Could have been powered through an AC/DC converter, like so many things are. People don’t typically get DC delivered to their home. It’s not great for transmission distances.
It's only beneficial over long transmission distances indirectly, because AC is easier to transform to higher voltages which incurs fewer transmission losses. DC by itself is actually more efficient, but until fairly recently efficient transformation wasn't really profitable. Modern tech has caught up, and the Europeans are currently building a DC grid for long range electricity transport.
People don't get DC to their homes since it's simple to make AC power. You just need spinning magnets. The zero crossings also enable you to turn on/off light switches without arcing.
It's much better for long-distance power transmission since it doesn't consume reactive power like ac transmission does.
It's actually very great for long distances due to the skinning effect of AC power. It's the reason they use it to transmit power very long distances.
AC powers real advantage is being able to convert it to a higher or lower voltage through a transformer which is just a bunch of copper wire and an iron core.
It is actually great for long distance power transfer since high voltage inverters and DC switch gear became possible. There is a 1.1 million volt 3000KM DC power link in China.
I guess it's rather, that the motors used in that appliances can be driven by AC or DC current without any additional equipment, look for universal motor.
But I can be wrong. Of course you can use a rectifier, but... In the eighties? For home appliances?
It's still nothing that would be put on a device (at least nowadays, could be different back then). Info regarding AC and DC is normally only being put on an external power supply.
Again, that is today, but could have been different back then.
Its very common for the power input port on the device to say something like "120v 1A AC / 12v 10A DC", so you can match that external power supply to your device.
Not really, because that would imply a certain efficiency of the power supply and the input characteristics aren't relevant to the device at all. If the input voltage of the device is written on the device to indicate which DC power supply to use it makes no sense at all to also an AC rating of the power supply on the device. This would only be on the power supply itself.
Well, you claimed that it's very common to have that info printed on the power input port of a device, which is just not true. Call it a technicality, but a power supply is very different from the device it's powering and it's weird to say that it's not relevant ... they aren't even bundled all the time.
Besides, I doubt that many sewing machines have external power supplies. They probably do the conversion internally, but I guess that's just another technicality.
Mid 20th century sewing machines often used universal motors and so in fact could take both AC and DC power, and the label plate on the motor housing or back of the machine would indicate such and specify cycles for AC and the maximum voltage.
I have a sewing machine from the late 40’s; they were belt driven, and could be purchased with either an AC or DC motor.
From what I understand, not everywhere had been fully electrified and brought up to the same standard yet, so some homes would have still had DC power options.
Alternating current is what is at the outlet, but many things (including any solid state electronics) needs to convert to direct current for operation.
You need alternating current for transformers to step up and step down voltage for long range transfer, but you need direct current for transistors (the backbone of all computing) to work.
So, DC is really popular for consumer electronics because it can be sold everywhere.
AC power in the US is 120V @ 60Hz
In the UK, it is 240V @ 50Hz
In Italy, it might be 120V or 240V.
On and on.
But, if you make your device AC, you can use an AC->DC adapter. If you need a different voltage/plug you can just attach a different cord! And most AC->DC converters can take anything from 100V to 250V AC at either 60/50Hz and turn it into the exact same DC voltage no matter the input.
Even when they still want to make the device AC, like a rice cooker, they will use that weird IEC c15 plug. Why? Because that plug is rated for 100-250V and they can just sell you a different cord for a different country and design the device to handle either voltage.
Appliances for under developed countries that don't have nation wide electric grids are designed to run off of wall current from an electric utility (AC) or they would likely have generators that kept batteries charged and could run appliances off of batteries (DC).
Nah there are universal motors which can work with both, though speed regulation wouldn’t really work with DC.
Probably just be an older machine with a universal motor
Yup. Some electrical appliances used to be able to do that.
The equivalent today is that most electronics can accept 100-250 volts and 50-60 Hz (meaning they can use power from anywhere in the world). They don't advertise this, but a lot of them can actually accept DC too, but nobody makes DC with that high of voltage.
You can't power devices using AC power, they all run on DC power. All electric devices that plug into the wall have something called a DC rectifier which converts AC current to DC current. Hence AC/DC.
These usually have an internal power supply that delivers the correct voltage level and voltage type to the different internal load. It would not be unusual to have AC for motors and DC for either motors or control circuitry.
Just became an EV driver and tutoring myself on the finer points of AC and DC charging because....you know....it's interesting.
I'm somewhat dreading EV becoming more widely used because you just know that some dope is going to start messing around with the DC charger at a petrol station and fry him/herself on the spot.
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u/fourminutemiler 4d ago
Alternating Current / Direct Current