Boat hasn't been used much for a couple of years and this has resulted in 2 out of 3 batteries totally dead - none of them can put out enough current to start the engine or pull up the anchor.
Two brand new 260AH AGM batteries were installed a while back and dad had an old but still working gel battery in the stern that he could manually parallel up with the house load for some reason (goes direct to the main circuits).
Some history:
How It Originally Worked
- Two batteries
- One main switch: 1, 2, both, off
- One main circuit for start, and house
- A smaller switch that isolated all nav equipment from the main circuit
- For part of that time we had a heavy duty diode bank that allowed lowest bank to charge first - that was discontinued at some point
- Cruise on both
- Isolate completely when moored with off
- Isolate completely overnight while asleep with off
- Switch to 1 or 2 before killing engine after anchoring (alternating between each bank day by day on a longer trip)
- Chew through that one battery with lights, pumps, electronics, etc until bed time
- Switch to 2 to start the engine
- Switch to both once started
- Pull anchor up with engine running and both batteries in parallel
- Batteries recharged while cruising to next location
Status quo: How It Is Now
Done on insurance a few years ago by an marine electrician:
- Dedicated start battery - isolation switch cuts off starter and key and kill button somehow
- Dedicated house battery - isolation switch cuts off house circuit, pumps and things
- Override link switch to bridge the batteries together for whatever reason
- VSR (voltage sensitive relay) that bridges the house bank to the start bank if the start bank is higher (I think, WTF if right)
- Some kind of accessory feed system that keeps the electronic systems connected ALL THE TIME even when the HOUSE BANK IS ISOLATED (and resulted in a dead house bank within a few months of being installed)
This has not been working for us at all. It sucks. The saving grace has been the old gel battery in the aft compartment that is wired into the house circuit directly and that you take the terminal off to isolate.
To get the boat usable for a little holiday away from terrafirma I put together a 1300CCA/800A-for-30s/160A-to-empty 16 cell headway 38120HP pack and replaced the 260AH starting bank battery with it. I nearly got a hernia and nearly sank the boat with a battery shaped hole in the bottom, but with some screaming and help from wife, we got it up onto the deck leaving room for the baby headway pack. Observations:
- 1300CCA is plenty to crank over and start the 8 litre C series Cummins (starts instantly) but in the event of some kind of issue, eg air in the fuel system, 32AH is not much capacity for repeated attempts
- Alternator goes to too high a voltage (15.2 or so) when unloaded (bad AGM batteries and full/fresh headway pack) and this can/will damage the headway LiFePO4 pack
- Isolation switch cuts off start bank from charging as well as loads, so is ALMOST fully isolated and can sit in fully charged state fairly healthy while cruising etc in this state
- Bridge switch feeds charging into starting bank even if starting bank is "isolated" and must be off to avoid over charging the lithium pack
- VSR can trigger without engine running and link good headway pack to bad house pack thus draining the headway pack for no good effect (ill intention of charging bad pack from good...) - I think this is why the starting wasn't as crisp after we left it all connected for a day and a half
- Anchor winch will not work without the lithium bank in parallel - the bad banks cannot produce high currents even after hours charging and even with the engine running - they're knackered
- Alternator current supply is less than winch current demand
- With the engine running the 32AH headway pack can lower and raise the anchor a decent distance without running out of juice (but not a lot of margin in deep water)
- After draining the headway pack the alternator has a load and the system voltage is determined by that pack - you can watch the voltage sit at 12.8 under load and about the same while charging and hit the isolate switch when you get to about 14.4 or so at which point the voltage spikes to 16V!
The above learnings have got me thinking about what I actually want to do once the boat is mine and I can start spending some money on it to make it right and reliable and trustworthy. Those requirements and initial design thoughts in the next post.