Electric auxiliary to Antarctica

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  • 20 Sep 2021 09:51
    Reply # 11103020 on 10752801

    What Jan and Arne say makes sense. but still leaves me a little puzzled.

    A 48 volt system is still going to need more than 48 volts to charge the batteries. Here is an example (Cinderella's Solar Panel Installation (sailingcinderella.com)

    This boat has two  SolarWorld 345w panels in series and installed on a bimini over the cockpit. Evidently this provides nominal 80V. So, even limiting the battery bank and motor to 48 volts, there are still significantly higher voltages there.

    I suppose, as Jan says, it is partly a matter of balancing safety and economics.

    Its just that I haven't come across any mention of this by manufacturers, or people who have installed their own motors (apart from the occasional comment about the need for care with high voltages). I wonder if there are any other reasons which relate to small boat electric engine systems, which makes 48 volts seem always to be the preferred system.

    Edit: I just did a bit more googling and found that the human skin, when wet, can have resistance as low as 500 ohms. That means 50 volts would be enough to push 0.1 amps through you which, in the right circumstances, is enough to kill. So, I guess that's enough reason to be wary of higher voltage battery banks.

    I'm glad I asked. It still puzzles me, if that is the main reason, why it is not spelled out more clearly in the literature.

    Last modified: 20 Sep 2021 10:37 | Anonymous member
  • 20 Sep 2021 09:06
    Reply # 11102920 on 10752801

    I think Arne is right, it's an industry standard based on safety. As far as I know it originated in old fashioned copper-wire telephony. 50v DC was the safe limit for a getting a tingle off a pair of wires without it being dangerous, especially for someone up a telephone pole fixing something, and safe for consumers in their homes.

    In renewable energy it seems to strike a good balance between safety and the economics of long wire runs. I think this must have influenced many PV panels having open circuit voltages around 60v for input into charge controllers. My domestic PV runs into the shed at 60v and an MPPT controller brings that down to 24v for the battery/inverter system. 

  • 20 Sep 2021 08:56
    Reply # 11102908 on 10752801
    Anonymous member (Administrator)

    Graeme,

    could it be that 72 Volt is above the 'safe' low-voltage limit? In my job, 24volt or 48volt were the standard DC-voltages used in our battery banks. These voltages could be handled by us without being certified AC-fitters.

    Nowadays, the big UPS-systems (Un-interrupted Power-Supplies) use around 400V battery banks, and these could easily kill a man, so need serious procedures to be safe.

    Arne

  • 20 Sep 2021 07:15
    Reply # 11102760 on 10752801

    I've got no plans for going to Antarctica, but I’m trying to educate myself a little on the subject of electric motor installations (in the context of Junk rigged  boats, of course). Rather than start a new thread I hope Jan won't mind me dropping a question in here.

    Spent the last couple of covid lockdown days googling everything I could find on the subject, and it appears that the commonest systems for small cruising boats are 5kw or 10kw – a variety of brands (ThunderStruck, GoldenMotor, QuietTorque) – but aways ALWAYS 48 volt systems.

    Given the advantages of higher voltage – say, 72 volt (less amps, cooler running) why is it that the small to medium size marine installations and kitsets always seem to be 48 amps?

    Obviously there is some practical reason, relating to boats, but in all the articles that I have read,  no one seems to give a reason. Is it to do with problems in arranging solar charging panels?

    Can someone explain it to me?



    Last modified: 20 Sep 2021 10:31 | Anonymous member
  • 15 Jul 2021 09:12
    Message # 10752801

    Here's an interesting article about a small boat taking giant steps. We all know that Roger Taylor went to the Arctic with no auxiliary propulsion but this Argentinian expedition was considerably longer and with three onboard. 

    https://afloat.ie/power/outboard-engines/electric-outboard-engines/item/51125-to-antarctica-back-without-fossil-fuels

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