Need 80-amp, 350 VDC fuse

[DonTom]

This is for an add-on to one of my electric motorcycles for the DC fast charging (DCFC). I want to protect a fuse with a smaller fuse. The bike has a 100-amp fuse inside the very heavy battery pack that took me about a week of hard work to replace. This blown fuse probably caused by a HV spike from a DCFC when it shut down. A known issue from some EV-GO DCFCs.

Normal current is around 60 amps at 300 VDC, 350 VDC when near fully charged but then a lot less current. Charges at around 18 KW or so, depending on the voltage and charge current at the time of the charging.

What I am looking for is an 80-amp fuse and holder that is good for around 350 VDC. I cannot find such in several searches. This will be at an easy-to get to location.

It's difficult to search for because it will show 350-amp instead of 350-volt fuses and other such problems.

Does anybody here have ideas for where I can find an 80-amp fuse & holder that is rated for 350 VDC?

-Don- Auburn, CA

 

[DonTom]

What is the difference between this fuse:

And:

And this fuse?

-Don- Reno, NV

 

[OldWEB]

DC is hard to protect from faults. If not properly sized, an arc that starts in a fuse or relay improperly sized to open the circuit, that arc can continue until "something" can extinguish it.
The fuse you are looking for has to be DC-rated for the voltage you will have at the amperage protection needed. So look for the DC voltage rating in the spec sheet, something I am having difficultly doing in your example above.
It is easier to find DC-rated circuit breakers and they are A LOT cheaper! Just know that this one is rated 250VDC for one pole, if you can use it on the + & - wires at the same time, or run the one wire through 2 poles in series to get 500VDC breaking capacity (the same 80A protection).

You mentioned voltage spikes causing the fuse to fail, if within the ratings a fuse does not care about the voltage, it only looks at the current. So what you may be experiencing is current spikes, maybe from opening and closing the charging circuit... those spikes will slowly "erode" the fuse element until the point what is left of the fusible link cannot handle the current through it and melt totally.
Fuses rated "slo-blow" handle the current rushes better than "fast-acting" fuses, but then take longer to blow at the set point and possibly causing more damage... that is the trade-off.

 

[DonTom]

The above fuse is rated for 690 VAC & 500 VDC. In my case, it will have the max of 350 VDC on it at a possible max current of around 70 amps. However, the charge rate can be adjusted, and I decided to always charge at 55 amps from now on.

In this case of motorcycle EV charging, as the battery SOC% raises, the charge current will drop near the end of the charge when the battery voltage is higher.

The voltage spikes from the charger will cause a big increase of current for a fraction of a second, but these fuses are slow blow. However, some EV-Go DCFCs have been known to have spikes at startup and at the end shutdown that can blow fuses in these bikes.

Another issue is the 90-amp fuse that was inside the battery pack (now replaced with a 100 amp) can get a lot hotter than the temp the fuses are normally spec'ed at. I have decided to protect that new 100-amp fuse with a similar fuse in series that is easy-to-get-to, but of 80-amps, located outside the battery pack. So yeah, a series fuse to protect another fuse.

But when I check on the web, I see this big change in prices for the same fuse. Perhaps the cheaper ones are counterfeit? And if so, how far off or what other problems are likely?

I did buy the box of ten fuses from E-bay shown in the bottom photo. They look identical to the 90-amp stock fuse that was in there originally as well as the 100-amp that is now installed. Only difference is the current ratings.

I also cannot find a holder for these types of fuses. No holder is used in the battery pack; the fuse is just bolted down. However, I was able to modify another make of fuse holder so the Bussman fuse fits.

So I am now all set up with all I need but I am still curious about the fuse prices.

-Don- Reno, NV

 

[Mark_K5LXP]

If a "spike" is blowing the fuse it isn't a slow blow, and consider it takes well in excess of rated current for some period of time even for semiconductor fuses. So a review of that charger is in order, it's either roasting the fuse at high currents for extended periods with insufficient cooling, it's seeing an actual fault event or there's a holder causing a heating problem. You might mitigate blowing the 100A with an 80A but it won't correct why the 100A is blowing. By your description this fuse has a ton of margin and would never normally blow. It's blowing, and when you ponder the spec's there's clear indication there's a pretty significant event causing it. It's implied that you'd be OK changing out 80A fuses instead of 100A but it won't fix the root cause.

Mark B.
Albuquerque, NM

 

[DonTom]

If a "spike" is blowing the fuse it isn't a slow blow,

It is all relative. A slow blow fuse will blow in less than a microsecond at a thousand times its rated current capacity.

IOW, how large of a spike? I do not know. But it has happened to several others, but only on the EV-Go chargers, not other makes.

But what could be happening in my case is the warmer temperature inside the Energica battery pack on hot days causes the fuse to blow on any little spike. Fuses are rated near room temperature which means the current they blow at drops a lot as fuses get warmer.

Same with CBs. Here on a hot day, I draw exactly 48-amps @ 240 VAC to charge my Tesla, In ten minutes on a hot day in the garage, the 60-amp CB will trip. It feds nothing else at all, just the Teala Wall Connector. Not a problem, I just delay the charging until 0300 hrs on hot days and then can charge at 48-amps. On cooler days, I can charge up at any time to 48-amps without the 60-amp CB tripping. If I want to charge during the hot day, I can have the Tesla to draw at a lower current such as 30 amps or whatever. Not a big deal but the point is temperature has a lot to do with how & when fuses & CBs blow or trip.

There is no possible way for me to know exactly why a 90-amp slow blow fuse blows at around 65-amps on only one make of charger, but I think it is safe to assume heat as well as a spike at shutdown.

Anyway, I now have the 100-amp fuse in the battery pack protected by an 80-am- fuse outside the pack and I will limit my charge rate to 55 amps (~275 VDC) on that motorcycle from now on which is a charge rate of around 15KW. That is just over 1C, it is a 13.4 KWH battery in that bike. The battery is capable of 2C charging, but the stock fuse is not. 275 VDC times 90 amps 24,750 watts at room temp on a battery that can charge at above 25 KW.

-Don- Auburn, CA

 

[DonTom]

I did some experimenting on this bike today, after figuring out how to get to the engineering screen where it shows stuff such as battery temperature and much more. Two pages of tech info. that is normally not seen.

Fuses and CBs are normally rated for 25°C (77°F). The current ratings drop quite a bit as the ambient temperature gets warmer.

My battery pack temp today was the same as the ambient temp after a 30-minute ride, was then at 33°C (91.5°F).

I went far enough to need a charge, and after the ten-minute DCFC (@17KW) the battery pack temp was 38°C/100°F but the outside temp was by then in the mid 90s.

Not that big of a diff so I am sure my 80-amp easy-to-get-to fuse will protect the 100-amp fuse inside the battery pack.

FWIW, changing the fuse in that battery pack was the biggest automotive job I have ever done. The battery weights close to 500 LBS making it very difficult to work with. To get to it, the bike has to be lifted above the battery with everything disconnected from it. And that is the easy part compared to getting inside the battery pack.

I am glad this job is over with, but I do not want to ever do it again. I also now limit my charging to 55 amps.

-Don- Auburn, CA