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I have project where I am using a motor driver DM860A2 to run NEMA 34 85 kg-cm stepper motor. Currently I have used a transformer to supply 48V AC during testing. I have with me four 2200 mah 11.1V LIPO rechargeable batteries which I plan to use as a power supply for the motor driver by connecting them in series providing 44 V DC. But I have concerns regarding the feasibility of the battery circuit and should I take any safety precautions.

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  • \$\begingroup\$ How did you compute load/charge Energy and discharge charge time vs capacity? It can be feasible if conservatively used and poor life expectancy if not. \$\endgroup\$ – Sunnyskyguy EE75 May 28 '18 at 14:01
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You should consider the aging effects of inbalance and use a smart charger that reduces CC at 80% so that equalization and balancer can be enabled in CV mode.

Also consider ESR of each cell rises in Series arrays so 4x3S cells with an estimated ESR of 25 mOhms when new and fully charged, if good quality.

You should also have a cutout voltage that depends on load current to around 20% SoC to prevent undercharging weakest cell when new and consider 20% to extend string life of weakest cell and thus achieve expected charge cycle counts or more. Your ESR may vary depending on weight , cost and supplier brand quality. So if 50 mOhms ax 12 you have 600 mOhms and thus with 2A get a 1.2V drop immediately.

Then factor another 15% drop in voltage during discharge. 20% is excessive, while 10% is more conservative.

Reduce idle current to 25% if possible or as holding torque required to conserve energy.

Recalc, total energy and losses from ESR with temp rise affecting aging yet giving lower ESR.

For understanding the dual slope nature in time of batteries V vs t , read here not counting the 3rd slope at 0% SoC.

How did you compute load/charge Energy and discharge charge time vs capacity?

It can be feasible if conservatively used and poor life expectancy if not.

Thermal sensing is best for safety for 30'C rise or so cut off or feel with hand if warm.

But most users abuse batteries to max out fly time and don't care about battery life time. Since you cannot monitor weakest cell in string of 12, you can only guess how unbalanced they are and. hope they are within 1~2%. This rises exponentially towards End of Life so that 1 cell becomes reverse charged or over charged or <3V undercharged.

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