Investigation ...6s1p or 4s2p, neu, cc neu... - RC-Monster Forums

MrMin · 04:24 PM

Just for fun, I tried to work out why a
2x Series 6s, 5Ah can have longer runtimes than a
2x Parallel 4s, 8Ah ... Taking into account most of the various factors.

Thats a HighVolage vs a LowVoltage system:

HV: Batt Internal Resistance in series (PRO)
Is cooler (less current in wire resistance) (PRO)
Run chance of cells discharging unequally (CON)

LV: Batt Internal Resistance in parallel (PRO)
Gets hotter (due to wire resistance - more current) (CON)
Better for cells discharging equally. (PRO)

I suppose the bearings and friction do not play a big role and then there is the foucault current and other losses.... (does anyone know the potential foucault current losses?)

Basically I think the cooler system with the lower kv is the better.
Only why is the lower KV motor better? Has it something with the characteristic efficiency curve? Dyno graph? What other factors play a role here?

Who is going to investigate this with me?

How can we find out about the materials of the rotor and stator and wire resistance...etc..

BrianG · 02.23.2009, 04:36 PM

Without knowing everything involved, I can only speculate that the low V system is running in its sweet spot. Maybe the rpms are running in a more efficient range in the low V setup. Maybe gearing is better?

However, right off the bat, 6s @ 5Ah is 111 watt hours. 4s @8Ah is 118 watt hours. So, if the power output is the same, the low V setup will have a slight advantage just looking at those numbers. As long as current is kept reasonable, either one will be comparable.

MrMin · 02.23.2009, 04:47 PM

Example: mmm combo 2200 setup for example. It seems like the HV runs cooler, that is less resistive heat loss. What other factors can be in favour of the HV setup or LV setup? Do we see electromag. eddy current losses? Apparently the HV and low RPM/V setup is better....why? It is 90% because of gearing, 5% bearing friction, ...what are the reasons governing the distribution of losses and theory here?

BrianG · 02.23.2009, 04:59 PM

Heavy currents will always be a major source of inefficiency (mechanical losses aside). Any resistance in wire, connections, etc will introduce larger voltage drops with high current. And yes, I'm sure eddy currents play a role too. Not to mention magentic saturation.

MrMin · 02.23.2009, 05:04 PM

Yes - But by how much!! I would like to make a table of the approximate role the various factors play...in % efficiency.. or even a graph plotting the various factors.

Any idea where I will find cc neu/neu 1515 1y specs that can assist on eddy current and mag. saturation calcs? It would be interesting to see how the hv lowrpm and lv highrpm variants react wrt these roles.

Ideas anyone?

SpEEdyBL · 09:54 PM

The biggest difference between a 4s setup and a 6s setup with theoretically equal power will be power lost as heat in the esc and wires (power loss = R*I^2), and therefore performance. Motor and battery temps will not be that much less with the 6s setup because, although you are drawing 2/3 the current, the equivalent motor for 6s will have (3/2)^2 times the internal resistance.

If you want a basic graph of motor efficiency, plot f(I) = (VI - R*I^2 - I0*V)/(VI) where V=volts, I=amps, R=internal resistance, I0= current at no load. That will give you the basic shape of a motors efficiency curve, but will not yield accurate efficiency values, due to voltage drop at the motor terminals, eddy currents and possible stator saturation at high currents. You can compare motors at different voltages though.

SpEEdyBL · 02.23.2009, 09:59 PM

http://www.castlecreations.com/produ...rs/nm1500.html has some specs on the neu motors. I0 is measured at 10 volts. This number is usually pretty constant no matter what voltage, unless the motor is nearing the high part of its rpm range, where it may increase very dramatically.

MrMin · 02.24.2009, 04:11 PM

Hey speedy,

That is not a bad idea. I'm just trying to predict why the efficiency curve for changes at certain voltages as well as other factors. The eddy currents will also change depending on the frequency of the switching..and then there is the back emf and effect under load/gearing... But the equ is not a bad start. I'll start with that one. Does anyone know the material of the stator in the cc neu 2200?

Just playing the numbers... for fun.

BrianG · 02.24.2009, 05:18 PM

Quote:

Originally Posted by MrMin

...Does anyone know the material of the stator in the cc neu 2200?...

Going out on a limb here, but I would guess it's a ferrous metal.

Pdelcast · 02.24.2009, 05:57 PM

Quote:

Originally Posted by BrianG

Going out on a limb here, but I would guess it's a ferrous metal.

The stator stacks are made with Japanese source .2mm thickness M19 electrical steel.

The stator design is Steve Neu's 15 series stator.

The windings use 180C Polyimide (Kapton) triple build OFC (oxygen free copper) wire.

The magnets are N38UH minimum material. (the highest quality high temp magnetic material available today.)

The shaft and rotor are made of stainless steel.

The case and end-bells are made from 6061 Aluminum

The bearings are NMB 5x16x5mm CNC quality ABEC bearings.

Anything else you would like to know?

MrMin · 02.24.2009, 05:36 PM

Conductivity ?

jzemaxx · 02.24.2009, 05:43 PM

Hmm very interesting. Right now my truck runs 2 X 5S 5K mah batts in parr (10K total mah). which is heavy but I need the runtimes for the mains.

If 2 X 3S (6S total) series 5K mah batts would do the same trick, then I will swap today and buy more batts. The increased voltage would give me the speed I need and the weight would drop off by a good bit as well.

phatmonk · 06:07 PM

Is the CC 2200 a copy of the older Neu 1515 series with a better purpose built case designed for surface use/1/8 trucks?

Pdelcast · 02.24.2009, 08:00 PM

Quote:

Originally Posted by phatmonk

Is the CC 2200 a copy of the older Neu 1515 series with a better purpose built case designed for surface use/1/8 trucks?

It's a Neu 1515 built under license from Steve Neu. Neutronics gets a royalty from every Castle/Neu motor sold.

We changed the case to seal it against dust/dirt/sand/etc.

MrMin · 02.24.2009, 08:03 PM

Quote:

Originally Posted by Pdelcast

It's a Neu 1515 built under license from Steve Neu. Neutronics gets a royalty from every Castle/Neu motor sold.

We changed the case to seal it against dust/dirt/sand/etc.

and thats why almost nothing else can compare to it. It's very interesting how much detail went into its design and quality build.