Jump to content

Battery Capacity, Longevity, and Manufacturer Reserves


WARPed1701D
 Share

Recommended Posts

I've always found this interesting... And my opinion is that the correct answers depend on how you define longevity - is that solely a period of time? 

Using really simplified logic (even though it may end up ruining my argument)... if I actively manage my battery - charging to ~80% / riding to ~50% - then I am using a but over a quarter of the full charge. Now that may mean my battery lasts for times longer, but when I went to school, 1/4 × 4 = 1

So this may occur over a longer period of time, but wouldn't the overall riding distance be about the same? 

In this case,  should "longevity" also consider distance? 

  • Upvote 1
Link to comment
Share on other sites

Longevity IMO is largest possible power output for the device over it's usable life (ergo miles) while remaining practical.

Indeed if using 1/4 of the battery resulted only resulted in 4 times more charges then you would not be getting anywhere, however I believe the suggestion at BU is to charge to 80% and drain to 30% and it will give you around 4 or more times the number of cycles at the cost of only getting 50% possible power from your batter per cycle. If you can do that realistically and practically then the net result is at least twice the usable power (miles) over the battery life.

My point with this post though is that our definition of empty is artificially inflated for safety by the manufacturer (a good thing) and what we think is 50% capacity usage is actually more like 33% in real terms. It explains why energy in during charging (as measured by a Charge Doctor) can seem oddly low for an apparently empty battery. We actually only have 66% of the battery's full potential available to us and when we limit our minimum charge level to 30% we reduce the available charge even further.

Worst case scenario: Assuming I charged to 80% as measured by charge doctor and discharge to 30% as measured by the wheel actual capacity used drops to just 27%.

This discussion also lends itself to storing our wheels. Ideally if you aren't storing for more than a year and the battery isn't to old with high self discharge you should store a Li-Ion battery at about 30% real world capacity as measured from 3.0V. In Inmotion's case this actually means you should store it completely empty as measured by the wheel itself as this is actually 33% real world charge. Charging to 30% as measured by the wheel means you end up storing the battery at over 50% real world capacity. Still not bad and certainly good for very long storage or older batteries that self discharge higher but not as good for shorter term storage, or in warmer conditions.

  • Upvote 1
Link to comment
Share on other sites

 Thanks for the reply KingSong69.

I couldn't find the definition of a cycle on BU's site. I assumed a cycle to be from the point of the given discharge until full again. Ergo charges of 50% represented 2 cycles rather than 1 of 100% total (2 x 50%). Either way it is an increase.

You are right of course to enjoy the wheel and not stress about it. I guess I'm raising this from several angles. If I've worked it all out correctly then (safety of the wheel aside) draining my V8 to empty actually still leaves 33% capacity in the cells and a voltage of 3.4 volts. People assume draining to empty is a huge stress on the cells but in our case of an artificially inflated empty level that is not so. Riding to empty should be of no detriment to the cell and as long as your wheel is proven reliable and safe at low charge values you should be OK to use all your power up.

In the case of my V8 which doesn't have the largest range it may mean I can happily (although gently) go another 5 or 6 miles more than I would have if I was worried about stressing the cell with a deep discharge.

  • Upvote 3
Link to comment
Share on other sites

11 minutes ago, WARPed1701D said:

 Thanks for the reply KingSong69.

I couldn't find the definition of a cycle on BU's site. I assumed a cycle to be from the point of the given discharge until full again. Ergo charges of 50% represented 2 cycles rather than 1 of 100% total (2 x 50%). Either way it is an increase.

You are right of course to enjoy the wheel and not stress about it. I guess I'm raising this from several angles. If I've worked it all out correctly then (safety of the wheel aside) draining my V8 to empty actually still leaves 33% capacity in the cells and a voltage of 3.4 volts. People assume draining to empty is a huge stress on the cells but in our case of an artificially inflated empty level that is not so. Riding to empty should be of no detriment to the cell and as long as your wheel is proven reliable and safe at low charge values you should be OK to use all your power up.

In the case of my V8 which doesn't have the largest range it may mean I can happily (although gently) go another 5 or 6 miles more than I would have if I was worried about stressing the cell with a deep discharge.

In the "industrial" 18650 world, most of the batteries are meant to run from -about- 3,3 volt to 4,2 volt.

So i guess your Inmotion 3,4 volt assumption is not completly "correct"....To drain the batterie to 3 volts and mean that a 0% charge...is possible, but not the standard. But...some cells can even be drained to 2,7 or 2,8 volts...so that would lead to take a look at the specific cell which is used in the wheel, and i guess this goes the wrong direction.

From my experiences with batteries i would assume they are in a range from 3,3 to 4,2 volts...that numbers i also know from my vaping gear, which uses the same kind of cells.

 

 

  • Upvote 1
Link to comment
Share on other sites

24 minutes ago, WARPed1701D said:

stressing the cell with a deep discharge.

From what I read on this forum, a lot of wheels will not let you stress the cells with deep discharge.  I'm thinking that the battery management systems of most high quality wheels protect the batteries pretty well.  You have good idea to make your batteries last longer by not charging all the way.  But like @KingSong69 said, it will be a long time before the batteries wear out.  Sounds like the V8 has good reserves at low battery.

  • Upvote 3
Link to comment
Share on other sites

51 minutes ago, KingSong69 said:

In the "industrial" 18650 world, most of the batteries are meant to run from -about- 3,3 volt to 4,2 volt.

So i guess your Inmotion 3,4 volt assumption is not completly "correct"....To drain the batterie to 3 volts and mean that a 0% charge...is possible, but not the standard. But...some cells can even be drained to 2,7 or 2,8 volts...so that would lead to take a look at the specific cell which is used in the wheel, and i guess this goes the wrong direction.

From my experiences with batteries i would assume they are in a range from 3,3 to 4,2 volts...that numbers i also know from my vaping gear, which uses the same kind of cells.

 

 

 Fair point. I was using info here...

http://lygte-info.dk/review/batteries2012/LG 18650 MH1 3200mAh (Cyan) UK.html

...for cell performance data,suggesting that a 3.0V discharge was a good end point  for these cells.

  • Upvote 1
Link to comment
Share on other sites

30 minutes ago, steve454 said:

From what I read on this forum, a lot of wheels will not let you stress the cells with deep discharge.  I'm thinking that the battery management systems of most high quality wheels protect the batteries pretty well.  You have good idea to make your batteries last longer by not charging all the way.  But like @KingSong69 said, it will be a long time before the batteries wear out.  Sounds like the V8 has good reserves at low battery.

 My conclusion precisely, although high quality  are the key words there. I have read many other posts though where people are concerned about running the charge low for reasons of battery damage. As it seems I'm on the right track with my assumptions presented here i hope it helps others.

Safety first though. Wheels with poor battery reserves may have you eating asphalt if you run them too low. I'm glad I found the cut off voltage for Inmotion wheels from a reliable source.

 

  • Upvote 3
Link to comment
Share on other sites

13 minutes ago, WARPed1701D said:

Safety first though. Wheels with poor battery reserves may have you eating asphalt if you run them too low.

I agree completely, it's hit and miss with cheap wheels with small batteries. 

Edited by steve454
Link to comment
Share on other sites

46 minutes ago, Keith said:

@WARPed1701D, just to pick up on an error right at the start of this discussion, I've just trawled through BU to check I'm not in error, at 3.4 volts off-load a Lithium Ion cell has somewhere in the region of 10% capacity left - not 33% as you stated.

 

Ok. Thanks for the correction. Do you have links to the BU pages. I'd like to learn more about this. 

Link to comment
Share on other sites

8 hours ago, WARPed1701D said:

Do you have links to the BU pages. I'd like to learn more about this. 

This is as good a place to start as any: http://batteryuniversity.com/learn/article/lithium_based_batteries. On this page is a graph of voltage against capacity comparing older coke anode batteries to modern graphite anode ones. The older coke anode batteries would have had around 30% capacity at 3.4 volts.

This fits with the LiPo batteries I use somewhat aggressively every weekend in model helicopters/planes. LiPo's are basically soft cased LiIon batteries with pretty much the same electrical characteristics, if, off load, a battery is down to less than 3.5V/cell I will put over 90% charge back into it, if it is way down at 3.0 volts it is only a tiny bit more. In practice I try to fly only down to 3.6V off load if I can. I also notice that batteries taken down below 3.4 volts or so are noticeably warmer when removed from the 'plane.

  • Upvote 2
Link to comment
Share on other sites

Thanks for the link. There are so many articles on that site and I had been concentrating on the ones regarding longevity and discharge. Must have skipped over the generic one until now.

Let me confirm your terms "off-load" and "on-load" voltages.

"On-load" is, I'm guessing, the voltage of the battery with a current draw. And as I understand it a high current draw lowers lower the output voltage which then recovers to the nominal value when the load is removed. Yes? With the highly variable load produced by the wheel motor I'm guessing this value fluctuates to some degree.

Now, "off-load". Do you mean the voltage as soon as the load this removed or after 10 minutes or so for the battery to rest. I understand even a fully depleted but healthy LI-ion battery will recover to near nominal voltage after a few minutes simply due to the electrode's affinity even though there is little capacity left to deliver.

Source of my assumptions: http://batteryuniversity.com/learn/article/discharge_methods

If that is the case then surely the voltage under load is the only reliable gauge of capacity. Yes?

Also I see posts where people report they drain their wheels to empty but then after a short period note that the remaining percentage of charge has increased into the teens or higher. This suggests that remaining capacity as declared by the wheel can be inaccurate at rest when the battery is very low on charge and that reported remaining charge is maybe only measured based on cell voltage?

 

 

Link to comment
Share on other sites

I wonder which wheel has the best battery management system, that allows high performance without cutout.  My guess would be IPS or Kingsong followed by Ninebot.  Gotway is high performance, needs a lot of rider skill to stay safe.

  • Upvote 2
Link to comment
Share on other sites

Some awesome information there @esaj Thanks for taking the time.

I guess in my original opening post where I say that, based on the 3.4V shutoff in the Inmotion wheels, there would be maybe 30% charge left in the pack when the wheel showed completely empty I was talking about the reading shown by the wheel at the point of initial tilt-back and shut off when it hit 3.4 V under a moderate load while riding (the 'on load' condition). I wasn't suggesting that there would be 30% charge remaining in the cells if the wheel reported a empty battery 'off load' after it had sat for a while to rest and recover. Getting to that point would, as you mentioned, be difficult as you would have to keep turning the device back on and riding further to enforce a deeper drain and so a lower resting voltage.

I'm not stressing too much about my battery pack but I like to understand how things work, what safeguards are built in already, and what I can do to maximize value and efficiency of my machine without risking my safety or my wheel's mechanical/electrical integrity. Based on these discussions I feel comfortable that I can charge to 80% on the Charge Doctor and discharge to 10% or less (if desired and with careful riding) and not be risking my battery. I'll do checks with the Charge Doctor when I get it to see exactly how much energy goes in after running to these levels but I expect that this kind of discharge cycle will use about 50% battery capacity which is a good amount for pack longevity.

  • Upvote 2
Link to comment
Share on other sites

2 hours ago, esaj said:

 Most of you have probably seen that picture a gazillion times already, but it's a good reminder of how much power these (relatively) small packs carry.

Before my accident I was not fully aware about the tremendous amount of power stored in the packs! Always treat EUC battery packs with the same degree of caution and respect as you would working with household current! 

 

 

Edited by Rehab1
  • Upvote 3
Link to comment
Share on other sites

37 minutes ago, Rehab1 said:

Before my accident I was not fully aware about the tremendous amount of power stored in the packs! Always treat EUC battery packs with the same degree of caution and respect as you would working with household current! 

Yes, the packs can be lethally dangerous if mishandled. Of course "mishandling" shouldn't mean pushing the connectors together, like in your case, but even DC-voltage is dangerous at higher levels and "right" conditions. A lithium fire or a pack exploding in your face is not funny, and if high enough current passes through your heart (like from one hand to the other, "conveniently" with your heart in the way), it will stop it. That's not to scare people, but to remind to be careful with these things. They're relatively harmless sitting inside the wheel (as long as not overcharged, overheated, short-circuited or let to discharge to a too low voltage and then recharged), but if you have to open up your wheel, disconnect the battery pack, and at least try to turn the wheel on after disconnecting the pack, or otherwise drain the capacitors on the board so no large voltages are there. Many people have replaced a burnt mainboard or bad battery packs without any trouble, but taking precautions is wise.

  • Upvote 2
Link to comment
Share on other sites

I probably don't represent the average rider, but I don't think I'll own any given wheel for more than a couple of years. So I just charge to 100 percent and don't worry about it. I'm more focused on having fun with the wheel. And since I enjoy long rides I'd rather have the additional 10% battery capacity for my longer ride than to extend the life of the batteries.

I did just get a fancy charger from EWheels so I may charge my Monster to only 90%, but only because it has such a huge range that I won't miss that 10% charge.

  • Upvote 2
Link to comment
Share on other sites

3 hours ago, zlymex said:

I don't care much about the battery as far as charge/discharge is concerned.

......<snip>......

 Some great info here about the importance of balancing the pack regularly, side effects of an imbalanced pack and how ensure it starts to happen when charging. Thanks. 

Edited by WARPed1701D
Link to comment
Share on other sites

2 minutes ago, WARPed1701D said:

 Some great info here about the importance of balancing the pack regularly, side effects of an imbalanced pack and how ensure it starts to happen when charging. Thanks. 

If you are really interested in charge values and all the things going on, i highly recommend a Charge Doctor V2!

with that tool you can monitor your batterie status, voltage, the Watthours and amps that have been loaded, and so on and so on....

with it you can also adjust to stop charging at a specific voltage or percentage....for example 90% or 66 Volt.

in the states ewheels.com is selling this great little tool!

  • Upvote 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...