Why dont we...

[David perry 1]

...Fit fuses anymore? Time was we all fitted blade fuses and the magazine articles went on, and on, and on, and on, and on, about fuses.

 

Today, no one seems to fit them.

 

Why's that then?

 

D

[Phil 9]

As a relative new modeller I have not seen the fuses you describe maybe you can enlighten me on where they were fitted ant the purpose.

The main purpose of any fuse in a circuit is to protect the equipment from large currents.( it also can help prevent electrical fires). for most house hold electrics the main safety feature (to protect people from shocks) is the earthling system.

if a fault causes a large current and blows a fuse that system is dead (off). If that circuit is the one driving a models servos for example and it is in flight it is going to come down.

there is little advantage of introducing a week spot in a circuit to protect equipment if it will only get damaged if it stops anyway.

the electrics in a model are so relatively cheap that any faulty item is replaced and not repaired so less need to try and protect it.

Another argument for not having fuses is just adds more connections (potential points of failure) into a circuit.

[Andy Harris]

I think the answer is simple(s)

 

We use ***way*** more power in electric models these days. I'm peaking at 1800W on an Inspire 60.

 

At 22.2V that's a current of 80A.

 

Metal to metal contact carry 80A will have some I2R losses and 80 squared x a tiny bit will be a few watts in a small place, which leads to high temperatures and early failure.

 

It is much safer not to have the fuse in aero modeling applications

 

[i12fly]

As Phil B says "...the main safety feature... ...is the earthling system."

That's the problem, we earthlings don't seem to be able to get things right

 

[Biggles' Elder Brother - Moderator]

i12fly - you beat me too it! I was thinking "That must be as opposed to the Alien System"!

 

BEB

[leccyflyer]

Posted by David perry 1 on 24/01/2011 17:29:52:

...Fit fuses anymore? Time was we all fitted blade fuses and the magazine articles went on, and on, and on, and on, and on, about fuses.

 

Today, no one seems to fit them.

 

Why's that then?

 

D

The preferred place to fit a fuse, for those who used them, was in the positive motor lead. The fuse would pop if the circuit pulled more than - say - 25amps, or whatever level was selected.

 

With brushless motors that isn't an option, so any fuse would need to be fitted in the main power lead from battery to ESC. With so many systems set up with a BEC that is really not a good option at all, resulting in the loss of radio control, and the model, if the fuse blows.

 

Then there is the fact that manyESCs contain internal over-current protection which is much better than that offered by the old fashioned fuse.

 

A fuse, in most systems, is just something else to go wrong and a point of failure, so, like switches, they are often ommitted in the quest for more reliability and robustness.

 

It used to be an insurance requirement to fit a fuse to all electric models flown under MAAC in Canada. Not sure if that is still the case, but it must be a dozen years since I've fitted a fuse to a model.