Con(fused) about fuses!

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barbs00

100 W
Joined
Jun 1, 2017
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107
Location
Australia....mate! (Gold Coast)
Hi All,

Looking for advice regarding over current protection for my ebike.

I have a BBSHD and 52v 14ah battery.

What kind of fuse should I get in terms of rated voltage and current?

Would a simple inline fuse suffice?
They all seems to be rated for only 12v - I assume these are not good as the voltage is so much lower?

I also see that some ppl are using solar circuit breakers like this....
https://www.amazon.com/MidNite-Solar-Breaker-150VDC-MNEPV50/dp/B00BSYSTN2

Not sure of the advantage of this over a simple fuse?

Cheers
 
http://m.littelfuse.com/~/media/automotive/catalogs/littelfuse_fuseology.pdf
In theory, you should use a fuse rated for the max voltage of the source. Look at ANL fuses if you want to do that. The circuit breaker you listed is rated for 150VDC and would provide protection up to 53A. so would also be fine as long as you don't pull than 53A. The advantage of the breaker is there's no fuse to replace. If it trips, you can just reset it and you could also use it as an power switch.
 
wesnewell said:
http://m.littelfuse.com/~/media/automotive/catalogs/littelfuse_fuseology.pdf
In theory, you should use a fuse rated for the max voltage of the source. Look at ANL fuses if you want to do that. The circuit breaker you listed is rated for 150VDC and would provide protection up to 53A. so would also be fine as long as you don't pull than 53A. The advantage of the breaker is there's no fuse to replace. If it trips, you can just reset it and you could also use it as an power switch.
Click to expand...

He actually wants ANN fuses, which are fast acting. ANL fuses can take up to 10 seconds, in which time, you can have a catastrophe on your hands.
 
Does it really take up to 10 sec ?
That seems like an eternity for a fuse.

How closely should I try and match the voltage?
The circuit breaker above is listed at 150VDC - my fully charged battery is 58.8v. Does it matter that the breaker voltage is much higher?

Also, the BBSHD with standard controller draws 30amps (not sure if this is peak or continuous?) so what do you think is an appropriate current cut off for the breaker or fuse?

Thanks
 
Voltage on breaker or fuse needs to be higher (or as high) as pack voltage because if the pack voltage is higher then it could continue to arc across the contacts as the device tries to break teh connection, preventing it from breaking it at all, or delaying it, or even causing a fire as the plasma arc heats up the device/holder/wiring.



That said, I've used a "24vdc"-rated 100A powerchair breaker on a 14s Li-NMC (around 58v full charge) bike and it did correctly break the circuit the couple of times the circuit drew too much current under load--but I wouldn't expect it to reliably do that every time, and mostly I was using it for a main power switch (engaged or disengaged only when not under load), not for it's breaker ability.
 
barbs00 said:
Does it really take up to 10 sec ?
That seems like an eternity for a fuse.

How closely should I try and match the voltage?
The circuit breaker above is listed at 150VDC - my fully charged battery is 58.8v. Does it matter that the breaker voltage is much higher?

Also, the BBSHD with standard controller draws 30amps (not sure if this is peak or continuous?) so what do you think is an appropriate current cut off for the breaker or fuse?

Thanks
Click to expand...

Make sure the voltage rating is higher than your battery voltage. Also the current rating should be higher than your expected peak by 2X (at least that's how I use them). Remember that lithium during a short will give HUGE amounts of amps, so a 200A fuse will definitely blow with lithium. Check for sale section.
 
Unless it's rated for DC, it's not appropriate to use for it, as it isn't designed to interrupt the arc except for AC (which has zero crossing).

In that case, it not only might not break the circuit, it might continue to arc inside and the plasma set fire to it and whatever it's contained in. :(

So be sure to use a DC-rated breaker for DC purposes.
 
As to the amp rating of the fuse or circuit breaker, it's important to remember that a large part of what you're protecting with a fuse/breaker is your wiring. That is to say, you don't want so many amps to be drawn at any time that the insulation on your wiring melts and results in a short.

So, the size of your wires and the type of insulation on your wires is important, as well as the temperature rating of your wire, whether the wiring is enclosed or in open air, etc., etc. For instance, even with the same battery, controller and motor, if you have several feet of 14AWG wire with vinyl insulation and which is enclosed within a box, you're likely going to need a fuse/breaker with a lower amp rating than if you have a couple feet of 8AWG silicone (or teflon) insulated wire in open air.

As mentioned above, there's also the fact that fuses/breakers can be slow blow or fast blow and so on. All making it a bit complicated. In the end, taking the simple approach, like was suggested above, twice your controller output is a good bet - just make sure your wiring can easily handle that many amps for several seconds.
 
G1050s said:
As to the amp rating of the fuse or circuit breaker, it's important to remember that a large part of what you're protecting with a fuse/breaker is your wiring. That is to say, you don't want so many amps to be drawn at any time that the insulation on your wiring melts and results in a short.

So, the size of your wires and the type of insulation on your wires is important, as well as the temperature rating of your wire, whether the wiring is enclosed or in open air, etc., etc. For instance, even with the same battery, controller and motor, if you have several feet of 14AWG wire with vinyl insulation and which is enclosed within a box, you're likely going to need a fuse/breaker with a lower amp rating than if you have a couple feet of 8AWG silicone (or teflon) insulated wire in open air.

As mentioned above, there's also the fact that fuses/breakers can be slow blow or fast blow and so on. All making it a bit complicated. In the end, taking the simple approach, like was suggested above, twice your controller output is a good bet - just make sure your wiring can easily handle that many amps for several seconds.
Click to expand...

Excellent points!
 
circuitsmith said:
Five 40A 12V automotive fuses in series?
Click to expand...


That's not how fuses work. :( Seriesing them doesn't protect you against a higher voltage, you just have five times the fuse resistance in the wire and five times the chance of a problem from a fuseholder or fuse failure.
 
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