Difference between phase amp and battery amp

[Uschi K.]

Hi,

I'm a bit puzzled and kindly ask for your help. I've a battery-pack that consists of 25s6p with 3,7V / 2250mAh per cell and a 5C rating. So per my understanding (yes, I know very limited) the total pack should be capable of 92,5V (hot of charger around 102V), 13,5Ah and 67,5A. So far so good ...

Now I've red about "battery amp" and "phase amp". battery amp should be 67,5A with my pack. What is the phase amp? Would it be possible to have higher phase amp (from controller to motor) then the battery amp is? I'm using a Lyen freeway controller. Thanks for your advise.

Cheers,
Uschi

 

[liveforphysics]

Your battery never see's phase current. Your FETs and motor ONLY see phase current.

The biggest factor I've seen for phase current multiplication is my size6 sevcon on deathbike pumping 660amps phase current while drawing 18amps from the pack (this is what happens when deathbike launches from a stop). That's a multiplier >30x. However, once I'm near top speed making peak power, the battery current creeps up to the mid-high 700amp range, while phase current stays ~660amps.

 

[John in CR]

LFP,

Can battery current really exceed phase current? How does that happen? Is the battery current pulsed while the inductance of the motor slows the phase current enough to be more of an average?

Your phase current multiplication is staggering. I have mine programmed for a 1.5:1 limit on the ratio, though I take it that actual can exceed programmed for a short time, but 30:1 is wow. I wouldn't mind 200-300A on 20A from the battery on launch, but 700A on your much bigger diameter motor is scary. Of course deathbike's ability to lift the front with your weight so far forward is to much for me. I'd want an inclineometer and anti-flip control before giving it a spin. I'm surprised you haven't done that already, so you could ride mono's out on deathbike.

 

[Hillhater]

But ..am i correct in thinking phase amps are not continuous, smooth DC current ?
it will be short "pulses" ( of some wave form), so the readings you see are "peak" most likely ?
Where as the battery current is a relatively smooth DC flow.

 

[liveforphysics]

LFP,

Can battery current really exceed phase current? How does that happen?

It's because the Sevcon's 660amp phase current rating is the RMS value of current on each of the 3 phase leads.

http://www.rapidtables.com/calc/electric/Amp_to_kW_Calculator.htm

"AC three phase amps to kilowatts calculation
The power P in kilowatts (kW) is equal to square root of 3 times the power factor FP times the current I in amps (A), times the line to line RMS voltage VL-L in volts (V) divided by 1000:
P(kW) = √3 × PF × I(A) × VL-L (V) / 1000"

The way it works out, once your motor is at a speed where the controller is no longer using PWM to buck phase current, battery current can reach a theoretical maximum of 1.73 (which is the root of 3) times phase current, but in practice it seldom exceeds ~1.5x, even with extreme timing advance at high RPMs (like deathbike uses).

 

[liveforphysics]

But ..am i correct in thinking phase amps are not continuous, smooth DC current ?
it will be short "pulses" ( of some wave form), so the readings you see are "peak" most likely ?
Where as the battery current is a relatively smooth DC flow.

The phase current on a Sevcon is shockingly close to a perfect sinus form, like >98% sinusoidal. The battery current is relatively smooth due to the controller caps filtering it pretty well.

 

[bigmoose]

I have always wanted to see scope traces of this phenomena. I always wondered if this was brought about by talking peak Phase amps versus average Battery Amps? We have to do the integrals right...

 

[liveforphysics]

I have always wanted to see scope traces of this phenomena. I always wondered if this was brought about by talking peak Phase amps versus average Battery Amps? We have to do the integrals right...

For additional info, you can put a cycle analyst with an appropriate sized shunt in series to watch phase current on a stock 2013 Zero with a size 4 that only does a peak of 420amps RMS phase current and watch battery current touch just under ~500amps. Should be capable of higher on paper, but it doesn't seem to get there in practice. Size 6's will draw high 700's (battery current), but I've never seen one break into 800A range.

 

[spinningmagnets]

I'd just like to double check my fuzzy understanding of phase/battery amp setting for common E-bikes...1.5:1 phase/battery starts out fairly easy (to reduce snapping teeth in an IGH, etc..no wheelies)... 2:1 launches a little harder... 3:1 phase/battery would be for wheelies and hard launches?

 

[bigmoose]

Do we agree that phase amps = battery amps at 100% duty cycle?

If we can't measure it, it would be great if one of the SPICE ACE's were to model it!

 

[John in CR]

I have always wanted to see scope traces of this phenomena. I always wondered if this was brought about by talking peak Phase amps versus average Battery Amps? We have to do the integrals right...

Unless voltage is different then that's what it feels like to me too, or do losses somehow fall out for the phase number?

 

[liveforphysics]

Do we agree that phase amps = battery amps at 100% duty cycle?

If we can't measure it, it would be great if one of the SPICE ACE's were to model it!

I can't agree, only because with the Sevcon, during "field weakening" (timing advance), you see Ibatt soar up while PWM duty stays fixed.

 

[bigmoose]

Luke, question still holds if PEAK phase amps = PEAK battery amps at 100% duty cycle, irregardless of timing.

I assume that your answer was based on the Sevcon holding the phase amps constant. ... I don't trust any "computed" instrument or current these days. What I mean by that is I am not sure what algorithm Justin has incorporated into the CA. Same goes for the Sevcon. Peak current, average current, RMS current, or some some variant...

The only way to know what is really there is two Tek A6304 Probes (500 Amps) with AM503B Matched Amplifiers (or their newer equivalents) and a dual trace scope one on the battery and one on a phase wire. Anyone ever make this measurement under load?

 

[Uschi K.]

Hi,

so what is your suggestion? Should I set the phase-amp to 1,5x battery-amp as a starting-point? Any additional suggestions to programm the controller to still have a (relativly) smooth start?
Kind regards

Lars

 

[izeman]

Hi,

so what is your suggestion? Should I set the phase-amp to 1,5x battery-amp as a starting-point? Any additional suggestions to programm the controller to still have a (relativly) smooth start?
Kind regards

Lars

hi lars. this depends on your motor. you didn't mention it, but i guess you mentioned a cromotor or similar DD hub for your raptor build.
1.5x is very conservative. you could start with that. some suggest upping this to 1:2.5 or 1:3 even.
of course you have to keep in mind that the higher the phase amp, the higher is the load to carry for the wires and windings. so heavy stop and go will heat up the motor quicker the higher your phase amps are set. phase wires (AND connectors!!) need to be up to the higher amps. 5.5mm gold bullets and 10 awg wires are the minimum it would use for it. i melt the insulation of 4mm bullets with a 60/120a setting.
i would go to 1:2 and see how you like it. if you're fine with it keep it