Battery/Bus Installation Complete

In 2024/2025, Saukura received a fully upgraded battery and distibution setup.

See here for the battery selection criteria, and my experience purchasing LiTime batteries.

Some minor tidying to do yet, but the installation is essentially finished. The improved lid in place. It's surprising how small changes can have a major usability (and therefore safety) impact. I was able to find M6 stainless steel-shafted knobs and these will be used to secure the lid, making it toolless. Hefty screw-fastened cable tie mounts repace the earlier type, and the hefty releasable cable ties used are not trimmed, making operation and retrofit much easier.

After a one-week customs delay, the Victron Lynx assembly and battery hold downs arrived. The existing cabling dismantled, consolidated, repaired and reassembled. Several runs of trunking were eliminated, several cables consolidated, and unused stuff removed. All cables were labelled, and proper fusing was incorporated adjacent to the batteries. It all works well and is much tidier and safer. As it was before, It would have been very difficult to troubleshoot, and should that be necessary, I am now extremely familiar with the setup.

The cumbersome battery box lid was cut in half lengthwise, and an inward-turned aluminium angle was added to each half to capture the outward-turned flange of the battery box. It now requires only two bolts per side to secure the lid, and these will be made tool-less by replacing the m6 screws with threaded screw-knobs. The batteries and cfompartment can now be accessed by removing two screw-knobs, and half of the lid, from either side. Electrical work requires opening the the portside only, and there is equally accessible storage on the starboard side. .

Installing the internal hold-down beams and rewiwing.

Basics of the new buss system

Negative 12VDC battery connections

Start and house batteries share a ground connection in the battery box which connects the Lynx Shunt's main ground bus. All other ground connections are made on the "other" side of the lynx shunt, via the Lynx distributor.

The common battery ground appears to be how the factory connected the batteries, though the main battery switches open both ground and positive sides on two banks. (two batteries, four switches) This seems at odds with the shared ground at the batteries, and would seem to risk ground currents reaching the hull via the engine. (though the MD-22 is supposedly isolated from its electrical system) I will need to confirm that the engine ground is isolated from the hull, and diagram the switching.

Positive-side connections

The two house batteries are connected in parallel, and the positive side is connected to the Lynx Shunt's 1000A main bus via cables less than 2' in length. The Lynx shunt contains a 250A fast CNN fuse, and is bolted to the 1000A bus of the lynx distributor, which breaks out four seperate fused connections and their negative cables. To these, are connected:

The main house panel/loads
The 1600VA multiplus 220v/70A inverter/charger
The 800W 125VDC inverter
The Alternator (via an ORION DC:DC charger)

The Linx distibutor (a Power In with fuses added) has an M8 bolt at its end, two which the two marine breakers are connected, one for each of the "renewable" power sources, solar and SailGen. The -ve sides of these are connected to the -ve side of the bus, via the BMV'712 smart shunt.

Repurposing the BMV12 and its shunt.

The existing Victron BMV712 battery monitor was made redundant by the installation of the Lynx shunt. Fortunately, the BMV 712 can be reconfigured as a current monitor. I had planned for this, and had drilled and tapped appropriate holes for the shunt in the lexan mounting plate. (in the photo below, you can see holes below the breakers) The BMV 712 now serves as a current monitor for "renewable" energy sources, and measures the sum of energy being produced by the Hydrogenerator and the solar panels.

Incorporating the Alternator.

The stock alternator (either 50a or 70a, not sure) is externally regulated using a Sterling Power Products unit, with start and house banks originally isolated by a split-charge diode. This appears to have been the stock arrangement. This diode has now been bypassed and the alternator, via the Sterling regulator, is connected directly to both the start battery and the Victron Orion 12/12-30 DC:DC charger, which is in turn connected to the Lynx distributor ( to charge the house bank). The DC:DC charger now provides the battery isolation previously provided by the split charge diodes, without the voltage drop penalty.

Some helpful reinforcement from Ben at Stering Power.

Alternators, when charging a lithium battery, urgently require current
limiting between the two. Without something to taper back the current and to
actually sustain a healthy continuous supply from the alternator we would
often see alternators running at full load for prolonged periods of time-
which inevitably can lead to alternator damage. Even if the battery bank
was only 50% discharged, we could be seeing the alternator running at full
yield for over three hours, and frankly I've seen alternators practically
glowing within one.

And when asked about incorporating the DC:DC charger:

2) Yes, this is the recommended approach. If the user needs more power, the
BB1240 would be an excellent consideration and is also more or less the
limit on what I would recommend for a 70A alternator.

I've read that unfortunately the Orion DC:DC charger runs as "hot as the Devil's dick". An overtaxed alternator would however run even hotter. It is obviously preferable to run each device within its respective operating limits, which is now assured. The Orion can only provide a maximum 30a to the house bank, (which can accept much much more) and hopefully this translates to a resonable sustained load on the alternator. I beleive the ORION can be programmed to limited the current further if necessary. Hopefully a coooler-running, more efficeient DC:DC charging technology will become available, however in this application I am happy to accept that the alternator is not sized to "fast charge" the LiFePo house bank, and am quite willng to live with the conservative 30a ceiling. . .

Powering the water maker

I ultimately decided that the simplest solution was to install the 12VDC Seawater Pro water maker up forward and to power it via the existing anchor windlass circuit, which happened to be sized appropriately.. .

Earlier Posts

Components of the buss and battery hold-down setup.

The battery box on OVNI 435 #6 measures 22.5" X 30.25"X 9.5" deep and is located below the cockpit. It is made of welded aluminum and is bolted in place. It has an outward turning 2" flange around the top, with a seperate, single-piece plywood lid, With the lid removed, the batteries are partially accessible from either aft cabin, with all electrical connections on the port side. (note - OVNI 435 battery boxes can vary in size)

The one-piece plywood cover is secured to the flange with machine screws and easily-dropped nuts, and it has a 2"X2" (approx) cleat around its perimeter. The cover is bulky and inconvenient, and access is more difficult than it needs to be. Fortunately, this can easily be improved.

Cables enter the battery compartment through randomly-drilled holes on the port side. There is no positive bus bar, and no fusing at the batteries, Over time, accessories with a mishmash of fuse styles (or none) had been stacked on the various battery terminals. none labelled, most with no means of disconnect. The cables intrude into the middle of the box, interfering with battery installation and removal.

The house bank's 4 group 31 batteries were connected in parallel with heavy, well-made jumper links that appear to be original equipment. With the limited clearance to the conductive cockpit sole above, caution is required when working here, especially with top-terminal batteries.

The starter battery was/is also in this box, furthest aft. Access is particularly inconvenient.

The photos below show:

how access is restricted by the cockpit,
how the cabling was installed and intrudes into the box.
The many live connections that must be made in an awkward, confined space.

Below left you can see that batteries must be placed in or removed from the box it in a fore and aft orientation. Below right shows a pair of terminals in the cockpit locker that were connected to the starter battery. Presumably this was to provide for boosting or charging. This DIY hack has been removed, and I will eventually relocate the starter battery to a more accessible location, probably in the port side cockpit locker.

What to do?

With the upgrade from 4 group 31 to 2 group 4d (ish) lithium batteries, it became a necessary to re-think the stowage of the batteries, and opportune to incorporate a bus bar, circuit protection, and a safer, more orderly layout.

Scope

determine battery orientation ensuring:

optimal use of space,
minimal wiring
tool-less method to install/secure/remove batteries. (small ratchet straps?)
must be easy to reconfigure with - at most - basic woodworking tools.
Battteries must be well secured
Ideally, either house or start betteries could be removed while leaving the others in place.

design/install distribution and circuit protection for current uses and future expansion

Likely this means locating the bus bar and fusing outside of and adjacent to the battery box for better access, however it must then be protected from accidental contact.
it should be easy and safe to disconnect each battery while leaving the other(s) in use.
a ATO/ATC "blade" fuse block may be required for some low-current accessory connections.

Improve the cover

Cut the existing cover in a fore and aft direction.
Incorporate a tool-less means of securing the cover so that either side can be quickly accessed.
Ensure that terminal fuses can be inspected and replaced from the port side.

Incorporate storage into any unused space if possible.
Insulate the interior sides of the battery box to reduce the risk of contact with a live conductor.
Provide clearly marked storage for spare fuses nearby.

The Physical part - Thinking inside the box.

Due to the size and shape of the batteries and the restricted access to the box, satisfying the above critieria is trickier than it first appears. Particularly item 1.6, as the batteries must be placed in the box in a fore-and aft orientation and then rotated atwhartships if that is the intent. This creates a bit of an assembly puzzle. See below, the mdf mock-up of the box and batteries.

I cut a thick rubber mat to size and placed it in the bottom of the battery box. This provides some cushion to the batteries, and will help prevent them from sliding. I ultimately decided to arrange the batteries as pictured above, with a hold down system made of stout oak rails, with two 2" wide rails at either end of the box, elevated off the bottom by 2". In the photo, mock-ups of these can be seen at the narrow ends of the box. Note that the postive terminals are at what will be the forward end of the box. The 2" rail width was chosen to provide a protected space for cables and terminal fuses around the perimeter of the box.

A second pair of rails, 2"X2" and movable, span the full 30" length of the box. In use, these are placed in the empty box, and slid under the raised. fixed rails. The fixed rails thus prevent these movable, longitudinal rails from lifting. The batteries are placed between the longitudinal rails as pictured, and against the forward rail. Ratchet straps looped around the movable rails are used secure both house and start batteries. As the strap is tightened, The rails are pulled upwards and towards eachother, and the batteries, between these rails, are pushed downwards against the rubber mat. Once the start battery is installed, wooden spacer blocks will be fitted into the remaining spaces to further secure the movable rails (and therefore the batteries) laterally, preventing any movement, and spacers will be added to the to the lid to further limit movement should the ratchet straps fail.

No tools are required, and the layout can be reconfigured as required in future.

Parts of Oak

The mdf protoype worked well, so a more refined version was committed to red oak. You can see the short end rails with the M8 bolt holes, and the movable rails with the added refinement of a cleat to secure the hold down strap. The straps were cut and loops sewn as shown.

Below you can see how the movable rails and ratchet straps engage the fixed rails to secure the batteries by pressing them downward into the rubber mat on the bottom of the box. Filler pieces will be fitted on site to further restrict movement of the rails. Also visible are some additional refinements to the rails.

Ready to be packed and shipped! The long rails are oriented as they would be in the box.

The Electrical Part - Safe and Simple?

Circuit Protection at Battery box

https://marinehowto.com/battery-banks-over-current-protection/

Based on the info above and the cabling already in place, the following circuit protection should be incorporated.

Battery 1 terminal fuses @150a
Battery 2 terminal fuses @150a
Inverter charger 1600w/70a (100A)
Small inverter. (40A)
70A Alternator via smart regulator (verify cable, regulator output)
House loads (125A per dwg, s/b fused already - where?)
Future water maker (100A circuit?)
200W (450W future) PV (50a)
200W Sailgen (50a)
Wind (50a) ** The wind generator may be retired.

That’s a lot…. Too much in fact. It will be consolidated.

Bus bars, circuit protection and monitoring

After having purchased the necessary bus bars and circuit breakers to upgrade the DC distribution, I struggled to design a safe and compact electrical layout that would work in the limited space available. This brought me back to Victron, and their Lynx bus bar range. I had previously ruled out this system as being too expensive, but, all things considered, it isn't.  Relatively few additional components are necessary with this system and it has an inherently safe design.
While the Lynx Shunt wasn't absolutely necessary, it provides the opportunity to further consolidate components. The Lynx Power-In has been "hacked" to incorporate fuses (google it) and now functions as a Lynx distributor .(minus the LED blown fuse indicator)  The fuses (and breakers) are of a type and rating to protect the cabling in the event of a dead short, they are not intended to protect the equipment. (Fuses are a topic worth investigating.) Two thermal breakers were added and provision was made for an additional Victron smart shunt to monitor non-GX compatible charge sources.
The components were arranged on a piece of 3/8” polycarbonate that will be fastened to (or very near) the port side of the battery box.  The polycarbonate was drilled and tapped for M5 allen head cap screws, to secure the Lynx devices, two thermal breakers and a future Victron smart shunt. Clearance holes were drilled for M5 screws which will would be tapped into the battery box to mount the entire assembly. These screws will also secure mounts for releasable cable ties to secure the cabling running below the lynx devices.

Below you can see the space around the perimeter of the batteries and the oval holes at either end of the battery box for the battery cables, which exit the box and connect to the adjacent bus bars (red and black covers in the photo.) There is very little cable exposed.
There is room for a third house battery if required but the removable hold downs might require some minor revision.
There are fuses on each battery terminal and a very fast fuse in the lynx shunt.
Load and charge source cabling will enter at the bottom of the Lynx power in, where it connects via a fuse to the bus bar. The Lynx shunt is located between all grounds and the battery negative.

Hopefully I can simplify and remove some of the massive amount of cabling and trunking that runs beside the battery box.

There are two less-than-ideal aspects to this approach:
one of the house batteries must be removed to remove the start battery. (I will relocate the start battery at some point)
There is no means to externally disconnect each house battery. This means that an unused battery cable would remain live unless first unbolted from the bus. While this is not unusual, and can be accommodated, battery disconnects or external fuses might be more convenient than terminal fuses.

Notes

Fuses required

CNN350DIN. Fast fuse for dead short, in lynx shunt.

Mbrf for terminal fuse disconnect battery. There is a problem here in that either end of the wire will remain live. For disconnect it should be at the lynx shunt.

Mega (50.8mm) fuses within the lynx shunt.

Littelfuse makes mega/AMG fuses as low as 40a