Motor and over-volting question

[morphix]

Couple of questions:

1) Generally speaking, are controllers made to work only with a certain motor, or is there a chance a controller will work with other makes of motor? Is there any risk of damaging the controller and/or motor by trying an unpaired motor and controller?

2) I've seen people talk about "over-volting" smaller 24v motors to get more power and speed from them..but don't know much about this..is there any rule on thumb to follow? Is there any risk it could damage the motor or shorten its life? And do you need to take any special precautions like monitoring/restricting the voltage and current if you say hooked up a 36V or 48V battery onto a 24v motor....how does the controller side of it work..I assume the controller has to be matched to the battery voltage?

 

[amigafan2003]

Couple of questions:

1) Generally speaking, are controllers made to work only with a certain motor, or is there a chance a controller will work with other makes of motor? Is there any risk of damaging the controller and/or motor by trying an unpaired motor and controller?

Only concern is sensorless or halls. A halled motor will work with sensorless controller but a hall only controller will not work with a sensorless motor. Other than that (excusing brushed/non-brushed) the yes - you can use most controller with most motors.

2) I've seen people talk about "over-volting" smaller 24v motors to get more power and speed from them..but don't know much about this..is there any rule on thumb to follow? Is there any risk it could damage the motor or shorten its life? And do you need to take any special precautions like monitoring/restricting the voltage and current if you say hooked up a 36V or 48V battery onto a 24v motor....how does the controller side of it work..I assume the controller has to be matched to the battery voltage?

If you add a higher voltage to a controller the watts will also increase. I.e 24v/15amps = 360 watts. 36/15amps = 540 watts. 48v/15amps = 720 watts. Voltage doesn't kill motors - watts do! Bear in mind you also change the efficiency curve of the motor by adding volts becuase it's rpm's are higher. And if you now doing 20mph @ 48v rather than 16mph @ 36v then you'll also require more watts to cruise @ 20mph, so you might need a bigger battery as well.

As for controllers/voltage - most 24v controllers can take a 36v battery and most 36v controller can take a 48v battery - depending on the caps installed on the controller. I.e. a KU63 only has 50v caps so a 48v battery (54.6v fully charged) would be too much but a 12s lipo pack (44.4v nminal - 50.2v fully charged) would be ok. Similary some controllers (lyen mini monster) can take a wide range of voltages - 24v to 63v for example. You really need to either know what your controller can take or pop the top off and the the voltage ratings printed on the components.

 

[flecc]

A few controllers have upper limit voltages above which they won't work, regardless of the components fitted. The controllers on my 36 volt e-bikes cut out at anything over 44 volts (+ or - 1/2 volt) with an LED overvolt signal,

 

[amigafan2003]

A few controllers have upper limit voltages above which they won't work, regardless of the components fitted. The controllers on my 36 volt e-bikes cut out at anything over 44 volts (+ or - 1/2 volt) with an LED overvolt signal,

That's a good point. You'd also lose lvc protection if you use a high voltage battery as well.

The obvious solution if to spend a little more and get a programmable controller.

 

[Deleted member 4366]

You can mix and match motors and controllers, but some combinations don't work so well. In theory, any sensorless controller can work with any motor, but some motors don't start very well when run sensorless: The Cute Q128 is a good example, although it runs fine apart from the initial graunch. Sensor controllers only work with sensored motors, except the BMSBattery ones which can run in both modes.

Although motors have a voltage written on them, it's pretty meaningless. Most RC brushless motors are categorised with the rpm per volt rather than voltage, which has a lot more meaning.

So, in choosing a motor, the first thing you need to think about is how fast you want to go, and then you have to consider weight and hills. A 250w motor can hold a sustained 24mph if you don't weigh much and your roads are flat. Generally, bigger motor can handle more power, but all motors can handle a lot more power if you can keep them cool. From my experience most motors can handle at least four times their rated power provided you only use the maximum power in their efficient range (around 80% max rpm)

So, in planning a build it's important to have a good combination of controller, motor and battery that should be matched to the speed and hill-climbing that you want. Motors will try to spin faster with more volts, but you need more torque to sustain higher speeds, or you can use smaller wheels for more torque and get the speed back by increasing the volts. It's no good connecting a high amp controller to a small motor because it'll just smoke the motor. There's always a maximum safe current that the wire in the motor can handle, but these values are fairly well reported for the common motors.

Another effect of the higher voltage is that it shifts the efficiency curve of the motor to higher rpm, so if you had a normal 250w 36v motor and you always ride at 15mph and then decided to fit a 48v battery, your motor would get a lot hotter and your w/mile would go up because you wouldn't have so much efficiency.

On ES recently there's been a lot of discussion about the effect of higher voltage on motors - whether it can increase max, torque as well as speed. The answer seems to be that it doesn't.

Controllers are best run at their rated voltage because of the various battery monitoring functions in the software and the ratings of the components; however, most will handle an extra 12v or so, but not so much lower volts because of the LVC.

In summary, you can run a 48v motor at 24v with a 24v controller at the same amp rating and it'll go half as fast except on steep hills, where it will be the same but not get so hot. You can run a 36v motor on 72v with a 72v controller of the same amp rating if you put the motor in 16" wheels, where it will run a bit faster (than 26"), but have much better climbing power.

 

[morphix]

Thanks very much guys for the replies and info.. I've learned a lot from this!

It seems then it's possible the Austrian guy who sold me my kit could be giving me bad advice to trick me into buying another kit from him, unless his controllers are the exception...he claims they will only work with his motors, but the controller itself looks bog-standard like most of the ones coming from China...heavy silver metal case and standard connectors and the motor itself is just a standard motor.

I think I may just risk it and buy a new 20" wheeled motor to try with the controller.. if it doesn't work I can always sell the motor or buy a new controller.. the controller as i mentioned before can be "programmed" via an LCD console which came with it..so you can set the wheel size for the motor and speedometer and power/speed legal compliance...

 

[amigafan2003]

IF it doesn't work just get another controller of ebay for £20 - they aren't expensive or hard to get hold of.