Relocating House Loads

[Theo Lewis]

Greetings A4 friends,

My A4 does now start reliably, purrs like champion for extended crossings and gets my crew (family) home safely after the knowledge provided by the post archives, forum contributors when the answers weren’t apparent, parts and advice from MMI, several bloody knuckles and of course… many magic words over the last few years. Best part is the boat is no longer a massive fire hazard. Thank you.

Since I am running reliably I am turning to the spaghetti bowls that are my electrical box, switch/fuse panel, instrument and ignition panel and finally engine compartment. Everything ON the engine now belongs there; replacing poor quality wiring, connectors, terminals and bad patch jobs will be ongoing. Rerouting and securing will also be entertaining. I do have a good assortment of Don Casey and Nigel Calder reference works to ponder.

Looking for some discussion on pros and cons to relocating the house loads from their original power source, which I learned from a schematic (attached) from this forum, is the outgoing side of the ammeter. I was relieved recently after an afternoon of boat yoga, wiring a new chartplotter, to find that my A4 appears to be wired as originally designed per the wiring diagram (attached). Albeit with a couple hundred patches, every kind of wire imaginable from Romex to audio speaker wire (how expensive is respectable tinned copper really!) All the gear, major parts of the boat are top notch but the wiring all appears to have come from garage scraps and the corner auto parts store.

My plan has been to preserve and isolate the engine wiring per the original schematic with the exception of removing the house loads. Instead follow what appears to be conventional wisdom and run a 30 amp cube fuse off one of the two House/Start batteries to feed the house loads and their spiderweb of systems and wiring. Also considering just running the 30A fuse off the battery selector switch.

Thoughts or advice welcome.

[Dave Neptune]

I rewired my E-35MkII a bit different than original. My goal was to shorten the runs where ever possible. The engine was in the middle of the boat, the "panel" and power switch was in the galley, the ammeter in the cockpit and the batteries were in the qtr berth. Copper was also cheap when the boat was built in 1970.

By moving the power switch close to the engine box and eliminating the analog ammeter I removed 30+ feet of cable that went back and forth to the cockpit a few times. I purchased an electronic ammeter so I could mount the "shunt" near the switch as the sensing wires can lead to anywhere you want.

My starting leads to and from the engine went from 25+ feet in both directions to under 4 feet and the panel feed from 20 feet to about 8 feet. The alt lead was a back and forth too and shortened to 2 feet. This really made a difference in voltage drops.

A good time to mount a remote start switch too.

Dave Neptune

[edwardc]

An additional point to ponder. In the original "conventional" wiring diagram, a heavy #4 (or larger) cable runs from the battery switch output to the the main terminal on the solenoid. ALL other DC loads are then taken from solenoid's large terminal.

To me, this doesn't make sense. When starting, the large starter motor current (around 60A?) will cause a noticeable voltage drop across the length of #4 wire. You can easily measure this by putting a voltmeter on the solenoid bat terminal when cranking. Often, the #4 wire size is undersized, given the total length of the "back and forth" wiring runs, and the voltage drop upon cranking is enough to "crash" sensitive electronics, even though the starter couldn't care less about it.

Instead, why not have a positive DC bus bar located close to the battery switch. The #4 starter cable, and ALL other DC loads, can come off of here. This avoids propagating the large-ish voltage drop of the starter circuit into all of the boat's electronics.

On my boat, with the original "conventional" wiring, the autopilot crashes and resets to "standby" mode when the engine is started, and the AIS portion of the radio hangs and simply stops producing position reports. Both of these conditions are easy to initially overlook until you realize that "something's not right!..."

In my upcoming DC rewiring/Lithium Battery upgrade, I plan to go even one step further, using a dedicated start battery that will completely isolate the starting transients from the DC house bus.

[joe_db]

This is a simplified diagram of my DC power wiring and what my battery switch looks like. The panel handles house, engine, and manual parallel. The hour meter and inverter switch are to the left of the panel.

[Al Schober]

My Tartan 30 ('73 vintage) had 2 group 27 batteries and an A/B switch when purchased.
When I sold it (30 yrs later), it had a group 24 dedicated to the engine and 2 group 27 batteries dedicated to the house loads. Each battery/bank had an on/off switch. Alternator output went directly to the house bank. When the house bank came up to voltage (12.8 or so) a VSR would close and send charge current to the start battery. System worked well.
I also had a battery monitor (Victron?) but only trusted the voltage and current readings. I never got to fully trust the 'state of charge' display. I learned to read the voltage/current during charge/discharge and judge how the battery was doing.
I never did install one of those 'emergency start' systems. Jumper cables seemed to satisfy the need, and never needed them.
Consider your needs and have your electrical system satisfy them. I had no TV or microwave, but did carry a 100W inverter. An inverter bigger than that won't work on a lighter plug but will need a better connection (hard wire?).

[joe_db]

Basic guidelines:
Get rid of the stock ammeter if you still have it, the alternator needs to be connected to the batteries by short and heavy cable with appropriate protection.
Get a voltmeter.
Don't divide the banks evenly, depth-of-discharge is everything to battery life. You want the biggest house bank you can manage and all you need is a group 24 or U1 size battery to start the engine.

[joe_db]

No relation to this person, but one of my battery panels came up on Fleabay:

https://www.ebay.com/itm/224493194480?epid=6012049686&hash=item3444d64cf0:g:LOgAAOSwUndgwoLO