Barry's Blog #133 - Perfectly balanced


The great battery meltdown of October 2019, which we showed you in video #094, opened up a whole new learning curve about storage, usage and management of electrical power on board a sailing yacht.

Moving forward to May 2020 and we decided that a job which had been slated for when we finally got back to Turkey would be brought forward because time was moving on and the new batteries were already 7 months old and still configured the same way as the original batteries that had died on us back in October.

Fortunately A B Sea had been on the hard since the end of October 2019 and her 600 watts of solar had been keeping the house batteries nicely topped off with little to no draw down of power because all systems were switched off while we spent 5 months living in the studio apartment on site at Livaditis boatyard in Greece.

When we moved out of the studio and back on board A B Sea in March 2020 we hooked into the 220v shore power which meant that even though we were now using electrical power on board, 95% of it was coming through the Greek electrical grid and there was very little draw down on our 12v house battery bank. Even the small amount that was being drawn, for the 12v fridge compressor, for example, was being topped off by the 220v shore powered battery charger. The problem and the fix

We have 3 x 100ah batteries on board that are dedicated to supplying our electrical needs day and night (when we're not connected to shore power). The biggest draw down of power is through the hours of darkness; during the daylight hours our 600 watts of solar panels recharge the batteries ready to go for another night. Rinse and repeat. What we didn't know, until it was pointed out to us by people whose job it is to design, install and maintain sailing yacht battery systems, is that the length of the cables connecting the batteries to each other are an absolutely vital part of battery lifespan management.

This is where my blog is going to get a little technical, but I'll keep it as simple as possible so you don't bleed from your ears or burst an eyeball.

Wiring option #1 is the absolute worst way to wire 4 batteries together with regard to balanced discharging and charging and here's why.

Not the way to wire your batteries

Battery internal resistance = 0.02 Ohms

Connecting cables resistance = 0.0015 Ohms per link

Total load on batteries = 100 amps

The top battery provides 17.5 amps

The next battery down provides 20.4 amps

The next battery down provides 26.2 amps

The bottom battery provides 35.9 amps

The bottom battery provides over twice the amps of the top battery. That is an enormous electricity draw down imbalance. The same is true when charging the batteries.

Wiring option #2 is a little better.

With the same 100 amp load and a small wiring modification

The top battery provides 26.8 amps

The next battery down provides 23.2 amps

The next battery down provides 23.2 amps

The bottom battery provides 26.8 amps

This is clearly a huge improvement over the first wiring option. The batteries are much closer to being correctly balanced. But they are still not perfectly balanced.

Wiring option #3.

Because of the limited space we had to work with inside the battery storage compartment and In light of the revelation and that equal length battery connection cables create a perfectly balanced discharging and charging environment, this is the option we decided to go with.

We had 6 equal length battery connection cables made locally in Limni and bought 2 x 4 lug bus bars from a chandlery in Chalkida on Evia island, Greece