## Watts = MPH eMotorcycle

General Discussion about large electric scooters and motorcycles and other things with no pedals.
noahpodolefsky
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### Re: Watts = MPH eMotorcycle

Your graphs are interesting, but there's no new information. They are just the derivative of an Ah vs V graph (the manufacturer's graphs turned sideways). The reason you have a spike is because the V vs Ah graph is flat there. If you invert the standard discharge curve, you'll see that the slope is highest at the peak in your graph.

The only way voltage will tell you capacity is to match to a data table at the exact same load. If your table is for .2C, then it only works for .2 C. If you're at 5C or 0 C the map is totally different.

Really, try what I said. Discharge two cells differently then measure the resting voltage.
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DrkAngel
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### Re: Watts = MPH eMotorcycle

noahpodolefsky wrote:The only way voltage will tell you capacity is to match to a data table at the exact same load. If your table is for .2C, then it only works for .2 C. If you're at 5C or 0 C the map is totally different.
Shift graph +.02V for reasonable accurate 0C.
Shift graph -.03V for reasonable accurate .5C. 55MPH cruising usage.

Voltage fuel level is designed to be measured at 0C, but is easily adaptable.
At higher "C" the lower and higher voltages would shift more than the "beefier" center of the discharge curve.
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noahpodolefsky
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### Re: Watts = MPH eMotorcycle

Sorry, its just not that simple. I'm happy to explain, but only if you're interested in learning why.
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neptronix
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### Re: Watts = MPH eMotorcycle

Ah, someone's trying to take up my job of arguing with the village idiot again i see.
But he is right in 1 way, and wrong in many others.

http://neptronix.org/forumpics/lipotuto ... hanics.gif

Already argued with drkangel about this one, but that's what a proper discharge graph looks like, and you can indeed tell what your SOC is with any 3.6-3.85v nominal type chemistry as they're generally all slopey as pictured ( this is a zippy brand RC lipo pack, of course turnigy looks exactly the same. ).

Lifepo4, nicad, SLA, NiMH, etc are all a bit different.

Get a proper discharge curve of your battery and you WILL know your SOC per voltage at no-load.
Any quality piece of battery charging or balancing equipment can produce this.

But this mah per 100th V is a stupid way of measuring things.
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noahpodolefsky
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### Re: Watts = MPH eMotorcycle

neptronix wrote:Ah, someone's trying to take up my job of arguing with the village idiot again i see.
I guess so...seems like a tough nut to crack...
But he is right in 1 way, and wrong in many others.

http://neptronix.org/forumpics/lipotuto ... hanics.gif

Already argued with drkangel about this one, but that's what a proper discharge graph looks like, and you can indeed tell what your SOC is with any 3.6-3.85v nominal type chemistry as they're generally all slopey as pictured ( this is a zippy brand RC lipo pack, of course turnigy looks exactly the same. ).

Lifepo4, nicad, SLA, NiMH, etc are all a bit different.

Get a proper discharge curve of your battery and you WILL know your SOC per voltage at no-load.
Any quality piece of battery charging or balancing equipment can produce this.
I agree, sort of. You need a curve where you discharge, then remove the load at regular intervals and let the voltage pop back up. (is that the red line in your chart?)

But then, resting voltage isn't instant, so if you have some zero load calibrated guage on your bike, how do you know if you've got a good reading if you only stop for a second or two? It can take a few minutes to hit the actual resting voltage. On top of that, the amount of energy you get out of a cell depends on the discharge rate, so you have to know what the C-rate was during all of the discharge to know what the SOC actually is (and since C-rate is never constant in the real world, it gets *really* hard to estimate from voltage alone). Just saying, it's not trivial.

I've got discharge curves for my lifepo4's (GBS). 60 Ah, and pulling 0.5C they hit 2.65V at exactly 2 hr (pretty much spot on spec). Then I disconnect the load, and they pop back up above 3V. I haven't actually done a graph of zero load at regular time intervals. I'll try that next time I have my discharge set up going (voltmeter and a strand of nichrome wire )

All I know is that my pack sits at about 80V and even after 25-50% discharge, if it sits for a few minutes it pops back up to about 80V. Pack voltage at zero load tells me almost nothing about SOC.

Maybe lipo is different, I have less experience with them (but I have some packs laying around that I'm going to start messing with just to learn).
But this mah per 100th V is a stupid way of measuring things.
Definitely agree with that. It's interesting to think about what it tells you, but seems mostly academic to me. It's redundant information of a normal discharge curve (but worse because it's misleading).

cheers
Last edited by noahpodolefsky on Nov 28, 2011 7:47 am, edited 1 time in total.
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DrkAngel
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### Re: Watts = MPH eMotorcycle

neptronix wrote:
Neptograph.JPG (40.4 KiB) Viewed 1885 times
Already argued with drkangel about this one, but that's what a proper discharge graph looks like, and you can indeed tell what your SOC is with any 3.6-3.85v nominal type chemistry as they're generally all slopey as pictured ( this is a zippy brand RC lipo pack, of course turnigy looks exactly the same. ).
How can you possibly tell the SOC (State Of Charge) when there is no Ah, or mAh, reference, or given factor?

If your graphs look alike, "as they're generally all slopey as pictured", and some "looks exactly the same", then your graphs don't seem to be telling you much.
One of my major gripes with this type of graph is that, a "truly" flat line would indicate infinite energy, an "almost" flat line might indicate 100x the energy of a "nearly" flat line.
Which, I, consider to be, ridiculously inaccurate.
Most all scientific advances are due to increases in degrees of precision.
I regard "Nepto-slopey" graphs as poor, lazy, maybe just sloppy, science.

The neptronix graph - pictured above - is possibly, among the most pitiable ... just look at it!
The odd mix of over, and under, information makes a nice mess.

There is, more information, than can be gleaned from - look alike "slopey" graphs!
For Example:

(Both, bottom of the discharge curves, would probably meet at 3.3V, at near 5mAh/100th V, I just didn't feel the need for, additional, deep discharge damage.)

On a "Nepto-slopey" graph, one would look a little flatter in the middle, the other, flatter near the bottom, giving little indication as to the degree of increased energy density, at differing voltages, during discharge.
Last edited by DrkAngel on Nov 28, 2011 11:15 am, edited 8 times in total.
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noahpodolefsky
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### Re: Watts = MPH eMotorcycle

One of my major gripes with this type of graph is that, a "truly" flat line would indicate infinite energy, an "almost" flat line might indicate 100x the energy of a "nearly" flat line.
Which, I, consider to be, ridiculously inaccurate.
It's not inaccurate, it's how lithium batteries work. Some have are flatter than others.

You seem to think that energy exists "between" 100ths of a V. This is wrong. You just happen to get mAh out at those voltages because of how your are collecting the data.

Anyway, seems like people have tried to explain all this, so I'm not going to waste any more time with it.

Have a nice time, and please be safe with those lico cells.
-Noah

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DrkAngel
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### Re: Watts = MPH eMotorcycle

noahpodolefsky wrote:
DrkAngel wrote:One of my major gripes with this type of graph is that, a "truly" flat line would indicate infinite energy, an "almost" flat line might indicate 100x the energy of a "nearly" flat line.
Which, I, consider to be, ridiculously inaccurate.
It's not inaccurate, it's how lithium batteries work. Some have are flatter than others.

You seem to think that energy exists "between" 100ths of a V. This is wrong. You just happen to get mAh out at those voltages because of how your are collecting the data.

Anyway, seems like people have tried to explain all this, so I'm not going to waste any more time with it.

Have a nice time, and please be safe with those lico cells.
Sorry, you just don't seem to be making any sense.
Get some sleep, and try again in the morning?
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noahpodolefsky
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### Re: Watts = MPH eMotorcycle

meh
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Jozzer
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### Re: Watts = MPH eMotorcycle

Just...buy a Cycle Analyst so you can see exactlyt how many amphours you use. Worth every penny, and will help you learn much from your EV..
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liveforphysics
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### Re: Watts = MPH eMotorcycle

DrkAngel wrote: How can you possibly tell the SOC (State Of Charge) when there is no Ah, or mAh, reference, or given factor?

If your graphs look alike, "as they're generally all slopey as pictured", and some "looks exactly the same", then your graphs don't seem to be telling you much.
One of my major gripes with this type of graph is that, a "truly" flat line would indicate infinite energy, an "almost" flat line might indicate 100x the energy of a "nearly" flat line.
Which, I, consider to be, ridiculously inaccurate.
Most all scientific advances are due to increases in degrees of precision.
I regard "Nepto-slopey" graphs as poor, lazy, maybe just sloppy, science.
Once again, I'm going to assume you're kidding, because nobody can be this stupid.

Did you know for many LiFePO4 cells, the slope not only can be flat, but goes UP in voltage as the discharge continues? (because the cell heats and Ri drops, or for Nickel, because ) Does that mean it's not only infinite energy, but it's making new energy? LOL
The x axis is time, which knowing the discharge rate (constant current) gives you capacity, but in a graph comparing a batch of cells in a pack as this one does, it doesn't matter what the numbers are, the purpose is to give you an idea of how matched the cells are.

This whole thing is so stupid though, I'm convinced you're just trolling, and I should quit taking the bait and ignore it.
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DrkAngel
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### Re: Watts = MPH eMotorcycle

liveforphysics wrote:
DrkAngel wrote: How can you possibly tell the SOC (State Of Charge) when there is no Ah, or mAh, reference, or given factor?
One of my major gripes with this type of graph is that, a "truly" flat line would indicate infinite energy, an "almost" flat line might indicate 100x the energy of a "nearly" flat line.
Which, I, consider to be, ridiculously inaccurate.
Most all scientific advances are due to increases in degrees of precision.
I regard "Nepto-slopey" graphs as poor, lazy, maybe just sloppy, science.
liveforphysics wrote:Did you know for many LiFePO4 cells, the slope not only can be flat, but goes UP in voltage as the discharge continues? (because the cell heats and Ri drops,

Which would make these "Nepto-slopey" graphs, worse than useless, for determining SOC!
Last edited by DrkAngel on Nov 29, 2011 8:25 am, edited 5 times in total.
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noahpodolefsky
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### Re: Watts = MPH eMotorcycle

fer chrissake...

can i declare this thread (un)officially closed?

maybe put a warning on page one, beware all ye who enter...by the time you get to page 3 you will be stupider.
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neptronix
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### Re: Watts = MPH eMotorcycle

I'm starting to believe that drkangel is a troll too.
I was thinking Idiot savant, but that's actually a compliment in one way which is apparently not deserved.

constant 8 amp draw, 5 amp hour pack, and a marker of the time at the bottom.. if you can't figure that out, you're retarded or trolling. The line is too blurry to tell.
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DrkAngel
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### Re: Watts = MPH eMotorcycle

neptronix wrote:constant 8 amp draw, 5 amp hour pack, and a marker of the time at the bottom.. if you can't figure that out, you're retarded or trolling. The line is too blurry to tell.
Damn! .... 5 amp pack, 8 amp draw for 30 min. = only 4Ah at a wimpy 1.6C discharge rate?
About 6 months ago, you claimed your 5Ah pack was outputting 5Ah+, more than 100% of rated, at a, I believe, 10C discharge rate.

Oops!
Found his post.
Postby neptronix » Mon Mar 14, 2011 12:41 am
neptronix wrote: Lipo gives me 100% of it's rated capacity at the 7C i have been discharging it at lately.
Now, it outputs, only 80% of rated, at a wimpy 1.6C discharge rate?
You must have really abused it for the past 6 months to damage it so severely.

Wait? ... No! ... your graph was made 5/15/2011 - 6 months ago ...

It would appear someone has been guilty of ... exaggeration? ...
Making up, falsifying, statistics? ...
Distorting the truth ... to "prove" their point ...
for the purpose of ... ?

Not for the first time, either!
Last edited by DrkAngel on Jun 17, 2012 8:27 pm, edited 5 times in total.
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Gow864
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### Re: Watts = MPH eMotorcycle

@neptronix, If this guy isn't listening to you, then just walk away. the name calling is antagonistic, childish and frocked! and it really doesn't put you in a good light.

I suppose you hoping for all the "like" minds to join in so you can have some fun. Can you guess what I'm calling you now?

Gow.

noahpodolefsky
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### Re: Watts = MPH eMotorcycle

Last edited by noahpodolefsky on Nov 30, 2011 12:45 pm, edited 1 time in total.
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### Re: Watts = MPH eMotorcycle

DrkAngel
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### Re: Watts = MPH eMotorcycle

DrkAngel wrote:
liveforphysics wrote:
DrkAngel wrote: How can you possibly tell the SOC (State Of Charge) when there is no Ah, or mAh, reference, or given factor?
One of my major gripes with this type of graph is that, a "truly" flat line would indicate infinite energy, an "almost" flat line might indicate 100x the energy of a "nearly" flat line.
Which, I, consider to be, ridiculously inaccurate.
Most all scientific advances are due to increases in degrees of precision.
I regard "Nepto-slopey" graphs as poor, lazy, maybe just sloppy, science.
liveforphysics wrote:Did you know for many LiFePO4 cells, the slope not only can be flat, but goes UP in voltage as the discharge continues? (because the cell heats and Ri drops,

Which would make these "Nepto-slopey" graphs, worse than useless, for determining SOC!
And more proof that, high C rate, discharge graphs, are ... worthless!
The cells heat up , due to excessive-damaging discharge rates - right?
Lithium technology, at reasonable charge-discharge rates, does not produce the waste heat that is common with SLA, NiMH, NiCd etc.
Non-defective lithium cells can "heat up" but this is due to excessive charge-discharge rates, or overly high-low voltages!
Lithium ion cells, typically charge at 97-99% efficiency = 1-3% waste heat, with a similar discharge efficiency, possible, but only with moderate discharge "C" rates.
If your lithium cells get hot, even warm, you are exceeding efficient use - damaging.

With a cheap-inefficient charger, cells may get warm, with heat conducted from charger.
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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liveforphysics
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### Re: Watts = MPH eMotorcycle

DrkAngel wrote: The cells heat up , due to excessive-damaging discharge rates - right?
Lithium technology, at reasonable charge-discharge rates, does not produce the waste heat that is common with SLA, NiMH, NiCd etc.
Non-defective lithium cells can "heat up" but this is due to excessive charge-discharge rates, or overly high-low voltages!
Lithium ion cells, typically charge at 97-99% efficiency = 1-3% waste heat, with a similar discharge efficiency, possible, but only with moderate discharge "C" rates.
If your lithium cells get hot, even warm, you are exceeding efficient use - damaging.

I can't believe you're not just trolling, but for the sake of other poor souls who might read this and believe it, I will clear up another of the messes you post.

A battery heats up because it has resistance, and you're passing current through it.
The energy that goes into waste heat is directly proportional with it's resistance.

For example, if you have a cell with a 50mOhm Ri (Internal Resistance), and you discharge it at 10amps, your voltage drop will be 0.5v, and the energy going into heating the cell will therefore be 1watt (0.5v*10a). You can also use I^2*Ri. (this 5watts is energy that was stored in the cell as potential energy, but is wasted in resistive heating of the cell, because every cell has internal resistance, and any amount of current, large or small, through any resistance, large or small, will have voltage drop, and heating equal to the voltage drop times the current)

If you have a nano-tech cell with a 0.8mOhm Ri, and you discharge at 10amps, your voltage drop is 0.008v, and your heating is 0.08watts.
If you discharge your nano-tech cell at 100amps, you have 0.08v of drop, and your heating is 8watts.

If you're using the best 18650 laptop cell on the market, the 3.1Ah NCR18650R, you've got 92mOhm of Ri. So, you discharge at 10amps, and you get 0.92v of sag, and 9.2watts of heating (which is going to make at pretty blazing hot in a minute or two). Discharge at 5amps, you get 0.46v of sag, and 2.3watts of heating.

If you take normal cheapo HK 5AH LiPo with an Ri of 5mOhm, and discharge it at 10amps, you get 0.05v of sag, and 0.5watts of heating. Discharge it at 20amps, you get 0.1v of sag and 2watts of heating. Discharge it at 30amps and you get 0.15v of sag and 4.5watts of heating. Discharge it at 40amps and you get 0.2v of sag and 8watts of heating. Lets look at that 8watts of heating number.

It's ~134g for that 5Ah LiPo cell. You're heating it at 8watts at 40amp discharge.

The best 18650 cell, NCR18650 is 45g, and 5amps (1.6C discharge), it's making 2.3watts of heating.

The specific heat capacity (the amount of energy per gram it takes to change a degree in temp) is roughly identical for both cells.

The difference in mass is 3x, the difference in heating is ~3.2x, over the course of a discharge, these cells would track each others temperature almost exactly, the LiPo cell at 8 times higher discharge current would finish ever so slightly warmer in this example.

Getting cells warm is a good thing. You don't want to store them warm for extended periods, because it decreases calendar life from accelerating the rate the solvents decompose, however, if you're using the cell, warm is better for the cell and MUCH better for the performance. This is why the Volt and Tesla have heating systems in there batteries, and why they won't even allow it to charge while its too cold etc.
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noahpodolefsky
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### Re: Watts = MPH eMotorcycle

I don't think he's trolling...just confused.

I agree with everything liveforphysics said, with a couple of additions.

Warm is good, hot is bad. The resistance of a cell isn't actually resistance is the usual sense, it's related the number of ions available to move across the cell. That's why a warm cell has a lower Ri, because at high temperature the chemical reaction produces more ions. (This is the opposite of "ohmic" resistance in a wire, where resistance *increases* as the wire gets warmer).

There's a 2nd mechanism that adds to resistance which has to do with diffusion of ions (called the Warburg element, related to the Peukert effect). It's why you get less Ah out when you discharge at a higher rate.

Hot is bad because it breaks down the electrolyte which forms a coating on the anode, which takes Li out of the system, lowers capacity and increases Ri.

There are two main components to battery temperature - energy in (heating) and energy out (cooling). The temperature will go up if heating > cooling (and down if heating < cooling). If heating = cooling, then the battery is dissipating energy as fast as it is making it and the temperature is constant. All else equal, smaller batteries can dissipate heat better because they have a larger ratio of surface area / volume.

Key variables are specific heat and thermal conductivity of the battery materials, battery construction and size, and ambient temperature. But there are so many variables, you pretty much have to measure things empirically for every battery type (which is why those plots are so *useful*).
Last edited by noahpodolefsky on Nov 30, 2011 7:22 am, edited 1 time in total.
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noahpodolefsky
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### Re: Watts = MPH eMotorcycle

Maybe too late - but this thread started with a pretty basic question about power and speed. I think we're kind of off topic (largely my fault, sorry).
-Noah

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DrkAngel
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### Re: Watts = MPH eMotorcycle

noahpodolefsky wrote:
DrkAngel wrote: Voltage is a great indicator ... at zero throttle.
All my graphs were made at minimal discharge rates (.2C), specifically, to minimize the distortion of "voltage sag".
Just have to coast for a couple seconds, to get good reading.
Try this - take two equal cells both fully charged. Discharge one 500 mAh, the other 1000 mAh. Now let them rest for a minute or two, then measure the voltage.

Let me know what you get.
Even better?
Discharge 1 cell 500mah, record discharge Voltage.
Then remove drain, record voltage at 2 sec, 1 min, 2 min intervals.

Discharge another 500mAh ... record ... repeat ...
repeat ...
repeat ...
repeat ... etc.

Removes possibility of cell variance, gives a decent map through the discharge curve.
Last edited by DrkAngel on Dec 04, 2011 12:47 am, edited 2 times in total.
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There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

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Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

### Voltage Rebounding

It has been, rather firmly insisted, that voltage has no relation to, SOC, capacity.
Also, there is adamant assertion that, there is some extreme voltage "recovery" time, after drain is stopped.
Most odd, is the statement that "Voltage is pretty constant through discharge." ... ?
In an effort to help debunk these myths, I propose the following...

"Voltage rebound" test.
A battery, not being drained, possesses a resting, or static voltage, with fully charged standard Li-ion cells this voltage is 4.2 volts, (rated).
The voltage of a battery tends to "sag" under use, drain, draw etc.
This sag is amplified, mainly by the degree of draw, but also, by the duration.
Different types of battery recover, or rebound, (return to a static-resting voltage), at different rates.
The purpose of the following test is to demonstrate, the voltage to residual capacity comparison, and ,the voltage recovery-rebound characteristics of lithium ion Cobalt cells, my most popular battery pack component.

2600mAh 18650 LiCo, Recycled, Red, "China", from Gateway Laptop
Discharged - iMax B6
Voltage measured at cell with digital voltage meter.
4.25V (pack lists cells at 3.6V, but has good mAh density, right to 4.2V+ )

500 mAh discharge rate
.2C drain - 500mAh discharge iMax B6 = 35mph cruising drain (projected build)

500 mAh drain ... [ < ............ Recovery ............. > ]
mAh .. Drain V ... 2 sec. ... 30 sec. ... 1 min. ... 2 min.
500 .... 3.98V .... 4.03V ..... xxxx .... 4.05V .... 4.06V - 80%
1000 ... 3.85V .... 3.90V ..... xxxx .... 3.92V .... 3.93V - 60%
1500 ... 3.75V .... 3.81V ..... xxxx .... 3.82V .... 3.83V - 40%
2000 ... 3.70V .... 3.75V ..... xxxx .... 3.77V .... 3.78V - 20%
2500 ... 3.65V .... 3.70V ..... xxxx .... 3.71V .... 3.72V - empty - w/reserve

1000 mAh discharge rate
.4C drain - 1Ah discharge iMax B6 = 50mph cruising drain (projected build)

1000 mAh drain . [ < ............ Recovery ............. > ]
mAh .. Drain V ... 2 sec. ... 30 sec. ... 1 min. ... 2 min.
500 .... 3.89V .... 3.99V ..... 4.02V .... 4.03V .... 4.04V - 75%
1000 ... 3.74V .... 3.84V ..... 3.87V .... 3.88V .... 3.89V - 50%
1500 ... 3.64V .... 3.74V ..... 3.76V .... 3.78V .... 3.79V - 25%
2000 ... 3.56V .... 3.66V ..... 3.70V .... 3.71V .... 3.72V - empty - w/reserve
2500 ... 3.21V .... 3.42V ..... 3.51V .... 3.56V .... 3.60V - Voltage sags badly - past usable
note: Apparently greater "draw" decreases output efficiency, however, there was no, noticed, cell heat production ... ?
Additional, possibly factors, for apparent, reduced capacity: Ambient air temperature might be the factor, 500mAh test was run at ~70F, 1000mAh at ~65F, temperature can greatly affect cell capacity and output capability!; (Typically, for Winter, I keep my packs warm in insulated bags.); Same cell as used in 500mAh test.

1000mAh test run immediately after charge light turned green.
Cell might not have received proper saturation charge?

Except at, nearing empty ...
Voltage rebound is very quick and relatively effective, at 2 seconds!
Longer "voltage rebound" times, are minor ... and very predictable-consistent!
Surprisingly, 1 minute - 2 minute "rebound" voltage increases, are identical, whether taken at .2C, or at a doubled .4C.

Given these stats, I could very easily gauge remaining fuel, by voltage, 2 second rebound, or 1 minute, for high accuracy.
Wow ... 30 seconds, looks just as accurate as 2 minutes!
Should have tested at shorter times, (between 2 sec & 30 sec)!

Will test my Lithium ion Cobalt (LiPo) cells next.
Comparison of electrolyte stabilization media should be interesting.
Last edited by DrkAngel on Mar 30, 2014 10:38 am, edited 3 times in total.
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parabellum
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Posts: 1993
Joined: Nov 19, 2010 9:55 am
Location: Dominican Republic, north.

### Re: Watts = MPH eMotorcycle

There is very easy way to know how much is left in the pack by going simple step by step procedure. (for bulk handling)

1) much cells IR, or just take cells with similar IR (so they behave similar in same discharge rates)
2) measure cells capacity under average planed C rate and make parallel strings (put all the batteries on the floor from lowest to highest and take 1 from 1 end next from other (or 2 and 2 or 3 and 3 and so on, to same string)
3) discharge the pack from full until lowest cell group hits the desired LVC. Remember the current drawn and discharged voltage value.

It is all actually needed. Amps and LVC should come close together on every full discharge (which is not recommended).