Fuse selection for custom eBike

I'm no electrician

I have two motor attach to two 52 volt battery on my solar eBike.
With both motor at maximum, I see around 2400 watts going out the battery.

I found some fuse rated 40A at 58 Volt but so far I melted 2 of those, when I go at full speed for a while.

Do you have advice on what type of fuse I should use.

I would prefer a small, light and waterproof fuse holder
but for now, I would go with a working one

Thank you

What melted, the fuse, or the fuse holder?

If it's the holder, you just need one with better contacts, preferably one without a spring to tension things, because if the spring heats up it loses springiness, and doesn't push as hard, so resistance increases, and spring gets even less springy, and spirals into meltdown.

The same thing happens with plastic holders where the slip-in contacts' pressure depends on the plastic--if it heats up and plastic distorts, it doesnt' contact as well and resistance increases and plastic heats up more and distorts...until meltdown.


I recommend bolt-on fuses because contact will be as good as the materials and surface area can be, and if properly installed can't vibrate loose either, unlike fuses simply slipped into holders.


I also recommend one fuse per battery, because you only have to use half the current rating for each one, and you are not stranded by a fuse failure (though you might want to limit yourself to half power if down to one battery if you do that). However, if you use full current rating per fuse, but the current is flowing thru two of them one from each battery, then each fuse only has to handle half of it, so heat generated is less, and less risk of problems.


I'd recommend rating the fuse well above what you will need to draw from the system, if it is there to protect against wiring faults.

If you're using it to protect against something else, there's probably a better solution.

I personally like dc circuit breakers appropriately rated for your needs, namely 30 amps. Here is an example of one suitable up to 30 amps:

https://www.ebay.com/i/252424298342?rt=nc&_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D2%26asc%3D20160908110712%26meid%3Dd05210ffa1824658b68953e461b4e928%26pid%3D100677%26rk%3D8%26rkt%3D30%26mehot%3Dnone%26sd%3D261979680916%26itm%3D252424298342%26pmt%3D0%26noa%3D1%26pg%3D2386202%26algv%3DDefaultOrganic%26brand%3DSolar

The breakers can also serve as a good on/off switch that can handle the current inrush to the capacitor in the controller.

Edit, I also like that the wires are attached securely to the breaker by the metal to metal screw down clamps.

you are completely right

1. yes it was the fuse holder that melted.
where do I look for the one you talk about. and what amp do you think I should use.

2. one fuse per battery.
originally I design this solar eBike to run in Asia where I knew I might spend days without seeing a person
so I double many thing.
- 2 set of solar panel, each one with it's own controller
- 2 motor each with a controller, one inside the rear wheel, and one the chain,
- 3 identical wheel, so I don't need to keep 2 differents type of tire and trip etc
- 2 batteries ... with one fuse

Thank you

... if your batteries are in series.
they are in parallel

when I click your link, it goes to Buying again, but with not result ?
maybe only you can see it.

Yes, for some reason the link goes to the previous page then the one I copied the link from. Tried again and got same result. Just click on the 30 amp circuit breaker on the page and it will take you to the detail page.

edit: Oops, I see my problem. Will fix the link above.

edit: Link fixed. Now points to a 30 amp breaker, as a representative example. There are many sources for these breakers in both the solar panel world and on the scooter sites with various amperage and voltage ratings.

ok, now the link work
Thank you

to increase my knowledge. I see this rated at 150 V DC. does that mean that voltage (tension ?) is less important as long as it is higher than the one on my electric circuit ?

Yes, you want to use a DC (not AC only!) rated breaker (or fuse) that is *at least* as high a voltage as the maximum voltage of the circuit it must break. Otherwise, it may arc across the opened circuit and cause a fire at that point, as well as not breaking the circuit so whatever caused it to blow in the first plac eis still getting power.

SunPoweredWorldTour said:

where do I look for the one you talk about. and what amp do you think I should use.

Click to expand...

Lots of different kinds. I'm using Bussmann ones on my trike, but that's just because I already had them. Littelfuse makes them too, as do other places. Bolt-on or Bolt-down fuses can be found via google searches from many places; I'd recommend first going to the manufacturer you want to use and using their tables to determine which one to use first.

The ones I'm using are in pictures here
https://endless-sphere.com/forums/download/file.php?id=210467
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833&p=1263618&hilit=breaker%2A#p1263618

For rating, as I said before, it depends on what you want the fuse to do for you, as to what you want to rate it for.

What specifically do you want it to protect? Wiring? Battery? Controller? ??

originally I design this solar eBike to run in Asia where I knew I might spend days without seeing a person
so I double many thing.

Click to expand...

Then you might be better off with the breakers Rassy suggests, so that you can simply reset them instead of having to change fuses--if you ran out of fuses you'd have to directly connect things to bypass, and then have no protection; if there was a good reason for the fuse to blow, it could then damage the equipment.

But it depends on what you're protecting, and against what, whether a breaker or a fuse is a better idea.

I'm using ones that look like this:
https://endless-sphere.com/forums/download/file.php?id=210435
from the linked post above.

amberwolf said:

...
But it depends on what you're protecting, and against what, whether a breaker or a fuse is a better idea.
...

Click to expand...

my knowledge is limited in this area. I was hoping to protect everything
where I worked, we had more of a programmed protection which could let pass high starting current but after that even a lower current would open the circuit. or a current level for a certain time and a higher lever for shorter time etc

but here.. I guess it only protect for an over current.

I found the problem.

I had a master switch, and
1- Contact became loose inside, it started to heat
2- Vibration cause the wire to break a little

SunPoweredWorldTour said:

my knowledge is limited in this area. I was hoping to protect everything

Click to expand...

You can, but not with just one fuse or breaker. But if you only use one, then a breaker or fuse intended to protect the system wiring would go right at the battery terminal itself.


Using a fast blow fuse would help protect electronics from overload situations...but the most likely kind of overload would be from a phase wire short on a motor, so you'd need the fuses on those, rather than the battery wires. Wouldn't hurt to have one on the battery-to-controller wires, but the small delay in power transfer between output and input of controller might be enough to let stuff fail before the fuse blows. FETs fail so fast anyway that it might not matter.

A fast blow fuse rated for MUCH higher than any normal system current (several times higher) would blow in the event of a wiring short, but wouldn't fail under other conditions. A breaker can then be used in series, rated for something closer to but still above the max normal system current. IF an overload occurs that's not "fatal", for a long enough time, it'll pop the breaker and you'll know there's a problem past that point.


So...what you want to protect shows you where (and what) to install protection.