RL70 Chartplotter Resets when Using ST5000+ Autopilot

[Capt.Don]

Hi, Now that the ST5000+ autopilot is working (today), I discovered another strange behavior with the boat's electronics. The boat has (in theory) separate house and starter battery banks. When setting the A-B-Both to starter AND engage ST5000+ autopilot, the RL70 chartplotter recycles and restarts. When put on standby, the chartplotter works as normal. When setting the A-B-Both to House or Both, the chartplotter and autohelm play nicely together and work fine.

I am in the process of untangling the wiring on this boat. I plan on reviewing all the wiring and electrical components, and comparing to the original specs. There's a Heart 10 charger/inverter, some sort of Xantrex module, along with a non-functioning battery combiner. All of this routes through the A-B-Both switch, along with alternator. Thankfully, no other sources of electrical.

My suspicion is that something is wired to the starter battery. When using only the starter battery, voltage is somehow leaking across (through the instrument or faulty battery combiner?), to the house bank, powering the other instruments. There may be sufficient voltage to run the wind, speed, depth modules, but not enough for the chartplotter, causing it to keep resetting. The funny thing, is it only happens when engaging the autopilot (set to Auto).

What do you think is going on? I think a complete electrical review is in order!
Thanks,
Don

[senormechanico]

Definitely a voltage sag causing the reboot of the chartplotter.
Could be undersized, corroded wiring, poor connections, weak or poorly charged batteries, improperly cross connected battery banks or a combination of all of the above.
Good luck.

[bstreep]

I would also guess voltage problem - that was the obvious sign of failing battery bank on our boat (obvious to everyone but ME). The Raymarine units are VERY voltage sensitive. As your autopilot engages, it draws down the battery to the point the chartplotter kicks off. You have anything else with a big draw you can check, like a windlass or electric winch?

[Capt.Don]

Thanks - yes, I can try the same experiment with the windlass, fridge or other electronics. With this happening only on the starter battery, this might indicate the starter battery is failing.

I think I have several issues to sort out: (1) unknown wiring with a failed battery combiner, (2) possible failing battery bank(s), (3) faulty connections. I need to figure out how the battery banks are wired with the A-B-Both switch, charger, alternator, inverter. There are also several wires connected directly to the starting battery. I'd like to understand why these aren't on the house bus. The fun begins.