Can someone explain the term stall?

[macribs]

I am having a language barrier problem here. I have not figured out the term of "stalling an electric motor". Or "to stall".
All I can understand is that stalling is bad and will melt your motor.

So what causes stalling?

How do one notice before hand that stalling is soon to happen?

What can be done to avoid that?


For an ICE vehicle stalling would occur ie at take off slipping the clutch. But how can one stall an electric motor that is DD without clutch? I guess there must be more to that word stalling in terms of electric motors?

 

[liveforphysics]

If you have a controller that measure phase current, then it doesn't matter if you're at 0rpm or even rolling backwards or whatever, you pin the throttle and it's the same copper loss heating you would have at any motor speed you pinned the throttle (until the motor speed gets so high the BEMF is near pack voltage and it can't draw full phase current anymore).

If you're using a simple style controller that only observes battery current rather than motor phase current, then you can be bucking down many hundreds of amps getting sent to the motor while the controller is only drawing say 30A off the battery (or whatever it's set for). In that situation, spending extended time with currents much higher than the motor can handle can cause failure.

If you have something like Justin's FOC controllers or an Adaptto or something with a Lebowski brain etc, then you don't have unregulated super high phase current while the motor is stopped or turning slowly.

 

[peters]

Stall is when you block the motor (with brake,... etc.) and apply high current (torque), so you can notice that.
I would also add that at stall the phase current does not alternate the motor windings, so the power heats only the actual loaded windings, not distributed evenly as it would be at rolling with the same phase current.

 

[major]

Stall = zero RPM. To stall = to force motor to zero RPM.

Stall is also referred to as "locked rotor". It is physically preventing the movement (or rotation) of the rotor. It is an important test condition for motors. Depending on the type motor, the torque at stall (called stall torque) can be the maximum torque which the motor is capable of developing. Induction motor are the obvious exception where stall torque is considerably less than the maximum developed torque.

Motor load is the torque opposing rotation. As this load is increased, motors typically slow down. When the load exceeds the motor's stall torque value*, rotation stops and the motor is stalled. It will continue to produce torque at stall and begin to rotate again when the load is reduced.

*In the case of the induction motor, it will stall when the load exceeds the motor's maximum torque (called breakdown torque) and then produce stall torque against the load.

The current at stall is called stall current. Stall current is typically the most current a motor can draw from a particular voltage supply. Since stall is zero RPM, there is no generated voltage (BEMF) in the armature coils, so the armature current is simply the applied voltage divided by the impedance of the winding. In most cases, stall current is limited by the motor controller.

Because RPM = zero at stall, power output = zero at stall. Power output for the motor is the product of RPM and torque. So if the RPM = 0, Power Out = 0. And efficiency = 0 at stall. All the electrical power into the motor is converted to heat.

 

[Punx0r]

Stalled = locked rotor

Sometimes you see in the technical data for industrial motors a specification for "locked rotor current" (maximum current drawn when stalled) or "locked rotor time" (maximum time the motor can be stalled without damage).

 

[d8veh]

When you go up a steep hill and your motor doesn't have enough torque, you go slower and slower until you are stopped, when the motor has stalled. Current is massive when your motor goes slowly, so damage to the controller and motor can happen very quickly if you keep the power on when the motor's stalled.

 

[dogman dan]

Full stall would be a rotor not turning. In effect, 100% of the power flowing through the motor is becoming heat.

Some say lugging the motor, or some call it stalling it to ride with full load going too low rpm. In this case, perhaps only 70% of the power flowing is made into heat. But say it's 1000w, 700w heater in the motor will overheat it very very fast. The normal would be more like 200w heat, but that the motor can radiate away fast enough to reach motor heat equilibrium below 250F, likely below 150F. A 700w heater reaches equilibrium somewhere, but we don't know because at about 450F the whole thing melts, phases short, solder flows, etc.

What is stalled? You can sort of feel it, as you ride up hills. Suddenly a 10% grade that doesn't stall the motor much becomes 15%, but the motor seems to just go bleah on you. It's steeper sure, but you can just feel that power vanish as your speed gets below 10-12 mph for most typical hubmotors in 26" wheel. If you had a temp sensor in the motor at that moment, you'd see an incredible increase in the heating.

Riding with a thermometer, it's a real good way to know the stall point rpm of you motor. You'll see that temp just zoom suddenly.

Bear in mind, this is at full load. You can ride 1 mph without stalling all day, if the load is light. Flat ground, tail wind, or just not so much grade. You can get up a hill stalling less, by just riding half throttle and pedaling. This will work on a 5% grade. Won't work on 15%. For hubmotors.

 

[macribs]

So best way to avoid stalling would be to attack steep hills WOT with close to max speed and keep the motor working in its most efficient power band for as long as possible uphill and then do pedaling lower throttle rest?

 

[Ohbse]

So best way to avoid stalling would be to attack steep hills WOT with close to max speed and keep the motor working in its most efficient power band for as long as possible uphill and then do pedaling lower throttle rest?

I don't think with the sort of bike you're anticipating building you will encounter a hill that provides enough resistance to stall out your motor. It's simply not an issue on higher power builds, especially not utilising non-trash controllers as Luke mentioned. In my case if I could somehow find a hill steep enough I would end up just doing a burnout rather than ending up with a locked rotor.

 

[macribs]

I don't think with the sort of bike you're anticipating building you will encounter a hill that provides enough resistance to stall out your motor. It's simply not an issue on higher power builds, especially not utilising non-trash controllers as Luke mentioned. In my case if I could somehow find a hill steep enough I would end up just doing a burnout rather than ending up with a locked rotor.

I will be using the QS v3 motor, max-e and 20s 40 Ah batteries. But frame, battery,motor, wheels and rider is all heavy components so that is why I asked, I feared the total weight of bike+rider would put massive stress on the motor up hill.

I feel I must try to avoid blowing up controllers or melt motors. Cos this build has blown my budget.
So I wanna be as sure as possible I don't do any stupid noobie mistakes when bike is ready. Blowing up an max-e is too expensive so I must read more, ask more questions and try to educate myself before build is complete to avoid havoc if that is even possible.

 

[Ohbse]

There is no way you will be able to stall the motor without all hell breaking loose.

If I drove up to a wall, touched it with front tire, applied front brake and then gave it full throttle it would either overcome the front brake and literally climb a vertical surface, followed by me falling off etc or it would let rip with a big smokey burnout. Frankly - I don't care for either outcome, but I can definitely say that it won't just sit there getting hotter and then explode. That scenario is only really for people with under powered (AKA legal) setups. I have come to a stop and done hill starts on the very steep ramps in my carpark building many, many times. 10% throttle and I'm shooting up the ramp faster than most cars would be able to with the limited traction on the shiny concrete.

 

[peters]

In my case if I could somehow find a hill steep enough I would end up just doing a burnout rather than ending up with a locked rotor.

hmm, if your controller provides that much current (200amps or so) to any hub motor today, then if you want to climb a long hill steep enough without burnout, then your motor will burn down within 2 minutes, does not matter if it is not stalled.
Even a continuous 100A overheats any non-cooled hub motor in just a few minutes.

 

[macribs]

While we are at it, I am also struggling to understand what is shunt.
I have googled and I have tried translator and still stand none the wiser. I found the wikipage but there are several meanings.
And I sort of remember a video where someone here made a shunt and this big lightning arc ignite. So that makes me think that shunt is used in a protective manner, is that correct? Or what is the function of a shunt in e-bike terms?

Shunts as circuit protection (wikipedia)

When a circuit must be protected from overvoltage and there are failure modes in the power supply that can produce such overvoltages, the circuit may be protected by a device commonly called a crowbar circuit. When this device detects an overvoltage it causes a short circuit between the power supply and its return. This will cause both an immediate drop in voltage (protecting the device) and an instantaneous high current which is expected to open a current sensitive device (such as a fuse or circuit breaker). This device is called a crowbar as it is likened to dropping an actual crowbar across a set of bus bars (exposed electrical conductors).

 

[Punx0r]

When talking about ebike parts a shunt is normally of the type used to measure current. It is a metal bar with a known, low resistance. The voltage drop across it is used to calculate the current flowing through it.

Here is an explanation and some images: http://hobohome.com/news/?p=537

 

[macribs]

Thx punxor. Where would be the right place to put a shunt? As close to the batteries as possible? On the "outlet" wire of controller or where do one put the shunt? And does all system require shunts to keep track of batteries etc?

And how does shunt wound motor apply to e-bikes? It seems to me that controllers are doing the filed weakening.
Ie the max-e has filed weakening. And will apply it to all motors connected, correct?

Shunt wound motor (wikipedia)

With the shunt wound motor's high-resistance field winding connected in parallel with the armature, Vm, Rm and Ø are constant such that the no load to full load speed regulation is seldom more than 5%.[14] Speed control is achieved three ways:[15]

• Varying the field voltage
• Field weakening
• Variable resistance in the field circuit.

 

[riba2233]

Macribs you need a lot more reading and learning. Shunt motor is DC motor, for ebike use bldc motors are commonly used, and adapto is for bldc motors (three phase synchronous motors with permanent magnets).

 

[macribs]

Macribs you need a lot more reading and learning. Shunt motor is DC motor, for ebike use bldc motors are commonly used, and adapto is for bldc motors (three phase synchronous motors with permanent magnets).

I know I do, and that is why I ask Q's to the good folk of ES. English is not my native tongue, and dealing with technical English terms make it even harder to keep up. And searching one term and finding multiple answers like I did on wikipedia sure does not help.

If you find my Q's to be too basic, you can just move on and find other threads to read. There is no point in getting condescending. I have stated several times over and over again that I have no knowledge of EE, and I even said I did not pay much attention back in high school in physic lessons. What you are doing here is neither helpful nor motivating. I am trying the best I can to read and learn here on ES.

 

[riba2233]

I'm just saying, you spent a lot of money, it would be a shame to blow something because of lack of basic knowledge. You've chosen DIY route, so you have certain responsibility towards your money and health. Don't get me wrong, I'm not trying to act smart or anything like that, I'm just giving you a friendly warning.
You just need to search better, all these stuff have been explained here. It's better to read and learn than to blow expensive stuff 8)

 

[dogman dan]

I'm totally ignorant what kind of build he's planning. But I do know that 2000w and above, you'd have to have a steep ass hill to not get up it pretty efficient.

WOT and charge up it definitely works when there is plenty of power, it won't be slowing down below 15 mph, let alone getting down near 8 mph.

For hubmotors specifically, stall tends to happen only at grades above 10%, if they have at least 700w. Just enough throttle to maintain 15 mph, with a medium pedaling effort, will get you up an extremely long 8-10% grade easily. For a 350w motor, you might need to back off throttle and crawl, the idea being to not exceed about 200w worth of your power making heat. 200w will radiate away and your motor won't melt. So backing off can result in 100w to the wheel, 100w to heat. Not so efficient, but at least the motor can cool as fast as it's heating.

 

[major]

While we are at it, I am also struggling to understand what is shunt.

Words have somewhat different meanings when used in different context. In the context here, shunt = current viewing resistor. Which means the shunt is a resistor which is used in a circuit such that the current flowing through it can be detected and measured. The shunt (resistor) is a very low Ohmic value so that is affects the circuit minimally. It is often made with a material which has no change in resistance for the indicated range of use, current and temperature. The shunt (resistor) is calibrated to a precise resistance Ohmic value.

When the shunt (resistor) is placed in the series circuit, the current flowing though it will be proportional to the voltage drop across it, V=I*R. The voltage is much easier to measure. So a typical current shunt may read 50 millivolts for 100 Amperes. It would then read 25mV for 50A. And 10mV for 20A. In this case the current shunt has a resistance of 0.0005Ω.


image from: http://www.learningelectronics.net/worksheets/ohm_law.html

 

[Arlo1]

MacRibs. I used a couple of china controllers before building my own. And I had one putting over 30kw into my X5304 there was never a problem of the controller blowing up when set up right on a motor with a decent amount of inductance.

With colossus it would blow up every dumb controller I tried so that's why I learnt to build my own.

My 18 fet hooked to colossus was a 60-1 ratio of phase amps to battery amps at a stall so 5 amps battery was 300 phase amps. But it was using phase amps to run and because it was a smart controller it survived.

So if you don't want to worry about blowing up controllers use one that has phase amp control and make sure its capable of running the inductance of your motor.

What are the specs on your motor?

 

[macribs]

@Arlo1. The motor is QS motor v3 = cromtor.

If you look at the pic below it is the first motor the 205 that is reality is the same as Cromtor.
If you want other specs I can ask the vendor (vito) about it.

KV of the motor has been measured at 9.3KV (9.3 RPM per 1 volt)
Inductance is 145uH
Hall sensors spacing is 120 degrees

 

[Arlo1]

I think you will be fine I was able to make my 24 fet survive at anything over 60 uH inductance phase to phase.

But if you want something that doesn't deal with glitches now and them get a quality sine controller. Like maybe a sevcon size 2 or 4. I would make sure someone has one mapped for the Cromotor though as some motors sevcon just can't run.

 

[macribs]

I will be using the Adaptto max-e controller, that is sine wave. My 20s14p battery is build specific for the adaptto BMS for balancing.
So that is the controller I will use.

Is there anything in particular I should be careful with when I plot the the settings, limits etc for the v3 in the adaptto?
I expect around 10-13 kw for short burst 10 seconds or so.

The max-e controller has 200A/350A nominal/peak phase current.

 

[friendly1uk]

If your coming to a halt through lack of power, your stalling. Once stopped, you have stalled.

In my car, if I mess up the clutch and the engine stops, you would say I have stalled it.

At low speeds my controller sometimes has timing issue's, I feel it trying to engage, but stalling. The power is being applied at the wrong time, so the bike won't move off. It is just stalling.



Hope this helps