Why do fuses blow?

Mando Commando

Just a quick one peeps - Why does a AEG fuse burn out? Will it happen again? What if I just short it and carry on as normal?

Cheers

Firekitten

Fuses blow because the charge going to it, is higher than the rating.

ie, there is a thin bit of wire inside, that will allow current upto say... 13 amps...

any less... no problem, More? it gets too hot, and it melts, breaking the circuit. its a safety feature.

Short circuiting the safety feature is.... largely useless, however bypassing it as you mean, is dangerous. The gun tends to surge current when there is a fault. thus, continued firing would either blow your motor, gears, or battery into a thousand tiny pieces.

So fuse blows to tell you to stop shooting in the politests way possible. Its for a good reason.

Will it happen again? depends if you fix the problem, or work out why its stopped. Jamms are normally a safe bet, either barrel or in the gearbox. Or it can be random. get a new one (depends on rating it needs) and see if it blows again, if it does, take it to an engineer to fixy.

clubberlang12

Alright Mando....long time no chat!!! Fuses are primarily protective devices. They are rated in amps( what current is measured in). The thin strip of metal in the fuse has a current rating .ie., it can safely carry a certain amount of amps before it will break because of the heat generated by the current passing through it. The diameter of the fuse determines its rating but the difference between 13amp or l;ets say 25amp is neglegible to the naked eye. The fuse is there to protect the motor from burning out from excessive current being drawn. You can bypass the fuse if you want but primarily the fuse is there for a reason. Also will depend on the size battery used as to the amount of current potentially passing through the fuse. /short term it is a solution but you carry the risk of motor damage long term dude.

Mando Commando

Cool, I wonder why suddenly there was too much load on the fuse? Battery problem? Both AEG and battery are well used.

Mando Commando

Well Clubber, just saw your post there after I posted, cheers bud

clubberlang12

No problem dude. First off, check your fuse.....it's rating, whether it is damaged. May not hve broke due to an over-load. Those fuses are brittle enough and the caps breaking either end will cause an open circuit. Next check your wiring for any breaks or open circuits. If after that all is sound, next step is the motor. If the motor is faulty or is getting jammed, ie...not being able to rotate or finding resistance when rotating it cause more current to be drawn. I would doubt it is the battery causing a surge unless it is shorting along the cables from the battery. If ya want to use my multi-meter just give us a shout.

Mando Commando

AEG is open in front of me now - spotted a little pinch on one of the wires in the stock. Would that do it do ya reckon? No metal in there for it to touch. Also a couple of previous one that are patched up with electrical tape, but they seem fine...

AirsoftEire.com

No one seems to have mentioned, one of the main reasons fuses blow is because users plug in a freshly charged battery straight off a charge. Batteries have a very high resistance within the first hour or so after charging so plugging it into the gun straight off a charge and firing is likely to blow a fuse, especially with a new battery, and especially if the gun manufacturer has a low amperage fuse installed.

Plenty of AEGs come with no fuse at all, so i wouldn't be too concerned about bypassing the fuse or using a higher rated fuse as long as you don't to the above.

Steve

Firekitten

/me wonders why mando ignored her entire post >>



Steve: They do? I've yet to come accross an AEG without a fuse, which dont ?

(Nice tip on the battery)

Damo 2k9

The G&G raider i had didnt come with a fuse, unless it was in the gearbox (which i dont think it was),

thermo

the magpul masada (uk and Ireland spec) does not have a fuse fitted, also a good lot of the VFC guns dont have fuses fitted. not all guns have fuses fitted, and they work perfectly without them.

Private Snafu

To be honest any AEG I put my hands on I rip the fuse right out of, 99.99999% of airsofters know if the gun stops shooting or makes an odd noise to take their finger off the trigger anyway

Firekitten

thermo wrote: »

the magpul masada (uk and Ireland spec) does not have a fuse fitted, also a good lot of the VFC guns dont have fuses fitted. not all guns have fuses fitted, and they work perfectly without them.

They do work perfectly without a fuse, ANY gun does. A fuse is a failsafe. It stops airsofter on adrenaline, ramming the trigger back when its jammed, and tearing thier gearbox to shreds. I consider them fairly useful.

To be fair, in the grand scheme of things, g&g raiders, (I know g&g guns WITH fuses) some vfc (again, all thier AK's ive had had fuses (blade type) and a masada dont constitude 'plenty of guns'. I wasnt aware that guns came without them, so I learned something new there. I considered them an integral saftey feature for more than one good reason. All the guns ive worked on over the years have been fused, bypassing them imo, is a temporary fix, and If I got one without, id probably fit one. it coming without, doesnt mean its not a good idea.

Bad nasty silly things that happen without fuses:
Gears / pistons / gearboxes can be chewed to bits
Hopup rubbers destroyed by bb jams and air nozzles broken/ tappets snapped.
batteries catching fire, and melting the gun (not just lipos)
trigger units melting.

That right there is a damn good reason to spend a couple of cents, vs 200€...

DeBurca

Firekitten wrote: »

They do work perfectly without a fuse, ANY gun does. A fuse is a failsafe. It stops airsofter on adrenaline, ramming the trigger back when its jammed, and tearing thier gearbox to shreds. I consider them fairly useful.

To be fair, in the grand scheme of things, g&g raiders, (I know g&g guns WITH fuses) some vfc (again, all thier AK's ive had had fuses (blade type) and a masada dont constitude 'plenty of guns'. I wasnt aware that guns came without them, so I learned something new there. I considered them an integral saftey feature for more than one good reason. All the guns ive worked on over the years have been fused, bypassing them imo, is a temporary fix, and If I got one without, id probably fit one. it coming without, doesnt mean its not a good idea.

Bad nasty silly things that happen without fuses:
Gears / pistons / gearboxes can be chewed to bits
Hopup rubbers destroyed by bb jams and air nozzles broken/ tappets snapped.
batteries catching fire, and melting the gun (not just lipos)
trigger units melting.

That right there is a damn good reason to spend a couple of cents, vs 200€...

I have to agree 100% with Kitty
I have seen the Tamiya plug melted in a scar, "O and the battery got a bit hot" was the comment by the owner
I always suggest to people that a fuse be fitted in their favourite AEG it is there for a reason which is to protect

NakedDex

Wow, how did I miss a thread about the electrical side of things? That's usually the grenade I jump on first.


Anywho, a quick scan of the posts show most of the bases have been covered, but I would like to add a few things.

The vast majority of rifles that have fuses use glass fuses. Some, mainly AK's, use blade type fuses more commonly associated with cars. They're both relatively cheap, so if they blow it's not really a big worry. However, if your rifle blows fuses regularly, then there's an underlying problem within your gearbox or electrical system that you really should sort out. Fuses are, as was mentioned, a failsafe. If it does indeed fail, there's a reason. Changing the fuse every time it goes is like putting a snooze button on a fire alarm; it's solving the annoyance without dealing with the cause.
If you're not comfortable opening a rifle yourself, have a store or one of the well known repair people on here do it for you. It could be as simple as a loose connection.

If you're experiencing regular blown fuses while firing on semi, but never on full auto, the solution is actually quite simple - a time delay fuse.
There are two types of glass fuse; fast blow and time delay. Fast blow fuses are the cheapest and most common. The provide the maximum amount of protection and pretty much cover the bases for everything these days. Time delay fuses are similar in operation to the fast blow ones, but the fuse wire inside the glass is either longer or thicker. Usually it's longer, and is noticeable by the coiled shape of the wire. This gives the fuse a few extra milliseconds of operation before blowing.
In airsoft, the instantaneous current drawn by an AEG is actually huge in comparison to most things - often up to 35A. This is where fast blow fuses suffer a bit. When firing on full auto, this surge current is drawn for a couple of milliseconds while the motor spools up to speed, then it steadies off to regular currents. However, if you rapidly fire on semi auto, you're drawing this surge current every time. In quick succession enough times, a fast blow fuse will blow due to overheating (not having had time to cool down between trigger pulls), where a time delay fuse will be more tolerant of such actions.
This surge current will be two or three times the rated voltage of the fuse, but this is normal so don't be alarmed when you see your rifles fuse is only 10A or so. Fuses are thermal overload devices, meaning they break when they get to a certain temperature. Surge currents in AEG's don't last long enough for this to happen under non-fault conditions.

If you want to use a fuse, don't replace it with a fuse of a higher current just because you don't want the inconvenience of it going at some stage again. If you're going to do that, you may as well replace it with a nail. It'll be about as effective in a fault situation.

There are thermal fuses available, which automatically reset after they get a couple of seconds to cool down. They're relatively cheap to buy and pure simplicity to install, and they solve the replacement/inconvenience issue without losing that protection. I also highly recommend them to anyone using a semi-only rifle, as they're the ones which most commonly blow fuses. Particularly the SR25 rifles, due to their long gearbox.


Finally, to echo some of the sentiment above, fuses are protection. Anything will run fine without protection, but it's when something goes wrong that you'll wish you had it. You can shove a piece of tin foil across the fuse carrier in the plug of your toaster and it will actually work perfectly, but where's your protection if that overloads and catches fire?
While a gearbox won't catch fire, I've seen overheated cables and connectors in various states of charred and melted goodness, all of which could have been protected by a simple, 15c fuse. The purpose of a fuse in any application isn't to protect you, it's to protect the device.






Oh, and to quash a myth I heard about removing fuses to "increase rps 'cos they suck up power from the battery", the resistance of a fuse is somewhere in the micro-ohms scale. It couldn't deplete even a single cell on a battery inside of a decade. You're not going to lose performance for having one installed. The only reasons some manufacturers don't install them is that it's cheaper not to bother.

Firekitten

good advice on the time delay Dex.... After another thread, im actually considering seeing if i can fit a tiny rcd to one of my aegs as a test

NakedDex

It wouldn't do anything. RCD's are leakage protection, rather than overcurrent protection. Plus, RCD's need AC or pulsating-DC to operate. Pretending, for a moment, that your AEG was actually running on AC power, it still would only protect you in the case of you touching a live phase. As I said about the fuse being designed to protect the device rather than the user, the opposite is the case for an RCD. It's designed to protect the operator from potentially lethal shocks, which is why the most common type trips at just 30mA.

An MCB is the resettable alternate to a fuse, doing the same job with more efficiency but lacking the high current rupture ability. This could, potentially, be used. It'd be a heck of a lump sticking out of your stock though, and offer no advantage over a regular thermal fuse (which is essentially one of the two devices in an MCB).

Firekitten

Perhaps im thinking of something else.... we use RCD's at work, that trip when surges happen... I'd know... i have to keep resetting the damn things after using 3000w strobes >> perhaps i do mean RCBO... (resitual current circuit breaker with overload protection)... those can get pretty small.

NakedDex

RCBO's are RCD's and MCB's in the same unit. They've been around for a good while now, but they're slowly becoming the standard. They suffer the same operational limitation as the RCD though, in that they need AC or pulsating-DC to operate. The only part of the device that you'd manage to use is the MCB though.

MCB's can be gotten reasonably small, so that's an option if you want, but neither will give you a benefit beyond that of a thermal fuse, since that's how both actually detect overloads anyway. All you'd be gaining is a manual switch and a magnetic trip for short circuits (which would be about as useful to you as a chocolate fireguard).

Firekitten

Well I'm mostly theorising badly, my power knolwage is ... relatively low, as I only 'use' high power kit, not work with it as such. I'm happy to mess with 3 phase, and trip things, but thats my limit... I'll bow to your superior knowlage. frankly, im happy with thermal fuses, they do thier job grand. I just like the thought of being able to reset the 'fuse' after an incident that ive resolved, meaning instant continual play... that or I carry some spare fuses (probably cheaper)

NakedDex

I should actually distinguish, when I said thermal fuse, I meant thermal reset fuse as opposed to a standard thermal break fuse.
Thermal reset fuses are basically an enclosed bimetal strip. When they "blow" by overload, the bimetal has actually just parted from the contact, breaking the connection. Given a few seconds to cool down, the fuse resets as the bimetal remakes the connection and normal operation is restored.
Think of it as one of those pesky RCBO's you have tripping, and resetting itself after the fault has passed, instead of you having to go and do it yourself. If it "blows", you'll be back in the game within a few seconds, and you won't have even needed to pull out a screwdriver.