Fuses?!?

G

Grymer

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Sooo. I've build a portable sound system and this just happened. I've build a pack of 18650 batteries (11s3p) with a total voltage of 46,2V. I've used a car fuse for the amplifier, but all of a sudden - The amp started bursting fire. I cut the connection between the battery and amp and the fire went out.

Now. I thought the fuse would've blown, but apparently not. I've used a 15A car fuse, but wondered if I should find something else, now that I'm working with 48V and not 12V. I'm from Denmark, Europe and would like a British or Chinese supplier (If you intend on linking items I should go for)

The amp is rated at 2x500w but probably only use 250w pr channel at peak.
 
What voltage is the amp rated for ?

We like pictures here .....
 
I am more curious about the amplifier Ive been in the audio game for some time and have never really come across amps with a native voltage that high. Most always 12v or AC voltage. You sure you didnt need to build a 3s11p pack?

In any case, always look at the voltage rating for the fuse most are rated for 32V DC. Exceeding that voltage you could end up with arching.
 
The car fuse is 32VDC, Thats most likely not the problem. You bought a chinese amp that was crap is my guess :p

15A at that voltage is 700W. doesnt take much to blow it. I would have used a 5A fuse at most!
 
Voltage range is not too relevant in a fuse. It's the current that matters.

Maybe the amplifier was designed for a lower voltage ? In that case, if powered from more, it will burn no matter the fuse you use.
 
Car fuse might arc, ie not cleanly blow, if their rated voltage is exceeded.

We need to know what voltage the amp supply rating is (and/or make & model)!

The batteries might have lower impedance than the amp is used to resulting in higher current peaks in the transistors, etc if driving speakers hard.
 
The amp is Chinese but they're pretty good quality.
https://www.parts-express.com/sure-...audio-amplifier-board-compact-t-amp--320-3369

The board can handle the voltage just fine. The battery pack is a pack I build myself.

I think what might've happened is a short connection. I wasn't around myself when it happened but my friend told me that a fire the size of a thumb bursted out next to one of the speaker outputs on the board. The plus and minus cables looked like they've been shaken out of the terminal over time, and might've touch eachother.

Back to the fuse. The amp was on without music running when it happened. I've held parties twice a week since new year with full volume for 2 hrs atleast and never experienced this or any other problems. Should I get a lower-rated fuse to avoid a fire hazard in the event of a short? Right now it's a 15A fuse but I might look for 10 or 8A instead.
 
Is the 15a fuse the recommended size?
 
Its nice that all are discussing the fuse, but since the fuse did NOT blow it had not anything to do with his fire. Whatever this caused, its not the fuse.

Is a Class D amplifier, what about the speakers, have they been connected, is that possibly necessary ?

Ops, first read then write :D :D
 
So it seems shorted output is the likely cause.
As often happens, the output stage "blew to protect the fuse"! Ie the junctions in the transistors are less thermal mass than the fuse & blow first.
Like daromer suggests maybe check the spec for the recommended fuse.
Using proper connectors like XLR or "speakon" speaker connectors helps avoid shorts.
 
Overmind said:
Voltage range is not too relevant in a fuse. It's the current that matters.

Maybe the amplifier was designed for a lower voltage ? In that case, if powered from more, it will burn no matter the fuse you use.
Click to expand...

The voltage range matters from a operating design andsaftey standpoint. There is a reason breakers, fuses, and other saftey devices have a max voltage rating.

The OP did use a fuse which was under rated for the application, it would be unreasonable to expect it to do its job.It becomes unpredictable and may not function outside of its operating range. Arching is most common occurrence.

Either way, I suspect the fuse might have nothing to do with the failure with the amp.
 
Redpacket said:
So it seems shorted output is the likely cause.
As often happens, the output stage "blew to protect the fuse"! Ie the junctions in the transistors are less thermal mass than the fuse & blow first.
Like daromer suggests maybe check the spec for the recommended fuse.
Using proper connectors like XLR or "speakon" speaker connectors helps avoid shorts.
Click to expand...

There are no other connectors on the board than the terminals. But I'll secure it better next time.

Sooo. I guess I'll have to go for a smaller fuse
 
Were you pushing the amp hard when it failed?

I looked at the product... it seems pretty cool. I am also a customer of parts express and find them to be a good reliable vendor. Perhaps reach out to them, maybe you got a defective item.
 
To get back on track. Im almost sure I shorted the connection between the terminals. I am surprised that the fuse didn't burn and would like to know where you get fuses when working with 48V?

Thanks
 
CrimpDaddy said:
Overmind said:
Voltage range is not too relevant in a fuse. It's the current that matters.

Maybe the amplifier was designed for a lower voltage ? In that case, if powered from more, it will burn no matter the fuse you use.
Click to expand...

The voltage range matters from a operating design andsaftey standpoint. There is a reason breakers, fuses, and other saftey devices have a max voltage rating.
Click to expand...
That is correct. Fuses have a rating for Voltage, it comes into question when the fuse tries to break a current. That is easier on AC than on DC, when you have both parameters the DC rating is most probably lower. AC does help to extinguish an arc, with DC you have just to use enough current (and something like 100 Volt) and you can draw an arc nearly endless, means several centimeters or more.
Especially said, the current breaking value of the fuse is not interfered by DC, it just might not be able to break a current when it tries. And the arc which stays has a HOT potential for damage just by heat.

The OP did use a fuse which was under rated for the application, it would be unreasonable to expect it to do its job.It becomes unpredictable and may not function outside of its operating range. Arching is most common occurrence.
Click to expand...

I have looked up the typical (european) car fuse, do you have the same in US ?
It is rated for 40 V.
So you are formally correct again, that voltage is exceeded by the OPs application. It might have still worked, because such a rating surely has a safety area, in that case as ALL those car fuses are rated the same, i suggest the lower amps have a little better switching capability.
But alas, it has not gone that far that the fuse even tried separating/arcing.
 
Cherry67 said:
Its nice that all are discussing the fuse, but since the fuse did NOT blow it had not anything to do with his fire. Whatever this caused, its not the fuse.

Is a Class D amplifier, what about the speakers, have they been connected, is that possibly necessary ?

Ops, first read then write :D :D
Click to expand...

You are correct, although the fuse probably should have blown. The idea of a fuse is to prevent fire in case of failure.
 
If you're trying to protect electronics you need fuses with an amp rating & time constant short enough to blow first before the transistor junction melts, eg "fast blow".
The 3AG type fuses can do 48V & fast blow.
 
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