LiFePo battery upgrade question

Gdetrailer wrote:

otrfun wrote:
The gist of my comment was to acknowledge a fuses lack of precision. Nothing more, nothing less. *If* a given 60a fuse would precisely open at 61a, then, yes, it could be effectively used for current limiting purposes (i.e., protect an alternator from excess battery charge current). Unfortunately, this is not the case. Given batch of 60a fuses of the same type and rating, they may open at 75a, 95a, or even 120a. These are totally unacceptable tolerances in respect to effectively protecting an alternator from excess current while directly charging a battery.

The "gist" of my comment towards your comments is even IF you were to use a fuse that was say 60A and blew open at 61A that would be a total misapplication if you were depending on a fuse to do this.

That would be pretty dumb to blow and replace a fuse each time you hit say 61A when there ARE devices out there that do that job far better automatically without the need to replace fuses or turn breakers back on.

Fuses and breakers are designed to protect the wiring from becoming the fuse and causing a fire, nothing more and nothing less than that.

Fuses are not "regulators" they are for catastrophic events like a short circuit.

If you want or need current limiting then you need regulator devices which are designed specifically to limit current draw (they do so by reducing the output voltage which limits the max output current).

Switching power supplies like the DC to DC charging units being discussed in this thread typically will have output current and/or voltage limiting already prebaked in.

If you are concerned about how much load the DC to DC power supply charger can draw from your alternator source then select a DC to DC power supply charger with a lower amperage output.

In other words, if 60A is the absolute max you want to draw from the alternator, then select a DC to DC power supply charger that has no more than 40A output capability or even less.

As always, include fuses from your power sources. Select fuse/breaker size to the max allowable amperage of your wire, place it as close to the battery(ies) as possible. Should have a fuse on the vehicle side and a fuse on the lithium battery side and the DC to DC charger goes in between both fuses.

Wow. Did you not see the "*" around the word if? It was a hypothetical to describe the type of precision necessary to safely and effectively protect an alternator while charging a battery directly. No such metallic fuse with such precision exists, so it's clearly a hypothetical.

To be clear: I am NOT, I repeat, NOT, proposing the use of a fuse to limit alternator current to the battery. Why? Because a typical metallic fuse doesn't have the precision or close tolerance to do so safely and effectively.

If you read my previous post I clearly support the use of a dc to dc charger. A 40a dc to dc charger is installed in our truck camper. We run our 11k a/c unit with our 200ah lifepo4 all the time when we're on the road. Need the dc to dc charger to charge our lifepo4 back-up in-time for next break. This dc to dc charger gets one heckuva work out everytime we're on the road during the summer. Works great.