Phase Amps vs Battery Amps

Question regarding e bike power, the controller has phase amps and battery amps, the phase amps are dependent on terrain/load if im not mistaken, which typically means your phase amps will be more than the battery amps. Now my question, if you where to dyno a bike is the power going to be consistent with the phase amps or battery amps?


Example, 72v battery, pushing 250 battery amps, 450 phase amps, would you calculate the total power with phase amps or battery amps?


Battery amps = 72v x 250 = 18kw (24hp)

Phase Amps = 72v x 450 = 32kw (43hp)

andrewgreene said:

Question regarding e bike power, the controller has phase amps and battery amps,.....

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Actually the controller doesn't have any amps on it's own. It converts the usable current your battery can deliver. And it will do so up to something around what it is rated for. The amp hours in a battery are what it can store and has nothing to do with the controller.

As for your motor phase current property's, it also has nothing to do with the battery storage (amp hours or watt hours however you want to calculate it.) I also has nothing to do with the current ("amps") your controller can deliver. Your phases will, in a properly working motor, spin the motor in relation to the current provide by your controller up to a point of saturation, and - or overheating and shouting out.

So to answer your question, your dynamo HP is a combination of:
the battery C rate (current deliverable) to the controller
the controllers ability to convert it into a rated wattage
the motors ability to utilize the wattage to a maximum HP for the given motor.

There is no direct correlation between battery watt hours (amp hours), or controller ratings with phase amps. Any number of combinations of battery size or chemistry, controller watts, and motor types and sizes make that something you have to calculate for an estimation with what you have. That goes something like this.



If you want to very accurately know what your bike will do, you will need to put it on a dynamometer. And then know that as the battery ages, you numbers will go down.

e-beach said:

andrewgreene said:

Question regarding e bike power, the controller has phase amps and battery amps,.....

Click to expand...

Actually the controller doesn't have any amps on it's own. It converts the usable current your battery can deliver. And it will do so up to something around what it is rated for. The amp hours in a battery are what it can store and has nothing to do with the controller.

As for your motor phase current property's, it also has nothing to do with the battery storage (amp hours or watt hours however you want to calculate it.) I also has nothing to do with the current ("amps") your controller can deliver. Your phases will, in a properly working motor, spin the motor in relation to the current provide by your controller up to a point of saturation, and - or overheating and shouting out.

So to answer your question, your dynamo HP is a combination of:
the battery C rate (current deliverable) to the controller
the controllers ability to convert it into a rated wattage
the motors ability to utilize the wattage to a maximum HP for the given motor.

There is no direct correlation between battery watt hours (amp hours), or controller ratings with phase amps. Any number of combinations of battery size or chemistry, controller watts, and motor types and sizes make that something you have to calculate for an estimation with what you have. That goes something like this.

HP.jpg

If you want to very accurately know what your bike will do, you will need to put it on a dynamometer. And then know that as the battery ages, you numbers will go down.

Click to expand...

Thats quiet interesting, you've summed it up pretty well. Its going to take me a minute to understand it though lol.. Thanks

e-beach that is one excellent answer.

Hi guys,
This issue was discussed a short time ago.

major said:

3-phase power.
Here's a short study I did a while back, for a different reason, but it shows some basic formulas.

https://www.diyelectriccar.com/forums/showpost.php?p=376274&postcount=9

Regards,

major

Click to expand...

That post is here:
https://endless-sphere.com/forums/viewtopic.php?f=30&t=94975&p=1524093#p1524093
Unfortunately the OP had a breakdown or something, but some useful tidbits can still be found.
Regards,
major

andrewgreene said:

Example, 72v battery, pushing 250 battery amps, 450 phase amps, would you calculate the total power with phase amps or battery amps?


Battery amps = 72v x 250 = 18kw (24hp)

Phase Amps = 72v x 450 = 32kw (43hp)

Click to expand...

Note also the voltage will vary even on the battery side a bit

but much more drastically on the motor side,

power (watts) can stay at a constant max level, but "distributed" differently between V&A and waste heat

at slow rpm V gets very low, and amps get very high (maybe burn out the motor if hill too long & steep and/or too much weight)

john61ct said:

andrewgreene said:

Example, 72v battery, pushing 250 battery amps, 450 phase amps, would you calculate the total power with phase amps or battery amps?


Battery amps = 72v x 250 = 18kw (24hp)

Phase Amps = 72v x 450 = 32kw (43hp)

Click to expand...

.......

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Phase wires don't have amps, unless you are using regenerative breaking. Upon breaking some amount of watts are generated. If you want to test this statement, disconnect your phase wires, hold them in your hands and see if you get a terrible shock. You won't. Unless you spin the wheel. If you have 450 phase amps pulsing through your phase wires, it is coming from the controller.

Also, the battery stores energy an will do it's best to keep up with a load. The battery doesn't push amps on it's own. It needs a load.

yes obviously, talking about while motor is operating not sitting still

Either running or not. Batteries don't push their current while not connected to a load. That is what makes them batteries. If batteries pushed their current while not connected, then they would be useless as batteries. They would discharge into the atmosphere. And, they don't push their current while connected until a load is applied. Otherwise they would go dead while your bike is parked at the market, left on, while you are shopping. As for phase wires, just don't hold them and turn the wheel.

No one is saying sources push amps

No one is talking about touching anything.

andrewgreene said:

Now my question, if you where to dyno a bike is the power going to be consistent with the phase amps or battery amps?

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power is power.

has nothing to do with phase amps vs battery amps.

except for efficiency losses, it is not different in one place than another within a system.

the dyno will give you the actual power output at the tire/road interface. it doesn't indicate the power within the electrical system, just the work done by the wheel.

the electrical system power is higher than that, because some of that power is lost as heat within the battery, wiring, controller, wiring, motor, and tire, before it gets to the dyno to measure it. (or to the road to push you forward).

Example, 72v battery, pushing 250 battery amps, 450 phase amps, would you calculate the total power with phase amps or battery amps?

Battery amps = 72v x 250 = 18kw (24hp)

Phase Amps = 72v x 450 = 32kw (43hp)

Click to expand...

doesn't work that way. power is always power, you don't get more in the motor than you do the controller, you always get less, because of efficiency losses.


but if you wanted to calculate gross system power, you would use battery amps x battery volts.


if want to calculate motor power using amps and volts, you would have to measure the *motor* voltage on each phase, at the *same instant* as the *motor* current on each phase, or else you *cannot* use those numbers together in a calculation.

you cannot use battery voltage and motor amps, they do not have anything directly relatable.

e-beach said:

Phase wires don't have amps,

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phase wires "have amps" flowing thru them anytime the motor is rotating (except under one specific case) regardless of whether it is being powered by the controller or braked by the controller, as long as the phase wires are connected into a circuit that connects them all (via electronics or directly).

for all practical purposes, you can consider that current is flowing one direction or another in a motor's coils (and thus it's phase wires) anytime it is spinning.

so yes, phase wires do "have amps".

amberwolf said:

....so yes, phase wires do "have amps".

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I agree, when the motor is rotating. However, to say a motor has phase amps that horse power can be derived from is not accurate. The HP doesn't come from the phase wires. It comes from the motor, controller, battery combination while under power. On their own, sitting on a shelf, in a stater, with nothing else to do but collect dust, phase wires have no current or HP, or amps to be found in them. So phase wires don't "have amps" the amps come from some place else.

just a useless and annoying argument

as if this is a court of law

try actually adding some value to the community instead of wasting our time

john61ct said:

just a useless and annoying argument as if this is a court of law try actually adding some value to the community instead of wasting our time

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Who are you referring to with that snappy comment?

Another way to look at it is the power will be volts x amps. When the phase amps are greater than the battery amps, it's because the motor is under load and not spinning at full speed, so the voltage across the motor will be less than the battery voltage.

The battery (amps x volts) will always be slightly greater than the phase wire (amps x volts) because there are some losses in the system. The motor and controller work like a switching buck regulator to boost the amps when the voltage is lower on the motor.

If you put a bike on a dyno and measured the power output, you should see roughly the same number on the battery power vs the phase wire power.

e-beach said:

Who are you referring to with that snappy comment?

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Commenting on the text content, not meant to attack you.

Can I ask what that weird sig on every message is supposed to signify?

It means happy electricity to you.

andrewgreene said:

Question regarding e bike power, the controller has phase amps and battery amps, the phase amps are dependent on terrain/load if im not mistaken, which typically means your phase amps will be more than the battery amps. Now my question, if you where to dyno a bike is the power going to be consistent with the phase amps or battery amps?


Example, 72v battery, pushing 250 battery amps, 450 phase amps, would you calculate the total power with phase amps or battery amps?


Battery amps = 72v x 250 = 18kw (24hp)

Phase Amps = 72v x 450 = 32kw (43hp)

Click to expand...

To answer your question simply (rather than e-beach'es more detailed, some would even say more 'correct' answer):

Phase amps x battery volts is a meaningless calculation. For instance, a simple 'proof' is that you cant get more power out than you put in... so 32kw out cant happen when your input is 18kw. It is useless in general though, because as ebeach explains the motor amps bares no direct relation to the battery voltage.

Battery amps x input voltage gives you your input power to the controller, and is usually pretty close to the motor input power too. It can be used as a back of the envelope measure of your motors likely performance, but does not account for things like efficiency of your controller or motor, so is a very roundabout guide, and could be off by a factor of 10 or more. Put 18kw into a little 250W motor and you wont get 18kw out, more like 1kw at best (just for an example). The rest will be heat, and that motor will burn quickly. That said, input power (battery) is regularly used as a measuring stick of a bikes performance, and is often used due to the relative ease of measuring those values (battery V and A). So long as the motor isn't massively underspec'ed as in the above example, it does give a reasonable, ballpark indication to how the motor/bike will perform.

Phase amps are due primarily to:
1.the rpm of the motor (lower enables more ph amps to potentially flow - see limits below) - thus it can be load (terrain) dependent but 'terrain' is not what actually dictates phase amps...
2.the 'size' of the controller (a bigger controller can safely transfer more current to the motor without blowing itself up)
3.the 'size' of the battery - both voltage and its output capacity (higher voltage pushes more current through the motors phase-phase resistance + inductance, at higher rpms, higher output capacity enables this without destroying the battery)

Phase amps are limited by:
-increased rpm - as the motor spins it generates voltage across its phases - this voltage is directly opposed to the battery voltage, and a 'lower' battery voltage means less current can be 'pushed' through the motor - see point 3 above.
- a motors phase-phase resistance - a somewhat fixed perimeter that will increase as the motor heats up, reducing the max potential phase amps for a given rpm.
- the controller - depending on setup, the controller will try to feed x phase amps to the motor, it is the 'brain' in the system that governs the current flow. it does this by rapidly connecting/disconnecting the battery to the motor phases (thousands of times per second), so that it limits the phase current thanks to the inductance and resistance in the motor windings/phases, and any back EMF from the motor.

phase amps determine:
-the motors output torque. up to a certain point, the motors output torque is more or less directly proportional to the phase amps. Double the phase amps, you double the torque. There are some practical limits, ie at some point the motor will 'saturate' and the 1:1 ratio will be dramatically reduced such that doubling phase amps past that point may only result in 10% more torque.
-the motors heat - heat is proportional to the phase current squared... so doubling phase current quadruples the heat generated in the motor. There are other sources of heat, but this heat (called copper losses) are often the primary source.


putting it simply - (phase A) x (motor V) = (battery A) x (battery V) = (input power).... battery V can be viewed as somewhat 'fixed' - it will sag under load but will generally vary to only a small degree compared to the other parameters. As such to balance the equation and get more phase A than you have battery A - its necessary that the motor V is less than the battery V, by a proportional amount.

All of what I've stated above is not strictly 'true'/'accurate', and leaves out some nuance for the sake of simplicity - but should give a good laymen understanding of whats going on, and how each number relates to the other. In reality there's far more to it than what said here, and the # can thus be quite different to what you'd be able to calculate with the above, but it'll get you in the ballpark for 90% of cases.