Limit current with resistors on ESCs

I have managed to blow up a couple of SimonK cheap 30a ESCs. Even though they are cheap, the cost mounts after a few blow-ups.

I intend to install a 30 amp fuse in the line to protect the next one I try to fry; but in the interim I was wondering if anyone could tell me what size resistor I could use to limit the current passing through.

I am using a 3S 1800mAh battery, which (supposedly) is going to give me 11.1 volts. The motors are the cheap A2212 motors from eBay running at 1000Kv and also a set of 1400Kv. It was while testing the 1400Kv motors that the ESCs blew. I am using them with a 10"x4.5" propeller.

Due to the violence of the blow-ups, I am going to assume that I am trying to draw far too much power from the battery for the ESC to handle.

Could you let us know which motors and props you are using so we can see.

An alternative would be to get some blheli32 ESC as they have built in current limiting features to help protect both your motors and ESC… about more expensive but we’ll worth it in my opinion.

1st you are using cheap to try and keep cost down, then buying more stuff to stop them blowing up.
2nd you are correct those 1400kv motors throwing a 10x4.5 are drawing to many amps, assuming those cheap 30amp esc are in fact 30 amp, come down to 8x4.5.
3rd not exact theory but in general if you tell an electric motor to spin at say 7,000 rpm it will keep drawing current until 7,000 rpm reached, my point there is those 10x4.5 are stalling those 1400 kv motors.
And finally i assume you are using cheap plastic 10x4.5 so good job the esc burn out, if they had gotten up to speed i’m sure they would have broken at that speed.
One thing i’ve learnt in this hobby is buying cheap is ok to learn on but not to fly on.

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Hi Alex and Dale589

I do actually have a 4in1 31amp ESC but I don’t want to use it, because it cost me a fortune and while I am still learning, it would just be a waste.

I don’t think it was the buying cheap that caused them to blow up, more like my lack of expertise and knowledge. The extra things I am buying to stop this future behaviour form recurring is very small. Less than $1 per ESC.

I do have a set of 8x4.5 props; they were sent to me for free by Banggood for spending over a $1000000 with them. I will try them out and see what happens. I had not previously thought about the relationship between the speed of the motors and the size of the propellers. I will think about it from now on. :slight_smile:
As for the buying cheap, yes I am, but I am also getting a small collection of good stuff as well. I have the Chaos 30amp ESCs and a 4in1 ESC. I did have some nice flight controllers before I stuffed them up. I don’t think that I will damage any more of them though. I will need to get some nicer motors sooner or later.

I wasn’t aware that there were significant differences in propeller quality.

Could you point me to some good ones and tell me what makes them gooder than the others. (Or should that be more gooder?)

1045 is too much prop for those 1400Kv motors. I ran 1000Kv on 3s with 1045 props with cheap HobbyPower 30A ESCs.

A 30A fuse is not gonna help. There are only a few things that will cause an ESC to fail. Either it is wired incorrectly, the motor is wired incorrectly, the motor windings are shorted (most likely by a mounting screw that is too long), or you crashed the aircraft and the motor(s) stalled, You obviously did something wrong, so why don’t you give us a detailed step by step description of what you did and why you did it…

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most plastic props are ok to use, but dont expect them to last long if spinning mega fast, centrifugal forces can get a little high.
i used plastic props on 8" build 4s, they were perfect until i started decent freestyle then they would just let go, carbon fibre now no problems.

“I don’t think it was the buying cheap that caused them to blow up, more like my lack of expertise and knowledge. The extra things I am buying to stop this future behaviour form recurring is very small. Less than $1 per ESC.”

I understand your expertise may be some cause of failings and thats good, at lease you are not burning good stuff out.
You dont need to buy extra stuff, just try and learn from mistakes and you’ll be fine.
Also a resister resits electricity and if you are going that way its pointless having a 3s !
Just make sure the motor is happy to turn the prop.

Very good comment, all to remember. :slight_smile:
Our craft falling out of skies can damage or kill
ALWAYS be responsible

buying cheap is ok to learn on but not to fly on.

Hello Clifton_Hipsher

Why wouldn’t a fuse have helped? The reason that the ESC failed is because I was trying to drag far too much power through it and so it overheated and blew up. That is what I did wrong. and as you say. that is far too much prop for those motors. (I know that now.)

If I had a 30 amp fuse in the line to the ESCs, then rather than the ESC blowing up, the fuse would blow when I try to pull more current than the ESC can handle. That is the purpose of a fuse; it sacrifices itself to protect others.

The drone was less than a metret off the ground at the time, I wasn’t really flying it, just testing it to see if it would stay level etc.

It is true that a resistor resists, but it also moderates. It isn’t the 3S (12v) that it will moderate, but the amount of 12v current that it allows to pass.

Just think of your house fuses (circuit breakers), where you have maybe a 10 amp fuse on the lighting circuit but a 30 amp fuse on the stove. They will both allow the 240v to pass, but one will allow a lot more current (amps) to pass because the stove needs to draw and use a lot more power than the lights do.

So, if I have a 12v 30 amp fuse in line with the individual ESCs, and then if I try to draw more than 30 amps, the fuse will blow, but the ESC will be saved.

I have gained a lot of new knowledge in the last few months and I am finally starting to get the hang of things.

Imagine , you are flying at an altitude of 50 meters. You punch out; motors take more amps than your fuse can handle … ; And the fuse blows to save the ESC !

Hello ambattuhari,

Now imagine a slightly different scenario where I don’t have the fuse and so instead of the fuse blowing moments before the ESC blows - the ESC blows instead.

There does not seem to be a lot of leeway in the ratings on ESCs. I have a Turnigy 4 way ESC on my desk that I have not yet been game to use, and it is rated at 31A. This seems to me to be indicative of the close tolerances of these items.

I do, however, take your point and I will consider things further. Maybe I will try to get 32A fuses.

Hey waste…

It sounds to me like your only problem is mixing incompatible hardware…anyone can learn to fly without too much damage just by practicing and asking questions when you don’t know something. Your solution to buy cheap escs and adding a fuse are only going to cost you more money and make your quad dangerous to yourself and anyone else you fly near.

First, The cheap ESCs will definitely burn out faster than a new, decent quality BLHeli ESC will. I have flown on 30A SimonK ESCs (sooo very long ago…) and have had them last a good amount of time…so, while they don’t last long, they don’t normally burn-out like that without a mistake or an unlucky crash. Plus, ESCs are designed to be able to regularly deliver a burst of power over the rated current. The better quality the ESC, the more current over it’s rating it can deliver in bursts. Typically, 30a ESC should be able to deliver 35 or 40 amps for 5 to 10 seconds without going up in flames. Using a 30 or 32 amp fuse would mean if you ever go over that amount then you’ll be dropping out of the sky for no reason, potentially damaging other components or even hurting someone nearby

I agree that the prop and motor size most likely drew more current than it could handle…so knowing that, you should be able to stop your ESCs from burning up in the future without a fuse or trying to figure out how to use current limiting resistors (which could have other negative effects like dropping too much voltage for the ESC to function or causing your copter to crash because it can’t get the power needed to complete a maneuver). Essentially, you’re looking to solve a problem by introducing more potential problems.

It is my opinion that as a noob you should be using new and decent quality hardware. Being a noob, flying with decent quality ESCs will give you more air time to improve. Plus, as the electronics improved, the way it feels to fly on one feels so much better. You’ll crash occasionally, but decent quality hardware can take a lot of punishment. Even the chinese knockoff parts are better than cheap old gear…SimonKs are just too outdated now.

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