Blown Fuse 15A ---> 25A? 30A?

[demco11]

Problem:

Fuse blew out in my gun! Need to repair it for tomorrow morning

Its a TM-SR16 but the internals are:
Systema m120 mechbox
Systema magnum motor
Built into a G&P metal body.
(also has a prometheus tightbore if that makes a difference)

I blew it out while using it on semi auto with a 8.4v 2400mAh battery pack. But I plan to be using it from now on with a 9.6v 2400 mAh Sanyo pack... and doing many short full auto bursts which I am sure will draw lots of current.

Does anyone have any input to give me on what fuse to get?
I was told **typically** upgraded guns from 300fps --> 400 fps blow their stock fuse (15A) easily and a 20A is a good replacement. Since this gun is upgraded slightly past 400fps and its going to be on a 9.6v 2400 mAh battery that perhaps a 25A or 30A fuse may be needed?

[Skladfin]

20A or 25A is a good replacement. Some people don't use one at all. You don't need to use 30A, I use a 11.1v lipo and almost never blow 15A fuses.

If you want to lower the current that runs through the wires, adjusting the motor height or properly shimming the gearbox would be a good idea.

[mcguyver]

I'm not surprised that an 8.4v battery running an M120 gearbox results in blowing a fuse, especially in semi. Semi requires your battery to deliver more current (due to lots of in-rush current on motor start), and your rounds/charge goes way down when using semi vs. full.

A 20A fuse should be sufficient, but the 9.6v battery is better if you plan to stick with semi. Or do both.

[ledor473]

I got a question about that, if the motor can handle 25A why we need to put a fuse?
Did a battery can really deliver more than 25-30A?

Did we put a fuse for protect the motor for the battery or from a short-circuit?

[mcguyver]

Your battery will deliver current as a function of time, and so will the motor draw current as a function of time. The smaller the time, the larger the current.

If a motor can draw 6-7 amps running, it could draw 40+ on start up, but only for milliseconds.

The motor could handle probably 100 amps if the time is sufficently small. The fuse is there to protect the system, especially if there is damaged wiring or a short-circuit in the system. By default, it may also protect the motor if it's sized properly.

[NovaKaynE]

Its good to have a fuse. The fuse will blow before any damage is caused to the gun. It's better to buy a 2 dollar pack of 25A fuses and have them blow out then spend upwards of 50 dollars to have something else in the gun replaced. A fuse is much easier to replace as well. No shimming or wiring, just pop it out and put a new one in. :P

I remember blowing my first fuse. The gun was brand new and I tried to splice wires to make the battery I had work with the gun. Not sure what happened but the fuse blew out and the gun some weird noises. Then it stopped working.

If the battery sent out a huge burst of juice through a gun without a fuse what could happen? Could it engage the motor faster than it should go and cause the internals to spin faster than they should go ending up in stripped gears or maybe sheared piston teeth? Aside from the guns electrical component shorting out?