i think if he sets his battery amp limit to 35 he will never hit the 40 unless he shorts but if he shorts it’d be more like 200 amps or something so no point doing so low a fuse as 40 and getting less efficiency and voltage sag always
If you look at some of the issues people have short circuiting batteries, the failure stays at the battery. A fuse downline of that isn’t going to help anything. Now if they catch fire and burn the ESC that stupid fuse isn’t going to help one way or the other. This is not cell level fusing like Tesla and some users have done.
Basically the only thing you have done by adding a tiny fuse/any is punish yourself.
- Created a weak point for no reason
- Added a high resistance/high heat spot
- Created the failure point at the most dangerous scenario on your board, that being high current draw.
- Maybe save your board instead of your face. (Pointless maybe)
- Created a board likely unsafe to ride
Your ESC has limits. Which include high transient limits. Which means you could briefly pull over 150a on most of the ESC we use before they overhear.
But keep the little fuse… Maybe wear lots of protective gear.
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why you say150a when the battery amp limit is maybe 100 on vescs
If this loopkey were in circuit with the battery and esc as I think they mostly are used, to turn the board on and off, then it would work if the esc broke and shorted and a huge current were to come from the battery. I kinda like the idea of an integrated fuse but it needs to be capable of way more amps and ultimately Id rather have the battery and esc circuit with no resistance and enjoy those benefits.
It was a arbitrary number since all ESC are different
Anti spark switch is only meant to not spark. After that you still want maximum current flow. I’ve read enough on this forum to know a fuse isn’t necessary.
i agree and i think if the esc were to somehow short it would probably blow apart and break the circuit and the fuse wouldnt help. the shorts Ive heard of that ended up causing a fire were in the battery cell connections to each other and not the main battery to esc circuit
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I’ve put a 100A fuse only to prevent the battery being on fire ”if” the vesc for some reason gets shorted/ welded (Probably/hopefully not). I did not intend to save the VESC itself.
Peronally I will never ever reach that high amount of current on my dual to be even close to breaking the fuse while riding, so I have ruled out the face to ground scenario due to that 
I found a fuse chart and it looked “more or less linear” For a 100A fuse, there would be a voltage drop of 50mV across the fuse at 100A. (Please correct me if I’m wrong)
Is this voltage drop of 50mV really noticeable in performance?
If the fault is inside the battery, the fuse of course won’t help… but then there must have been something else that was severely overlooked in the design or choosing of material.
If your board will never fail, you don’t need the fuse. However, I don’t plan to crash on my head either but I wear a helmet anyway
Hi again… so if we asume losses are irrelevant, maybe the question is,
- _does a fuse protects something in any case?, What are the scenarios? Is there a failure mode where current is waterfalling due to a short somewhere? How probable is that? we would save in this case batteries?
- If it saves something… As was mentioned before fuse breaks while riding… Is guaranteed to be launched out of the board? Lets take it this way, if i do a electric scooter, does the fuse make sense?
Regardsss!
can you post the fuse chart please? 50mv isn’t anything but what resistance is the 100a fuse and what is a 40 amp fuse’s resistance? how much voltage drop would you have gotten with the 40 amp fuse we can figure it with ohms law current going through anything is non-linear I think. be nice to visualize what size wire will melt at what current and don’t want to do it at home
If you weren’t going to fall if it fused sounds like a good idea but I don’t think the escs create an open short when they fail and the fuse wont save a battery internal short so there’s no point
Fuse won’t cause any issues as mentioned previously as far as heat build up, adding any significant resistance, or voltage sag. While the fuse must have higher resistance than the wire that it is protecting in order to function, a 40amp fuse is still low resistance.
From that datasheet you can see that a 40amp fuse has a resistance of 0.00144ohms. If we pump 40amps through it, which can be done for 360,000 seconds before blowing, we would have a voltage drop of 0.0576V! You will not notice that sag in voltage. You can also check out the graph for current versus time to see how high a load it can handle for how long. As you can see, a 40amp fuse will never blow due to a 40amp draw on an esk8, something that may seem counter-intuitive.
I’m fairly new to the hobby of esk8 so I don’t have too much knowledge of the typical failures. The fuse would most likely help you in the event of a short between your battery wires (after the fuse that is). As long as the fuse was sized properly, I think you are going to face plant no matter what the failure is if it is bad enough that it would blow a fuse.
I guess the only thing to think about is that just about every commercially designed power circuit that I have seen employs the use of fuses.
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so how many amps does a 40amp fuse protect against?! why the hell would they call it a 40amp fuse if it takes 40 amps for 100 hours? so tiny voltage drop thanks for doing the math. I don’t think the fuse on a loopkey is going to be any help if theres a short in the battery still and i haven’t heard of an esc breaking into a permanent short.
A 40amp fuse will protect your circuit from any current above 40amps technically speaking. My understanding of fuse ratings is that the rating of the fuse is the minimum current it takes to blow the fuse … eventually. When sizing fuses, it is common to select a fuse rated for 125-200% of your normal operating current. It really depends on what current you want to protect against. In our case we would want to protect against a dead short which would result in a huge current draw in the 300-600amp range or maybe more. Taking the 40amp fuse, at 500amps the fuse will blow in 2 hundreths of a second.
In summary, in order to size a fuse, you really need to understand the dynamics of the system to know the length of time and magnatude of the currents your protecting against.
But I agree, the fuse will not protect you from any issues with your battery pack. It will only protect the battery wires that go from the fuse to the VECS. I don’t think it is a bad idea to have a fuse given all the stories I’ve read of issues cause by all of the vibrations.
Ok so this is getting interesting… Do we know from this forum a case where the fuse saved his battery pack and did not die on the event? We will never know i guess haha. My conclusion is, if does not fit to a realistic short scenario, and u risk of blowing the fuse while riding and fly off the longboard,adding the potential tradeoffs on performance… then there is no point at all arguments against? 