The energy solution for South Africa is DC power.

[Nicodeamus]

So you're saying we need to basically rebuild the entire grid then?

and we need to use a more costly energy heavy system. DC = Voltage to be carried over and not ampage implying that more energy is to be used since the definition of voltage = energy per charge.

 

[Swa]

So you're saying we need to basically rebuild the entire grid then?

The house. Most DC supplies would be self generating and only use the AC grid as backup.

 

[Swa]

and we need to use a more costly energy heavy system. DC = Voltage to be carried over and not ampage implying that more energy is to be used since the definition of voltage = energy per charge.

What?

 

[Nicodeamus]

What?

DC generated systems requires more voltage to be used to beat the initial resistance of wires. A high voltage for the same output the AC gives.

Voltage = energy /charge

More energy used = more power needed!

Therefore DC is more expensive.

 

[Swa]

DC generated systems requires more voltage to be used to beat the initial resistance of wires. A high voltage for the same output the AC gives.

Voltage = energy /charge

More energy used = more power needed!

Therefore DC is more expensive.

DC appliances currently convert from AC.
conversion = wasted energy


Btw power is voltage multiplied by amperage. So AC appliances don't use less energy they simply have a higher voltage at a lower amperage in any case.

 

[ToxicBunny]

The house. Most DC supplies would be self generating and only use the AC grid as backup.

Oh ok.. so we must then convert our houses to use something different from the grid and different from the rest of the world.. yes that's a great solution to everything.

Just rewiring a house is not a trivial or cheap exercise. I've just moved my db at home and it cost me r10k... rewiring the house would have been at least r30k as a rough guess.

 

[ToxicBunny]

Oh and that figure doesn't include the cost of jury rigging all my existing AC appliances to run on dc while we wait for the manufacturers to produce dc native appliances that we can buy from shops.

 

[Swa]

Oh ok.. so we must then convert our houses to use something different from the grid and different from the rest of the world.. yes that's a great solution to everything.

Just rewiring a house is not a trivial or cheap exercise. I've just moved my db at home and it cost me r10k... rewiring the house would have been at least r30k as a rough guess.

And this is why we can never have nice things. You are forgetting a few very important details. A lot of appliances are already using something different than the grid. LED lighting runs more efficiently off DC and a few models have separate conversion and lighting units which are ready to run off DC. Even so it's more cost effective to make your own. There's already a range of DC appliances made for camping. If homes are equipped for DC the range will only become larger.

You don't need to rewire your house. You reuse the wiring. Need to charge a phone or laptop? DC. Have a tv with a wall transformer? DC. Need to power a PC? DC.

 

[itareanlnotani]

The problem with that is that the DC voltages in use in the items are not at the same voltages.
So you'll still need step down transformers or DC-DC transformers to change the power to whatever level the device needs.

You also still have the tiny issue of load.

Assume your computer is 300W or 500W. @ 12v DC thats V*A= P [ 12v * ? = 300W | 300 / 12 = 25Amps ]
Thats just one device. 25Amp cable ain't cheap. Running household devices on 12v DC is not going to happen unless *all* the devices on that circuit are low current draw.

The only things you'll be running at 12v DC will be low current draw devices.
eg Filament LED / COB LED's (which are 2w/4w/8w currently@230v AC) or 230v * ? = 2W | 2 / 230 = 0.008A

So lots of those @ 12v DC on a single wire without problems. Although they still going to need a DC - DC device as LED's usually run somewhere between 14v and 30v depending on how many LED's inside the filament.

You also have the issue of current drop. DC current drops at high amp draws mean only short runs are possible.
So that computer would only be able to run a few meters at best away from the DC source.

You can solve that by running higher voltage DC throughout, but then theres really no benefit, as everything needs a DC-DC transformer. More importantly, if you run the house at higher DC voltages, you also need different cable.
DC requires single strand copper, AC can run over multistrand (due to skin effect).
Guess what costs more money.
I have a 20 metre run of single strand @ 600V in my house from my DC side (solar 36v * 16 @ 8A). My cable is UL rated for 1000v. Its a lot more expensive than any other cable in the house.


Lets recap on the negatives of DC cabling.
1) At Low voltages (say 12v), you get a lot of voltage drop at even moderate current draws, so you either have to run higher voltage to your device, or only use short cable runs to overcome impedance.
2) Higher voltage DC cabling needs single core cable which isn't cheap.
3) Due to current draw / cable requirements, you can't put many moderate draw devices on a single circuit, as it will melt.
4) DC you need to make sure that the device is plugged / wired with the correct polarity. If it doesn't have a protection diode, then whoopsie, its dead.

 

[The_Unbeliever]

The problem with that is that the DC voltages in use in the items are not at the same voltages.
So you'll still need step down transformers or DC-DC transformers to change the power to whatever level the device needs.

You also still have the tiny issue of load.

Assume your computer is 300W or 500W. @ 12v DC thats V*A= P [ 12v * ? = 300W | 300 / 12 = 25Amps ]
Thats just one device. 25Amp cable ain't cheap. Running household devices on 12v DC is not going to happen unless *all* the devices on that circuit are low current draw.

The only things you'll be running at 12v DC will be low current draw devices.
eg Filament LED / COB LED's (which are 2w/4w/8w currently@230v AC) or 230v * ? = 2W | 2 / 230 = 0.008A

So lots of those @ 12v DC on a single wire without problems. Although they still going to need a DC - DC device as LED's usually run somewhere between 14v and 30v depending on how many LED's inside the filament.

You also have the issue of current drop. DC current drops at high amp draws mean only short runs are possible.
So that computer would only be able to run a few meters at best away from the DC source.

You can solve that by running higher voltage DC throughout, but then theres really no benefit, as everything needs a DC-DC transformer. More importantly, if you run the house at higher DC voltages, you also need different cable.
DC requires single strand copper, AC can run over multistrand (due to skin effect).
Guess what costs more money.
I have a 20 metre run of single strand @ 600V in my house from my DC side (solar 36v * 16 @ 8A). My cable is UL rated for 1000v. Its a lot more expensive than any other cable in the house.


Lets recap on the negatives of DC cabling.
1) At Low voltages (say 12v), you get a lot of voltage drop at even moderate current draws, so you either have to run higher voltage to your device, or only use short cable runs to overcome impedance.
2) Higher voltage DC cabling needs single core cable which isn't cheap.
3) Due to current draw / cable requirements, you can't put many moderate draw devices on a single circuit, as it will melt.
4) DC you need to make sure that the device is plugged / wired with the correct polarity. If it doesn't have a protection diode, then whoopsie, its dead.

Well put.

This is also why that 12v car kettle takes so long to boil water btw. It all comes down to the basic law of electricity. V=IxR or I=V/R or R=V/I

You cannot change the law of electricity!!!

 

[xumwun]

Check the posted articles. DC works better on the supply backbone. AC was chosen at a time when DC was unfeasible for the transformer tech but at the same time you had to step up the supply voltage because of the losses. Transformer tech has advanced a lot since then to be able to use DC properly plus most consumer generating tech has DC output.


You miss the point. It won't be powering a kettle, geyser, vacuum, or any other appliance you only use occasionally. The point is to reduce the load on the main grid and being able to more efficiently self generate and use power. I am using quite a few appliances on DC right now anyway so there's no good reason not to have a DC supply. If power goes off with only a few batteries and solar panels I can remain switched on for the duration. Being able to boil a kettle in 45 minutes would be preferable to not being able to boil one but for water, cooking, and geyser gas is actually a good option. The only thing left which we require Eskom for seems to be the vacuum.

DC will not go through any transformer no matter how advanced it is.

 

[Paul_S]

It is very difficult to build circuit breakers for high voltage / high current DC network. Fuses have to be five times as big for secure quenching of the arc. Switches need much bigger and elaborate blast chambers due to the capacitance of the grid and the totally different arcing behaviour."

+1
I had to replace my geyser thermostat this weekend and was surprised to see how low the DC rating was on the thermostat.
AC rating: 250V 20A
DC rating: 250V 0.1A :wtf:

So the contacts in the thermostat can only handle 1/200th of the current if you're running DC instead of AC at the same voltage.
This is on Satchwell VKF 7 and VFK 11 thermostats which are fitted to just about every type of geyser in SA.

 

[Swa]

The problem with that is that the DC voltages in use in the items are not at the same voltages.
So you'll still need step down transformers or DC-DC transformers to change the power to whatever level the device needs.

Most equipment actually functions off 12V. It is therefor the ideal voltage to use. Phones charge on 12V chargers. Laptops charge on 12 chargers. Camping gear is made for 12V. Our latest TV has a 12V wall transformer. The highest voltage in a computer is 12V. The list goes on and if 12V is the standard in use then most manufacturers will design around that instead of using some arb non-standard voltage.

You also still have the tiny issue of load.

Assume your computer is 300W or 500W. @ 12v DC thats V*A= P [ 12v * ? = 300W | 300 / 12 = 25Amps ]
Thats just one device. 25Amp cable ain't cheap. Running household devices on 12v DC is not going to happen unless *all* the devices on that circuit are low current draw.

The only things you'll be running at 12v DC will be low current draw devices.

Most DC devices are low current. The only example is the PC but even there the situation isn't so bleak. Don't confuse a cable's AC current rating for its DC current rating. DC can handle more current than AC, in practice roughly twice as much. So a standard 15A cable can do at least 360W at 12V.

eg Filament LED / COB LED's (which are 2w/4w/8w currently@230v AC) or 230v * ? = 2W | 2 / 230 = 0.008A

So lots of those @ 12v DC on a single wire without problems. Although they still going to need a DC - DC device as LED's usually run somewhere between 14v and 30v depending on how many LED's inside the filament.

DC-DC step-up or step-down converters are only needed where the electronics can't function on standard voltages. There's only a few of these special types in use and most of it is in PC's where there's already a switched mode power supply doing multiple voltage conversions. LEDs can generally function at any voltage between its forward voltage drop and breakdown voltage. 12V is more than enough for most.

You also have the issue of current drop. DC current drops at high amp draws mean only short runs are possible.
So that computer would only be able to run a few meters at best away from the DC source.

You can solve that by running higher voltage DC throughout, but then theres really no benefit, as everything needs a DC-DC transformer. More importantly, if you run the house at higher DC voltages, you also need different cable.
DC requires single strand copper, AC can run over multistrand (due to skin effect).

That's bollocks. There's no single strand requirement and any voltage drop would be mainly due to the power source. Transformers and some types of batteries feature a voltage drop that scales with a rise in current drawn. Lead-acid batteries don't feature much of this.

Guess what costs more money.
I have a 20 metre run of single strand @ 600V in my house from my DC side (solar 36v * 16 @ 8A). My cable is UL rated for 1000v. Its a lot more expensive than any other cable in the house.

Well there is your problem. Nobody else is advocating 600V when 12-24V would suffice for most applications.

Lets recap on the negatives of DC cabling.

You haven't listed any valid ones.

DC will not go through any transformer no matter how advanced it is.

I don't know where you're coming off but nobody said anything about putting DC through a transformer. The transforming tech where needed is very different than a standard transformer in isolation.

 

[Paul_S]

Most equipment actually functions off 12V. It is therefor the ideal voltage to use. Phones charge on 12V chargers.

Huh?
Most modern phones charge using 5V (USB interface) and they step this down internally to charge the battery.
Li-Ion = 3.7V
LiFePO4 = 3.3V

Laptops charge on 12 chargers.

Depends on the laptop but most of the one's I've used have 19 or 20 Volt chargers.

 

[TEXTILE GUY]

The energy solution for South Africa is DC power.

Well the ANC have been on POWER and that is DEFINITELY NOT the solution ....

 

[Rickster]

/snip

Paragraphs dude, come on.

 

[itareanlnotani]

Most equipment actually functions off 12V. It is therefor the ideal voltage to use. Phones charge on 12V chargers. Laptops charge on 12 chargers. Camping gear is made for 12V. Our latest TV has a 12V wall transformer. The highest voltage in a computer is 12V. The list goes on and if 12V is the standard in use then most manufacturers will design around that instead of using some arb non-standard voltage.

No, it doesn't.
Phones generally use 5v DC @ 2A or 500ma, depending on negotiation with the USB socket.
They convert this internally to 3.3v for SoC, and ancillary circuits. Charging circuits will use different voltages depending on how many batteries in the device. Lithium is usually 3.2v, but designers can run stuff in higher voltage (batteries in series), or higher ampage (batteries in parallel) depending on their specific design.

The highest voltage in a computer is indeed 12v, but there are a number of 12v, 5v lines.
Modern CPU's can use 100w on their own, and higher end graphics cards are often in the 300w range.
Add in other bits, hard drives / ssd's etc, and you can easily hit 500w.

500w @ 12v = 41amps. PC power supplies have multiple rails, and supply multiple 12v over parallel cables.
Are you going to run twice the cable to supply one single computer. I have explained this a couple of times relatively clearly.
If you don't understand basic concepts, suggest do some further reading of why I keep pointing it out repeatedly.

That's bollocks. There's no single strand requirement and any voltage drop would be mainly due to the power source.

Suggest read up on skin effect (which affects A/C cabling, and cabling requirements for high voltage DC, before claiming "bollock's".

Well there is your problem. Nobody else is advocating 600V when 12-24V would suffice for most applications.

It quite obviously won't be sufficient for most applications as has been pointed out repeatedly at length by myself and others, and the solution for that is running at higher DC voltages. DC works for low current draw, at short lengths. If you have higher current draws, the voltage loss is high at standard cable lengths. Assume you have 20m from your DB. Calculate the voltage drop over the size cable you'd need to run a 500w computer. Or a kettle. Or a vacuum cleaner. Or a tv. Or anything really that uses a few hundred watts of power.


Low voltage DC will work for specific situations, but only a narrow subset of daily used items.
If all your house uses is a cellphone, and some low voltage 12v lighting, then great, DC will be a solution (for short cable runs).
For anyone else, not really.

Higher voltage DC would work - eg 240v DC would work, but then again, the cable sizes aren't a benefit, and you still need DC - DC voltage regulators to step down DC voltages to what the device needs.

 

[Swa]

Huh?
Most modern phones charge using 5V (USB interface) and they step this down internally to charge the battery.
Li-Ion = 3.7V
LiFePO4 = 3.3V

A common misconception. That's the voltage of the battery but you need a higher voltage to "push" current into the battery otherwise it will offer resistance to the flow of current. The 5V is therefor not stepped down and you can even use a higher voltage as long as it won't break down the internal circuitry.

Depends on the laptop but most of the one's I've used have 19 or 20 Volt chargers.

http://www.geewiz.co.za/laptop-chargers-docks/21-universal-car-adaptorcharger-for-laptops.html
It charges off 12V.

No, it doesn't.
Phones generally use 5v DC @ 2A or 500ma, depending on negotiation with the USB socket.
They convert this internally to 3.3v for SoC, and ancillary circuits. Charging circuits will use different voltages depending on how many batteries in the device. Lithium is usually 3.2v, but designers can run stuff in higher voltage (batteries in series), or higher ampage (batteries in parallel) depending on their specific design.

See above.

The highest voltage in a computer is indeed 12v, but there are a number of 12v, 5v lines.
Modern CPU's can use 100w on their own, and higher end graphics cards are often in the 300w range.
Add in other bits, hard drives / ssd's etc, and you can easily hit 500w.

500w @ 12v = 41amps. PC power supplies have multiple rails, and supply multiple 12v over parallel cables.
Are you going to run twice the cable to supply one single computer. I have explained this a couple of times relatively clearly.
If you don't understand basic concepts, suggest do some further reading of why I keep pointing it out repeatedly.

Yes you keep pointing it out but with no logic of physics behind it. I already explained this. Few PCs use 500W and those that do don't do so constantly as well.

Suggest read up on skin effect (which affects A/C cabling, and cabling requirements for high voltage DC, before claiming "bollock's".

I know what the skin effect is but apparently you don't. Much like a capacitor that only stores a charge on the edge of a conductor AC introduces the effect that current only flows through the outward edge of a conductor. AC therefor actually needs multi-strand cable to handle current effective. Since DC doesn't suffer from the skin effect the main factor is the combined gauge of the wire and not whether it's single- or multi-strand.

It quite obviously won't be sufficient for most applications as has been pointed out repeatedly at length by myself and others, and the solution for that is running at higher DC voltages. DC works for low current draw, at short lengths. If you have higher current draws, the voltage loss is high at standard cable lengths. Assume you have 20m from your DB. Calculate the voltage drop over the size cable you'd need to run a 500w computer. Or a kettle. Or a vacuum cleaner. Or a tv. Or anything really that uses a few hundred watts of power.

*sigh*
As I have pointed out the voltage drop is due to the limitations of the power supply and not the length of cable. Voltage drop through the cable is negligible and affects AC current as well. Apparently you are unaware of how much power Eskom loses through the grid. Also for the umpteenth time as I and others have pointed out you won't be running a vacuum or a kettle on the DC supply.

Low voltage DC will work for specific situations, but only a narrow subset of daily used items.
If all your house uses is a cellphone, and some low voltage 12v lighting, then great, DC will be a solution (for short cable runs).
For anyone else, not really.

That "narrow" subset happens to include all the devices that are used constantly for long lengths of time. If you and others still don't get this you probably never will.

 

[Paul_S]

Phones charge on 12V chargers. Laptops charge on 12 chargers.
http://www.geewiz.co.za/laptop-chargers-docks/21-universal-car-adaptorcharger-for-laptops.html
It charges off 12V.

Dude it steps the voltage from 12V to a higher one to charge laptops.
Output: DC 15/16/18/19/20V 4A DC 22/24V 3.3A 80W Max
So you're back to wasting power with DC-DC boost converters.

Also for the umpteenth time as I and others have pointed out you won't be running a vacuum or a kettle on the DC supply.

Then what's the point?
I don't see the logic about having to have two separate standards for appliances. At least at the moment everything runs off 220-240V 50Hz AC.

 

[ambo]

A common misconception. That's the voltage of the battery but you need a higher voltage to "push" current into the battery otherwise it will offer resistance to the flow of current. The 5V is therefor not stepped down and you can even use a higher voltage as long as it won't break down the internal circuitry.

But that is still not 12 V

http://www.geewiz.co.za/laptop-chargers-docks/21-universal-car-adaptorcharger-for-laptops.html
It charges off 12V.

Yes - and it contains a DC-DC converter that is creating a higher voltage. As per the specs: "Output: DC 15/16/18/19/20V 4A DC 22/24V 3.3A 80W Max"

DC-DC converters are at least as inefficient as AC-DC switch-mode power supplies - often far worse.

*sigh*
As I have pointed out the voltage drop is due to the limitations of the power supply and not the length of cable. Voltage drop through the cable is negligible and affects AC current as well. Apparently you are unaware of how much power Eskom loses through the grid. Also for the umpteenth time as I and others have pointed out you won't be running a vacuum or a kettle on the DC supply.

Your lack of knowledge and arrogance is growing tiresome.

Voltage drop is due to resistance. There is some resistance in the source (power supply), some in the cable and normally the majority of the resistance is in the load. The biggest reticulation challenge however is the resistance in the cable. Voltage drop is highest when the current in the cable is high. This will happen when trying to trying to carry too much power at too low a voltage. The way to combat that is to reduce the current - but if you still need a significant amount of power then you need to raise the voltage.

12 V is too low to reticulate usefully for more than about 20 metres unless you have extremely thick and expensive cabling. The only reason 12 V is popular is due to its use in cars and thus with cheap lead acid batteries and cigarette lighter accessories. Most industrial and business grade DC systems use either 24 V or 48 V.