Electric outboard drive for small cruisers

  • 20 Apr 2020 09:41
    Reply # 8910412 on 8809939
    LiFePO4 batteries can safely charge between -20°C to 55°C (-4°F to 131°F). However, at temperatures below 0°C (32°F) the charge current must be reduced, until the temperature is >0oC (32oF), as follows:

    1. 0°C to -10°C (32°F to 14°F) charge at 0.1C( 10% of the battery capacity)
    2. -10°C to -20°C (14°F to -4°F) charge at 0.05C (5% of the battery capacity)

    Source: Charging instructions (PDF) from RELiON's documentation page.

    So they don't cut off the charging completely but instead lower the rate. That's interesting, didn't know that was an option. But I would've thought that it would be healthier to instead do it as you suggested, by placing a heating element inside the battery casing. The power consumption of that would be miniscule compared to the gains in charging rate.

  • 20 Apr 2020 08:12
    Reply # 8910231 on 8905396
    Oscar wrote:

    Horst, I haven't decided on a specific BMS yet but in important thing to look out for (if it applies to your cruising ground) is that it has a low temperature cut-off (usually configured around 5 deg C) as LiFePO4 cells are damaged if charged below freezing. You can test if it works by putting the temperature sensor in ice cold water and measure whether the charging stops.

    An alternative to low-temp cutoff on the BMS would be to have it on the charge controller instead, if solar is your only power source. For example Victron sells separate temperature sensors that you can hook up to their products. That said I think it's more sensible to have it on the BMS level so that you're protected whatever charging method you use.


    I'm puzzled about how my Relion batteries seem to get around this. The data sheet clearly says that the temperature limits for charging and discharging are -20˚C to 45˚C  and -20˚C to 60˚C respectively. Could there be some self-heating that cuts in at low temperatures? Nevertheless, I should look at the charge controller manual and see if I can set a lower limit.
    2 files
    Last modified: 20 Apr 2020 08:16 | Anonymous member
  • 17 Apr 2020 15:13
    Reply # 8905733 on 8809939

    I've just watched Will Prowse build a 24V LiFePo battery

    https://www.youtube.com/watch?v=E4pN4DVPOcY

    I thought he was very clear and informative on the process and possible pitfalls. Particularly, I went back over the preferred charging profile several times, as I will need to set up a user-defined charge profile on my MPPT controller:

    Charge limit:   28.8V

    Absorption voltage for maximum battery life:   28.2V

    Float voltage:   27.7V

    Charge/discharge bandwidth for long battery life:   26.6V - 25V

    Last modified: 17 Apr 2020 15:37 | Anonymous member
  • 17 Apr 2020 10:26
    Reply # 8905396 on 8809939

    Nice initiative David!

    Horst, I haven't decided on a specific BMS yet but in important thing to look out for (if it applies to your cruising ground) is that it has a low temperature cut-off (usually configured around 5 deg C) as LiFePO4 cells are damaged if charged below freezing. You can test if it works by putting the temperature sensor in ice cold water and measure whether the charging stops.

    An alternative to low-temp cutoff on the BMS would be to have it on the charge controller instead, if solar is your only power source. For example Victron sells separate temperature sensors that you can hook up to their products. That said I think it's more sensible to have it on the BMS level so that you're protected whatever charging method you use.

    And it's obviously worth being skeptic about super cheap products. There are a lot of good independent reviews of solar equipment (battery cells, BMS's, solar panels etc) on Will Prowse's channel. Electricseas.org as you mention is a good resource as well, many interesting project threads to read through, and the article you linked to seems like a good read, thanks!

    I'll try to post here when I figure out what I'm going to buy and why. So far, in addition to the cells, I've also ordered a 24V to 12V converter.

    Last modified: 17 Apr 2020 10:27 | Anonymous member
  • 17 Apr 2020 07:29
    Reply # 8905230 on 8809939

    I've edited the heading for this topic from "Electric drive for Weaverbird" to "Electric outboard drive for small cruisers", so that Oscar and anyone else who is adding outboard electric propulsion to boats in the 18 - 23ft range can post here, on their own work, and we can keep all the info we gather in one place.

  • 17 Apr 2020 02:24
    Reply # 8904999 on 8896661
    I bit the bullet the other day when I found a great deal for 8x 190 Ah aluminium cells for €1180, so will have a 4.5 kWh battery bank. Now I see further reduced the price slightly, those cells would cost €1108 today. Will take a while to arrive from China though (30-60 days from looking at the comments in the reviews).
    On the website it says "Customers should configure a BMS..." What are you going to use? How to decide which BMS is working correctly with these cells?

    electricseas.org is an interesting forum when it comes to electric propulsion on boats. And this appears to be a good read about LiFePo4s on boats: marinehowto - lifepo4 batteries on boats


  • 14 Apr 2020 08:07
    Reply # 8897465 on 8809939

    Now I'm kicking myself for not doing more research into LiFePO4 batteries. I might have spent a great deal less. But I comfort myself with the knowledge that the Relion batteries have a robust inbuilt BMS, and it's difficult to mistreat them.

  • 13 Apr 2020 20:31
    Reply # 8896661 on 8883295
    Anonymous wrote:

    I must say that I think I'm going to actually enjoy this electric outboard, whereas I was tolerating, at best, the petrol outboard. It's quiet, instantly there ready to go when needed without worrying about whether it's not fully warmed up and might stall, and the control when approaching to pick up a mooring is vastly better.

    That's great to hear! Just like I've been envisioning it.

    I bit the bullet the other day when I found a great deal for 8x 190 Ah aluminium cells for €1180, so will have a 4.5 kWh battery bank. Now I see further reduced the price slightly, those cells would cost €1108 today. Will take a while to arrive from China though (30-60 days from looking at the comments in the reviews).

  • 09 Apr 2020 00:20
    Reply # 8888266 on 8809939

    For your use you might consider something like a clear-lidded pelican case for the enclosure.  The model of meter I have has a button on the screen that gives you state of charge info.  I haven't played with it as it's not of much use if you are monitoring an alternator.  But, for your use maybe that might make a useful fuel gauge?  An enclosure with an opening clear lid might allow this kind of function to be retained.

    As I do with most cheap electronics, I took mine apart and gave it a coat of conformal coating.  Maybe that would be good enough if you could mount yours somewhere it wasn't too wet.  The version I have with the button would probably also need a blob of dielectric grease into the momentary switch to extend its life.  

  • 08 Apr 2020 20:56
    Reply # 8887980 on 8809939

    I agree, a Hall Effect ammeter is easier to install than one with a shunt, and seems to be cheaply available if I buy it direct from China.

    If I then install it in an IP67 enclosure, I think it would be fit for purpose.

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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