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48V 300a - fusing and wire size help pls

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bluenomads

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For the boat, the electric motors will likely be 48V DC, 20kW, but we'd only ever run 15kW continuous - partly because of the battery pack, but largely because we want range not speed!
Battery is 48V, 16S 304's, and at 1C can produce 15.6kW at 52V (for about 80% of an hour or 48min; we'd almost always be around 5kW).
I'm limiting voltage to 48V as the other items off the battery pack - inverter, charger, solar panel MPPTs and even windlass and bow thrusters are all relatively (!) easy to get compared to higher voltages.
BMS is JK which together with an external contactor can handle up to 500A.

Could I get a check my fusing and wiring sizes:
  • Class T fuse right at/next to the battery of 350A - correct?
  • I'm having trouble with wiring size since 300A isn't "normal" :)...
    • 120sqmm is the largest I can easily get, and I've read different opinions on whether that is enough for 300A. - Will that be enough for a 1.5m run (not including return) of 300A?
    • if 120sqmm isn't going to be enough, what can I do??
      • I could go double 70sqmm (2 x 00 AWG) = 140sqmm instead.
        Or double 95sqmm (2 x 000 AWG) = 190sqmm.
        However, I read of possible problems with multiple wires as the resistance of one may be slightly different to the other, and even if separately fused (175A?!) it won't fix the resistance problem.
        Thoughts?
      • Other options?!
Thanks to another thread, I have looked at Baymarinesupply but they seem to just be another opinion - they show 2/0 can handle the load with a 0.55% voltage drop or about 0.28V for a 12' run (or 4/0 giving a 0.18V drop). 2/0 is only 65sqmm which seems a bit insane for 300A!
 
I use the Bay Marine Supply calculator for my wiring and I came up with 2/0 just like you did. Go with the 120sqmm if you want. Because of the higher voltage you can get away with smaller wire.
 
Also saw that BayMarine supply chart mentioned is assuming 105°C rated insulation but that is sometimes hard to find and why I listed a source above.

Edit: BayMarine sells 105°C cable as well but is PVC insulation. Might be better in marine environment. But that is why you see different "opinions" is because it isn't always clear what insulation rating is being used for the rating.
 
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Thank you everyone for the comments, they help.
I can get the 120sqmm so will go with that.
Ancor is not easy to get here unfortunately.
Our local Springers have a 120 but it's rated as "Maximum operating temperature: 75°C in normal Use OR 105°C where not subject to, or protected from, mechanical damage (refer AS/NZS 3008.1.1:2009) AMP Ratings are to AS/NZS 3008" which could be considered 105C compliant - or not!
 
bluenomads said:
However, I read of possible problems with multiple wires as the resistance of one may be slightly different to the other, and even if separately fused (175A?!) it won't fix the resistance problem.
Click to expand...
Nothing wrong to use 2 smaller conductors to carry high current. Even Tesla do this in some of his charge station to have more flexible cable. I did this sometimes.
Smaller lugs, more flexible cable, easier to find, go for it. But don't use 2 fuses. Both cable should be connect to 1 fuse.

The thing I really want to know is: What 48V motor could take 300A continuous? It's huge :oops:
 
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yabert said:
Nothing wrong to use 2 smaller conductors to carry high current. Even Tesla do this in some of his charge station to have more flexible cable. I did this sometimes.
Smaller lugs, more flexible cable, easier to find, go for it. But don't use 2 fuses. Both cable should be connect to 1 fuse.

The thing I really want to know is: What 48V motor could take 300A continuous? It's huge
Click to expand...
Most motors in the 10-20kW, even up to 30kW, are 48V: Quiet Torque, Bellmarine, Elco, etc.
Rare to find one under 6-20kW at other than 48V.
Note that these aren't outboards for pushing a dinghy onto the plane (although many of those are 48V as well), they are for yachts and motor boats up to many feet ("many" meaning how fast your want to go for how long: we have a 50' power cat and 10kW will be fine)
 
bluenomads said:
Most motors in the 10-20kW, even up to 30kW, are 48V: Quiet Torque, Bellmarine, Elco, etc.
Click to expand...
Thanks, I have my answer: No one of those companies offer motor rated for 300A continuous at 48V.
Really useful information about 15 kW inboard motor at 48V.
Bellmarine and Quiet Torque use 2 motors to acheive 15 kW. Higher power = higher voltage. Except for the liquid cooled TorqueMaster 20W EVO, but it's list as ''special''.
And Elco most powerful 48V motor is rated 20 hp ''comparable''. So nothing to do with a real 15 kW.
 
Hey Yabert, you're right!
The Bellmarine EVO was the one we were looking at! When I did research a few years ago, there seemed to be many more, but can't find them now. Kudos to you.
I'm wondering if the change (as I perceive it to be) is that for 15+ kW you really do need to be at higher voltage - cabling, losses, etc.
One of the reasons we will/may still need the higher amperage is that - still to be decided - we may run 2 smaller motors (if not EVO), say 8kW, off the one battery pack (since we are a power cat). Hmm, some decisions pending!
 
That is a healthy battery pack.

Would it make any sense to consider to break it into 2 parallel packs for redundancy or other reasons?
 
bluenomads said:
we may run 2 smaller motors (if not EVO), say 8kW, off the one battery pack (since we are a power cat). Hmm, some decisions pending!
Click to expand...
If you are interested to build your powertrain from motor/controller you can take a look at:
-Motenergy motor
-Golden motor
-QS motor

The moternergy seem to be use by some marine motor compagnie like Elco and Quiet Torque.
 
One thing I learned installing many car audio systems over the years is run the largest guage wire you can fit for future proofing. You will absolutely need 4/0 for that much amperage and to lessen the amount of voltage drop. I highly recommend getting 4/0 OFC tinned that has a silicone insulation. 4/0 is heavy and the PVC insulation does not flex easily. This is some of the most high quality wire you can buy, I have used this brand for the last few years for any DC wiring. https://www.knukonceptz.com/sp/kolossus-fleks-black-40-gauge-powerground-wire/
 
Is that chart for welding cables while welding? Or is that NEC for home and business?
 
It has all sorts of welding duty cycle info in there. So I don’t see how it can be applied without some finesse. And if you have the finesse then maybe should have started from a more directly appropriate table
 
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