Do I really need a fuse?

[Sunder]

Fuse holder has become dodgy lately. I can put a brand new fuse in there and 10 minutes later, it's covered in soot, indicating poor contact has been made. I have to jiggle the fuse a bit to get good contact again, and going over a bump can put me back in the same position.

In 3 years, I've blown a few fuses, but they've all been 20 or 25 amp fuses going up hills, so load based blowning, not short circuits.

Do you think it's safe to just delete the fuse from the wiring harness? It will be a (small) pain to replace it instead.

 

[Ypedal]

it's not something to recommend.. but none of my personal bikes have fuses..

" Whoops " happen on occasion, without a dedicated fuse, something gives.. fast... usually the andersons never even make full contact, they just blow apart instantly... as you poop yourself and your heart rate doubles .

 

[amberwolf]

Its up to you, but wtihout a fuse if you ever have anything that shorts your battery wires together (or internal short in the controller that does that, like via fried FETs or regulators or caps), then unless you have a BMS that will cut off power, it'll pour current thru the wires until they heat up enough to melt insulation and/or burn, and if the cells are capable of high current and/or are a type that tends to burst into flame upon shorting, you could end up with quite a fireball.

I have a breaker on mine, and it's high enough current that I don't worry about it tripping on any motor loading, but it should trip on a dead short (it does on a test). I have considered a fuse, too, or in place of the breaker, but haven't got htat far in my new wiring harness yet, so haven't decided. I prefer the breaker because I can reset it after I remove the fault, and don't have to carry spares with me, or worry about running out of spares in fixing the fault. (cuz I probably couldn't get home in any reasonable time on pedals alone, and can't really walk the bike very far). It's also my main power switch.


Personally, I'd rather have *something* to break the circuit in case of dead short, be that a fuse, breaker, or at the least a very short segment of very thin wire lap-soldered across a gap in the main wiring so that it could desolder under the heat from a short circuit and break the connection. A fuse is better than that would be, though.


IF the fuse holder is a problem, you can either use a differnt type (blades work better than cylindrical glass, and have waterreistant holders), or solder a length of pre-stripped wire to your spare fuses, heatshrink them to protect the fuse's connections from shorting against anything, and then solder in a non-leaded fuse in place of the holder, and heatshrink it.

If it blows on the road, just cut it out and twist in the spare, after you've made sure it's only caused by a temporray overload.

 

[wesnewell]

All the fuse does is protect the battery and connectors from direct short. If you're blowing 20A fuses, get a 40A blade fuse (ATC or maxi) and you won't blow them again without a direct short. I've been using one like this with a 40A fuse for over 3 years without blowing a fuse on a 40A controller and 88.8V lipo pack. $1.28 at Walmart for the holder. I had fuses for it.

 

[999zip999]

I unplug bike batteries if not in use. Just saying. I haven't used a fuse in 5yrs. But thought if it.

 

[Modbikemax]

All the fuse does is protect the battery and connectors from direct short. If you're blowing 20A fuses, get a 40A blade fuse (ATC or maxi) and you won't blow them again without a direct short. I've been using one like this with a 40A fuse for over 3 years without blowing a fuse on a 40A controller and 88.8V lipo pack. $1.28 at Walmart for the holder. I had fuses for it.

Wrong! A fuse is designed to stop the wiring from getting hot and starting a fire.
If you have 30 amp cable use a 30 amp fuse, if you have 50amp cable use a 50 amp fuse.
The battery can deliver hundreds of amps in a short circuit.
If you are cooking fuses before upgrading the fuse you may also need to upgrade the wiring.
Those automotive push in fuses are usually rated below the point where the wiring they are designed to protect will catch fire and way above the normal load it is feeding.
If you are drawing 30 amps continually you should look at fitting 60 amp cable or more with a 60 amp fuse.
Automotive blade fuses over 30amps have a much bigger connector designed to handle higher current.

Fuses are not designed to protect equipment.

 

[Sunder]

Thanks guys.

Blowing fuses is not the issue, the bad contact is, so either I replace the fuseholder or get rid of the fuse altogether.

I'm thinking I replace the fuse holder for now, but change the wiring so that I can plug it in directly. That way if the new fuse holder is also dodgy or becomes dodgy, I can wire around it without tools on the road.

 

[Sunder]

Does this look like a good replacement for a fuse?

25 Amp Circuit Breaker

These circuit breakers are rated at 250VAC
- SAA approved.

Specifications:
• Maximum voltage 250VAC or 50VDC
• Will hold 100% of rated current indefinitely at 25°C
• Derate at higher temperatures
• Manual push reset
• Insulation resistance >100MOhm
• Mounting hole diameter 12mm
• Size 46(H including terminals) x 35.7(D) x 14.6(W)mm

% of Rating Time to Trip
100 Indefinite
150 < 1 hour
200 4.0-30.0sec
300 2.5-11.0sec
400 1.6-7.0sec
500 0.8-2.5sec
600 0.6-1.7sec

Problem is, I go to 35A for a few seconds at a time, and it will "derate" in hotter weather (can get 45*C here easily, before we even think about the heat the controller generates inside a pannier bag). The next size fuse up is 70a, but only 24v, which on a 48v system isn't going to be good.

 

[Alan B]

Solar system circuit breakers handle DC and are available in various values up to 63 amps. They will hold awhile at full current before tripping.

 

[dnmun]

if you solder the two legs of the wire to each end of these spade fuses then it is easy to wrap a wire around the legs to make the connection around the fuse when it burns open so all you have to do is just expose the spade legs and wrap wire around the legs to make a temporary connection. a BMS is better though.

 

[TotalConfusion]

I went down to my local Car Audio at Erina and bought myself a Mini ANL 80 Amp fuse holder and fuse and with over 4000km on it i havnt seen a problem and it cost me under $20 with a 3 pack of spare fuses plus the one that came with the holder.
Im running a 40Amp Grin controller at 88 Volts.
These fuses Screw into the holder for a great conection and they are also gold plated.

 

[amberwolf]

I snipped all but the part relevant to my reply:

25 Amp Circuit Breaker
• Maximum voltage 250VAC or 50VDC

which on a 48v system isn't going to be good.

If you have 48V system, keep in mind it is actually above 50V until it's pretty much dead, for many packs (depends on chemistry and number of cells). For my own 14s NMC pack, for instance, it's average voltage is around 54V or so, I think, and it's full charge is 58.4V.

That's not much above the max, but if you really want to stay within the CB's ratings, you'll need a higher voltage unit.

It only matters at all because that voltage is usually the limit at which it is *guaranteed* to break the arc across the contacts that can happen as high current is flowing at the instant it starts to disconnect. If it cant' break the arc, it doesn't work and you still have a short circuit, AND you have a plasma arc inside the breaker, too, which is VERY hot and almost certainly will start a fire if it goes on long enough. Whether it does will depend on other things, like whether your wires melt first, or the pack dies, or whatever caused the short burns thru and breaks the connection, etc.


I couldn't comment on the likelihood of it happening, but it's possible.


The same is true of a fuse, if it has a voltage rating, then that is why it has one--and why the AC rating is so much higher--because of the zero-crossing point of voltage in AC, which gives the breaker more of a chance to extinguish the arc with a smaller contact gap than with a DC voltage at the same conditions otherwise.



That said, I"m pretty sure my breaker isn't rated for anywhere near the voltage I have on it, but it is designed for DC. I can't read the markings anymore (worn off) so to find out what it 's ratings actually are I'd have to find the pics of it in the CB2 thread from a few years back when I got it and started using it. If I had a breaker rated for the voltage I use, I'd use it, though--I just don't happen to, and I can't usually go buy the things I should actually use, and have to make do with what I happen to have.

 

[Sunder]

I run 12S lipo charged anywhere between 48v and 49.2v (4.0v per cell and 4.1v per cell).

As I'm getting fitter, I've reduced my needs from 5Ah for my ride to less than 3Ah, and I've got a 16Ah pack, so I hope to increase its longevity by charging often, and charging to a lower voltage.

There is another DC circuit breaker at that store, but it doesn't say what voltage it's good for, except that it is "recommended for car audio and solar systems". Solar systems can be up to 72v or even 144v here in Australia, but I wouldn't want to risk it if it was designed for 12v and as you described, has such a small gap, 49.2v can arc across it.

I think I will try the 50v @ 25A breaker. It's only $8, a few spare anderson connectors and 20 minutes of work to make it. Another Christmas break task.

 

[Alan B]

The one I bought is 63A 150VDC rated solar circuit breaker. I see they also have 30A units. MidNight Solar.

I have not installed it yet, plan to put a pushbutton and charge resistor circuit in parallel to reduce the surge current to the contacts when closing.

 

[Sunder]

The one I bought is 63A 150VDC rated solar circuit breaker. I see they also have 30A units. MidNight Solar.

I have not installed it yet, plan to put a pushbutton and charge resistor circuit in parallel to reduce the surge current to the contacts when closing.

Cool. I might have to ask the store's employees about the max voltage, though if it's not on the packaging, I doubt they will know. (Such is the nature of pretty much any franchise based store these days.)

But it does encourage me to think that if solar circuit breakers are rated to 150vdc, then anything that says it's designed for solar is likely to hold up that much.

 

[Alan B]

It should be marked on the breaker.

I wouldn't assume anything about the ratings. Breaking DC arcs requires design elements. Many solar systems are low voltage and don't need the higher values.

 

[marty]

Series 187 Marine Rated Circuit Breaker
25-150A, 48Vdc

Buy at a boat shop.

Data Sheet:
View attachment BUS_Tns_Series_187_MRCB.pdf

 

[friendly1uk]

Fuse good. Fuse give proper electrical isolation.

Oh, Result. My ~12 year search is over. An 80A MAXI fuse and holder for $3.50
http://www.ebay.co.uk/itm/NEW-MAXI-BLADE-FUSE-HOLDER-SPLASHPROOF-INLINE-FUSES-CAR-80AMP-MAXI-FUSE/280770956431?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D28111%26meid%3D5a6ebb71520b4424bf945c16bcb0d476%26pid%3D100005%26prg%3D11472%26rk%3D1%26rkt%3D6%26sd%3D280723368561&rt=nc

Well it's new to me anyway. I have paralleled my last 20A standard holder. It's maxi's from now on

 

[Punx0r]

I'll be ditching my Maxi fuse holders for soldered-in ANL fuses. The Maxis are just too bulky.

 

[marcn]

The one I bought is 63A 150VDC rated solar circuit breaker. I see they also have 30A units. MidNight Solar.

I have not installed it yet, plan to put a pushbutton and charge resistor circuit in parallel to reduce the surge current to the contacts when closing.

+1

We've got one of these. They also have in rush protection and will prevent arcing if you don't have a precharge installed elsewhere.

It protected all our connectors when we blew a FET from a short.

 

[Sunder]

Would you mind linking an Australian source?

Thanks,

 

[Alan B]

Fuse good. Fuse give proper electrical isolation.

Oh, Result. My ~12 year search is over. An 80A MAXI fuse and holder for $3.50
http://www.ebay.co.uk/itm/NEW-MAXI-BLADE-FUSE-HOLDER-SPLASHPROOF-INLINE-FUSES-CAR-80AMP-MAXI-FUSE/280770956431?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D28111%26meid%3D5a6ebb71520b4424bf945c16bcb0d476%26pid%3D100005%26prg%3D11472%26rk%3D1%26rkt%3D6%26sd%3D280723368561&rt=nc

Well it's new to me anyway. I have paralleled my last 20A standard holder. It's maxi's from now on

Check the voltage rating on your Maxi Fuses. Many are not rated for high enough voltage, some are. If they are not rated for your voltage level they can arc, melt, and burn, and generally fail to protect as required.

Also many Maxi fuse holders are not rated for high current.

They can be a good solution, or not, depending on voltage and current involved and the particular components used.

 

[Sunder]

Fuse good. Fuse give proper electrical isolation.

Oh, Result. My ~12 year search is over. An 80A MAXI fuse and holder for $3.50
http://www.ebay.co.uk/itm/NEW-MAXI-BLADE-FUSE-HOLDER-SPLASHPROOF-INLINE-FUSES-CAR-80AMP-MAXI-FUSE/280770956431?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D28111%26meid%3D5a6ebb71520b4424bf945c16bcb0d476%26pid%3D100005%26prg%3D11472%26rk%3D1%26rkt%3D6%26sd%3D280723368561&rt=nc

Well it's new to me anyway. I have paralleled my last 20A standard holder. It's maxi's from now on

Actually, having a look at that link, I can see it's identical to what I have right now.

It was "okay" for 3 years, as in it did the job. Seemed to get fairly hot, but lately, it's what's been dodgy. Brand new fuse goes in there, and 10 minutes later, it's really warm and the fuse has soot on it.

 

[Alan B]

Good data. Fuseholders that develop additional resistance cause overheating and early fuse failure. It is either low quality or not rated for the current level in this service.

 

[marcn]

Would you mind linking an Australian source?

Thanks,

Hi Sunder,

I purchased it from Amazon and used my ship forwarder since it was too expensive at the one store I found in Australia. Happy to get you one with free shipping to Australia, then you pay from Sydney to wherever you are. I have a few things waiting to be forwarded that are much larger, so they can just pop the breaker in the box.