Oct 13, 2017, 02:50 PM
Ronaldo Nogueira
Question

Motor current x winding scheme x termination

Hi folks,
I was thinking about how to get more power with less temperature on a brushless motor and a few questions came to mind:
- when a motor is pulling X amps, is this the same current that flows through the wire (or strand) on each tooth?
- if the above is true, then a winding/ termination which leads to less turns/ tooth will be more efficient as it would allow for a thicker wire, am I correct?

I was thinking about choosing winding schemes which lead to less turns and also Y termination to reduce the number of turns to a minimum (as long as I can get the kv I want).
Just wanted to know if there is something I'm missing on this strategy.

Ronaldo
Oct 13, 2017, 07:21 PM
just look at it smokin'
Quote:
 Originally Posted by ronaldopn Hi folks, I was thinking about how to get more power with less temperature on a brushless motor and a few questions came to mind: - when a motor is pulling X amps, is this the same current that flows through the wire (or strand) on each tooth? - if the above is true, then a winding/ termination which leads to less turns/ tooth will be more efficient as it would allow for a thicker wire, am I correct? I was thinking about choosing winding schemes which lead to less turns and also Y termination to reduce the number of turns to a minimum (as long as I can get the kv I want). Just wanted to know if there is something I'm missing on this strategy. Ronaldo
Hello!

It does not work like that, less current is required for more efficiency.
You can parallel windings too, and connect to delta if you want higher Kv, that only means lower voltage and higher current.
2x voltage 0.5x current is the same power.
It is just, mosfets are expensive to handle the current, so going high voltage is an option for high power.
So you should reconsider your strategy, to make the BLDC motor cooler:
-run it with 180° commutation (and sine if required),
-install the strongest magnets available
-rewind and achieve better copper fill (lower resistance)
-optimize the magnetic path to reduce losses at magnet edges and reduce airgap, if it is an (d)LRK motor you could experiment with stator flx barriers too.
-heatsink/fan the motor
in this order.

Z
 Oct 13, 2017, 08:08 PM Ronaldo Nogueira Thanks Z, my question was generic but can be also very specific. Let's say I have the original motor with a dLRK wind with 16T Delta. If i rewind it using dLRK wye I can reduce the turns to 9 which means I would be able to use a much thicker wire than if I would if i had to make 16 turns. Let's say we plan to run it on 12S 80A max power system. In my very simple view (wouldn't be surprised if I was wrong ), if the same current X amps is flowing on each tooth of both windings then the thicker wire will mean less resistance/ heat and more efficiency. This is obviously assuming current is the same on all teeth (which I don't know if is true). Ronaldo
Oct 14, 2017, 05:32 AM
just look at it smokin'
Quote:
 Originally Posted by ronaldopn Thanks Z, my question was generic but can be also very specific. Let's say I have the original motor with a dLRK wind with 16T Delta. If i rewind it using dLRK wye I can reduce the turns to 9 which means I would be able to use a much thicker wire than if I would if i had to make 16 turns. Let's say we plan to run it on 12S 80A max power system. In my very simple view (wouldn't be surprised if I was wrong ), if the same current X amps is flowing on each tooth of both windings then the thicker wire will mean less resistance/ heat and more efficiency. This is obviously assuming current is the same on all teeth (which I don't know if is true). Ronaldo
You need at least 17 turns delta with the same diameter wire to get better efficiency than 16 turn delta.
(Termination does not make any difference in efficiency)
Answering your original question, motor current is 2x for 0.5x voltage @ 0.5 Kv, reason why high voltage is used for high power is the resistive losses, and the cost of high current mosfets.

Z
Last edited by z-matrix; Oct 14, 2017 at 05:51 AM.
 Oct 14, 2017, 02:11 PM Registered User Ronaldon. Con cualquier terminacion obtendras los mismos resultados si igualas el empacado de cobre y la resistencia. With any termination you will get the same results if you equate copper packing and resistance. https://aeromodelismoelectrico.blogs...rmination.html
Oct 15, 2017, 01:15 PM
Ronaldo Nogueira
Quote:
 Originally Posted by manuel v Ronaldon. Con cualquier terminacion obtendras los mismos resultados si igualas el empacado de cobre y la resistencia. With any termination you will get the same results if you equate copper packing and resistance. https://aeromodelismoelectrico.blogs...rmination.html
Saludos Manuel,
This is what I don't understand. If I have a winding with more turns (thus longer length), wouldn't it have a higher resistance than a shorter wire (less turns) with thicker diameter?
 Oct 15, 2017, 07:24 PM Registered User como en que ejemplo?
Oct 16, 2017, 05:43 AM
Ronaldo Nogueira
Como este amigo
I ordered this Sk3 6364 for a new project and it should arrive in a week.
The motor specs say it has 16T (probably delta) for 213kv. I want to rewind it for the same kv but more power/ less heat.
On TC5 you can see my options (yellow cells). As far as I understand if I rewind dLRK wye I'll need only 9 turns instead of 16, 17, 18 or 30 for LRK delta. This means I will be able to use a much thicker wire or maybe 2 wires to fill the same slot which translates into less resistance. Also, 9 turns mean a shorter wire which translates into even lower resistance.
Obviously I'm assuming the same current flows through each tooth but I don't know if it is true.
Ronaldo