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Oct 12, 2021, 03:52 AM
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powercroco's Avatar
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24N20P winding with 4 part-motors on scorpion HK7455

Base for the rewinding was a scorpion HK 7455, made for driving an electrical surfboard

The owner of this motor wanted more n-spec to use more power.
Battery should stay with 14S 16.000mAh.
So i got it for rewinding.

I used the possibility, to wind it with 4 partmotors, each over 6 teeth.

about used winding scheme:

Every single part-motor was tested for n-spec and power.
Then 1, 2, 3 and 4 of them in parallel.
In parallel switching the n-spec does not change from 1 to 4 partmotors.
Only the efficiency and the amps capability increase.

After these tests I decided to do a more improved winding with about 20% more coppersquare - mainly to have fun. (last photo)
the effect of the additional copper was low.

I found in testing, that each of these part motors was able to work with more than125A.
Under watercooling conditions in real use, every part motor would be able to take this also for longer tiime.
Means, all 4 together are able to take 500A. Unfortunally actually there is no battery good enough to provide these amps.

In the real use log on water we found up to 350Amps in acceleration - only 17kW.
Motor temperature was max. 80°C - no problem for the wires and the insulation.
The "feeled" power in use was significantly increased compeared to the serial motor the owner said.

The 6mm battery plugs unsoldered themselfes already at these Amps.
So he changed them to 8mm plugs and high temperature solder also in the ESC-motor connection.

Clearly the bottleneck in his setup is and stays the battery.
Last edited by powercroco; Oct 17, 2021 at 12:03 AM.
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Oct 13, 2021, 03:12 PM
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Fourdan's Avatar
Hello Ralph
Good job
It seems you adopted
1) 4t+4t (on two successive teeth) dLRK YYYY
2) 6t +6t
What Kv you have measured for 1) and for 2) windings ?
What Io no load for 1) and for 2) (preferably for 2 different voltages (or more)could be 10V and 40V) ?
What Rphph for 1) and for 2) ?
Latest blog entry: Scorpion Calc
Oct 14, 2021, 12:14 AM
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powercroco's Avatar
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both variants have 2+2turns each group.

first try was with 2x1,32mm wire in parallel.
second try with 3x1,18mm wire in parallel.
so you have 12 leads in parallel in the complete motor. means, the same coppersquare as a single 4,1mm wire.

I found for both 350/V, what also was the target for rewinding.
resistance of the second winding is about 4 milliohm.
no load I found about 15Amps at 49V.

but you know, I don't like the more or less theoretical calculated curves by using these data.
Their results are to optimistic and don't show the real life - the effects of copper warming in use p.e. they don't show.
but everybody knows, that the resistance of a copper lead climbs with 0,39% / °kelvin.
If you have 50° kelvin more in real use and the resistance climbs by about 20%........
Oct 14, 2021, 05:04 AM
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Fourdan's Avatar
Hi Ralph
All is clear now for me (windings 2t+2t YYYY, Kv , Io @ 49V)
Another question : total weight (g) of the 2nd solution ?
You are right, the ohmic losses are climbing with the copper temperature (+4/1000 per °C)
In my algorithms, I try to take into account this important fact
Latest blog entry: Scorpion Calc
Oct 14, 2021, 06:29 AM
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powercroco's Avatar
Thread OP
Hi Louis!

The way the engine is used, the weight is pretty unimportant.
1kg more or less has less effect than if the surfer uses his board before or after lunch.

In fact the motor is also build with a lot of additional mechanical stability for a long life.
I think, if this would be needed the weight could be reduced by some grams.

Anyway, I have weighed the completed motor for 2220g with the better winding and 25cm long input leads.

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