Power limits of a Nine Continent 500W 9C motor...

Well, I have it on my Greyborg V2 frame on 20S2P LiFePO4 Headway battery pack. Controller is set to "give" 30A max because of possible motor melting. That gives me around 54km/h top speed which is only 1km/h more than my wife's bike and her is 48V configuration with same motor...

Could you guys tell me, from your experience, is it safe to give him a little bit more Amps to increase top speed a little bit more, or to buy some other motor?

Some suggestions?

The only answer is to put a thermistor into the motor, monitor the temperature and understand it's thermal limits. Your situation is unique right down to the weather you are having right now, nobody can easily forecast how things will work out when you exceed limits. Honestly you are already pretty high on the power it sounds like.

Hall sensors come in a variety of temperature limitations, but any heat much above ambient is going to accelerate it's aging, what this means is a hotter running motor will have a short life span on hall sensors. Magnets lose some or more of their magnetism if they get too hot, copper's(phases) resistance increases as it gets hotter and eventually some other bad things happen to it that I don't really understand, shields/seals and the grease can go bad when they get too hot involving your bearings meaning the oil from the grease will leak out and you'll end up with ruined bearings and so on. Lots can go wrong if you overheat your motor and you won't know about overheating until it's too late unless you have a thermistor installed. Putting your hand against the hub motor shell is not a reliable method for determining internal motor temperature and probably a really bad idea.

In my mind what is likely to happen when people continue to blindly push their motor to higher and higher temperatures is the bearings become screwed, the friction gets greater from the bearings, motor runs even hotter, and then either the halls go or something worse. In summary, 80c-100c is likely a good limit for your motor, you can blast your motor for a very brief time to at saturation to get there or you can try and push the motor really hot but manually change the power either through something like a cycleanalyst or just the modulation of the throttle.

If you are really looking to push your motors install a thermistor, use a cycle analyst version 3 to automatically roll back the throttle if the motor gets too hot, and either spray the motor with boeshield t-9 and vent the motor(drill some holes on the side of the hub shell to let air pass through for enhanced cooling) or put some automatic transmission fluid into the hub to act as a thermal transfer fluid. With direct drive hub motors venting seems like a pretty good direction so long as you don't care about how it looks too much.

thank you for your answer.

So about 70v fully charged x 30 amps. Only about 2000w.

Much depends on the kind of ride, but I would not worry about melting that motor street riding it on that power level.

Dirt riding it, then it just depends on the weight, the grade, deep sand, etc. But you could very likely ride that thing very hard for 30 min before overheating it too much.

Bearings? Really? I always blow halls first, or just smoke shit out of those 28mm motors when I pushed them way too hard. 3000-4000w.

If you are going to ride this bike hard off road, then the thermometer in the motor is almost a must. Hard enough trail, you can smoke a motor in 20 min. But if the trail will allow you to ride it up at 15 mph, no worries IMO. A thermistor in the hub will allow you to see a heat spike before it gets the motor above 250f. Vent holes will help too, particularly with cooling off an overheated motor quicker.

I am 85kg, plus Greyborg.

Mainly roads, almost no hills, just flat surfaces and I ride it mostly around 40-45km/h when on "open" road. That speed is too much if you are on bicycle tracks but you already know that.

Vent holes? I should drill those by myself?

In addition to what others mentioned, how you ride plays a huge part in how much heat the hubmotor makes, because the most heat is made during the early part of acceleration due to higher phase current, and heat created in the windings goes up by the square of current.

At top speed cruising, current limits set in the controller shouldn't even come to play. Current limiting can be used to limit top speed, but that's generally only with fast wind motors (higher rpm/volt) and low current limits. Increasing current limits increases acceleration, and typically has little, if any, effect on top speed. If your controller is programmable then maybe you just have a bad setting. eg If the controller has a 3 speed switch setting, but no speed switch is installed some controllers default to speed setting 2, so that would need to be set to 100% to get the proper top speed. If you use a Cycle Analyst or another ebike computer, that could be artificially limiting your top speed.

First, determine where you stand now:
-Compare your top speed to the no-load speed. The closer actual speed is to spinning it up with the wheel in the air, the more efficiently you are running and the lower the stress on the motor.
-See how hot you're motor is running now under different riding conditions. That will give you a baseline to compare to higher current you try later. It also helps you learn what makes more heat, which can enable you to run higher settings without modifications and without heat issues. Even using your hand to feel how hot the motor is can be better than nothing. Guys use to ridicule me about using my hand as my only temperature measure, but I've only installed a temp gauge on one bike and I very rarely turn it on, yet I run higher power through hubmotors than anyone and I've never burned up a motor I was riding.
-Check your top speed with different riding positions. Above 30kph or so wind resistance becomes the primary factor, so maybe you're just giving up a lot of your top speed to the wind compared to your wife's bike.

They can live at 2400 watts for a while. Depends on the wind. On hills do the hand temp test. 3200watts will cook it, if not watching. Sure it will take 5,000watts but for how long.
A temp sensor for high wattage and off road or mud and sand plus hills ect.
Volts make speed 24s ?

Something like 10.2hp is the power limit, because 150A was 10rwhp, 200A was like 10.1hp and 400A was 10.2hp (rapidly followed by flames).


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Fire the camera man ( person ).

Liveforphysics,

I recall that was a significantly larger motor than the 28mm stator 9C the OP has. No way his motor can make 10hp without a clown wheel and 200V+, and even then iron losses may prevent it. Justin tested the common 9x7 (or was it 7x9?) wind 9C, and he said saturation started at 70A phase current.

John in CR said:

First, determine where you stand now:
-Compare your top speed to the no-load speed. The closer actual speed is to spinning it up with the wheel in the air, the more efficiently you are running and the lower the stress on the motor.

Click to expand...

It is around 72km/h in the air and around 18km/h less on the road...

Again, at the voltage you are running, 30 amps is not the max that motor can handle. So unless you go higher you should be able to get decent run times. 40 amps (controller amps) is quite possible, but run time needs to shorten then. When I tried to run 40 amps of 110v, I began to overheat much faster! So I consider 72v 40 amps the max that still yields a decent run time without overheating the motor. Saturation is much more, but I needed to have at least a 10 mile run before flames.

Yes, remove the covers and drill vent holes if you want it to cool back off faster. This is definitely effective for letting out the heat when you stop rolling. Typically the motor will spike heat when it stops getting that 50-60 kph air cooling. Lots of approaches to the size and placement of the holes. John in CR has a good thread on it, and his style works good. Too big holes can weaken the cover.

Put a temp sensor in the motor, if you really want to know how hot your winding is. When the temp stops going up, you have reached heat equilibrium for that day's weather, and the kind of riding you are doing. Then you can run infinitely, if you are not already overheated.

On that type of motor, I used to overheat fairly often in summer, running 72v 40 amps. But in winter no problem. So I'd dial down the amps to 20 amps in summer. When it got to about 32c outside. That was without vent holes.

The difference in speed from your bike to your wifes. Are you sure both motors are the same winding? Sounds like your wife's bike has a very fast rpm winding. Typical 9x7 winding on 48v would only go about 45 kph, with a 170-200 pound rider.

100% sure that motors are identical, and bought from the same shop.

I think I will go with 35A and that will be a good solution. And, about temp sensor, how to install it? Where to buy it? Any suggestions?

If you all understand me, I don't want to push it to the limits all the time, just want to have some "reserve" power if needed. :lol:

hi grga
i run my 9C 8x8 on 24s lifepo with a 60amp controller.
i have upgraded the phase wires (through to windings) and oil cooled it, but i dont have a temp prob.
i can run it continuously at ~2kw as long as my speed is up, and tend to keep it below 3 on the hills (just with throttle and pedalling). after 15- mins or so of hill climbing it is barely warm (hand test) at these levels.
before the mods i ran it at 60v/40a with no probs at all.
im fairly careful (because i dont have a temp probe)- this power level is not without risk, i could prob fry it without trying too hard!
anyway hope this helps
kdog

thank you kdog, 60V 40A actually IS my goal but I wanted to hear other experiences.

60v 40 amps will be fine for that motor. If you cruise at less than full speed, you will only be pulling about 1500w, or around 15 amps. It can do that all day on the flat, with no need to cut holes. 50 kph cruise is not a problem. The problem is stop and go, hard riding, up hills, off road, or racing. Then you pull the 2000 w or so at 5kph too much.

Is the unloaded rpm of the motors the same? That would be weird if so.

What's sort of odd really, is how fast her bike is, on just 48v. She got 2000w too?

FWIW, your speed is exactly what I'd expect for 20s lifepo4, and 30 amps max, and a 9x7 winding.

But her speed should be closer to 45 kph on 48v, with the same winding. And that would be possible with only 20 amps. If she is a lot lighter than you, and has 48v 40 amps, that could explain it. She'd be capable of getting closer to the no load speed than you can.

yes, you are right, at 35km/h it pulls around 6-7A and at 40km/h around 12A so I think that setting with 40A will work for sure and I will try it. only thing I have to watch is to run slowly from zero.

wife is a little more than 30kg lighter than me and her bike is 7-8kg lighter than mine, for sure. I don't know exactly her controller setting but I think it is around 30A, like mine, only on 48V.

however, I think I could "grab" a little bit more speed on 40A controller setting.