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

Thread Starter

DMahalko

Joined Oct 5, 2008
189
Well, there is no generally available SPICE model for the TL783 for LTspice. This one person suggests using the LM317 spice model as a substitute...

http://www.rocklinger.se/Elektronik/Simulering/LT_Spice_models_en.html

but using that, the simulation voltage output results are wrong as far as I can tell when I use the example resistor values from the TL783 app note.



I'm checking to see if TI's own "TINA-TI" SPICE simulator has it.

http://www.ti.com/tool/tina-ti&DCMP=hpa_amp_general&HQS=Other+OT+tina-ti
 

Thread Starter

DMahalko

Joined Oct 5, 2008
189
Interesting. Section 240 ("Overcurrent Protection") of the 2008 NEC makes no specific mention of such derating for DC.

At the beginning of Section 240, search for "DC", whole word results only. Nothing comes up about a derating requirement for AC vs DC.

http://www.garnernc.gov/Publications/Inspections/2008 National Electrical Code.pdf


The only match for "DC" in section 240 has nothing to do with this:

240.15 Ungrounded Conductors.
(B) Circuit Breaker as Overcurrent Device
(2) Grounded Single-Phase and 3-Wire dc Circuits. In grounded systems, individual single-pole circuit breakers with identified handle ties shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads for single-phase circuits or 3-wire, directcurrent circuits.


The abbreviation "D.C." with periods is not used in the code.
The word "direct" does not appear in section 240.
 

Wendy

Joined Mar 24, 2008
23,477
I missed the start of this thread, and haven't had a chance to read through it yet. One thing about the initial post caught my attention though.

Flourescents:

Submarines used a ballast resistor with flourescents. This is exceedingly wasteful, but they had the bulkheads to disapate power with (water cooling, indirectly).

You can not use a inductive ballast with DC. The whole point of an inductive ballest is the current limiting without the heat generation, which is what makes a flourescent so efficient.

We do not allow the conversation here at AAC due to beginners willing to kill themselves or other people, but a capacitor as a ballest for AC on mains is basically the same principle. If you want to discuss this offline send me a PM.
 

Thread Starter

DMahalko

Joined Oct 5, 2008
189
I suppose this means you don't want me to post my TINA-TI test circuit for an isolated 125v 20a DC power supply? (It's actually stable in TINA up to 125v 40a DC, but I just want an upper-end component safety margin due to possible design inaccuracies, and easier thermal dissipation.)



The earliest mercury-vapor lamps did not have automatic "starters". Instead there was a large pool of mercury inside, and the lamp was physically tilted sideways so the mercury runs down to the other end to get the arc going, then tilts back and flows back to the pool, bringing the arc along with it.

Illustration of how this worked:
http://www.lamptech.co.uk/Documents/M6B%20Manual.htm

Actual example of the device:
http://books.google.com/books?id=WM...ge&q=tilt start mercury arc rectifier&f=false



Early mercury arc AC to DC rectifiers worked similarly. It was physically tilted sideways to splash mercury on an electrode to get the arc going.

In case the arc goes out, some devices had automatic tilt mechanisms to restart the rectifier.

http://books.google.com/books?id=WM...ge&q=tilt start mercury arc rectifier&f=false
 

takao21203

Joined Apr 28, 2012
3,702
It's kinda why use $1000 for an experiment or to proove a point when you can for $10.

And why use 20pcs. of a component when one is sufficient.
 

takao21203

Joined Apr 28, 2012
3,702
Interesting. Section 240 ("Overcurrent Protection") of the 2008 NEC makes no specific mention of such derating for DC.

At the beginning of Section 240, search for "DC", whole word results only. Nothing comes up about a derating requirement for AC vs DC.

http://www.garnernc.gov/Publications/Inspections/2008 National Electrical Code.pdf


The only match for "DC" in section 240 has nothing to do with this:

240.15 Ungrounded Conductors.
(B) Circuit Breaker as Overcurrent Device
(2) Grounded Single-Phase and 3-Wire dc Circuits. In grounded systems, individual single-pole circuit breakers with identified handle ties shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads for single-phase circuits or 3-wire, directcurrent circuits.


The abbreviation "D.C." with periods is not used in the code.
The word "direct" does not appear in section 240.
AC or DC discussion is not subject of the N.E.C.
Main subject is safety of electric installations.

Since there has to be a large safety margin it's largely irrelevant if you run AC or DC through cables.
 

nsaspook

Joined Aug 27, 2009
13,560
Interesting. Section 240 ("Overcurrent Protection") of the 2008 NEC makes no specific mention of such derating for DC.

At the beginning of Section 240, search for "DC", whole word results only. Nothing comes up about a derating requirement for AC vs DC.

http://www.garnernc.gov/Publications/Inspections/2008 National Electrical Code.pdf
The NEC codes, while valuable are not the last word on electrical power circuit design. DC power is an area where little is in code but the 2012 -> 2014 versions will have updates due to Solar Energy systems becoming widespread and common.

DC vs AC breaker design.
http://www.ewh.ieee.org/soc/pes/switchgear/F11Minutes/F11HVCBa3.pdf
 

Thread Starter

DMahalko

Joined Oct 5, 2008
189
From that PDF:

"High-Speed DC PCB S/C Test
800 Vdc, 200kA peak, Cleared at 170kA, Two Opening Tests"

Hello? Can we come back down to the small scale?

I am not talking about circuit breakers for power plants and transmission lines, or 50,000 watt loads. Those have always been weird and always will be, whether AC or DC. Arc stretching, arc cutting blades, arc puffers, and mineral oil baths are normal for such equipment.

Oh yes, so the really huge breakers cut the AC current when it crosses the zero mark on the sinewave? That's neat, I didn't know they did that.


But how many residential grade home circuit breakers do that? I expect the answer is going to be none, unless they cost a fortune. Most residential breakers are simple mechanical affairs with a couple springs, a heating element, and bimetallic contacts, there's no "zero crossing" sensor in there.

I would be intrigued to know why we can generally use say a 1 amp AGC 250v AGC fuse universally for RMS AC or DC circuit interruption -- which is a thermal switch that melts or vaporizes to the open state -- yet we're supposed to be doing something totally unique and special if we're talking about a 1 amp 250v breaker -- which is basically a heating element and thermal switch.

 

Thread Starter

DMahalko

Joined Oct 5, 2008
189
It's kinda why use $1000 for an experiment or to proove a point when you can for $10.

And why use 20pcs. of a component when one is sufficient.
Your analogy does not mean anything to me.

One massive power transistor might certainly be sufficient for this task if you have virtually unlimited resources available to you as an electrical engineer in a design firm, are an expert at thermal dissipation design, have specialized expensive thermal analysts tools to test with, and are able to custom-specify specialized cooling components such as heat pipes for the task.

Me? I'm trying to pick a general heatsink out of Newark and hope it works. If I need a fan, well, I'll figure that out with an IR temperature probe during the initial load testing, powering parallel strings of 100 watt incandescent light bulbs.

This heatsink looks fairly decent for up to 110 watts of thermal dissipation. It's big, fat, and finny. And 1.71°C/W. I like that.
http://www.newark.com/aavid-thermalloy/os518-150-b/heatsink-1-71-c-w-to-218-to-220/dp/51R7028
 

strantor

Joined Oct 3, 2010
6,839
this post is fussier than my 5m/o daughter.

Anyway, this sounds like the situation strantor would cobble together some junkyard parts on the cheap.

120V * 20A = 2.4KW
2.4KW / 746 = 3.2HP

So strantor would be looking for a 3 - 4HP 180V Permanent magnet DC motor to couple to an AC motor to act as a generator.

Like this one. I did not shop around for the best price, that's your job. This is just an example. You can probably get one of these used for much cheaper.

So, our motor is 1750 RPM @ 180V. It will act as a generator since it's perm mag. If we spin it 1750 RPM (conjecture warning) I would expect it to generate 180V. But we only want 120V, so we need to spin it slower.
Proportion:
180V/1750RPM = 120RPM/X
X=1167RPM.

Do you really want exactly 120V I figure you want a little more to offset voltage drops across household wiring, so I'm making the executive decision to round up to 1200RPM.

Now we need something to drive it, and (conjecture warning) we could probably shoot for that same 3HP mark. Oh wow, look this one spins 1200RPM, no need for reduction gears! Straight shaft-shaft coupling, awesome!

So, there's your 120V dynamo. Using the parts I linked to, you would pay ~900$ but I know you can pay a fraction of that if you do the due diligence of sourcing the parts used from scrap/junk dealers.
 

nsaspook

Joined Aug 27, 2009
13,560
From that PDF:

I am not talking about circuit breakers for power plants and transmission lines, or 50,000 watt loads. Those have always been weird and always will be, whether AC or DC. Arc stretching, arc cutting blades, arc puffers, and mineral oil baths are normal for such equipment.


All of the effects that happen at high wattage happen at lower wattage (arcing, ...) the magnitudes are different but the effect of DC arcing of not opening a circuit during a fault when a breaker designed for 120 AC is used in a 120 DC circuit are then same. DC or AC/DC rated breakers are different from the general power panel types you see at the big box store. The arc will sustain about 1v/mm above 50VDC when the contacts open unless there is a mechanism (Arc Chute,permanent magnetic elements) to stop the fault current. Once you get voltage levels seen in grid-tie PV systems (600VDC+) it becomes critical to use DC rated devices.

http://www05.abb.com/global/scot/sc...b63c1257909002cb503/$file/1sdc007104g0202.pdf
 

takao21203

Joined Apr 28, 2012
3,702
What I really don't like is when people request high precision, ultra deep filtering, when it's absolutely not needed.

When you use a TRIAC dimmer you will get some distortion but that's largely irrelevant, only to see if AC appliances can work from DC.

It's mainly a concern for the grid. Who cares about assymetric load currents, if it is only for a short experiment??

When you use a 4700uF cap. for 200V rating, try to short it, and you will not bother about kA currents anymore.

So the AC is also better since there is zero crossing. If DC is shorted, the arc will not extinguish so easily.

Really I would not bother to use a TRIAC dimmer to shift 170V to 120V. They are only problematic if you need to use larger phase shifting. And to give a **** about ripple and distortion.:eek:
 

strantor

Joined Oct 3, 2010
6,839
high precision, ultra deep filtering, when it's absolutely not needed.
I agree, those household appliances which are primitive enough to not realize they're being run on 120VDC instead of 120VAC aren't going to care much about ripple.

Actually, if they're designed to run on 120VAC but they run fine on 120VDC then they should run fine on anything in between. So a simple bridge rectifier on the incoming AC should do the job.
But I have a feeling that wouldn't satisfy.

All this talk about designing power supplies and such, I wonder if you can make something that can't be unmade by a vacuum cleaner? I'm talking about robustness. Household appliances are not going to be kind to your power supply. how much current does a leaf blower draw when you turn it on? Probably enough give a 20A P/S a lot of grief. Any idea how much inductance 200ft of romex snaked through walls and coiled up in an attic has? probably enough to make a semiconductor-killing spike of epic proportions.

This is why my mind went straight to the mechanically coupled dynamo. It is the definition of robust. You can't hurt it if you want to. Plus, the AC motor will be on an AC breaker, so no need to worry about the breaker not being able to break the arc (which it probably wouldn't be able to with DC). Plus it will be smooth like you want.
 

takao21203

Joined Apr 28, 2012
3,702
What I have here for DC supply is a large welding transformer (ironically output is AC), a 4700uF cap. + large 6 Amps. Diodes.

I have a 500VA toroid as well, which has upto 105 volts DC output.

We have 240V here in Europe, means 340V DC. This will give nasty shocks if touched, and potentially it is deadly.

I don't recommend OP to go to a tool shop and ask for two welding transformers to abuse them as DC (or AC) power supplies.

It is also explicitely not allowed according to the manual.

I do however have understanding that OP wants to research and to experiment!

What I recommend is at first to test ideas on small scale, and then if larger power level is needed, only build a supply for experiment, that will just barely satisfy the requirements.

Overdoing things like a resource intensive power supply, is the wrong way to go, and not a good example.

For instance build a small TRIAC regulator, using a small TRIAC, same case like 2n3904, and rectify it, and for instance run a fridge bulb on it!

I have done this to learn something about TRIACs. And I am proud of this work of mine. It's cheap, nice, it works, and it is resource effective.

Then try a small DC motor, for instance. Why the heck does it have to be ultra precize 120v with 0.0001% ripple and 40A?

It's far more interesting to use the TRIAC and use full regulation range, and observe behaviour.

For sure OP will proceed in some way, and will notify AAC forum of the results, maybe including pictures.
 

Thread Starter

DMahalko

Joined Oct 5, 2008
189
I've already said, have to treat 125v DC with the same respect as 125v RMS AC, using similar wiring methods, insulation, receptacle boxes and covers, sockets and plugs, etc. It'll look just like an AC outlet, except for the phrase "DC power only" next to it.

I will exercise caution with the circuit interruption. Fuses are cheap enough, with high DC breaking capacity.

http://www.newark.com/littelfuse/0314015-hxp/fuse-cartridge-15a-6-3x32mm-fast/dp/26K8518?in_merch=Popular%20Fuses
250v AC / 125v DC, 15A fuse
breaking capacity: 750 A @ 250VAC / 10,000 A @ 125VAC/VDC
$0.67 each
 
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Wendy

Joined Mar 24, 2008
23,477
Search. 15 seconds. Google, Linear power supply

http://www.cnccookbook.com/MTCNCDictLaptoMPG.htm

Screenshot:


Uh, no. The web is full of erroneous knowledge, which you seem bound and determined to add to. That is a unregulated power supply. The term linear power supply refers to the components and how they work to regulate the voltage. A transistor and a op amp are both linear amplifiers, though they do have nonlinear areas. The output of the above power supply is not stable, unless you add a linear voltage regulator. There are also current regulators, something totally different.

I'm not sure of your technical background, but you got this one way wrong. Writing articles does not make you an expert. I write continuously, and I am occasionally wrong. Which is better, an author who is willing admit he doesn't know everything, or someone who is willing to spread disinformation rather than getting it right?

The reason AC won over DC is mainly transformers, a very low tech solution to convert voltage. Transformers are one the the few man made devices that can exceed 95% efficiency with simple components. Transformers allow the transmission of power over the grid efficiently. This has not changed much in over 100 years.

It is with the advent of power solid state that we can convert DC voltage levels efficiently. Usually that is by converting the DC into AC and using (what else?) transformers.

I notice you have dismissed the importance of reactive components (coils and caps) as current limiting components. Are you under the impression they dissipate heat like resistors? Coils and capacitors don't generate heat while limiting current. This means they are extremely efficient, which is another reason AC is going to be used for a very long time. The above I have just stated are fundamental facts, and do not change for anyones convenience.
 
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