Unexpected/weird On/Off switch behavior in 12v DC System

[aseid28]

Here's the setup:

• 400ah battery bank on 12v has a positive line that connects to a 400a fuse, then to a Blue Sea On/Off Switch, then to the positive Bus Bar, then to the Fuse Box, then to the Loads.
• Loads come back on the negative to the Fuse Box, then the negative Bus, which goes to the ground, and also connects to the negative terminal on the battery.
• There is a battery monitor attached to the negative battery terminal, plus a small sensor attached to the positive terminal of the battery (so, should be operating on a separate circuit not divided by the On/Off Switch).
• There is a solar charger that attaches to the positive and negative bus bars and provides power to the system.
• Lastly, there is an AC-to-DC Shore Power system that attaches provides power to the positive and negative bus bars.

Now, here's where it gets weird...

• The On/Off switch it set to "Off". So, the battery circuit should be broken. The Shore Power and Solar Charger are operating on separate circuits, but they're both turned off, so are not supplying power to the system.
• The Battery Monitor is also operating on a separate circuit, so it also does not rely on the Switch to be "On" to operate. It is reading 13.36v which seems normal.
• I flip the switch to "On". The battery circuit should now be complete and power should be reaching the positive Bus directly from the battery. However, not only does no power reach the positive bus, everything goes dead, even the Battery monitor operating on a separate circuit. Like, the battery monitor voltage immediately drops from 13.36 to 6 to 2 to 0 and then goes dead.

Now, it gets even weirder...

• If I turn the switch back to "Off", after a little bit of time (maybe 10 seconds), the Battery Monitor comes back to life and shows the voltage of the batteries at 13.36v.
• Now, if I flip the Shore Charger on, my Loads all function (this is expected; they're on a separate circuit from the Battery).
• Then, I flip the On/Off switch to "On" and nothing changes; the Shore Charger is still powering the loads. Cool Beans.
• Now... I turn the Shore Charger off. And... the loads continue operating as normal. The battery is supplying power to the loads, the Battery Monitor readings are normal, etc.

So, if I want my battery to work, I need to:

1. Turn on Shore Power
2. Flip Battery On/Off switch to "On"
3. Turn off Shore Power.

And then my batteries work.

So, this isn't ideal at all, but most importantly I have no idea why/how that could all possibly be happening. Can anyone help??

thanks so much -

Andrew

 

[James]

You need to turn the battery switch on so the system goes ”dead” as described above.

use a multi meter set on volts and measure the voltage across the batteries, then the bus bar and so on until you find where the power stops flowing.