curiouscarbon
Science Penguin
 Joined
 Jun 29, 2020
 Messages
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An incandescent light bulb is purely resistive and has a power factor of 1. Anything that shifts the phase of the frequency (inductive load) alters the power factor of an AC circuit. LEDs are DC, so any related power factor is from their ACtoDC driver.Does this mean it runs at just 9 watts, like a 9 watt lightbulb?
If you were running AC it depends on the power factor which they didn't tell you. So, if a device consumes 9 watts of "true power" and has a power factor of .5, from your supply it'll consume 9 / .5 = 18 watts.If I had a 12v battery with 90wh of capacity, this would run for 10 hours?
These are some amusing illustrations, but I have a question about "RWS" [RMS?]. In some limited reading I did, this seems to be a measure of how many watts a given device consumes. The device I'm looking to power claims "Power consumption at full brightness •9W RMS".
RMS is about how the AC power is measured, the RMS voltage in an AC circuit gives about the same amount of power as an equivalent DC voltage. RMS = root mean square What folks in the U.S. think of as 120VAC it's really 120 VRMS, which is about 340V peak to peak (see image right). VRMS = Vpk / √2. So, 170Vpk / 1.41 = 120 VRMS. 

thank you for education!There are two different types of power factor: displacement and distortion. Displacement power factor is associated with motors, when the current draw is in the form of a sine wave, but not synchronized, or in phase, with the voltage. Distortion power factor is associated with power supplies, when current is pulled only at the peak of the voltage sine wave, but in phase with it. Battery chargers and nonincandescent lights cause distortion power factor. AC power generation and distribution is most efficient when the voltage and current are both sine waves in phase with each other. Any deviation from this causes the power factor to be less than 1. "Apparent power" is the RMS voltage multiplied by the RMS current, measured in voltamps. "Real power" is the useful power transferred to the load, measured in watts, which is less than the apparent power if the power factor is less than 1. If you're the power company, your cost of generation and distribution is based on the apparent power. If you're the customer, your benefit is based on the watts. Say you're using 50 watts with a power factor of 0.5, To support this the generators, power lines, transformers, etc. have to be sized to supply 100 watts, even though only 50 watts are being consumed. In general, residences are billed for watts and industrial customers are billed for voltamps. I consider the reactive power more as wasted infrastructure than wasted electricity. Some of it goes up in heat, but a lot of it is never generated in the first place.
very good pointAs a "professional nitpick" , I should like to add that I like the analogy with the pack of crisps (chips) a little bit better because while binging on beer head may eventually get you drunk, no amount of compression will turn the extra air in the bag into crunchy bits of potato solids.
RMS is a way of equating AC power to the DC heating equivalent assuming the power factor = 1.0. This is based on heat rise measured in a noninductive resistor. What this really means is that RMS only means anything for purely resistive loads which is virtually never the case in real life.These are some amusing illustrations, but I have a question about "RMS". In some limited reading I did, this seems to be a measure of how many watts a given device consumes. The device I'm looking to power claims "Power consumption at full brightness •9W RMS".
Does this mean it runs at just 9 watts, like a 9 watt lightbulb? If I had a 12v battery with 90wh of capacity, this would run for 10 hours?
That is a very detailed response that I can only presume is accurate.RMS is a way of equating AC power to the DC heating equivalent assuming the power factor = 1.0. This is based on heat rise measured in a noninductive resistor. What this really means is that RMS only means anything for purely resistive loads which is virtually never the case in real life.
When specifying industrial AC electrical equipment the power capacity is rated in always in VA (Volts x Amps). This absolutely tells you what the equipment is capable of dealing with without the marketing games flaky companies engage in.
AC power that is not specified as RMS is pure smoke and mirrors (they are not even pretending to tell you the truth). Like those 200W powered PC speakers that come with a 12V @ 1A power supply (6W per channel). Even when they use the term RMS they are still probably lying to you. A $400, 2000W inverter will typically ends up delivering 1000VA at best.
Peak RMS power is basically calculated as the maximum power an inverter is cable of delivering into a dead short right before the inverter emits the magic smoke and stops working. That is why that same $400, 2000W inverter claims 200% surge capability. Yah, for less than half a cycle. Then the overload protection engages (you hope) and turns it off. Good luck starting a motor with that.
I worked in product marketing while I was going to school for my EE degree. We used to joke that the difference between salesmen and marketing people is that at least the marketing guys knew when they are lying to you. For the good of my soul, the company I worked for at the time was a top quality manufacturer.
What folks in the U.S. think of as 120VAC it's really 120 VRMS, which is about 340V peak to peak (see image right).
Yeah, that's not the case, at all.There is no such thing as "RMS power"  it is likely a term invented by some sales or marketing department.
*grabs popcorn and reading glasses*This is an interesting subject. Both RMS Power and RMS Watts are a fiction created by the Federal Trade Commission.
The FTC also incorrectly assumed that the measurement of the power in Watts would be RMS Watts. It's not. It's Watts.
There's no such thing as RMS Watts.
In summary, RMS Voltage is correct, but there's no such thing as RMS Power or RMS Watts.
Or stated differently, the Voltage that's measured is RMS Voltage, but the resulting power is Average Power and it's measured in Watts.
it makes sense to me to do root mean squared algorithm on the voltage, but i would assume amps would be linearly time averaged, that is mean average over entire time sample