240 Volt Charging
A battery lifetime approaching ten years is possible if properly maintained at 100% charge for all of its life when not in use. Remember, starting batteries should not be allowed to discharge below 80% and deep cycle batteries below 50% of capacity. If your battery has lasted only one or two years, don’t blame it, charge it.
The key is to maintain a disciplined charging cycle. It is not good enough to expect the motor with an average alternator to recharge the battery after a trip if you have enjoyed the stereo or turned lights on at night. Also, you must compensate for self discharge which is approximately 1% per day for flooded lead acid batteries. If the boat is moored, a solar panel is essential to keep the battery maintained. If the boat is stored at home or at a marina, 240V charging is the answer.
In the past, battery chargers consisted of a lump of iron, some copper wire and a rectifier. They dumped a random charge into the battery, commonly causing battery gassing and overcharging. Undercharging was also typical as there is usually no way of telling if the battery is fully charged.
The current generation of chargers are constructed like switch-mode computer power supplies. These multi-stage chargers are compact, lightweight and efficient. They usually have a much higher output than the old ferro-resonant charger. Most importantly, they are intelligent.
The multi-stage charger can sense the battery status and react accordingly.
The first stage is the bulk charging stage where the charger will charge at the full rated current until the battery voltage reaches the set absorption voltage.
The following stage is the absorption stage where the absorption voltage is constantly maintained while the battery absorbs the full charge. Charging current progressively falls during this stage, which can last several hours. Once the battery is fully charged, the charger switches to the float mode, where the voltage is maintained at a lower level. Most chargers will sense when loads are placed on the battery and then act as a power supply, so that power is not drawn from the battery.
This is sometimes referred to as the fourth stage.
Most smart chargers have selectable settings to cope with the different charging requirements of flooded lead acid, AGM or Gel batteries. The beauty of these chargers is that they are designed to never overcharge the battery and to maintain it at 100% level.
After your boating trip, you can head home, connect the charger and leave it on 24/7 without fear of damaging the battery. The great advantage is that every time you take the boat out, you are assured that the battery is 100% charged. I consider smart chargers to be an investment in battery longevity rather than an initial cost.
It is important to size the charger correctly. Current capacity (Ampere rating) should be at least 10% but no more than 25% of the battery Ah rating.
Some AGM batteries can tolerate higher charging current, so consult the battery manufacturer’s specifications. Many multistage chargers have a temperature compensation facility.
This means that the charge rate can be automatically adjusted to compensate for changes in battery temperature.
This can be significant in larger installations. The temperature sensor is often incorporated in the charger, but a better system is to have it located on the battery case and wired back to the charger.
Desirable features in a charger are: thermal overload protection, reverse polarity protection against accidental reversal of the output leads, short circuit protection, output overload protection, interference suppression and charging status display.
Many battery chargers have two or three outputs, enabling connection to multiple battery banks without using splitters or voltage sensitive relays.
There may be variations in the charging voltage and current from the different outputs to cater for different sizes of battery banks, e.g. deep cycle and starting banks.
When using a charger, make sure it is switched off before connecting or disconnecting from the battery and always connect the battery cables before connecting to 240V. If you are contemplating a permanent installation, be aware that the 240V wiring must be installed by a licensed electrician.
Solar panel Charging
By now you will have gained the impression that I am keen on having batteries maintained at 100% level. If you keep your boat at home or on a marina, yoChargingu will have access to 240 volt power for battery charging. On a mooring, it’s a different story.
Your only option is to maintain the batteries by solar or wind power – unless you can arrange an extension lead many kilometres long. Solar tends to be the preferred option especially to keep the bilge pump operational.
Solar panels have two different basic structures. The most common are crystalline panels (the sparkly ones), either mono or polycrystalline. Less common are amorphous panels (the grey ones).
Amorphous panels have the following advantages: cheaper than crystalline, they wake up earlier in the day and go to sleep later, perform better in high temperatures, are shade tolerant and can usually withstand more abuse.
The big drawback is that they are less efficient and therefore require more real estate than crystalline for the same power output. There is also a perception that because most amorphous panels emanate from Asia and are priced accordingly, they are inferior to crystalline panels.
Amorphous panels do tend to lose power over their lifetime while crystalline tends to be more stable.
My experience is that I have had a 32-watt Unisolar flexible amorphous panel beavering away on my boat for ten years now, with no discernable degradation in performance. These are great panels for boats but unfortunately are temporarily unavailable.
About now, solar power articles usually delve into the mathematics of appliance ratings, battery capacity, amphour calculations, days of autonomy and system efficiencies. If maths isn’t your forte, then some basic assumptions will suffice.
Firstly, if your aim is to keep the batteries topped up with intermittent use of perhaps the bilge pump and lighting, then a solar panel rated at 10% minimum of the battery capacity will suffice.
A 10-watt panel will be enough to trickle charge a 100Ah battery and keep it at 100%. Make sure the panel has a direct path to sunlight and is not obscured by rails or booms. Place the panel flat if the boat moves around, or at an angle if the position of the boat is fixed, aiming it toward north and in Sydney, at an angle of 35 degrees to horizontal.
A regulator is not mandatory for this 10% ratio, however at only $30, is desirable. Without a regulator, connect a blocking diode in series with the positive lead to prevent current feedback to the panel at night. The grey band on the diode goes towards the battery. Also fuse the solar panel. For larger systems, or where significant loads such as refrigeration must be maintained by solar power, calculations must be made. A complete system analysis can be obtained at nominal cost. Otherwise, simply mount the biggest panel you can afford that will fit on the lid of your boat.
But don’t expect a 60-watt panel to keep the beer cold. Invest in upgraded wiring and regulator and possibly a battery monitor. Then you can observe the number of charge or discharge amphours, percentage of charge left in the battery and predicted charge or discharge times.
If there is insufficient solar input, add another panel or if you haven’t enough space, perhaps a portable charger to top up the batteries or run the alternator for a while.
Don’t use one of the cheap 240 volt petrol generators with a DC output. The charging output is technically known as ‘bugger-all’.
The thing to keep in mind is that the sun shines a fair bit in Australia. Its output is free (although can come at some cost). Why not use it? Most boaties know this, especially yachties who tend to favour free things.
Pity Australia seems incapable of formulating a long term strategy for the use of solar power for mass electricity generation. The industry is fragmented and indecisive. Incentives are all short term and politically motivated. The take-up has been pathetic and now the manufacturing industry have packed their bags. Maybe we can make a difference.
Solar panel Regulation
Once a decision to fit solar panels has been taken and the size of the panels determined, consideration must be given to regulation of the charge from the panel(s).
Solar regulators are relatively small solid state devices that control the amount of energy that feeds the battery from the solar panel, by sensing the battery status. Most now are microprocessor controlled so that they can monitor system parameters and give an accurate picture of battery condition and charging requirements.
They are connected between the solar panel and batteries.
Solar panels typically produce charge at about 17V. This is too high for battery charging and can damage the batteries, so the regulator (also called a controller) must reduce the charging voltage.
Once the battery is fully charged, continued charging at this level would also cause damage, so the regulator must also sense when this has occurred and stop feeding further charge to the batteries. Overcharging will lead to battery gassing, loss of electrolyte and overheating.
To determine the required rating of the regulator, divide the total rating of the panels (in Watts) by 17V. This will yield the current (Ampere) rating of the regulator. The regulator must be oversized by at least a third, but if more panels are to be added at a later stage, doubling the required capacity is recommended.
If the panels are small relative to the battery size, it is possible to do without a regulator. As a rule of thumb, if the charging current is less than 1% of the Ah rating of the batteries, a regulator is not essential. However, regulators are relatively cheap compared to the cost of panels and batteries, so it is recommended to always fit a regulator.
Most regulators incorporate diodes that prevent a reverse flow of charge to the panels at night, an additional reason to always fit one.
The better regulators allow selection of the charging voltage appropriate to the battery technology being used, i.e. flooded, AGM, Gel etc.
Some regulators have a load circuit onto which the loads can be connected.
Often this circuit will have a protection circuit which shuts down the loads when battery voltage falls below a set minimum. On some regulators this circuit is one that only turns on when there is no current being fed in from the panels, i.e. it is effectively a photo sensitive switch that can be used to turn on and off circuits at dusk and dawn, e.g. an anchor light. It must be noted that the total output of this circuit is limited to the rated output of the regulator.
This is severely limiting, and can make its use quite inappropriate, especially in installations where a relatively small system is fitted in order to just keep a basically fully charged battery topped up while the boat is not being used.
Under no circumstances can starter, inverter, winch or thruster circuits be connected to load terminals. Generally, it is not recommended to use the load circuit on boat installations.
Most regulators have at least LED indicators that give an indication of the current state of charge of the battery. More sophisticated models have LCD displays that will indicate battery voltage, Ah collected/day and Ah used/day. It’s like having a fuel gauge for the battery. Some will let you know whether the charge cycle is in bulk, absorption or float status, and can store historical data to enable you to log system performance.
It must be noted that the battery Ah monitoring function will only be accurate if all loads are connected to the load circuit of the regulator. As this is impractical for most boats, a stand alone battery monitor with a high current shunt, through which all loads are connected, is required for proper battery monitoring. If a battery monitor has been fitted to the batteries, the basic regulators are more than adequate.
Some of the more sophisticated regulators are supplied with an external battery temperature sensor. This adjusts the charge cut-out voltage with respect to the battery temperature.
Higher voltages are required to complete charging as the battery temperature drops.
A few regulators have a feature where two batteries can be controlled simultaneously. _
*Gavin Sorrell works in collaboration with Aquavolt Electric Boat Parts. Tel: 02 9417 8455 www.aquavolt.com.au