Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and the Yahoo Answers website is now in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.
?
Is it right that they are closing Yahoo Answers?
2 AnswersOther - Yahoo Products2 weeks agoHow this LED board works on AC/DC10-30V?
We can see it rectifies AC and has a cap to smooth it.
There are 12 LEDs here presumably in series.
LEDs need 2-3V, so if input is 30V voltage would be 2.5V per LED, just right.
But what if it's 10V, then voltage across each diode is only 0.8V.Are we to assume there is a boost here to step those 10V to 30V? I see no inductors.Or maybe LEDs are in parallel with a zener to keep the voltage around 3V?What you think?
1 AnswerEngineering2 months agoWhy the diode across the transistor at 0:55?
It can't by a flyback for the primary cause when transistor is off there is no path for primary to close.
Engineering2 months agoIs he running ICs with 110V?
That dimmer seems like regular TRIAC dimmer and he says frequency is 60Hz, i see no transformer, it all points that he is.
2 AnswersEngineering3 months ago
What limits the TRIAC gate current here?
Continuation from last question. It is not clear to me what limits the gate current in this dimmer circuit once TRIAC is on. Let see exactly what happens. At first TRIAC is off and current must go through R1 and VR1, once the cap is charged DIAC fires TRIAC gate and it's on. You can see below now there is a low resistance path for gate current only limited by R2, since this is 1kW dimmer we can assume R2 is small resistance. It seems there is nothing here to limit the gate current while TRIAC is on.
2 AnswersEngineering3 months ago
Strowger phone system?
I understand how direct phone to phone line is established through various selector switches, but i don't understand how are multiple phone-phone lines established through those same switches at the same time. I don't see any clear explanation of this.
1 AnswerEngineering4 months agoVan Der Graff question?
We know max voltage attainable by VDG is proportional to sphere radius and inversely proportional to breakdown of surrounding air, as nicely explained here https://www.youtube.com/watch?v=yaeITv9Ytko Question is does adding external capacitance to the dome increase max V. We can add capacitance by putting another sphere against the main one which is effectively doubling it's size and voltage, we can other sphere at distance connected by wire, another sphere can also be a plate of regular capacitor.. Do you see where i'm going. As far as i know adding such external capacitance, that is, charging capacitor(s) with VDG does NOT increase it's max voltage, but why not. According to logic it should as we are effectively increasing the dome size, doesn't matter if dome is all one piece or two pieces connected together.
1 AnswerEngineering5 months agois there a way to detect battery voltage WHILE IT'S CHARGING?
in case you don't understand the question which you probably don't, let me draw it to you, if 12.7v battery is being charged by another 12.7 battery, voltage across the battery that is being charged is always 12.7 (due to other battery) despite the fact it may be at 10.5v or 11v. is there any way to detect it's voltage while it is being charged.
5 AnswersEngineering6 months agoSlayer Exciter aka mini Tesla Coil question?
How does base of the transistor not get damaged by being directly connected to HV, because current is small?
2 AnswersEngineering6 months ago
Is this correct?
As north pole sweeps across the wire to the right, voltage will be induced that would push electrons up.
1 AnswerEngineering7 months agoHow does BLDC motor controller no hall work?
It just creates a 3phase rotating magnetic field? But how does the field synchronize with the rotor magnets?
1 AnswerEngineering8 months agoIs short roller chain more efficient than long one?
2 AnswersEngineering8 months agoWire amps question?
Why in all these tables amp rating is bigger for bigger temp, isn't it supposed to be the opposite, lower the temp, more amps it can carry.
4 AnswersEngineering8 months agoHow big battery you recommend for 5kw RMS 12V inverter?
Do you think 3x140ah is enough?
Engineering8 months ago
Inverter earthing?
I know in regular power system neutral is earthed as shown in screenshot below, but what about an inverter.
For example in this Chinese inverter earth terminals are not connected to anything. Where are they supposed to be connected to, to neutral, earthing rod or both (as in screenshot below)?Skip to 6:20https://youtu.be/oLHQnnZSysQ
Engineering8 months agoVan Der Graaf question?
This guy claims his VDG is 1mV, he used a sphere 320mm with 300mm cylinder inbetween the halfs. According to standard values, 1mV should be aproximatelly 67 cm diameter sphere, and i think his cylinder has much less surface than that. I assume it's probably not 1mV, more like 0.5mV, what you think?
Physics8 months ago
