The Revenge of DC...

The story below is a basic history of AC and DC transmission, and use.

If (early DC proponent) Edison had only succeed in getting the Electric Chair called the "Westinghouse", we might have an easier time finding DC charge points today...

I've been meaning to post the question, how widely available is DC, and do these locations offer practical benefits for BEV charging? Any synergies for DC Charge stations located at DC users, such as those reported below?

...in conventional data centers, with hundreds of computers, electricity might be converted and “stepped down” in voltage five times before being used. All that heat must be removed by air-conditioners, which consumes more power.

In a data center redesigned to use more direct current, monthly utility bills can be cut by 10 to 20 percent, according to Trent Waterhouse, vice president of marketing for power electronics at General Electric.

“You can cut the number of power conversions in half,” Mr. Waterhouse said.

On a far smaller scale, SAP spent $128,000 retrofitting a data center at its offices in Palo Alto, Calif. The project cut its energy bills by $24,000 a year.

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http://www.nytimes.com/2011/11/18/business/energy-environment/direct-current-technology-gets-another-look.html?hpw" onclick="window.open(this.href);return false;

I work in the phone industry and we have been 48v dc for decades. A lot of the data center guys have access to DC equipment, but because it is ofter co-located with my phone stuff, it is also designed for 48v dc.

We have some huge DC battery plants at at work (one 2v cell can hold 2000 amp-hours) and I'm sure that if I had access to them, that I could charge up to 6 empty leafs before depleting them. Having said that, there is no chance that my company will ever let it happen for two good reasons.

The first is that the battery plant is expensive. They also measure battery life in discharge cycles and don't want to reduce its lifetime. They have enough trouble replacing them when they ought to and before they wear out.

The second reason is the big gotcha though. Since we provide telephone service, and that is used for 911 lifeline communications, we are government regulated to maintain so many hours of battery backup capacity. Sure we could keep track of how much the plant charge is depleted and stop charging leafs at some point, but the risk of having to file the FCC paperwork if we were wrong, and likely paying penalties for that, is not something that they will risk.

Funny...

I was walking around my house the other day looking at all the charger bricks my family has around the house for cell phones, laptops, flashlights, etc and then thinking about all the DC motors and controllers used by our appliances (well pump, fridge, etc). Then there is the Inverter for my solar panels that costs me 7% of the energy my panels generate converting to AC. Holistically it seemed inefficient.

This got me to thinking: What if my house had a big (centrally located) AC->DC rectifier and outlets equipped with a dial for common DC voltages (9v, 6v, etc) & amperage (4mA, 3.5mA, etc) in each room of the house? If appliances all had DC plugs (in addition to the AC) that bypass their on-board rectifier would I actually save power? Certainly my solar power would be better used and the main rectifier could be designed to reduce ghost loads that all those power bricks that aren't plugged into devices draw, but would a single large scale rectifier be more efficient in use than the forty or so sprinkled around my house?

I suppose that it saved a lot of energy then there would be more people calling for it, so I guess not.

So I assume these "dials" you are talking about at the outlets are just switches to pick the correct voltage, not variable voltage DC/DC converters? The latter would get very expensive. The former would require lots -- I mean lots -- of wires, some of which might have to be really heavy gauge. I guess each dial could send a signal to a corresponding central switch, so you would only need one pair of wires for each outlet, but then you wouldn't be able to put multiple outlets on one circuit, so you would still have a lot more wiring than at present -- plus the cost of all those switches.

Ray

planet4ever said:

So I assume these "dials" you are talking about at the outlets are just switches to pick the correct voltage, not variable voltage DC/DC converters? The latter would get very expensive. The former would require lots -- I mean lots -- of wires, some of which might have to be really heavy gauge. I guess each dial could send a signal to a corresponding central switch, so you would only need one pair of wires for each outlet, but then you wouldn't be able to put multiple outlets on one circuit, so you would still have a lot more wiring than at present -- plus the cost of all those switches.

Ray

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I was thinking more like those wall warts you can get from RadioShack with multiple amperage and voltage. There would be low voltage ones for computers, phones, etc and high voltage/amperage for appliances. I didn't think about not being able to daisy chain like you can with AC, which means home run to the central rectifier for each outlet, ugh pricey. If the outlets were mass produced they should be cheaper than dimmers, but again, it requires a huge change from the same 110 plug for everything that we have today, so its pretty obvious it won't happen.

I was just wondering if that would really reduce wasted energy through heat loss, ghost power loads from rectifiers that have no loads but still draw current etc, or would we just be moving the loss to something else b/c DC doesn't carry as far.

I think the simple answer here is that you simply run a parallel 12 volt DC system in your house. Many solar powered homes run both 120 VAC and 12 VDC for exactly the reason you described, to avoid the loss in efficiency in the conversion. Many, many appliances are available in 12 volt versions, as well as light bulbs. Also, from there it is a simple matter to regulate it down to the lower voltages needed by cellphone chargers, etc, using the regular car adapters in most cases. I use the 24 VDC from my one solar setup directly to drive a freezer and a backup water pump for my well.

keydiver said:

I think the simple answer here is that you simply run a parallel 12 volt DC system in your house. Many solar powered homes run both 120 VAC and 12 VDC for exactly the reason you described, to avoid the loss in efficiency in the conversion. Many, many appliances are available in 12 volt versions, as well as light bulbs. Also, from there it is a simple matter to regulate it down to the lower voltages needed by cellphone chargers, etc, using the regular car adapters in most cases. I use the 24 VDC from my one solar setup directly to drive a freezer and a backup water pump for my well.

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Keydriver, Would you mind sharing the details of your DC freezer and 24 VDC - model info and size (and pictures if easy)? How much do you think you save by going this way. Other reason for doing this besides cost shavings?
Also, What are some of most common DC appliances that people use besides freezers. Is this common in Florida?

You can get most any appliance you want in 12V DC, which are built for the RV/Marine/off-grid markets.

Generally (mostly due to much lower production volumes, I expect.) the costs are higher, and the selection much smaller, than for 120V AC.

As an aside, when I was looking for a rural home site, I considered either the all DC or dual DC/AC wiring option for off-grid locations.

I decided to stick with the grid, mostly because I realized my ICEV vehicle use on the “road grid”, caused far higher environmental and monetary costs, than would my on-grid home.

6 months and almost 5,000 miles post-LEAF, Averaging about 200 kWh (almost all of it cleaner and cheaper off peak) in my BEV (plus about 1-2 gallons of gas per month for my ICEVs), and 300 kWh (and about 10 gallons of propane) for my home, the relative costs of fueling my home vs. my vehicles, have reversed.

DC is great if generated locally. not so much if you have to pay to have it transported even a few miles. so ya, with solar, wind, etc., DC would save a ton. cost a ton to implement, etc.

i think we should all get an elliptical and hook up a generator to charge a battery to run all our small chargers on. i have cellphones, game systems, TV conversion giggy widgets, etc.

this solution allows us to live longer (great exercise) and live cleaner!!

but then again...this solution is about as practically as every other one mentioned here. (keeping in mind the first sentence)


i know a PC'er who built a home off the grid (mostly because the grid was several miles and several thousand $$ away) it was DC and yes it was a compromise but allowed him to reduce his carbon footprint by quite a bit. he did supplement his power with a generator but most of it came from wind and solar.

but barring an empty lot. converting something already there has to be a monumental task

lkkms2 said:

keydiver said:

I think the simple answer here is that you simply run a parallel 12 volt DC system in your house. Many solar powered homes run both 120 VAC and 12 VDC for exactly the reason you described, to avoid the loss in efficiency in the conversion. Many, many appliances are available in 12 volt versions, as well as light bulbs. Also, from there it is a simple matter to regulate it down to the lower voltages needed by cellphone chargers, etc, using the regular car adapters in most cases. I use the 24 VDC from my one solar setup directly to drive a freezer and a backup water pump for my well.

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Keydriver, Would you mind sharing the details of your DC freezer and 24 VDC - model info and size (and pictures if easy)? How much do you think you save by going this way. Other reason for doing this besides cost shavings?
Also, What are some of most common DC appliances that people use besides freezers. Is this common in Florida?

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Go to http://www.homepower.com" onclick="window.open(this.href);return false; as a good source for this info.

I didn't actually do it for cost savings, but for backup during hurricane power outages. The more things you can load on to the DC, the less has to be on the inverter, or can be run from some other source if the solar fails, even jumper cables from my car. The freezer is a Sundanzer. They are designed to work on as little as only one solar panel, for off-grid applications. The pump is a Shurflo pump designed for RV use, which parallels my regular pump. During the last hurricane, Wilma, I had hot running water for showers, TV, computer, pretty much everything but AC for 5 days.

12 volts DC can actually be fairly inefficient unless you run heavy wires and/or have short runs. The I2/R drop can waste energy in the form of wire heating due to the relatively high currents required at the relatively low voltage...

TomT said:

12 volts DC can actually be fairly inefficient unless you run heavy wires and/or have short runs. The I2/R drop can waste energy in the form of wire heating due to the relatively high currents required at the relatively low voltage...

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Which is one reason BEVs and Hybrid cars use high-voltage traction batteries. 80KW at 12 volts would mean 6667 amps! Very heavy wiring!

TomT said:

12 volts DC can actually be fairly inefficient unless you run heavy wires and/or have short runs..

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...or you draw very lower current. Things like cellphone chargers, 12 volt CFL bulbs, portable emergency tv's, and even my freezer draw so little current that the wire loop resistance is negligible. It has its uses, but as noted above this is why we use much higher voltages for most applications.

edatoakrun said:

I've been meaning to post the question, how widely available is DC, and do these locations offer practical benefits for BEV charging? Any synergies for DC Charge stations located at DC users, such as those reported below?

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You're a few years late for DC power stations

http://cityroom.blogs.nytimes.com/2007/11/14/off-goes-the-power-current-started-by-thomas-edison/" onclick="window.open(this.href);return false;

The uses in your article are site-generated (e.g., motor-generators running on AC), and at voltage specific to the task at hand. Unlikely the voltage would match the LEAF's charging needs directly.

Anyway, essentially a DC fast-charger is just another form of site-generated DC already.

Nubo said:

edatoakrun said:

I've been meaning to post the question, how widely available is DC, and do these locations offer practical benefits for BEV charging? Any synergies for DC Charge stations located at DC users, such as those reported below?

Click to expand...

You're a few years late for DC power stations

http://cityroom.blogs.nytimes.com/2007/11/14/off-goes-the-power-current-started-by-thomas-edison/" onclick="window.open(this.href);return false;

The uses in your article are site-generated (e.g., motor-generators running on AC), and at voltage specific to the task at hand. Unlikely the voltage would match the LEAF's charging needs directly.

Anyway, essentially a DC fast-charger is just another form of site-generated DC already.

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Yes, but some DC "sites" are quite extensive, such as the 600 V DC San Francisco Muni Railway, and 1000 V DC Bay Area Rapid Transit system.

http://en.wikipedia.org/wiki/Muni_Metro" onclick="window.open(this.href);return false;
http://en.wikipedia.org/wiki/Bay_Area_Rapid_Transit" onclick="window.open(this.href);return false;

I don't expect that either operation would find the additional draw of BEV chargers, to lead to additional PG&E demand charges...

I believe PG&E may still have some DC underground transmission lines in SF as well. IIRC, some were still in use, as recently as a few years ago.

edatoakrun said:

Yes, but some DC "sites" are quite extensive, such as the 600 V DC San Francisco Muni Railway, and 1000 V DC Bay Area Rapid Transit system.

http://en.wikipedia.org/wiki/Muni_Metro" onclick="window.open(this.href);return false;
http://en.wikipedia.org/wiki/Bay_Area_Rapid_Transit" onclick="window.open(this.href);return false;

I don't expect that either operation would find the additional draw of BEV chargers, to lead to additional PG&E demand charges...

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But, afaik, you couldn't just plug a LEAF into a 600V or 1000V system. The voltage would need to be adjusted. So what would be the advantage of needing a DC-DC conversion device vs. an AC-DC conversion device?

Nubo said:

But, afaik, you couldn't just plug a LEAF into a 600V or 1000V system. The voltage would need to be adjusted. So what would be the advantage of needing a DC-DC conversion device vs. an AC-DC conversion device?

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There is a tiny efficiency advantage starting with DC..

Herm said:

Nubo said:

But, afaik, you couldn't just plug a LEAF into a 600V or 1000V system. The voltage would need to be adjusted. So what would be the advantage of needing a DC-DC conversion device vs. an AC-DC conversion device?

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There is a tiny efficiency advantage starting with DC..

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Yes, but that DC at the rail station, etc, was already converted from AC. Unless the facility is generating its own power directly as DC.

Herm said:

Nubo said:

But, afaik, you couldn't just plug a LEAF into a 600V or 1000V system. The voltage would need to be adjusted. So what would be the advantage of needing a DC-DC conversion device vs. an AC-DC conversion device?

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There is a tiny efficiency advantage starting with DC..

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Is it "tiny"?

That's what I was asking, whether the AC/DC conversion is a significant inefficiency and expense, and whether any existing available DC sources offered any advantages, for DC charge-point installations.