On any boat, looking after your batteries is one of the most important routine tasks, right up there with engine maintenance and checking for leaks! On an electric narrowboat, where the battery bank represents a four-figure and, in some cases, a five-figure investment, the ante is well and truly upped.
On “Old Nick” we will be having 24 x LC2-800 Lead Carbon batteries from Leoch, the reasons for this choice were detailed in a previous post, and in this post we want to focus on how we need to look after them to achieve the maximum operating life-span.
A Lead Carbon battery is based on the same Lead Acid battery technology found in your car. As anyone who has left their lights on knows, if you fully discharge a Lead Acid battery it has a serious effect on the health of that battery and it will never quite be the same again. Repeatedly discharge it and you will soon be needing to replace it.
Fortunately, with a Lead Carbon battery, the negative plates in the battery are coated in carbon, which not only improves the charge and discharge performance, but also almost completely stops the “sulphation” of the plates, which is what causes Lead Acid batteries to ultimately fail and cease to accept a charge.
That is not to say that we can regularly “leave the lights on” and completely discharge the batteries of “Old Nick”. Doing that, would still seriously put the health of the battery bank at risk. But, we can expect to be able to regularly (3000 or more times) take out 50 to 60% of the battery’s power, during cruising and normal usage, and still have a good set of batteries.
Here is an expected lifetime graph of the LC2-800 batteries on “Old Nick”
So the first thing to understand from the graph above is what DOD(%) is. DOD stands for Depth of Discharge and is a measure of the amount of power that has been taken out of a battery. It is the inverse of the other popular battery measurement, State of Charge (SOC). So a DOD of 100% is a flat battery, while a SOC of 100% is a fully charged battery.
So now that we have clarified what DOD(%) is, we can study the red line on the graph and see what number of discharge/charge cycles we will be able to achieve if we limit the level of DOD to say 50% (3300 cycles) or 60% (2750 cycles).
At this stage we also need to mention PSOC – Partial State of Charge. Normally with Lead Acid batteries, you need to fully charge the battery otherwise a build-up of lead sulphate crystals occurs (sulphation) which makes it more difficult to charge the battery and reduces its capacity to hold a full charge.
The good news is that with Lead Carbon batteries there is little or no sulphation and so the PSOC concerns, normally associated with Lead Acid batteries, are not an issue. In practice, this means that should you have a particularly long day cruising and there is not enough solar to fully charge the batteries, you will not do any damage to the battery bank. This is particularly important for a continuous cruising boat, where during the winter you will very rarely achieve full charge on the battery banks.
So this raises the question of how to charge the battery bank when you are away from a marina. In the summer, with the amount of solar panels we intend to have, it should be possible to rely almost 100% on solar to keep the batteries topped up. However, at other times we will need to run the generator to recharge the batteries.
There are two types of generators; DC output and AC output. The DC output type is identical to the setup you have in your car, where the alternator creates a higher voltage than the battery voltage and current flows into the battery. Initially, the current flow is high but then as the battery starts to reach 80-90% SOC, the current reduces and it takes a long time to go from 90 to 100%. Running the diesel generator for this long period is inefficient and it is better to stop the generator and use solar to top up the last 10%.
With an AC output generator (the type we will have on “Old Nick”), the generator creates 230v AC (mains) power and this goes to the Victron Quattro adaptive, 4 stage battery charger. This has some key advantages, over using a DC alternator to charge the batteries:
- The Quattro can generate a higher charging current than the DC output from a typical alternator
- The 4 stage battery charger can be configured for different battery charging profiles i.e. Lead Acid, Lead Carbon, Lithium, etc. rather than the alternator’s “one charge fits all” approach
- The visibility of the charging process and battery state is improved with the Quattro’s smarter charging system
Even with the smarter charging of the Quattro, there still comes a point where it is more efficient to switch off the generator and let solar do that final top-up.
Armed with this information about the best way to maintain and look after our Lead Carbons, Ortomarine will help make the whole process easier by programming their innovative colour touch screen controller to automatically start the generator when the SOC drops down to 55% and then switch the generator off when the SOC gets back up to 88.
We will of course monitor our batteries very closely, but knowing that the Ortomarine controller is keeping an eye on things, will certainly give us peace of mind and avoid any potentially damaging low DOD situations.
We have covered quite a lot in this post, and hopefully it has all made sense, but if you have any questions or observations please add a comment below or use the “Contact Us” page.