## Kelly Phase Amps to Battery Amps

### Kelly Phase Amps to Battery Amps

Hey Guys,

I googled and couldn't find an answer that computes in my brain.

Kelly controllers are rated in phase amps (not to mention that they are rated mostly at 30s peak amps and not continues).

All I need is to know is by how much to divide the phase current rating to get the equivalent battery current rating.

I thought it was to divide by 3 but I guess it isn't exactly like that.

I googled and couldn't find an answer that computes in my brain.

Kelly controllers are rated in phase amps (not to mention that they are rated mostly at 30s peak amps and not continues).

All I need is to know is by how much to divide the phase current rating to get the equivalent battery current rating.

I thought it was to divide by 3 but I guess it isn't exactly like that.

Mongoose EC-D 2007 (18" motocross wheels), 21s 10Ah LiPo, Greentime 72V 110A Controller (soldered shunt), 9kg Hub Motor

### Re: Kelly Phase Amps to Battery Amps

"Phase amps" is really another way of saying "motor current". So the question is asking about the motor to battery current ratio.

The ratio is not fixed, it changes with motor back EMF, which is to say with speed. At low speed this ratio can become large like 10 or even more, while at full speed the ratio approaches 1. A middle value of 2.5 is often used as an "average" value, but this refers to a fairly low speed and is not a constant ratio.

The ratio is not fixed, it changes with motor back EMF, which is to say with speed. At low speed this ratio can become large like 10 or even more, while at full speed the ratio approaches 1. A middle value of 2.5 is often used as an "average" value, but this refers to a fairly low speed and is not a constant ratio.

### Re: Kelly Phase Amps to Battery Amps

Damn...so if I have a 500A motor current (30s and then continues is 200A) with a QS205 hub motor and a 72v LiIon pack (84V fully charged), how can this be calculated?Alan B wrote: ↑Jun 14 2018 5:54am"Phase amps" is really another way of saying "motor current". So the question is asking about the motor to battery current ratio.

The ratio is not fixed, it changes with motor back EMF, which is to say with speed. At low speed this ratio can become large like 10 or even more, while at full speed the ratio approaches 1. A middle value of 2.5 is often used as an "average" value, but this refers to a fairly low speed and is not a constant ratio.

I just need to know the average.

Mongoose EC-D 2007 (18" motocross wheels), 21s 10Ah LiPo, Greentime 72V 110A Controller (soldered shunt), 9kg Hub Motor

### Re: Kelly Phase Amps to Battery Amps

It depends on the throttle, the load, inertia, resistance of the motor, controller and battery. Best way to calculate that kind of thing is to use a model of the system and run it under different conditions, and gather info from that. Since it is not a constant, is the average even meaningful? Who cares and why?

Usually when something gets complicated like this it indicates that the wrong question is being asked in the first place. Why are we asking this question? Trying to size something?

Usually when something gets complicated like this it indicates that the wrong question is being asked in the first place. Why are we asking this question? Trying to size something?

### Re: Kelly Phase Amps to Battery Amps

If you want to compare the Kelly to other controllers that are rated on battery current, 3x would be pretty close.

"One test is worth a thousand opinions"

### Re: Kelly Phase Amps to Battery Amps

I sell controllers, so people are used to max battery amp draw, so if I speak in phase amps they wouldn't know if they battery would fit that controller.Alan B wrote: ↑Jun 14 2018 9:09amIt depends on the throttle, the load, inertia, resistance of the motor, controller and battery. Best way to calculate that kind of thing is to use a model of the system and run it under different conditions, and gather info from that. Since it is not a constant, is the average even meaningful? Who cares and why?

Usually when something gets complicated like this it indicates that the wrong question is being asked in the first place. Why are we asking this question? Trying to size something?

Also for me, I want to know the amount of power to expect, so if I'm used to a simple 100A controller that draws constant 100A from my battery then it's important if the Kelly controller can go only 60A constant while it's rated at 300-500A

Mongoose EC-D 2007 (18" motocross wheels), 21s 10Ah LiPo, Greentime 72V 110A Controller (soldered shunt), 9kg Hub Motor

### Re: Kelly Phase Amps to Battery Amps

It's not hard to figure out

The rest like 300A for 20Sec is just Bullshit anyways. Who the hell boasts about 20 Sec of peak power anyways?

if the 300A were temp based it would be a different story, but sadly it's not.

You simply multiply 120A*72V=8640W, which is maximum Continuous output.The rest like 300A for 20Sec is just Bullshit anyways. Who the hell boasts about 20 Sec of peak power anyways?

if the 300A were temp based it would be a different story, but sadly it's not.

### Re: Kelly Phase Amps to Battery Amps

I never asked how to calculate the wattage, we are talking about phase amps compared to battery amps which are not the same thing.

- skeetab5780 10 MW
**Posts:**2148**Joined:**Jun 15 2009 10:58pm**Location:**MA-
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### Re: Kelly Phase Amps to Battery Amps

an example with 55/130A kelly 72v rated controller

motor current: 80%

130A * 0,8 = 104A phase

battery current: 50%

104A * 0,5 = 52A battery

52a for 10sec boost and 26a continuous batt current

For different controllers just change the values

motor current: 80%

300A * 0,8 = 240A phase

battery current: 50%

240A * 0,5 = 120A battery

120a 20sec boost and 60a continuous batt current

motor current: 80%

130A * 0,8 = 104A phase

battery current: 50%

104A * 0,5 = 52A battery

52a for 10sec boost and 26a continuous batt current

For different controllers just change the values

motor current: 80%

300A * 0,8 = 240A phase

battery current: 50%

240A * 0,5 = 120A battery

120a 20sec boost and 60a continuous batt current

Youtube channel http://www.youtube.com/skeetab5780

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Kuberg Freerider Project https://endless-sphere.com/forums/viewt ... 28&t=90187

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### Re: Kelly Phase Amps to Battery Amps

The ratio varies, so there is no simple and exact answer for all cases.

However if you want a maximum battery current value then you can make some simplifying assumptions. The maximum battery current is nearly the same as the maximum motor current. The battery current will never be larger than the motor current.

One way to look at it is with speed ratios. If you are operating at half the maximum speed of the system, the current multiplication will be about two. This is due to power conservation. The power into the controller is essentially equal to the power out of the controller. At half speed the motor requires half the voltage, so the controller is stepping the battery voltage down by half, and thus multiplying the current by two. So in this case battery current will be half of motor current.

If you accelerate to a higher speed the voltage required by the motor (due to the back EMF) will increase and the current multiplication will drop. At top speed the multiplication will be essentially 1x, so battery current will equal motor current. This does not mean the current will be maximum at this point because the back EMF is preventing that, maximum current will be at a slightly lower speed when acceleration is still taking place. But the relationship between battery current and motor current will approach 1:1. Exactly where currents will peak and the ratio at that point will be dependent on a lot of things, but it is likely between 1:1 and 2:1.

For maximum performance the motor current capacity of the controller should be matched to the maximum current the motor can handle. The battery current available should be nearly as high if you want full performance. Make it equal to have some margin. If you plan to limit power somewhere in the controls then these values can be reduced.

However if you want a maximum battery current value then you can make some simplifying assumptions. The maximum battery current is nearly the same as the maximum motor current. The battery current will never be larger than the motor current.

One way to look at it is with speed ratios. If you are operating at half the maximum speed of the system, the current multiplication will be about two. This is due to power conservation. The power into the controller is essentially equal to the power out of the controller. At half speed the motor requires half the voltage, so the controller is stepping the battery voltage down by half, and thus multiplying the current by two. So in this case battery current will be half of motor current.

If you accelerate to a higher speed the voltage required by the motor (due to the back EMF) will increase and the current multiplication will drop. At top speed the multiplication will be essentially 1x, so battery current will equal motor current. This does not mean the current will be maximum at this point because the back EMF is preventing that, maximum current will be at a slightly lower speed when acceleration is still taking place. But the relationship between battery current and motor current will approach 1:1. Exactly where currents will peak and the ratio at that point will be dependent on a lot of things, but it is likely between 1:1 and 2:1.

For maximum performance the motor current capacity of the controller should be matched to the maximum current the motor can handle. The battery current available should be nearly as high if you want full performance. Make it equal to have some margin. If you plan to limit power somewhere in the controls then these values can be reduced.

### Re: Kelly Phase Amps to Battery Amps

Nice explanation Alan. But I think he just wanted to know what the max battery current was since he just read the peak phase current in the Controller description.

And as i pointed out, you can get the Info. if you read the last few lines in their description.

And as i pointed out, you can get the Info. if you read the last few lines in their description.

### Re: Kelly Phase Amps to Battery Amps

Good point, I've never messed with Kelly controllers. Always useful to read all the manufacturer's specs. And apply reasonable margins.

### Re: Kelly Phase Amps to Battery Amps

Hi guys,

A while back we discussed the relationship of battery current and motor current, phase current (rms) in a 3 phase motor. I took the standard 3 phase power formula and set it equal to the battery power (Vb * Ib). This assumes zero controller loss but should give a good approximation.

P = √3 * U * Irms * cosΘ

That is power in a 3-phase sinusoidal system. P in Watts, U is line to line RMS Voltage, Irms is RMS phase current and cosΘ is power factor.

Of course the battery power is Vb * Ib.

So, Vb * Ib = √3 * U * Irms * cosΘ

Or, Ib = √3 * (U/Vb) * Irms * cosΘ

With an inverter synthesized sinewave, the peak voltage cannot be greater than Vb, and the maximum RMS value of U = Vb/√2. Substitute that into the equation:

Ib = √3 * ((Vb/√2)/Vb) * Irms * cosΘ

Or, Ib = (√3/√2) * Irms * cosΘ = 1.24 * Irms * cosΘ

So it would appear that battery current can exceed RMS phase current at full voltage to the motor and when the power factor is better than 0.81. Of course this assumes no inverter losses for simplicity sake.

Originally posted here: http://www.diyelectriccar.com/forums/sh ... hp?t=92045

But there have been several threads on ES on the topic.

Also, I think Kelly attempts to output sinewave but most BLDC controls do not.

Regards,

major

A while back we discussed the relationship of battery current and motor current, phase current (rms) in a 3 phase motor. I took the standard 3 phase power formula and set it equal to the battery power (Vb * Ib). This assumes zero controller loss but should give a good approximation.

P = √3 * U * Irms * cosΘ

That is power in a 3-phase sinusoidal system. P in Watts, U is line to line RMS Voltage, Irms is RMS phase current and cosΘ is power factor.

Of course the battery power is Vb * Ib.

So, Vb * Ib = √3 * U * Irms * cosΘ

Or, Ib = √3 * (U/Vb) * Irms * cosΘ

With an inverter synthesized sinewave, the peak voltage cannot be greater than Vb, and the maximum RMS value of U = Vb/√2. Substitute that into the equation:

Ib = √3 * ((Vb/√2)/Vb) * Irms * cosΘ

Or, Ib = (√3/√2) * Irms * cosΘ = 1.24 * Irms * cosΘ

So it would appear that battery current can exceed RMS phase current at full voltage to the motor and when the power factor is better than 0.81. Of course this assumes no inverter losses for simplicity sake.

Originally posted here: http://www.diyelectriccar.com/forums/sh ... hp?t=92045

But there have been several threads on ES on the topic.

Also, I think Kelly attempts to output sinewave but most BLDC controls do not.

Regards,

major

### Re: Kelly Phase Amps to Battery Amps

Whats written below in the kelly website is phase current and not battery current, it's not the same thing and thats what we are discussing here.

To my question:

I understand that there is no simple formula but if you would be in a position like me of selling "regular" controllers that are rated at battery current, then how would you rate a kelly controller that is 500A for 20s and 200A constant to customers that only understand battery current?

### Re: Kelly Phase Amps to Battery Amps

i the next few weeks i will replace my current motor with a new 4kW QS hub. i already have a 300A KLS kelly controller.

the suggested currents ate 160A battery amps and 250~300 phase amps at 60V.

i will run it at 88V so i have to be a tad more conservative.

still, good for 15kW peak, should make it pretty brisk of the line.

i will do a capture with the scope and see the actual signal going to the motor. it should be sine wave. in any case it is virturally silent, a LOT better then regular PWM controllers.

the suggested currents ate 160A battery amps and 250~300 phase amps at 60V.

i will run it at 88V so i have to be a tad more conservative.

still, good for 15kW peak, should make it pretty brisk of the line.

i will do a capture with the scope and see the actual signal going to the motor. it should be sine wave. in any case it is virturally silent, a LOT better then regular PWM controllers.

Lithium beats liquid dinosaurs.

### Re: Kelly Phase Amps to Battery Amps

15kw? I guess you are talking about phase ampsflippy wrote: ↑Jun 15 2018 3:29ami the next few weeks i will replace my current motor with a new 4kW QS hub. i already have a 300A KLS kelly controller.

the suggested currents ate 160A battery amps and 250~300 phase amps at 60V.

i will run it at 88V so i have to be a tad more conservative.

still, good for 15kW peak, should make it pretty brisk of the line.

i will do a capture with the scope and see the actual signal going to the motor. it should be sine wave. in any case it is virturally silent, a LOT better then regular PWM controllers.

### Re: Kelly Phase Amps to Battery Amps

150 battery amps @ 85V.

Its a scooter, not a bike. battery is 4.2kWh, it can do 300+ amps continous.

Its a scooter, not a bike. battery is 4.2kWh, it can do 300+ amps continous.

Lithium beats liquid dinosaurs.

### Re: Kelly Phase Amps to Battery Amps

The system I was referring to was not sinewave, in the case that only two conductors have current at a time. Three phase systems use all three conductors simultaneously so equal power occurs at lower current compared to two wire systems as major's math shows. The OP didn't state which Kelly model or type they were interested in, so this is a valid point.major wrote: ↑Jun 14 2018 11:57pmHi guys,

A while back we discussed the relationship of battery current and motor current, phase current (rms) in a 3 phase motor. I took the standard 3 phase power formula and set it equal to the battery power (Vb * Ib). This assumes zero controller loss but should give a good approximation.

P = √3 * U * Irms * cosΘ

That is power in a 3-phase sinusoidal system. P in Watts, U is line to line RMS Voltage, Irms is RMS phase current and cosΘ is power factor.

Of course the battery power is Vb * Ib.

So, Vb * Ib = √3 * U * Irms * cosΘ

Or, Ib = √3 * (U/Vb) * Irms * cosΘ

With an inverter synthesized sinewave, the peak voltage cannot be greater than Vb, and the maximum RMS value of U = Vb/√2. Substitute that into the equation:

Ib = √3 * ((Vb/√2)/Vb) * Irms * cosΘ

Or, Ib = (√3/√2) * Irms * cosΘ = 1.24 * Irms * cosΘ

So it would appear that battery current can exceed RMS phase current at full voltage to the motor and when the power factor is better than 0.81. Of course this assumes no inverter losses for simplicity sake.

Originally posted here: http://www.diyelectriccar.com/forums/sh ... hp?t=92045

But there have been several threads on ES on the topic.

Also, I think Kelly attempts to output sinewave but most BLDC controls do not.

Regards,

major

Kelly makes a lot of controllers. Many are not sinewave.

Kelly's own FAQ shows a battery current vs motor current graph that shows battery current approaching but not exceeding motor current. This shows current multiplication from 5x at low speed tapering to 1x as speed is increased. The lower part of the graph where current multiplication exceeds 5x is not shown.

### Re: Kelly Phase Amps to Battery Amps

Its this model:Alan B wrote: ↑Jun 15 2018 8:03amThe system I was referring to was not sinewave, in the case that only two conductors have current at a time. Three phase systems use all three conductors simultaneously so equal power occurs at lower current compared to two wire systems as major's math shows. The OP didn't state which Kelly model or type they were interested in, so this is a valid point.major wrote: ↑Jun 14 2018 11:57pmHi guys,

A while back we discussed the relationship of battery current and motor current, phase current (rms) in a 3 phase motor. I took the standard 3 phase power formula and set it equal to the battery power (Vb * Ib). This assumes zero controller loss but should give a good approximation.

P = √3 * U * Irms * cosΘ

That is power in a 3-phase sinusoidal system. P in Watts, U is line to line RMS Voltage, Irms is RMS phase current and cosΘ is power factor.

Of course the battery power is Vb * Ib.

So, Vb * Ib = √3 * U * Irms * cosΘ

Or, Ib = √3 * (U/Vb) * Irms * cosΘ

With an inverter synthesized sinewave, the peak voltage cannot be greater than Vb, and the maximum RMS value of U = Vb/√2. Substitute that into the equation:

Ib = √3 * ((Vb/√2)/Vb) * Irms * cosΘ

Or, Ib = (√3/√2) * Irms * cosΘ = 1.24 * Irms * cosΘ

So it would appear that battery current can exceed RMS phase current at full voltage to the motor and when the power factor is better than 0.81. Of course this assumes no inverter losses for simplicity sake.

Originally posted here: http://www.diyelectriccar.com/forums/sh ... hp?t=92045

But there have been several threads on ES on the topic.

Also, I think Kelly attempts to output sinewave but most BLDC controls do not.

Regards,

major

Kelly makes a lot of controllers. Many are not sinewave.

Kelly's own FAQ shows a battery current vs motor current graph that shows battery current approaching but not exceeding motor current. This shows current multiplication from 5x at low speed tapering to 1x as speed is increased. The lower part of the graph where current multiplication exceeds 5x is not shown.

kellyMotorCurrentAndBatteryCurrent.JPG

http://kellycontroller.com/kls7275h24v- ... -1475.html

it seems by your graph that if I hit full throttle bursts then I will get 500A from the pack?!

### Re: Kelly Phase Amps to Battery Amps

Yes, for the first 30 seconds.

### Re: Kelly Phase Amps to Battery Amps

i think most motors will have reached their top speed before the 30sec mark.

with my old 1.5kW motor i do 0-30mph in under 5 seconds (limited to 150A phase) and with the new motor i expect to be well under 3. so any suggestions what i should do with the other 27 seconds?

Lithium beats liquid dinosaurs.

### Re: Kelly Phase Amps to Battery Amps

Not my graph, as stated earlier. Graph is from Kellys FAQ.

Just because a controller is rated to some current doesn't mean you will reach that current in a particular setup. The voltage, motor and wiring resistance, battery resistance, throttle setting, load, motor speed, etc also have to be right for the current to reach a particular value. The controller rating just means the controller components can handle it.

Just because a controller is rated to some current doesn't mean you will reach that current in a particular setup. The voltage, motor and wiring resistance, battery resistance, throttle setting, load, motor speed, etc also have to be right for the current to reach a particular value. The controller rating just means the controller components can handle it.

### Re: Kelly Phase Amps to Battery Amps

So in real life, which is the closest Kelly controller to a controller that is rated 100A continues battery current?

Also, what is the difference between these two kelly controllers?

http://kellycontroller.com/kls96501-808 ... -1356.html

http://kellycontroller.com/kls96501-808 ... -1485.html

They are rated 96V and below in the links it's written that it's rated for 18V-Nominal*1.25

Does that mean that they go up to 120V?

Also, what is the difference between these two kelly controllers?

http://kellycontroller.com/kls96501-808 ... -1356.html

http://kellycontroller.com/kls96501-808 ... -1485.html

They are rated 96V and below in the links it's written that it's rated for 18V-Nominal*1.25

Does that mean that they go up to 120V?

### Re: Kelly Phase Amps to Battery Amps

the H is not isolated.

and yes, 96V nominal means 120V max voltage. so 28S max series battery.

and yes, 96V nominal means 120V max voltage. so 28S max series battery.

Lithium beats liquid dinosaurs.