Fuse Selection

Hey,

I'm planning on getting the ME0909(48V, 100Acont, 300A peak (30sec)) motor and the Kelly KDZ48400 controller. I'm using 2/0 gauge wire (70mm2) with 8mm stud ring connectors secured in by M8 screws and washers. In an effort to make sure everything is safe, I'm planning on getting a 325A fuse placed very close to the + battery terminal. This was extremely hard to find but eventually I found it here http://uk.farnell.com/siba/90-058-05-325a/fuse-fork-lift-truck-325a/dp/607710
That seems like it should be able to cope with 48V 300A. Next I needed a fuse holder. I found this
http://uk.farnell.com/littelfuse/177-5701-0001/fuse-holder/dp/307282?MER=bn_level5_4NP_LastViewed_2
which does support my fuse. Here's my question in regards to this fuse holder and fuse

Q1 - Is it safe to not have a fuse cover on it? I've seen loads of fuse holders with plastic covers on them and I can't find one for this. Should I just heatshrink it? Or should I just put it in the conduit like the rest of the 2/0 AWG wiring?
Q2 - Will my 8mm stud size lugs fit onto the terminals of the fuse holder?
Q3 - Are there any cheaper fuse holders from eBay, etc, that would suit my fuse. I could only find ones rated for 32V max and 100A.

Thanks

Some points:

If a fuse (or breaker) isn't rated for at least the voltage it's used on, there is no guarantee it will be able to break the circuit under load.


Heatshrink should be fine at that voltage as long as it's secured so it doesn't vibrate and rub on a frame or something; my fuse is bolted to the 14s NMC battery output lug on one side and the output cable on the other, and simply heatshrunk over all that. I use no holder; my fuse looks a fair bit like yours except it has brass terminals wtih slotted holes instead of open slots. I used 1/4"-20 hardware to bolt them together (bolt, washer ,fuse tab, battery terminal/cable lug, washer, lockwasher, nut).


I have what's left of some model Zero's wiring harness, and both the traction pack fuse and the lighting/etc DC-DC output fuse are both heatshrunk into the harness.

Thanks for the reply. Is it necessary to have the fuse connected directly to the battery + terminal? Or can have a small bit of wire connecting the + terminal to the my fuse?

Also, do I need to consider any other safety fuses etc? (you mentioned a output fuse? not sure what you mean). At the moment I have two toggle switches for cutting off 18V supply to my controller and this 325A (rated for 80VDC) fuse connected near the + battery terminal. Is there anything else I should consider adding?

n1866878 said:

Is it necessary to have the fuse connected directly to the battery + terminal? Or can have a small bit of wire connecting the + terminal to the my fuse?

Click to expand...

You can do it however works best for your system. There's no hard rules about it, just whatever your best judgement is based on your system's design and limitations and layout.

I preferred to simplify my wiring, and remove two connectors/lugs from the system (the one on the battery terminal end of the short wire, and the one on the fuse end of the short wire). This slightly lowers the resistance of the wiring, and it should increase reliability in that there is now one less bolted connection to potentially come loose.

It does raise the possibility of the fuse's tab fatiguing and breaking from repeated vibration, etc., however since mine hangs straigth down from teh battery and the wire on the other end of the fuse is secured in place, it's not likely to receive enough to cause problems. It hasn't yet and I think I've been running it this way most of a year or more now. (I change stuff all the time so hard to remember for sure).

Also, do I need to consider any other safety fuses etc? (you mentioned a output fuse? not sure what you mean).

Click to expand...

If you mean in the old harness from the Zero (not what's on my trike), there's a fuse for the output of the DC-DC converter that runs the lights, so if there is a short in the lighting harness (like a crash takes out a light and twists the wires together) it doesn't blow up the DC-DC or start a fire in the wiring.


At the moment I have two toggle switches for cutting off 18V supply to my controller and this 325A (rated for 80VDC) fuse connected near the + battery terminal. Is there anything else I should consider adding?

If you have a secondary power supply for lights or whatever, I'd put a fuse on the output of that, like they did on the Zero.

I didn't have one, and managed to short my lighting wires myself at least twice in different situations working on the trike, and a third time (previous to those) where a pinched wire shorted the lighting power, and nearly ended up with a fire every time--I had to replace melted wires, including significant amounts of the wiring harness. If I'd had a fuse any of those times, most likely it'd've blown long before the wires got that hot. :/

So now I have a circuit breaker right at the separate lighting pack battery (it *does* have a short wire to the positive), but I still need to put a fuse in there.

BTW, I *also* have a circuit breaker in the main battery line, mostly as a "hidden" secondary security measure (switch) than as a safety shutoff--but it's there anyway. It's rated lower than the fuse, so theoretically should trip first in the event of a long enough overcurrent. But the fuse would go immediately in the event of a wiring short, or dead short controller failure, etc., to protect the wiring itself, and battery.

I've considered taking it out next time I'm in there, because it does add some resistance and does have some voltage drop across it (very small amount, but any loss is still a loss).



Oh, also...with a fuse, I do recommend carrying spares and the tools to change them, in case you know what caused the fuse to blow and repair it roadside, so you can then get back on the road under power.

Fantastic reply. Perfect. I'll go ahead with a fuse near + battery and a two switches for 18V to controller. I'll also add in a fuse for the secondary controller power/lighting battery.

One last thing - I saw in some places people used contactors like these (http://kellycontroller.com/emergency-contactor-kemg-125a-125a-continuous-p-1176.html) and these (http://kellycontroller.com/main-contactor-kzj-48vdc-coils-400amps-p-1154.html). Do I need them or is my setup with a 325A fuse on B+, fuse on controller power line, key switch for controller power and toggle switch behind brake pedal for controller power enough. Is the contactor necessary?

I used fuses on my early builds but have moved to circuit breakers. Proper fuses do work but they get hot in operation and make a real mess if they ever pop without the proper enclosure. A proper fuse mounting with covers and clearances takes a lot of space, there's a reason for this. Many low cost fuse housings fail when the current gets high because the connections are not really properly designed.

Proper circuit breakers are not small either, but they do provide the master disconnect switch feature and they contain the arc and don't make a big mess if they pop. They must be DC rated breakers of course.

Good luck with your build.

Thanks for the reply. Is there any particular circuit breaker / contactor product listing on eBay/Amazon that you would recommend as well as the 325A? I'm new to this and there's so many different specs available.

48V @ 100A cont. and 300A peak for 30 seconds.

I used solar circuit breakers, but I'm running 75V 80A so the choices I made won't help. I did try a 63A breaker at first, but on a big long hill it did trip, so I went to a 100A breaker. For 300A I might try two 150A breakers ganged in parallel. They will hold a long time at 325A if the breakers have airflow. Make sure they are DC rated for your use, breaking the DC arc requires devices designed for it. I've also gone to paralleled smaller cables which makes things easier than the heavier wiring.

Wow. Are there any easier alternatives? I've never dealt with stuff at this voltage/amperage before. Some other places suggested that a fuse would be enough but I want to be extra cautious. What about this one?

https://www.aliexpress.com/item/60A-80A-100A-150A-200A-250A-300A-Car-Audio-Amplifier-Circuit-Breaker-Fuse-Holder-AGU-Style/32817086454.html

I don't see a voltage rating, is there a spec sheet?

Ah. Forgot. That was rated for 12VDC. I found this one rated for for 300A 32VDC - not the 48VDC I need but will it work?
https://www.ebay.com/itm/182543083339

I also found this one
https://www.ebay.com/itm/Waterproof-200A-DC-48V-Surface-Mount-Manual-Reset-Type-Circuit-Breaker/182543083397
rated for 200A 48VDC

When operating a circuit breaker (or fuse) beyond it's rated voltage it may fail and not perform as expected. Very hard to predict.

Ah I see. I found a 48VDC breaker but it's only 150A.
https://www.ebay.com/itm/DC48V-Circuit-Breaker-with-Manual-Reset-Type-T3-High-Amp-Switchable-Waterproof-A/183283792544
I'm assuming that it will trip when my motor boosts to 300A for 30 seconds.

Probably, but 2 in parallel will probably work.

Oh. The current would split ? meaning 150A on each one? Wouldn't that trip them both ?

EDIT:
I found these
https://www.ebay.com/itm/182543083397
48VDC 200A breakers, so in paralell neither should trip even if the resistances differ.

Also how would I recombine the wires after - do Y-splitters exist for cable size that I'm using(2/0 AWG)? Or can I just put the lugs on the two individual cables and then at the motor terminal I can try and put both lugs at once on top of each other onto the motor terminal.

The resistances of two same circuit breakers will be very close, it is related to the trip current. The resistance of the breaker generates heat that trips the breaker. There should also be a magnetic trip mechanism for short circuits (very high currents).

I've seen stranded cable split into two equal bundles of strands, and then heatshrink used to re-insulate them. I would either do that, or use a hydraulic crimper to crimp the 2/0 to a pair of conductors each half the area, and feed the breakers with those. It might not be perfect, but using the 200A models would give you a nice margin. Or keep looking and find that 350A or 400A breaker.

Ah I see.
Instead of the breaker, could I just use a 325/400A fuse along with this main contactor
http://kellycontroller.com/main-contactor-zjw-48vdc-coils-400amps-p-90.html
?
So my full setup would involve 325A/400A fuse, main contactor.
And on the low voltage 18V, a smaller fuse, and two key switch, toggles to shut off controller PWR.

Any ideas how to connect up a contactor? Can i just use a simple key switch or toggle switch to it?