What sort of short circuit protection do I need?

[Pinesal]

I have a 54v battery pack and I expect to have occasional draw of up to 30 amps. I am. Having the hardest time trying to figure out what I need to protect myself and my bike.

Should I use a fuse? I find lots of automotive fuses but they are rated for 12v to 32v. I see other fuses that say 120v. But I don't see fuse housings for most of these.

Maybe I need a circuit breaker? I can only seem to find household breakers at the hardware store.

Can someone offer some insight into the type of protection I use and also how to implement it?

 

[TristanP]

Should I use a fuse? I find lots of automotive fuses but they are rated for 12v to 32v. I see other fuses that say 120v. But I don't see fuse housings for most of these.

I will copy/paste my post from a recent topic with pretty much the same question.

Littelfuse has 58 VDC blade fuses with a 1A thru 40A rating. They also sell different blade fuse holders, for example stackable inline fuse holders with crimp connectors, to allow for easy replacement of fuses.

These fuses and holders are widely available through various sellers like Mouser, Digikey, etc.. Also they are not really expensive with under a dollar if you buy 10 fuse holders and a few dollars for a fuse. (Which you actually don't need to replace ever, if things go right.)

http://www.littelfuse.com/~/media/automotive/datasheets/fuses/automotive-fuses/littelfuse_tac_ato_58v_blade_fuses.pdf
http://www.littelfuse.com/~/media/commercial-vehicle/datasheets/automotive-fuse-holders/littelfuse-fuseholder-fkh-datasheet.pdf

I would advise against all the, just as expensive, Chinese garbage without appropriate ratings. Regardless a setup being low or high voltage your battery pack actually is able to deliver a lot of amps in a short period.

 

[vk4bxi]

one comment about the "cheap" auto fuse is there is something that you can do to improve its performance when it operates. For many years there have been permanent magnets added to the contacts of DC relays. If the current flow is in the correct direction the magnets will push the arc away from the line between the contacts and make the arc longer. This helps cool the arc and dissipate the arc energy (in other words it can handle more volts and current). So with the availability of small high performance magnets one could put one on each side of a fuse (a N S pair that would clamp together strongly). If one drills a hole in the top of the fuse (to let the arc out ) and correctly connects the positive side of the supply to the correct pin of the fuse, then you will have a high performance fuse !
For those who want to do this then you need a compass to make sure that you know which pole is which ( the compass will point to the north pole of the magnet duh, actually no ! the compass North will be attracted to the south pole of the magnet )

then
.....battery side positive

...........X|X..........
............|............
..........N | S........
............|...........
...........X|X.........

load side negative

so you are looking at the top of the fuse with current flowing from the positive side of the battery (top) down to the load side (negative) with the magnet north on the LHS of the fuse with the north of the magnet touching the plastic body of the fuse.

with this arrangement the arc will be forced up. (do drill a hole in the top of the fuse at least a 1/4 inch). If you get it wrong the arc will go down but at least it will be longer.

Bob

 

[Alan B]

Fuses need to be rated for the DC current, voltage and operating temperature in the application.

Fuse holders must also be rated for the conditions of use. We see a lot of failures of fuse holders in ebike use. They probably don't have the requisite ratings, they are just cheap plastic clones fabricated without actual engineering. NRTL rated fuseholders get bulky at these voltages and currents.

The best protection for ebikes lately has been discovered to be solar rated AC/DC circuit breakers. These have DC ratings at currents and voltages that are consistent with ebike applications.

The BMS in your battery, if there is one, should also provide some level of protection against short circuits. A circuit breaker is a good backup to the BMS protection.