connect the AC transformer to the main panel.

    This could be a weird little renaissance for DC utility voltage, the same way DC is making a comeback for long distance high voltage power transmission using huge switched-mode power converters.
     
    Last edited: Jun 24, 2012
  2. KJ6EAD

    Senior Member

    Apr 30, 2011
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    :confused: Why have you posted this? Should it be in a blog instead? What kind of feedback are you looking for and what's with the comma or apostrophe between paragraphs?
     
    Last edited: Jun 24, 2012
  3. takao21203

    Distinguished Member

    Apr 28, 2012
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    Tesla vs. Edison!

    Simply put, 240VAC will go upto 340V momentarily, and this gives more torque to start up motors, without to run the high power continuously.

    Large DC motors aren't so easy to commutate as well so 3 phase is used for these.

    about , 3

    when you write like this on your job, you may be sent to a doctor to check for various mental health syndromes. Throwing over board 100 years of tradition just from the viewpoint of your own opinion, which does not even seem to be backed by experiments/experience.

    We're at a point that we throw away so much electronics every year that I don't really care about putting some old obsolete electronics on the sacrificial altar of historical testing and research.

    I would not recommend to write like that if you do a professional report for your job.

    Generally, the NEC doesn't make any distinction between AC/DC, all they care about is voltages

    How old are you?? I mean just the age group.
     
    KJ6EAD and #12 like this.
  4. DMahalko

    Thread Starter Senior Member

    Oct 5, 2008
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    ,

    Since you asked. Some posting systems strip out whitespace between paragraphs. Quite annoying. The comma is a filler symbol. Periods are used to terminate SMTP messages so it's not a good choice for a spacer. Commas seem to work fairly well.

    I am approaching 40.

    Blog? Blogs are basically one-way communication. I would like to discuss this topic, which is ridiculously obscure. But there is simply no forum I am aware of where this is discussed. This general electronics forum is about as close as I can find.



    (? whew, made it)

    120v utility DC is DEAD as far as general purpose use goes, and whatever knowledge of it there is, is held in 100 year old books at this point.


    I would like to experiment with DC power from a dynamo, but that too is a dead technology, and I'm not too thrilled about the prospect of having to CNC machine and hand-wire one for a hobby project. Though as far as I can tell, most appliance universal motors can probably be operated as a shunt or series wound dynamo through some minor field coil rewiring.

    Dynamos with field coils were started the same as portable AC generators now. No-load start using residual magnetism in the core to get it going, let it build up internal voltage, then connect load when the output voltage stabilizes.
     
  5. takao21203

    Distinguished Member

    Apr 28, 2012
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    I hope you enjoy contributing to AAC.

    And it's a public forum, not a job role.

    I have researched about Tesla myself, but by no means totally inclusive.
    He made the first, or one of the first AC generators. At Edison they indeed favoured DC transmission.

    Be aware that many ideas actually don't make it, for various reasons such as for instance marketing.

    I don't know if you can handle welding transformers or even if you want to have these around, and if you want to go to a shop and ask for them.

    But this would be a cheap source for high-current DC. No-load can be upto 60V, and it's still 50 volts if you draw some Amps.

    At larger power levels 50Hz transformers don't have much loss actually, so it's not a big problem. And no existing wiring is not compatible with DC for various reasons, neither the motors, switches and all that.

    120V electronic converters would be very expensive unless they become mass produced.

    http://batteryuniversity.com/

    maybe this website is interesting for you?
     
  6. #12

    Expert

    Nov 30, 2010
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    The way you write does not suggest that you want an answer.
    May I suggest that one of your sentences end with a question mark?

    Next idea: The white space just above this line demonstrates that you do not need to contrive a solution to the non-existant problem.
     
    KJ6EAD likes this.
  7. DMahalko

    Thread Starter Senior Member

    Oct 5, 2008
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    So you're berating me for not having done the experiments that I am describing wanting to perform.
     
  8. takao21203

    Distinguished Member

    Apr 28, 2012
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    I use something like this time by time:

    Code ( (Unknown Language)):
    1.  
    2. some text that belongs together
    3.  
    4. *****
    5.  
    6. some text that is about a different topic
    7.  
    Wikipedia would throw a crank at me if I try to introduce this as a new way of delimiting ;)
     
  9. DMahalko

    Thread Starter Senior Member

    Oct 5, 2008
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    I figured this post would be better off on its own rather than as a reply to the other threads about why I am looking for an IC-based 120v DC regulator.


    That one:

    Undefined resistor wattage in an application note

    http://forum.allaboutcircuits.com/showthread.php?t=71515


    And that one:

    What is an "offline regulator" / TIP150 ?
    http://forum.allaboutcircuits.com/showthread.php?t=71451


    This one? Well probably not. I don't own any antique devices myself for testing:

    PWM Controller for giant antique 20+ HP DC motors?
    http://forum.allaboutcircuits.com/archive/index.php/t-14815.html
     
  10. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    No I am just saying this likely will not be very successful. If you have interest to do it, then maybe limit it to one or two specific technologies, not all together, so many experiements which could cost you space, money and effort, with little prospects of financial improvement or gains, or breakthrough in technology.

    Maybe see it that way, if electric installations would all be based on DC, it would be all too easy to do the calculations. So it's a way to keep people busy on their job, and make money with installations which are so difficult to calculate and to do them safely, that only trained experts can do it properly.
     
  11. #12

    Expert

    Nov 30, 2010
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    I believe I just figured out which category DMahalko fits into.
     
  12. DMahalko

    Thread Starter Senior Member

    Oct 5, 2008
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    I am not looking to sell anything or make any money. This is simply historical research for the fun of it.

    Probably the results of each experiment will show up on Youtube.
     
  13. DMahalko

    Thread Starter Senior Member

    Oct 5, 2008
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    Okay, phrasing as a question.

    Is there a commercially-available prebuilt regulated 16-20A 120v DC power supply that can be obtained inexpensively, as in for less than $1000?

    The general feel so far from my prior postings here is no, there is not. It will have to be custom built.

    My previous research of a 120v battery charger for this did not work out. The vendor tells me the DC output is merely an SCR, very choppy.



    That TL783 still looks like a good option. Total parts cost is low. $1.95 for the regulator itself from Newark.

    I suppose I could go the fully parallel block-assembly route.

    If (1) TL783 = .7 A @ 125vDC then
    - 10 TL783 in parallel = 7 A @ 125vDC for $19.50
    - 20 TL783 in parallel = 14 A @ 125vDC for $39.00

    The expensive part ends up being the high-wattage isolation transformer, but if you need it, you need it. Perhaps I can get one used.


    A prebuilt power supply would be preferred however if anyone is aware of one.
     
  14. takao21203

    Distinguished Member

    Apr 28, 2012
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    Sounds a bit curious to me.

    What about a Variac and then simply rectify it?

    And I must say 1 Amps. is a lot of current for me already.
    But I am rather a low voltage guy, even 5 volts is old fashion already.
     
  15. DMahalko

    Thread Starter Senior Member

    Oct 5, 2008
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    The intent would be to get as smooth and flat of an output as possible, so that there's no "poisoning of results" from the AC ripple. A basic linear power supply with caps can't really fully get rid of the ripple, plus since it tracks the input, sags, spikes, and all else will carry over to the linear DC output.

    I would like the equivalent output of using a lead acid battery string but without having to blow $1000 on ten short-life $100 deep cycle 12v batteries.

    I don't yet know how stable the output would be from just one (parallel group of) TL783. Perhaps they would need to be stacked in serial fashion one after the other to get progressively smoother output.

    I have a old Tektronix 2200 oscilloscope so I can examine the output DC.



    It looks like the TL783 may work fine with just the two reference and minimum-draw resistors and nothing else (after the bridge rectifier / 1:1 isolation / initial filter caps), if the limit is 700mA per unit. Are heatsinks needed? Fan? Still looking.

    Put a diode and SPST on the DC output of each one to isolate them from each other (easier troubleshooting), a 16A slow blow fuse on the input and output, and gang 30-40 of em to deal with motor startup surge current.

    Heatsink density may be a problem. I suppose I could have a single PCB with 20 heatsinks on top and 20 on the underside. (Will ExpressPCB drill the heatsink holes for me? Heh)

    While I am sure the experts would say, "you dummy you can do that with a huge X power transistor in Figure 19 of the application note with that regulator, you don't need all those parts", I don't see anyone stepping forward, so parallelizing appears to be the least complicated route to get the job done as a non-EE hobbyist.


    The costs of parallelizing are not insanely high:

    TO-220 heatsink -- $2.21 for 1 to 100
    http://www.newark.com/fischer-elektronik/sk-104-50-8-sts/heatsink-to220/dp/46T6892

    TL783CKCSE3 -- $1.19/ea for 25 to 50
    http://www.newark.com/texas-instruments/tl783ckcse3/ic-adj-linear-reg-1-25v-to-125v/dp/10M0615?in_merch=Popular%20Power%20Management%20Products



    And oh yeah, I'm curious about these modern energy saving variable frequency drives for industrial electric motors. So you take 120v AC, turn it to DC, then make high frequency AC fed to an induction motor? Hmmm, sounds like it might possibly accept 120v DC as input too even if not rated for that, which means induction motors don't work on DC but technically could?

    Someone should test that. I can probably find someone throwing out an old single-phase VFD somewhere, that they don't need.
     
  16. #12

    Expert

    Nov 30, 2010
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    These statements seem contradictory. You believe a linear power supply can't really work, but a TL783 linear regulator can? Are you just typing random thoughts as they come to you? Are you asking if a linear regulator will work as well as a linear regulator chip? I'm having so much trouble making sense out of this.
     
  17. DMahalko

    Thread Starter Senior Member

    Oct 5, 2008
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    A linear power supply to my knowledge is just a transformer, bridge rectifier and a capacitor. Maybe a resistor to try to limit output a little. Very simple. This is used in wall wart power supplies all over the place.

    There is minimal DC voltage regulation with a straight linear power supply, other than some sinewave ripple smoothing by a nice fat capacitor. Output voltage is all over the place depending on current draw.


    A regulated power supply / IC uses a separate reference/sense circuit on its output with a known resistive value to adjust the output voltage.

    Regulated power supplies may require a minimum power draw to keep the output voltage from rising. Page 8 of TL783 application note: The recommended R1 value of 82 Ω provides a minimum load current of 15 mA.

    I assume I'm not telling you anything you don't already know.
     
    Last edited: Jun 24, 2012
  18. #12

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    Nov 30, 2010
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    You told me one thing I didn't know. You don't know what a linear power supply is. A transformer with a rectifier and a capacitor is not a linear anything.

    Look at my blog#5 (starts with "LM723"). Change a few resistor values and add some parallel transistors on the output stage and you have a high voltage linear regulator that can handle some serious amps with millivolts of ac ripple on the output.
     
  19. DMahalko

    Thread Starter Senior Member

    Oct 5, 2008
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  20. #12

    Expert

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    You win. I bow to your superior knowledge.
    If it only takes you 15 seconds to learn what I didn't learn in 40 years, I should probably get out of this profession.
     
    Last edited: Jun 25, 2012
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