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How does a fuse protect a battery? I know that it prevents short circuits, but what about overcharging and over discharging?

I asked a previous question here, and the recommendation I got was to get a fuse.

If a fuse dosent prevent overcharging or over discharging, than what should charging and discharging look like?

I built a 48V 80A NiCd battery pack. I have no idea of where to buy a BMS system or what kind of voltage detection IC I need to prevent overcharging/overdischarging. I need to know what people do to protect a battery pack like this one, or if they protect it at all.

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    \$\begingroup\$ It doesn't prevent overcharging or discharging. \$\endgroup\$ – user1850479 Feb 25 at 20:11
  • \$\begingroup\$ But it is still good to have a fuse in series with the battery pack to prevent fire (wires can catch fire when too much current flows through them) in case of short circuits and a current that becomes too large. Note that the fuse protects against currents getting too high. It does NOT protect the battery from over charging in any way. Some extra advice: educate yourself on batteries. A 48 V battery pack can be dangerous so you must know what you're doing. Start here: batteryuniversity.com \$\endgroup\$ – Bimpelrekkie Feb 25 at 20:46
  • \$\begingroup\$ Are you sure you're using NiCd, and not NiMH? NiCd has been illegal to manufacture in much of the world for decades, and I doubt there are many cells remaining that still function. \$\endgroup\$ – Hearth Feb 26 at 20:57
  • \$\begingroup\$ Its NiCd. @Hearth \$\endgroup\$ – Circuit-B0ARD Feb 27 at 1:12
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A fuse doesn't protect a battery from overcharging or discharging.

It also doesn't prevent a short circuit, however if a short circuit happens then hopefully the fuse will blow preventing fire or damage to equipment caused by said short circuit. The fuse blows and makes the system safe if correctly installed but the short circuit is still there and must be found and repaired.

If the fuse is not blown then it just looks like a wire to the rest of the circuit, so your battery is free to overcharge all it likes, or trickle discharge with no opposition if your circuit allows, a fuse only cuts connection in the case of drastic over-current, or other parameters sometimes, like temperature, in the case of specialty fuses.

I think the easiest option for you would be to buy a premade 48v NiCd charge controller, make sure it's 48v compatible and meets the current draw requirements of your system, and also is compatible with the input voltage level you intend to supply it with. Google search gives me plenty of results that fit the bill (assuming solar as the charging source) but as always check your specifications and make sure it's rated to charge a 48v NiCd battery at your available voltage, well over your expected current levels, both charging and usage current, with a protection fuse at the least between the charge controller and battery but if you are not sure then it can't hurt having a correctly rated fuse near the beginning of every live line until you are sure which ones you may be able to safely omit. Also, make sure the wires in your system are big enough to easily handle your highest expected current at any point in the system. You could certainly make a circuit yourself but that would require a lot of understanding, and as mentioned, 48v is dangerous and as such not a project to try and learn fundamentals with.

(I think this answer would be better as a comment but I don't have the rep yet, mods please delete if appropriate)

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