Oct 13, 2020, 11:34 AM
Registered User
Question

# I need advice for this motor

Hi gents! I got the motor in the picture from a friend who rewound it with a 9 turn, 30 gauge wire, Y.
The size of the motor is 1303 and I wonder what could be the maximum current I may feed it.
Am I right if I guess that a 3x2 prop could be too much with a 2s Lipo?

### Images

Last edited by Guizzo 17; Oct 14, 2020 at 02:06 AM.
 Oct 21, 2020, 06:43 AM Jack Most brushless motors will handle about 3 Watts of power for each gram of their overall weight. And as the power increases from that the motor will get warmer and can eventually damage itself. Watts = Volts x Amps - if that is a 6 gram motor and you are using a 2S battery at 8 Volts you don't want to use it continuously at much over 48 Watts (6g x 8V = 48W). That was my mistake, you don't want to use it continuously at much over 18 Watts (6 grams x 3 = 18). And on a 2S battery that would be with the motor drawing about 2.25A at 8V (2.25A x 8V = 18 Watts) To test it run the motor for one minute or so at half throttle and then feel the motor base with your fingers, if it is so hot you cannot keep your fingers on it, you are drawing too much current. And the solution for that would be to use a smaller propeller or reduce the throttle some. Jack Last edited by jackerbes; Oct 21, 2020 at 05:55 PM.
 Oct 21, 2020, 02:22 PM Greediest Suer Shouldn't that be 6 grams x 3 watts ?
Oct 21, 2020, 05:56 PM
Jack
Quote:
 Originally Posted by Ron H Shouldn't that be 6 grams x 3 watts ?
Yep, that was my stupid mistake! I have corrected it and thanks for pointing that out.

Jack
 Oct 21, 2020, 07:31 PM Greediest Suer No problem, I figured it was a simple mistake. But someone might see it and apply it at any time if not corrected. No need to have bad information tied to your good name here.
 Oct 22, 2020, 04:43 PM Registered User Thread OP Thanks Ron. But what puzzles me is that the wire needs to carry 2.25A for 18watts which, IMO, is a bit too much for a 30 gauge wire, or am I wrong?
 Oct 22, 2020, 05:57 PM Jack There are three sets of windings there if I understand the motor right, so the 2.25A would be the total for the three. Wouldn't that make each set of windings be drawing about 1/3rd of the total. If the poster had identified the make and model of the motor we could give better answers I think... Here is a similar motor and it says it is wound with 27 AWG wire if I understand their advertising: https://fpvcycle.com/products/fpvcyc...2mm-prop-shaft Jack
 Oct 23, 2020, 12:52 AM Registered User AFAIK, two of the three phases fire at the same time, while the third measures back EMF to synchronize the speed. So each wire would carry 1.25A - which is perfectly fine for 30AWG wires. If you're concerned, cut the wires shorter, but I wouldn't worry about it.
 Oct 23, 2020, 12:23 PM Registered User Thread OP Jack, the motor was rewound with a single 9 turn, 30 gauge wire with star connection. It was sold by Hobby King but, unfortunately, it is not more available. Originally it was wound with a single 12 turn, 32 gauge wire, which fused under a 3x2 prop load, fed by a two cell Lipo. Skylar, what you say may be right for a Delta connection, however for a Star is sure that one phase carry all the current. Anyway I found what I was looking for in the net. Max current for a 30 AWG wire is 0.52Amp Thank you both for your interest.
Oct 24, 2020, 12:16 AM
Registered User
Quote:
 Originally Posted by Guizzo 17 Anyway I found what I was looking for in the net. Max current for a 30 AWG wire is 0.52Amp
I'd be interested to know the source of that information. Can you provide a link?

Quote:
 Skylar, what you say may be right for a Delta connection, however for a Star is sure that one phase carry all the current.
It's actually the other way around. As shown in the diagrams below:
In Delta, phase A-B consists of coil 2 placed in parallel with coils 1 & 3 in series.
In Star, phase A-B consists of only coils 1 & 2 in series without coil 3 being used.

But let's not debate the current carrying capacity of Delta vs Star. What I meant was that the ESC fires two wires together while the other
wire senses back EMF. That has been my understanding... not that I'm an expert on the subject of ESC's. Perhaps Ron can confirm if it's correct or not.

"Don't believe everything you see on the Internet" -- Winston Churchill
Last edited by Skylar; Oct 24, 2020 at 04:36 AM.
 Oct 24, 2020, 05:26 PM Registered User Thread OP Skylar, the net gives you different answers, I choose the one that looks sensible to me! The rationale is that I do not need all the Watts this motor may adsorb and I prefer to stay on the safe side! Links are here and here For what concerns Star or Delta, I see that we misunderstood each other! Cheers!
Oct 25, 2020, 04:55 AM
Registered User
Quote:
 Originally Posted by Guizzo 17 Skylar, the net gives you different answers, I choose the one that looks sensible to me! The rationale is that I do not need all the Watts this motor may adsorb and I prefer to stay on the safe side! Links are here and here
Thanks Guizzo 17. Both those links point to www.buildmyowncabin.com where "ampacity" of very long wires are discussed. 7000ft is mentioned in the video. I'm sure you'll appreciate that in brushless motors, and especially your small motor, we are dealing with much shorter distances. So I tend to not limit myself by the rules for domestic wiring. IOW, we are not wiring houses, just small motors.

Here is the table in the video that you linked.

Let's take an example. The motor pictured below was rewound by Dr Ralph Okon (powercroco) and it draws several hundred amps! I'm not sure, but I think the wire diameter is in the region of 1.6mm dia. According to the ampacity table, the safe current for 14 gauge (1.6mm) wire is 15A max. So this winding exceeds the "ampacity" rule for house wiring by a very great margin.

Ok, I agree, that is an extreme example and the motor is not run for very long. A better example would be motors using 80A and 100A ESC's. And if you look at their conductor sizes, it would be obvious that those motors also exceed the ampacity rule by a large amount.

Therefore, the "Max current for a 30 AWG wire" is quite a bit higher than 0.52Amp when we're talking motors.

Last edited by Skylar; Oct 25, 2020 at 05:37 AM.
 Nov 20, 2020, 12:05 AM Sokol I did something similar with a small 10g brushless motor: https://hobbyking.com/en_us/18-11-20...___store=en_us custom rewound , Y , 36 Turns per tooth , AWG 33 wire , Kv= 635 , Battery 2S 300 mAh 30C, APC 7*3.8 SF Propeller , Static test current draw at full throttle : 2.2A @ 8V , ~17.6W into the ESC. page in my blog: https://www.rcgroups.com/forums/show...ll-13-diameter Latest blog entry: Brooklyn Dodger