What fuse to use?

Liam.great98

100 mW
Joined
Sep 20, 2013
Messages
42
Location
Burlington, Ontario
I'm making a 24 volt, 250 watt bike with a brushed mid drive motor. I'm wondering if it' nescessary to have a fuse, and what the rating should be. My controller doesn't have a plug to attach a fuse, so I'd assume I just put it in series with my batteries. For a 24v 250w system would a 20 amp fuse be good? And does it matter if the fuse is regular, or slow blow?
 
With a low power setup like that it won't be difficult to find a fuse holder to do the job

I lstarted using a fuse on my bike a maxi Blade fuse

http://www.technobotsonline.com/maxi-blade-fuse-holder-30430.html

they do up to about 80 amp fuses.

Stick in something like a 30 or 40 amp to protect yourself from major shorts but won't cause hassle by random blows under acceleration.

I don't use a fuse in my system 8=20-24s liPo (84 -100 volt) and 140 amp peaks as I can't find a fuse holder that is small enough and does not keep melting. I eventually used a 'soldered in' fusible link, good for 300 amps or so. So in case of a full on short in the controller it MAY eventually protect the battery pack.
 
Alright, thanks. In terms of a fuse holder, I was thinking of using an automotive fuse and avoiding a holder all together. Then I could just slide spade connectors onto it and just have it in the middle of the wiring. I'll try a 20 amp duse first and move to 30 if it blows.
 
24V systems usually have controllers that draw more amps than higher voltage systems. I doubt a 20A fuse will be large enough. I'd start with a 40A maxi fuse. If you know the max amp draw of your controller, just get a fuse 10A larger than that.
 
From Teklektic:

http://www.electricbike.com/custom-build-gallery-teklektiks-dual-motor-yuba-mundo/

Alan used a 50A magnetic marine breaker for the main power disconnect switch (Blue Sea model #7230). These types of breakers are very rugged and are intended for high-humidity/salt-air use. They are designed for up to 65V-DC and can handle interruption currents up to 7500A making them virtually indestructible in this application. “They start to trip at 62A and with a couple of controller shorts, the CycleAnalyst never recorded a spike greater than 180A before the breaker switched off”.

The 50A breaker has worked flawlessly and tripped so quickly that the 50A Maxi fuses in the battery packs never popped. “For around $15, I cannot recommend this breaker more highly”. It is not rated for weatherproof use, so Alan mounted it upside-down to discourage water entry. A 5W / 330-Ohm resistor and pushbutton provide a standard pre-charge circuit to prevent arcing when switching on the breaker.
 
Also, should I put the fuse between the batteries and the controller, or the motor and the controller? Or both? I'm thinking if the motor overheats or gets struck or the wires break or something, then it would ruin the controller.
 
Liam.great98 said:
Also, should I put the fuse between the batteries and the controller, or the motor and the controller? Or both? I'm thinking if the motor overheats or gets struck or the wires break or something, then it would ruin the controller.
as close to the battery as you can physically place it.
-for a 250W (500W peak) 24V system use a 30A fuse . important note: Actually, this advice is dependent upon how much current your chosen controller can source.
 
Should it go on the positive or negative side of the batteries? Or does it matter? I know there would be a tiny bit more current on the negative side, contrary to conventional current flow, but I don't imagine it would matter which side I put it on...
 
Liam.great98 said:
Should it go on the positive or negative side of the batteries? Or does it matter? I know there would be a tiny bit more current on the negative side, contrary to conventional current flow, but I don't imagine it would matter which side I put it on...
conventional current flow -is- from the negative to the positive... but no matter.

In a "closed" system like a battery-powered bike it matters not whether the fuse is in the positive or negative paths.
Tradition -or- common practice would have the fuse on the positive pol of the battery.
 
Ah, thanks. I'm sure you can tell, this is my first bike conversion project so I'm learning. I'm also 15. I got some 20, 30, and 40 amp fuses today so I'll start with the 20, if it blows a lot then I'll switch to 30, etc.
 
middriveebike said:
Sometime the bike is chassis grounded.
It makes it much for easier to short on the positive wire than the -ve one.
So it makes sense to fuse the positive wire on the battery.
-this is for clearing up any misconceptions you may have
I've not seen every e-bike ever manufactured (they've been made since the 1880's thereabouts)
I've yet to see an e-bike "grounded"
caveat: I've only owned -or- seen/worked on four manufactured e-bikes so far.
All others I've built for myself (about six so far)
It makes no difference if you installed the fuse on the batterys' positive or negative terminal.

I understand not everyone on this board is an expert in electronics so I'll keep this discussion as simple as possible. (i r x purt)
All electrical circuits no matter their complexity can basically be broken down to a power source (B) that feeds it's power into a load (fig 1)
The load be simply be described as a variable reactance consisting of resistance (R), capacitance (C) and inductance (L)
The current flow is no different between the positive or negative "terminal" of the power source. The current flow of any complete circuit is what it is and goes from one terminal to the other, as determined by the load.
-whether a fuse in inserted on the power sources positive or negative* terminals' makes -0- difference. (fuse inserted before the 'ground' connection (little triangle at the bottom of Fig 2 and 3))
If the current goes above the fuses' rating, the fuse will stop the flow of current. (although not instantly, which is sometimes a porblum)discussion.jpg
 
Is it safe to use a piece of say 18awg or higher wire as a fuse? Perhaps use some heat-shrink tubing as a heat shield.

Just use two of your connectors and pass the electric through some 18+awg wire is my idea.
 
18awg wire will probably require 100's of amps before melting and blowing. You can buy maxi blade fuse holders really cheap.
http://www.ebay.com/itm/10-GAUGE-INLINE-MAXI-FUSE-HOLDER-WITH-1-FUSE-2-PIECES-TOTAL-NEW-/400580449432
Might find cheaper if you shop around.
 
ONly problem with maxi blade fuse holders if you use high curent is the bloody things melt...but I understand not everyone is pulling 70-80 amps..with 140 peaks :twisted:
 
Yep. One should really use an ANL type fuse. It will withstand the higher DC voltages. Personally, I use an ATC blade fuse at 100V 40A. A direct short will melt the crap out of it, but at $1.28 for the holder, I really don't care. It's just there to keep a direct short off the battery pack.
 
Those ANL fuses look awesome, I will look into them :)
ANL_Fuse.jpg


Edit: Only £1.50 to replace too!
 
wesnewell said:
Yep. One should really use an ANL type fuse. It will withstand the higher DC voltages. Personally, I use an ATC blade fuse at 100V 40A. A direct short will melt the crap out of it, but at $1.28 for the holder, I really don't care. It's just there to keep a direct short off the battery pack.

I have a 80 amp maxiblade fuse...or bigger? cant remember now just soldered directly to the wires and heat shrunk over the top. if you use the maxi blade holders for high current, the holders always
melt. the fuse leg always corrodes , and creates a high resistance joint between it and the fuse holder...so it gets hot.

Better off finding a round cartridge fuse, sand filled type better, solder a wire either end and heat shrink the lot.
 
I was going to use a nut, washers and bolt on one of them ANL fuses to clamp my 10/12awg wire.
Should make a good connection in theory, just waiting for bits to arrive so I can give it a try.
Edit: probably put in a box too since I don't think I would be able to heat-shrink over that contraption!
 
They make fuse blocks for anl fuses. The fuses will break if you bend them too much.
http://www.ebay.com/itm/100-AMP-ANL-Fuse-Holder-Voodoo-nickel-fuseholder-0-4-8-GA-inline-/251311350911
 
That's spot on, thanks for that!
Looking forward to making my ebike safe. A fuse could of saved me many $ on replacement lipos if I had added them at the start! They can protect from accidental shorts.
 
I don't think you can hurt lipo by shorting them out. They will just blow the connectors off in a big bag and flash. At least that's what happened when I accidentally shorted positive to negative on my 24s pack. Burned a couple fo holes in my fingers, but the worst part was i had to solder on new connectors before I could ride. Moral. If if not light enough to see the wire colors, don't hook them up.
 
wesnewell said:
I don't think you can hurt lipo by shorting them out. They will just blow the connectors off in a big bag and flash. At least that's what happened when I accidentally shorted positive to negative on my 24s pack. Burned a couple fo holes in my fingers, but the worst part was i had to solder on new connectors before I could ride. Moral. If if not light enough to see the wire colors, don't hook them up.

That happened me too, it bloody hurt :( I hate pain! Sometimes my concentration lapses while I am hooking batteries up, then bang!
At least if the fuse goes, it will keep my finger intact!

I just got these in the post today:
2013_12_05_13_27_40.jpg

2013_12_05_13_27_26.jpg


Do you think they will blow with my 45A ESC? I run 22s2p 10ah. Gotten 40mph out of it :)
 
60A anl should be good. I use a 40A fuse with a 40A controller and it hasn't blown in 2 years use.
 
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