The device used to top up the batteries in a defined manner is inconspicuous, but its importance for boat operation comes right after the main engine: without power in the batteries, almost nothing works on board these days. The right choice is therefore very important.
For the layman, the wide range on offer is simply overwhelming - there are over ten different versions of some devices. As a sizing guide, let's assume a typical small touring boat with two people and a consumption of around 30 ampere hours per day.
This corresponds to an average load on the consumer battery with a current of 1.25 amps.
With a good compressor cooler and moderate use of the radio and lights, a small chart plotter and LED lights, this is a realistic value in summer.
The size of the boat is almost irrelevant. Of course, a larger crew with more energy requirements throws this calculation out of kilter. It's better to buy bigger: a good charger cannot be too big.
Equipped with lead-acid batteries totalling 150 ampere hours, this imaginary holiday boat can comfortably spend a night at anchor. The lead-acid battery is considered empty when half of its capacity, i.e. 75 ampere hours, has been used. The other half is regarded as an iron reserve; tapping into it has a very negative effect on the service life.
DIMENSIONING
The battery should be full again after one night in harbour. In 16 hours of mooring time with shore power, the 75 ampere hours must therefore be charged back into the battery and supplied to the on-board power supply - together with losses, this makes around 100 ampere hours.
In practice, devices in the class between 20 and 30 amps have proven themselves for the above requirements. This is the starting point for this test with devices for fixed installation from Cristec, Leab, Quick, Sterling, Votronik and Whisperpower.
TECHNOLOGY
All seven candidates are processor-controlled and operate according to the high-frequency principle without heavy components.
This means that the conversion of the voltage from the mains to the battery does not work at the slow mains frequency of 50 Hz, but at several tens of thousands of Hz.
The still existing transformer is therefore extremely small and light. In addition, the number of oscillations is above the range of perception of the human ear, which is why no humming or whistling can be heard from a properly functioning high-frequency charger.
Quiet operation and lack of weight are immediately noticeable. Electrically, an invisible point is much more important: the charging voltage is largely independent of varying mains voltage. This is noticeable in crowded harbours when a few volts are lost after a few extension cables and distribution sockets.
In the test, we varied the mains voltage using a regulating transformer to explore the limits: Full power should be available from around 190 volts. Some devices even work with 110 and 230 volts without switching.
A fan causes unordered noises in five test subjects. In all cases, these are dependent on the load of the charger but are not always acceptably quiet.
The night mode offers a remedy. In this mode, the power is reduced for a certain period of time, usually ten hours, so that the device can operate without a fan or at minimum fan speed.
We measured the noise emission under full load at a distance of one metre. This means that the values are comparable with each other, but do not represent the installation conditions on board. In addition, typical ship noises such as wind and waves may be louder in terms of measurements, but are more likely to be tolerated.
The categories charging technology, side effects, starter battery, dimensioning, efficiency, as well as a conclusion and statistics appear in the detailed report in the October issue - in stores from 14 September.
