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I want to charge a lithium-ion battery using a lead-acid battery, but I want the two batteries to be isolated from each other. Is there any way to achieve this?

Edit: Both the batteries are rated for 12 Volts and the charging current can go upto 20Amps

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    \$\begingroup\$ Use a transformer-based converter. Your question will need more detail of your requirements before you get any more detail in the answers. \$\endgroup\$
    – Neil_UK
    Commented Mar 16, 2023 at 8:23
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    \$\begingroup\$ 12V car charger -> 5V USB port -> any USB-5V powered Li-Ion battery charging circuit (this last one is complex so just buy a charger circuit for Li-ion battery) \$\endgroup\$
    – micropyre
    Commented Mar 16, 2023 at 8:42
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    \$\begingroup\$ Using an isolated DC-DC converter between the lead-acid battery and the Li-ion battery charger seems a good way forward. You can google what's in italics to learn more. If you want more detail, please add your specific requirements to your question. \$\endgroup\$
    – ocrdu
    Commented Mar 16, 2023 at 10:12
  • \$\begingroup\$ What voltage? For each battery. \$\endgroup\$ Commented Mar 16, 2023 at 13:59
  • \$\begingroup\$ @ocrdu I looked into a DC-DC converter, I do have one at my disposal, but I need to control the current. which I am not able to do with the one that I have despite it having a potentiometer dedicated to control the current. Maybe it is just the fault of the specific converter that I have. \$\endgroup\$ Commented Mar 17, 2023 at 9:19

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I want to charge a lithium-ion battery using a lead-acid battery, but I want the two batteries to be isolated from each other. Is there any way to achieve this?

You can use a Qi-compliant wireless charger like this: -

enter image description here

Figure 4: A Qi-compliant wireless power system, with Panasonic's AN32258A and the NN32251A. The article (called Wireless Charging) also shows other options such as this: -

enter image description here

There's also this non-Qi-compliant circuit from Wireless Charger Design Principle Concept Explained: -

enter image description here

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  • \$\begingroup\$ Thanks, Andy, This could work for me. Will I be able to control the current or will it be fixed? \$\endgroup\$ Commented Mar 20, 2023 at 5:17
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Many isolated DC-DC converters exist. Use one to power your battery charger.

Such converters are similar but not identical to other switching converters you may be familiar with, such as buck or boost converters, but the coil is replaced by two separate coils, making a transformer. The design may be slightly different to optimize energy transfer through the transformer. Feedback signals are opto-isolated.

You can get one that has the same voltage input and output, or you can get one that changes the voltage - a capability that comes practically for free since there's already a transformer in the middle.

Technically, it should be possible to make an isolated battery charger using the same principles, but it would be a quite niche part and I doubt they are made, so unless you want to make one from scratch, I would stick with an isolated converter feeding a normal battery charger. (Google tells me you can buy an isolated 12V lead-acid charger that is sometimes useful in some automotive applications like towing)

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    \$\begingroup\$ I wouldn't say they are similar to switching converters; they're a type of switching converter. \$\endgroup\$
    – Hearth
    Commented Mar 16, 2023 at 14:02

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