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Mini ANL fuse & holder

Scott Hersha

Well Known Member
It was getting a little crowded where I had my “electrical power center” mounted on the firewall of my RV6 build, so I decided to use a mini ANL fuse to make mounting and servicing easier. It protects the 6 awg B-lead wire going forward to my alternator.

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The B-lead wire is obviously not connected yet, but the exposed portion of the connector will be cover with heat shrink.
 
I use the “midi” fuses quite often, smaller version of the old ANL.
The fuse you show though is not the “normal” midi fuse I use.
Not sure about mounting on the engine mount, likely be in they way down the road.
 
I use the “midi” fuses quite often, smaller version of the old ANL.
The fuse you show though is not the “normal” midi fuse I use.
Not sure about mounting on the engine mount, likely be in they way down the road.

Yep, possibly. The only thing I could think of that would cause an interference was an exhaust system hanger. Should be pretty easy to move though.
 
A “mini ANL” is a fuse, not an ANL current limiter - size accordingly

I’ve studied the data sheets for Bussmann ANL current limiters and Littelfuse MAXI, MIDI, and ATO/ATOF fuses.

These are my thoughts and conclusions; hope they’re helpful.

A Littelfuse MIDI or a "Mini ANL" fuse should be placarded with a higher number compared to a Bussmann ANL current limiter. I put “Mini ANL” in parentheses because it’s not an Bussmann ANL and it opens at a significantly lower current level; seems to be nominally compatible with a Littelfuse MIDI but at the same time it’s a bit of an unknown because complete data sheets are not published. ANL is a Bussmann part number that has been co-opted by others whose products don’t necessarily have the same time-to-open versus current characteristics.

I haven't been able to find a definition or history of current limiters, but, at least in the case of the Bussmann ANL current limiters (which Bussmann calls “non-time-delay low voltage limiter”) of the ratings used in homebuilts (80A and under), it seems like a Bussmann ANL current limiter is a fuse designed so you don't have to calculate how much larger than the load to size it, just use one placarded for your load if it protects a bus feeder or alternator rating if it protects an alternator B lead. For instance, a 60A Bussmann ANL current limiter will carry over 100A indefinitely whereas a 60A Littelfuse MIDI or a “Mini ANL” would open in as little as two minutes.

IMO one could reasonably size a Littelfuse MIDI fuse or a "Mini ANL" fuse 1-1/3 times the alternator rating but I go conservatively higher (1.68 as explained below in the notes I put on my schematic) which still opens with less energy compared to a fuselink.

Summary of opening times:
  • Littelfuse ATOs and ATOFs are manufactured from 1 to 40A. Difference between ATOs and ATOFs seems to be in type of plastic overmold material but interchangeable for homebuilt use. Bussmann ATCs have similar enough time-to-open versus current characteristics to be interchangeable.
  • Littelfuse MAXIs are manufactured from 20 to 80A. Bussmann MAXs and MAXIs have similar enough time-to-open versus current characteristics to be interchangeable with Littelfuse MAXIs.
  • Littelfuse MIDIs are manufactured from 23 to 200A. Bussmann AMIs have similar enough time-to-open versus current characteristics to be interchangeable.
  • % of rating, minimum seconds to open:
    • ATO or ATOF (3-40A times are shown here but these fuses are available down to 1A), MAXI (all ratings, 20-80A), MIDI (23-125A times are shown here but these fuses are available up to 200A)
      MIDI 135 and 350% values are estimated because data sheet does not list them.
      ANL data sheet lists only average melt times so I’ve done some estimation there.
      % of rated current... ........……….…….…….... seconds to open..........……….…….…....
      ............................. ATO..…………... MAXI.……..…. MIDI.…………... ANL - 60A rating
      135%..................... 0.75 to 600... 60 to 1800... 110 to 4800... never opens
      200%..................... 0.15 to 5..….. 2 to 60.……... 3 to 100........ 100 or more
      350%..................... 0.08 to 0.5…. 0.2 to 7.…..… 0.3 to 10…….… 2 average

These are the notes I put on my schematic re alternator B lead fuse/current limiter/fuselink:
  • Littlefuse MIDI (or, alternatively, Bussmann AMI, physically interchangeable with and sized the same as a MIDI) fuses are specified on this schematic for the alternator B leads versus legacy Bussmann ANL current limiters because they are physically smaller; 30 mm vs 61 mm bolt center to center.
  • Bussmann ANL current limiters with the same rating as the alternator could be used but Littlefuse MIDI fuses of a higher rating are chosen. It is assumed the alternator is capable of 120% of its rated output, this is divided first by 0.75 (nuisance blowing factor per Littelfuse "Fuseology" document) and then by 0.95 (temperature re-rating factor per Littelfuse MIDI fuse data sheet, a conservatively high 170F firewall temperature is assumed).
  • Main alternator: (60 * 1.2) / (0.75 * 0.95) = 101A, close enough to 100 to choose a 100A MIDI.
  • Vacuum pad alternator: (35 * 1.2) / (0.75 * 0.95) = 59A, a 60A MIDI is chosen.
  • MANLs aka Mini ANLs (which are not ANL current limiters but rather fuses similar to Littelfuse MIDIs) are physically interchangeable with Littelfuse MIDIs but are not specified on this schematic because manufacturers are unknown although Bob Nuckolls says MANLs such as KnuKonceptz are OK. If used, MANLs should be sized like Littelfuse MIDI fuses.
  • Alternate for alternator B leads is FLW (fuse link wire) 6" long and 4 awg smaller that the B lead, PICO brand is common; available from 10 to 20 awg.
  • FLW is a slightly cleaner installation; Bussmann ANL current limiters, and especially Littelfuse MIDI fuses, open with less energy.

Bob Nuckolls is currently favoring FLW for alternator B leads but IMO one could argue for a Bussmann ANL current limiter or Littelfuse MIDI (or, alternatively, Bussmann AMI) fuse because a #10 copper wire (main alternator FLW for a 6 awg B lead) melts at a relatively high 330 A.

BTW, Bussmann makes a current limiter called ANN (which Bussmann calls “Limiter, Very Fast-Acting”) which is on 61 mm bolt centers like the ANL but opens at significantly lower current levels compared to the ANL. No reason we should consider it.

Here's the Bussmann catalog description of ANL/ANN limiters:
  • Circuit limiters typically used in fork lifts, marine, aviation, and battery charging systems. ANL limiters are fast-acting and ANN limiters are very fast-acting.
  • ANL: Non-time-delay low voltage limiter for use in isolating faults in battery operated systems.

You heard it from some guy on the internet.
.
 
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I don't know what size Mini ANL you chose but it should be placarded with a higher number compared to an ANL.

I haven't been able to find a definition or history of current limiters, but, at least in the case of ANL current limiters of the ratings we use, it seems like they are designed so you don't have to calculate how much larger than the load to size them, just use one placarded for your load. Note a 60A ANL will carry over 100A continuously.

This is the note I put on my schematic:
  • Littlefuse MIDI/Bussmann AMI fuses are specified on this schematic for the alternator B leads versus legacy ANL current limiters because they are physically smaller.
  • ANL current limiters with the same rating as the alternator could be used but MIDI fuses of a higher rating are chosen. It is assumed the alternator is capable of 120% of its rated output, this is divided first by 0.75 (nuisance blowing factor per Littelfuse "Fuseology" document) and then by 0.95 (temperature re-rating factor per Littelfuse MIDI data sheet, 170F firewall temperature is assumed).
  • Main alternator: (60 * 1.2) / (0.75 * 0.95) = 101 A, close enough to 100 to choose a 100 A MIDI.
  • Vacuum pad alternator: (35 * 1.2) / (0.75 * 0.95) = 59 A, a 60 A MIDI is chosen.
  • MANLs (mini ANLs), which are physically interchangable with MIDIs, are not specified on this schematic because manufacturers are unknown although Bob Nuckolls says MANLs such as KnuKonceptz are OK.
  • Alternate for alternator B leads is FLW (fuse link wire) 6" long and 4 awg smaller that the B lead, PICO brand is common; available from 10 to 20 awg.
  • FLW is a slightly cleaner installation; ANLs, and expecially MIDIs, open with less energy.

Bob Nuckolls is currently favoring FLW but one could argue for an ANL or MIDI because a #10 copper wire (main alternator FLW) melts at a relatively high 330 A.
.

My mini ANL is a 50 amp current limiter. It protects a 6 awg line going forward to my 40 amp alternator. I’m not worried about my 40 amp alternator frying that wire if there is a short for two reasons. First - it’s on the aft end of the wire run and would do nothing in the event of a short if the alternator feeds the short, because it can’t overcome the fuse. Second - if there is a short, the battery is the bomb that can melt things and will feed the short, and it is therefore the only reason for this ANL fuse. The current limiter will melt before the 6 awg B-lead does. The 40 amp alternator is not capable of melting a 6 awg cable, since it is basically self regulating. There’s no way it can exceed the 75+ amps required to melt a 6 awg wire, however, the battery can, hence the current limiter on the battery end of that wire. I also have a 50 amp maxi fuse protecting the main bus feed on the 6awg line going from the battery/alternator feed before it goes through the firewall. So there are basically two current load protectors on this line from the alternator to the battery, then to the main bus. The ANL current limiter only protects the line going forward to the alternator, not in the other direction. And the maxi fuse only protects the line going aft through the the firewall to the cockpit. For both of these lines, the only thing capable of exceeding the current carrying capability of the 6 awg lines is the battery, hence the fuse (quick), and current limiter (slow).

I could/can use a midi fuse for this application/fuse holder, but I couldn’t find one of the appropriate load rating locally, so I chose the MINI. There is no advantage either way as far as I have been able to discover, but I will have substitutes on hand before I fly.
 
It was getting a little crowded where I had my “electrical power center” mounted on the firewall of my RV6 build, so I decided to use a mini ANL fuse to make mounting and servicing easier. It protects the 6 awg B-lead wire going forward to my alternator.

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View attachment 23083

View attachment 23084

View attachment 23085

The B-lead wire is obviously not connected yet, but the exposed portion of the connector will be cover with heat shrink.

Hi.
Do you use fuses on both sides of the "B-Lead" wire from the alternator to the main bus?
It is important to protect this wire on both sides since a "Short Circuit" between this wire to A/C GND must be protected in both cases: 1. when the power source is the alternator and 2. when the power source is the battery through the main bus.
Ariel Arielly
RV8a
4X-OAA
 
Do you use fuses on both sides of the "B-Lead" wire
No, the "B" lead is big enough to carry the full output of the alternator without overheating. The alternator is not capable of putting out much more than its rated output. Even if there was a fuse at the alternator end of the "B" lead, it would not blow from maximum alternator output. And you would not want it to blow while supplying the aircraft electrical system with maximum current.
 
No, the "B" lead is big enough to carry the full output of the alternator without overheating. The alternator is not capable of putting out much more than its rated output. Even if there was a fuse at the alternator end of the "B" lead, it would not blow from maximum alternator output. And you would not want it to blow while supplying the aircraft electrical system with maximum current.

Hi.
My question is what happens if there is a short between the B-lead to aircraft ground while the master solenoid is "ON" and the main bus, to which the B-lead is connected to, is "Hi"?
This is the case that power is feed to the B-lead from the other side.....

Ariel
 
If the alternator "B" lead is connected to the main power bus, then the "B" lead should be fused just like the loads are.
 
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