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Home » Product & Planning Guide » Charging » 12V DC Alternators on
Canal Boats & Narrowboats


The gentle hum of a canal boat engine running when moored on the towpath is due to the boat owner either producing hot water or recharging the battery bank.

The engine is running a generator known as an alternator which is replacing used battery power.

The most basic system is the one commonly found on our road vehicles. A alternator is a small generator that is designed to produce AC electricity. Hence the name. Electronic components inside the alternator called diodes convert the AC power to DC in order for us to charge our batteries.

As a side, there are AC alternators that we use in the canal boat market for generating “regular” electricity for running washing machines etc. but that's another chapter.

Back to our engine/charging alternator....... A voltage regulator, mounted either inside the unit or externally, regulates the output of DC electricity for the purposes of battery charging.

Early and modern basic units output a constant voltage. As we have seen this is not the best for long term battery management. Therefore, the latest voltage regulators use the 3 stage charging process we have detailed above. Intelligent regulators are also available as an add on upgrade for basic constant voltage units.

A common size for a leisure system alternator os 70 amps but units up to 200 amp output are available. A common upgrade uses a 175 amp unit but careful consideration has to be given to belt and pulley sizes to maximise output at the low engine speeds we experience in canal boats.
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