Hi, I'm getting ready to set my RPi 4 + MacArthur with power module.
Looking at the docs, I understand that 12V should be permanently connected to the battery and the system will power up from the N2K 12V connected to SW so that it powers up together with the rest of nav system.
My question is how to do this when the boat has two batteries and a selector switch. If 12V is permanently connected to one battery, but then I select the other battery to power the electronics, the Hat would get power from two different sources.
Isn't this a problem? Are those two circuits completely separated or will the two batteries try to balance out through the Hat?
Thanks!
Without some details on how your boat is wired, it's rough to answer your question, but if your battery selector switches just mover the house and instruments from one bank to another (or both at once in parallel) it shouldn't make a difference.
It's a standard two battery, 1-2-Both switch setup.
Question is, what happens when 12V is permanently connected to Bank #1, selector switch is set to Bank#2, and therefore 12V SW is powered by Bank#2.
Are 12V and 12V SW circuits completely isolated? Because if they're not, then the two batteries will balance out through the Hat.
Simplified drawing:
[
attachment=3317]
12V SW and 12V are not isolated by the proper electrical term. There's no direct connection between the inputs, but there are a few diodes, transistors and resistors between the two. For details see the schematic available here:
https://github.com/OpenMarine/MacArthur-HAT
There should be less than a mA flowing between the two connections. So I think you're probably fine, as long as there's a shared ground between the two batteries.
Surely, both batteries go to a positive bus on your 12v panel which feed all your electrical needs.
Connect to this positive bus.
(2025-03-05, 07:30 AM)Adrian Wrote: [ -> ]12V SW and 12V are not isolated by the proper electrical term. There's no direct connection between the inputs, but there are a few diodes, transistors and resistors between the two. For details see the schematic available here: https://github.com/OpenMarine/MacArthur-HAT
There should be less than a mA flowing between the two connections. So I think you're probably fine, as long as there's a shared ground between the two batteries.
Thanks, I guess this is the schematic you mentioned.
[
attachment=3319]
Looking at this, it seems that even if I switch batteries with the selector switch, the RPi would still be powered by the permanently connected 12V.
So how do people usually connect the RPi+Hat to their system? Do you just connect the 12V to the selector switch instead of directly to the battery? I will then have to remember to turn off 12V SW before turning off the main power, otherwise the system won't shut down properly, right?
(2025-03-05, 08:52 AM)Lazzz Wrote: [ -> ]Surely, both batteries go to a positive bus on your 12v panel which feed all your electrical needs.
Connect to this positive bus.
They go through the selector switch. That's my question, how do you connect it to make the system fool-proof. With a direct connection of 12V to a battery, the system is protected even if someone (me) accidently turns off the main power.