Author Topic: Battery question for begginers  (Read 6165 times)

Offline Ayalmilo

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Battery question for begginers
« on: July 31, 2013, 06:52:50 PM »
Hi to all

Case 1 :two batteries one is 48v 6.6 ah and the second is 48v. 12ah
Lets say that both have the same max and continuous discharge rate.
Apart from the  longer distance that the second battery  will yield ,how. About the other parameters such as top speed ,acceleration.. Are these going to be the same in both batteries?

Second question is  when they say that the Smart Pie top power is 400w.if I use a  lifepo4 battery  48v 12ah with max discharge  continuous of 25ah. That means 48*25 which is close to 900w ,is the motor able to absorb this power?

Thanks for your kind answers

Offline Leslie

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Re: Battery question for begginers
« Reply #1 on: August 11, 2013, 10:19:15 AM »
The first answer is, with more AH behind your output, will lower your full circuit resistance.  Expect slightly better system efficiency, much better battery efficiency, thus a much longer battery life, and a tad more top speed against the wind and up hills on max programmed controller settings, because the paralleled batteries will slump less volts under heavier loads.

The power through the controller is limited via a shunt that controls the controllers pulses time width "PWM" (Pulse Width Modulation) at each phase switching, so the differences between batteries are only cosmetic from the controller stage unless you change the programming or shunt resistance values.


The answer to question 2 is, yes and no.

The motor is dumb.  It can absorb 1000's of watts at any given moment of time, what makes the Smart Pie so smart is the controller I believe.   So if you change nothing in the controller, do not raise the battery voltage, or rewind the motor, then the answer is No! More AH will not make the motor more powerful with a small controller set to factory settings.

Its a controller thing that is limiting the motor. 

Now the better question is, if you manage to get more than 400 watts into your Smart Pie, how "LONG" will the motor tolerate the load?  You can run these motors much higher than their rating depending on what you use them for.

The larger motors I reckon for most people, its safe up to 2 kilowatts at 48v, too much current, can flex the coils and they wear out, plus at the lower voltages, the impedance of the motor may cause heat pushing massive wads of amps through the copper parallel winding strands.  The Pie is not wound with lots of conductor strands, so lower volts at stupid high currents with a big load will see more heat than with higher volts at lower current.

The MP runs most efficient with most controllers between 36v and 72v between 25 to 50 amps.

These medium sized MP3's will run fine at common voltages at 50 amps for most people, but not so much with the controllers.

The smaller mini motors, I wouldn't go over 18 amps and 36v. 


And for the HBS series 30 amps at 48v is plenty.

It depends on your average riding, for example hills, wind, and rider weight.

I carry some heavy loads often.  I found a well tuned Pie can pull a lot of weight limited perfectly and the motor will not get hot.  Maybe a little more slowly, but the MP hubs definitely have the diesel motor power thing going on for their weight class.

If you want more speed, you need to increase the voltage.  This will give you both more torque and speed. As to why voltage can give torque on our motors, but more amps dosent give more speed "research induction, wind resistance, ion engines and dev your own theory.   

1v @ 1 miliamp can get you moving at the speed of light if you have enough time and almost zero resistance, but not down here on earth.

Mass Speed, Torque, and Resistance has a linked relationship with Voltage, Current and electrical Resistance in motors.


For instance, it is commonly said that more current offer more torque, however, to drive a motor faster one requires more torque.

It is the way we view torque when we parallel our packs or series the mix up occurs.  Torque too is a physical attribute of mass, through the electromagnetic conversion process, can be paralleled, or series as current is an integral and essential component of any higher voltage induction that does occurs when stacking voltage cells up to higher potentials.  When you add a series pack you still get that packs amp hour in watts, and that amp hour torque thus must be is translated into the speed, as you get to your destination faster, you save amp hours.

Our controllers performance can exploit a lot of the interactions between amps/torque/voltage/speed, and pull of some neat tricks, and our batteries can make us go nice and fast, but it work up to a point where the worst enemy of all hits us, and this is the big hills and wind resistances.   

Batteries simply do not yet have the tech or energy density to do this big hill climb or impossible break neck speeds very well.  If we could make a battery 3 times lighter, then we will be competing with some good source.
« Last Edit: August 11, 2013, 11:05:08 AM by Les »

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Offline MAGICPIE3FOCUSPOWER

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Re: Battery question for begginers
« Reply #2 on: August 11, 2013, 10:27:44 AM »
Don't forget the BMS, that's the main problem for battery output.

Offline Leslie

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Re: Battery question for begginers
« Reply #3 on: August 11, 2013, 11:05:36 AM »
Like Amps is a component of Voltage, Torque is a component of Speed.  Vice-verse if you must, but you can not have one without the other.  Imagine testing voltage with your probes if no current passed through them, it cant be done, just as you can not have mass traveling at a speed without an amount of  torque applied to overcome initial inertia, and maintain momentum against kinetic losses that the mass experiences due to frictions, resistances and maybe some predictable spacial entropy down the track relevant to light year calculations..

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Offline Leslie

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Re: Battery question for begginers
« Reply #4 on: August 11, 2013, 11:17:18 AM »
Oh yes.  I totally bypass my BMS FETS n Shunts.  But those shunts will pass loads more current than the battery will manage.

The BMS shunts are on the negative terminal, there is a slight V drop over them, if a huge load is experienced, a larger drop occurs over the shunts, which triggers a switching circuit to switch your BMS fets off, before anything gets toasty.  BMS shunts are used for over current protection, not so fast for the short circuit protection at 48v though.

If you were to bypass the BMS fet gate, and latch to it always on, the battery would be able to make the BMS fets catch on fire with a heavy enough load.
« Last Edit: August 11, 2013, 11:26:16 AM by Les »

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Offline Leslie

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Re: Battery question for begginers
« Reply #5 on: August 11, 2013, 11:35:07 AM »


Here is a LiFePo4 battery management system we call a BMS.

See the shunts mentioned, they are the long shiny bars soldered on the bottom right section of this circuit board.

These SHUNTS limit the battery's output from large loads that could damage the transistors lined along the fare right edge of the PCB.   The transistors are used for switching the battery off when you over charge or discharge the pack, its called LVC and HVC (low-high voltage protection).


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Offline Leslie

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Re: Battery question for begginers
« Reply #6 on: August 11, 2013, 11:45:21 AM »
Hey just thought of a way to do short circuit protection.  One conductor requires a minimal shielding strand, this shielding runs to the switching circuit, and we can detect voltage potential differences before they arc and have the power shut down.
« Last Edit: August 11, 2013, 11:48:38 AM by Les »

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Offline Morgen 3Eman

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Re: Battery question for begginers
« Reply #7 on: August 11, 2013, 06:47:26 PM »
Hi  Les,

WHAT!???

TTFN,
Dennis

Offline Leslie

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Re: Battery question for begginers
« Reply #8 on: August 12, 2013, 06:46:57 PM »
Dennis could you stop being so rude and bullying me on theses forums?

Please.
« Last Edit: August 12, 2013, 07:05:27 PM by Les »

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Offline Bikemad

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Re: Battery question for beginners
« Reply #9 on: August 13, 2013, 02:47:12 AM »
Les, there is a huge difference between expressing a lack of understanding regarding something that has posted and bullying.
Having read your initial post about short circuit protection I can totally understand where Dennis is coming from, as Dennis appears to have written exactly what I was thinking.

I find it hard to comprehend how expressing disbelief or not understanding something you have posted could possibly be misconstrued as bullying, and I'm pretty sure that anyone else reading this thread will have seen no indication of any bullying whatsoever.

Alan
 

Offline BikeSlob

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Re: Battery question for begginers
« Reply #10 on: August 13, 2013, 04:47:10 AM »
Well, I'm bookmarking this thread. I very good place for me to start understanding my new MP3's 48v10ah battery.