Battery relocation project - BF10.4

BCBigfoot106 wrote:
I was thinking of using a battery isolator to seperate the two batteries. To prevent any cross draining between batteries. I was thinking of using a 90 amp isolator. It has 3 posts. One for each battery and one labeled, "Alternator", which would go to the converter? I'm guessing it's a diode based one, like you described. You said they cause a voltage drop?

Yes, that is how they are connected, and yes, they will always have some voltage drop. If the charger has a remote sense wire you can put that around the isolator and it will compensate - at least for the one being measured. But most RV chargers don't seem to have remote sense.

Are you running two battery banks in the TC? The modern thinking is to just parallel them and run them as one large bank. There is a good argument for doing so, it minimizes the depth of discharge and thus maximizes lifetime. However you may have other reasons. If two banks, I would use an automatic charging relay rather than the diode isolator. This is an ordinary relay with a simple circuit that senses when charging voltage is present (more than around 13.5V or so) and closes the relay. Whenever you are charging, they banks are parallel, whenever not, they are separated. Blue Sea is a good brand but there are many that do the same thing. Some have a manual override so you can parallel them with a switch if you need the full capacity for some reason.

As far as fuse size, at the battery. Does this need to be slightly larger than the largest draw on the batteries? I think my Happijacs have 2x20amp fuses. So 50 amp fuse?

I'm going to use AGM's and I have a PD 9160 converter. I have some #2 wire to do the runs to the converter.

Usually you choose fuse sizes to protect the wire. Any connected device should have its own overcurrent protection, if needed. So if the smallest connected wire is #2, you might use a 200 amp fuse. Of course you can go smaller. The idea is in the event of a short, you blow the fuse rather than burn the wire (and your camper), i.e., the wire always has higher current capacity than the fuse. My Happijacks seem fine on a 30 amp fuse (and have their own fuses as well). If you have a #2 running from the battery to the charger or an inverter and also a #8 feeding the DC panel (typical in a TC and what mine has) then you really want to fuse the two lines separately, as close to the battery as possible. I am using a 50 amp for the #8 and a 200 amp for the #2. This is a very convenient way to do that (though as others have pointed out the fuses are expensive at around $15 each). Two high current independent fuses right at the battery terminal.