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Is It Time for DC Outlets In Houses?  RSS feed

 
Jerry Ward
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With the changes in technology I wonder if it is time to re-open the War of the Currents. While I understand that transmission of power require AC for efficiency, however most of our electronics require DC power in the guts of them to make them work. When I think about the number of things I have plugged in and the vast majority have some kind of transformer stepping the voltage down and converting it to DC. Therefore I wonder if it wouldn't be better to have a high efficiency transformer in one place in the house to produce DC and then route it to the devices that need it. In computer server rooms you are starting to see DC powered racks, that is all the devices in the rack are powered by DC.

Some problems/issues I see:
1. You lose efficiency trying to send a lot of current via DC unless you use REALLY thick wire. But most of the devices I'm talking about are low current.
2. There is no "standard" DC voltage. I have stuff that goes from 3V-24V and changing voltage in the DC world is a hit in efficiency
3. It would be a pain to retrofit an existing house to run both AC & DC to each room.

Advantages:
1. You could have a good sized battery that is intermittently recharged from the grid. This would keep these electrical device up and running during a power outage, how long depends on the size of your battery.
2. All of the individual transformers at every device could be eliminated.
3. Easy to add alternative energy since most of it is DC and could be feed directly into your house without needing to go through an inverter.

Unknowns:
1. How much power would you really save? Many of these DC devices are very low power users. I suspect that many times the wall wort transformer wastes more power then the device actually consumes. Would you ever save, for example, the amount of energy it takes to make the additional copper wire you are using to distribute this DC power?
2. I know I should put such transformers on some kind of switch and turn it off, but this is an area I just plain lazy and will not likely do it. Plus things like a clock you need powered up all the time. Maybe the solution is to put batteries in these devices and recharge them as needed, unplugging the charging transformer when not in use. But the device would stay up and running without constantly running a transformer.

Some food for thought and I welcome all comments. My real understanding on this stuff is over 25 years old, back when I was in electronics classes. Some things remain the same, but I sure others have changed. I started thinking about this again because I just got a new 32" LED TV and it has a transformer with a very small wire running from the transformer to the TV. Just based on the cord size I would say this consumes less than 1/10th the power of the old CRT's.

My $.02 worth (well maybe $.05)

 
Len Ovens
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Jerry Ward wrote:
Some problems/issues I see:
1. You lose efficiency trying to send a lot of current via DC unless you use REALLY thick wire. But most of the devices I'm talking about are low current.

Voltage is voltage, AC or DC. Low voltage AC would have the same problems. 100 to 130v DC would work with a large number of "AC" objects we already have... Most motors in drills, vacuums, and kitchen appliances will run on DC for example. Incandescent lamps will work and probably some of the LED lamps too (maybe even CFLs). Most computers will work (switching power supplies are fun)


2. There is no "standard" DC voltage. I have stuff that goes from 3V-24V and changing voltage in the DC world is a hit in efficiency

This is in some ways a plus. Transformer based wall warts are not efficient. A lot of the new ones are switchers and only suck as much power as needed at the time. The PS for my netbook draws nothing when the battery is charged and the power off... a normal transformer based PS would draw full power all the time. The PS for my netbook would probably work as is from DC, but a transformer PS would not.


3. It would be a pain to retrofit an existing house to run both AC & DC to each room.

Yes, but the reason for wiring DC would (for now) be off grid living. What needs AC? There are some power tools that do. some could have the motor replaced with a dc motor (there are lots of powerful new ones out there) or they could use an inverter after the switch for that tool alone. Still, when being off grid or using a battery, the big AC appliances tend not to be installed. There is no reason technically a drier could not run on 220vdc with a dc motor, but the battery to run it would have to be big and costly.

The disadvantages I see:
the controls we use now might not work. Any triac control would not work on DC. Even the average switch used for ac work might be trouble for DC. AC has a zero crossing all the time so if an arc starts it will stop at the next zero crossing (1/120th of a second). With DC that doesn't happen so the switch has to be bigger and have contacts that separate farther in the off position.


Advantages:
1. You could have a good sized battery that is intermittently recharged from the grid. This would keep these electrical device up and running during a power outage, how long depends on the size of your battery.
2. All of the individual transformers at every device could be eliminated.
3. Easy to add alternative energy since most of it is DC and could be feed directly into your house without needing to go through an inverter.

As you can see, most of you disadvantages could be moved to this group too just by looking at them differently.


Unknowns:
1. How much power would you really save? Many of these DC devices are very low power users. I suspect that many times the wall wort transformer wastes more power then the device actually consumes. Would you ever save, for example, the amount of energy it takes to make the additional copper wire you are using to distribute this DC power?


The savings could be as high as 80% by supplying your own power and removing the transmission line losses of the grid. These might not be your savings, but system wide. The power co would rather have those losses and sell you power that not make money from you


2. I know I should put such transformers on some kind of switch and turn it off, but this is an area I just plain lazy and will not likely do it. Plus things like a clock you need powered up all the time. Maybe the solution is to put batteries in these devices and recharge them as needed, unplugging the charging transformer when not in use. But the device would stay up and running without constantly running a transformer.

I think if houses had a standard dc voltage, manufacturers would make devices to suit. It would mean 1 less bit to make and ship and no CSA/UL approval needed. Both a cost savings and faster to market of a new design. Look at the number of things that will charge from a USB port (phones, mp3 players, cameras). I am sure one plug could be multi-voltage easing the house wiring problems.... 5 and 12 volts would cover just about any low power need. Switching power supplies would fix all else.


Some food for thought and I welcome all comments. My real understanding on this stuff is over 25 years old, back when I was in electronics classes. Some things remain the same, but I sure others have changed. I started thinking about this again because I just got a new 32" LED TV and it has a transformer with a very small wire running from the transformer to the TV. Just based on the cord size I would say this consumes less than 1/10th the power of the old CRT's.

My $.02 worth (well maybe $.05)



Made me think too.

Are you sure the LED tv has a transformer? A lot of the new wall warts are switchers.

My first thought is more how can I get rid of a lot more of my power use so this could work? My old drier uses a lot of power, but I can put a dehumidifier running at 700w in a room and hang my clothes up in there and they dry almost as fast as in the drier... plus it keeps the room from going moldy It seems like more work to hang everything, but I have to hang it up after drying anyway.

Cooking and heating are the other big uses. PAHS would take care of the one.... cooking (and hot water and food chilling) are not so easy...unless we burn something.
 
                            
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If you used solar power this would make some sorta of practical use. The problem with just doing it is you have to go through a conversion from AC to DC so you are already losing if you do it in real time. You could charge batteries, but it becomes complicated. DC batteries don't do well with high voltages (they explode), so you have to step down, or voltage divide. Voltage dividing is worse than using a transformer because you bleed it off in heat.

I would have DC sockets for the common voltages at each socket. It would be something like 3,5,9,12 (have to research it a bit). You could even have an "odd one" where you voltage divide with a potentiometer and mark the voltages. You can achieve this by just using several batteries that allow you to stack the voltages. You tap in where you want what voltage. The farther up the chain, the higher the voltage. You prevent the voltage from increasing by using diodes between the batteries.

The most difficult part is actually by-passing the power section in all the stuff you have that does not have an adapter outside of itself. In many cases this would require you to have a decently intimate knowledge of the power section so you can feed right into the output (most likely connect to capacitors that are right after diodes). You can't bypass the power section because many of today's electronics actually run on several different voltages within themselves. This requires a schematic... some are free others cost you. They can cost more than some devices are worth. The other way around is using a multimeter to find out what voltage is after rectification; that you have to duplicate off the wall.

These are some of the reasons even the hardcore DIY guy into electronics doesn't bother.

The price of refrigerators, washers, dryers, blenders, and anything with an electric motor would become astoundingly expensive. They can run on DC motors but DC motors are instant on-off things that can go in reverse. Even if you put in fail-safes to prevent people from totally screwing them up, it would cost money. The bearings in them have to much, much better. The overall build is of an entire different quality. In commercial settings they can turn on and reverse thousands of pounds back and forth like it is nothing, on a dime, in an instant, but they machinery has to be built to handle that stress.
 
Len Ovens
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Kull Conquered wrote:If you used solar power this would make some sorta of practical use. The problem with just doing it is you have to go through a conversion from AC to DC so you are already losing if you do it in real time. You could charge batteries, but it becomes complicated. DC batteries don't do well with high voltages (they explode), so you have to step down, or voltage divide. Voltage dividing is worse than using a transformer because you bleed it off in heat.


And batteries have other problems... charging from AC would be a loss, battery leaking is a loss... Not worth while. Either use AC or go off grid.


I would have DC sockets for the common voltages at each socket. It would be something like 3,5,9,12 (have to research it a bit). You could even have an "odd one" where you voltage divide with a potentiometer and mark the voltages. You can achieve this by just using several batteries that allow you to stack the voltages. You tap in where you want what voltage. The farther up the chain, the higher the voltage. You prevent the voltage from increasing by using diodes between the batteries.


5, 12 and 100v is what I would do. 5v would be a usb (with usb current limits), 12 an automotive cigar lighter style (12-15 amp) and 100v might be the electric forklift style... with a switch... Maybe not, at that voltage I would be choosing low current stuff because it would only be done if off grid... no electric ranges or even driers. But a switch for sure, at that voltage an arch could be quite long. Maybe an auto switch that turns off/on when the plug is part way out. Many electronic things, (computers, newer tvs, printers etc. would run as is on 100v (100v is the bottom of the 115vac spec... or is it 105? Most things will run on 100 anyway) Anything that had to have ac would have it's own personal inverter added after the unit on switch. Not sure if this is the best way, just that I don't want to leave an inverter running all the time. My feeling is that most _new_ wall warts are 5 volt and a lot of things just plug into the usb port anyway. There is a huge selection of 12v things for the rv market and they are all 12v. !00vDC would power many 120vac things... not clocks... but at least some lamps. (no dimmers) Many hand tools. It may cost more to set up a dc fridge than a horizontal freezer run at fridge temps. But there are lots of dc fridge bits around if needed anyway. Better to find some passive way of keeping things cool or fresh (don't pick till needed?)


The most difficult part is actually by-passing the power section in all the stuff you have that does not have an adapter outside of itself. In many cases this would require you to have a decently intimate knowledge of the power section so you can feed right into the output (most likely connect to capacitors that are right after diodes). You can't bypass the power section because many of today's electronics actually run on several different voltages within themselves. This requires a schematic... some are free others cost you. They can cost more than some devices are worth. The other way around is using a multimeter to find out what voltage is after rectification; that you have to duplicate off the wall.


think about the electronics that are useful in an off grid type of setup. Many of them use switching power supplies inside. The input is a fuse then a bride rectifier (maybe a MOV first) Dc with no transformer... less cost to make, lighter to ship, easier to get lower energy certification... Lots of stuff uses them even a lot of wall warts. Just a matter of choosing the right stuff.


The price of refrigerators, washers, dryers, blenders, and anything with an electric motor would become astoundingly expensive. They can run on DC motors but DC motors are instant on-off things that can go in reverse. Even if you put in fail-safes to prevent people from totally screwing them up, it would cost money. The bearings in them have to much, much better. The overall build is of an entire different quality. In commercial settings they can turn on and reverse thousands of pounds back and forth like it is nothing, on a dime, in an instant, but they machinery has to be built to handle that stress.


Most blenders use dc motors already... same with most small kitchen appliances, hand drills, skill saws, angle grinders.... vacuum cleaners. Not sure what the best dc voltage would be for them though. Less than 120v as it is 100% duty cycle.

Things that don't have dc motors include washing machines, dryers(off grid?), dish washers(off grid?), chillers (fridge/freezer/aircon) central heat (off grid) and most stationary tools. There are a few ways to DC-ifie them. A generator run one day for a few hours for this purpose and to equalize the batteries. Next an inverter would work easy though to run one all the time would not be best though the better ones have a high and a low mode depending on what the draw is. For a freezer I would put a small inverter after the thermostat. While most ac ventilators are ac motors, there are lots of 5 and 12v brushless DC fans about, some quite powerful. Someone in an off grid situation could do just fine on DC if they put some thought to it.... And really, anyone living off grid had better put thought into it or they will have dead batteries that need replacing every two years...or spend a lot of money on enough solar panels and batteries to power "anything"... think 200 amp service. Not sure where there will be enough room to grow any food with that much solar power.

Anyway, there are lots of options. I would not use voltage dividers for anything though 12v dc wall wart replacers generally do that. Most things that use wall warts actually handle quite a wide range of voltages... not just what the wall wart says it puts out.... just measure what that is. At no draw a 9v wall wart puts out 12v. Something that requires "6v" will run on 5v or 9v. Most 12v things will handle as much as 16v
 
                            
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You make it sound simple... but that is very complicated and beyond most means.

I think you might be surprised at the different voltages of wall warts. (and the switching ones are ok but too noisy for many applications)

Uh I would would want to check that anything runs off 100v or even near it off the rails (rectification). They have transformers. You have to step that down and skip the transformer or you are not doing anything but being as wasteful as with AC. Computers these days have 3.3, 5, 12, -12 in them from the power supply

Hand tools that use DC are battery powered, and most are worthless compared to their wall powered counter parts. Good drills (cordless) run on 18v; anything else is just wimpy these days.

The point of voltage dividing is to remove inefficiencies of anything between power source and the thing being used. Also noise is kept at zero, enhancing the life and fatigue level (for the user) of all electronics.

Personally I think AC is pretty darn good as is for what we need, on grid. Perfect, no, versatile? Very. Problems? Using it for heat... excessive stupid stuff, low build equality making things less efficient.
 
Len Ovens
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Kull Conquered wrote:You make it sound simple... but that is very complicated and beyond most means.

I think you might be surprised at the different voltages of wall warts. (and the switching ones are ok but too noisy for many applications)

Yes there are lots, but there is a difference between what the wall wart says it puts out and what gets measured. What the wall wart powers can generally handle a large range of input voltage. Right off the top, ac line voltage can vary over 20% and still be within spec. Then the wall wart varies depending on load... most wall wart powered things massage the power after it gets in the box... the wall wart is only used because it is already CSA/UL approved which allows fast turn around to market that having the whole box approved. It is much simpler than it seems. A big part of it is being careful of what you buy in the first place. Anything that expects a well regulated voltage from the wart uses a switched one. I don't know what these "many applications " are that switching power supplies cause problems with... there are so many of them around now I don't see how one could get away from them.


Uh I would would want to check that anything runs off 100v or even near it off the rails (rectification). They have transformers. You have to step that down and skip the transformer or you are not doing anything but being as wasteful as with AC. Computers these days have 3.3, 5, 12, -12 in them from the power supply


A computer power supply is a great example... a look inside and there is a transformer... but, that transformer never sees 60hz ac... or any ac really. It sees spikes of 120v (or so) DC. Trace the wiring (I have) the AC comes in and is rectified to DC right off. Then it gets chopped and the transformer gives all the required voltages. Only one of those voltages (normally 5v) is used for feedback to determine pulse width to feed into the transformer. It would run on DC at 100 volts or 200volts most of them.


Hand tools that use DC are battery powered, and most are worthless compared to their wall powered counter parts. Good drills (cordless) run on 18v; anything else is just wimpy these days.


Nope. Anything noisy, that has brushes is actually a DC motor. I was talking about wall powered hand tools. The stationary ones with capacitor start are AC only.


The point of voltage dividing is to remove inefficiencies of anything between power source and the thing being used. Also noise is kept at zero, enhancing the life and fatigue level (for the user) of all electronics.


A voltage divider is the essence of inefficiency. This is why nobody uses inline voltage dropping any more, everyone is looking for the energy star rating... and uses a switcher. Even a transformer is more efficient than a voltage divider and probably puts less noise out. A properly designed switching PS can be very quiet too. There is no such thing as "zero noise", even just a piece of wire with no DC on it has some noise it has picked up from the environment. This is the principle of the old crystal radio.


Personally I think AC is pretty darn good as is for what we need, on grid. Perfect, no, versatile? Very. Problems? Using it for heat... excessive stupid stuff, low build equality making things less efficient.


Yup. if grid is what we have ac is great. dc plugs are only of use in an off grid world. Heat from AC? not the best use, but better than gas... at least my wallet thinks so... but then I live in a land of hydro, no coal fired plants here (or nucs either). Wood is probably better if copicing and a high mass heater are used. Heat pumps? I would need huge savings to pay for the unit let alone all the ducting or water lines in any reasonable time frame.... by then it would need repair... and then talk about noisy, they are.
 
Abe Connally
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we wired our house with both DC and AC, because we run completely off a solar/wind system.

All lights are DC, as well as the fridge, deep freeze, and water pump. We have DC car adapters for the computers.

We did it this way in case of inverter failure (we've had several in the decade we've been living like this).

So, each plug int he wall is actually 2 plugs. One AC and one DC, and they are marked accordingly.
 
Len Ovens
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velacreations Hatfield wrote:we wired our house with both DC and AC, because we run completely off a solar/wind system.

All lights are DC, as well as the fridge, deep freeze, and water pump. We have DC car adapters for the computers.

We did it this way in case of inverter failure (we've had several in the decade we've been living like this).

So, each plug int he wall is actually 2 plugs. One AC and one DC, and they are marked accordingly.


DC plugs are 12V? What kind of socket do you use? RVs seem to use the cigar lighter style.
 
Abe Connally
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Len Ovens wrote:
DC plugs are 12V? What kind of socket do you use? RVs seem to use the cigar lighter style.

Yes, our DC plugs are 12V, straight from the battery bank. We use regular 2 prong plugs for this, but mark them 12VDC, and they are a different color.

We modify the cords on things to make them work.

We tried the cig lighter adapters initially, but found that they wear out fast, usually making a bad connection, then heating up and melting the plastic casing.
 
Len Ovens
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velacreations Hatfield wrote:
Len Ovens wrote:
DC plugs are 12V? What kind of socket do you use? RVs seem to use the cigar lighter style.

Yes, our DC plugs are 12V, straight from the battery bank. We use regular 2 prong plugs for this, but mark them 12VDC, and they are a different color.

We modify the cords on things to make them work.

We tried the cig lighter adapters initially, but found that they wear out fast, usually making a bad connection, then heating up and melting the plastic casing.


I can see that. It is something to remember when I get to that point. Besides, it might make the code checkers happy if I have to deal with them We had (at work) connectors rated for 30amps burn up after 10years use at 6amps. They were used in 3phase motor circuits. I think what killed them was the constant vibration of the machine.

Do you have any fusing/breakers between the battery and the receptacle? Generally ac style breakers are good for dc use up to 24 volts. They normally have the ac and dc voltage rating printed right on them. These are what I used in our boat for nav lights and instruments. I found a bunch of small amp breakers in machines we were removing. (1 to 5 amps) Saved them from the dump.

I would have thought to use 3prog, just because they can only be plugged in one way. Some of the two prog plugs have two blades the same size. A bridge rectifier in the plug would protect from that too.
 
Abe Connally
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Do you have any fusing/breakers between the battery and the receptacle? Generally ac style breakers are good for dc use up to 24 volts. They normally have the ac and dc voltage rating printed right on them. These are what I used in our boat for nav lights and instruments. I found a bunch of small amp breakers in machines we were removing. (1 to 5 amps) Saved them from the dump.

We use 12 vDC breakers and fuses. You have to be careful using AC stuff, cause DC is hard on the contacts.

I would have thought to use 3prog, just because they can only be plugged in one way. Some of the two prog plugs have two blades the same size. A bridge rectifier in the plug would protect from that too.

Our 2 prong plugs are like that. One side is bigger than the other, so they can only plug in one way.
 
                            
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Strange... I would of never thought that hand held grinders where DC.

I think you confused my idea of a voltage dividing scheme with a traditional one that would use resistors. My suggestion has no resistors, no efficiency loss. The only thing in the circuit would be diodes and batteries. Instead of starting with a higher voltage and dividing down, you start with the lowest battery voltage you want and add more to increase the voltage. You use the diodes to prevent power taps earlier on at lower voltages from gaining voltage from the rest of the batteries in the circuit. So you could have a 3v, diode, 2v (to make a total of 5v), diode, 4v, diode, 3v. Giving you 3, 5, 9, and 12 voltages available. Obviously the 12v would have more amperage available. This is just an idea to suit the many needs of different voltages things require.

Perhaps we should have a topic about replacing transformer supplies with switching ones in order to increase efficiency. I however in many applications recommend some forms of filtering on them. You may consider noise to be irrelevant but... I haven't met anyone who doesn't until they get exposed to what no noise is like!
 
Trond Hogstadt
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For those wanting to use DC power alongside the normal 120 VAC home power there is a code compliant method to avoid potential problems with mixing the AC and DC. All plugs and receptacles listed for home use are given NEMA identification numbers. The usual 120 VAC grounded receptacles and plugs are a NEMA 5-15 (15 amp) or 5-20 (20 amp) type. As long as the home does NOT have any 240 VAC outlets anywhere the NEMA type 6 (6-15 or 6-20) may be used for DC low voltage circuits. The pins are oriented in such a way that it is impossible to plug one type into the other. This is what I use in my off grid home with both AC and DC circuits.

There is a chart of NEMA types here.... NEMA chart, PDF

For breakers the SquareD brand, QO and QOC series of breakers are approved for DC low voltage use, up to 24 volts. Strictly speaking they should not be used on a 24 volt battery system as under charging a 24 VDC battery system will have greater than 24 volts present. Also as the AIR rating of the QO and QOC series is low any system should have a proper DC rated fuse between the battery and the breaker, otherwise a short circuit down stream could cause the breaker contacts to weld or fail.


The hard part is finding a wall switch that can handle the DC current and is also NEC approved.
 
                            
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Hm... I use Neutrik connectors in my projects these days. Cheap, lowest noise, great contacts. Otherwise I splurge for Hubble/Bryant stuff.
 
Len Ovens
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velacreations Hatfield wrote:
Do you have any fusing/breakers between the battery and the receptacle? Generally ac style breakers are good for dc use up to 24 volts. They normally have the ac and dc voltage rating printed right on them. These are what I used in our boat for nav lights and instruments. I found a bunch of small amp breakers in machines we were removing. (1 to 5 amps) Saved them from the dump.

We use 12 vDC breakers and fuses. You have to be careful using AC stuff, cause DC is hard on the contacts.


These ones have a dc rating printed on them as well as the ac rating. But if I was buying new, dc breakers are not overly expensive so I would use them. The breakers I have say 240vac or 24vdc. I would guess that the arching would be about the same. I have seen 3 used in series (a 3phase set with common trip) for higher dc voltages. Having looked at the price of a 260vdc breaker of only about $10 to $14, I can only guess that this was done to avoid sourcing another component and keep parts count down.... on an $800000 machine? (well more than double that now, this was 15 years ago)
 
Trond Hogstadt
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I perhaps should have stated that one problem I ran into was the need to have everything inspected and approved by the local code officials. Even though it's completely off grid the long tentacles of the government found me. There was very little available at the time (2005) that was DC rated and approved under the NEC.
 
                            
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Or if you want insurance... They don't take kindly to things you didn't buy from some bastards.
 
Len Ovens
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Kull Conquered wrote:Strange... I would of never thought that hand held grinders where DC.

I think you confused my idea of a voltage dividing scheme with a traditional one that would use resistors. My suggestion has no resistors, no efficiency loss.


Resistors, transistors, diodes...


The only thing in the circuit would be diodes and batteries. Instead of starting with a higher voltage and dividing down, you start with the lowest battery voltage you want and add more to increase the voltage. You use the diodes to prevent power taps earlier on at lower voltages from gaining voltage from the rest of the batteries in the circuit. So you could have a 3v, diode, 2v (to make a total of 5v), diode, 4v, diode, 3v. Giving you 3, 5, 9, and 12 voltages available. Obviously the 12v would have more amperage available. This is just an idea to suit the many needs of different voltages things require.


I am assuming you mean zener diodes. Just to simplify things lets start with 12v in and 2 6v zeners for a centre tap of 6v. For safeties sake there would have to be a resistor or transistor in line to deal with the variable voltage going in to the battery (up to 16v normally). A transistor in a constant voltage would do the job well enough. So lets assume a rock solid 12v line and 2 6v zeners that are exactly 6v. First thing is that this will get really hot. We have a battery that can throw 100amps at us and two 6v zeners will look like a short (till they blow). So that won't work unless there is a resistor in series to limit current. If the normal charge voltage is 15v and we want to be able to draw 6v at 1amp (.3amps is pretty common for one wall wart, so this would take three) So we have 3v across our resistor. 3v at one amp is (conveniently) 3ohms. Ok, first thing is, one amp is flowing all the time... even with nothing plugged in. Thats 15 watts all the time. Now we plug something in that draw 1/4 amp at 6v. In parallel with the load is the diode. The load gets 1/4 amp and the diode to keep the voltage at 6 v now only draws 3/4 amp, but the one stacked on top is still drawing 1 amp. And of course our current limiting resistor also has an amp going through it. As you can see this not at all efficient. 15watts for a 1.5 watt use: 10 times.

Next lets look at the standard voltage dividing power supply using a transistor pass element in place of the top zener diode and the resistor. The transistor is driven such that the emitter is always 6v. For our use the circuitry that drives the transistor will not be considered nor the power that drives it. When there is no load The transistor is turned off (practically we will have a very high resistor to keep things stable) and so no current flows. That is 0 watts use (this is not true as the circuitry to drive the transistor uses some as does the capacitor as it leaks at least some). Now we plug in the 1/4 amp 6v load. It gets the same 1.5 watts of power. The transistor has 9v across it at the same 1/4 amp and so uses 2.25watts. This is 3.75 watts to supply 1.5. Much better, but still not great at more than twice the power used to do the job.

In both cases excess power used is dissipated as heat... better have it inside during the winter

The switching power supply is a bit trickier. It actually works a lot like an inverter... todays inverters anyway. (or a 3 phase ac motor soft start/speed control) We start with the same 15v input. For the output we use a 6v battery (we'll call it a capacitor ). Our circuit will test the voltage of the battery very often... say 20000 times every second or more. If the voltage is less than 6v we will give it a pulse of 15v till it comes back up to 6v. Leaving out the control circuitry this is 100% of the power going in goes out. Now that 15v spike (120v spike in the average computer) sounds like a lot of noise. So we do filtering The battery we use to fill up is the first stage of that. Then it would go through a choke/inductor and into a second capacitor (pi filter). The neat thing about this is that the capacitor can be much smaller than in a transformer/diode style power supply, because the frequency it is filtering is much higher too. As it happens, we can make better quality capacitors in smaller sizes, that have less leakage and last longer. After MOVs, electrolytic capacitors are the thing that goes most often in a power supply. Anyway, with the switching PS, the main use of power besides the load is the control circuitry. The main drawback is that (like the series pass regulator) there needs to be some quiescent current flow to keep things stable. As mentioned there will always be some noise (same as ac power).

The whole area of noise is another whole topic. Making the supply absolutely clean when the loads are noisy.... doesn't make sense. That hand drill that plugs into 120vac makes so much noise that a CFL light in the same circuit actually gets brighter when the drill is running. The brushes are making and breaking all the time. The computer I (and whoever reads this) is using... the power supply regulation is not so much to tame the noise from the switcher as to filter out the noise the CPU/memory/buses/drives throws back at the power supply... Take a look at a scope of the power supply lines and then at the power close to the CPU, notice all the bypass capacitors all over the Mother Board... one for each chip pretty much. I don't disagree that less noise is a good idea, I just wonder if I am willing to give up all these things that make lots of noise.

One solution is to start designing around a smaller selection of voltages... this is already happening. The number of 5v things that work with a USB plug is getting bigger all the time. What things use low voltages anyway? Cell phone... 5v usb. MP3 player... if you aren't using your phone for that... 5v USB. Camera, if you aren't using the cell phone for that, those 1.5v cells can be charged from 5v. Wireless phone... do we really need this? (cell phone seems to work for that) We used to get by with one land line in the house... or using a neighbour's before that. Radio? 12v... most of them are fine with about 10v up to 16v... regulator inside? I would guess so. There are not too many 9v things around any more... that I can think of. Laptop? 18v... not sure how well it would do on 16v. But the little PS is too light to have a transformer in it... switching PS... probably 48 to 100 v dc would be fine. I would guess that most CFLs have a switching PS and 120v LED lamps the same (though they may use other tricks). But if I was off grid I would look for 12v lamps no matter the technology.

Really, If I am off grid, I would be looking to limit all things that use power. I expect to be busy and have less time for "entertainment". I expect to cook on wood and heat with it, but design smart so I don't need a lot. I hope to see more live music... unplugged. (If it needs to heard a mile away, there are always battle pipes ) I expect to be more responsible for the little bit of the world I can control and care less about other people's messes. So in the end I would be looking for light... and something to call home with. It would be hard to get rid of this computer thing... and I enjoy making loud music... a bit of a rocker at that.

<rant>
However, with some of the changes coming down the internet pipe... It may not exist as we know it much longer. The law makers want to censor it dramatically. Paul's anti-CFL project may be enough to see permies.com blocked for example.... I am working on a Linux distro (ubuntu studio) as a tester right now and got into a discussion with someone over encrypting hard drives (them talking and me listening for the most part) when I asked why someone who wanted real time audio would want to give up performance for encryption on the drive. This is someone involved (in the USA) in environmental protests. They have had their computers taken by the police already. They have rescued video from camera chips the police have reformatted because they took video of the police trying to stop protesters in the "land of the free". I remember the days of the BBS when I talked to people all over the place. It was sort of an underground kind of a thing, self regulated as the "sysop" had the power of "god" on their system. If they didn't like the way one of their users was behaving... That user was gone. Then internet came along and there was this anarchy that you could be whoever you wanted... but along with that was the commercialization that came with it. It was more "I want this I go here to get it." The good thing though was there was a level playing field. Anyone could talk. Anyone could set up a web page. That is changing. The big money wants the whole thing for selling me what they have for sale. They do not want people like permies telling them how to do the same thing for less or no money... or telling me that their new money making CFLs are bad. They do not want an independent musician using the internet to distribute music. They are still playing the "I gotta have all the money" game. These are just the things the USA Government and assorted interests want to do. (have you written to your representative and voiced your opinion on these things? I can't I am not a citizen) The whole electronics world (internet most of all) is in my mind very fragile. My feeling is that it could disappear very quickly. Books (paper ones) are precious. They last a long time as compared to electronic media. Floppies are a thing of the past... I don't even have a computer that will read them. CDs that were written 10 year ago are starting to have problems... we think we have backups, but those fail too. We have so much information how do we find the stuff that is right? If someone floods the internet with false info it makes the truth really hard to find. And when the false copies are more numerous in a crash situation, guess what gets recovered. I have started saving certain web pages as PDFs (step one) as I have seen so many web sites with some excellent info that I have book marked go away. The next step is to print them. If I can buy the book, it may be cheaper (even better used). Anyway... enough. Our freedoms are going.
</rant>
 
                            
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I am with you on SOPA and that stuff. Yes I have.

They don't represent the people though.
 
C. Letellier
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Location: Greybull WY north central WY zone 4 bordering on 3
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Some comments.

First off for the motors themselves if the motor is brush type and has a segmented commutator it is a universal type motor. Those can all be run on AC or DC. The problem comes in with the switching and other electronics that may be on board. Motors like routers with the soft start feature or things like drills with variable speed features may include electronics that are not compatible with DC use. So be aware not all tools can be used on DC even if they have a universal motor.

Second zener diodes are a very poor choice for voltage regulation directly. Their place is as an accurate voltage to compare to rather than wasting enough power to balance loads. Best regulation with lowest loses is with a switching type supply to change voltages. Instead of building up to various voltages likely the device should build down. Make 12 volts, from that make 5 volts and so on, on down. Or directly make each one from the original voltage.

Low voltage DC in houses probably won't ever become common. The reason is the greater needed wire size. Say a breaker in my house is currently a 20 amp breaker covering 3 outlets. Lets say it is drawing near rated load. That is 20 amp at 110 volts for 2200 watts. Now lets say the same load was going to go 12v DC. Now the same load would need wire for 183 amps. Now the wire is way larger. Probably nearly all low voltage wiring will be done for permanent wiring connections so the exact load is known when it is wired.

There was a smart outlet technology thing that appeared in Popular Science about 15 or 20 years ago that the outlet would decide by communicating with the device plugged into it what power was needed whether it be AC or DC and what voltage. Anyone know if what happened to that technology?
 
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