In the winter of 22-23 I upgraded the electrical system in our J/105, Kinship, after our experience in the 2022 Chicago-Mac race (which is about 300 miles).  This post is about why and how I did the upgrade, and what the results have been.

We bought Kinship in 2019 and during our first three seasons I really didn’t think much about the electrical system.  We were mostly buoy racing and we never had a problem with the batteries.  However, during the 2022 Mac race we needed to run the engine after every two hours on batteries to keep the charge level up.  Also, every time we started the engine all of our electronics would reset.

After the race, I questioned some other Fleet 5 owners and learned that our experience was not normal.  So, in the winter of 2022-23 I set out fix our system, which consisted of:

  • Two Lifeline 80Ah AGM batteries
  • A Hitachi 55A alternator
  • A Guest “1, 2, Both” battery switch
  • A Blue Sea Systems voltage meter at the navigation table
  • A Promatic AC battery charger
  • Wiring

I believe the alternator, switch, charger and wiring were probably all as delivered from the factory in 2000, but I’m not totally sure.

My goals for the project were to:

  1. Power the boat for at least six hours after recharging with the engine
  2. Avoid instrument dropouts when starting the engine
  3. Be reliable, resistant to human error, and easy to operate
  4. Be safe
  5. Be compliant with the J/105 Class Rules

What was Deficient in the Existing System?

The first thing I had to do was determine which parts of the existing system I could keep and what needed to be replaced. Here’s how I evaluated each part:

Lifeline AGM Batteries

Lifeline batteries are widely considered to be among the best AGM batteries available. At the time I was redoing the system, our 80Ah batteries were less than one year old.  Provided they had sufficient storage for the loads I needed to power, I planned to keep them.

(Why I didn’t replace them with lithium batteries is another post.)

Picture of AGM batteries in J/105 sailboat

Hitachi Alternator

Photo Hitachi 55A alternator in J/105

The stock, internally-regulated Hitachi 55A alternator had worked fine for us for daysailing, even when we sailed Kinship off a mooring ball for two years.  However, its performance during the 2022 Mac left a lot to be desired.  I suspected it wasn’t performing as well as it was supposed to (although I never had it tested).  I also learned that even if the alternator was working to spec, an externally- regulated alternator would be able put energy into batteries more quickly.

(Marine How To, the brainchild of marine electrician extraordinaire Rod Collins, was invaluable to me in understanding this and many other things related to this project.  Thank you, Rod!)

Guest “1, 2, Both” Battery Switch

The standard-issue “1, 2, Both” battery switch on Kinship was also an issue. I wanted to fix the electronics dropouts, and the only way to do that definitively is to separate the circuits for starting the engine and for house loads.  Also, separating them would also mean we couldn’t accidentally use all of the available energy for house needs and then be unable to start the engine.  In other words, it would be more resistant to human error.

Blue Sea Systems Voltage Meter

The voltage meter in the nav station was a poor substitute for a proper battery monitor.  While it is possible assess the state of charge of a battery based on the voltage across its terminals, the voltage that corresponds with each state of charge changes with the amount of load on the battery and several other things. Even worse, the meter at the nav station was affected by voltage drop in the wiring between the battery and the nav station.  We did get by this way for a few years, but it was probably about as accurate as wet finger in the air.  I wanted something I could put in the cockpit and tell the crew “If the battery get to 30%, start the engine.”


Promatic AC Charger

The Promatic AC charger, while over 20 years old, appeared to be working fine. It even had different programs for different types of batteries, one of which was pretty close to what Lifeline recommends. I decided to replace it anyways, though, because a newer one would allow programming that more precisely matched Lifeline’s recommendations.  It could also provide temperature-compensated charging. At this point, though, I might have been suffering from a bit of gear acquisition syndrome.

Photo of Promatic AC charger in J/105


I am not an electrician or electrical engineer, but I do run a local solar company, so I know a bit about electricity and safety.  The electrical system on Kinship was not safe, and certainly not up to current standards. It was missing essential fuses, some of the wires were just big enough if you squinted, there were unprotected battery cables in the engine compartment, and many of the terminations were substandard. In my view, all of this had to get fixed. (It is also interesting none of this was mentioned in two surveys of the boat.)

The New System

Now let’s look at what hardware I chose for the new system and how it fits together.

Lifeline AGM Batteries

Based on their reputation and age, I wanted to keep the Lifeline AGM batteries. However, I needed to make sure they had enough capacity to run the boat for at least six hours after being recharged by the alternator for an hour.  I started by creating an energy budget (based mostly on manufacturer spec sheets). We would consume 5-7 Ah / hour in normal operation:

Energy budget for J/105 sailboat

With the help of Lifeline’s technical manual, I was able to determine that one 80Ah battery would power the boat for 8-11 hours if coming off a 100% charge (i.e. from shore power) or 6-8 hours after being recharged by the alternator for an hour:

Table with charging times and run times for J/105 sailboat

We decided this was sufficient to give it a go with one 80 Ah house battery.  (We subsequently found my estimates were pretty accurate.)

(A few notes:  First, in these calculations I assumed the alternator would only put out 50A, which might be conservative for the 70A alternator we ended up with — see below. However, there are a variety of reasons an alternator may not always put out its nameplate power, especially as the state of charge goes up. Second, these calculations assume using the house battery down to 30% SoC. Battery manufacturers usually recommend 50% to maximize the life of the batteries. However, this is a race boat, so keeping the weight as low as possible is just as important as battery life. Also, 90% of the time we are just racing during the day so it is only occasionally that we’d be going this low. Finally, I already owned and paid for these batteries!)

Balmar 70A Alternator and MC-618 External Regulator

Knowing that the existing batteries were fine, I knew that I needed to find a way to get more energy into them quickly when using the alternator.  One option would have been to simply replace the alternator with a new version of the same thing, but I wasn’t sure if the problem was the alternator itself or simply that the alternator and its internal regulator weren’t capable of putting energy into the batteries quickly enough. I figured that if I was going to the trouble of replacing things at all, I might as well replace them with things that would increase the capability to put energy in the batteries faster. Therefore, I decided to replace the Hitachi with a Balmar 70A alternator and MC-618 regulator.

Picture of Balmar 70A alternator
Picture of Balmar MC-618 regulator

Blue Sea Systems “On / Off / Combine” Switch and Automatic Combining Relay

The stock “1, 2, Both” battery switch didn’t allow separating the circuits for starting the engine and house loads, which caused two problems. First, the electronics would drop out and restart when we started the engine.  Second, we could accidentally completely drain both of the batteries with house loads and then not be able to start the engine, violating my goal that the system be resistant to human error.

I solved this by installing a Blue Sea Systems “On, Off, Combine” switch instead.  In one motion, this switch separately switches two circuits on or off (one for house and one for starting). In almost all circumstances, these would be the only positions used.  However, we can combine the batteries if we want. This could be useful if the start battery is for some reason not able to start the engine on its own or if we want to risk draining the start battery to get just a few more hours of energy for the electronics without the distraction of running the engine (for example, one hour from the finish of a race).

Since the engine battery and house battery circuits would now be separated, though, I needed a way to make sure they both got charged.  The solution was an automatic charging relay (“ACR”).  This automatically combines the normally separate house and starting circuits when it senses that a charging source such as the alternator or AC charger is present. 

Balmar SG-200 Battery Monitor

I installed a Balmar SG-200 battery monitor to replace the simple voltage meter. This is a much more sophisticated device. It reports the actual state of charge of the house battery on a small display in our cockpit, so I achieved my goal of being easy for the crew to operate. It also has a low state of charge alarm function.

Picture of Balmar SG-200 battery monitory

Blue Sea Systems P12 AC Charger

Picture of battery charger

As mentioned above, I’m not sure I really needed to replace the Promatic charger, but I replaced it with Blue Sea’s P12 charger.

A Lot of New Wiring

Replacing the alternator, battery switch, and AC charger, plus adding the regulator, battery monitor, and ACR required significant additions and changes to the wiring.  While I was working on all of that, I also replaced or upgraded a lot of other wiring or wire terminations.  Finally, I added:

  • Bus bars for the house positive, start positive, negative, and grounding/bonding
  • Wires to bring the alternator output directly to the house battery bus
  • An alternator disconnect switch
  • Fuses (and replaced some glass AGL fuses with easier-to-read ATC fuses)
  • Labeling on most wires

Here’s a line drawing of the electrical system (click to enlarge): 


Wiring diagram of electrical system in J/105 sailboat.

The Results

During the 2023 Mac we went about 11 hours before needing our first charge and then 6-8 hours between charges after that.  The instruments now stay on when we start the engine, and the system is certainly easier to operate and more resistant to human error.  Time will tell about reliability, but the system is certainly safer in the meanwhile.

Here’s a photo of the front of the battery compartment, where a lot of the new stuff comes together:

Picture of electrical system on J/105 sailboat

The Value of the Journey

I spent a lot of time on my back and/or in tight quarters during the winter I did this upgrade.  And all of these little boxes, wires, and doodads added up to around $2000, so this project wasn’t cheap.  To a large extent, though, I just think about it as the cost of a hobby.

It’s a hobby with benefits though.  I met my project goals, but I also have a much better sense of how the electrical system of Kinship actually works. If we ever have a problem at sea, I’ll potentially be in a position to do something about it, whereas before I would have just been in the dark.