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Fuse selection (blow times)

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Simon:
I am designing a fuse board. A PCB with one connection in and several out individually fused. This is automotive for brushless fans so no large inrush currents. But I am uncertain about the time to blow I should choose.

I seem to have a choice of 5 seconds with 200% current and 60 seconds with 200% current. Unfortunately SMD fuses do not seem to follow any standards in case size so I can't pick one later.

So is 5s too fast? but isn't 60s a bit long? I know that my safer bet is 60s as they will never blow accidentally.

OM222O:
Have you considered using a PTC fuse + fast blow?

if the PTC doesn't manage to reduce / stabilize the current within 5s, that means there is definitely something wrong.

generally a fast blow on it's own should be good enough though.

Simon:
have you ever tried to find 40A SMD PTC? I gave up, they are not popular and expensive. The brushless fans look after themselves so really this is just to satisfy the project requirements.

OM222O:
you didn't mention any current specs  at first :-/O


--- Quote from: Simon on August 23, 2019, 07:38:52 am ---I am designing a fuse board. A PCB with one connection in and several out individually fused. This is automotive for brushless fans

--- End quote ---

most car batteries are rated for upto 200A max ... you can't have "several fans" each drawing 40As if you also want the car itself to do anything ... also I'm curious what kind of automotive fan draws 40A? that's more inline with electric jet engines  :-DD

anyhow, if they have built in protection and you just want to satisfy the project requirements then it should be obvious ... just go for the 60s ones since it doesn't matter?

Simon:

--- Quote from: OM222O on August 23, 2019, 09:32:30 am ---you didn't mention any current specs  at first :-/O

most car batteries are rated for upto 200A max ... you can't have "several fans" each drawing 40As if you also want the car itself to do anything ... also I'm curious what kind of automotive fan draws 40A? that's more inline with electric jet engines  :-DD


--- End quote ---

Oh well, I guess I must be crazy using several 30+A fans :palm:

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