Undervolting.

[jjesse47]

Quick question for the group. As a electrician I understand that running a load at lower voltage will raise the current as per ohms law ( voltage and current being inversely proportionaL ) .A fixed wire gauge running at a higher current will produce more heat on said wire. For example an air conditioner motor with a multi voltage tap  either 240v or 120v will draw twice the amperage at the 120 v tap  then the higher 240v tap. Going with the higher voltage produces less heat on the wire. The question is why does under volting produce lower thermal output, isn't wattage based on work done v x a + wattage  and if the efficiency stays the same the thermal output is the relation of wattage and efficiency no matter how your wattage is derived ( lower voltage and higher amperage or vice versa )? For example 1 volt at 10 amps is 10 watts  and 10 volts at 1 amp is 10 watts. Both loads in my profession would produce the same thermal output given the efficiency stays the same . One would think the work done by the cpu would be the same as the load stays the same or does the load decrease because the cpu slows down?  Im just trying to satisfy my ocd mind and get this straigt . Thanks for helping me understand the difference as I am defiantly not a electronic technician.

[Jurrunio]

Actually, CPUs pull the same current regardless of voltage (unless it crashed or something) because it just wants electrons to run through the transistors. That's why undervolting increases the efficiency of the CPU.

[jjesse47]

OK so it does increase the efficiency.  thanks

[KarathKasun]

Power = Capacitance*Voltage^2*Frequency

 

Reducing voltage significantly reduces power usage.

[jjesse47]

thanks I just pulled out a great electronic book I had and just found that.... thanks 

[KarathKasun]

AFAIK the capacitance value for modern CPUs is in the 0.9 to 0.95 range.  I am not 100% sure about that number, but I seem to remember seeing that when doing a research paper on the topic.

[Mira Yurizaki]

The thing with CPUs is that they're entirely reliant on voltage levels for signaling. The work is really to get the voltage levels to the correct place. And as long as the threshold is met, the CPU is fine.

 

It also helps to know how transistors work. They don't really act as resistive loads per se (if you're doing paper napkin analysis, they have no resistance). For CPUs, it's typically MOSFETs or an evolution of them. And these act more or less like a faucet, with the voltage affecting how much the handles are turned and the current being the water that flows through. So undervolting actually decreases the current flowing through the system. And less current running through means less heat is generated because everything still has a resistance value to it.

 

Also the Power = Capacitance (of a transistor) * Voltage ^ 2 * frequency came from https://software.intel.com/en-us/blogs/2009/08/25/why-p-scales-as-cv2f-is-so-obvious-pt-2-2

[AntiTrust]

great question though

[jjesse47]

wow thanks. II see the value of joining float plane. Its nice to get educated answers without ridicule for being uninformed. thanks to all that responded

[MyName13]

12 hours ago, jjesse47 said:

As a electrician I understand that running a load at lower voltage will raise the current as per ohms law

???

 

I = U / R, decreasing the voltage will decrease the current.You are mistaking ohms law with P = U * I (where you can have same power with lower voltage at higher current).I'm shocked that nobody has mentioned this yet.

[KarathKasun]

5 hours ago, MyName13 said:

???

 

I = U / R, decreasing the voltage will decrease the current.You are mistaking ohms law with P = U * I (where you can have same power with lower voltage at higher current).I'm shocked that nobody has mentioned this yet.

It seems like the OP was talking about induction motors and similar, where amperage can increase as voltage declines.