Fuse CONFUSE

keyboardcowboy · 09-19-2009, 07:47 AM

recently my laptop power adaptor died,when i tested the external fuse (5A-250V) it was blown not knowing that the bridge rectifier has shorted i replaced the fuse with a wire and plugged it back in,there was a spark and the adaptor died again.When i opened the adaptor i found another fuse with a rating of 3.15A-250V which was also blown..Now the confusion is that shouldn't the internal fuse have blown out first due to lower rating..If it had blown first there wouldn't have been a spark when i replaced the external fuse with a wire...Both fuses are in series.

**Krankshaft** · 09-19-2009, 11:23 AM

Where is this second fuse located on the secondary?

Doesn't make much sense to have 2 fuses on the primary.

Toasty · 09-19-2009, 02:19 PM

Are you trying to start a fire?

Primary (5A) died when bridge blew, internal died when you BYPASSED the first fuse with a WIRE!

If you're lucky, you didn't fry everything in the adapter. If your not, crank out the bucks to buy a new one.

They're not kidding, and it's not a suggestion nor recommendation when they say "For continued protection against risk of fire, Replace with same type and rating of fuse".

Toast

keyboardcowboy · 09-19-2009, 05:51 PM

The 5A Fuse is located inside the plug whereas the 3.15A Fuse is located just before the rectifier inside the adaptor..does this means that 3.15A fuse failed to do its job?

kikkoman · 09-19-2009, 06:27 PM

this illustrates that there are FAST and SLOW fuses.

Toasty · 09-19-2009, 09:02 PM

a-Ha! Fused plug. Different interpretation of purpose than "the external fuse...".

That fuse protects the cord, such as in a set of outdoor decoration lighting. If you chop the cord, it blows the fused plug. Typically a quick-blow fuse.

>>does this means that 3.15A fuse failed to do its job?<<
No. It means the excess current drawn was killed by the quick-blow fuse in the cord before there was enough time for the slow-blow fuse in the adapter to react. It's a matter of milliseconds, but it's enough to take out one before the other.

When you "hot-wired" it, the internal did its job to protect what's now left of the adapter.

Pictures and more info (make, model, etc.) will help, if you're keen on fixing it.

Toast

keyboardcowboy · 09-20-2009, 09:01 AM

well,i got it fixed,but was confused in the sequence in which the fuses went out..its clear now..thanx

09-19-2009, 07:47 AM	#1
keyboardcowboy Member Join Date: Apr 2006 Posts: 67	Fuse CONFUSE recently my laptop power adaptor died,when i tested the external fuse (5A-250V) it was blown not knowing that the bridge rectifier has shorted i replaced the fuse with a wire and plugged it back in,there was a spark and the adaptor died again.When i opened the adaptor i found another fuse with a rating of 3.15A-250V which was also blown..Now the confusion is that shouldn't the internal fuse have blown out first due to lower rating..If it had blown first there wouldn't have been a spark when i replaced the external fuse with a wire...Both fuses are in series.

09-19-2009, 11:23 AM	#2
Krankshaft Super Moderator Join Date: Jan 2007 City & State: New Jersey, USA Posts: 2,292	Re: Fuse CONFUSE Where is this second fuse located on the secondary? Doesn't make much sense to have 2 fuses on the primary. __________________ Elements of the past and the future combining to make something not quite as good as either.

09-19-2009, 02:19 PM	#3
Toasty Badcaps Veteran Join Date: Jul 2007 City & State: East Coast, USA Line Voltage: 220-221 I'm a: Professional Tech Posts: 3,917	Re: Fuse CONFUSE Are you trying to start a fire? Primary (5A) died when bridge blew, internal died when you BYPASSED the first fuse with a WIRE! If you're lucky, you didn't fry everything in the adapter. If your not, crank out the bucks to buy a new one. They're not kidding, and it's not a suggestion nor recommendation when they say "For continued protection against risk of fire, Replace with same type and rating of fuse". Toast

09-19-2009, 05:51 PM	#4
keyboardcowboy Member Join Date: Apr 2006 Posts: 67	Re: Fuse CONFUSE The 5A Fuse is located inside the plug whereas the 3.15A Fuse is located just before the rectifier inside the adaptor..does this means that 3.15A fuse failed to do its job?

09-19-2009, 06:27 PM	#5
kikkoman Badcaps Veteran Join Date: Jul 2007 City & State: Heart of Darkness Posts: 683	Re: Fuse CONFUSE this illustrates that there are FAST and SLOW fuses. __________________ "Every normal man must be tempted at times to spit on his hands, hoist the black flag, and begin slitting throats." - H.L. Mencken

09-19-2009, 09:02 PM	#6
Toasty Badcaps Veteran Join Date: Jul 2007 City & State: East Coast, USA Line Voltage: 220-221 I'm a: Professional Tech Posts: 3,917	Re: Fuse CONFUSE a-Ha! Fused plug. Different interpretation of purpose than "the external fuse...". That fuse protects the cord, such as in a set of outdoor decoration lighting. If you chop the cord, it blows the fused plug. Typically a quick-blow fuse. >>does this means that 3.15A fuse failed to do its job?<< No. It means the excess current drawn was killed by the quick-blow fuse in the cord before there was enough time for the slow-blow fuse in the adapter to react. It's a matter of milliseconds, but it's enough to take out one before the other. When you "hot-wired" it, the internal did its job to protect what's now left of the adapter. Pictures and more info (make, model, etc.) will help, if you're keen on fixing it. Toast

09-20-2009, 09:01 AM	#7
keyboardcowboy Member Join Date: Apr 2006 Posts: 67	Re: Fuse CONFUSE well,i got it fixed,but was confused in the sequence in which the fuses went out..its clear now..thanx

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