Pragmatically speaking, can't you get more turns of a smaller wire into a given slot size than larger wire? Does this mean that for a given motor size that a higher voltage rating might indicate higher efficiency or performance?
BTW, thanks for the discussion. I'm a mechanical guy and am still learning about these electric doo-dads.
I believe you are correct. A higher copper fill will make a motor more power dense, and I would think that efficiency may improve, but doesnt necessarily have too...
Originally Posted by Frank
You can use parallel strands of finer wire opposed to thicker if it allows for better slot fill, so, no it is not necessarily true. But that means you have more insulation on the wires and insulation consumes slot space and is non productive.
Originally Posted by Frank
I was responding to Biff's example.
Originally Posted by sparky_mark
And I did use a published motor curve so it can be considered a real world example. While you may not need 30hp for 60mph, you certainly can use 30hp at 60mph for various reasons like a strong headwind, uphill or acceleration.
Originally Posted by Biff
I did the tests Ted spoke of and what was found with a 45 pound weight was depending on the gear I started in made more difference than the extra weight. Starting in 1st or 2nd with and without extra weight was Identical but as you start in 3rd-5th the heavy tests got way slower times than without the extra weight. Voltage sag showed out in the same way too but the weight had no difference in those tests, just more sag in the higher gear starts along with more heat.
In the end I could of built a bike that had no trans and followed years of conventional wisdom, or just converted an existing platform but that would have been easy and pushes no limits for me, I wanted something different that gave me a challenge. Looking back I wouldn't do it any different at all.
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Your ideal method to fit the most copper in the slot is to simply slide a solid bus wrapped in a thin film of kapton down the slot. (see, solid-slot motors, and the difficultly of controlling these low inductance beasts, it's a case of extremely high motor performance and efficiency capability, but controller tech isn't up to the point of controlling them effectively)
Your second best option is what Remy does, custom forming flat strips of copper and welding the ends down close so end-turn loss is minimized. (see Remy HVH)
Your third best option (though extremely difficult labor to do) is to wind square enameled wire into the slot stacking blocks of copper cross section to fill the slot.
Your 4th best option is a single strand of the fattest wire that fits the slot to make the number of turns you need. This is because the ratio of copper cross section to wasted insulation space is minimized if there are no additional parallel strands.
Your 5th best option (and what is most commonly done because the winding process is easy to do with human hands) is bundles of fine wire. This can not achieve the copper fill theoretical limits that a single large wire can achieve because of the additional wasted volume of the insulation, however they easily straighten and lay flat in the slot where the bigger thicker wires tend to bow when wound by humans.
If you had big wires and small wires with no insulation, it would make no difference on your limits of copper fill. Small wires with insulation will always be theoretically worse than big wires with insulation. However, in practice when wound by human hands rather than a machine with plastic die it forces through the slot to make each pass lay flat in the correct place, small wires generally result in the best fill.
Here is a decent page going over the geometry and copper fill associated with large wires vs small wires, and should clear up many of these misconceptions.
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Agreed...and I'll just add, in my opinion, the elegant simplicity of direct drive.
And yes, Chris, on the fun part, but for me, not to beat the horse, but the fun is in not shifting - and pretending I'm in the launch tube of Battlestar Galactica.
Canyon carving is so much better without your rear wheel getting jerked around on downshifts under braking. You can run that much closer to the limit safely. You never have that problem of exiting in the wrong gear either, you're always in the right gear. I do quite a bit of riding Electrics with gas bikes, the shifting delays and interruptions seem so dinosaur. My GSXR1000 has crazy power, but in a technical set of twisties, I run faster on a zero because you don't have to leave margin in the tires for the back torque jerks upsetting the chassis on downshifts. I know some super bikes made in the last few years have special back torque limiting clutches to help reduce that problem, they likely feel better.
Originally Posted by podolefsky
Doesn’t a bunch of fine wire also reduce heat from eddy currents? Rather like the laminations in a stator core?
Originally Posted by liveforphysics
It does in an ironless motor (which is why they use litz wire). In a motor with iron, the copper never has flux lines cutting through it, this is the job of the iron to attract and guide the flux lines from the head of the tooth down the shank of the tooth. The copper doesn't attract or guide the flux, the iron does very effectively, and keeps it all away from the copper in the slot.
Originally Posted by Square Wave
This is true even with motors where they fill the slot very wide so it's bulging with copper out exposed between the edges of the tooth heads. I had thought it would be a massive eddy current failure, but it turns out, the iron guides 100% of that flux down it's heads and into the shaft of the tooth and the copper doesn't see a thing (other than the net change in flux of the iron core it's wrapped around, which is what creates the BEMF). Take the iron out of that picture, and you've got yourself an eddy brake. Put the iron in, and you've got a pretty free spinning motor (just normal core-losses).