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May 23, 2001, 12:43 AM
Balsa Kamikaze
Jensst's Avatar
Thread OP

Current draw on my Promax Cobalt 4013 - scary discovery...


Hey guys,

I have a problem with my Promax 4013 cobalt motor. The last few flights I didn't get the performance from it as I expected so I was about to retime it properly. Here's what I did today and my strange discovery:

Maxxprod (producer) recommends to find the "neutral timing position" of the motor first before retiming it. "Neutral" means where the motor draws the lowest no-load current and it should be close to the value they specify in the data sheet. This value is 2.9A for my motor.

So I charged up my 8x500A, took a 10A ampere meter, plugged it between battery and ESC and was expecting to see ~2.9A since I didn't touch the timing of the motor yet. But guess what I measured at no-load: 7.5A!!! Man, that's scary lots of amps!
So I adjusted the timing from there to get closer to the 2.9A specified - but the lowest I could get was 4.5A, still 1.6A (+/- 0.1A measure tolerance) over the given spec.

Here's what I am wondering:

- Is my 8 cell setup the reason? The manufacturer does not specify the number of cells the no-load current of 2.9A should be drawn.
- In general: isn't a 4.5A no-load current for a neutral timed (cobalt) motor too much?
- Is it possible that the ESC (Castle Creations Pegasus 35) "consumes" the difference of 1.6A?! Sounds very unlikely to me since my Pixie 14 ESC with a Speed 400 6V just draws 0.9A no-load with the same 8 cells setup.

For sure will I contact Maxxprod with my problem, but maybe you guys already have any hints for me? Is my measurement setup screwed up or is it simply the motor?

_Jens
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May 23, 2001, 08:13 AM
Registered User
Andy W's Avatar
The ESC won't "consume' current. Current draw is the same throughout the circuit. You could lose voltage there, but that would drop the current, we won't go there..
That is high for a no-load reading for most any motor, especially a "speed 400" sized motor. There is almost certainly a problem with it. No idea what it could be, however.
..a
May 23, 2001, 09:33 AM
jrb
jrb
Member
jrb's Avatar
What volts/cell count do they list for the NL Io?

I'll bet a lot of folks are ruining their cells & getting close to wiping out their ESCs with these motors.
May 23, 2001, 10:42 AM
Balsa Kamikaze
Jensst's Avatar
Thread OP
Quote:
I'll bet a lot of folks are ruining their cells & getting close to wiping out their ESCs with these motors
...because of the high current draw of these motors?! The Pegasus is rated for 35A so that should be fine. The 500As are quite small but work for now.

jrb, Maxxprod specifies 7 cells for static current draw test, so i assume it's also for the NL Io. So I should be fine with my 8 cells test setup.

_Jens
May 23, 2001, 10:43 AM
Sometimes it works!
GYROGEARLOOSE's Avatar
OK, I'm no expert, but here's my take on this.
ANY of the smaller motors, up to and including .15 size, are timed on 6 volts. The I/o is established at 6 volts. Anything different and your results are going to be different.
For reasonable results, do not use nicad packs, they fluctuate too much and drop off too quick. You will drive yourself to total fustration. Use a regulated power supply or an automotive or RV type battery. On some of the cheaper ones you can probe around and find the center cell connector and tap into that for a good approxamate 6 volt supply. Probably one of the large 6 V lantern batteries would work ok, but I haven't tried one.
I hope this helps... -gyro-

May 23, 2001, 10:59 AM
Balsa Kamikaze
Jensst's Avatar
Thread OP
Just phoned Maxxprod and they brought some light into this story:

The 2.9A they specify are measured on 6 cells/7 volts. That could explain the 1.6A difference I have.

GYROGEARLOOSE, Maxxprod also recommended a power supply for the timing procedure. If I shouldn't use my NiCads, what about soldering 4 or 5 huge 1.5V alkaline batteries together? Do they "fluctuate" too?

UPDATE: I also phoned with Kirk at Newcreations and he said the same. 8 cells are way too much for timing, it should be a 6V constant power supply. (GYROGEARLOOSE, you say you are not an expert?! )

That's the solution of the riddle. Hope anyone else can profit from this story in the future...

_Jens

[This message has been edited by Jensst (edited 05-23-2001).]


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