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balachai avatar image

MRBF fuse in Lynx Distributor at 48V?

I've got a couple of circuits which need fuses lower than 100A, and I'd like to connect them to the positive and negative busbars inside my Lynx distributor. Mega fuses fit perfectly (as the Lynx dimensions are intended for those) but 48V Mega fuses are all greater than 100A.

So I'm looking at MRBF fuses. The Lynx housing has enough vertical space to mount them, I'll just need to replace the bolts with longer ones.

The other issue with MRBF fuses is voltage rating - I'll be charging my battery to a max. of 57.6V, which is below the fuse's max rating of 58V (can interrupt 2,000A at 58V). So that seems OK. However MRBF product info only mentions 12V, 24V and 42V systems. Perhaps they're avoiding mentioning 48V systems because some of those charge their battery above 58V, which is not the case for me? I've also got a Class T fuse at the battery.

Any thoughts?

https://www.amazon.com/Marine-Rated-Battery-Fuse-MRBF/dp/B0761MGW6Q

fuses
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2 Answers
balachai avatar image
balachai answered ·

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! :-)

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The nuts of the M8 and M5 bolts will clash according to my measurements, this is the challenge.

My current idea is to take some 6mm bar stock to make an extension tab at each end of the midi fuse. Then cut a 0.4mm slot with slitting saw to accommodate the terminal of the BF1 fuse. If the 0.4mm has 4.5mm of metal below it then that section can be threaded for a very short stainless countersunk screw. If the countersunk screw does not protrude out the bottom then we should avoid any clashes with the M8 fixings.
Hopefully I would still be able to achieve a 4.5Nm torque on the M5 screw without pulling the copper thread out - it will probably be fine.
I am slightly concerned about the lack of washers with this method, there is a chance that the screw could back out with expansion and contraction. Thread locker will not help here.
Another way is some sort of right angled extension to allow the BF1 to be bolted vertically (rotated 90° about its length). This will allow the use of proper washers etc. The caveat here is the height. I'm OK with height, I have lots of it in my fuse cabinet.
There is more thinking to do.

The 1000A interrupt rating is a little lower than I might like, however the BF2 (Mega) fuse is also 1000A.
My fuses are mounted in a metal enclosure which helps too.

Where I currently have 80A fuses, I'll use 100A Mega fuses, my wiring there is adequate. My other circuits need fuses greater than 100A, so the Mega fuses will cover those.

wkirby avatar image
wkirby answered ·

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.

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