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I was wondering if I could use a battery as Vin to a DC DC converter to charge another battery.

Example: Using a Li Ion battery pack and having it go through the DC to DC converter to charge a LiPo battery pack.

More specifics: My idea was to have a Li ion pack be able to charge a Lipo pack by going through the converter or press a switch to have the Lipo pack charge the Li Ion pack. I'm wanting to be able to charge either batteries while using it. Like flying a drone or using an eboard etc.

While in flight for example be able to use a Lipo pack as the source supplied to esc while being charged by the Li ion pack, or use the Li ion pack as the source supplied to the esc while being charged by the Lipo.

Batteries: Li ion 4s2p (3.7/4.2v 20/40 amps per cell) Li po 4s (1500 mAh supposedly 120c)

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  • \$\begingroup\$ Why do you want to complicate the circuit and increase weight? Use just one battery. Of course it can be done. That is how the 5V power banks work. You need a boost converter to boost the 3.6V up, so it can charge the other battery. You also need current limiting circuitry, and also possibly circuitry to detect end of charge and end of discharge to avoid battery damage. \$\endgroup\$ – Indraneel Jan 14 at 23:27
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    \$\begingroup\$ One battery is better at being discharged than the but lacks mAh, the other is isnt as good at discharging but has good mAh. Li ions are great for long flights but not doing especially high punch outs, whereas Lipos are great at punch outs but lack mAh for long flights. My idea was sacrificing a bit of weight to get the best of both worlds. Using a Li ion during flight but if I wanted to punch out I could use the Lipo. It would also serve as redundancy. \$\endgroup\$ – Emmanuel Erausquin Jan 14 at 23:47
  • \$\begingroup\$ what happens when the LiPo battery runs out of power? ..... the ESC will get its power from the Li Ion battery via the LiPo battery? \$\endgroup\$ – jsotola Jan 15 at 0:09
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Both the Li Ion and LiPo are 4S configurations with different capacities but similar voltages so either one can be higher. You could use a bidirectional buck boost charger or consider my design, which is incomplete. Using 50 mOhm P FETs or lower and 20mOhm Choke rated for desired 2x charge current.

The impedance of 130uH is about 4 Ohm at 5kHz.

enter image description here Choice of high or low side bridging is a matter of preference

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  • \$\begingroup\$ the 100mΩ is just a ballpark battery string ESR and its heat is internally dissipated ,which you can change in the simulation. MOSFET beta ~1/RdsOn \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 15 at 0:09

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