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'[EE] Fuses Required - 1 or 2?'
2011\12\01@125041 by Gordon Williams

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Darn, caught again.  Tag added.


> Hi,
>
> I'm going to be running a 48V (at 3W) boost converter and a 5V (at 5W)
buck
> converter off of a 12 V battery.
>
> Is it a good practice to have a fuse on both supplies' inputs or just 1
for
> the system?
>
> >From a bit of research my understanding is that I should use a slow blow
> fuse to handle the inrush current into the converters and I should size
the
> fuse at 150% the nominal rate.  Is that in the right ball park?
>
> Gordon Williams
>
> -

2011\12\01@130952 by jim

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I'm not sure what the industry standard might be, or what is dictated
by whatever governing body, but my
preference would be to fuse both supplies individually.   To me, it
makes sense to fuse each individually.
This might help troubleshooting later somewhat by possibly telling you
which supply was drawing too much
current, and therefore might tell you which circuits to concentrate on
if and when it happens.
If this is a very high volume product, fusing each might add enough
cost that it might be deemed
uneconomical.  If it is a low volume product, the cost won't be as
scrutinized.
If it's a onesey - twosey product, the extra cost won't really be felt
at all.

This is my take on your question.  
Regards,

Jim

> ---{Original Message removed}

2011\12\01@143615 by Matt Bennett

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On Thu, December 1, 2011 12:09 pm, spam_OUTjimTakeThisOuTspamjpes.com wrote:
{Quote hidden}

>> ---{Original Message removed}

2011\12\01@152445 by Dave Tweed

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Gordon Williams wrote:
> I'm going to be running a 48V (at 3W) boost converter and a 5V (at 5W) buck
> converter off of a 12 V battery.
>
> Is it a good practice to have a fuse on both supplies' inputs or just 1 for
> the system?

It isn't a question of "practice" -- it's a question of what makes sense for
the particular system.

Does it make sense, or conversely, present any risk to have only one converter
working? If you want the whole thing to go dead if there's a fault on either
converter, then use a single fuse.

On the other hand, you must also consider whether an overload on one converter
can reasonably be expected to blow a common fuse. If that fuse is too large,
then it may not make sense, and you'll actually need to create a seperate
interlock system that shuts everything down in the case of a fault.

There's no simple blanket answer for this sort of question.

-- Dave Twee

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