Controller and volts

[Cyclomania]

So I am trying to understand basics of controllers, amps and batteries.

So for example if I have a controller of max current 45A.. And a battery of let us say 48 volt and 20ah. And then I switch battery, but keep the same controller, to a 72volt battery 20AH. Will this have an effect on the bike at all? For example will the bike increase in top speed but not in torque? Or how does that work when the controller draws the same max current regardless?

 

[slaphappygamer]

Most likely, you will blow your existing controller due to the voltage change. If you change your controller to accommodate the 72 volts, your bike will go faster.

 

[Cyclomania]

Most likely, you will blow your existing controller due to the voltage change. If you change your controller to accommodate the 72 volts, your bike will go faster. If your new controller is 72v 45a, your torque will stay the same. Amps regulate torque and voltage regulates the speed.

Ah okay. So if I switch from 48volt battery to 72 volt battery and the controller stays the same I will only increase top speed on flat ground, correct?

Assume the controller is a 48-72volt controller with max current of 45A and stays the same when I switch battery.

Then this is the case right? Increase in top speed but no difference in torque?

 

[slaphappygamer]

Just know that many 48 volt controllers have 60 volt capacitors. If you connect your 72 volt battery to that controller, it will go up in smoke. You will hear a loud POP! Other components may get damaged due to that event.

 

[E-HP]

So I am trying to understand basics of controllers, amps and batteries.

So for example if I have a controller of max current 45A.. And a battery of let us say 48 volt and 20ah. And then I switch battery, but keep the same controller, to a 72volt battery 20AH. Will this have an effect on the bike at all? For example will the bike increase in top speed but not in torque? Or how does that work when the controller draws the same max current regardless?

Both speed and torque will increase significantly, by about 30% or more across the board at the same current level, provided that your controller is designed to handle the higher voltage

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

 

[slaphappygamer]

So, torque will increase as total wattage increases, not just amperage?

Also, thanks for the graph. I just can’t view the entire graph on a mobile device. Safari won’t let me side scroll on that page.

 

[Cyclomania]

Both speed and torque will increase significantly, by about 30% or more across the board at the same current level, provided that your controller is designed to handle the higher voltage

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

Hmm yeah interesting.

Yes the controller is a 48-72volt controller. That can handle either 48 volt battries or 72volt batteries. The max current is 45a at all times.

So by just changing the battery to another battery I would get a lot more torque and speed. Good to know.
But how does that work? When the max current is always 45a from that controller?

Could you explain to me how that works? I get a bit confused by the fact that the max current is alway 45. So I did not know if it would make a difference. Not quite sure about the underlying mechanism and how the battery is shooting in more wattage into that motor.

Should I think about it like this: 48*45=2160
And
72*45=3240

?

Is that the reason why speed and torque increases? You multiply voltage and max current amps?

 

[E-HP]

Hmm yeah interesting.

Yes the controller is a 48-72volt controller. That can handle either 48 volt battries or 72volt batteries. The max current is 45a at all times.

So by just changing the battery to another battery I would get a lot more torque and speed. Good to know.
But how does that work? When the max current is always 45a from that controller?

Could you explain to me how that works? I get a bit confused by the fact that the max current is alway 45. So I did not know if it would make a difference. Not quite sure about the underlying mechanism and how the battery is shooting in more wattage into that motor.

Should I think about it like this: 48*45=2160
And
72*45=3240

?

Is that the reason why speed and torque increases? You multiply voltage and max current amps?

There are folks that can explain this better, but the way I think of it is that torque is proportional to current, but not battery current, which in your case is limited to 45A, but motor/phase current, which is not, and can be as much as 3 times the battery current. Voltage doesn't directly affect torque, but the higher voltage allows more motor current to flow, so increases torque indirectly.

Note that depending on your controller, and whether it controls speed vs power, going to 72V can make the bike difficult to ride without something to control the throttle ramping.

 

[spinningmagnets]

A "mosfet" is a type of on/off switch that sends current to each of the three phases in the motor.

They have a max voltage rating and a max current rating.

The size of the fet, and the quantity of fets per phase determines the amount of current the controller can flow.

Many controllers use the small and cheap fets, and instead of using one large expensive fet per phase, they will parallel 2, 3, or 4 fets per phase of the small and cheap ones.

This is why you often hear about 6-fet, 12-fet, and 18-fet controllers.

 

[Cyclomania]

Note that depending on your controller, and whether it controls speed vs power, going to 72V can make the bike difficult to ride without something to control the throttle ramping.

Hmm ok. Good to know. How do you mean? It starts to be "jumpy" or not as smooth or something?

 

[Cyclomania]

Voltage doesn't directly affect torque, but the higher voltage allows more motor current to flow, so increases torque indirectly.

Hmm ok. So one way or another, the higher voltage will make the bike both faster and more torquier, as long as the controller is a 48-72volt controller that can allow both 48 or 72 volts. Ok.

 

[Andje]

If you use 45 amps at 48 volts you are outputting 48*45=2160 Watts going through the phase wires to your motor.
If you use 45 amps at 72 volts you are outputting 72*45= 3240 Watts.
So yes, it will increase max RPM of the same hubmotor due to the increased voltage, as well as torque at all rpms due to the overall wattage increase.
No motor is 100% efficient, so they heat up. Some of the watts turn into heat. So the more you put in, the more it heats. If you put enough in for long enough, any motor will heat up the varnish on the coils of copper wire, it will burn off and a copper to copper short will occur in the windings and the motor burns out. If your kit was well matched the motor will be able to take full power for longer then the battery can output it, but that's not always the case. If you increase the wattage you increase the overall risk of it burning. If you are monitoring the internal temperature of the motor then you would know if it was getting too hot. If not you need to play it by ear.

 

[E-HP]

Hmm ok. Good to know. How do you mean? It starts to be "jumpy" or not as smooth or something?

Fundamentally, at 48V, the throttle controls the voltage going to the motor between 0V to right around 48V. At 72V, the throttle is controlling a range of 0V to 72V, so the throttle will feel more sensitive, requiring less of a twist for the same results. Compounding that is that fact that hall based throttles are already sensitive in the lower range, and slight twist at 72V can land you on your back in a split second.

 

[Cyclomania]

Fundamentally, at 48V, the throttle controls the voltage going to the motor between 0V to right around 48V. At 72V, the throttle is controlling a range of 0V to 72V, so the throttle will feel more sensitive, requiring less of a twist for the same results. Compounding that is that fact that hall based throttles are already sensitive in the lower range, and slight twist at 72V can land you on your back in a split second.

Mm ok. Any type of throttle that would be more suitable perhaps? If I want to increase the power I mean. Perhaps I could change that one up as well when I switch?

 

[Cyclomania]

No motor is 100% efficient, so they heat up. Some of the watts turn into heat. So the more you put in, the more it heats. If you put enough in for long enough, any motor will heat up the varnish on the coils of copper wire, it will burn off and a copper to copper short will occur in the windings and the motor burns out. If your kit was well matched the motor will be able to take full power for longer then the battery can output it, but that's not always the case. If you increase the wattage you increase the overall risk of it burning. If you are monitoring the internal temperature of the motor then you would know if it was getting too hot. If not you need to play it by ear.

Ah I have always wanted to try an experiment with statorade and/or hubsinks if I go hard on the voltage. But I don`t know if these are necessary ? Some guys think these works well. But I have heard others say these are unnecessary and that they does not work.

In the winter here in Scandinavia I think the weather often takes care of the heat build up. All of my blown controllers and motors have basically occurred during the warmer half of the year.

How do you monitor heat? Heat camera? Most of these are quite expensive last time I checked. Any cheap alternative to those?

 

[calab]

You touch the motor after a big pull, can touch the controller to and see how hot it is.

If you can lay your hand on the cover of the hub motor and leave it there for 1-2 seconds then you should be alright.
Can install a temp reader, bbq themometers to a lcd display or use a Cycle Analyst with appropriate controller connection for CA.

If you have to go to those lengths to cool your motor down, you might as well try it and see how the mods go with the aluminum heat sinks, statorade, mini dc fans glued to holes in the cover, or cutting holes in the cover or just sell the old motor and buy a bigger motor.

 

[serrrg10]

A "mosfet" is a type of on/off switch that sends current to each of the three phases in the motor.

They have a max voltage rating and a max current rating.

The size of the fet, and the quantity of fets perphase determines he mount of current the controller can flow.

Many controllers use the small and cheap fets,, insteadof using one large expensive fet per phase, they will parallel 2, 3, or 4 fees per phase of the small and cheap ones.

This is why you often hear about 6-fet, 12-fet, and 18-fet controllers.

Basically you are right. But the heat generated during on/off switching also plays a role. So
3 cheap TK150E09NE mosfets have thermal resistance Rth about 0.63/3 ~ 0.21 with one expensive have same?

 

[Andje]

Some controllers have a line in for a thermistor. This is a tiny resistor sized electrical component that changes resistance when it changes temperature. One would normally open the motor and glue it up under the windings to give a temp reading from the most crucial component.
They certainly make small displays that take a thermistor input and show you a temp reading if your controller isn't compatible or you don't use a cycle analyst as a display.
That being said, I ran for years without using them, and just sort of got a feel for how hot the motor would get under various circumstances and knew what I could do with it. Seat of my pants. Agreed that cold whether helps up to a point.
The statorade seems controversial. It definitely increased heat transfer to ambient via air cooling, but some people did indicate that they had issues with it dissolving the epoxy that held in the permanent magnets. I don't know enough to confirm or deny, but most of us have never used it in high powered applications.