Kelly Phase Amps to Battery Amps

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rg12   10 kW

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Kelly Phase Amps to Battery Amps

Post by rg12 » Jun 14 2018 5:23am

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

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Re: Kelly Phase Amps to Battery Amps

Post by Alan B » 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.

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Re: Kelly Phase Amps to Battery Amps

Post by rg12 » Jun 14 2018 8:34am

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.
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?
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

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Re: Kelly Phase Amps to Battery Amps

Post by Alan B » Jun 14 2018 9:09am

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?

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Re: Kelly Phase Amps to Battery Amps

Post by fechter » Jun 14 2018 10:01am

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

Post by rg12 » Jun 14 2018 2:28pm

Alan B wrote:
Jun 14 2018 9:09am
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?
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.
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

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Re: Kelly Phase Amps to Battery Amps

Post by eee291 » Jun 14 2018 4:28pm

It's not hard to figure out
kukuk.PNG
kukuk.PNG (26.4 KiB) Viewed 744 times
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? :lol:
if the 300A were temp based it would be a different story, but sadly it's not.

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Re: Kelly Phase Amps to Battery Amps

Post by rg12 » Jun 14 2018 5:31pm

I never asked how to calculate the wattage, we are talking about phase amps compared to battery amps which are not the same thing.
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Re: Kelly Phase Amps to Battery Amps

Post by skeetab5780 » Jun 14 2018 5:49pm

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

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Re: Kelly Phase Amps to Battery Amps

Post by Alan B » Jun 14 2018 6:04pm

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.

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Re: Kelly Phase Amps to Battery Amps

Post by eee291 » Jun 14 2018 6:32pm

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.

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Re: Kelly Phase Amps to Battery Amps

Post by Alan B » Jun 14 2018 7:06pm

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

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Re: Kelly Phase Amps to Battery Amps

Post by major » Jun 14 2018 11:57pm

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

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Re: Kelly Phase Amps to Battery Amps

Post by rg12 » Jun 15 2018 3:25am

eee291 wrote:
Jun 14 2018 6:32pm
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.
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?
Mongoose EC-D 2007 (18" motocross wheels), 21s 10Ah LiPo, Greentime 72V 110A Controller (soldered shunt), 9kg Hub Motor

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Re: Kelly Phase Amps to Battery Amps

Post by flippy » Jun 15 2018 3:29am

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. :mrgreen:

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.
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Re: Kelly Phase Amps to Battery Amps

Post by rg12 » Jun 15 2018 5:15am

flippy wrote:
Jun 15 2018 3:29am
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. :mrgreen:

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.
15kw? I guess you are talking about phase amps
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Re: Kelly Phase Amps to Battery Amps

Post by flippy » Jun 15 2018 5:20am

150 battery amps @ 85V. :mrgreen:

Its a scooter, not a bike. battery is 4.2kWh, it can do 300+ amps continous.
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Re: Kelly Phase Amps to Battery Amps

Post by Alan B » Jun 15 2018 8:03am

major wrote:
Jun 14 2018 11:57pm
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
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.

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
Kelly motor vs battery current graph
kellyMotorCurrentAndBatteryCurrent.JPG (30.72 KiB) Viewed 676 times

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Re: Kelly Phase Amps to Battery Amps

Post by rg12 » Jun 15 2018 9:16am

Alan B wrote:
Jun 15 2018 8:03am
major wrote:
Jun 14 2018 11:57pm
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
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.

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
Its this model:
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?!
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Re: Kelly Phase Amps to Battery Amps

Post by eee291 » Jun 15 2018 9:56am

Yes, for the first 30 seconds.

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Re: Kelly Phase Amps to Battery Amps

Post by flippy » Jun 15 2018 10:27am

eee291 wrote:
Jun 15 2018 9:56am
Yes, for the first 30 seconds.
i think most motors will have reached their top speed before the 30sec mark. :wink:

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? :mrgreen:
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Re: Kelly Phase Amps to Battery Amps

Post by eee291 » Jun 15 2018 10:38am

flippy wrote:
Jun 15 2018 10:27am
eee291 wrote:
Jun 15 2018 9:56am
Yes, for the first 30 seconds.
i think most motors will have reached their top speed before the 30sec mark. :wink:
Yes, but not the next time you accelerate.

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Re: Kelly Phase Amps to Battery Amps

Post by Alan B » Jun 16 2018 12:49am

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.

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Re: Kelly Phase Amps to Battery Amps

Post by rg12 » Jun 18 2018 11:59am

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?
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Re: Kelly Phase Amps to Battery Amps

Post by flippy » Jun 18 2018 12:29pm

the H is not isolated.
and yes, 96V nominal means 120V max voltage. so 28S max series battery.
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