We're currently having a very heated debate on /int/ about electrical engineering and now we need your help. The original question was this:>Anon has two phone chargers with the same power output. Why does one of them feel hotter on the surface than the other while charging?One very autistic person who claims to be an electrical engineer insists that P=R*I^2 is a complete answer to this question. Meanwhile other people gave more nuanced answers explaining different kinds of losses in electrical components and the role of thermal management such as heat sinks. The autist responded with almost trollish screeching, making a few very outrageous claims. Could you please confirm their falsehood?1. He claimed that there is no difference between ohmic and non-ohmic losses. In particular he said phenomena like dielectric loss, hysteresis loss or switching loss were all just special cases of P=R*I^2.2. He claimed the thermal design was completely irrelevant to the surface temperature and can be ignored because only the heat generated by resistors matters.3. He claimed chargers do not contain a transformer. Any circuit diagram of a charger I've seen so far seems to disagree with this claim. Please enlighten us, /sci/.
>>16781764That is exactly how discussions go here as well.
>>16781764>One very autistic person who claims to be an electrical engineer insists that P=R*I^2 is a complete answer to this question.It's not. If both chargers are outputting the same voltage and current then they have the same resistance and deliver the same power. Differences in heating most likely come from AC losses, different regulator levels, and different materials>He claimed that there is no difference between ohmic and non-ohmic losses. In particular he said phenomena like dielectric loss, hysteresis loss or switching loss were all just special cases of P=R*I^2.he's not wrong, but that's not a useful point unless you know the exact active resistance of each component at each moment in time>He claimed the thermal design was completely irrelevant to the surface temperature and can be ignoredhe's right, for the wrong reason. your charger loses some X watts of power and that will turn to X watts of heat, thermal management just moves heat from the components to the casing faster, but in extended usage you'll end up at the same temperature eventually unless your circuits burn out>He claimed chargers do not contain a transformercompletely fucking wrong
>>16781773First point isn't true. A computer can charge a cell phone at nominal voltage and current.
>>16781773>It's not. If both chargers are outputting the same voltage and current then they have the same resistance and deliver the same power. Differences in heating most likely come from AC losses, different regulator levels, and different materialsthis is plain wrong. you can have higher or lower efficiency dc/dc converters. losses can come in switchers due to miller capacitance and different switching frequency, not only "resistor heating", apart from any AC-DC conversion losses bullshitsurface temperature depends on case material (thermal resistance) and case surface.
>>16781803>AC-DCdepending on filtering>surface temperature depends on case material (thermal resistance) and case surface.assuming identical setups for heat generation say Rth (JA) for a semi
>>16781773Could you explain the second point? Non-ohmic losses are governed by completely different equations. The only thing they might have in common with ohmic losses is that some of them are somehow generating heat by movements of electrons. That doesn't make them ohmic. I wouldn't even agree that all of these losses result in heat.
>>167817641. and 2. are definitely correct. 3. Idk. Source: I worked on flicker noise in resistors.
Joule heating P = I^2 R exists in both ohmic or non ohmic conductors. The difference is how current scales with voltage.
>>16781764Him saying it is all P=R*I^2 is the only component that is remotely *technically* accurate.It handwaves a bunch of shit while driving home the point that the charger is substandard shit.>>16781813This is a consumer device with an exposed surface, not a switchboard/breaker mounted object. If they didn't design for surface temp, it's garbage.>>16781818This comment is not on topic. You wanted resistance and temperature.
>>167817641. is technically true but loses useful nuance in diagnosis2. that is false, because while all of the heat is generated by resistive elements, it's obviously false that the only resistive elements are dedicated resistors. And thermal dissipation very much matters.3. This is very likely true because switched supplies for small devices are super cheap and easy these days.
>>16781888>1. is technically true How so? Hysteris loss for example is governed by completely different laws and mechanisms. How would you reduce this to ohmic resistors? >3. This is very likely true because switched supplies for small devices are super cheap and easy these days.But a switched transformer is still a transformer. It transforms high voltage to low voltage via inductivities regardless of whether this is controlled by a switching logic.
>>16781764>same power output>no mention of the power inputbecause OP had one of them up his ass before he used it.
