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I built this small RC deadbolt lock and everything works great, however, I need to fix the issue of battery life before it is finished. Originally the circuit had a 3.7V, 800 mAh battery. I would like to hook up a total of of 3.7 V, 12000 mAh or so, my question is will the circuit only draw what it needs from the batteries or will this fry the circuit?

Sorry if this is a rookie question, my knowledge of this is not too extensive.

Thanks!

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    \$\begingroup\$ Thought experiment: What does Ohm's law tell you? (\$ V = IR \$.) \$\endgroup\$ – Transistor Apr 7 at 18:38
  • \$\begingroup\$ You can't change capacity that much without checking out the charging circuit. Cutoff current is based on total capacity, so if you charge a 12 Ah bank to the cutoff current of a 0.8 Ah bank, you'll overcharge it and wear it out fast. \$\endgroup\$ – K H Apr 8 at 6:11
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Everything will be fine as long as you keep same battery chemistry for same voltage levels.

mAh - is the battery capacity. More capacity = more "running time" for the same current draw. It has nothing to do with how much current actually flows through your circuit.

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Correct, but verify each cell is charged within 1% difference max. before shunting them as 3Ah is 20~ 50 mOhm ESR so 1% of 3.8V full charge is 38 mV or about 1A , which OK to equalize charges, but if more this , expect that the strongest cell delivers most of the current until its voltage drops for the others to share. Then the strongest cell will lose performance to match the weakest or until all the same SoC and ESR from same or aging.

This is a good solution.

A better one might put in a coil pair on lock and door jam and send some power to keep it floating below 3.8V. You can figure that out with Q resonant coils using a smaller gap than diameter coil at from 100kHz to 1MHz from your past experience of ~ 2.8Wh / X hours. Tune for MPT something like 100mW with an LED +Si diode for 3.8V limit

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  • \$\begingroup\$ With ferrite, you can make the loop smaller and use end to end across gap. even 74ALC’ family’ CMOS differential can supply W from CAT3 or magnet wire to a remote door jam from 3.3 to 5V into an LC tuned circuit for Zo= 50 \$\endgroup\$ – Tony Stewart EE75 Apr 7 at 19:15

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