The Sumpners Afloat

This winter we had a few “jobs” that we wanted to do, but Electrika has taken up more or our spare time than expected, so we are only just getting round to them.

You may remember a previous post “It’s not easy bein’ green” where we documented a new “Solar Eco Mode” that Rob at Ortomarine developed for us to maximise our solar yield and minimise our shore power costs. Well we have been using this mode in Ortomate (our control and display system) for the last two winters, whilst in the marina, and we are very pleased with the results. In fact, the clicking over of the Quattro between shore and solar has become a regular sound track to our mornings and evenings.

This winter, I had a “eureka” moment whilst looking at the graphs on our Victron VRM cloud server. Every night the Quattro would click over to shore power and start its Bulk/Absorption/Float charging cycle, just as it was supposed to with the shore power topping our batteries back up to 100%.

As you can see from the graph above, which shows our shore power usage in January, the power taken each day was fairly consistent, with occasional higher days, if we were doing some laundry, cooking, etc. You can also see the significant reduction when we were off the boat for a week to visit family.

The Absorption phase of the charge process is the most inefficient and also the one where the batteries are subjected to the highest voltage (nearly 60v on a 48v battery bank) which over long/repetitive periods could affect battery life. This got me thinking as to whether less frequent charges might be more efficient and after a quick chat with Rob at Ortomarine, we decided to give it a test. Before I knew it, Rob’s engineer Simon had “Dropboxed me” an update and instructions on how to upload it.

The new “Eco Mode” feature now lets the batteries discharge down to 60% SOC (state of charge) before switching to shore power and then once the batteries are up to 100%, disconnects the Quattro from the shore. On Old Nick, this averages out at around a 3 day cycle i.e. two days with no shore power, purely using the batteries/solar and one day connected to shore power to re-charge the batteries from 60% to 100%. You can see this new charging pattern after the update in the image below, which shows our shore power during February.

To see if we had managed to improve our power usage with the new mode, we took two 9 day snapshots during January and one during February and recorded the daily power usage figures in a spreadsheet. Then we totalled the power used during each 9 day period and compared them – see the results below.

We need to do some more tests, but initial results are pretty promising and we appear to be getting between a 14% and 26% reduction in shore power usage, plus giving our Lead Carbon batteries a much easier life.

Applying these findings to LiFePo4 batteries, is not likely to provide as much saving as their charge profile is different. Effectively, a LiFePo4 will continue to bulk charge almost to 100%, followed by a much shorter (minutes rather than hours) absorption stage. However, there are definitely battery health benefits in reducing the number of times you charge back up to 100% and in fact LiFePo4 batteries will last longer if they are charged to 90% and only occasionally fully charged to 100%.

By fine tuning the Ortomate software and how it controls the Victron battery charger, Ortomarine hope their new Eco mode can bring benefits to both Lead Carbon and LiFePo4 battery powered vessels. I owe Rob a big thank you (or beer) for his time and effort in tweaking an already useful Eco Mode and look forward to seeing a 20% reduction in shore power costs next winter and healthier, happier batteries.