Any reason why MRBF seems to be recommended over ANL so often around here?

[sprucegum]

A bit confused. I keep reading a generality that MRBF fuses have higher current interrupting capacity than ANL (usually from posts asking about class T alternatives), but I keep finding the opposite in spec sheets.

Apples to apples: BlueSea MRBF 5000A @ 32V vs BlueSea ANL 6000A @ 32V.

Spec wise, the ANL appears to be (slightly) superior in terms of IAC (and usually cheaper). Certainly I'm not seeing anything indicating a reason to prefer the MRBF.

Is there another aspect I'm missing?

 

[TimE]

A bit confused. I keep reading a generality that MRBF fuses have higher current interrupting capacity than ANL (usually from posts asking about class T alternatives), but I keep finding the opposite in spec sheets.

Apples to apples: BlueSea MRBF 5000A @ 32V vs BlueSea ANL 6000A @ 32V.

Spec wise, the ANL appears to be (slightly) superior in terms of IAC (and usually cheaper). Certainly I'm not seeing anything indicating a reason to prefer the MRBF.

Is there another aspect I'm missing?

Class T or NH00. 20,000A AIC. I won't use MRBF or ANL for fusing at the battery. Lesser rated fuses may work elsewhere in the system

 

[ricardocello]

48v systems (up to 58v rating) need class T or maybe MRBF, the voltage rating makes the dc arc harder to suppress

 

[HarryN]

In my mind, the main advantage of an MRBF fuse is that it is placed right on the battery terminals, so it stops the current right at the source of the power.

As a practical matter, for a 24 volt system, I would instead use one of the blue sea 187 series breakers for each battery. That way you have the circuit protection as well as the ability to turn it off to do maintenance and upgrades down the road.

This assumes that the breaker AIC is rated higher than the battery AIC requirement, which usually isn't too difficult

 

[sprucegum]

I understand that ANL is specifically not rated for 32V max. Beyond that, though, I can't see anything other than a form factor preference (or a preference to ANL for price and slightly higher IAC). While at the higher voltage, the ANL wont work, at the lower voltage, it appears to extinguish higher amperage arcs better than the MRBF.

@HarryN - I thought those 187 series breakers are polarized (they have a load and a line labeled). I would love to use one otherwise and they seem ubiquitous (or the 285 is more ubiquitous but has a specific fine print "* Do not use as a switch where high inrush currents are expected.").

I haven't been able to find any spec sheet state definitively that they were or weren't, but the hive-knowledge I read on this forum said if there's any directionality hint on the studs, they are likely polarized. (And, I've also read that polarized are supposed to be a fire risk between two opposing sources of SCC/Battery).

 

[HarryN]

I understand that ANL is specifically not rated for 32V max. Beyond that, though, I can't see anything other than a form factor preference (or a preference to ANL for price and slightly higher IAC). While at the higher voltage, the ANL wont work, at the lower voltage, it appears to extinguish higher amperage arcs better than the MRBF.

@HarryN - I thought those 187 series breakers are polarized (they have a load and a line labeled). I would love to use one otherwise and they seem ubiquitous (or the 285 is more ubiquitous but has a specific fine print "* Do not use as a switch where high inrush currents are expected.").

I haven't been able to find any spec sheet state definitively that they were or weren't, but the hive-knowledge I read on this forum said if there's any directionality hint on the studs, they are likely polarized. (And, I've also read that polarized are supposed to be a fire risk between two opposing sources of SCC/Battery).

The 187 breakers are a fantastic 12 and 24 volt breaker. I use them all of the time.

They were specifically designed for marine engine room rated use, which is a pretty impressive requirement as it is not only a really good breaker, but also non sparking so it will not ignite fumes in an engine room and that is a big deal in the marine world.

It is a thermal breaker, so it disconnects on the temperature of the internal link, so it is possible for them to pass through a current surge for a short period of time vs most hydraulic magnetic breakers will trip faster. Hydraulic magnetic breakers are amazing for what they can stop, and the way that they stop the arc is to use the magnet to "blow the arc out of the breaker" (usually ), sort of like blowing out a candle, so they are less often used in flammable atmospheres.

The 187s are routinely used with batteries and circuits that include both charging and discharging.

I am not sure of your exact plans, but even in a 24 volt system with a 50 amp SCC, that is ~ 1000 watts, which is a pretty reasonable size system. There isn't any way for the solar panels to supply much more than their rated output (they are self limiting ) so I am not sure how that can be a fire hazard.

On the solar panel to SCC, there is a push to have both the (+) and (-) terminal open, so needing a 2 pole breaker to open.

I should go back and look again, but I believe that the MRBF fuses also fully contain the arc within them while tripping vs ANL do not. That is also the big selling point of a T fuse - it contains the arc during a trip so is engine room rated.



_______

There is nothing more impressive than the specs on a T fuse, but you are not going to be able to pass a start up surge current though one either. It will trip and now you need to go in and replace that $20 fuse and are back to where you started.

If you want to, you can add together an MRBF fuse and the 187 breaker in series for each battery and be certain that it will shut off unless it is a ridiculously capable battery, but I have tested those for fun on a dead short and they trip just fine even in a 48 volt AGM system. That is not scientific / engineering quality testing, just an indicator for fun.
____________

Again - you have to look at what the battery is capable of delivering ( the AIC ) to make sure that it is within the capabilities of the safety device.

A fairly large parallel battery pack can overwhelm a safety device vs pulling it down to for instance 100 - 200 amp-hr batteries in parallel rarely can over whelm something like a 187 breaker.

 

[sprucegum]

Thanks @HarryN for that thoroughness. It seems on this forum that if you follow every 1/1000 gotcha you quickly end up with only one solution (class T) according to the hive-think, yet, in 90% of built systems and examples, even by lithium battery manufacturers (who often show an ANL or MRBF being used), there's a much broader array of solutions (as you mentioned with the bussmann breakers in the boating community).

My system is quite small. 1200W array, 50A SCC, 100Ah 24v (EVE LF105 cells). Reading around, it appears no one really is 100% confident of how to calculate short circuit current when it's not listed in the spec sheet, nor which additional sources of resistance to account for (thus people are probably larging choosing based on fear rather than confident knowledge).

Based on this thread (which is a mix of hunches and deductions), I would get:
27.6v / ((0.5mohm AC Impedance Value * 8 cells) * 2[for bms] * 2[for bus bars]) == 1,725A

That's before additional resistances that would potentially be between the short and the battery (like the failing equipment itself, etc). Interestingly that's not far off from the one research paper listed that measured 1000A for a 150Ah pack (which everyone appeared to be critical of, though I don't know why they'd trust their hunches over a published research paper).

So I don't believe the AIC is actually going to be that big of an issue in my case.

For reference, I have found ANL fuses that are ignition protected (as MRBF are).

On the reverse-polarity issue, if it's a thermal/bimetallic type fuse I agree it shouldn't have any issue with polarity. But it's interesting why it would still be labeled as to the battery side.

I have heard people argue that with the specific setup of an SCC and a battery, that polarity is probably not too big of a deal (so long as the plus is oriented towards the battery side), because of the huge disparity in amperages in the event of a short circuit. But the forum resources a polarized (usually magnetic) breaker between SCC and Battery is stated to be a big no-no.

The most authoritative response to the issue I've found is this post on the midnite power forums by one of their founders who developed their line of breakers. He says:

Our testing shows that with available currents from a PV array, they work perfectly in both directions. That is more of a problem with batteries although we have not seen contact welding until you use battery voltages over 100 volts. You do want to get the battery plus connection connected to the + [....] Even though it isn't a real problem, the NEC is now requiring non polarized breakers. [...] After having shipped 2 million of these din rail breakers, we have yet to find one that has ever failed to open, so it doesn't sound like it is much of a problem.

Again, the actual practices seem to be fine, but concerns still seem to abound on forums and on paper and even in regulatory bodies. I don't think videos like these (which are using huge voltages -- 376V vs a battery system at max 48v) help us think soberly:

 

[HarryN]

If it helps any, most of the DC breakers in the range that is interesting for RV use are actually made by Carling (now part of Littelfuse ) , BUS or CBI. They are all first class companies with a solid team.

Almost everyone else is just re-labeling and or re qualifying them and then putting on their own label. There is nothing at all wrong with that and it has really brought DC breakers into the mainstream at reasonable prices.

Midnight needed a 150 volt DC breaker to match with their 150 volt solar charge controllers, so they purchased I believe 120 VDC breakers with good specs and went through the process of re-qualifying them to 150 VDC, which is a fair amount of work. I remember watching one of their videos about this testing and the amount of battery pack power required to qualify it is approaching the surreal level.

I have an 80 VDC / 30 amp rated mil spec Carling sitting on my desk but they are a bit challenging to find. It does not have any polarity indicators on it that I can easily see at least. It is kind of a specialty setup that I use sometimes.

This is the main page for carling C size breakers if you would like to dive in to a deep technical read of breakers. BTW, just because a breaker setup is "possible" does not mean that you can actually buy it easily in distribution. You kind of have to just deal with what you can buy.

The C size breakers do not have particularly large terminals - roughly 1/4 inch studs, so I try to use this size at not more than 50 amps and usually 30 amp applications.

There are versions out there where they gang a couple together in parallel to increase the current rating, but if you want just one breaker that can really flow a lot of current, I think that you are more or less at your decision point with the info that you have in terms of options.

https://www.carlingtech.com/hm-cb-c-series

I am not in any way a breaker expert, but I have researched this area quite a bit and these things are impressive.