ESC efficiency & heating on less than full throtle?

EFOIL.builders Electronics (ESC, remote, batteries)
1

This i maybe a dumb question but anyway:

It is said on RC forums that running an ESC on “half throttle” is very hard on it, heat might increase(to higher than on full throttle) and efficiency will also be weak. Wonder, would this apply also related to current? Let’s say you have a 150A rated ESC running it on full throttle but only using 75 amp, how is the efficiency affected at this situation? Probably some high end ESC’s hawing settings for this also but just on a principal level interested related to a basic ESC.

2

Maybe this would help, was posted few days ago.

3

Usually the escs are block comutated. And on half throttle there are much more switching cycles than on full throttle. That means they work very inefficient and will heat up very quickly. But that’s not depending on the current. The efficiency is only depending on throttle percent. But anyway. Less current means also less heat.

4

OK, thanks for both replies. So it looks like its OK to have plenty of current reserve in the ESC but cruising speed should be close to motors full throttle so ESC does not have to work so hard on switching cycles. Is there a problem for the motor efficiency if the load(ampere draw) on full throttle is much less than max? What i mean is that the motor would not be working that hard to achieve the rpm for the load( lets say you have 5KW motor but utilize only 3KW om max throttle when cruising? Sorry again if question is stupid…

5

I have no idea, all i know “every” motor building company/person shows current voltage momentum efficiency etc graph/characteristics. My best guess would be efficiency of motor is the same regardless of from where is getting power in. There are more/less modular esc’s, the better they drive the motor, closer u get to rated efficiency. Thats how i see it and what i learned from more experienced people on here.

6

the question isn’t stupid at all :wink: , i have been looking on that for the last 2 years…

  • it is depending on the type of the motor inrunner (smaller less torque) or outrunner (bigger more torque less rpm…)

  • the numbers given are not always real…

  • a small motor cannot turn a big propeller and this no point to use a big motor to turn a small propeller

  • as the load increases the rpm will drop and it is best to stay around 80% of what it sould be

so if you take a SSS inrunner 56104 500KV given for 14000W and 50 000rpm
so max would be 100V and 140A
but you will use it at 50V and you want to stay at 70A for a continious use
so you will have only 3500W left for your use

if take a big outrunner 100KV given for 7000W at 60V and 115 A
at 50V and 60A you will get 3000W

at start a motor given for max 130A (my first built) can give a lot more, i have +220A pics

so yes it is hard to choose the correct motor for each set up: geared or not, big propeller low rpm or smaller with higher rpm (jetdrive)…

7

I think rpm will not drop if u use a too big prop. It will just pull much more current and that causes burning escs and motors. My sss56104 pulled more then 300amps as my gear broke and the rpm was the same as before. What we need is a ecu that is measuring the back emf and has a current limit. Also a sinus commutation would be really helpfull. The problem is that these ecus are really expensive. And I only know one small company that is producing them.

8

I agree if the propeller is way to big , but it is hard to find the sweet spot between size and pitch , i am talking about small rpm drop before the amp goes up , efficiency more than Breaking limits
See my post “rpm drop Rm I0 …”

9

Sounds pretty complex indeed. One of the issues we have is same with bigger boats too. The resistance of water is like always driving uphill in a car… and the equipment is usually not designed for that! Car engines in real boats is also a challenge to get working reliable(needs to be modified), torque area and requirement are much more thougher in the Marine environment.

I am not that deep into electronics, but must admit that i was kind of shocked when understood limitations of an ordinary ESC when operating at part throttle.

Wonder how Torqeedo have solved this, must be different type of control unit than RC ESC :smile:

I am trying to build a E Surfing type board. Will do it little differently, straight shaft, outrunner inside the hull. The plan was to use a 6384 motor (120KV /120 A) and running a outboard prop. At 22-23 V rpm would be the same as on a 4-5 hp outboard. 3000w(or litle less) at shaft should be good for 30 kmh … But now expect that the torque will not be enough and Amp will be sky high…and smoke will come out :slight_smile: Now seriously considering same motor but a twin setup. It will ease the load on the motors so then maybe torque is enough, Amp per motor will be much less, maybe can even use for each motor a cheap 150A Flysky watercooled ESC, Yamaha copy prop. Lets see!

10

I would go with a 80100 50kv or 70kv , 12s , a vesc 6plus and a propeller torqeedo v10/350 on 180l board :grimacing:
Or even a 83100 watercooled if you want the motor inside , the outrunner not watercooled will burn for sure

11

@alexandre then you are right. Got your post wrong. I will take a look into your thread :wink: I have found out that kezen rc has diagrams on their site regarding the thrust rpm an power. With a little calculation I think it is possible to get a good working thruster. But they are expensive. And I don’t know if they are efficient.

12

I agree, good advice, but for the propeller have some comments. We can get a Torqeedo prop to work(and have been used also), but really don believe its the optimal design for what we want. Believe Torqeedo philosophy is to utilize high torgue with low rpm and and relative large diameter compared to equivalent gas outboards. This works well on relatively heavy boats and moderate speeds. We have very light boats and looking for higher speeds. Foils i don’t know that well but for a planning e surfer, with the right controller and motor, believe a aluminum outboard type prop should work better than Torqeedo prop if we are looking for speeds closer to 30km/h.

A reason believe this is that on light dinghies small gas powered outboards beats " equivalent" Torquedo when doing planning speed lightly loaded. In displacement speed the situation is different though.

Probably need to prove this (not easy) but don’t believe a propeller optimized for 700 -1300 rpm is the best possible choice for our application. The v10/350 is the best option looking at the measurements, the diam /pitch is pretty close to “ordinary” propellers so that one can work, still wondering how it performs in the required 2500-3000 rpm as that it is not designed for originally.

This motor would probably work pretty well, cooling is an issue though?

13

I’m building an e-surf (instead of e-foil) as well. I’m going to use dual 56104, 64mm jet drive and geared. I feel like one of the biggest inefficiencies is not using the full rpm range of the motor. If my motor is capable of 50k rpm, I’m not using the full power of the motor if I don’t use most of those rpms.

My chosen kv is 1000kv, which means it has a max voltage of 50V and can handle 280A. But the key is that at 48V, I’m using most of the RPMs.

The problem is that 50k RPM is too much, so I’ll gear down for the optimal rpm of my jet drives, which is around 12k or so, so about 3.33:1.
Now, I’m using the full power of the motor and due to gearing, I can choose to get 3.3x more thrust or use 1/3 the current, depending on my impeller pitch.

I lot of people use the 360kv or 500kv motor at 48 volts, but that means they’re only using 33%-50% of the full rpms of the motor. Instead of 5:1 gear ratio they could be using 10:1 or 15:1 and get 2x or 3x more torque using a higher pitch prop or 1/2 to 1/3 the current draw using same prop. This is assuming a target rpm of 5k for props, not jet impellers.

Even tesla uses a 10:1 gear reduction and not direct drive. I understand that DD is much easier to maintain and design, but it’s not optimal efficiency. You’re wasting current and power doing so. You could be riding longer or faster or both.

14

Yes but it is hard find à gearbox that will handle the rpm , chief gearbox is no more available , super chief ? Why not but the smallest in 4:1 i think and 3000w only

15

In jet drives motor is usually inside the hull right? So motor diameter is not a problem. If Your target rpm is 12000 and want to use a 48V, why not use a direct drive motor of 250 KV, no gearbox? Sorry maybe not understand the post. if You choose a motor optimized for 48v and 250 KV you can utilize 100% of Your motor without no gearbox when running 12K rpm?

As a side comment think jet drives are much more complicated to optimize than "ordinary " props, they are still no much used in boats other than very specific applications, also the operating efficiency is not that great although safety aspect is very good.

16

I could use a direct drive 250KV motor if and only if the max RPM limit of the motor was 12k. Then I yes, I would be utilizing the full capabilities of the motor. But most of the time, the chances of finding a motor that has a max RPM that matches exactly what you need and produces the required thrust is rare. I’ve yet to find such a motor.

But simply taking some motor and finding ONLY the kv that you need is going to be inefficient. If I take that 56104 and happen to get it at 250KV in direct drive configuration, then I’m leaving a huge amount of power off the table. Because its capable of 50k rpm but I’m limiting it to turn only at 12k rpm.

But let’s say I go bigger. I use this 23kw(max) TP100 inrunner:

s-l1600
s-l1600.png958×453 50 KB
. Its 3x the mass of my 56104 motor. However its max RPM is only 25k. If get the motor at 250KV so that at 48V, it runs at 12k rpm in direct drive. But I’m now losing 50% of its full power. I could gear it 2:1 and get 2x more torque at the same current or at 1x torque use only 1/2 current. But I’m not gearing, going direct.

Now you might be asking how does it compare to the 56104 1000kv geared? The TP100 motor has no max torque spec, but it is roughly 3x the weight of a 56104 so I’ll guess and give it 3x more torque. So TP100 = 3x. I take my 56104 and gear it 4:1 to get 50k->12k, so 56104=4X torque. My smaller, geared 56104 beats the DD tp100. But that’s not all. The 56104 produces that torque at 280A. The TP100 requires 480A. I’m producing more torque at way less current because of gearing. Now this all changes the moment you gear the TP100. If I gear it 2:1, I now have 6x torque, which beats the 4x torque of the geared 56104.

I think its easy to forget that high RPM IS power. A formula 1 engine runs at 20k max RPM. They’re tiny, only about 1.6 liters, yet produce over 800hp, compared to about 180hp you normally find in a 1.6L engine. Most of that extra power comes from the high RPM. The fact that its an ICE doesn’t matter. RPM is power just as much as displacement (or in the case of electric motors, stator mass). I can take a motor that is 1/2 the mass but spins 2x as fast and it will have the same power as a motor that is 2x the mass but spins 1/2 as fast.

1 Like
17

Yes, finding a gear box is the challenge. But because I’m not making an e-foil, I don’t need planetary gears. I can simply make a chain drive with a big chain that can easily handle 12kw.

So I do understand why e-foil has been restricted in that manner. But with enough cost, you CAN get a 15:1 planetary gear, but it just gets too expensive in the size (56mm diameter) that is needed.

18

I forgot to add - changing the KV of the same motor doesn’t change its torque! All of those different KVs of the TP100 motor above all produce the same max torque. That’s why simply changing the KV of the motor doesn’t actually help you use the full capability of the motor.

19

do you have a link?
Never saw a gearbox capable of 50-100kRPM, especially not the high gear, double stage with more than 1:6

Nor does it change the speed. It just changes Torque/A and Speed/V.

It is not losing, if you never had the power. the 56104 1000KV is for ~60V and the 56104 300KV is for ~130V, sure the 1000KV version can take much more current due to thicker windings but in the end power capability keeps the same. Then it is your turn what suits you best… going higher amps or going higher voltage.

The point is: yeah, you could downsize the motor a lot, if there was a motor with sufficient torque at low RPM. But our problem is that the (max) power has to be at a given RPM or in other words at a given torque.
Personally I dont care if the motor is able to supply >2x max Power I need, as long as there is no other doable solution.

20

There are 15:1 but not any that can handle 50k rpm, agreed. But that’s because there’s no profitable market for such a gearbox. If there were, I’m sure it can be done, probably with cooling and lubrication. My point was that its possible to produce such a gearbox, not that one is currently available.

Never said it did? In the end 50k RPM is the max rpm regardless of the KV of an 56104 motor.

It is not losing, if you never had the power. the 56104 1000KV is for ~60V and the 56104 300KV is for ~130V, sure the 1000KV version can take much more current due to thicker windings but in the end power capability keeps the same. Then it is your turn what suits you best… going higher amps or going higher voltage.

I don’t think you’re following my point. I distinctly said that the max wattage and RPM remain constant for a given motor, no matter the KV. The 56104 is a 14kw max motor, period, regardless of the winding. I mentioned this quite clearly. But yes, I’m not losing power, the power is indeed there, but I’m not utilizing the full capability of the motor by not running to nearly its max RPM. By not using the full powerband of the motor, you’re effectively losing power.

BTW, the 1000kv motor is a 50V motor, at least every link I could find:
https://www.ebay.com/itm/SSS-56104-1000KV-brushless-motor-RC-Boat-/152640203720
https://www.mhz-watercraft.com/shop/en/motors/449/sss-56104-brushless-inrunner
https://www.tfl-hobby.de/Motore–Halter–usw-/Brushless/TFL-56-mm/56104/BL-Motor-56104-1000KV—7D.html
https://picclick.com/SSS-56104-1000KV-brushless-motor-RC-Boat-152640203720.html

All of these say 50V. Where did you find it at 60V?

The point is: yeah, you could downsize the motor a lot, if there was a motor with sufficient torque at low RPM. But our problem is that the (max) power has to be at a given RPM or in other words at a given torque.
Personally I dont care if the motor is able to supply >2x max Power I need, as long as there is no other doable solution.

You can get low end torque through gearing. Imagine if I had a motor that only had 1 ft-lb of torque, but could rev to 1 million RPM. I could gear that 10000:1 and get 10000 ft-lb of torque and still have enough remaining rpm to turn wheels or props or whatever at 1000 rpm. Of course, no such magical engine exists, but it illustrates that torque and RPM can be interchanged via gearing. As i mentioned before, high RPM, low torque engines, like the formula 1 engine exists, and I guarantee that a formula 1 engine could out accelerate a 500hp engine with 2-3x the low end torque. Who do you think would win a bicycle race? A powerlifter who can squat 800 lbs but is on a single speed bike, or an average man who can only squat 200lb but has a 15 speed, geared bike? I put my money on the average man. And I bet he’s less tired too. Gears always win, which is why every real vehicle has them, cars, boats, propeller driven planes, etc.

I get, I fully understand that with our DIY e-foils we’re limited to 5:1 or 6:1, so we literally can’t use the full 50k rpm of the sss motor. But make no mistake, by doing so, even if no choice, we’re missing out on a massive amount of power. Which is why I’m going e-surf so I can gear to my heart’s content and use the full power of the motors.

1 Like