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Comment: Re:Main use of household current is high-voltage A (Score 1) 317

by bobbied (#49793201) Attached to: How Tesla Batteries Will Force Home Wiring To Go Low Voltage

You'd think that most of the "heating" devices in your home would work fine on DC with only a few modifications. Especially that water heater and ALL of the incandescent light bulbs in the house...

Did you know that a lot of your electronic devices work great on about 100V DC and wouldn't require any modifications? Most modern switching power supplies really don't care if it's AC or DC on the input, they work just the same either way. Don't just go out and hook up your expensive flat screen to the Prius battery (it can damage stuff sometimes) but chances are it would work... My Laptop charger, a PC desktop and LCD display along with a 30A 12VDC switching supply for my radios all worked just fine...

Personally, I think we should go with HIGH voltage DC, use it where it makes sense, and not freak out about having to convert it to AC when the need arises.

Comment: Re:Use High voltage DC stupid... (Score 1) 317

by bobbied (#49792903) Attached to: How Tesla Batteries Will Force Home Wiring To Go Low Voltage

Heh I should have read your whole post before replying to the first line, but let me pick you apart in another one instead.

1. Most stuff just works on high voltage DC as discussed above. Most switching power supplies simply don't know or care about AC or DC and due to their efficiency switching power supplies are used in almost everything electronic.

Absolutely wrong. The first thing most power supplies do is step down from high voltage AC to something in the general range of whats needed on the highest output value. They step down with a transformer. That transformer only works with AC, if you put DC in it, you're just going to burn it up as it turns into a magnet carrying more current (because its not AC, so the there is no inductive resistance, so there is more current). Please don't give anyone advice on electricity. Ever.

You are living in the past on this one. Most modern electronic equipment utilize switching power supplies because they are cheaper to make, lighter and more efficient. Modern switching supplies almost invariably just rectify the AC into DC as the first step, usually using a full wave rectifier. Full wave rectifiers don't care if you feed them with AC or DC, you get DC out either way and as long as you have the right DC voltage range coming out of the rectifier, the switching power supply will work just as well on AC as DC. Where this is not UNIVERSALLY true (you CAN damage some stuff doing this), it is generally true.

Now, I want to point out to you that I did say there where exceptions. Devices that employ transformers and induction motors will NOT work on DC. That includes CFL's, Ceiling Fans, some Wall warts, most major appliances and the like, but it's pretty obvious they won't run on 12 V DC either...

2. It's easier (and more efficient) to use high voltage DC for charging the batteries. All you need is a rectifier to convert that 220 into about 250V DC and charge the batteries, which is about as simple and efficient as it comes.

... You do realize those batteries you're referring to are actually made up of a bunch of smaller batteries right? There is no single cell at 200v. You aren't charging one 200v batter, you're charging a handful of 12v batteries that you're just blissfully ignorant of.

And you seem to be ignoring the fact that that 12V (aka 13.8V) battery *really* is just a number of 2.3 Volt cells (like 6) strung into a series to get you up to 12 V. So we put 100 in series and get a working voltage of about 230V DC? How's that an issue of ignorance? Or, parish the thought, we just take 10 of your standard 12V batteries and connect them in series to get 120 (138) Working voltage?

It's all for naught anyway because different battery chemistry gives you different cell voltages. But no mater what the battery chemistry, you just string enough cells in series to get you up to the desired working voltage... Or that's what electrical engineers had been designing a long time before I got my EE degree..

3. It's easer (and more efficient) to make an inverter that uses high voltage DC as input. It's pretty easy to just flip the current one way then the other to get AC sufficient to run most induction motors and transformer powered devices.

You have absolutely no idea what you're talking about. The conversion from DC to AC is THE BIGGEST LOSS in the inverters you're referring to. The actual transformer itself is pretty damn efficient if designed properly. Dealing with high voltage DC is extremely dangerous. It ARCs over distances that AC won't. You can put 200v AC traces on a circuit board with little space between them. Do the same thing with the same DC voltage and the board is going to randomly arc all over itself.

So are you claiming that YOUR design where you use a transformer to step down to 12 V THEN rectify it (which is the classical DC supply design) is indeed more efficient than just rectifying it at 120V? Um, don't you have the transformer losses AND the rectifier losses where my design only has the rectifier losses? Further, I would contend that your 12V rectifiers at higher current will actually have MORE losses than mine which run at lower current and would have less IR losses. But don't let pesky facts stop you..

Arcing is an issue, Just because I didn't discuss it here, doesn't mean I'm not aware of it. Yes, you will need to change some stuff out like Circuit breakers and wall switches. You are likely to be required to put in metal pull boxes and conduit for the wiring too. The electrical and building codes and a competent electrician should be employed to keep things up to code. However, that doesn't change the fact that a LOT of stuff in your home can easily run on DC without modification.

Also, I'd like to point out that the fine article is suggesting LOW VOLTAGE DC is the solution. One is going to need to rewire their home for that solution too, I'm just suggesting that the more efficient and cost effective solution is to go with high voltage DC. I'm not claiming that there are not issues to be dealt with, only that these issues are easier and cheaper to deal with than wiring the house for 12V..

4. It's more efficient to use higher voltage in terms of wire size because IxR losses are less for the same power transfer. Chances are the same wires you have now will be fine, but if you go to low voltage (say 13.8V like in your car) you are going to need bigger conductors to avoid the voltage drops over long high current runs. Use higher voltage and lower current, and stick with the wires you have.

The first part is true, larger wires are better for lower current loss. The rest of this is false. DC has different properties than AC. Insulators, wire spacing, and load will behave differently at 200v AC versus DC. You CAN NOT use the same wiring unless you want to burn the building down. Please don't ever tell people anything about electrical wiring, you're going to get someone killed.

Sir, respectfully I disagree that wire size would need to change all that much if you assume you switch to a similar voltage DC from AC. However, I will agree that there ARE issues with DC that will need to be addressed. Arcing of DC when switching is a problem which would require changing out AC switches currently in place (Circuit Breakers and light switches). But I don't think the standard house wiring would necessarily need to be altered that much in conductor size, but I would defer to your local licensed electrician and building codes for a full list of what you are going to need to stay within code.

Full disclosure.. I hold a BSEE and have an interest in emergency power operation of Ham Radio equipment. I've experimented with some of what I suggest here and it works with caveats as noted, at least for the things I've tested. My laptop charger was fine, my desktop PC and LCD display worked great as did the Switching DC power supply for my radios. If you hook up your expensive Flat Screen TV to the battery in your Prius, usually it works, it might not and it might self destruct. Without looking at the power supply design, there's no way I can tell you which option you will get.

Comment: Re:Use High voltage DC stupid... (Score 1) 317

by bobbied (#49792319) Attached to: How Tesla Batteries Will Force Home Wiring To Go Low Voltage

We need to use HIGH voltage DC at about the same voltage as your house is now, forget about going "low voltage" DC.

No, we don't.

120v AC will kick you off of it if you touch exposed wires.

120v DC will cause you to clamp down if you grab onto a wire or device that electrocutes you, and worse still, it'll kill you at much lower voltages than AC.

Um, no, it's exactly the opposite situation. Both AC and DC can shock and kill at high enough voltages, but AC is what you cannot let go of and DC is what usually bumps you off. DC induces all your muscles to contract at the same time all at once which cause a quick jerk which often disconnects the victim, AC has the effect of pulsating all the muscles, which incapacitates the victim but not inducing one big jerk. The rule of thumb is that AC is about twice as lethal at the same current/voltage over DC.

I understand your confusion though. Most DC people are exposed to runs in the 5-48 volt range because this is what modern electronics usually use internally. Officially 48 volts is "dangerous" and "lethal" but in reality is not usually going to hurt you if you happen to cross it. However, the real dangerous stuff that is DC usually runs in the thousands of volts (A Tube TV 9K to 25K) or a radio amplifier (600V to 2.5Kv) which will kill you pretty quick if you become the path to ground. Normal 110V in your home usually takes awhile to kill you.

It's kind of amusing though to go back though the history of Edison/Westinghouse (DC/AC) debate. Edison used this problem of AC "grabbing" people over DC's safety to his advantage. He called electrocution "being Westinghoused" for a reason and electrocuted an elephant in a now famous film to make his point. Brilliant PR move, but a bad idea for electricity distribution.

Where there are increased dangers of using DC over AC, electrocution is actually one of the dangers that is reduced.

Comment: Re:Wait... What?!? (Score 1) 317

by bobbied (#49792105) Attached to: How Tesla Batteries Will Force Home Wiring To Go Low Voltage

Less voltage = less eff. More voltage = more eff.

0.o

I think Tesla needs to go back to school. At low voltage, you can only push so many Watts before you run into resistance and heat issues. The higher the voltage, the more Watts you can push through the same size wire. This is why the car industry is moving towards 24 volt systems, because 12 volt systems max out at about 1.5KW's An ex. At 12 volts, my whats-a-ma-giger wants to consume 500 watts. for that much power, I will need to push ~"42" AMPS! Ho boy! Now that's an instant electrical fire! Now lets say my device runs on 110 volts and still consumes 500 watts. That's roughly about 5 amps we need to push (pull) down the line. Perfectly safe with standard house hold wiring.

So far, so good... Your understanding of electricity is fine so far...

And a second thing. DC requires MUCH THICKER CABLING at the same voltages and amperage than AC does. This is because you don't push the electrons in only one direction with AC, you push them back and forth and they never have to run all the way down the line leading to less long distance loss, and loss as heat. That is why we use AC. Could anyone imagine the size a DC cable would need to be at those high voltages?!

Um.. Not exactly true. DC requires thicker cabling because it is usually lower voltage and higher current (as you stated above). The flow of electrons changing directions is NOT an issue. The average current flow for the same power is the same, and it doesn't matter if it's AC or DC. In fact, AC might be argued to be a bit less efficient because you have to add all the reactive components to the AC current flow. Induction motors present high inductive (current lagging) loads, which means that there is actually MORE current flowing for the same power transfer in AC. Electrical engineers call this the "power factor" and it describes why Volts X Amps doesn't always equal power transferred (In fact it rarely does for anything but pure resistive loads.) So AC wires end up a bit larger for the same load...

Now what IS a problem for DC is protection of circuits. DC has a tendency to arc over when you try and turn it off, where AC doesn't do this as much by virtue of the fact that it's actually OFF (zero voltage and current) 120 times a second. There is a certain amount of inductance in any DC circuit that can sustain the current by generating some high voltage spikes as the magnetic field collapses. This increased arcing causes switch contacts to wear out faster and sometimes can be enough to sustain the circuit's current, though it's been turned off. Arcs are really hot too, so they can cause fires. But there are ways to deal with this (separating contacts by greater distances and opening them faster, or arresting the arc using capacitors).

So you are on the right track, but not correct on that last bit..

Comment: Use High voltage DC stupid... (Score 2) 317

by bobbied (#49791799) Attached to: How Tesla Batteries Will Force Home Wiring To Go Low Voltage

We need to use HIGH voltage DC at about the same voltage as your house is now, forget about going "low voltage" DC. MOST things in your home will run JUST FINE on DC with a few notable exceptions. AC induction motors will NOT work, nor will anything that involves an old fashioned transformer, but most modern electronics with switching power supplies work great on anywhere between about 90V to 200V DC without modification. Most switching power supplies just convert the AC into DC right up front and won't know the difference. So, all you do is provide inverters for the things you cannot easily change (like for your appliances) and just feed DC to the rest of the stuff that doesn't care. What you DON'T do is go to low voltage DC and suggesting this is just crazy talk. Why?

1. Most stuff just works on high voltage DC as discussed above. Most switching power supplies simply don't know or care about AC or DC and due to their efficiency switching power supplies are used in almost everything electronic.

2. It's easier (and more efficient) to use high voltage DC for charging the batteries. All you need is a rectifier to convert that 220 into about 250V DC and charge the batteries, which is about as simple and efficient as it comes.

3. It's easer (and more efficient) to make an inverter that uses high voltage DC as input. It's pretty easy to just flip the current one way then the other to get AC sufficient to run most induction motors and transformer powered devices.

4. It's more efficient to use higher voltage in terms of wire size because IxR losses are less for the same power transfer. Chances are the same wires you have now will be fine, but if you go to low voltage (say 13.8V like in your car) you are going to need bigger conductors to avoid the voltage drops over long high current runs. Use higher voltage and lower current, and stick with the wires you have.

5. Current battery technology for EV's and hybrids uses about 200V DC to start with, so there are less modifications to the technology when adapting to a home use. If we stick with a common battery pack voltage it will increase the economies of scale in their production and allow the use of old automobile packs that have reduced capacity as power storage in homes where the size and weight of the battery is less important. If you go low voltage, you either have to convert the 200V down to 12 or 48 (and incur the conversion loss) or modify the battery pack to operate at the lower voltage.

I know that traditional DC systems run at multiples of 12 Volts because they are usually built on Lead-Acid batteries and that much equipment is commercially available that uses 12 and 48 volts based on this. But going to 12 or 48 volts is not the right answer. It's really just the traditional solution based on past thinking and limitations. Running 200V DC is a more viable and long term solution that will work fine with a lot of existing AC equipment, plus is compatible with a ready source of batteries which are commercially available (and if purchased used, pretty cheap).

So, NO, we DON'T want to start using low voltage DC... We want to use HIGH voltage DC.

Comment: Re:Automatic presumption of govt incompetence... (Score 1) 186

by bobbied (#49786013) Attached to: Charter Strikes $56B Deal For Time Warner Cable
And you sir are painting with a wide brush. Bad people do BAD things, one cannot deny that, but in China, the government selectively chooses not to enforce its laws and allows bad people to do bad things. So you now claim that ALL people do bad things because a few have in the past? Or, to put it another way, capitalism is bad because it is abused in China? Capitalism has its problems, but as a method for generating wealth and lifting the standard of living for the majority, it cannot be beat. And it certainly cannot be beat by a government program...

Comment: Re:Governments contract private companies. (Score 1) 186

by bobbied (#49784661) Attached to: Charter Strikes $56B Deal For Time Warner Cable

You have more than one choice... Perhaps one wired choice is all you have, but there are other providers out there. I'm guessing they are more expensive and likely lower bandwidth, but you have choices.

Now, if you where *really* in the boonies, 10 miles from anywhere like where I grew up in South West Missouri, THEN, we had 2 viable broadband choices. A marginal Cell Phone based provider using a cell tower about 10 miles away or the Hughes satellite option which has broadband bandwidth and really long latency.

But I'm saying that for the VAST majority of people in the USA, broadband is available, usually from multiple vendors. I don't think we really have a huge broad band problem. Yea, there are places you won't get wired service, but the number of people who live in these areas is pretty limited.

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