Max Line and Phase Amps

[tedo]

I have watched days of youtube videos and read tons of threads, but can not break the code on this. What do I set in the Fardriver "parameters" as my Max Line Amps and Max Phase Amps? Is there a mathematical rule for this? I am more interested in Max safe power than range.

Fardriver 961800
QS268 Hub 20kw peak 40kw
Amorge 96v 64AH Lithium 400A Peak 640AH

Thanks for any help.

 

[bananu7]

Line or bus amps are what the two cables going to your battery see, as DC current. Limited by your battery.

Phase amps are what appears on the other end, on the three phase wires leading to the motor. Because those are AC between phases, they can reach higher values during the motor rotation. As such, limited by your motor capacity, but practically 268 should take however much you can throw at it (especially given that you should be monitoring motor temps with a cutoff anyway, and thermals is going to be the limiting factor in the motor itself).

 

[tedo]

So would I just put the same numbers in the program as the battery allows via the BMS?
400 and 640?

Some answers I found said 90% of BMS for Line and then that number x 2.5 for Phase.

Assuming BMS is 400 on mine, then that would be 360 and 900. Way different numbers.

 

[amberwolf]

What's the hardest you want to push your battery? If you don't want to push it to it's absolute limit, then choose a point as far below that as you prefer, for "line" amps.

Phase amps is what your motor can take, and isn't directly related to the battery.

So would I just put the same numbers in the program as the battery allows via the BMS?
400 and 640?

Per your post above (quoted below), 640 is Ah, not A (completely different unrelated things).

Amorge 96v 64AH Lithium 400A Peak 640AH

If your battery is 400A *peak* then you should find out what it's *continuous* rating is, and use something below that as the controller's "line" limit.

 

[tedo]

Ya I mistakenly put AH after 640. I meant Amps. It is 400A continuous and 640A peak.

I don't understand a lot of this. So is the controller like a capacitor? Can it hold and then deliver more amps than the battery is capable of? I am making an assumption the battery can deliver 640 amps (peak). Whatever peak means.... I have no idea if that is for 1 second or 1 minute.

My math says the motor can handle (40000 peak/96v) 416 amps. Is that correct? Again, not knowing what duration peak means.

This stuff is hard for me to understand. Sorry.

Here is a pic of what Amoge sent me

 

[bananu7]

We started with currents, and now you're talking about power. The battery power is relatively straightforward, with perhaps a minor caveat that a charged battery can deliver more with the same max current. The motor power is a much more complex affair, as we're dealing with AC, inductive loads, motor back-emf etc. I can't say I understand every bit of it.

But regardless of all of those interactions, a motor supplied with voltage will receive some current, part of which goes into mechanical power and part goes into heat. Regardless of how complex it is to predict the behavior, you can observe the effects by directly measuring motor temperature. As long as it stays under whatever limit you set for yourself, practically you can put more into it. if you derive a perfect formula, and then enclose the motor with poor ventilation, the manufacturer's specs won't really mean much in your practical example.

We don't generally do that with batteries because the risks of overload are much more severe, and the cells degrade rapidly when used past the limits, that's why battery current is more cautiously adapted below the design limits. Motors on the other hand are mostly a bunch of metal wire in magnets with enough thermal mass to rely on thermal shutdown before they start to melt their insides.

 

[dominik h]

It depends also on the used BMS.
My battery can do 800A continious.
I have set my 721800 to 400A battery current, as my JK-BMS died after 13 seconds with 500A constant load, but survived 400A for 3 times 30 seconds and also 450Afor 3 times 20 seconds.
I have set phase current to 1400A (QS72V10000W Motor with single 25mm² phase wires) but I think your motor can handle much more.
The more phase current you set the more tourque your motor will produce at low revs.

I have now driven 3000km with this settings.
0-100kph in 6.3seconds and topspeed 125kph without weakening field.

If you can get boost and boost duration working on your controller, i would go for 380A normal battery current and 500A boost for 5-10 seconds.
And 1500-1600A phase current.

I'm not a friend of "all in".

Before I had installed a ND72680, which was used 5000km with 280A battery and 630A phase current, then I bought the bigger 10kw Motor.

Be sure to set the right temperature sensor in the fardriver App, as this will prevent the motor from overheating during uphill or full speed runs.
If the winding gets hotter then 140C the controller will reduce power. The more it gets towards 160C the less power the controller will send to the motor.

 

[tedo]

It depends also on the used BMS.
My battery can do 800A continious.
I have set my 721800 to 400A battery current, as my JK-BMS died after 13 seconds with 500A constant load, but survived 400A for 3 times 30 seconds and also 450Afor 3 times 20 seconds.
I have set phase current to 1400A (QS72V10000W Motor with single 25mm² phase wires) but I think your motor can handle much more.
The more phase current you set the more tourque your motor will produce at low revs.

I have now driven 3000km with this settings.
0-100kph in 6.3seconds and topspeed 125kph without weakening field.

If you can get boost and boost duration working on your controller, i would go for 380A normal battery current and 500A boost for 5-10 seconds.
And 1500-1600A phase current.

I'm not a friend of "all in".

Before I had installed a ND72680, which was used 5000km with 280A battery and 630A phase current, then I bought the bigger 10kw Motor.

Be sure to set the right temperature sensor in the fardriver App, as this will prevent the motor from overheating during uphill or full speed runs.
If the winding gets hotter then 140C the controller will reduce power. The more it gets towards 160C the less power the controller will send to the motor.

This is great info. Thanks for the temp and duration numbers as I could not find that anywhere. I'm a helicopter pilot and live by numbers like these.

So I will set 380 for Line current and that makes sense. But you are saying 1500 amps for phase current? Where do that many amps come from? Won't that hurt the battery? If my battery peak amps are 640 then I thought I could not draw more than that. I thought the BMS limited it to 640. So is the controller storing energy like a capacitor to to give the motor over 640 amps?

 

[bananu7]

It's more like a transformer/voltage converter.

Oversimplifying to a basic DC model, the controller presents itself to the battery as some resistance, which given current battery voltage, produces some battery current. On the other side, the engine windings have much lower resistance, so applied with the same (or, effectively through PWM, lower) voltage, can produce much higher currents.

Imagine battery voltage = 80V, controller (equivalent) resistance = 0.25Ohm - in this case we get 320A of battery current. Now imagine the engine is actually single phase, but with resistance 0.05Ohm, and the controller is operating at 50% PWM. We get 40V output voltage, divided by 0.05 gives us 800A of phase current.

The phase current corresponds almost linearly to torque produced.

The reality is more complex because our motors are three-phase, and the current flows between the motor phases, summing to 0. The phase current limit specifies the maximum current between a pair of connectors. Additionally, neither the controller nor, especially the motor present themselves as purely resistive loads. Motor's load and the rpm-based back-EMF hugely impact the calculations.

 

[stancecoke]

So is the controller storing energy like a capacitor to to give the motor over 640 amps?

The motor current is different from the battery current. That's an effect of the pulse width modulation.

battery current = duty cycle * motor current.

Especially at low speed the motor current can be much higher than the battery current.

 

[E-HP]

The Grin simulator does a good job at showing the relationships of battery vs motor current, and what happens when phase current is limited. System A has phase current set to 3x battery current, while System B has phase current limited to 2x battery current. With the sliders moved to 0mph, you can see the differences in phase vs battery current and torque between the two systems at launch. The flat spot in the torque curve for System B shows visually what happens when the phase current is limited. That flat spot makes a big difference when attempting a full throttle acceleration run from a standstill, since it affects the launch, as you can see in the acceleration figures.

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[tedo]

It's more like a transformer/voltage converter.

Oversimplifying to a basic DC model, the controller presents itself to the battery as some resistance, which given current battery voltage, produces some battery current. On the other side, the engine windings have much lower resistance, so applied with the same (or, effectively through PWM, lower) voltage, can produce much higher currents.

Imagine battery voltage = 80V, controller (equivalent) resistance = 0.25Ohm - in this case we get 320A of battery current. Now imagine the engine is actually single phase, but with resistance 0.05Ohm, and the controller is operating at 50% PWM. We get 40V output voltage, divided by 0.05 gives us 800A of phase current.

The phase current corresponds almost linearly to torque produced.

The reality is more complex because our motors are three-phase, and the current flows between the motor phases, summing to 0. The phase current limit specifies the maximum current between a pair of connectors. Additionally, neither the controller nor, especially the motor present themselves as purely resistive loads. Motor's load and the rpm-based back-EMF hugely impact the calculations.

You are a genius. Thanks.

 

[tedo]

The motor current is different from the battery current. That's an effect of the pulse width modulation.

battery current = duty cycle * motor current.

Especially at low speed the motor current can be much higher than the battery current.

Ahhh. Ok. This is what was confusing me. But that makes sense. And how I can have more past a given amp limit on the battery. I am over here writing this down with my crayons!

 

[amberwolf]

I am over here writing this down with my crayons!

They won't give me crayons anymore....

 

[tedo]

The Grin simulator does a good job at showing the relationships of battery vs motor current, and what happens when phase current is limited. System A has phase current set to 3x battery current, while System B has phase current limited to 2x battery current. With the sliders moved to 0mph, you can see the differences in phase vs battery current and torque between the two systems at launch. The flat spot in the torque curve for System B shows visually what happens when the phase current is limited. That flat spot makes a big difference when attempting a full throttle acceleration run from a standstill, since it affects the launch, as you can see in the acceleration figures.

View attachment 365074

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

That is cool. So there is really no downside to putting phase amps really high in regards to the battery.... as long as the BMS protects the battery. Phase amps would just be limited to what would damage the motor then. Is there a good rule of thumb on max phase amps given a motor's known KW and Volts?

 

[dominik h]

The easiest way to explain phase amps is to calculate the power.

At low revs the voltage on the motor is low. At top speed the voltage is high.
P=UxIxsqrt3
If you are starting from a standstill, the voltage may be 10V for example. The motor itself has nearly 0Ohms, so the controller has to restrict the phase current to not get damaged by to high currents.
10Vx500Ax1,73=8650W
The controller will draw 93A from the battery
8650W/96V=93A

With more phase current at the same voltage you get more power.
10Vx1500Ax1,73= 26kw
The controller will here draw 280A from the battery.
To simplify these calculations there is efficiency and cos Phi missing. But the numbers are only changed slightly.

 

[dominik h]

Is there a good rule of thumb on max phase amps given a motor's known KW and Volts?

There is no rule of thumbs.
You start with a low number of phase current and then you raise it until you think it is enough or the motor starts heating very fast.

Before I had installed in my 190kg scooter with 7,7kwh batttery a QS260 60V5000W Motor running at 77V nominal voltage.
With the ND72680 set to 280bA and 630pA I could heat the motor in three runs from 0-100kph to 130C. During normal driving it only sometimes reached 140C where the controller starts to reduce power. I think this motor was maxed out in my heavy scooter.
The new QS10kW sees 400bA and 1400pA and it doesn't heat up as fast as the old 5kW Motor. I think this one could be feed with a little more power.
The old motor had 13mm² phase wires the new has 25mm² phase wires.
Yours has 2x20mm² phase wires, which will be capable of even more phase amps for short burst.
I would start with 1300pA and drive and see if it is accelerating fast enough for you, if not raise it to 1500pA and look if it heats to fast, if not ad another 100pA.

Heating of the motor depends on how long you apply high currents. Basic calculation for heating is I²xTime .
So 500A for 10 seconds will produce the same amount of heat in the motor as 1000A for 2.5 seconds.
But you only need high phase currents for acceleration and only at lower revs.

They sell your motor also with the ND962600 Controller.

The nominal phase current should be written in the datasheet from the manufacturer, but that current ist at nominal power at high revs for 24hours. That current will be around 200A.

 

[tedo]

There is no rule of thumbs.
You start with a low number of phase current and then you raise it until you think it is enough or the motor starts heating very fast.

Before I had installed in my 190kg scooter with 7,7kwh batttery a QS260 60V5000W Motor running at 77V nominal voltage.
With the ND72680 set to 280bA and 630pA I could heat the motor in three runs from 0-100kph to 130C. During normal driving it only sometimes reached 140C where the controller starts to reduce power. I think this motor was maxed out in my heavy scooter.
The new QS10kW sees 400bA and 1400pA and it doesn't heat up as fast as the old 5kW Motor. I think this one could be feed with a little more power.
The old motor had 13mm² phase wires the new has 25mm² phase wires.
Yours has 2x20mm² phase wires, which will be capable of even more phase amps for short burst.
I would start with 1300pA and drive and see if it is accelerating fast enough for you, if not raise it to 1500pA and look if it heats to fast, if not ad another 100pA.

Heating of the motor depends on how long you apply high currents. Basic calculation for heating is I²xTime .
So 500A for 10 seconds will produce the same amount of heat in the motor as 1000A for 2.5 seconds.
But you only need high phase currents for acceleration and only at lower revs.

They sell your motor also with the ND962600 Controller.

The nominal phase current should be written in the datasheet from the manufacturer, but that current ist at nominal power at high revs for 24hours. That current will be around 200A.

This is all really great info. Thanks. The only thing I see about amps on the power chart thing they post is 287 for just about every RPM so it is pretty useless info. The motor is supposed to be a 1670RPM model. The guy at SAI told me I needed the ND961800 and not the 2600 so I went with that. Amorge made the battery with dual QS10 4 AWG discharge leads and said that is what I needed. Speaking of phase wires, mine has 6 of them. 2 of each color. I am assuming they get colocated and run to their respective colors on the controller. I keep reading stuff on here about 6 phase motors and dual controllers, but I am guessing that is not my case and I have a 3 phase motor. The wires with the coating are only 8mm. They must combine them all to get the 40mm claim.

 

[dominik h]

The 20kw motor is adverticed with 2x20mm² phase wires per phase, they go to the same connection in the motor and are paralelled, you have bought a standard 3 phase motor and for a scooter the nd961800 will be more than enough.

 

[tedo]

The 20kw motor is adverticed with 2x20mm² phase wires per phase, they go to the same connection in the motor and are paralelled, you have bought a standard 3 phase motor and for a scooter the nd961800 will be more than enough.

So the battery BMS claims 400a and 640 "peak amps". You suggest setting line amps to 380. Will I NEVER pull more amps than that? When do I use "peak amps" from the battery? Is that only an option if I wire up a boost switch? If I do not want to wire a boost switch can I just limit line amps with the speed selector and have speed 3 go up to the peak line amps? Say 380 in #2 speed and 600 in #3 speed?

 

[bananu7]

380A at 96V nominal will be... fast. I'd set it up like that, do a couple rides and see if you need more power at all.

 

[dominik h]

You can also set the 600A on speed 3 and 380A on speed 2, depending on how long your BMS can support peak current .

Or use the boost function, with a separate boost switch.
Or like I do, no speed switch used and no boost. I have set it to D and use my 400A on a full twist of the throttle. Everything else is regulated with the throttle.

 

[j bjork]

You can probably set up the bms with how long you can run your "peak amps", or at least see what it is set to if it is locked. Anyway, I dont think it will really be a problem because unless you have a really high top speed or something, you will only hit these kind of battery amps for a very few seconds.

 

[tedo]

You can probably set up the bms with how long you can run your "peak amps", or at least see what it is set to if it is locked. Anyway, I dont think it will really be a problem because unless you have a really high top speed or something, you will only hit these kind of battery amps for a very few seconds.

Thanks. I asked Miranda at Amorge what the duration is for peak amps so waiting on that reply. I like the idea of setting the amps higher than I need and limiting it with the speed switch. From what I read, the "output" percents in the speed limit both Line and Phase to a percent based off what I used for "Max". With that in mind my limiting feature is Phase Amps of 1500 at 100%. So I think I will make my Max Line Amps 470 then the line amps can be limiting by the speed switches to 350 and 400 still giving me good Phase Amps of 1125 and 1275. Then button 3 I can use for 100%. Just not sure what duration I can use it for yet at WOT. Learned that even though the controller is a ND961800 it is actually a Max Phase of 1500. The "race" version of that controller is 1800. Weird.

 

[dominik h]

Interessting, with the 721800 I have I can set 1800A, but my current clamp meter can measure only up to 900A , so no idea if it really does 1800A or only 1500A as I can not measurse it. For my scooter the set 1400A are enough.