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from various experiences modems, access points, and other devices will often run fine even with power adapters of lower voltages (compared to their original power adapter).

I am wondering if using a power adapter that has lower voltage leads to power savings?

as a side question, what could be the possible undesirable effect of running with a lower voltage power adapter? (assuming that the device runs fine with no stability issues)

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  • Run fine does not mean you will not burn it out faster. Oct 1, 2013 at 23:38
  • You should never run a device with an adapter that has a substantially different voltage rating, whether higher or lower. You can generally run a device with an adapter that has a higher/lower current or wattage rating, within reason. The savings (if any) are unlikely to be significant, however. (And some cheap adapters are almost guaranteed to be worse.) Oct 2, 2013 at 0:46

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It depends on the design of the device. If the device, for example, has a 9V-12V input and a linear power regulator like a 7805 on its DC input, then yes, reducing the voltage will save power and make the device run cooler. The fact that dropping the input voltage makes the device use less power suggests that this is the case.

If, however, the device has a smarter regulator on its input, dropping the input voltage could cause the regulator to overheat (because it needs more input current to get the same power). However, in this case, the device should draw at least slightly more power when the voltage is lowered.

You can't assume an untested device will behave in a particular way though. You have to either measure the behavior or look at its power input circuitry. If reducing the input voltage causes the device to draw less power and it appears to operate reliably, it is probably safe to operate it at the lower voltage. You are very unlikely to reduce device life, however, you may find it more likely to crash or reboot.

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  • Here's a real world example with a DC/DC step-down switching regulator in Linksys WRT54G routers: kioan.users.uth.gr/wireless/wrt54g/supply.html In this case it works from ~6 to at least 15V with only small differences in power consumption.
    – Limer
    Oct 12, 2021 at 20:13
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That lower rated adapter might be less efficient at converting power and produce more waste heat than the higher voltage rated adapter. And as a result even if it the device functions, the lower adapter would be drawing more current. And turning more of it in to waste heat. So you would need to test the adapter for its conversion efficiency.

I would not use a device with an adapter that isn't rated for the same current draw in volts and amperes as the device requires. Although one could look for an adapter with a higher conversion efficiency.

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I say no based on the following logic.

Electronic devices are designed to run on a very specific voltage. If they accept a range of voltages, then they usually will regulate the voltage to the voltage they need, especially if their output voltage and current does not vary with input much like your modem (and unlike stereo amplifiers which will output more voltage with a higher input voltage)

This being said, the electronic device AFTER the regulator would draw the same current and voltage (if the regulator output a perfect voltage) meaning it would draw the same power (watts) as well. The regulator circuit is probably not 100% efficient so it would actually waste energy in its conversion up or down. So in the end, you would draw more power if you input a voltage other than the designed operating voltage.

Since non-switching power supplies voltage varies with curernt and therefore have a large range of output voltage (12V PS might output 17V under no load conditions), it is likely your model has some sort of voltage regulating circuitry.

If there is no regulated voltage, then we can assume that the electronic components do a have a voltage range they can work in, BUT it usually is small and therefore you could only lower the voltage a very small amount.

This leads to two logical conclusion. (1) you can input a lower voltage and it will be regulated back up leading to HIGHER power draw or (2) the voltage is unregulated which means you don't have the option of lowering the voltage a significant amount to see any real gains.

That being said, efficiencies vary greatly between power supplies. Power supplies are usually rated for both output AND input. So it would be a better bet to find a power supply that draws less amperage from the wall given the same output current with a similar ripple voltage. Or search out a way to tell a more efficient PS from the less efficient one. That is a whole 'nother topic.

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