Looking to replace a blown fuse

Thread Starter

SeanV123

Joined Nov 12, 2020
68
Hello, recently a 315mA glass fuse blew in my soldering iron and I'm looking to replace it. Since there is no electronic hardware stores near me I have resorted to getting a fuse from an appliance. My question is, which sort of household appliances would have a 315mA fuse?
 

Ian0

Joined Aug 7, 2020
2,227
A small one! Before you go to a lot of trouble finding one, why did the original fuse fail? If you soldering iron element has failed or shorted to ground, your search will be in vain!
 

Thread Starter

SeanV123

Joined Nov 12, 2020
68
A small one! Before you go to a lot of trouble finding one, why did the original fuse fail? If you soldering iron element has failed or shorted to ground, your search will be in vain!
I switched it on and the fuse just blew. I took it out and tested it with a multimeter and it wasn't working. Also i can see it blew as you can see the blackened area around the fuse
 

KeithWalker

Joined Jul 10, 2017
1,786
Hello, recently a 315mA glass fuse blew in my soldering iron and I'm looking to replace it. Since there is no electronic hardware stores near me I have resorted to getting a fuse from an appliance. My question is, which sort of household appliances would have a 315mA fuse?
The fuse is to protect the supply from short circuit and overload in the Iron. Check the resistance of the element and check for a short to ground before you use it again. 315mA is an odd value for a fuse. I doubt whether you will find one in a household appliances. A half amp glass fuse should offer you ample protection for a simple device like a soldering Iron and should be available at your local hardware store.
 

Thread Starter

SeanV123

Joined Nov 12, 2020
68
The fuse is to protect the supply from short circuit and overload in the Iron. Check the resistance of the element and check for a short to ground before you use it again. 315mA is an odd value for a fuse. I doubt whether you will find one in a household appliances. A half amp glass fuse should offer you ample protection for a simple device like a soldering Iron and should be available at your local hardware store.
Thank you. Yes I have checked everything and it is definetly the fuse. Are you sure a 500mA fuse will work okay? Will it not draw too much current into the iron and burn the components out ?
 

KeithWalker

Joined Jul 10, 2017
1,786
Thank you. Yes I have checked everything and it is definetly the fuse. Are you sure a 500mA fuse will work okay? Will it not draw too much current into the iron and burn the components out ?
The the value of the fuse has no effect on how much current the soldering iron uses. It is just there blow if a fault causes the current goes too high.
 

Thread Starter

SeanV123

Joined Nov 12, 2020
68
315mA is a very standard value for a 5x20mm fuse.

Is it a fast-blow or time-delay? If it is for a soldering station with a transformer it's probably time-delay. If it's a mains voltage iron, then it is fast-blow.
Yeah it's a mains voltage as I've it plugged into a socket on my house
 

LesJones

Joined Jan 8, 2017
3,179
As you are asking about a fuse I do not think you are capable of verifying that nothing is faulty in you soldering station. Is there a transformer in the soldering station base unit ? What is the wattage rating of your soldering iron /station ?

Les.
 

Tonyr1084

Joined Sep 24, 2015
5,977
Fuses blow for two reasons: First, they can blow from fatigue and old age. They're similar to a light bulb in that they can get warm and expand, then cool and contract. Over time they can fatigue to the point of failure. The second reason why they blow is because an over-current event took place. Sometimes it's a one-off event, but that's extremely rare. The bad news is that if it happened once it will happen again. The main reason why a fuse blows is because something has failed in circuit causing an over-current to exceed the fuse rating.

Suppose you have a circuit that regularly draws half an amp. If you put a 1 amp fuse in circuit the circuit will still draw half an amp. Even if you put a 10 amp fuse in circuit, the circuit will still draw half an amp. But when something fails - goes to a hard short, or even a soft short, the circuit can suddenly draw more than one amp. Even more than 10 amps, assuming the power source is capable of that much current. Mains voltage is typically on a circuit breaker of either 15 or 20 amps. So if your circuit goes to a dead short and you have a 40 amp fuse, the fuse won't blow but the breaker will trip.

Now - before you start replacing fuses, find out what caused the original fuse to blow. Otherwise you're exposing the electronics (assuming it has electronics) to further potential damage.

Now: 315mA at 120VAC is 37.8 watts. So your soldering iron, if it ONLY has a heating element in it, will be less than 38 watts. I've heard of 40 watt irons, but that would require a higher amp fuse. Some soldering irons have a two wire plug. In that case the tip of the iron is not grounded. IF your iron has a three wire plug then the tip is grounded. If so - and you attempt to solder on something that is plugged in, there's a chance the fuse could have been blown out because of an over-current event caused by touching a live circuit without current limiting. To be honest, we don't know WHAT iron you own. you've given no pictures, no model number, no brand name, nothing. So all we can do is try to cover ALL bases in the Hopes to be correct in Our diagnosing of the problem. Really, we need more information about the iron and what you were doing when the fuse blew.
 

Ian0

Joined Aug 7, 2020
2,227
If so - and you attempt to solder on something that is plugged in, there's a chance the fuse could have been blown out because of an over-current event caused by touching a live circuit without current limiting.
Yes, that should blow a fuse, but not the fuse in the soldering iron.
 

Thread Starter

SeanV123

Joined Nov 12, 2020
68
Fuses blow for two reasons: First, they can blow from fatigue and old age. They're similar to a light bulb in that they can get warm and expand, then cool and contract. Over time they can fatigue to the point of failure. The second reason why they blow is because an over-current event took place. Sometimes it's a one-off event, but that's extremely rare. The bad news is that if it happened once it will happen again. The main reason why a fuse blows is because something has failed in circuit causing an over-current to exceed the fuse rating.

Suppose you have a circuit that regularly draws half an amp. If you put a 1 amp fuse in circuit the circuit will still draw half an amp. Even if you put a 10 amp fuse in circuit, the circuit will still draw half an amp. But when something fails - goes to a hard short, or even a soft short, the circuit can suddenly draw more than one amp. Even more than 10 amps, assuming the power source is capable of that much current. Mains voltage is typically on a circuit breaker of either 15 or 20 amps. So if your circuit goes to a dead short and you have a 40 amp fuse, the fuse won't blow but the breaker will trip.

Now - before you start replacing fuses, find out what caused the original fuse to blow. Otherwise you're exposing the electronics (assuming it has electronics) to further potential damage.

Now: 315mA at 120VAC is 37.8 watts. So your soldering iron, if it ONLY has a heating element in it, will be less than 38 watts. I've heard of 40 watt irons, but that would require a higher amp fuse. Some soldering irons have a two wire plug. In that case the tip of the iron is not grounded. IF your iron has a three wire plug then the tip is grounded. If so - and you attempt to solder on something that is plugged in, there's a chance the fuse could have been blown out because of an over-current event caused by touching a live circuit without current limiting. To be honest, we don't know WHAT iron you own. you've given no pictures, no model number, no brand name, nothing. So all we can do is try to cover ALL bases in the Hopes to be correct in Our diagnosing of the problem. Really, we need more information about the iron and what you were doing when the fuse blew.
Hi, I have a weller wtcp 51 iron. It was given to me by a friend recently who had it for a few years. I assume the fuse just wore out as you said.
 

djsfantasi

Joined Apr 11, 2010
7,693
Yes, that should blow a fuse, but not the fuse in the soldering iron.
Why not? Assuming that the fuse is in the hot line AND the plug isn’t polarized, if the plug is reversed, the fuse is on the neutral line. From plugged in device hot, through the fuse, and to neutral, is a dead short. The device neutral is protected for 15A; the iron is protected for 0.5A. The iron fuse will blow.
 

Thread Starter

SeanV123

Joined Nov 12, 2020
68
And isn’t the soldering iron plugged into the soldering station? What if the heating element failed and shorted out? Or...
Yes that is an option I'll have to investigate. However as previously stated, I removed the fuse and I can confirm it blew. Now I've to investigate why it blew. Thank you very much.
 

Tonyr1084

Joined Sep 24, 2015
5,977
Some of the features:
Features & Benefits

• Supply 220 V in / 24 V out
• Temperature accuracy ±10% of nominal temperature
• Antistatic Tip earthed via mains lead
• Safety transformed Class II 230V/24V to 50 Hz
• Power output: 55 W

This means it has an internal transformer. The iron itself runs on 24V. The tip is grounded to earth ground via the power cord. So we can assume the Weller fuse didn't blow because of an accidental exposure to an external current source. So the failure is from within. Since I didn't find a schematic on the machine I can't begin to guess where the failure might be. But it would seem that it has something to do with either the 220VAC input or the 24V output. And I don't know if that's AC or DC. IF it's DC then there's a possibility the rectifier could have blown the fuse. But it could also be a bad cap or some other electronic component inside the base unit.
 
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