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I want to make a simple SPICE simulation which mimics this power-bank(batteries in series) discharge in time. Basically the power-bank is made up of 4 x 5V batteries in series. And in my case it will power a laptop which requires 20V and max 65W.

Now my following model of course doesn't show it, there's no discharge:

And here are the specs of the power-bank in detail:

enter image description here

I want to obtain a SPICE model which can show how would the power-bank discharge when supplying 20V for a laptop and assuming the laptop is drawing 3.2A .

How can this be modelled(very estimate crude model is enough) in SPICE?

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    \$\begingroup\$ The power bank isn't made of four 5V batteries in series. The 20V output does not come from a 20V battery. There is a voltage converter that boosts or bucks the internal battery to 20V while the actual batteries discharge, so the voltage stays at 20V until batteries are empty and it shuts down. So you could simply look at discharge curve of a 5Ah lithium cell with constant 5W discharge. \$\endgroup\$
    – Justme
    Commented Nov 14 at 23:22
  • \$\begingroup\$ Are you sure? But it says 4-cell battery 5000mAh in specs. Do you mean they are in parallel? \$\endgroup\$
    – pnatk
    Commented Nov 15 at 0:07
  • \$\begingroup\$ I'm also wondering how can discharging battery be modeled in SPICE. \$\endgroup\$
    – pnatk
    Commented Nov 15 at 0:10
  • \$\begingroup\$ I am 100% positive. The description says they are lithium cells. Lithium batteries are not 5V batteries but nominally 3.6V, 4.2V when full and empty somewhere below 3V as defined by battery manufacturer and different value may be used by this device. And their internal organization in series/parallel/both is unknown - the capacity might just be a sum of all batteries together, or then they really are all in parallel. If you want to model a lithium battery, model the battery, not the device that has batteries. \$\endgroup\$
    – Justme
    Commented Nov 15 at 0:23

2 Answers 2

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You can use a large capacitor to roughly emulate a battery. For example, for a 5Ah battery with a 1V drop in voltage over that discharge value, you could use a capacitor with (5*3600)/1V Farads or 18,000F.

Of course that's not a very practical value of capacitance, but its easily done in Spice.

Below is a simple LTspice simulation of such a capacitor being discharged by 1A constant-current source.

It shows the battery simulated voltage (green trace) versus the charge removed from the battery in Coulombs[ampere-seconds] (yellow trace).

Note that the removing 18k Coulombs (5Ah) drops the voltage by 1V, as expected.

enter image description here

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This schematic take account of "transient" change.
Some components may be changed.
It present the behavior of ULTRAFIRE 3000 mAh battery (~ verified).

enter image description here

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