Usable Watt-hours?

[Klepo]

Ive been looking around to find out the different of usable watt hours vs watt hours of the battery, but haven't found much other than li ion can use 90% of the stored energy.

So the question i have a 52v 17ah so 884 wh
If you can only use 90% lets say 800 wh. my eggrider is only reading about 650 or so fully charged and it says when i use 300wh is about 43% off my battery. i have it set to the 52v 17 ah in settings.

Does this mean the battery is not what is says it is? Error in reading? Or is that actually what i can use from it and am misinformed.

Thoughts,answers,recommendations all welcome.

Regards
Jacob.

 

[john61ct]

First off, unless you have the gear and knowledge to do rigorous testing of actual energy vs power capacity and ideally ESIR, you really have no idea of what you are getting from 99% of "reasonably priced" online vendors, they all lie and cheat

at least 90% are outright fraudsters.

B. use Ah amp hours not Wh once you've decided on a voltage level.

3. The higher your average DoD% per cycle, the shorter the lifespan of your pack. Shoot for quality cells, not counterfeit, not B grade out the factory back door or even secondhand sold as new.

Which requires not buying based on low price.

There are hundreds of objective testing reports, learn how to interpret them. High energy density is in opposition to high power density, figure out what your use case really demands, no such thing as "the best" cells, only best for specific needs.

No display or BMS measures pack Ah capacity at rest, nor can be all that accurate wrt SoC% in use.

The current rate causes both to vary radically.

To get accuracy with these numbers you need to climb a pretty steep learning curve, and invest in some quality electronics gear most hobbyist don't bother with.

From a practical POV seat of the pants, growing your intuition with experience of a given rig and terrain, is usually good enough.

 

[pwd]

Your 650 watt hour figure seems about right compared to the pack's 884 wh rating.

You have to also consider that most battery packs will have a low voltage cutoff that is triggered somewhere around 2.7-3.1V per cell which may be around 10% to 20% stage of charge. Another factor is that the capacity rating is given at much lower current draw compared to your e-bike. For example: the battery pack capacity is rated for 17aH but that is probably only measured at 1C or less (17A or less). Your e-bike might draw more than 17A; so the capacity will be less. Then there are things like cell age, ambient temperature, charge cutoff voltage etc... that will affect usable capacity.

 

[E-HP]

Ive been looking around to find out the different of usable watt hours vs watt hours of the battery, but haven't found much other than li ion can use 90% of the stored energy.

So the question i have a 52v 17ah so 884 wh
If you can only use 90% lets say 800 wh. my eggrider is only reading about 650 or so fully charged and it says when i use 300wh is about 43% off my battery. i have it set to the 52v 17 ah in settings.

Does this mean the battery is not what is says it is? Error in reading? Or is that actually what i can use from it and am misinformed.

Thoughts,answers,recommendations all welcome.

Regards
Jacob.

You can use it all, but it's not good for the battery, and "all" will go down the more you do. Everyone sets their own limits on what they are comfortable with for "useable" energy, so charging to 4.2V /cell and discharging to 3V / cell and watching the pack's capacity quickly degrade over time is something people want to avoid. For many, the useable capacity is charging to 80% and discharging to 20%, so 60% of the pack rating for regular riding. If you're planning a long trip, charging to 4.2V right before the ride will give you the extra range without hurting the pack (if you use it right away), getting you 80% of the pack capacity, and 20% left if you really need to discharge lower.
I never use the battery display as a way of determining the state of charge, so can't advise on that.

 

[john61ct]

Backing off from the harmful-to-longevity charge setpoint of 4.2V

doe not actually sacrifice much capacity utilization (range) at all.

Even 4.15V is helpful, 4.10V even better.

But going to the "coddling" 4.05V is still not sacrificing anywhere **near** 20% off the top end.

Depends on the specific chemistry, model cell and the stop-charge profile algorithm, but usually in the 6-10% range.

 

[MadRhino]

The best investment for any ebike, is a quality battery with a fair margin of extra capacity. That is because the battery then keeps cooler, safer, and does last longer.

 

[Klepo]

So the pack didn't say it was 884 wh i just did the math from 52x17 and was seeking more information as i figured that was 100% of the battery's power.

It is a quality pack from em3ev, i was just wanting to get some more info it uses 35E cells, i did get the 90% cut off charger knowing that it is better for the battery not to be fully charged(didn't have the money for the grin charger) so from the sum of what you guys have said im guessing that the 600 wh at full charge is about right give or take. Thank you all very helpful group! hope everyone has a great weekend!