If the battery fails on a mobile phone, why is it unusable even when it’s plugged in to the wall?
There are many older electrical gadgets that can work with either batteries or being plugged in. Take an old fashioned alarm clock or stereo. If there’s no batteries in it, and you plug it into the wall it will work. If you unplug it, it won’t work unless there are good batteries in it that are charged. So why can’t a mobile phone work when plugged into the wall when the battery has failed?
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among other things, the battery is functionally a voltage converter.
the electricity going into the phone is 5 volts, which is fine for charging the battery, but the battery discharges at 3 or 4 volts into the computer.
there are voltage changing circuits for DC voltages that don’t require a battery (there’s a giant one in your microwave) but it’s a lot of unnecessary work.
A simple reason is the electronics may not handle the current of running the device and charging the battery. Either they used cheap wiring or worried about the excess heat generated.
Cell phone batteries power the phone. When you plug in a phone, it doesn’t supply power directly to the device. It supplies power to the charging circuit that controls when to send power to the battery to charge it.
If you wanted to be able to bypass the battery and get power to the phone by plugging it in, the phone would need additional circuitry to bypass the battery and manage the flow of power which adds to space requirements and heat generation.
For a device that is supposed to be mobile, adding a bunch of hardware to it so it works when it’s not mobile is kind of missing the point.
Depends on a unique design. A car battery is one example. Electricity is actually in spikes. During periods of no current flow, the alternator needs current from the battery to maintain fields. An alternator cannot charge a battery when the battery does not exist; to provide power between electrical spikes.
Some electronics work just fine without a battery – only on a charger. Other chargers provide too little current. To slowly recharge that battery. The recharger cannot provide enough power on its own to power semiconductors.
That is only two of maybe ten different reasons why electronics can or cannot operate without or without a battery. Every design must be discussed uniquely.
Just to be clear (to disspel disinformation). No battery does surge protection. That urban myth is promoted by scammers who sell magic hardware at inflated prices to the most technically naive.
Often a device’s circuitry is just solely connected to the battery, and when tou plug it into the wall, it becomes a situation of: the device is plugged into the battery, and the battery is plugged into the wall. So the wall has to fill up the battery a little bit first, before the device can use any power!
And sometimes it gets more complicated! Batteries change their voltage as they drain or are charged, with the voltage decreasing as it is less charged. And some circuitry might need a specific voltage minimum to function. Or charging AND draining a battery simultaneously when it’s low on charge may stress the battery unnecessarily, or cause the device to function unreliably, so it checks to make sure your batter has at least, say, 3% before it can turn on. These are just some reasons!
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