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

[Planet Indigo]

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.

 

[6zfshdb]

Using a fuse on any electrical device is always a good idea. An e-bike, with all it's moving parts and exposed wiring, has a high potential for developing a short somewhere in the system. A fault could cause a fire and / or damage expensive parts.

There should be no problem using a 32V fuse in a 48V system. A mismatch is only important for higher voltages. I use a 40 amp 32V fuse with my Pedego 48V ebike and have had no problems.

A good place to look for fuses:

https://electricscooterparts.com/fuses.html

At the bottom of the page, there is an explanation of fuse voltages.

 

[rich c]

What do you intend to protect? The battery pack or the controller? An inline fuse would will only protect a short between those two parts. It won't protect the entire system. It's my understanding that heat is the bigger killer of eBike components. Long hills at full current draw is more likely an issue than a shorted wire. Battery mounting is also critical. Having that big mass bouncing around is not kind to any sliding connector that permits battery removal. But again, not a short. It's your decision on using a fuse or not.

 

[indianajo]

E-bike controllers have fet transistors directly connected to the battery input. These are prone to shorting across, which since batteries have a typically 50 A discharge limit, would damage a $400-700 battery if it happened. I've looked in my controller, and I can't say I respect the design or build quality. They didn't even install heat sink compound between the fets on a heat spreader bar, and the nice external aluminum case they weren't screwed too. That ribbed aluminum case is a decoration, not a functional heat sink. At least in the cheap models I bought. Heat can cause fets to short.
As amp repair people say, a $5 transistor will always blow to protect the $1 fuse, so you can't protect the controller with the fuse. However, controllers are about $30, whereas batteries are $300 up.
I've used 32 v fuses on 85 volt DC amplifier circuits, where theywork fine. 32 v fuses are not suitable for 125 VAC circuits or higher, where they can short across. There are not 48 v fuses to my knowledge. 125 VAC fuses (3AG) are not rated for DC either. So in my opinion 32 v rated auto blade or 3AG fuses are best. I fused at 30 amps, haven't blown it yet though I did get up to 25 mph once for a mile.

 

[Alex M]

48V DC, 35A fuse.

Not sure you need it for $122. I doubt you will find a cheap blade fuse of these specs.

 

[harryS]

Many decades ago, an EE professor asked us senior electrical engineering students what we would do about an arc welder that was blowing the 15A fuses in his garage. While we spouted on abut changing the wires, etc, he smiled and took a penny out of his pocket. Just a funny story. As far as I know, the old doc never burned his house down. \

We kit ebike builders probably are the only people that need fuses to protect us from our foolishness with batteries with dangling connectors, but controllers and batteries do have safe guards, so I don't deem them necessary. In fact, my dolphin batteries have fuse slots that were never wired in.

 

[AHicks]

The Rad batteries (dolphin style) use a 40 amp blade type fuse built into the case.