Manage energy on board

Managing energy on board is never easy.

Assuming that the onboard systems are in good condition and maintenance, at this point problems arise when you are at the bottom, in off-engine fishing or sailing.

icaptain. battery monitor victron
Example of Victron Energy Battery Monitor equipped with BlueTooth device

It is in these cases, in fact, that the long periods of engine use put a strain on the on-board accumulators. Having the engine access on board when not needed becomes uneconomical for fuel consumption and for the accumulation of hours of use, unecological (we investigate for no reason) and uncomfortably especially at night while someone tries to rest or sleep.

We look at alternative energy production methods such as photovoltaic panels, which can be a very valuable tool for help in these cases, because beyond their installation, we want to focus on the actual energy management methods.

Many boats, even the most expensive and equipped, are equipped with inadequate charging status indicators since most of these instruments are based on just reading the voltage of the batteries. Such systems can give false alarms in case of high but short absorptions; in other cases they go to alarm when it may be too late to set in motion.

These devices are face meters that base the indications, provided to the display, LED indicator or hands, on a basic concept that does not take into account the real capacity of the installed batteries.

This principle of indication is based in the direction of these values (indicative values for 12V systems, for the 24V it is enough to double the value):

  • From about 14V: Battery being recharged
  • From about 13V: Battery charged in maintenance
  • From about 12.8V: Fully charged battery
  • From about 12.4-12.5V: Battery at 50
  • Less than about 11.8-11.9: Battery completely discharged.
icaptain. Analog face. Manage energy on board
This instrument does not measure the state of charge with respect to the capacity of the batteries, but only on the basis of their voltage

The fundamental problem is related to the lower ends, if the onboard device warns us that we have reached below 12V and we do not have a dedicated engine battery we will hardly be able to get started; If you have discharged the engine batteries at the same time or the same is accidentally “dead” means not to start.

If we use utilities such as winches or electric winchs we may have temporary false alarms that are still annoying that alarm us unnecessarily.

A serious and efficient system must essentially be equipped with:

  1. Microprocessor to perform basic electronics calculations
  2. Shunt (amperometer) for reading the current in and out of the battery.
  3. An exit that can operate a small alarm device.
  4. For more advanced bluetooth devices for connecting with a mobile app from which you can set up your device, keep the charge status under control even from your smartphone or tablet, and record consumption trends.

Remember that the electric size that tells us the capacity of the batteries are the Ah: a fully charged 100Ah battery will provide us 100Ah when it discharges? Unfortunately not. It depends on how you download/charge it and especially on the construction technology (Open Pot Lead, Gel, AGM, Lithium ).

Returning to the management device; the same must be able to be set in relation to the technology we are equipped with.

icaptain. Shunt. Manage energy on board
500Ah shunt, essential for accurate readings of charged or unloaded current

Often you get scared thinking about the costs to be faced, but nothing is more wrong. Such a device costs from 120-150 euros for those less advanced with a manual configuration and up to 250-300 euros for the most advanced systems equipped with bluetooth and dedicated mobile app.

All in all, the expense is feasible considering that a facemeter can cost up to 80-100 euros.

We also recommend the choice of devices equipped with temperature sensor: the charge/discharge is different depending on the ambient temperatures.

We complete the article by talking about the installation, assuming that it must be carried out by experienced personnel (Caution iCaptain declines any liability for damages caused by the reading and interpretation of this article).

Whether you are the one who makes it or rely on a specialized technician, you need to know the risks that you can face when working with batteries or on-board electrical systems using all the necessary precautions and individual devices. Protection.

A technician will usually take between 100 and 300 euros to carry out the work, it depends very much on the difficulty of passing cables and the conditions of the on-board system, in particular the fact of finding many utilities directly connected to the batteries instead of go through the main picture; these utilities will have to be reduced to a single connection.

The installation is in itself simple, the shunt must be mounted on the negative of the battery pack to be monitored; It may seem complex but simply cut the negative battery cable immediately after connecting to the batteries, put some heads and connect them to the same having the following precautions:

  • Shunts have a line (they have to read the current coming in and the one coming out sequentially) so you have to be careful to plug the battery and load/recharge in the right position.
  • From the negative battery to the shunt there should be no other connections, any charging or draining connections will be connected on the shunt in the appropriate location.
icaptain. Esempio installazione BVM Victron. Gestire l'energia a bordo
Example of installing a BVM 712 from Victron Energy

At this point you need to connect a cable from the Shunt to the positive battery to be monitored (or one of the batteries in parallel in the case of multiple batteries) and pass the supplied cable from the shunt to the display/calculator.

Once the device is turned on, various parameters will be set, including:

  • Battery capacity.
  • Battery technology.
  • The desired alarm levels.
  • Other settings you want.

To require high accuracy to the system, the batteries should be left in charge for at least 24-36 hours, in order to do so always from the device settings (having at this point the certainty of the full charge) you will synchronize device from the appropriate menu.

In the case of the following battery monitors, we recommend the following battery monitors, which are accurate and reliable:

We are sure that this article will help you to resolve the problems related to the management of the charge on board; good wind at all!