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In my application I have a motor that may require high currents (~140A) for some seconds. But I need to power the system for many hours from a 48V 10A switched mode power supply. The motor is current controlled, so the resulting voltage is not super important.

I thought about buffering the system with a 12S 3.6Ah 30C/60C LiPo battery. It's rated for 14A charging. The 48V/10A supply is then basically an IU-charger that will never completely top up the battery.

schematic

simulate this circuit – Schematic created using CircuitLab

How can I protect the battery from deep discharging? If possible, I'd like to avoid having to design a custom power management board.

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You can't get around having some kind of power management board for a 12S lithium battery. Fortunately most of them come with an integrated battery management system (BMS) that takes care of shutting off before overdischarge/overcharge, but it may not be quite what you want since it will do that by disconnecting from the load. Note that you cannot just charge the battery at 48V forever without damage -- you will need a proper CC/CV charger. Additionally, 3.6Ah sounds like you're only putting one of these in parallel, for a 12S1P setup. I'm not sure exactly what cells you're planning, but 140A is a very large amount of current to pull from a single series of cells -- you may find that your batteries will last much longer if you parallel more than one. I think if you went this route you'd probably find that building a custom power management board would be the way to go.

That said, for this particular application, have you considered using lead acid? High current for a short time followed by a slow trickle charge is exactly what car batteries are optimized for, and will probably perform better than Li-ion in this case -- lead acid excels at high current bursts. Weight and size would go up, but cost would go down, and no BMS or custom board would be required.

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  • \$\begingroup\$ I looked at a SLS XTRON 3600mAh 12S1P pack. I did think about lead acid first, but read somewhere that they really only do 3C for some seconds? So I need something like 7*6V/45Ah, which will weigh well over 50kg. Do you have a recommendation for a power management solution? I saw the TI PMICs but they don't seem to offer anything in this high power range. \$\endgroup\$ – Laurenz Nov 28 '18 at 10:07
  • \$\begingroup\$ You probably heard the 3C thing about a deep cycle lead acid, not a lead acid starter battery. This page explains the difference: batteryuniversity.com/learn/article/lead_based_batteries. A starter battery is generally capable of providing hundreds of amps for some seconds (500-1000 is common for car starters). Since that's overkill for your application, you might try to find starter batteries for small engines, i.e. motorcycles, lawnmowers, etc. \$\endgroup\$ – Nate Strickland Nov 28 '18 at 17:45
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    \$\begingroup\$ Four of these, for example, would be 35kg, $200, and could be dropped in to your application directly: autozone.com/ignition-tune-up-and-routine-maintenance/battery/… \$\endgroup\$ – Nate Strickland Nov 28 '18 at 17:46
  • \$\begingroup\$ As for Li-ion power management, I don't have a specific product recommendation, but look into BMS and charger solutions for electric bikes -- they tend to fall in a similar power range. Note though that batteries of this size are usually disconnected from the load when charging, so if that doesn't work for you there may not be a off-the-shelf solution. \$\endgroup\$ – Nate Strickland Nov 28 '18 at 17:54

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