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Energy issues onboard

We have a brand new narrowboat and are newbies as continuous cruisers. After 5 hours cruising our batteries are not fully charged. Is that normal as we do not have anything on whilst we are cruising except the WIFI. When we are moored up we watch TV for a couple of hours and the batteries go down to 11.8 so we have to charge them up again. We flush the toilet a couple of times and put the lights on for short periods of time i.e. 5 to 10 mins. Our setup is 4 x SMF VETUS MATINE BATTERIES 12 V 145 AH (20H) with a VICTRON MULTIPLUS 12V 3000 VA 120AMP. The alternator for the domestic batteries is 240AMP plus solar panels to top up 20AMP. Our domestic consumables are Vetus pump out toilet, fridge 12V, freezer 12V, LED lighting, Playstation 4 240V, TV 240V 133W, Satelite dish and 4G receiver and WIFI system and a digital radio 240V.
Please could you advise us if this is normal or is our system faulty somewhere?
many thanks

Asked by: costas  | 10.07am, Monday 26 February

WW says:

Unfortunately, your system is not at fault. As you cruise, the alternator will charge the batteries- as the charge level rises in the battery, resistance increases, which increases the voltage at the battery, so the alternator reduces output. Quite quickly, most alternators slip into "trickle" mode, even though the batteries can still take more current.
This is quite common. When moored up during the day in summer, the solar panels may well top up the batteries to near full (but as you will have some consumers, such as fridges, on).
Incidentally, the voltage will drop considerably when there is a draw on the batteries- it is only the resting voltage of the batteries (with no load applied) that gives you a good indication of charge levels.
There is always a chance that one of the cells within one battery may have failed- ideally disconnect the batteries and measure the voltage of each battery individually- and discrepancy will show up there.
Lastly- the best thing for charging batteries when cruising, is to fit an external alternator controller, which turns your alternator into a smart charger. One such as the Sterling Alternator to Battery charger, would mean that all the useable output of your alternator can be taken, and that there is a multi-stage charging profile to the battery bank- as your Victron does when connected to the mains supply.
Also, you battery bank gives you around 250Ah of useable capacity (about 40% of total capacity)- if you use a lot of 230V power, this can soon deplete the battery bank- and 5 hours cruising without an external alternator controller is unlikely to reach full recharge.#
However, before installing an alternator controller, I would double check the condition of your batteries individually with a multimeter. Unfortunatley your batteries are sealed for life, which does mean that you can't charge them quite as fast (or easily to as full) as you cannot let them reach gassing voltage for any length of time- and you cannot top up the electrolyte level. Open cell lead acid are much easier to maintain and might be worth considering them when ultimately you come to replace the batteries- especially for liveaboard use.

Mark Langley  | 12.44PM, Monday 26 February

Your boat has quite high electrical demands; a fridge and a freezer that will consume a reasonable amount of power. Using mains equipment puts additional stain on the batteries. Is your WiFi mains powered? Do you leave your inverter on continuously? The inverter will consume 20W (unless set to AES or search mode) continuously, before adding in the supplied 230V power, which equates to 40Ahr over a 24hr period. Using 12V equipment where possible, phone chargers etc, will reduce your electrical consumption.
As Mark suggests, it might be as well to look at your charging system (alternator and controller) and to do an electrical audit to put figures on your daily consumption. There is a handy tool on this website.

Rupert Smedley  | 9.18AM, Tuesday 27 February

Readers say:

Thanks for your answers they clear up some conserns and I am going to look in to few other issues .

costas  | 4.09PM, Tuesday 27 February

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