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I am wondering what are the affects to current in a parallel circuit and if the current can be run in parallel in the same way as with voltage (eg. To power 3 phones in Parallel would I need 3 times the current)

Edit: I am using the phones simply as a example I am trying to power 10 laptops at 19.5 volts (running them in parallel) . And each laptop needs 8 amps to run So my question is to power the 10 laptops in parallel do I need 8 amps (the power necessary for one laptop) or 80 amps (The power necessary for 10 laptops).

Super potateo
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    What kind of phone? Landlines? Mobile phones - in which case you are discussing mobile phone power supplies. Please [edit] your question to explain and since you are struggling with the technical details please explain why you are asking. – Transistor Aug 01 '20 at 20:16
  • Yes, three times the current. Or, if the phones are different, you can just add up all the currents. For example phone 1 needs 0.5 Amps, phone 2 needs 1 Amp and phone 3 needs 1.4 Amps. So the supply needs to be able to provide 0.5 + 1 + 1.4 = 2.9 Amps. Also, all three phones must use the same rated voltage (for example 5V). – user57037 Aug 01 '20 at 20:18
  • I agree with Transistor. You should explain exactly what you are trying to do, maybe add some pictures or diagrams. This is so we can give you a better answer to your question. Right now I am not exactly sure what your question really is. – user57037 Aug 01 '20 at 20:19
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    This appears to be answered by our canonical question on power supply selection: [Choosing power supply, how to get the voltage and current ratings?](https://electronics.stackexchange.com/questions/34745/choosing-power-supply-how-to-get-the-voltage-and-current-ratings) – Tom Carpenter Aug 01 '20 at 22:21
  • To charge 10 laptops at a similar rate. you definitely need 80 amps. however, If you are just trying to power them up, you can work with fewer amperes. for example, my laptop needs 2 amps to handle normal workload. In my case, I would need 19.5V at 20Amps to power 10 similar laptops. hope this helps – JaySabir Aug 01 '20 at 22:32
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    Right, so it's not phones. Thought experiment: One laptop requires 19.5 V at 8 A. If ten laptops could run from the 19.5 V supply at 8 A what would stop you powering 1000 laptops from 19.5 V at 8 A? – Transistor Aug 01 '20 at 22:33
  • Transistor wow that is a really good point but you could not power 1000 laptops from the power because of the resistance of the circuit – Super potateo Aug 01 '20 at 23:04

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Each laptop will draw the current it requires to run the CPU and peripherals. This will vary and may be much less than the 8 A specified - particularly once its battery has finished charging. The total current required will be the sum of the individual currents.

Note that the 8 A measurement is taken at the DC output of the power supply. The mains current will be lower by approximately the inverse of the input-output voltage ratio.

Assuming you have a great big 19.5 V PSU, it will have some rated current limit beyond which it will fail to operate properly, either by failing to give the full 19.5 V or by thermal shutdown.

Cable resistance will also cause the voltage to sag in proportion to the current. Other things to watch out for include over-heating of plugs and sockets.

Transistor
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