Electric drive for Weaverbird

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  • 04 Apr 2020 10:45
    Reply # 8878498 on 8809939

    Thanks, Kurt, that's encouraging. Now 'all' I have to do is to get through the current situation unscathed, complete my installation and be in a position to go out and get some real-world data myself.

  • 03 Apr 2020 21:15
    Reply # 8877876 on 8809939

    A little real-world data from pretty careful measurements I've taken over 2 seasons, in canals and up & down the River Thames:

    minim makes a little over 2 knots on 250W electric input.

    2.5 knots on 450W

    3.25 knots on 1100W and that is nearly top speed

    So, with her 280W solar panel in good sun, she glides through the middle hours of the day for free, or sits still & recharges from a cloudy yesterday, and she confirms the classic shape of the power-speed curve - slow is easy.

    (Newbridge Coromandel; 6.4m oal, 5m wll; ~1 tonne displacement.

    Motorguide 24V '82lb thrust' trolling motor; 9 inch diameter 3-blade prop.

    3840WHr lead-acid battery bank.)

    mehitabel is 12m, ~11 tonne and makes >2.5 knots on 1100W - even big and slow is easy.

    (really good data is hard to get in open & tidal water, of course. but over a long time, that's quite reliable for mehitabel too.)

    Economics? Well, if I replaced mehitabel's tired (AGM) batteries now, I'd spend more than I would have for diesel over the ten years they've served. But I'm eking them out, and it's not too difficult.

    Cheers, Kurt





  • 27 Mar 2020 16:38
    Reply # 8862370 on 8809939

    Yes, David, I purchased a chinese hydraulic crimper from eBay a couple of years back, rather quaintly described as "Hydraulic Pliers"  - one of my better tools, it made all the battery, inverter and alternator cable making an actual pleasure.... and ~£20 from memory.

    I think that the pressure is such that you achieve a "pressure weld" of the cores and lug - this is the same process that "wire-wrap backplanes" achieved in the 70s in computers of the day - the point pressure of the wire being wrapped around sharp-cornered pin was high enough to achieve the same result... and they were ultra reliable, with thousands of connections on a single backplane you would soon know if the process was less than perfect or allowed any corrosion...

    Last modified: 27 Mar 2020 16:39 | Anonymous member
  • 26 Mar 2020 15:51
    Reply # 8860213 on 8860153
    Darren wrote:  Here is another example, the pic on the left is made with an indent crimper, like I mentioned earlier in this thread and the pic on the right is made with a hexagonal die, like the kind David bought.  

    When I made the butt splices, I was able to look down inside after I'd crimped one end. I can confirm that 10 Tonnes of pressure on hexagon dies is pretty darned effective at squashing the copper cable and terminal into a solid mass.

    For the copper strap.  The strap itself should be fine left bare, but the mechanical connections are best with something to exclude air and liquids.  Silicone dielectric grease is the gold standard, but has the drawback that it is silicone.

    I carry a 50 gram tin of silicone dielectric grease aboard. That's enough to last a lifetime, it only needs a little smear on the surface to be protected. It's great stuff for any kind of plug and socket connection - phone and tablet charging sockets in particular.


  • 26 Mar 2020 15:19
    Reply # 8860153 on 8857430
    Anonymous wrote:

    Plain, un-tinned  copper will corrode at the joint, would solder tinning the wire ends before crimping be a good idea?  Likewise a copper strap.

    I used to be a follower of the solder faith, and I suppose none are as devout as the converted, so please excuse me if this sounds like I'm once again mounting a soap-box :-)  If you don't have extra time on your hands due to Covid 19, then the bottom line is crimps are great with glue lined heatshrink, otherwise, hopefully what follows is either entertaining or informative.

    Glue-lined heatshrink can be used for insurance for crimped terminals. Heat it not just until it shrinks, but until you see a little glue ooze out of both ends.  However, the crimp itself is almost as good as the wire are resisting corrosion.  Keep in mind, there are millions of cars driving around on salt-laden roads in the winter.  All of their connections are crimped and most are less protected than you will do on your boat.  Lots of folks have seen, made or inherited poor crimps and this probably makes them more concerned than necessary.  A proper crimp matches the ferrule to the wire size so there is little extra space before the crimp.  During the crimp both the wire and the terminal deform to create a join that should not have any gaps.  It should be air tight.  I've actually gone to the trouble to cut a lug in half, acid etch it, and view it under the microscope to confirm that I can make crimps this well.  But, for those that are wiser with the use of their time, here is one example of what a good crimp should look like.  Here is another example, the pic on the left is made with an indent crimper, like I mentioned earlier in this thread and the pic on the right is made with a hexagonal die, like the kind David bought.  

    For a person at home, or on their boat, most industrial means of inspecting crimps are impractical (expensive, specialised equipment, etc.).  However, there is a pretty good relationship between mechanical strength and electrical conductivity in crimps.  So, buy a couple extra lugs and make a test piece.  If you can come between the UL and Mil Spec tensile strengths listed in this table, you're making good crimps.  Your test apparatus need be no more complicated than the rafters of your garage (or a tree branch), a bucket, a bathroom scale, and a way to keep yourself (especially toes), away from danger should the connection fail.  Weigh things on your scale and add them to the bucket until you meet the spec weight or the connection fails.  Please use sense in testing, don't use something stretchy (use chain rather than nylon line) in the test rig so that things don't fly about if they break, wear some safety glasses, be responsible for your own safety.  If you use a plastic bucket, think about how strong it and its handle are.

    For the copper strap.  The strap itself should be fine left bare, but the mechanical connections are best with something to exclude air and liquids.  Silicone dielectric grease is the gold standard, but has the drawback that it is silicone.  Maybe it's just me, but silicone seems to like to go everywhere and also has the property of being impervious to virtually all solvents and cleaners.  Thus, years later you may wonder why you are getting fish-eyes when you refinish your brightwork because you have long-forgotten the silicone fingerprints you left behind.  I keep a small tube of silicone dielectric grease for things like VHF coaxial connections that need the very best.  I've used a fair bit of Grote Ultra Seal, mostly because it is easy for me to get locally.  It is some kind of petroleum based grease.  It seems to get thicker and darker as it ages on the connections.  However, I've pulled apart stuff more than ten years old and it still seems to be doing its job.  Get the tube version for less mess.  Lanolin is another alternative.  Lots of us have experience with Lanocote.  This is Lanolin with petroleum distillate added to make it workable through a wide range of temperatures, it may have other additives.  I'd just as soon not have the petroleum distillates, so I've been using straight anhydrous lanolin for a while now.  It seems to work just as well, and your hands are silky smooth at the end of the project.  During Canadian winter temps you need to keep the container in your pocket or it gets too cold and hard to work with.


  • 26 Mar 2020 00:07
    Reply # 8859250 on 8857430
    Anonymous wrote:

    Good subject and lots of useful info.  
    I have to say that soldering wires is an art I have never mastered, copper pipe fitting I can do.

    Plain, un-tinned  copper will corrode at the joint, would solder tinning the wire ends before crimping be a good idea?  Likewise a copper strap.


    From the post below: "The problem most folks will run into is that by the time you get a part as large and heavy as battery cable hot enough to solder, it is very easy to have the solder wick along the wire." This means the stranded wire you paid extra for becomes one solid wire more likely to break with flexing.  Also ... as if that is not enough, a layer of solder before crimping means the crimp will not be fully tight or as tight as it would be with no solder. If the solder gets hot enough, it moves to a part of the joint with more space for it leaving the joint loose which leads to more heat and eventually smoke... There are covering for battery terminal connections, depending on the battery chemistry involved. That is why your car probably has lead posts and lead ends on the cables... and still corrodes in an acid fume environment. Lithium based (or sealed) batterys have less problems in this area. For salty air, shrink wrap (the best is the stuff with melty goop inside) is the easiest stuff to use. Done properly, it leaves no air next to the copper.
  • 25 Mar 2020 10:45
    Reply # 8857430 on 8809939

    Good subject and lots of useful info.  
    I have to say that soldering wires is an art I have never mastered, copper pipe fitting I can do.

    Plain, un-tinned  copper will corrode at the joint, would solder tinning the wire ends before crimping be a good idea?  Likewise a copper strap.

  • 24 Mar 2020 19:25
    Reply # 8854329 on 8854277
    Anonymous wrote:

    It depends... for making the cells into a battery, they provide copper straps which need no soldering (most other cells would be similar having screw on terminals). However, if you are going to make your own cables (which will probably be needed) most people like to use solder even with crimp ends to keep oxygen and water out of the join. There are others who say crimp only as the join may heat and the solder run out and the join fail. Certainly crimp first and solder after as the crimp is what gives a good mechanical join.


    A properly done crimp shouldn't need anything else.  With a proper crimp the wire "cold flows" into an airtight mass.   Add some glue-lined heatshrink and you should have a lifetime connection.  If you can't do or get a proper crimp done, then adding solder might help, but is definitely second best.  The problem most folks will run into is that by the time you get a part as large and heavy as battery cable hot enough to solder, it is very easy to have the solder wick along the wire.  This leads to a stress riser between flexible wire and hard solder that is prone to breaking strands and creating a high-resistance failure point.  If you solder you have to be very certain that you also restrain the cables well beyond the joint so that the fragile transition between solder and cable doesn't fail.  If you are going to solder do some test pieces and then destroy them and see how far the solder has moved along the wire.

    Crimpers for small wire gauges are cheap.  If you are doing lots of large wires then even a big crimper is pretty cheap spread over the job.  Also, online and locally it is not hard to get crimps done on big wires fairly inexpensively.  One of the great things about LiPO4 batteries is that they can provide and accept astounding currents.  However, this can also end up testing the reliability of your connections.

  • 24 Mar 2020 19:11
    Reply # 8854313 on 8853495
    Anonymous wrote:

    Darren,

    Excellent tips regarding the charge controllers, thank you!

    Jami,


    As for LiFePo4 in general I really don't see any practical reason* for anyone to use lead acid batteries for anything anymore, so I would've switched even without converting to electric motor. When you factor in usable amp-hours and overall life expectancy, LiFePo4 is actually less expensive and a far superior battery technology.

    *) except short-term financial


    LiPO4 do have some problems, that mean they're not the best choice for everyone:

    1) They are damaged if charged below freezing temps.  This can be overcome, but if you have depleted batteries and can't use them to warm themselves you can get yourself into a pickle.

    2) They have a habit of destroying alternators if all you do is add them to an existing boat.  Their high charge acceptance rate will cause many alternators to kill themselves trying to supply the batteries.  This can be overcome, but it means LiPO4 is not a drop-in solution.

    3)  You have to have a functioning BMS to keep them working.  With lead-acid batteries you can charge them in all sorts of unsophisticated ways in a pinch.  Not so with LiPO4.

    4)  With LiPO4, a single error in over-discharge can destroy the batteries and leave them inoperable.  A BMS should prevent this, yet there are lots of examples of LiPO4 being destroyed this way.

    They're still a fantastic battery choice, but there are ways in which lead acid are better.  Something like Firefly carbon-foam AGM can offer a better compromise for someone who wants high-performance with fewer headaches.  For someone who is technically inclined, or with deep pockets, Lithium might make a better choice.



  • 24 Mar 2020 18:59
    Reply # 8854305 on 8809939

    The Haswing motor came with a short cable with crimped terminals and heat-shrink, to link two 12V batteries. It's not as large in diameter as the 25mm2 cables that are permanently installed in the motor; I think it's only 16mm2. I've assembled it for the moment, just for trials, but the right solution must be a short flat bar of copper, brass or aluminium, with the two batteries close together. Thanks, Len, for the idea of flattening some copper tube. I calculate that standard 15mm tube will give me more than 35mm2 cross sectional area.

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