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I am currently using a AC-DC adaptor with specs:

  • AC-I: 100-2040V~50/60Hz 1.6A
  • DC-O: 12V 5A

Which is powering up 8 DC motors,

  • 4× 12V 6W
  • 4× 12V (wattage not specified, the motor is meant to be attached to a car battery)

How do I determine what fuse to use, and where to place it?

Do I place it after the adaptor and before the motors? And which fuse to use?

Do I place it before the adaptor, onto the AC current? And which fuse to use?

Can I place a fuse at both places?

I'd like to proect the system against all possible over-current scenarios.

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    \$\begingroup\$ the question where to put it depends on what you want to protect. You're not saying that. \$\endgroup\$ – Marcus Müller Jan 24 at 13:19
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    \$\begingroup\$ How can anyone tell you which fuse to use if you haven't even specified the normal and stall currents for the motors? \$\endgroup\$ – Elliot Alderson Jan 24 at 16:22
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If you want to protect against all scenarios, you should put a fuse before and after the AC-DC adaptor. Since motors draw large amounts of current for a short time when they start, it's difficult to calculate the value of the fuse exactly. For the same reason I would suggest a power supply at least twice as many amperes as the motors would take. A reservoir capacitor could help too. Yet, depends on the type of motors. I would strongly suggest glass fuse on holder clips so that they can be easily replaced. On the AC side, you can use a 2A circuit breaker or replaceable fuses. Whatever is easier. A rail mounted circuit breaker would require a wall mounted enclosure but it will be much more professional an installation. It can also be mounted in the main cabinet if you have a power line dedicated to it.

On the DC side I would put fuse holder clips for the standard 5*20mm. Buy a few different values. If you see that it blows too fast, put one with a higher value. You can fine-tune the exact amperage for your fuse to be as safe as possible.

I would not use resetable fuse unless the short condition will happen frequently and predictably without being a damageable condition.

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