How to burn out your alternator while direct charging LiFePo4

[Trebor English]

SW, thanks for the continued reminders on this topic, I just have 1 last question. While I understand that the 1-2-both-off switch is big, what I don’t quite get is how turning it off would be any different than the solenoid on/off toggle.

I suppose the other option is a cheapo WM marine battery connected thru the 1-2-both switch so that juice from the alternator did have somewhere to go, yet would even the momentary “off” as you switch between them be a problem?  Dissimilar battery chemistries he we go.

Edit, read the first link, basically boating is an expensive hobby! It was a good discussion of alternators and temperatures. Still keeps the water muddy for vehicles though, I know you have both the variable voltage setpoint and the additional cooling but for many, that won’t ever happen.

I’m still wondering what all these lithium drop-in peeps are thinking when they install such a power hungry battery, even if they have 0 or 2 gauge wiring to feed it.

The "1-2-both-off" switch can connect either, both or no battery to the alternator.  A switch to turn on and off the connection from the alternator to the house battery never turns off the starter battery leaving the alternator with no battery.  If the alternator is producing some amps it is because it has both RPM and field current.  Take away the battery and the same amps and field current will make a higher voltage.  Before the engine control computer can turn off the field current the voltage could get high enough to roast stuff. 

Even a momentary, brief to human time scale, could be a long enough time to roast electronics. 

A "1-2-both-off" is usually set up so that the order is 1-both-2-off-1-both-2-off rotating one direction and 2-off-1-both-2-off-1-both rotating the other direction.  That way switching from 1 to 2 can be both between 1 and 2.  Rotating the opposite direction you get off between 2 and 1. 

With the engine running the intermediate "both" position assures always at least one battery.  Without the engine running the intermediate "off" position assures that dissimilar batteries aren't connected to each other.  

Meanwhile, the LiFePo4 BMS shuts off the battery when it is full.  If it is the only battery at that time and it goes off then you have a no battery condition.  That could cause a roasting.