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I am trying to stimulate a Li-Ion battery charger for an an electric scooter. Here is a diagram of my circuit in LTSpice: enter image description here

The topmost circuit is the oscillator. It creates a 0V to 12V square wave with 10 kHz frequency. The npn transistor here (2N3904) is the "inverter", i.e it shifts the square wave 180 degrees. Although this "new" signal is a bit distorted I found that it created the largest DC voltage (V_DC node). Here is a diagram of these two signals, which are responsible for switching the transistors in the circuit on the bottom left. enter image description here

The circuit in the bottom left is the DC to AC converter and the one in the bottom center is the AC to DC converter. In between is the transformer. The DC to AC converter is located inside the charging station while the AC to DC converter is located inside the scooter. The transformer "exchanges" voltage from the station to the scooter. When I exclude the circuit on the bottom right, the waveforms are: enter image description here

The circuit in the bottom right is my attempt at a shut off circuit / low voltage protection circuit. As a lithium battery charges up its terminal voltage increases. When the battery reaches its capacity then the terminal voltage will fall at a slight rate as forward current is still being applied. There are sense circuits out there that will detect this change in voltage rate from increasing to decreasing. This is what I was trying to make here and I am not sure if I succeeded. Here are the output voltage and current waveforms. Here, the 500 microFarad capacitor represents the battery: enter image description here
enter image description here enter image description here

Have I succeeded in creating such a shut off / low voltage protection circuit here? If not, what is "wrong" about by outputs and what should I expect? Additional, what circuits can I use to create such a circuit? Finally, can anyone provide a 12Volt Li-Ion battery LTSpice model, like a .lib or .txt file (I tried looking online but couldn't find any)?

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  • \$\begingroup\$ Li-ion batteries have to be charged using a CC-CV charger, not whatever this is. I don't see any way to monitor or set the charging current, let alone safely shut it off when charging is complete. \$\endgroup\$
    – Finbarr
    Jan 17, 2021 at 19:27
  • \$\begingroup\$ Batteries are more like 10kF / n Cells with an ESR x n cells and a secondary RC for the memory effect which is charged during CV for a shorter duration on fast charge cycles. \$\endgroup\$ Jan 17, 2021 at 19:31
  • \$\begingroup\$ "Finally, can anyone provide a 12Volt Li-Ion battery LTSpice model". Don't ask multiple questions: the local enforcers with close your question for "needs focus". \$\endgroup\$ Jun 9, 2023 at 14:32
  • \$\begingroup\$ @DavideAndrea We local enforcers have our hands somewhat tie re what we are 'allowedto allow' :-(. That said, the question has survived well over a year so far, so the local enforcers have not been too too stroppy. \$\endgroup\$
    – Russell McMahon
    Jun 9, 2023 at 15:02

2 Answers 2

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First and foremost, don't do it. Use the original charger for the scooter. Over and over apartment fires were started from small EVs that were charged with a non-original charger. Not worth the risk to property and lives.

Secondly, you're under the common misunderstanding that a cut-off based on battery voltage protects a Li-ion battery. It doesn't. A li-ion battery is protected by checking the voltage of each individual cell. That's the job of the BMS, not the charger.

Your Li-ion battery MUST be protected by a properly designed and installed BMS!

Thirdly, you're missing a crucial requirement of Li-ion chargers: CCCV. What you have there is a "power supply" not a "charger" You must use a CCCV charger with Li-ion batteries. Attempting to charge a Li-ion battery with a power supply will at best not work, may damage both the charger and the cells, and at worst start a fire.

CCCV means that both the voltage and the current are limited to precise values. Your power supply does neither.

If you want to play with power circuits, great! But not when it comes to Li-ion. Be safe.

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  • \$\begingroup\$ +1 Yes! Vent with flame is to be avoided. \$\endgroup\$
    – Russell McMahon
    Jun 9, 2023 at 15:03
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I don’t understand what you trying to do. To charge lithium we use CC CV mode. We use constant current to charge the cell until it reach full voltage then switch to constant voltage to charge until the current dropped below 0.1 of CC current then we cut the charger off and indicate full chart. Also you should use BMS module to protect battery and keep cell voltage balance.

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