Designing and building a new electrical system with 450AH house battery bank and monitor

One of the biggest issues with Stops and taking it cruising was the capacity of the house battery.

The original house and engine batteries on Stops.

All it had was these two batteries one for the engine and other for the house..A total of 55Ah!  This obviously was not going to cut it, Stops had been setup for day sailing but cruising would require a much bigger battery bank.Not only that, I needed to add energy generation and monitoring systems and upgrade the size of all the wiring to accommodate the higher amperage from the new sources.

This was the probably the most complex project I had to do and so I got a quote from a couple marine electricians. The cheapest was $7,000 without all the parts, so I decided to do the job myself 🙂 Nigel Calder’s Book was my bible. I also validated some of design and equipment choices on cruisers’ forums.

I broke down the key tasks to upgrade the whole battery system. This was before I could add solar, wind and the high output alternator.

  1. Figuring out the size and type of house battery bank I needed
  2. Designing a new wiring system to accommodate all the new systems including solar, wind, high output alternator and a battery monitor.
  3. Building a house battery box to store the batteries
  4. Upgrading the engine batteries
  5. Installing a new battery switch and engine battery trickle charger
  6. Upgrading all the high amperage battery wiring on the the boat
  7. Installing the battery monitor

Figuring out the size of the house battery bank I needed

First job was figuring out the typical electrical usage on my trip to see how big a bank I needed.

Figuring out my electrical usage on passage and at anchor

My calculations came up with around 100 Ah/day on passage and 85 Ah/day at anchor, so I needed a house battery bank of 400 Ah (rule of thumb is 4 times your daily usage). My plan was to also have 3 sources of energy, Solar and Wind to generate the majority of the energy and then a high output alternator on the engine to top up when the engine was running. I didn’t want to run the engine just to charge up the battery for multiple reasons, the environment, limited diesel carrying capacity and the noise and smell it generates at anchor.

Location for new house battery box

First task was to find a place to build a battery box close to the engine. I found a good spot under the aft cabin bunk where a drawer was located. Next task was figuring out what batteries would fit in this area to give me a capacity of 400 Ah. My preference was AGMs but I couldn’t find a size that fit into the space and gave me the Ah i needed.

Trojan t105s.. they were heavy 🙂

After a lot of research I opted for Trojan 105 deep cycle golf cart batteries. They were proven for offshore cruising and were half the price of marine battery equivalents. I bought 4 Trojan T105s to provide 450 amp hours.

Designing a new wiring system to accommodate all the new systems

The existing basic electrical system

I drew out the existing AsIs wiring system and it was pretty basic. Because both engine and house batteries were both of the same type the charging systems (shore and alternator) were connected to both at the same time.

Logical circuit diagram with all the systems I intended to install

But with different battery types for my house and engine I had to install a trickle charger to charge the engine battery from the house battery. So in the design all the four different charging systems charged the house battery and the engine battery was charged by the echocharger trickle charger (see logical circuit diagram above). To implement this I also need a new battery switch with just on/off and both settings for when the engine battery was dead.

Physical layout of the new electrical system

I was also going to double the capacity of the engine battery so it didn’t need to be charged that often.

Building a house battery box to store the batteries

The trojans fit well

The Trojans fit into the space pretty well but because they were lead acid batteries I needed to build a sealed battery box around them to hold any acid in case of spills in rough seas or a knockdown.  To do this I used tri-ply wood and glassed all the wood on the inside.

Cutting the triply to size

First I cut the tri-ply to create the box.

Covered the inside edges with fiberglass

Next I laid up fiberglass cloth on the inside edges with resin.

Applied fibreglass to all edges of the box and sealed it to the floor

I then glassed the tri-ply to the floor creating a box that was sealed with fiberglass all around. I also created a vent to let out the battery gasses to prevent accumulation. The battery lid was also made of fiberglass.

The completed fiberglass sealed battery box under the aft bunk, with batteries installed!

I also installed straps to hold the batteries down in case of a knockdown. The green caps are hydrocaps which I installed to reduce gas emissions and water refills. I would highly recommend them for lead acid batteries.

I put hinges on the old drawer facade which opened to the breakers and fuses.

Upgrading the engine batteries

New engine battery bank

I ordered new AGM batteries that fit into the space of the old battery box and connected them together to double the capacity of the engine battery. I also installed straps  to hold the batteries down in place in case of a knockdown.

Installing a new battery switch

Drilling out the hole to out the batter switch

I installed a Bluesea battery switch that had additional fuses for the bilge pump and items wired directly to the battery.

The new battery switch and echocharger installed!

I also installed the echocharger (engine batter trickle charger) right next to it.

Upgrading all the all the high amperage battery wiring on the the boat

Once I had all the equipment installed I set about replacing all the existing battery and high amperage wiring because of the increased loads expected as well as the increased wiring distances to the house battery. Estimating the max amperage loads allowed me to calculate the gauges needed.

The magic crimping tool!

After the wire was ordered I used a special heavy gauge wire crimping tool to attach the lugs.

A finished cable with the headshrink and fireproof cover

I then heatshrinked the ends and covered the cables in the engine compartment with a fireproof sheath.

The wiring behind the new battery switch

Wiring the new battery switch took a lot of time.

Installing the battery monitor

With 4 different charging sources working at different times, it was critical to know the state of charge of the house battery. The old way of measuring voltage doesn’t really work since you need to disconnect all the charging sources and leave the battery overnight to get an accurate idea of the state of charge. This is why I decided to invest in a battery monitor. First to tell me the state of charge of the battery banks, especially the house battery and also tell me the current flowing in and out of the house battery so I can monitor the efficacy of the charging sources. I chose a Victron 602 because it was highly rated on cruiser forums.

Installing the shunt in the house battery

First step was installing the shunt in the house battery wiring and checking it worked.

I then installed the head at the chart table so I could see the battery status at all times. In the photo, the state of the charge of the house battery is 82.4%. Great thing to know 🙂

Next job was installing the charging sources: solar, wind and the high output alternator. No rest for the wicked 🙂

Project Summary

Total cost: around $1,500. A lot cheaper than $7,000 the electrician quoted me 🙂

Total project time: Around 3 months from the initial design and equipment choices to it fully working and installed.

Update in 2012 after 13,000 miles of sailing.

Everything worked great, no failures at all with any part of the system. Only thing was that the battery monitor lost accuracy after a few weeks, so I had to recharge the batteries to 100% every 3-4 weeks.

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Author: Chet

Avid sailor.

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