24, 36, 48 or more volts?
- Thread starter skutter
- Start date
How are you measuring capacity?
10Ah @ 36V is a hell of a lot more than 10Ah @ 24V.
Barking?
Example: I have two Ping LiFePO4 batteries, one 24 volts 15 ah and one 36 volts 10 ah. Both machines to which they are fitted have the same range, around 23 miles.
I expect one of the boffins on the forum will work out the watt/hours, which is the best way to compare the different voltages versus amp/hours.
By the way, it's not a good time of year for barking up trees, you could well finish up buried in leaves!
All the best
Bob
Yes Skutter, That's incorrect.
Example: I have two Ping LiFePO4 batteries, one 24 volts 15 ah and one 36 volts 10 ah. Both machines to which they are fitted have the same range, around 23 miles.
I expect one of the boffins on the forum will work out the watt/hours, which is the best way to compare the different voltages versus amp/hours.
By the way, it's not a good time of year for barking up trees, you could well finish up buried in leaves!
All the best
Bob
That's easy to do...
watt-hours = volts x amp-hours
so...
36V x 10Ah = 24V x 15Ah = 360Wh
watt-hours is a measure of energy in the battery which translates to the range you can expect
PS. These values won't be exact because battery voltage drops as it is discharged but it is close enough for our purposes.
Thanks, it makes sense now.
Using the example 36V 10Ah battery, would a motor rated 360W theoretically run for 1 hour (obviously discharge isn't a straight line and depends on load)?
Sorry if I'm being a bit thick here.more volt = higher speed.
The limit is 25 km or 15 m.
Regards,
Jo
But does >voltage = >speed with the BRUSHLESS motor types?
As far as I can work out it doesn't necessarily....
Why?
Well with a BRUSHED motor the more energy you put into the windings the fast the motor moves onto the next set of contacts, which then send it to the next set & so on. So >voltage = > speed.
However, with the brushless types (i.e. stepper motors) the movement from one motor position to the next is controlled by the external control circuit. It is this which sets the maximum speed through how fast it switches between the "steps".
So >voltage doesn't mean more speed (unless you didn't have sufficient uumph to reach top speed before).
It means more ACCELERATION as the motor has more energy to switch between steps, so it can do it faster.
Or have I got this completely wrong?!?!
So if you want to go faster, change(hack) the controller (& you might have to up the voltage too to provide sufficient energy).
Which leads me to ask.. why do motors come with different RPMs? Is it different optimal RPMs?
Cheers
Steve
The controller for a brushless DC motor does the job of the brushes, so overall it behaves just like a brushed motor.
See post in other thread - you still get a max rpm that is proportional to the voltage available.
Motors come with different stated rpms for two reasons.
One might be that they have internal gears and there are different ratios available (Bafang and Tongxin, for instance.)
The other is that the same motor may have its windings connected or arranged differently, so it has a different slope on the graph of no load speed vs voltage. (Crystalyte do this. 406, 407, 406, etc are the same mechanics and same amount of copper, but the copper is wired up differently.)
Nick
See post in other thread - you still get a max rpm that is proportional to the voltage available.
Motors come with different stated rpms for two reasons.
One might be that they have internal gears and there are different ratios available (Bafang and Tongxin, for instance.)
The other is that the same motor may have its windings connected or arranged differently, so it has a different slope on the graph of no load speed vs voltage. (Crystalyte do this. 406, 407, 406, etc are the same mechanics and same amount of copper, but the copper is wired up differently.)
Nick
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Me at the back with another question.....
If the controller for a brushless motor is doing the job of the brushes in a normal DC motor. How does it know where and when to apply volt/power to the windings as the rotor is turning?
Is this where the hall effects sensors are needed? eg. intelligent controller, it knows the rotor position?
If so....how would a controller 'manage' a non hall brushless motor?
If the controller for a brushless motor is doing the job of the brushes in a normal DC motor. How does it know where and when to apply volt/power to the windings as the rotor is turning?
Is this where the hall effects sensors are needed? eg. intelligent controller, it knows the rotor position?
If so....how would a controller 'manage' a non hall brushless motor?
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Yes, that's exactly what the Hall sensors do.
Without Hall sensors it can still be done, by monitoring the back emf from the windings. Of course, that only works when the motor is already turning, so getting started can be a problem.
I'm led to believe that there is no standard solution to operating without sensors. Even in a single design there may be different techniques used at different motor speeds.
Nick
...and for cars it's 70mph.more volt = higher speed.
The limit is 25 km or 15 m.
Regards,
Jo
I suppose this is down to the design of the controller then. I was envisaging a "crystal" controlled oscillator. Where the frequency (& hence speed) of the state changes was fed from a voltage independent source.
However if a voltage/power controlled oscilator is what's used then >voltage = > frequency = >speed.
However if you swap say a 24V controller for a 36V controller, then you are back to square 1 aren't you, as the oscillator is already calibrated for the higher voltage? Or are 36V motors geared to spin faster?
Cheers
Steve
Steve,
Forget the oscillator. The controller responds to the motor - the switching is driven by the motor movement, not the other way round.
If controllers are labelled 24 V, 36 V etc, that is usually only the settings for the battery - there is often a circuit that operates a cut out if the battery voltage gets too high or too low.
Here's a very brief summary:
With a DC motor, the controller is like a throttle and turns down the power. The motor will then find its own speed, depending on the power delivered and the load. E-bikes are done this way.
With an AC motor, the controller is like a speed control, it does set the rate of commutation. The motor tries to run at the speed commanded by the controller and draws whatever power is needed. Higher power electric vehicles are done this way.
Nick
Forget the oscillator. The controller responds to the motor - the switching is driven by the motor movement, not the other way round.
If controllers are labelled 24 V, 36 V etc, that is usually only the settings for the battery - there is often a circuit that operates a cut out if the battery voltage gets too high or too low.
Here's a very brief summary:
With a DC motor, the controller is like a throttle and turns down the power. The motor will then find its own speed, depending on the power delivered and the load. E-bikes are done this way.
With an AC motor, the controller is like a speed control, it does set the rate of commutation. The motor tries to run at the speed commanded by the controller and draws whatever power is needed. Higher power electric vehicles are done this way.
Nick
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Ahh I see! I was making it WAY too complicated! So basically the pulse from the hall sensors triggers the controller into the next step state. I was thinking it was more like the AC motor you describe. (I come from a digital world!)
So these controller things are not as complex as I thought.
Cheers
Steve
As Nick says, the controller current is switched when indicated by the hall sensors. There is also a much higher frequency switching which turns battery current on and off at a variable duty cycle, making the controller behave like a DC to DC converter, reducing the supplied voltage. This allows the controller to vary the speed of the motor (instructed by the twist throttle) and also limit the battery current (measured across a shunt resistor)
John, that was my next question! How do they vary the power? So they pulse it at different duty cycles. Makes sense.
(I should know all this really, my dad used to supply power thyristors to drive electric trains and cars. Tut tut).
So the logical next question after this is, how much do the different motors and controllers accept overvoltage? I think that's a question for the speed junkies on endless sphere with their practical testing...
Cheers
Steve
Yes the ES guys are into that. Most motors can cope with a fair amount of overvoltage. They often replace the MOSFETs and capacitors in the controller to ones that will work at higher voltages.
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