Any electronics people on here?...

[Wobblers]

Cheers. The picture in the first message was for illustration only (i.e. just to show you what type of fuse I was referring to...Do they call it a 'push-through' resistor?, i.e. because you can push it into an electronic 'bread-board?).
How do you know it is 0.25W just by looking at it?

I have a schematic describing the resistor as 2R2 NRF25.

It's a through-hole component because the wire leads go through holes in the printed circuit boards and are soldered on the other side. Electronic components come in standard packages - carbon resistors usually come in brown and the shape is that of a 0.25 W resistor. It's best to measure the length of the resistor and compare it to the dimensions that SloMo gave to be sure of the power rating. A quick google, and it seems that NRF25 is a resistor series manufactured by Philips, though there seems to be remarkably little information on it, so it's probably not a fusible resistor. You could probably get away with replacing it with a higher power resistor - though if the component's in the power supply section (the bit where the mains comes in - there'll be a transformer nearby) I'd ask for advice on an electronics forum from people who know what they're doing rather than this amateur!

 

[Wobblers]

Before replacing any resistors, I'd be trying to find out what caused the old ones to burn out in the first place!

There's often a large surge when you switch things on as capacitors charge up and transformers are energised. It's not uncommon to see fuses blow as quite a lot of electronics designers forget about this and only consider the steady state conditions. If it were me, I'd probably stick an oscilloscope across the resistor (after replacing it) to see just how large a current is pulled when it's first turned on: anything over 0.25 A and the resistor is being overloaded, though it wouldn't burn out in such a spectacular fashion until you put an amp or more across it.

 

[Maz]

Well, judging by the size of the resistor, it's a fair bet that it's a 0.5W power rating.
I'm going up to 2W with the replacements, so fingers crossed.
Cheers.

 

[Wobblers]

Well, judging by the size of the resistor, it's a fair bet that it's a 0.5W power rating.
I'm going up to 2W with the replacements, so fingers crossed.
Cheers.

Good luck!

Remember the burnt finger rule: if it gets so hot it burns your finger, there's probably something wrong! Though don't try that when it's powered up!! Turn it on for a few seconds, turn it off at the mains - and unplug to be sure. Capacitors can store quite a wallop for some time, so take care. The "one hand in a pocket" trick is also handy to know: if you keep one hand safely in a convenient pocket you're less likely to get an electric shock and very much less likely to get a fatal shock across the heart. Take care!

 

[ColinJ]

This reminds me too much of a friend who used to put 13A fuses in all his plugs because 'the low amperage ones keep blowing'!

Er, yes, that would be the designed function which prevents the spontaneous combustion of your ring main, wouldn't it?

 

[snailracer]

This reminds me too much of a friend who used to put 13A fuses in all his plugs because 'the low amperage ones keep blowing'!

Er, yes, that would be the designed function which prevents the spontaneous combustion of your ring main, wouldn't it?

The fuse in the plug protects the cord. The ring main is protected by the fuse in the junction box.

 

[snailracer]

Unfortunately that would half the resistance (http://www.sengpielaudio.com/calculator-paralresist.htm)

Just buy the highest power rating there is, having too high wouldn't compromise anything, just would cost a few pence more.

One could parallel 2 resistors, each of double the resistance of the one being replaced, which would double the power dissipation without changing the equivalent resistance seen by the circuit. This could be extended to 3 parallel resistors, each 3X the resistance of the resistor being replaced and so on. The problem with this is that a lot of the power is actually dissipated in the metal tracks the resistor is soldered to, so the tracks might burn up instead.

 

[ColinJ]

The fuse in the plug protects the cord. The ring main is protected by the fuse in the junction box.

Actually, you are correct. Assuming that somebody hasn't fixed the problem of those fuses blowing by replacing them with nails ...

 

[Maz]

One could parallel 2 resistors, each of double the resistance of the one being replaced, which would double the power dissipation without changing the equivalent resistance seen by the circuit. This could be extended to 3 parallel resistors, each 3X the resistance of the resistor being replaced and so on. The problem with this is that a lot of the power is actually dissipated in the metal tracks the resistor is soldered to, so the tracks might burn up instead.

There's not enough space to have resistors in parallel, but I take your point. Thanks.

 

[subaqua]

Actually, you are correct. Assuming that somebody hasn't fixed the problem of those fuses blowing by replacing them with nails ...

have seen that in a pub in Minera - called out to " no power and lights" what they meant to say was 2 wall lights blown off the wall with black flashmarks, a light switch welded in the closed position and a blown DNO cut out fuse . stupid buggers had put a wire nail in the lighting fuse after gradually increasing the fuse wire size over the last few months as the fault "developed" took 10 minutes to fix the light fittings but cost the pub a large fee from MANWEB

 

[ColinJ]

I was on a cycling holiday on the Costa Blanca and my group had stopped off at a seaside cafe at Javea, north-east of Benidorm.

After lazing around in the sunshine drinking coffee for half an hour, I went into the cafe to use their toilet. It was off a gloomy corridor at the back of the cafe. I went into a dingy cubicle-like room and couldn't see a thing so I ran my hand around the wall trying to find a light switch. Suddenly, I found my fingers inside the back of the switch! The front plate was hanging off the wall with all the wiring exposed. Flipping heck - talk about dodgy wiring!

One year later, on another Costa Blanca trip, we called in at the same seaside cafe.

More lazing around in the sunshine drinking coffee and eventually into the cafe to use their toilet. The front of the light switch was still hanging off the wall with all the wiring exposed!