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Gotway MSX battery safety margin

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Posted (edited)

Hi guys, I'm starting to get the range on the battery where I would like to understand what kind of margins I have left.  does anyone here know what kind of margins I need to leave when I'm running there and back on a fairly level path (I know this is subjective) ?  I've been returning and have about 65% battery at the halfway point, however that leaves me with 30% of the battery capacity when I return home which may be too much.  I'd like to extend my journeys a bit longer (assuming my feet can deal with it!) however I don't know how much battery I need to leave as margin.   I don't want to run the battery out on my return home.

 

Any thoughts or ideas all welcome.

 

by the way I'm getting to ranges of about 50 miles at this point with about 30% capacity left.  This is reported by darknessbot.

Edited by Gazza-usa

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7 minutes ago, Gazza-usa said:

Hi guys, I'm starting to get the range on the battery where I would like to understand what kind of margins I have left.  does anyone here know what kind of margins I need to leave when I'm running there and back I fairly level path ?

This should depend very much on your maximum and average riding speed, anf on your other accelerations behaviour...

You'll see a big difference if you drive constantly 20 km/h or mostly 40 km/h with many neck btaking accelerations.

11 minutes ago, Gazza-usa said:

i've been returning my have about 65% battery however that leaves me with 30% of the battery capacity when I return home which may be too much.

If you have some "established driving patterns" for most of your tracks note the used capacity and milage and you'll know.

And you'll see if you have about fairly constant Wh/km numbers or wildly varying on mood...

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Posted (edited)
35 minutes ago, Chriull said:

This should depend very much on your maximum and average riding speed, anf on your other accelerations behaviour...

You'll see a big difference if you drive constantly 20 km/h or mostly 40 km/h with many neck btaking accelerations.

If you have some "established driving patterns" for most of your tracks note the used capacity and milage and you'll know.

And you'll see if you have about fairly constant Wh/km numbers or wildly varying on mood...

Thanks.  I haven't figured in my speed demon moments!!   Typically I do a fairly consistent 15mph on my regular runs.  I'm pushing my distances now since I'm more comfortable with my riding skills and stamina.  I'm just trying to figure out what kind of distances I can realistically get without running out of power.   Maybe I'll just have to incrementally push it and then do some top-off runs locally to see how far I can push it.  I'm not an aggressive rider,  more of a cruiser but as time goes on I'm sure I'll get a bit more cocky.  I've started dropping off curbs now !!

Edited by Gazza-usa

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12 minutes ago, Gazza-usa said:

Thanks.  I haven't figured in the my speed demon moments!!   Typically I do a fairly consistent 15mph on my regular runs.  I'm pushing my distances now since I'm more comfortable with my riding skills and stamina.  I'm just trying to figure out what kind of distances I can realistically get without running out of power.   Maybe I'll just have to incrementally push it and then do some top-off runs locally to see how far I can push it.  I'm not an aggressive rider,  more of a cruiser but as time goes on I'm sure I'll get a bit more cocky.  I've started dropping off curbs now !!

You could always take off on a normal one way trip and just keep going until it stops? Have someone ready to call (if you carry a phone) or stay within walk of a bus route or something? Ima have to do this for myself very soon, as I have yet to ride until stranded and would really like to know. Only way to be sure is to ride like normal as your weight and habits differ than ours. Maybe pick a windy day and ride into the wind, so your mileage is conservative?

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16 minutes ago, ShanesPlanet said:

You could always take off on a normal one way trip and just keep going until it stops? Have someone ready to call (if you carry a phone) or stay within walk of a bus route or something? Ima have to do this for myself very soon, as I have yet to ride until stranded and would really like to know. Only way to be sure is to ride like normal as your weight and habits differ than ours. Maybe pick a windy day and ride into the wind, so your mileage is conservative?

It's always windy where I am 😉  If not on the outbound it will be on the return.  Very consistent weather by me.

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14 hours ago, Rywokast said:

gotway only lets the batteries drain to 3.3V.. unless youre consistently arriving home with less than 10% battery remaining i wouldnt worry about it at all.. thats why the speed throttling on them is usually negligible until youre literally scraping the bottom of the barrel

Thanks.  So in essence you are saying that you can drain down to 0% without causing damage to the batteries as this isn't really 0% battery charge ?

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Posted (edited)
1 hour ago, Gazza-usa said:

Thanks.  So in essence you are saying that you can drain down to 0% without causing damage to the batteries as this isn't really 0% battery charge ?

absolutely.. its nowhere near the minimum recommended voltage.. its not bad at all for the batteries, BUT it is not extremely safe to always be riding that low thats why it slows you down.. because minimum voltage or not, gotway says 3.3 is minimum so you should act accordingly, just take it easy if youre below 10%

Edited by Rywokast

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I have ridden my MSX down to 5% many times. Since the tilt-back begins when the level reaches 0%, one is forced to ride very gently and economically at that point. But otherwise the wheel feels and behaves just the same it does on 100% battery, so at least small bumps haven’t been an issue.

I always go chill as the battery level decreases, it’s what I consider to be the safe approach.

 For the absolute maximum range the only way is to ride it down to zero to learn what the end of the range is like. Maybe ride tightening circles around your destination to avoid having to walk for too long?

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As a note, charging your battery to 80% instead of 100% (4.00V vs 4.20V) tends to double the life (batteries are usually rated at 500 full cycles, I'm hearing in EUCs they last about 300). Discharging to only 30% (3.77V) instead of 0% (3.27V) should also  double thier life. That would take your battery life from 300 cycles to 1,200 cycles, although your trips would be about the distance you're tanking now. 

Remember that since the cells are in series and don't like to be over or under-charged, its good to balance charge them regularly. I've heard the figure "every third charge," and that seems really reasonable to not put undue stress on a slightly less ambitious cell.

Hope this helps! 

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18 minutes ago, WI_Hedgehog said:

As a note, charging your battery to 80% instead of 100% (4.00V vs 4.20V) tends to double the life (batteries are usually rated at 500 full cycles, I'm hearing in EUCs they last about 300). Discharging to only 30% (3.77V) instead of 0% (3.27V) should also  double thier life. That would take your battery life from 300 cycles to 1,200 cycles, although your trips would be about the distance you're tanking now. 

Remember that since the cells are in series and don't like to be over or under-charged, its good to balance charge them regularly. I've heard the figure "every third charge," and that seems really reasonable to not put undue stress on a slightly less ambitious cell.

Hope this helps! 

SO setting my charger to 4.0 vs 4.2 will double the life of my batteries? How much % of range is lost as I read something about the higher voltage carrying more distance than lower. Not in a linear fashion. Double the life of a battery sounds great, especially if its at less than 10% loss in mileage. Fwiw, I never discharge below 20% and rarely below 60%.

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12 hours ago, mrelwood said:

I have ridden my MSX down to 5% many times. Since the tilt-back begins when the level reaches 0%, one is forced to ride very gently and economically at that point. But otherwise the wheel feels and behaves just the same it does on 100% battery, so at least small bumps haven’t been an issue.

 

Do you know at approximately what percent your wheel starts beeping?  I got my first "low voltage" alert last weekend ("more than 14.4km/h, low voltage, 3 beeps every 2 seconds" - according to the beep code thread) and I'm not really sure how much margin I actually had left.  The wheel didn't feel any different other than the beeping.

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Charging "slower" creates less stress on the battery, so while a fast charge of 1C is safe, it tends to heat the battery and cook the chemicals inside, wearing it out sooner. 0.5C is generally the fastest I've seen suggested, with 0.1C being optimal. This seems to be why EUCs come with "slow" chargers. It's true slow chargers are cheaper, but when you're buying a $2,000 wheel the extra $10, $20, or $50 it would cost the manufacturer to upgrade the charger isn't a huge consideration...a much faster charger would be &$10 more, faster yet another $10... Slow chargers are present less risk of fire, and since many people charge their wheels without closely watching them, slow charging is much safer.

4 hours ago, ShanesPlanet said:

SO setting my charger to 4.0 vs 4.2 will double the life of my batteries? How much % of range is lost as I read something about the higher voltage carrying more distance than lower. Not in a linear fashion.

 

Exactly right, a little more voltage on top results in far more power. In racing we used to charge past 4.2V to 4.35V because of the insane power (with almost no voltage fade) the batteries had. The batteries lasted for 2 to 4 races on the same day (recharging to 4.35V between races), but then they were trash. So if you wanted to win, the cost was $60 in batteries (and a possible LiPo fire).

So figure charging to 4.35V per cell is incredible power and range, a chance of fire, and the batteries should last 4 charges. 4.20V/cell is great power & range, 500 charges, and almost no chance of catching fire. The cells should be able to be charged 500 times, so the convention is a maximum voltage of 4.20V/cell. BUT, if you charge to 4.00V/cell the cells last for 1,000 charges. You lose 20% capacity, so will roll 20% less distance on your wheel. There are a lot of discussions around this, several of them on this site, so they're easy to find. The convention is charge to 80% capacity which is about 4.00V (depending on the cell it's 3.98V to 4.02V) and you'll gain 2x the number of recharges. 

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I'm reading the ECU guys are getting three times the battery life by charging to 80%, probably based on the discharge profile. I don't know if that's always the case, but figure the batteries will last 2x to 3x as many charges.

The same is said of the low end, and I've seen that myself. Electric motors draw power, so as the voltage falls they draw more current (P=I*E). Current flow heats everything up, especially the batteries, again shortening their life. Gotway cuts off the battery at 3.30V, King Song at 3.00V. There is voltage sag under load, but as you can see from the chart, in general King Song batteries will last longer, and in practice they often seem to. If you use your batteries until they're at a resting voltage of 3.75V or so, they should last 2x as long as if you run them down to 3.27V. Again, you'll give up another 20% of your range, but your batteries will last 2-3x as long, which is a good part of why I'm hearing "Buy the biggest battery you can afford" over and over again--the EUC will last longer if you stress the battery less. (And if you crash it less, but that one seems obvious...) 

Temperature plays a large part, but that's also getting off on a tangent... 

I'm also reading EUCs are hard on batteries and only get about 300 recharges if the pack is run full-charge to near-empty. I think that's due to the packs being largely parallel. When the whole pack is discharged to about 3.00V/cell, and one cell is a bit weak, it is stressed to say 2.98V, shortening its life. Next time it's stressed to 2.97V, and next 2.96V. I think that cell keeps getting weaker at a faster rate and stressing the other cells in parallel with it, so eventually that parallel branch goes to 2.2V/cell while the rest of the pack is at 3.1V/cell. This is why balancing is important, and a few guys here are watching how low their parallel branches go. 

If a branch is going low, there are two choices: 1.) Don't run your battery to 0%, and 2.) over-charge the branch. If each branch is balanced charged at 4.00V/cell, charge up the weak one to 4.05V, and it won't get run down so far.

The first is optimal, don't work the branch of cells so hard. 

The second option extends the life of the branch, kind of balancing out EUC range with the natural wear of the cells. Instead of a branch going way low, now a branch is just a little high, and a little low, and lasts a lot longer. There's a thread around here somewhere about how to build a cheap 1-cell charger from a USB power brick and an 1-cell charging circuit. 

All this is a little more effort, but if an EUC battery pack is expected to last 2-3 years AND costs $1,200 to replace, well, I'd rather save myself that money every 2-3 years with a little more effort. 

 

 

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15 hours ago, BarrettJ said:

Do you know at approximately what percent your wheel starts beeping?

Whenever the momentary battery level goes below 15%, it beeps. All GW warning beeps are based on the momentary battery level only, and some people are under the impression that they are power consumption based warnings. In practice the difference is subtle though, and the end result is the same.

 When the momentary battery level reaches 0% the beep changes to a different kind, and the wheel tilts back.

 At slow speeds the beeps are also a little different, but the thresholds are the same.

14 hours ago, WI_Hedgehog said:

The convention is charge to 80% capacity which is about 4.00V (depending on the cell it's 3.98V to 4.02V) and you'll gain 2x the number of recharges. 

If the charger is modified to output a max voltage of 4.0V per cell, maybe more balancing would happen compared to the current 80% charging procedure which will just stop charging before the CV mode has begun.

 

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On 5/2/2020 at 1:40 AM, WI_Hedgehog said:

As a note, charging your battery to 80% instead of 100% (4.00V vs 4.20V) tends to double the life (batteries are usually rated at 500 full cycles, I'm hearing in EUCs they last about 300). Discharging to only 30% (3.77V) instead of 0% (3.27V) should also  double thier life. That would take your battery life from 300 cycles to 1,200 cycles, although your trips would be about the distance you're tanking now. 

Remember that since the cells are in series and don't like to be over or under-charged, its good to balance charge them regularly. I've heard the figure "every third charge," and that seems really reasonable to not put undue stress on a slightly less ambitious cell.

Hope this helps! 

 

 ~300 cycles doesn't seem like all that much, for a daily MSX commuter like myself. Maybe I should be more cautious in charging to 100% 

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Posted (edited)
16 minutes ago, Justin Boivin said:

 

 ~300 cycles doesn't seem like all that much, for a daily MSX commuter like myself. Maybe I should be more cautious in charging to 100% 

I dropped mine down to 84v from 84.2.   If you ignore  bias and do the math, 300 cycles per battery is WAY more costly than using gasoline. I'm still letting it charge to full, only NOW my charger thinks 84v is full. I don't know if this helps, but there's no way i can be diligent enough to make the habit of stopping it at 80%. Not to mention, 30 miles is already not enough, if i stop at 80%, I'll probably lose 30% of that figure, as the top % of battery carries MUCH more distance than the bottom %.

Edited by ShanesPlanet

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10 hours ago, Justin Boivin said:

 ~300 cycles doesn't seem like all that much, for a daily MSX commuter like myself. Maybe I should be more cautious in charging to 100% 

On one hand, for guys like myself who live in cold weather climates it's about battery longevity, so buying more battery than needed is not optimal.

On the other hand, commuters like yourself are indeed the ones who have to look at how many charges per day they're doing. One full charge might mean replacing the batteries yearly. Two half-charges (to 4.2V) might mean you get an additional year of use due to shallower depth-of-discharge, so bringing a charger to work (or leaving a second one there) may have excellent Return On Investment.

 

10 hours ago, ShanesPlanet said:

I dropped mine down to 84v from 84.2.   If you ignore  bias and do the math, 300 cycles per battery is WAY more costly than using gasoline. I'm still letting it charge to full, only NOW my charger thinks 84v is full. I don't know if this helps, but there's no way i can be diligent enough to make the habit of stopping it at 80%. Not to mention, 30 miles is already not enough, if i stop at 80%, I'll probably lose 30% of that figure, as the top % of battery carries MUCH more distance than the bottom %.

What voltage does the Battery Management System start to balance at? 84V, right? (4.20V x 20 cells = 84.00V) So you need more than 84.00V to keep pushing electrons into that system to end up at 84.00V. The LiPo chargers I've used turn off when current flow is lower than (let's say 100 milliamps, for simplicity). So if the BMS clamped voltage at 4.20V like it should, you could put 86V into it and the BMS would cut off charging on each cell branch as it reached 4.20V, when all branches were full only a trickle current would flow to power the BMS (under 100mA), and the charger goes into Standby mode (charge complete).

Disclaimer: I don't know your BMS and how it is functioning.

But re-read this:

On 5/3/2020 at 4:40 AM, Chriull said:

Balancing happens by a resistor beeing put in parallel once one cell reaches at about 4.2V.

Charging to 80% even with saturation stage instead of just cut off will start _absolutely no_ balancing!

Charging to 80% with cut off once 84V are reached will give some minimal balancing - but not worth to be mentioned.

Real 80% balancing charging would require a charger output voltage of 4V*20=80V and the BMS to apply the bleeding resistors at 4V (or a bit below), too.

Would not even require "communication" between charger and BMS... Just some more intelligence in the BMS. (Cut off charge input with the protection mosfet, measure charger max (no load voltage) set according balance voltage threshold, open mosfet to start charging...)

Could maybe come with some future smart BMS if the circuitry allows programming this balance threshold voltage by app - so one can set manually charger voltage and BMS threshold.

^^^This is how top-balanced charging works. What we really want is smarter bottom-balanced charging. (That's probably not happening in the next 3 years due to the cost & size of smart BMSs.)

What will work is charging the pack to 4.00V and manually boosting weaker branches, as @alcatraz.shared with us:

 

For an in-depth discussion between really smart people see the thread below. Note I do high-current charging (not on EUCs- they don't currently support it), BUT the caveat is the charger MUST support temperature sensors. As soon as a cell starts warming up the current must lowered in order to maintain a "high" charge rate. So yes, LiPo cells can be charged to 80% capacity in 45 minutes with a bottom-balanced charger, and to 95% in one hour 10 minutes, all depending on the cells and cell age, but only with a smart system

 

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13 minutes ago, Rywokast said:

300 cycles seems ridiculously low to me...

The cycles in the datasheet are a minimum guaranteed value. The 300 cycles are a speculation based on the higher burdens by the EUC compared to the datasheet specifications.

And GW wheels don't have "real full cycles" - just downto 3.3V.

And the charge cycle count just gives the number of (minimum) 80% still retained.

13 minutes ago, Rywokast said:

and as you can imagine it has has waaaaaaaaay more than 300 cycles.. i have not noticed ANY degradation on the battery at all

As long as the cells are nicely matched and don't start getting imbalanced and by this destroy 1-2 cell groups they seem to have quite some lifetime.

Especially the 6(+)p configurations!

Ps.: Just out of curiosity - how long is your trip to work? How many weeks per year you can make the ~5 rides to work?

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3 minutes ago, Chriull said:

The cycles in the datasheet are a minimum guaranteed value. The 300 cycles are a speculation based on the higher burdens by the EUC compared to the datasheet specifications.

And GW wheels don't have "real full cycles" - just downto 3.3V.

And the charge cycle count just gives the number of (minimum) 80% still retained.

As long as the cells are nicely matched and don't start getting imbalanced and by this destroy 1-2 cell groups they seem to have quite some lifetime.

Especially the 6(+)p configurations!

Ps.: Just out of curiosity - how long is your trip to work? How many weeks per year you can make the ~5 rides to work?

yea i get that, people see that and think full charges but thats not actually a full cycle so you have to count for that, so its impossible to actually know how many "cycles" you have.. but still unless theres a problem no one needs to worry about having a wheel for a year and replacing the battery xD trip to work is very short only ~5 km one way, i work downtown and dont want to have to worry about my wheel being beaten up or dropped etc, plus the other employees like to screw around on it lol.. probably 50/52 lol... weather doesnt matter i just use an umbrella if it rains, i got rid of my car a while ago and the only time ill opt to take the bus is if there is a foot of snow on the ground.. which is extremely uncommon here

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4 minutes ago, Rywokast said:

trip to work is very short only ~5 km one way

 

4 minutes ago, Rywokast said:

probably 50/52 lol.

3.5 * 50 * 5 * 10 km is "just" 8750 km.

The 20s6p wheels with ~40-60km (?rather more?) range per charge with 300 to 500 cycles should make 12000 to 30000 km.

But from the reports here it seems most problems are dead cells ("pack not charging to 100%") and not range loss by degradation.

So either the problem is manufacturers not nicely matching cells or by starting, slight degradation cells get imbalanced over time (with no real chance for the BMS to balance this.

Or the packs needs (from some "mid" age on) at every charge balancing to have a chance to survive (stay balanced) and 80% charging is "the way" to kill a pack?

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7 minutes ago, Chriull said:

 

3.5 * 50 * 5 * 10 km is "just" 8750 km.

The 20s6p wheels with ~40-60km (?rather more?) range per charge with 300 to 500 cycles should make 12000 to 30000 km.

But from the reports here it seems most problems are dead cells ("pack not charging to 100%") and not range loss by degradation.

So either the problem is manufacturers not nicely matching cells or by starting, slight degradation cells get imbalanced over time (with no real chance for the BMS to balance this.

Or the packs needs (from some "mid" age on) at every charge balancing to have a chance to survive (stay balanced) and 80% charging is "the way" to kill a pack?

yep... i dont think i have ever once seen an euc with that many km on it lol, either people trash them before that point or they end up selling them for something else way before they ever get close to that number, be interesting to see in a few years if people are approaching those numbers.. its a real shame manufacturers arent implementing intelligent bms' that would actually balance every single charge regardless of the charge level so you could get max longevity and safety, but i suspect that would go against their reasoning as they wouldnt be able to sell as many if they never died lmao

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2 hours ago, Rywokast said:

yep... i dont think i have ever once seen an euc with that many km on it lol, either people trash them before that point or they end up selling them for something else way before they ever get close to that number, be interesting to see in a few years if people are approaching those numbers.. its a real shame manufacturers arent implementing intelligent bms' that would actually balance every single charge regardless of the charge level so you could get max longevity and safety, but i suspect that would go against their reasoning as they wouldnt be able to sell as many if they never died lmao

The other item of concern is bearings...are the bearings in Wheel_X serviceable with moderate effort, like changing a tire's innertube?

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I get around 50km on my MSX 84v and after letting it rest it might be at 30%.
The other day I went for a 57.5 km ride with a friend. I hit the 5 beeps at 45.8 kmh and battery went down to 9% at that point.
I have 9500 km on it. Been riding it since Jan 2019.

I have done 90km rides on it before... but as time has passed I just end up riding faster and faster.

Usually battery articles will state that one can expect degradation down to 80% after 300 full cycles.
So you can charge to 80% and get that 80% now, or charge to 100% until it gets degraded to 80% and get that 80% later.
I doubt many people will ride their wheels for 10000 km and those who do probably will have a new wheel by then as well.

I get maybe 10km more range on my 16X (7500km).

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