Engine fire

[Hayden Watson]

Is the red wire going to the alternator fused near the alternator? Was the start battery switch ON? Is the alternator output wired directly to the batteries or does it go through the Start battery switch?

I would determine if it's possible that the positive alternator post contacted the engine....

Engine was a 4JH? ?

It is a common misconception that the B+ wire from the alternator to the battery should be fused near the alternator. This is incorrect.

The output from the alternator cannot exceed the max specified output of the alternator and the wire should be properly sized for that current so there is no need for a fuse near the alternator.

The fuse is to protect the wire from a short to the battery which can easily exceed the ampacity of any wire and should be as close as possible to the battery. It does not protect the wire from current output of the alternator. On my boat with 560Ah of LFP battery, I have a Class-T within 6" of the battery positive terminal. I then have another 200A MRBF fuse where the alternator wire connects to the positive charge buss. The MRBF is probably not needed but it predated the LFP and Class-T

 

[dlochner]

. I then have another 200A MRBF fuse where the alternator wire connects to the positive charge buss. The MRBF is probably not needed but it predated the LFP and Class-T

It really depends on the wire size from the positive bus bar to the alternator. If the ampacity of the wire is greater than the rating of the Class T fuse, then the MRBF is not necessary, if not then the MRBF is.

 

[ice breaker]

So if my engine started and ran without any issues, then the fire circuit to the pressure switch was ok? So if there was pressure in the fire extinguisher, why did it fail to go off?

Yes I would agree with that. I am not speculating on the fire, just sharing my experience with Sea Fire. Glad that I have one installed.

 

[Hayden Watson]

It really depends on the wire size from the positive bus bar to the alternator. If the ampacity of the wire is greater than the rating of the Class T fuse, then the MRBF is not necessary, if not then the MRBF is.

Correct. I have 2/0 from the battery to the alternator which has an ampacity of 350A if memory serves so I do not need the MRBF.

 

[dlochner]

Correct. I have 2/0 from the battery to the alternator which has an ampacity of 350A if memory serves so I do not need the MRBF.

The 2/0 has a rating of 330a outside of an engine space and 280 in an engine space. Assuming a 300a Class T you're right on the edge, probably OK, safer with the MRBF.

 

[Hayden Watson]

The 2/0 has a rating of 330a outside of an engine space and 280 in an engine space. Assuming a 300a Class T you're right on the edge, probably OK, safer with the MRBF.

200A on both. I am limiting my system to 190a max due to other components. The alternator is 250A and hit 242A at 6000rpm on the manufacturers test stand. This is the max alternator speed that can be produced with my engine. I have then put a 0.5ohm x 100w resistor onto the field wire which limits the max output to 190A if all else fails and the full 14v is fed to the stator. From there, the output is further controlled by PWM control on the field wire to limit the output to anything I want.
I chose the 250A large frame because it has superior cooling to the small frame and has enough over-capacity to allow it to run full time at 190A without overheating.

 

[artboas]

Art, I think you mean the fuel shutoff solenoid? I don't think there are a "choke" on a diesel.

Yes, that’s what I meant.
I know of an engine fire that was caused by this several years ago