How recommended is it to put a fuse between the battery and controller?

This is going to be my first ebike, a 1000W 48V rear hub motor.
My battery is going to be a Li-ion 13s5p 17.5AH.
My controller states a "maximum rated current" of 30A.
Do I really need a fuse between the battery and controller?
Is it in the "nice but not really needed" category or is it widely recommended?

If it's really recommended to use one, can I use a 32V 35A blade fuse? The seller of my kit includes that fuse and insists that 32V will be ok despite a 48V system, but Wikipedia/other online sources say the voltage must match, although I've found a forum topic saying it doesn't have to...

So basically:
- Is using a fuse a luxury or pretty highly recommended?
- If a must, can I use that included 32V 35A blade fuse or would I be better off with nothing since it's under rated voltage?
- If a must and I must use a 48V fuse, where can I find a 48V 35A blade fuse since my local stores don't seem to carry them in 48V?

Thanks to anyone who could help me with this.

No, it doesn't have to match voltage and if your Battery has a BMS you don't need a fuse.

Thanks, that's good to hear but:
1) Does that mean that if there was a short in the controller (or somewhere else) or if the motor was stalling and pulling too many amps, the BMS would act as a fuse and protect the battery?
2) Could someone explain why fuse even have voltage ratings (although I've seen some without any!) if the voltage rating can safely be ignored? I'm just trying to understand here.

I use a DC circuit breaker, like these: https://www.amazon.com/60Amp-Circuit-Breaker-Marine-Stereo/dp/B076GVLGPY/ref=asc_df_B076GVLGPY/?tag=hyprod-20&linkCode=df0&hvadid=228763672776&hvpos=1o2&hvnetw=g&hvrand=4519342040754664055&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9029427&hvtargid=pla-391768430529&psc=1 mostly for theft protection. Also nice when working on things, probably don't need it but I've used them a lot in small off grid solar systems so was familar with them, they work great (and I use them on my 52 V bikes, though they are only rated to 48 VDC) and are mechanically robust with good sized lugs for large ring terminals, and 1/4" holes in the base for mounting, and less then 30 bucks!

craneplaneguy said:

I use a DC circuit breaker, like these: https://www.amazon.com/60Amp-Circuit-Breaker-Marine-Stereo/dp/B076GVLGPY/ref=asc_df_B076GVLGPY/?tag=hyprod-20&linkCode=df0&hvadid=228763672776&hvpos=1o2&hvnetw=g&hvrand=4519342040754664055&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9029427&hvtargid=pla-391768430529&psc=1 mostly for theft protection. Also nice when working on things, probably don't need it but I've used them a lot in small off grid solar systems so was familar with them, they work great (and I use them on my 52 V bikes, though they are only rated to 48 VDC) and are mechanically robust with good sized lugs for large ring terminals, and 1/4" holes in the base for mounting, and less then 30 bucks!

Click to expand...

How does that prevent theft? Can't the guy just pedal away anyway?
I plan to take my battery with me when I lock the bike, too pricy...

fuse is a must on wires to battery
you never know what can happen , just common sense , no much technical.
suppose you disconnect battery for any reason and accidently touch +/-

Fuses are a must!

The proper way is to install a properly rated fuse on the positive (+) side.
https://www.mouser.com/Circuit-Protection/Fuses/_/N-ba85y?P=1yrlnnzZ1yx4attZ1yx4hjo&Rl=ba85yZer5eZ1z0x866Z1z0x65cSGT&Keyword=48V-DC&FS=True&Ns=Pricing|0



The post below makes sense to me.
https://www.quora.com/Does-it-matter-if-you-put-switch-fuse-in-a-DC-Circuit-on-positive-terminal-or-negative-terminal

Typically the negative terminal is ground. So if you put the switch, fuse there (on the return path) then when the switch is open the whole circuit will be sitting at high potential. Tt won't be "on" but if someone were to touch something they could get hurt as they now provide a path from "high" to ground.

That doesn't matter from a safety perspective at low voltages, but you might still damage things - especially since the current will flow without a fuse (since the fuse is uselessly on the negative terminal where it isn't protecting anything!)

So the switch and fuse go on the positive terminal. Then when they are off the circuit is disconnected and grounded.

In some systems (telephony, cars) you have negative voltage (-48V, -12V) and the postive is ground: in this case you would do the reverse

Click to expand...

miro13car said:

fuse is a must on wires to battery
you never know what can happen , just common sense , no much technical.
suppose you disconnect battery for any reason and accidently touch +/-

Click to expand...

markz said:

Fuses are a must!

The proper way is to install a properly rated fuse on the positive (+) side.
https://www.mouser.com/Circuit-Protection/Fuses/_/N-ba85y?P=1yrlnnzZ1yx4attZ1yx4hjo&Rl=ba85yZer5eZ1z0x866Z1z0x65cSGT&Keyword=48V-DC&FS=True&Ns=Pricing|0



The post below makes sense to me.
https://www.quora.com/Does-it-matter-if-you-put-switch-fuse-in-a-DC-Circuit-on-positive-terminal-or-negative-terminal

Typically the negative terminal is ground. So if you put the switch, fuse there (on the return path) then when the switch is open the whole circuit will be sitting at high potential. Tt won't be "on" but if someone were to touch something they could get hurt as they now provide a path from "high" to ground.

That doesn't matter from a safety perspective at low voltages, but you might still damage things - especially since the current will flow without a fuse (since the fuse is uselessly on the negative terminal where it isn't protecting anything!)

So the switch and fuse go on the positive terminal. Then when they are off the circuit is disconnected and grounded.

In some systems (telephony, cars) you have negative voltage (-48V, -12V) and the postive is ground: in this case you would do the reverse

Click to expand...

miro13car said:

fuse is a must on wires to battery
you never know what can happen , just common sense , no much technical.
suppose you disconnect battery for any reason and accidently touch +/-

Click to expand...

Click to expand...

So, I've installed my fuses in this way, but given that my system really doesn't use grounding, so I'm not sure that it really matters whether the fuse is on the positive or the negative. I have mine on the positive side just to keep with convention but I see no other advantage. Am I missing something.

BTW, I agree with the use of fuses even if you have a BMS. I have to imagine that a dead short could possibly kill a BMS, so I'd rather spend a few pennies on a fuse (or circuit breaker) to protect it. I know my configuration is non-standard, but if I had a fuse on the battery side of my booster (as I do now) it might have saved the booster from frying itself. Hard to say for sure.

markz said:

Fuses are a must!

Click to expand...

I don’t use any. With high C-rate RC lipo, the battery connectors do vapourize when they are shorted. The high Amps they supply doesn’t make it easy to fuse protect them anyway.

I have had connectors melt on me.

Battery: Hobbyking 4mm bullets with the red plastic housing that almost shorted.
Battery: HK 4mm bullets with individual housing that almost shorted.
Phase: ^^^^^^^^^^^^^^^ individual housing.

Planet Indigo said:

craneplaneguy said:

I use a DC circuit breaker, like these: https://www.amazon.com/60Amp-Circuit-Breaker-Marine-Stereo/dp/B076GVLGPY/ref=asc_df_B076GVLGPY/?tag=hyprod-20&linkCode=df0&hvadid=228763672776&hvpos=1o2&hvnetw=g&hvrand=4519342040754664055&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9029427&hvtargid=pla-391768430529&psc=1 mostly for theft protection. Also nice when working on things, probably don't need it but I've used them a lot in small off grid solar systems so was familar with them, they work great (and I use them on my 52 V bikes, though they are only rated to 48 VDC) and are mechanically robust with good sized lugs for large ring terminals, and 1/4" holes in the base for mounting, and less then 30 bucks!

Click to expand...

How does that prevent theft? Can't the guy just pedal away anyway?
I plan to take my battery with me when I lock the bike, too pricy...

Click to expand...

Ha ha, your are correct sir! I meant at least they'd have to pedal I guess. I use them for about 90% electrical reasons, and 10% a half assed theft prevention. Lame, I know, but it makes me feel a bit better as I'm too lazy (and trusting, theft is not a big problem where I'm at), and my batteries on two of my 3 bikes are not easily removable.

Fuses are problematic on ebikes. Most cheap fuse holders melt before they open because they are such low quality.

When fuses are not rated for high enough voltage they arc over and often melt, not breaking the circuit cleanly.

Circuit breakers turn out to be a better thing to use. They must be rated for DC and at least the voltage and current that will be used. They are often cheaper than a quality fuse and holder, and they can be used as a main power switch (if they are rated for that service).

If the battery has a BMS it is supposed to electronically protect the system. If it fails (which happens, how much quality is there?) the result may be a destroyed battery, melted wiring and possibly a fire.