Electronics > Beginners

DC powered device : is a fuse needed ?

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ratatax:
Hello,
I'm designing a pcb for a device that will get 12V DC from a power adapter. The power adapter itself is well protected against short circuits, over voltage and is certified in almost all countries.
I'd like to know if a fuse is still needed on my 12V input. Would you put one ?

I can tell my users to only use the provided adapter so I'm not faulty if they use a shitty one that catches fire, but I'd like to know what is the best practice here, what choice would you take for your project.

RoGeorge:
Best practices is to put a fuse if there is a risk to catch fire.

The whole idea of having a fuse is to protect against fire when things go wrong in unpredictable ways, so relying on the power supply protections is not good enough.

Also, the "not my fault" approach if the customer uses a wrong power adapter will still hurt your product badly.  If a single unit will catch fire, no matter the reason, people will find out and avoid your product(s) in the future or, someone else might make a product review and point out your product can set the house on fire.  Not good for business.

As an example, PC motherboards (DC powered) have fuses for the external connectors that carry enough power.

radiolistener:
If your power supply can provide high power, then fuse definitely must have.

For 13.8 V 40-60 A power supply I also recommend to use thyristor over-voltage protection and reverse polarity protection, because if something will going wrong, such power may burn in fire even PCB of your circuit and make serious damage.

The idea is that thyristor make short circuit in case of over voltage and take all power through self to protect your circuit.

For example, BT152-400R can handle 200A for 10ms, which should be enough to burn out fuse:

Zero999:

--- Quote from: ratatax on August 25, 2019, 08:18:05 am ---Hello,
I'm designing a pcb for a device that will get 12V DC from a power adapter. The power adapter itself is well protected against short circuits, over voltage and is certified in almost all countries.
I'd like to know if a fuse is still needed on my 12V input. Would you put one ?

I can tell my users to only use the provided adapter so I'm not faulty if they use a shitty one that catches fire, but I'd like to know what is the best practice here, what choice would you take for your project.

--- End quote ---
How thick is the cable?

If the power adaptor can output a higher current, than the cable can take, before it cuts out or current limits, then a fuse is required.

For example, suppose your adaptor is only 1A and the cable has a cross-sectional area of 0.52 and insulation which can take 60ÂșC, then there's no need for a fuse, as the cable will be able to handle the short circuit current. On the other hand, if the power supply is capable of 15A, then you definitely need a fuse, as the cable will start to smoke, if there's a short circuit.

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