[sdiy] Polyfuse Tripping Current values

[Barry Klein]

Module based lets most everything else still operate - but the polyfuse
could perhaps cycle - depending on what caused the failure to begin with.
Supply based shuts down the whole system without you knowing the cause.
Polyfuses usually are slow acting and won't protect against overvoltage
shorts and the like.  I wonder how often anyone has one go.
Module based fuses may be more cost effective and a sure way to know who
the "bad guy" is...  But it sorta depends if that is what you want to happen
vs an op amp going and you have a spare and pop it in and be good to go.

Barry


-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of blacet at blacet.com
Sent: Monday, January 10, 2011 11:07 AM
To: Graham Atkins
Cc: SDIY List
Subject: Re: [sdiy] Polyfuse Tripping Current values

I use the polys on EACH module PCB. That way you can dial in the value for
each module and any faults will cause that module to "blow".

I can see problems trying to do a whole rack of modules at once. What
happens if you want to rearrange your modules?

> On 10 Jan 2011, at 16:12, Justin Owen wrote:
>
>> Hey all,
>>
>> Belated Christmas & HNY wishes to everyone - hope you all had good/
>> fun/safe (or recoverable...) times.
>>
>> Based on the advice I've had here I'm going to add polyfuses to this
>> power supply breakout module I'm working on.
>>
>> My Analogue Systems rack has each rail divided into 3 busses - each
>> with a 1A fuse on, my Doepfer rack uses a single 400mA fuse on the
>> mains transformer AFAIK.
>>
>> So, first up - considering a) that I'd like to build a breakout
>> module for each rack and b) that I've no idea what current draw the
>> prototype circuits that might be powered off it will have - what
>> Tripping Current should I specify for the Polyfuse to be
>> *reasonably* safe?
>>
>> ...and secondly, is there a rule of thumb for specifying a Tripping
>> Current for a circuit that I *do* know the current draw of?
>
> You build the racks first thern measure the current draw, you can't
> "specify" something unknown.
>
> Graham
>
>
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