Moving Away From Heavy E-Bikes

[PCeBiker]

That's a computer generated graph.
It's too square and chunky and all the spikes are evenly spaced.
It's a list of samples and averages.

 

[Stefan Mikes]

That's a computer generated graph.
It's too square and chunky and all the spikes are evenly spaced.
It's a list of samples and averages.

This is from the e-bike RAW data. I could of course add the markers. Why not?

Battery Voltage On A Ride As Function of Battery Percentage.

Criteria for the graph:
-- Coasting filtered out
-- Single Assistance Level (Eco)

Unlike hub-drive motors, mid-drives operate with variable power. It makes all the voltage sag discussion irrelevant. (It is noteworthy the motor could draw even 280+ W at the 12% of the battery charge. Note the voltage was pretty low at that battery %).

 

[PCeBiker]

All ebikes vary the power to maintain a PAS level speed.
My geared hub motor was using ~170 Watts to go downwind and ~450 Watts to come back upwind at the same speed. Each way the Watt meter was bouncing around trying to maintain the set speed.

I'm actually trying to find a way to get my controller to put out a constant power but I'm finding it difficult to do.

I don't care what speed I'm going, I just want it to put out say, ~100 Watts continuously and I don't think I can set up my controller/display to do that?

That second red graph looks more like a real time graph, but the dots suggest sampling and the computer drew the curve.

 

[PCeBiker]

In the end, cell resistance(and resulting sag) is what defines the life of a battery (assuming no individual cells have died yet)

Can you explain to me how a bad cell can lead to a fire?
I assume it becomes overcharged then gets hot?

 

[linklemming]

This is from the e-bike RAW data. I could of course add the markers. Why not?



View attachment 150398
Battery Voltage On A Ride As Function of Battery Percentage.

View attachment 150399
Criteria for the graph:
-- Coasting filtered out
-- Single Assistance Level (Eco)

Unlike hub-drive motors, mid-drives operate with variable power. It makes all the voltage sag discussion irrelevant. (It is noteworthy the motor could draw even 280+ W at the 12% of the battery charge. Note the voltage was pretty low at that battery %).

Sorry but that is not raw data at least in the engineering sense but interpolated data over time. Raw data would occur at something like 60Hz (or higher) meaning there would be thousands of values. Simple computer sampling theory.

Most likely, it keeps track of voltage when not supplying power and averages that over time. If advanced, it could determine cell resistance based off voltage at various loads, in any sense it would still be averaged.

All this can be found in the TSDZ2 open source software code, I doubt specialized/brose has gotten around well understood physics

Your last statement is completely false and actually moreso on your(and mine) 36V bike compared to most chinese 48V systems.

Voltage sag under load is identical for my BBSHD, GMAC and DD motors using the same battery under the same load

 

[linklemming]

Can you explain to me how a bad cell can lead to a fire?
I assume it becomes overcharged then gets hot?

I havnt looked into it much so Im definately not the expert on cell failure, especially when charging.

That being said, I am concerned about failure that can occur due to shorted cells. For a parallel section, if a cell shorts, all the other cells dump their current into the shorted cell causing it overheat and potentially catch on fire. No BMS can account for this. I try to only use batteries that have individually fused cells like em3ev and luna(wolf), pretty sure the big 4 are using fused cells as well.

I sold a Juiced CCX to a neighbor last year with upgraded GMAC motor and he has ridden the snot out of it and the battery probably has 9k miles on it now. Just a few weeks ago, it stopped balancing charge anymore as noted by his satiator charger. Not sure what that means but I convinced him to get a new battery

 

[Stefan Mikes]

Sorry but that is not raw data at least in the engineering sense but interpolated data over time. Raw data would occur at something like 60Hz (or higher) meaning there would be thousands of values. Simple computer sampling theory.

Most likely, it keeps track of voltage when not supplying power and averages that over time. If advanced, it could determine cell resistance based off voltage at various loads, in any sense it would still be averaged.

All this can be found in the TSDZ2 open source software code, I doubt specialized/brose has gotten around well understood physics

Your last statement is completely false and actually moreso on your(and mine) 36V bike compared to most chinese 48V systems.

Voltage sag under load is identical for my BBSHD, GMAC and DD motors using the same battery under the same load

What you are saying here is a pure sophistry (translated to Simple English: Bullshit).

An industrial Distributed Control System (DCS) has a resolution (sampling frequency) of 1 s. The sampling frequency of the Specialized system is 1 s, too. It seems you know very little of Measurement & Control.

Are you trying to tell me your voltmeter gives your eyes the sampling frequency of 60 Hz? Ha. Ha. Ha.

 

[PCeBiker]

That being said, I am concerned about failure that can occur due to shorted cells.

So I assume it's possible for a cell to short itself out internally?

 

[PCeBiker]

Are you trying to tell me your voltmeter gives your eyes the sampling frequency of 60 Hz? Ha. Ha. Ha.

That raw data could be fed to a voltmeter and it will show you the "average", but the average is done very fast, like 2 or 3 times a second or more.

My needle voltmeter samples continuously but is a tiny bit "averaged" due to the mass of the needle and the time it takes to accelerate it.

Some needle meters are in fluid to smooth out the movement so they aren't so twitchy.

 

[PCeBiker]

An industrial Distributed Control System (DCS) has a resolution (sampling frequency) of 1 s. The sampling frequency of the Specialized system is 1 s, too. It seems you know very little of Measurement & Control.

Your graphs aren't showing every 1 second sample.
I count about 90 dots on your red graph.
You didn't drain a fully charged battery to 10% in a minute and a half.


If you hooked up a voltmeter directly to your battery you would see the real time voltage as it is happening, not what the computer decides to show you on a screen.

 

[linklemming]

What you are saying here is a pure sophistry (translated to Simple English: Bullshit).

An industrial Distributed Control System (DCS) has a resolution (sampling frequency) of 1 s. The sampling frequency of the Specialized system is 1 s, too. It seems you know very little of Measurement & Control.

Are you trying to tell me your voltmeter gives your eyes the sampling frequency of 60 Hz? Ha. Ha. Ha.

Are you actually trying to imply that all sampling in the world occurs at 1Hz. Thats an insane and completely false claim. I have worked in the embedded software industry for well over 35 years including avionics flight controls, measurement, test, simulation and most recently spacecraft attitude and control.

They all use sampling frequencies based on the desired inputs, performance, accuracy and hardware used. I can provide examples all day long.

https://www.sciencedirect.com/topics/engineering/nyquist-theorem#:~:text=Nyquist's%20theorem%20states%20that%20a,higher%20than%20this%20is%20necessary.

I never implied anything about my eyes and 60Hz, you need to stop being so emotional when presented with facts

Most likely the display has a refresh rate lower than 60Hz anywho

 

[linklemming]

Your graphs aren't showing every 1 second sample.
I count about 90 dots on your red graph.
You didn't drain a fully charged battery to 10% in a minute and a half.

Its pretty common knowledge in the RC industry that 18650 cells shouldnt be totally discharged in less that 1/2 hour due to their high internal resistance.

I have used High Current RC Lipo packs for FPV drone flying and discharged them in a minute...they usually puff and dont work anymore..sometimes catching on fire

 

[linklemming]

If you hooked up a voltmeter directly to your battery you would see the real time voltage as it is happening, not what the computer decides to show you on a screen.

Most likely, the data being shown while sampled at 1Hz(by the app) is sampled at higher frequencies within the embedded firmware within the motor and then averaged according to some criteria (of which I have mentioned previously). That data (before being averaged) is what is considered RAW data in any engineering discipline.

I cant believe we are even debating this

 

[PCeBiker]

I've got to reduce my sampling rate.

I spend more time looking at the display than looking at the road.

I think I'll cover it with duct tape once I get it set up. Lol

 

[PCeBiker]

When a cell overheats it overrides the "vent" so to speak and it cascades very quickly, oft times taking the rest with it

I assume a bad cell is more inclined to overheat?

 

[linklemming]

When a cell overheats it overrides the "vent" so to speak and it cascades very quickly, oft times taking the rest with it

Interestingly on a pack that had a bad cell and required disposal, I disassembled it to individual cells and discharged each one with a small automotive light bulb.

How did I know each cell was done?, you could hear the noise of the cell venting when the voltage got low enough

 

[PCeBiker]

Ohh,..
I figured that they would vent when they overcharged?
Started to boil or something like that.

 

[Stefan Mikes]

Most likely, the data being shown while sampled at 1Hz(by the app) is sampled at higher frequencies within the embedded firmware within the motor and then averaged according to some criteria (of which I have mentioned previously). That data (before being averaged) is what is considered RAW data in any engineering discipline.

I cant believe we are even debating this

My whole point was the voltmeter was not needed at all for a high quality mid-drive motor e-bike. All you need is a reliable battery %, possibly Wh remaining in the battery, and maybe the W/km (or mile) data field. The new Specialized Mastermind e-bikes have all such data available for display, including a reliable Range Remaining and Range Trend (that is, whether you are losing or gaining Range depending on the current ride conditions). Add to it MicroTune (adjusting the assistance in small increments as you ride) and Smart Control (ensure you will make your ride goal still with the battery charge), and it is more than most e-bikes can provide. For a practical cyclist, the Cadence and Rider's Power fields are extremely important, and not found on many e-bikes.

Now, could you show me similar charts to what I showed before? Or, you are just tawking?

 

[PDoz]

My whole point was the voltmeter was not needed at all for a high quality mid-drive motor e-bike. All you need is a reliable battery %, possibly Wh remaining in the battery, and maybe the W/km (or mile) data field. The new Specialized Mastermind e-bikes have all such data available for display, including a reliable Range Remaining and Range Trend (that is, whether you are losing or gaining Range depending on the current ride conditions). Add to it MicroTune (adjusting the assistance in small increments as you ride) and Smart Control (ensure you will make your ride goal still with the battery charge), and it is more than most e-bikes can provide. For a practical cyclist, the Cadence and Rider's Power fields are extremely important, and not found on many e-bikes.

Now, could you show me similar charts to what I showed before? Or, you are just tawking?

nah, you just need a light bike that rides well so it's fine if the battery is flat.

 

[Stefan Mikes]

nah, you just need a light bike that rides well so it's fine if the battery is flat.

I own one Still, I prefer some assistance.

It happened to me to pedal each of two heavy e-bikes I own/ed unpowered, either in rough terrain (Trance E+) or upwind (Vado). It was because riding the Giant Auto mode had just been a silly idea (Trance) or the electronics was obsolete at that time and the system hung (Vado).

I have never been out of the battery juice afterwards.

20th July 2020. After having had ridden for 10 km unpowered on Giant Trance E+ through the marshes, lost (the wet phone with GPS went bananas), in torrential rain. Never ever again! (Strava, thank you for helping my memory!) Note: I dropped my e-bike on the wrong side; I had had enough!