someone good at electronics.. help needed..

[elusiver]

this is totally un-astro-related.. but thought i'd ask.

Rajah.. ;)

what's the difference between a slow blow and fast blow fuse?

I've got a dead TV, so I opened it up to take a look and it's a blown fuse. From the markings and google i've found it's a 15amp fuse 250v fuse.. checked jaycar and dse but they list 2 types of fuses.. fast and slow blow. I don't know which to use.. can i use either??? any help would be great..

el :)

[netwolf]

Hi Elusiver,

The diffrence is that a slow blow can withstand a transient overload in current. Meaning a high current condition that lasts for a short period. But if the high current is sustained the fuse will blow. Fast blow are the opposite end of the spectrum, where even a short overload conition will blow the fuse.

Here is a good run down on fuses.
http://en.wikipedia.org/wiki/Electric_fuse

Regards
Netwolf

[h0ughy]

El,

my 2C worth
is there anyway you can put up a picture of the fuse, fast blow fuses have generally speaking a thin wire in them, the slow blow has wire wound in the fuse and looks thick. Also the serial number and model number stamped onthe fuse may help to identify it.

[avandonk]

Slow blow is better.They can resist (excuse the pun) transient currents that exceed the rated current before going open circuit.

Odinary fuses will operate (blow) due to recrystallisation of the metal that makes up the thin wire,as they get older.They blow before their rated current is exceeded.

If you are protecting solid state devices,they will protect the fuse.
If you are protecting high current applications,the fuse will protect them.

If this is not clear ask me.

Bert

[Stu]

Slow blow fuses are used when you are expecting the odd current spike but the average current still needs to be below a certain value to stop components over heating or blowing up.
eg. tungston lights, heating, inductive loads (motors, fridges, fluro lights, hand tools)

Fast blow fuses are used when part of the circuit needs to be protected against any voltage higher than a certain value.
eg. most digital circuitry

You will usually find both types, but it sound like the fuse that blew is on the main power input so I'd guess it would have been a slow blow. I'm not sure whether the TV will draw a heap of current at the start to fire up the tube or not, you could always but in a fast blow and see if it lasts or not.

[janoskiss]

If in doubt, replace with fast blow, because that offers the higher level protection of the two.

[elusiver]

thanks for the replies :D

i tried taking a photo of it.. but i can't figure out how to get the macro to work on it.. and not keen enough to wake her up to ask... so sorry couldn't get a better pic..

markings are T3.15AL 250V

it doesn't looks.. well.. normal.. usually they have a wire or strip of metal inside it.. but it looks quite 'solid' and burnt up..

thanks

el :)

[johnno]

Hi All,

Elusiver,
I am an ex Electronics technician,
Your fuse is a thermal (slow blow) 3.15 amp type.
if it has blown,there usually is a reason,and quite often you will find,that when you replace the fuse,it will blow again.
A very good indicator,is if the fuse has simply died of old age.it will just be open in the centre.
If the fuse was killed,it may look black,or have little copper coloured beads inside.

PLEASE be aware a colour tv has lethal voltages inside,EVEN WHEN UNPLUGGED,
There is 25,000 volts up on the final anode,which stays there for quite some time,just waiting for someone to touch it.

2nd thing,your blown fuse may have blown just after the main filter capacitor charged up,(at switch on),and it also has about 340 volts dc,just sitting there,with a great deal of current,which you may feel,when you try to replace your blown fuse,as it now has somewhere to go.YOU

The most dangerous power supply is the microwave oven,they have 2000volts dc at the main filter capacitor,which WILL kill you,in fact it will vaporise,the end of a screwdriver.

I just read it looks all burnt up,I will practically guarantee,it will blow again if you replace it.
You have a problem,either in the internal power supply,or the Degaussing circuit,NOT USER FIXABLE.

PLEASE BE CAREFUL.

Regards.John

[RAJAH235]

Another Tech. totally agrees with John. Your pictued fuse 'Blew Up'. Means a major fault. Do not attempt to repair yourself. :D L.

[MiG]

One of our monitors, an LG CRT, stopped working one day. About a year later I replaced the fuse (a slow blow ceramic, but I couldn't find a ceramic one) and it works fine. The fuse wasn't rooted like the one shown in this thread.
I have no idea why it blew in the first place. Any ideas?

Flyback transformers from thrown out CRTs are cool. I've possibly overloaded one (it doesn't seem to work as well anymore) and wrecked two MJE13007 transistors (high voltage switchmode PS transistors, and they still died) while playing with HV arcs.

[RAJAH235]

Moisture/dead bugs/mice/ants/dust/smoke gunk, etc etc etc........ Needed time to dry out? :shrug: If it's electronic, who knows.......... :poke:
You should ALWAYS replace a blown fuse with the SAME type. DO NOT SUBSTITUTE!
A ceramic fuse will not explode like a glass 1. They are usually sand/glass filled.
HTH. :D L.

[mkk85lam]

This question is totally off-topic, but here goes:
Hi there,
I was wondering if anybody out there has any electrical engineering/electronics experience with using U.S. electronics for a "world-wide multi-voltage" AC100-240V, 50/60Hz type set-up?
The item in question is a dvd player that has the following power supply/fuses etc.-labelled on the internal power supply board.
"T3.15AL/250VAC"-I suppose this is the dual voltage fuse?;
"DG1U 5VDCII 0.25W c RU sa TV-5" and "3A/120A 250V~ DEC china C781 A" on another item- Is this a auto voltage toggle switch?;
The question I have is this:
Question1)
Is this item/dvd player, able to run on "world-wide multi-voltages of AC100-240V, 50/60Hz", as it looks like it is a switch-mode/switching dual-voltage power supply?
Question2)
Would I need to reconfigure or change any of the fusing/internals of this power supply board, in order to make this dvd player AC100-240V?
Question3)
With the T3.15AL/250Vac fuse, does the "T" mean & indicate that its "slow-blow" and able to work on AC100-240V?
Another question:
##Would I need to convert the Fuse to a "T1.6AL/250VAC", if I were to use this dvd player in Australia's power supply, of AC220-240V, 50Hz?##
The spec's sheet say's:
Output power: 42W
Power requirements(voltage): 120V, 60Hz(although they only ever tell us that its just allowed to run on U.S. 120V on these U.S. specified electronics)
Thanks you very much for your help in this matter.
Any or all feedback would be greatly appreciated.
Best Regards,
Mark Lam
email: mkk85lam@hotmail.com
PH:+61+2 9564 0988
mob: +61+419 811 812

[Barrykgerdes]

In the old days before switchmode power supplies transformers needed the correct voltage input.

Modern switch mode power supplies are not so critical as they have an internal feed back that self adjusts the output so that they can work from 100v to 250v mains. Most of the simpler type do not fuse the input side, just the output. If the input side is fused the fuse value will need to be set for the input voltage.

If in doubt read the instructions!

The ceramic type fuses are mostly the HRC type and are filled with a flame retardant for use where explosive gases may be present. and there is a special fuse that many techos carry. A piece of copper/brass that neatly fits the fuse holder. NOT RECOMENDED!

As a side issue on fuses we used to have a transmitter that worked from 400v 3 phase. The wall supply (distribution panel) used HRC fuses and the transmitter 8 amp slow blow. We needed 20 amp HRC's in the main board to handle the turn on surge. Even so "C" phase often blew. This did not stop the transmitter working. Just made it run on 1/2 wave HT.
Peak power was the same but average way down with a great hum on the carrier. Many times I got called out after the maintainers could not find anything wrong. I just went to the main board and changed "C" phase fuse. Problem solved.

Barry