/sci/ - Science & Math » Thread #13207005

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Anonymous Sat 29 May 15:27:22 2021 No.13207005 View Reply Original Report

Quoted By: >>13207087 >>13207119 >>13207234 >>13207289

Apparently Im retarded and cant figure this out.

What happens if I use a batterypack that has lower rating voltage than the device I'm using, it's about 1.5V? Faster discharge or will it shut off when pushed? Thanks

Anonymous

Anonymous Sat 29 May 2021 15:48:03 No.13207087 Report

Quoted By:

>>13207005
I'm not sure what the answer is but now I'm curious. We can just use baby's first Ohm's Law and say that, since the resistance of the device does not change and the voltage of the supply is lower than desired, the current supplied will also be lower than desired, right? So a faster discharge wouldn't really make sense. I can't think of a reason why the device would shut off when pushed unless it's just common practice for EEs to implement such measures to prevent idiots like you (and me) from trying to use a battery pack with too low of a voltage rating. I dunno, anon. I think we need an EE or someone with more life experience to chime in.

Anonymous

Anonymous Sat 29 May 2021 15:54:06 No.13207119 Report

Quoted By:

>>13207005
it depends on the device. if it’s a typical piece of personal electronics it most definitely won’t turn on and may damage the device

Anonymous

Anonymous Sat 29 May 2021 16:13:33 No.13207234 Report

Quoted By:

>>13207005
Depends on the device. Most good devices come in with built in security features that prevent misuse like this, which could mean the device refuses to start up. It doesn't really matter if the device could actually run on the lower voltage but instead it just blocks you out because something bad might happen. The other likely outcome is that the device works but slower or weaker in some way. For instance flash light might shine with weaker light or that sort of thing. This is especially true for lower voltage since batteries tend to lose power as they age or as they are on low charge so most devices like the above flash light are built to handle a small loss. This is doubly true if the voltage difference between what you are attempting to use vs what you should be using is small since a 100 volt device missing 1.5 isn't as big of a deal than 2 volt toy missing 1.5. Obviously lower voltage "can't" fry the circuits so it's less likely that the device just shuts off entirely as opposed if you tried using too much power, but it can still damage it some way like lower power resulting in some cycle that needs certain threshold power failing and thus it might still refuse to operate. You will most likely use the power in less efficient way leading to lower battery life as well (especially if the battery is low voltage because it's smaller/worse and not some artificial limitation you have set).

There shouldn't be much harm in trying though since any competent device won't be damaged by the attempt as this is the sort of stuff they expect people to mess up and have prepared how to deal with. It might just not operate or it might in reduced capacity or it might operate normally.

Anonymous

Anonymous Sat 29 May 2021 16:21:09 No.13207289 Report

Quoted By:

>>13207005
The battery pack rated voltage is the average voltage it can output. It starts at a few hundred millivolts higher when fully charged and voltage goes down as it discharges. If you keep discharging the battery below its lower voltage limit (a couple hundred millivolts below its nominal voltage) it will drop voltage much much faster until near zero and you'll probably kill the battery. If your device needs a higher voltage than your battery can provide, then it will simply not work, as for all intents and purposes the lower voltage battery will appear as it was a discharged battery of the proper nominal voltage.

Anonymous

Anonymous Sat 29 May 2021 16:26:50 No.13207325 Report

Quoted By: >>13207339 >>13207500

OP here, thanks for reading this and helping me understand it.

I was powering a single board computer, that runs of 5V at 0.5A with a 3.5V batterypack.

Anonymous

Anonymous Sat 29 May 2021 16:30:47 No.13207339 Report

Quoted By: >>13207390

>>13207325
It might turn on or dont, it wont get damaged. The logical gates have threshold voltages that are not exactly 0 or 5 volts, they have a tolerance. It could be that anything from 0 to 2 volts counts as 0 while anything from 4 to 6 counts as logical 1. Too much voltage will burn the device.

Anonymous

Anonymous Sat 29 May 2021 16:43:28 No.13207390 Report

Quoted By: >>13207500

>>13207339
It boots and runs fine under load, but I was wondering how it affected the battery life

Anonymous

Anonymous Sat 29 May 2021 17:12:18 No.13207500 Report

Quoted By: >>13207575

>>13207325
>I was powering a single board computer, that runs of 5V at 0.5A with a 3.5V batterypack.
>>13207390
>It boots and runs fine under load, but I was wondering how it affected the battery life

SBCs use SMPS (switch mode power supply) to generate working voltage from the input voltage. Kinda like how a stun gun can generate 1000's of volts from a 9v battery, the SMPS can take the input voltage and change it to what it needs, but with high accuracy. It really depends on the SMPS topology as to whether or not it will function correctly at a lower voltage or not.
In your case, it seems to work just fine on a lower voltage, but your battery life will be reduced since its having to pull more current to convert the voltage to working levels.

Anonymous

Anonymous Sat 29 May 2021 17:29:41 No.13207575 Report

Quoted By:

>>13207500
Yes, this was exactly what I was looking for. Thank you.

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