So has there been a solution found for hot swapping batteries on a drone without powering down to reset the volt,mah,batt %? When flying long mapping missions hot swapping is ideal to avoid restarting mission / recalibration of mapping sensors. I know there was some talks of there being a fix on the next update. I haven’t seen anything that doesn’t a large amount of DIY wizardry and coding. Any information on this is welcome.
You can usually power the flight controller with a USB battery bank to keep it online while you change the main battery, it depends how your machine is setup, you could have issues with sensors like rangefinders that are powered from the main 5v rail and not the USB rail not coming back online .
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If still interested, here is a relatively simple hot-swap circuit that uses two P-MOSFETS with two resistors as ideal diodes, (requires no specialized IC) to isolate the two batteries during the swap while minimizing the voltage drop of using regular diodes for this purpose.
LTspice simulation of the circuit is shown for swapping between two batteries.
When both batteries are connected during the swap (at 0.5 sec of the sim), both MOSFET’s gates go high, turning M2 off (M1 may be on or off, depending upon the MOSFET’s Vgs threshold voltage and the relative battery voltages, but that makes no significant difference).
The current from the higher voltage of charged Bat1 then goes through M1 (its substrate diode if it’s off), while M2’s substrate diode blocks any current into Bat2.
(Note that the Bat2’s current (blue trace) goes to zero as soon as the charged Bat1 is connected.)
After the discharged battery is removed (at 1s), the opposite MOSFET’s gate voltage goes to ground, which turns it fully on to give a very low drop from the charged battery to the output, equal to the MOSFET on-resistance times the load current.
If it would be okay to control the negative side of the batteries instead of the positive (which is likely for most applications), then N-MOSFETs could be used, since they generally have a lower on-resistance as compared to P-MOSFETs for a given chip size and are thus somewhat cheaper.
The circuit can be built on a small perf board.
If the battery voltage is below 10V, use logic-level MOSFETs (max. Vgs threshold <2V).
there is a long post about ideal diodes here