question

I am in a similar predicament. I will soon be moving up from a 24V to a 48V system which means that all of my 32V Mega fuses need to go. As you have discovered, 100A is the lowest rating in the 58V Mega fuse range. Also the prices for these fuses are very high. The cheapest price I can find is from a large distributor in Texas.

I don't like the MRBF fuse because of the longer stud requirement and also there is a lot off fiddling around with insulated bushes and nuts.

I do like the Littelfuse BF1 58V range which are sensibly priced too. That range covers 30A - 200A.
All this sounds great except that the BF1 is much shorter. So I am currently mulling over a couple of designs in my head to fabricate some adaptor plates which wouldallow the BF1 to be used in a Mega space.
I'll post my ideas if I find a working solution.

Thanks wkirby. You're right the MRBF fuses seem fiddly. The BF1 fuse looks identical to a Midi fuse, which is what I'm leaning toward at the moment. The 58V Midi fuses are Victron products and clearly state that they're intended for 48V systems, unlike the MRBF ones. My only concern is that their interrupt rating is probably only around 1,000 A (like those BF1 fuses).

On another discussion forum someone suggested that it's possible for a fuse like this t 48V to sustain an arc when failing, driven by high current from the battery. I figure:

- That's the purpose of the Class T fuse at the battery - if the battery is driving high current into a fault, the Class T fuse will blow.

- Victron specifies the use of "58V for 48V product" Mega fuses in its Lynx Distributor, which I trust. And the Midi fuse has the same voltage rating.

I like your "adaptor plate" idea. My starting thought is 30mm length of copper bar stock with 9mm and 6mm holes drilled next to each other. Place it on the Lynx positive busbar's M8 bolt and attach the fuse with a standard M5 stainless bolt. Same at the other end of the fuse. The difficulty is the M8 & M5 bolts are so close that their nuts might clash*.

It would be great if Victron supplied Midi adapter plates with the Lynx, or just released 58V Mega fuses in lower amp ratings.

Sounds painful! :-)

I have looked at this in detail and there doesn't seem to be a solution. The AIC of Mega or Midi or even ANN CNN fuses is not high enough for lithium banks and also not suitable for any LA over bank over 150Ah AGM with a small saftey margin when looking at potential short circuit situations.

The limitation is physics, as the length of the fuse body is directly correlated to the the voltage and the quench capabilites. Midi, Mega or ANN will not satisfy the calculations for anything bigger than stated above if I comply with our local regs.

My bank has a potential of atleast 12.5kA so HRC, NH, 10*38 etc type fuses are the only options.

What makes it even more difficult to determine is that the regs regarding DC series fusing are almost non-existant. In the industrial world of 3 phase VAC you would be allowed to use series fuse calculations to accomodate for all the components to be protected at maximum incoming kVA from the transformer. Although it is better if you can use components in the circuit design to meet the required numbers without using the downstream fuses in series as the method.

In the DC world I would not like to use series ratings for fuses and would rather have all components used be capable of full load break, full AIC and max 75% rating on continous current*temp derating factor. (Schneider technical engineers in particular stressed that we must respect the 80% continuos current derating factor when dealing with DC using their switch disconnectors).

Put in simple terms this means that you would have to calculate conductor size using Adiabatic equations and also calculate the "let through current" of the main battery bank fuse before assuming the Class "T" will actually protect anything downstream. I would not be too bothered with a bank of a few SLA batteries in an RV or Boat but for large LA and certainly lithium I would like to design all the circuit (main and branch) with AIC rated fuses at the battery short circuit potential.

Our local regs/code state-

quote-

"The over current device (either a fuse or circuit-breaker) must:
- Have a trip value and response time as specified within the charge controller manual.
- Be rated for operation at d.c., at 125% of the nominal battery voltage.
- Have an interrupt rating greater than the potential battery short circuit current."

In summary all fuses in main and branch circuits to be rated at 125% of nominal battery or supply voltage (which at 48VDC*1.25 gives us 60VDC so the Victron Lynx 58VDC Mega fuses are out of the picture) and with an AIC of the maximium short circuit current that can be generated form the battery or PV. This is what our local regs/code require. This automatically gets rid of the use of Mega, Midi, ANN, CNN, ATO and 6kA-10kA DC rated MCB's. Alternatives I use are for the smaller stuff are the 10*38 fuse carriers rated DC20B (not to disconnect under load) which can be DIN mounted and have fuses cabable of 50kA AIC DC. Using the HRC or NH on the bigger stuff.

On this premise, the use of Mega and Midi and CNN fuses is out of the question.

I am also guilty of spending over a thousand pounds on all the Lynx range before realsing the limitation is the available fuse ratings at 58VDC. I only looked at the 1000A 60VDC rating and didn't think that the fuses would be a problem.

A real shame as the Lynx stuff is really good value for what you get, and makes tidy install.

Little fuse do make 70VDC Mega fuses but the size is 5mm longer on centres and they have insufficient AIC properties.

I did email Littlefuse a few weeks ago to ask them if they have any margin on the 58VDC that would allow us to use them and meet code/regs. They replied saying 70VDC fuses are available in Mega fuses. Although they are larger and will not fit the Lynx and AIC are @1kA.

The reality is now that we are moving into the Lithium world of big AIC ceramic type fuses that are the size of a hotdog, are going to be the norm. For anyone wanting to use MCCB's in the new lithium world, you must seriously consider leaving them for use in AC applications. That is just my opinion from experience over many decades.

As I have written in previous posts, watch the Romanian install of the Victron kit in the container on youtube, their whole design is based on NH fuses for a reason.

If Victron are listening, @mvader (Victron Energy) would it be possible to offer a retrofit for the Lynx Power In and Lynx Distributer that will allow the use of HRC fuses to accomodate for the minimum 60VDC fuse rating, as these are really fantastic modular affordable units. There are some fuses that are @45-55mm on centres with huge AIC and they will fit under the case.

Alternatively a retrofit for the Lynx Power In, an insulated bus bar that could be bolted to the 8mm incoming and protrude 30mm out of the existing cable entry holes in the casing so you can bolt a fuse carrier straight to it. Currently I am just using 50mm of 50mm square cable and 2 lugs one bolted to the power in and the other to the fuse carrier. Industry use droppers for this same function. If you could make one for the lynx and sell in a pack of 4 this would solve the 58VDC fuse problem people are facing when going to 48VDC systems.

regards