Kosmic compact fuse idea

[CyprusFlyer]

Received a new Kosmic 160 today for my TDR after I crashed a few weeks ago.
One thing I did not like was the fuse sticking out the front, even with the fuse holder.
So had an idea to make it more compact, probably wont work the same with the cool variants.

Only downside I see is an extra wire but very happy with this one:
Made a spacer out of some Teflon bar I had lying around, Delrin probably ideal but didnt have any. Made in 2 pieces with a hole for a 4mm bolt and machined a channel in the bottom for the Kontronic Lug.

Now then. the bolt has to have one end insulated otherwise no point in having a fuse because the bolt will short out the assembly, bypassing the fuse. Used some thin tough plastic to make a tight fitting washer and use a short piece of planker type servo rod outer that screwed nicely up the thread, see photos.

I used a spare motor cable and formed a lug on the other end by clamping a ring of the copper wire ( I could just about plait it at the ends and twist) around a 5mm bolt. Then soldered, cut off excess and pressed it flat in a vice, will need heatshrink eventually for extra strength.

I saved about 2mm by filing the bottom of the locknut and then the end of the bolt when it was done up. Plenty of clearance but will double the heat shrink in that area and use some double sided tape to eliminate any vibes/movement.

Note that at both ends the lugs are clamped directly on the fuse, not the holder, also that bolt is 4mm v the stock 5mm. I suppose that this could be taken further, ie if someone could make a plastic fitting that went off the lug and supported all the fuse holder, perfect!

[jamin_00]

I like it but see one potential issue.

As I understand and I'm by no means a sparky but the fuse is there also to stop the case going live in the event of an internal short circuit. Should it be used in the traditional way when an internal short circuit happen, the case will be protected as this will not get grounded but this way as the wire is attached directly to the neg terminal, then to the fuse, if the fuse blows you still have this wire from the tab going to the fuse holder which by looking at that pic the nut is extremely close to the case so this could easily be bent down in a crash or something that would then ground the ESC case and potentially cause a bigger issue after the event.

Does that make sense or am I wrong in my thinking there but that is also another reason the fuse is on the neg and not the pos terminal.

[CyprusFlyer]

The fuse serves the same purpose as those in your household consumer box, not there to protect the wives hair dryer but rated so that the wire in the wall cannot catch fire, the fuse goes before the high current can generate enough heat, similar big fuses installed in cars off the lead acid battery, same reason. The fuse could be on the positive terminal, either way we break the circuit at any point, doesn't matter.
So if any component in the system should go short, that fuse should prevent a fire, not about stopping the case going live. The way I have it is just the same electrically, mechanically, yes I need to mitigate against that nut being able to short against the case, so as mentioned, double up on heatshrink in that region and put some thick double sided tape + I have filed down the nut and bolt smooth so that it cannot rub through the HS. I may stick a small bit of that thin plastic stuff there too for belts and braces.

My trade is electronics engineer but none of us is immune to oversight, so any comments welcome.

BTW my last horrific crash saw the Kosmic wiped out, Lipos up in flames but fuse was just fine, quite Ironic lol.

[mkovalcson]

Originally Posted by CyprusFlyer

BTW my last horrific crash saw the Kosmic wiped out, Lipos up in flames but fuse was just fine, quite Ironic lol.

You won't get an LOL from me about that.

I assume that the fuse couldn't do anything to stop your batteries from igniting because they shorted during the impact on something more directly than the ESC.

[CyprusFlyer]

Yes a sad day, in fact the crash happened because I had GenAce batteries that came with EC5's, different specs to my normal, slightly loose. Anyway, whole pack became disconnected, no buffer pack, no control, Lipos took a terrific shock load, buckled and internal short.

[Nelvick]

In the way you have that installed the fuse is not doing nothing because the screw is connecting the circuit. The fuse will not interrupt the circuit in case of overload or short circuit.


Sent from my iPhone IOS 7 using Tapatalk 2

[Nelvick]

My bad. I won't see the ring. You are right !!


Sent from my iPhone IOS 7 using Tapatalk 2

[CyprusFlyer]

OK, more than happy with this and installing in my new TDR.
Photos of the finished solution below, opted to glue some plastic sheet below that nut with rubbery contact adhesive.
Filed another 1mm off the nut and plenty of room above the top plate now, whole assembly is solid and no worries at all with it. Also some more pics of the components needed, especially the insulator solution for the top of the bolt Leave you to work out how to heat shrink both ends of the fuse

[NevErSn0w]

I like it! I now need to work out how to use with 200hv kool

Sent from my GT-I9305 using Tapatalk

[Nelvick]

Having a longer cable from the power source does not affect the performance and efficiently in the heli ???

[CyprusFlyer]

Originally Posted by Nelvick

Having a longer cable from the power source does not affect the performance and efficiently in the heli ???

No, a few inches of good quality cable is insignificant, the resistance of the supplied cable could probably not be measured unless it was on a 100m drum!

[jchen]

Hi Guys,
While we're on the topic of fuses, has anyone look for another version ?
I just had a heavy auto landing/crash when I experience power cut off.
When measured fuse with a DVM across, there was no connectivity.
Peeping into the fuse, it look ok so decided to dissect the fuse. Lou
& behold the fuse bar broke off at the part joining to the tab. Closer
examination shows that it fracture & broke off cleanly. This would
mean that the fuse is prone to failure after prolong usage when it's
expose to vibration & not to mention possibility of prelim fracture
when we're bolting down the fuse.

[CyprusFlyer]

I think maybe you were unlucky considering that there are a large number of users, or, the fuse has been used without a fuse holder and metal fatigue a problem maybe?
I think Kontronic were a little bit lapse in this area and should have provided a suitable holder that ensures that metal fatigue is not a factor. For this reason I would never entertain using this fuse just bolted and hanging off the lug!

[jchen]

Your probably right CyprusFlyer

[CyprusFlyer]

Well about 30 flights absolutely no problems at all, so just to say I am happy with the compact fuse idea but then it is just a simple solution. Actually the idea came from Kontronic anyway, when I took my crashed Kosmic appart, I noticed there were small plastic insulators for the bolts that clamp the 5 contact lugs through the Kosmic case, otherwise they would all short out.