Fuses: which can be different from rated specs, Amps or Voltage?

[PetunZ]

I blew a fuse on a Sony Audio Receiver a while back. I wanted to replace the fuse and I wasn't sure which to get. I need a 3.15Amp 125V fuse. My problem is this:

I went to a Radio Shack near my house, and they said that the voltage doesn't matter, only that the current needs to be near the rated current. He suggested going with a 3A 250V fuse instead of a 4A 250V fuse just to be "safe". Ergo, I bought a 3A 250V fuse (set of 4).

I put it into my device and it subsequently blew (after plugging it into the wall socket).

Then I went to a different Radio Shack and asked the clerk and he said that the voltage must be the same, although current can be interchanged, depending on how much "safety" I want to give my receiver. So now I bought a 4A 125V fuse, and I'm wondering if I've already blown my circuitry with the 250V fuse :/ Any advice/suggestions?

 

[Navid]

Originally posted by: PetunZ
I blew a fuse on a Sony Audio Receiver a while back. I wanted to replace the fuse and I wasn't sure which to get. I need a 3.15Amp 125V fuse. My problem is this:

I went to a Radio Shack near my house, and they said that the voltage doesn't matter, only that the current needs to be near the rated current. He suggested going with a 3A 250V fuse instead of a 4A 250V fuse just to be "safe". Ergo, I bought a 3A 250V fuse (set of 4).

I put it into my device and it subsequently blew (after plugging it into the wall socket).

Then I went to a different Radio Shack and asked the clerk and he said that the voltage must be the same, although current can be interchanged, depending on how much "safety" I want to give my receiver. So now I bought a 4A 125V fuse, and I'm wondering if I've already blown my circuitry with the 250V fuse :/ Any advice/suggestions?

The voltage of a fuse is a safety measure. After a fuse blows, it is supposed to block the current. But, if the voltage is too high, there may be some current flowing through parasitic capacitance. That is why you need to use a fuse with a voltage setting equal to or higher than what you need.

It is the current setting of the fuse that is very important. When the fuse is not blown and the circuit is working, the fuse is supposed to allow the current to flow. But, it is supposed to blow if the current flow goes over the setting. The current is the maximum current that the device is supposed to draw. You are not supposed to use a fuse with a higher current setting. If you do, you are risking damage to your device.

Your device may require calibration or a fix. It sounds like it draws more current than it should. That is why the new fuse blew. Putting a 4A fuse in it and turning it on is a mistake. I am surprised that someone at RadioShack told you to do that!!!!

 

[lenjack]

It's Radio Shack...why be surprised?

 

[PetunZ]

Navid,

Thanks for the quick response. So should i return the 4A-125V fuse pack and look for a 3A-125V fuse? RadioShack didn't have any 3A-125V ones, so I guess I'd have to go somewhere else to find one.

 

[Navid]

Originally posted by: PetunZ
Navid,

Thanks for the quick response. So should i return the 4A-125V fuse pack and look for a 3A-125V fuse? RadioShack didn't have any 3A-125V ones, so I guess I'd have to go somewhere else to find one.

I meant that I thought that the 3A 250V fuse should have worked fine.
The reason it does not work, I suspect, is that something is wrong with the receiver that draws more current that it should. Unless you have made a mistake and the receiver needs a higher current fuse.

How do you know that it needs a 3.15A fuse? If you are sure about that, the only thing I can think of to do is to take it for repair and or return it for a replacement.

Is it still under warranty?

 

[Lonyo]

If you NEED 3.15 amps, then getting a 3A fuse wouldn't work, because you would be drawing >3A, so the 3A fuse would blow.
A fuse is supposed to blow when you go over its rated voltage, and you have to use a fuse higher thna the voltage you require (obviously).
That's what I was taught IIRC.

 

[JimPhelpsMI]

Hi, Fuse voltage has only to do with how big a gap is blown in the element. Higher voltage, larger gap. Fuses are mostly used to prevent a fire if a short occurs, so usually something else is wrong if it blows again. If a device and fuse are many many yrs old sometimes the fuse get "fatigued" and blows for no good reason. A new fuse usually fixes those. Jim

 

[PetunZ]

The circuit board clearly states that it uses a fuse that is 3.15A-125V. Also, the fuse itself (the one that blew originally -- no pun intended) has 3.15A-125V inscribed onto the metal connections. The sony receiver probably isn't under warranty anymore since it's been almost 5 years since it blew.

I'm still confused as to whether current or voltage is changeable. From what I understood, if the current goes higher than the rated current, then the fuse would blow, cutting off the current so that the wires to the circuit wouldn't melt. What's the difference between these rated voltages? Again, for further clarification, is the 250V or 125V the correct choice? Are they both usable?

Edit -- Since the original fuse rating was 3.15Amps, shouldn't a 3.0Amp fuse be okay? I figured the Sony Receiver wouldn't draw as much as 3.0A since the fuse is only rated to 3.15A. Is that a correct assumption? I was hoping that the receiver itself wasn't blown but I'm guessing that is why the 3A-250V fuse blew too.

Edit #2-- Jim, what do you mean by "how big a gap is blown"?

 

[Navid]

Originally posted by: PetunZ
The circuit board clearly states that it uses a fuse that is 3.15A-125V. Also, the fuse itself (the one that blew originally -- no pun intended) has 3.15A-125V inscribed onto the metal connections. The sony receiver probably isn't under warranty anymore since it's been almost 5 years since it blew.

I'm still confused as to whether current or voltage is changeable. From what I understood, if the current goes higher than the rated current, then the fuse would blow, cutting off the current so that the wires to the circuit wouldn't melt. What's the difference between these rated voltages? Again, for further clarification, is the 250V or 125V the correct choice? Are they both usable?

Edit -- Since the original fuse rating was 3.15Amps, shouldn't a 3.0Amp fuse be okay? I figured the Sony Receiver wouldn't draw as much as 3.0A since the fuse is only rated to 3.15A. Is that a correct assumption? I was hoping that the receiver itself wasn't blown but I'm guessing that is why the 3A-250V fuse blew too.

Edit #2-- Jim, what do you mean by "how big a gap is blown"?

125V or 250V should both work as long as the required fuse is rated 125V. AS long as you do not go below 125V, you are OK.

The current should be 3.15A. Definitely not more. I made the exact same thinking as you did thinking that the receiver does not draw even 3A and the 3.15A rating is only for safety margin. However, if the receiver really draws 3A and the safety margin of the fuse is only 0.15A, then, the 3A fuse would not work and you would need a 3.15A fuse. But, I highly doubt that.

So, in short, I think that a 3A fuse should have worked. Since it didn't, I suspect that something is wrong with the receiver that makes it draw more than 3A causing the fuse to blow.

 

[PetunZ]

I see. Thanks for your help.

Oh, a pretty dumb question: Does the orientation matter when installing the fuse? Like, is there a clear positive and negative or can I just put it in either way...

 

[Zepper]

A 3A fuse should have worked fine in your situation. The fact that it blew again means there is a short in your equipment. That is why the fuse is there in the first place - to prevent a simple component failure (short circuit) from becoming a conflagration. Better a fuse than your house, don't you think? Just get the receiver repaired at a reliable shop - probably just a transistor or IC needs replacing so it shouldn't get too expensive. Locating a short is easy.

.bh.

 

[Jeff7]

Originally posted by: PetunZ
I see. Thanks for your help.

Oh, a pretty dumb question: Does the orientation matter when installing the fuse? Like, is there a clear positive and negative or can I just put it in either way...

Nope, fuses aren't polarized. They're basically a piece of wire inside a glass tube.

 

[montag451]

Basically, if your equipment is blowing at 3 amp, might as well stick a 4 amp in and see what happens.

If it blows the equipment, its pretty much confirming that it is dead anyway, and so, it is saving you some valuable time.

 

[Jeff7]

Originally posted by: montag451
Basically, if your equipment is blowing at 3 amp, might as well stick a 4 amp in and see what happens.

If it blows the equipment, its pretty much confirming that it is dead anyway, and so, it is saving you some valuable time.

However, I wouldn't recommend running it for extended durations with a 4 amp fuse - something might overheat when you're not paying attention.


Check out Hosfelt Electronics. Search for part number 31-278.
GMA type fuse, 5mm diameter x 20mm long, 250V, 3.15A. $5 minimum order though. They've got all kinds of nifty stuff - even aluminum mesh fan filters, and chrome plated fan grilles.

 

[Navid]

Originally posted by: montag451
Basically, if your equipment is blowing at 3 amp, might as well stick a 4 amp in and see what happens.

If it blows the equipment, its pretty much confirming that it is dead anyway, and so, it is saving you some valuable time.

With all due respect, this is not a good advice.

You may have a failed component. By putting an over-rated fuse in and turning it on, you risk damaging a lot more.

 

[VirtualLarry]

Oh, and never, ever, replace an automotive (or truck) wiring fuse, with a regular wire, even for very short travel distances... (dont ask. )

FYI, replacement fuses should have the same current rating, and same or higher voltage rating.

(If the actual current drawn by the device is lower than the fuse rating by far, you can usually get away with a slightly lower-current one too, at the risk of it being a little bit trigger-happy and blowing early. A fuses' current rating is generally for safety, to prevent overcurrent from heating up wires/components and starting a fire. Likewise, you can use a slightly higher current rating, at the risk of a lesser "safety margin" for the device, and likely also cause it to no longer meet the original factory UL-approved specs either.)

Fun fact: the original model of SegaCD drives used to have a problem, they would blow their internal soldered fuses for no real reason. Replace them, and generally they work fine. I fixed a bunch once for a fellow that owned a used game shop, he got in quite a few used ones with that issue, that's how I know.

 

[oboyco]

Reminds me of the two guys in a pickup at night when the headlight fuse blew. They found a .22 cal cartrige on the floor and put it in the fuse holder. Everything fine for about five minutes, then the cartrige went off and hit the driver in the testicle. He drove off the road. They lived.

Actually as has been said before, the voltage doesn't matter as long as it's rated at or above the input voltage, an amp is an amp.
Fuses just don't blow for no good reason, there is some kind of a problem for sure if a fuse blows after replacement. Going to a higher rating is not a good idea (fire insurance paid up?), less is ok.

 

[PetunZ]

Thanks for all the help guys. I ordered the fuse from that website along with some rechargeable batteries to put it over the $5 mark. We'll see how it goes.

 

[Zepper]

I'm thinking that's a pretty small fuse for a receiver. How many total Watts output does it have, and how many amplifier channels? Does it give the voltage/amps rating on a plate on the back or bottom?

.bh.

 

[ribbon13]

3A 120v input....

that's about right for a 5wpc 8ohm class D stereo amp. Seriously... WTF?

Do yourself a favor and pick up a Marantz 1060 on ebay.