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Charging Aux outboard battery

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I have acquired an electric outboard for the tender to our boat Princess Zena - after going through the pros and cons of electric vs. petrol, so i don't want to revisit that.

The outboard is a MinnKota Endura 30, and we have an 85Ah wet leisure battery - which works well for short trips and poking about, and will be find for most of our use (weekend trips) as I can bring the battery home to charge.

Sometimes, however, we do manage to get 10 days of boating at a time, so I really need to come up with some sort of solution to charging the tender's battery - I have had some ideas, but was interested in what other people did with this problem.

- Princess Zena is quite high sided, and the tender not brilliantly stable, so if possible I'd like to leave the battery in the tender for charging.

- We haven't really got anywhere convenient to put it on the main boat either

- PZ has a 65A alternator with conventional regulator, charging the engine battery, and sterling 50A battery to battery charger charging the domestic bank (220Ah).

So, I'm thinking of fixing something like Waeco IU Charging converter (probably the 8A version) near the stern of the main boat, to provide a regulated supply which can be run outside to the tender battery - charging it from the domestic battery when needed.

Does this sound like madeness, is there a much simpler solution I'm missing - or is this why people have petrol OBs (we don't really have anywhere to store one).



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Seems like an elegant solution Chris, though frankly a simple waterproof plug and socket tapped at the stern would suffice for your purpose. With the correct length lead you could even charge underway. The OB battery would never reach above the tapped battery voltage and a simple diode and a fuse would prevent any mishaps.

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Are you suggesting just a Socket from the 12 domestic electrics? If so, would my flat leisure battery in the dinghy draw excessive amperage once connected? (it is 20' from the domestic batteries to the stern, and I don't want to use 25mm2 cable!).

The thought of charging while underway had crossed my mind - we don't have davits though, so I'd need to be careful to start draping electrics in the river :shocked

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Indeed I am, If it were really flat then it might draw quite a bit of current but I suspect 8mm sq would be quite adequate if protected. Provided only the cable and not any joints draped in the oggin occasionally then I can’t see an issue. Main thing is to ensure any extension to the OB is not vulnerable to damage. As I said your original suggestion is an elegant (and probably preferred) solution, this is just a bit cheaper.

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OK thanks, it's useful to have someone concurr - I haven't found any ready solutions mentioned elsewhere, surprisingly.

i think I'll probably go with the waeco unit - in fact - i might kill two birds with one stone and fit a 'live only when engine running' outlet in the rear locker for an electrc cool box that Mum I promised my 3 years ago since it has an option for that, and it saves playing with relays.

Whether she (PZ) gets the 8 or 20A unit depends how naughty she is at next week's hull inspection :o

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