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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