H guys I am a little confused about how a motor rated at 500w could be expected to become a 2000 W one by increasing the current and voltage. I would have thought the ability of the motor to use power above its VA rating would be limited by the conductor thickness of the internal windings of the motor combined the motors inductance. I read here on the forum That the 9 continent motors become 2000 W by an increase in voltage and current. Is there some weird way the motors are rated at 500 W?
Hub motor increased power rating over rated power.
- Thread starter _Chris_
- Start date
Jeremy Harris
100 MW
The simple answer is that the majority of hub motors are given a quite arbitrary rating, based on some completely unknown test method (if they even test them properly) and that also some of the data is often wildly innaccurate, perhaps because of language issues, perhaps because of sales people not having a clue about the products they are selling. Here in the west we'd expect a rating to be based on a standardised test method, not so with far eastern manufactured bike motors, from what I've seen.
The main problem is understanding what the quoted motor rating actually is. Is it the maximum continuous power rating? If so, at what ambient temperature and at what motor current?
Current plays the most significant part in determining a motors rating, as it's current, in the main, that generates heat in the windings from I²R loss. This means that you can, for example, take a motor rated at 500W at 36V and run it at 72V and get 1000W; as far as the motor is concerned it's still handling the same current so will run at more or less the same temperature.
There's also the peak versus continuous rating issue. Ebikes rarely run at more than a kW or two for more than a short period of time, so the average power may well be down around the manufacturers supposed rating.
One things is for sure, treat ALL Chinese motor "specifications" with a pinch of salt unless you've got good independent evidence to suggest they are right. More often than not they are just a guide, with the true figures being somewhat different.
The main problem is understanding what the quoted motor rating actually is. Is it the maximum continuous power rating? If so, at what ambient temperature and at what motor current?
Current plays the most significant part in determining a motors rating, as it's current, in the main, that generates heat in the windings from I²R loss. This means that you can, for example, take a motor rated at 500W at 36V and run it at 72V and get 1000W; as far as the motor is concerned it's still handling the same current so will run at more or less the same temperature.
There's also the peak versus continuous rating issue. Ebikes rarely run at more than a kW or two for more than a short period of time, so the average power may well be down around the manufacturers supposed rating.
One things is for sure, treat ALL Chinese motor "specifications" with a pinch of salt unless you've got good independent evidence to suggest they are right. More often than not they are just a guide, with the true figures being somewhat different.
I supose the best way would be to put an ammeter in the circuit between your battery and motor. That way if your motor is drawing 30 amps at 48 V then the power input would be 1440 Watts and the output would be less than that because of circuit losses and inefficiencies?
So for a 9C motor to be an eqivalent 2000W motor at 48v it would need to draw 41 Amps. Can Ping batteries do that?
So for a 9C motor to be an eqivalent 2000W motor at 48v it would need to draw 41 Amps. Can Ping batteries do that?
Jeremy Harris
100 MW
_Chris_ said:
There are a few issues when it comes to trying to measure electrical power that the motor is actually using. Firstly, the current from the battery to the controller isn't the same as the current from the controller to the motor. Apart from the motor current being three phase and the controller current being DC, the controller acts as a voltage converter, a bit like a variable, stepless, transformer. It can reduce the motor voltage, and increase the motor current, so you can get a situation where the supply from the battery to the controller is 36 V at 20 A and the supply to the motor is around 12V and 60 A. In practice there are small losses in the controller to account for, but this give a general idea.
Ping batteries aren't good at high current, the maximum is usually around 1.5 to 2 times the Ah rating, so for a 20 Ah pack no more than 30 to 40 A at most.
dogman dan
1 PW
They can, but they don't like it. I recomend a max of 30 amps for a 20 ah size. The bigger the battery, the more amps 1.5c is. Personally, I find pings suffer when used at 2c continous.
Motors do have a max power, and above that, you tend to make increasing amounts of whatever you are giving it into heat. I tend to say 1500w is a good number to call the max for typical dd motors found in kits. So that's 9c, muxus, conhis, golden etc.
Not that you can't add more. I had a real fun ride last weekend on 72v 40 amps. With that particular motor winding, I see real 2500 max wattage. Er, but it did melt my motor because I was up in the mountians.... Just melted the halls, so I got it fixed yesterday. The windings are nice and toasty black, and the string burned away, but no shorted windings
.
So far..... I've not melted down a motor at 72v 20 amps. About 1500 watts seen on the CA. So the limit is somewhere there, between 1500w and 2500w imo. Much depends on the ride. I keep smoking motors climbing really steep hills, or on the racetrack. Never fried one just riding in town so far.
Motors do have a max power, and above that, you tend to make increasing amounts of whatever you are giving it into heat. I tend to say 1500w is a good number to call the max for typical dd motors found in kits. So that's 9c, muxus, conhis, golden etc.
Not that you can't add more. I had a real fun ride last weekend on 72v 40 amps. With that particular motor winding, I see real 2500 max wattage. Er, but it did melt my motor because I was up in the mountians.... Just melted the halls, so I got it fixed yesterday. The windings are nice and toasty black, and the string burned away, but no shorted windings
.So far..... I've not melted down a motor at 72v 20 amps. About 1500 watts seen on the CA. So the limit is somewhere there, between 1500w and 2500w imo. Much depends on the ride. I keep smoking motors climbing really steep hills, or on the racetrack. Never fried one just riding in town so far.
Samd
10 MW
Good points above about power/voltage/and current (especially current).
It's worth mentioning that there is some good data on here regarding what-starts-to-fail-at-what-temperature.
Particularly different hall sensors start to fry at different temps, and magnets start to de-magnetise. I think Doctorbass has some info on his posts regarding cooing via water/oil beyond certain temps.
To that end, the kind of casing material and shape matters - as to how fast a motor can shed heat from it.
And if it is a geared hub, the gear material matters, to what end will it strip?
Some hubs are rated at a continuous use level, some data you see here will be peak dumps, maybe for a quick burst across traffic lights, or longer bursts up hills.
These are all factors to bear in mind....
It's worth mentioning that there is some good data on here regarding what-starts-to-fail-at-what-temperature.
Particularly different hall sensors start to fry at different temps, and magnets start to de-magnetise. I think Doctorbass has some info on his posts regarding cooing via water/oil beyond certain temps.
To that end, the kind of casing material and shape matters - as to how fast a motor can shed heat from it.
And if it is a geared hub, the gear material matters, to what end will it strip?
Some hubs are rated at a continuous use level, some data you see here will be peak dumps, maybe for a quick burst across traffic lights, or longer bursts up hills.
These are all factors to bear in mind....
spinningmagnets
100 TW
A temperature probe is pretty cheap. Get one as soon as possible, and that is the final determination of what a hub should actually be rated at. Also, not all watts are the same.
For example, 48V X 20A is roughly 960 watts, but...24V X 40A is also about the same. Amps = heat, plus the lower voltage provides less torque, so its more likely to draw the max amps available.
You must also consider the load that is to be applied and how much heat the hub can shed. Lets imagine two identical E-bikes on a medium uphill, but one rider is very skinny and and the other is very heavy. If they both use the same voltage, the variable is how many amps each bike must draw to maintain its top speed (or at least "try to"). The heavier the load, the more amps the controller will draw to try and keep up.
In addition to the temp probe, its a good idea to get a CycleAnalyst, and most controllers will allow a CycleAnalyst to limit the max amps the controller will draw. This allows you to cap the max amps in your system to just below the temperature where it would be damaged, based on the load you are applying on your particular commute.
And as a final note, even if you determine that a 48V hub system that you own can operate at 750W continuously without overheating, but will overheat if loaded with 1500W continuously. You can usually put 1500W through that system for a short temporary load, as long as it isn't for very long.
For example, 48V X 20A is roughly 960 watts, but...24V X 40A is also about the same. Amps = heat, plus the lower voltage provides less torque, so its more likely to draw the max amps available.
You must also consider the load that is to be applied and how much heat the hub can shed. Lets imagine two identical E-bikes on a medium uphill, but one rider is very skinny and and the other is very heavy. If they both use the same voltage, the variable is how many amps each bike must draw to maintain its top speed (or at least "try to"). The heavier the load, the more amps the controller will draw to try and keep up.
In addition to the temp probe, its a good idea to get a CycleAnalyst, and most controllers will allow a CycleAnalyst to limit the max amps the controller will draw. This allows you to cap the max amps in your system to just below the temperature where it would be damaged, based on the load you are applying on your particular commute.
And as a final note, even if you determine that a 48V hub system that you own can operate at 750W continuously without overheating, but will overheat if loaded with 1500W continuously. You can usually put 1500W through that system for a short temporary load, as long as it isn't for very long.
cwah
100 MW
Jeremy Harris said:
That's an really really interesting information to know. Does that mean that motor output power is not defined by the watt but rather by the amps?
For example, a 350W motor would be rated for 10A at 36V. Now let say I decide to use 120V battery, does that mean I can put 10A*120V=1200W continuous on a small motor such as a cute100 of 2.1kg??
And if I go on a dual cute100 I'd be able to use my bike at 2400W continuous and 5000W peak???
Unfortunately not Cwah, because you have to consider how much power is making heat instead of motion, which brings me to my point.
When most of us talk about the power of our bikes, we talk about the power we see on the watt-meter based on amps and volts from the battery, which can be completely different to the power the motor makes. When going up a hill, a 500w motor might actually be making 500w, but with 1500 or even 2000W showing on the meter if it's labouring.
When most of us talk about the power of our bikes, we talk about the power we see on the watt-meter based on amps and volts from the battery, which can be completely different to the power the motor makes. When going up a hill, a 500w motor might actually be making 500w, but with 1500 or even 2000W showing on the meter if it's labouring.
dogman dan
1 PW
The catch 22 is that so very very very few of us increase only the volts. The common controlers are 36v 20 amps 48v 30 amps and 72v 40 amps. So 99% of us double the amps when we double the volts.
I've never fried a cheap hubmotor using 72v 20 amp controller, and now I understand better why. But the 72v 40 amp controller makes the bike ride so much mor fun! And about once a year, I am having so much fun I smoke another motor. Cheap motors though, so not a huge deal.
I've never fried a cheap hubmotor using 72v 20 amp controller, and now I understand better why. But the 72v 40 amp controller makes the bike ride so much mor fun! And about once a year, I am having so much fun I smoke another motor. Cheap motors though, so not a huge deal.
cwah
100 MW
d8veh said:
Damn... it was too good to be true.
Maybe the power rating is simply the ability of the motor to dissipate heat, as this is the main factor that would kill a motor at high voltage and high amps.
John in CR
100 TW
cwah said:d8veh said:
Damn... it was too good to be true.
Maybe the power rating is simply the ability of the motor to dissipate heat, as this is the main factor that would kill a motor at high voltage and high amps.
Exactly, IME it's a realistic continuous power rating. Maybe is because I stay at a higher quality end of the spectrum buying motors direct that are made for the Chinese market where overstating the power or junk for selling only overseas won't fly. They're built for bigger loads which has enabled me to run them at much higher than rated power without a failure.
John
cwah
100 MW
ahah, my little direct drive from Conhismotor is rated 250W and a frequently pull 3000W (peak) on it :lol:
Similar threads
