4WD
$50 site donor 2024
It’s been many years since locomotives moved from DC to AC motors … VFD/IGBT etc …
That is a very different thing. It is diesel generator powered and that AC is really not a constant frequency AC that we power our grid at (60Hz in US). If anything it is more of an inverter powered AC, driven from a DC generated by the diesel generator.It’s been many years since locomotives moved from DC to AC motors … VFD/IGBT etc …
I was thinking if home is powered by DC it would be 240V DC, no reason to stay with 110V anyways as the rest of the world run fine on 220/240V AC.The advantage to Alternating Current power systems, and why they are so widely accepted, is because of the Transformation factor and conductor costs of the transmission system, due to low I^2*R losses at high voltages.
The DC system only has a place in power generation when the power sources and the loads are very local (close to each other.) Otherwise, the I^2*R power losses in the conductors will be very high.
Something else to consider; Many appliances need 120V, which is a split from the 240V supply using the Neutral lead.
How would you do this with DC, assuming all motors could operate on AC or DC.
I think you're still neglecting the I^2*R losses that would be inherent in such a DC system for a typical 20kW home requirement. The gauge of copper needed for the feedlines would become cost prohibitive.I was thinking if home is powered by DC it would be 240V DC, no reason to stay with 110V anyways as the rest of the world run fine on 220/240V AC.
Powerline would still be high voltage if not locally at 240V, I would think the grid would be where it is now or use the HVDC transmission we are using anyways. It would just be a matter of whether to switch the last mile to 240V DC or 110VAc per phase.
For backward compatibility I would imagine the 3 wire on the pole would become 2 110VAC phases and the last one turn into a 240V DC, and homes will be wired with an additional 240V DC from the pole, and "some" appliances and sockets will turn into a new 4 prong plug that's backward compatible, so it can use the existing 110V, existing 220V split phase, or DC 240V (or some reasonable conversion kit that change the wiring of heating element from split phase 220V to the 110V powering the 110V motor and electronics, but the heating element go into DC). New appliances or electronics will just use the 240V DC directly, like car charger, HVAC, induction range, computer, home electronics that use switching power supply, etc. To me this make sense.
If this movement gain momentum it would be another 200 years before the 110V / 240V AC finally be converted into 240V DC. Or, maybe 3 phase into the house and running 3 phase motor, 3 phase charger, 3 phase induction range and call it a day. We can't even move our nation to metric, what am I thinking.
You would still have to have power supplies in everything. Desktop computer power supplies must supply +12V, +5V, +3.3V, -12V, and +5Vsb. Induction ranges need AC current to work. A pretty big reason why HVDC transmission is used at all is because it doesn’t require 2 separate grids to synchronize together.I was thinking if home is powered by DC it would be 240V DC, no reason to stay with 110V anyways as the rest of the world run fine on 220/240V AC.
Powerline would still be high voltage if not locally at 240V, I would think the grid would be where it is now or use the HVDC transmission we are using anyways. It would just be a matter of whether to switch the last mile to 240V DC or 110VAc per phase.
For backward compatibility I would imagine the 3 wire on the pole would become 2 110VAC phases and the last one turn into a 240V DC, and homes will be wired with an additional 240V DC from the pole, and "some" appliances and sockets will turn into a new 4 prong plug that's backward compatible, so it can use the existing 110V, existing 220V split phase, or DC 240V (or some reasonable conversion kit that change the wiring of heating element from split phase 220V to the 110V powering the 110V motor and electronics, but the heating element go into DC). New appliances or electronics will just use the 240V DC directly, like car charger, HVAC, induction range, computer, home electronics that use switching power supply, etc. To me this make sense.
If this movement gain momentum it would be another 200 years before the 110V / 240V AC finally be converted into 240V DC. Or, maybe 3 phase into the house and running 3 phase motor, 3 phase charger, 3 phase induction range and call it a day. We can't even move our nation to metric, what am I thinking.
Hmm, I did some reading, and it seems like DC can tolerate higher voltage (say 240V AC is rms and it is actually 679 Vpp), and if the DC is converted from the same high voltage AC at the last loop it will come into the house as 679VDC (safety be darned, let's say). Then the I^2*R loss would actually be less than 240VAC (wouldn't 240VAC still have I2R loss?), and certainly with 679VDC it is less current and therefore less loss than 240VDC (I should have thought of that first).I think you're still neglecting the I^2*R losses that would be inherent in such a DC system for a typical 20kW home requirement. The gauge of copper needed for the feedlines would become cost prohibitive.
And turning AC into DC would require massive rectifiers which in turn have their own power losses.
I still fail to see that you have provided any system advantages for DC over AC transmission.
Yes, if home is DC powered it would still need to convert from hundreds Vdc to 12V and below. It won't be free conversion just maybe slightly less loss with pwm step down. If converting from high voltage AC to low voltage DC is not too expensive but converting from high voltage AC to high voltage DC is, then it is not worth it.You would still have to have power supplies in everything. Desktop computer power supplies must supply +12V, +5V, +3.3V, -12V, and +5Vsb. Induction ranges need AC current to work. A pretty big reason why HVDC transmission is used at all is because it doesn’t require 2 separate grids to synchronize together.
Agree, it is like why do we need delicate CVT if we have reliable 9 or 10 speed automatic.I have one of those ECM fan motors on my "high efficiency" home AC unit. It drives the condenser fan. Expensive little guy, that lasts 5 years in the harsh environment. I've gotten good at repairing it, using components from the last removals.
Really, it's silly. Any quality fan induction motor is about 90% efficient. This motor is 93% efficient and can vary it's speed depending on whether the home AC is running the 2.5 or 5 ton compressor. Any well designed induction motor can efficiently run multiple speeds too. At 1/6th the initial cost!
Replacing that motor multiple times, has cost me far more than the few dollars of power it's saved.
In any design, always optimize the important stuff first. A motor that uses 50 cents worth of power per month won't save much if it's made twice as efficient.
I’d be less concerned about I2R losses and more about conversion losses.You DC advocates need to do some transmission system calculations using HV, MV, and LV home power requirements.
That's one big thing with AC vs DC, getting shocked by AC at least allows the muscles to quiver which makes it easier to get free from the shock. Straight DC just causes a clamp down that doesn't let go.I got my elbow on 480vac 3 phase once and survived. That was enough to get my attention . I was working alone on an X-Ray Heart Cath Lab and the X-Ray tube rotor chassis swung in and got me. I had Navy electronics training and they had all sorts of cautions about have someone nearby to pull the plug if you got attached to DC.
SCR or mosfet current controllers.How do you step down a DC voltage unless you use a large and inefficient, power robbing rheostat to do so? What constitutes a variable load and how do you control it?
If you ground the gate well enough ( use a transistor that has a low enough C to E voltage drop when in saturation ) you can pull enough of the internal self feeding gate current out of the SCR to cause it to turn off.When a voltage is applied across a thyristor no current flows because neither transistor is conducting. As a result there is no complete path across the device. If a small current is passed through the gate electrode, this will turn "on" the transistor TR2. When this occurs it will cause the collector of TR2 to fall towards the voltage on the emitter, i.e. the cathode of the whole device. When this occurs it will cause current to flow through the base of TR1 and turn this transistor "on". Again this will now try to pull the voltage on the collector of TR1 towards its emitter voltage. This will cause current to flow in the emitter of TR2, causing its "on" state to be maintained. In this way it only requires a small trigger pulse on the gate to turn the thyristor on. Once switched on, the thyristor can only be turned off by removing the supply voltage.
The operation of the thyristor considered in this way is relatively straightforward to understand.
How Does a Thyristor / SCR Work? Basic Operation » Electronics Notes
A thyristor / SCR can be considered as two back to back transistors to explain its operation and how it works.www.electronics-notes.com
So how do you turn off an SCR off in a DC line?
I only have limited knowledge of power electronics but most of what I know tells me switching from high to low voltage with minimal loss requires some sort of FET, may not be MOS but other design, and with some sort of PWM to reduce loss and capacitor / inductor to filter out noise / buffer the output.If you ground the gate well enough ( use a transistor that has a low enough C to E voltage drop when in saturation ) you can pull enough of the internal self feeding gate current out of the SCR to cause it to turn off.
But, as Supton has posted, there are other devices that will work for that application.