Swapping Lead acid for LiPo on my "house" battery, alternator charging questions

[DiploStrat]

If you want to use this switch as a manual jump start, then you need to wire it AROUND the B2B. And, if a jump circuit, all of it has to be rated to carry at least 100A, 200A would be better.

Remember, a B2B (or at least every one that I know) will pass current only from the starter battery/alternator to the camper battery. To jump start, you need to provide a route around the B2B, in effect, going the other direction. (I know, electricity isn't exactly directional, but I hope you get the idea.)

 

[concretejungle]

If you want to use this switch as a manual jump start, then you need to wire it AROUND the B2B. And, if a jump circuit, all of it has to be rated to carry at least 100A, 200A would be better.

Remember, a B2B (or at least every one that I know) will pass current only from the starter battery/alternator to the camper battery. To jump start, you need to provide a route around the B2B, in effect, going the other direction. (I know, electricity isn't exactly directional, but I hope you get the idea.)

That's what I was worried about! OK if I hit an emergency I'll just pull the lithium battery out and use jumper cables! I was concerned that the dc to dc charger is a one way device.

 

[DiploStrat]

Methinks you are over panicking! This is REALLY easy.

-- Wire at jumper gauge from starter battery to a terminal.

-- Wire, again at jumper gauge, from the camper battery to a terminal.

-- Wire the B2B between the terminals. (Again, use the wire gauge recommended by the B2B manufacturer.)

-- Wire, jumper gauge, terminal to terminal, bypassing the B2B.

-- Put your Blue Sea (or other) switch in the bypass circuit.

In normal use, the bypass switch is open, so that the B2B charges your camper battery. In emergency, when you need a jump, simply close the switch and the camper and starter batteries will be in parallel. After the engine starts, open the bypass switch again.

This isn't hard.

 

[DiploStrat]

My conventional wisdom is that if you can run either battery flat, you have a poor design or poor practice.

Let me tell you about the time I left the ignition key on for a week ...

 

[concretejungle]

this has been very helpful. I have just enough knowledge to be dangerous!

Attached is my horrible wiring diagram for how I plan to wire this stuff up (without the switch). What do you think?

 

[WVI]

What's the wire from the Alt to the fuse?

 

[concretejungle]

What's the wire from the Alt to the fuse?

That is the power lead from the alternator to a fuse then back to the dc to dc charger. I wanted to fuse it up front near the alternator and not back at the rear of the truck where the DC to DC charger will be. I always thought you should fuse your hot wires as close to the power source as possible.

 

[WVI]

could you not do away with that as the battery on the vehicle should do the same thing??

 

[concretejungle]

about 7 years ago I replaced the OEM wiring harness on my cruiser with a new OEM wiring harness. When doing that I replaced the OEM lead from the alternator to the battery with 4 gauge marine grade wiring. So I feel pretty good about it.

 

[concretejungle]

well, it's done! Everything is working, no breakers popped or fuses blown. The new victron devices all updated their firmware and are functioning great. The first thing I've had to get used to is the fact that the lithium battery holds its charge while it's sitting. I was so used to having to keep the solar panels hooked up while my truck sits to keep the lead acid auxiliary battery topped off. Now, this lithium battery is at the same charge it was a week ago!

the only thing I did not do was wire the jumper switch in. I just did not want to run that heavy gauge wire that long of a run.