Battery charging for the occasional rider

[Paultr]

How many here always charge their batteries fully every time they need a charge?

As I understand it, batteries like to be kept in the 40-70% range of their capacity. I can understand that if you are a daily commuter user you have no choice other than recharge to full but for someone like me who uses their bike maybe 2 or 3 times a week with a typical journey of <10 miles there appears to be logic in only charging up to 80% or so when the battery gets down to 30%. This would result in charging the battery once a fortnight rather than once a month as I do now. What do the folks who understand our battery chemistry think ?

EDIT: I suppose if you extend this logic further you could 'top up' the battery with a small charge after every journey and try to keep it at 70% ....

 

[KirstinS]

Personally I think this is overthinking things, other views will no doubt be available !

For 2 or 3 times a week use I’d just charge after each ride and keep the battery topped up. My own view is that a “storage” charge doesn’t really apply when we are talking days rather than weeks and months .






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[Benjahmin]

I agree with Kirstin. Maybe do two rides (20 ish miles) and charge, but generally batteries benefit from not being deep cycled (full to empty). Li-ion batteries have no 'memory effect' so charging after each use ensures that the cells stay in balance. This is the real issue with partial charging, balancing only occurs at full charge (unless you have a smart arse charger).

 

[Paultr]

Thanks for the replies
I presume that balancing must occur if you charge fully as you say as all the individual cells must become full. I am not sure though that by trying to keep the cells in the optimum window is overthinking it as the battery/s are the single biggest cost of my system. I do realise that I need to research more and find out whether some kind of smart charger would be cost effective for my kind of occasional use.

 

[Nealh]

It's not a smart charger that is needed but a programmable bms which you can then set the balance voltage to suit your requirements.
Unless you have a smart/programmable bms then you need a full charge on maybe every 1/2 doz to keep cells from straying, balance occurs above 4.15v per cell.
I only charge fully the night before use other wise batteries are left sitting at between 3.7 - 3.9v per cell.

Deep discharging in my view is 2.8 - 2.9v per cell, most of my bms lvc is 3.3- 3.4v per cell by the time sag has taken effect to dip lower then this.

 

[Paultr]

Thanks Neal

The battery I have is "17AH HL downtube battery with Panasonic 18650-B cells". I have a multimeter so can determine overall voltage but how would I find out how many cells I have ?
I assume there must be banks of cells in series to make up the 36V and these banks wired in parallel to make up the desired capacity.

You mention a programmable bms. Is there one model that stands out as the one to get and is it likely to save money or is it just a question of being able to charge efficiently to extend range/life of battery ?

 

[Woosh]

ow would I find out how many cells I have ?

10S5P, 50 cells.
If you charge your battery to 39V-40V instead of full (41.5V), you will certainly prolong the life of your battery but this needs to be taken together with other factors:

1. rebalancing: the BMS draws its own energy consumption from 1S out of the 10S, causing that (5P) block to have a lower voltage than the other 9S. Over time, the difference can cause problem. You need to rebalance the battery once every couple of months. There, you have two type of BMSes, one that can rebabance at whatever the voltage (or SOC, state of charge) and the more common in e-bikes, via bleed resistors which is done after the charger goes green. So you charge fully the battery once every couple of months and leave the charger on for another half/an hour.
2. frequency: you still need to use the bike as often as possible, every day is best! Batteries need to be working as often as possible.
3. acceleration: which is proportional to the voltage of the battery. You lose about 5%-7% acceleration when running at 80% instead of 100%.

 

[Paultr]

Thanks Tony

I was guilty when I started this thread of not googling for the answer first ! Now I have done I realise just how much info there is on this subject (including the amazing revelation that Tesla uses the same battery format that I have - if it is good enough for Elon it is good enough for me!).

When you say the BMW draws it's energy from one cell do I infer from that that it needs to be wired into the structure of the battery or is it just plug and play ?

 

[gray198]

the manual for my Oxygen states that when charging battery it should not be unplugged until fully charged, which is what I tend to do anyway, but am curious as to reasoning behind this. Also when it states that battery can be charged for, say, 800 cycles is this the amount of times it is put on charge or the times charged from being empty. So in other words if charging after doing only 10 miles, does that count as one of the 800?

 

[Nealh]

Programmable/smart bms are > then $100 and probably worth it if you are building your own pack with very good quality cells.
For OEM or off shelf packs it is more about as you say charging efficiently and awareness to promote battery life. Most packs with reasonably good cells will see about 5yrs + good life if not abused.


Drawing high amps/derestricting and leaving packs stored at full SOC will reduce life capacity over time.
Charge at ambient temps and keep packs in doors or in a dry cool place not a damp cold shed etc.
Riding in the rain is generally fine but leaving packs out in the rain for long periods will lead to water ingress.

 

[Nealh]

Lithiuim charging is counted as one full charge for life cycle.

You can part charge a battery if wishing to raise to a certain voltage level if not using for a while but it is detrimental if you do this for regular use as mentioned the cells will not balance as well as underperforming with low SOC.
Batteries like to used and charged often they don't like sitting at full SOC.
When buying li-on cells they always come at approx. 3.5 - 3.7v from the factory/supplier.

 

[Benjahmin]

I bought my Ezee kit in November 2014. It has a rack battery with unknown, to me , cells (I suspect they are pouch cells). I've kept a charging diary, and have charged after evey ride. Rides are variable in length ( 9 - 36 miles, average probably about 15 or 16) and regularity, some times 2 or 3 times a week, sometime 2 or 3 time a month.
Battery has had 273 charges and is still going strong. Obviously it's age means that capacity is starting to drop, but these days I parallel it with another battery for longer rides.
It charges from the supplied 4A charger and is always left to go green, occaisionally left for a few hours in this state (if I'm busy or whatever).

Really, I think you are causing yourself uneccasary angst. Use your bike, enjoy it. Best thing you can do for your battery is not use prolonged periods of high current draw, so, use the lower power settings. You get assist and still get excercise, all round winner I'd say

 

[Nealh]

The Oxygen manual is for practicality, for buyers without battery management knowledge to prevent said battery from under performing from part charging causing the unbalancing mentioned.

It can be equally bad practice to leave fully charged if the end user is an infrequent rider. A fully charged cell is like a pressure valve waiting for energy release, fine for the short term but not so for the long term leading to demise in capacity usage.
Capacity is the useable ah/wh a battery stores and not necessarily the total voltage capacity it can obtain at a full SOC, it is only when a current is applied that we see how the voltage acts and then can see how cell capacity is holding up.
Every now and then it is what we hear when someone asks a question about their battery not performing very well and then go on to say it charges normally or the charger goes green.

 

[Nealh]

Cells don't have an infinite life, the more use you get out of them the better.
You have to ask your self if better value or life has been had from a battery that has been used very regularly (weekly) over 3 - 5 years or one that is only used only a few times (less then monthly) a year over a longer period.

 

[gray198]

is it too simplistic to say that if a full charge = 30 miles the lifetime of the battery at 800 charges should equal 24000 miles. I suppose there will also be an age factor to take into consideration, ie natural deterioration of cells

 

[Paultr]

.....
Really, I think you are causing yourself uneccasary angst. Use your bike, enjoy it.
.....

This depends on your personality - for me (a bit of an anorak) it is the exact opposite. I really enjoy and get a kick out of knowing what is going on with any tech product I use in my day to day life. I almost get as much pleasure in discovering how new things work as I do from using them.
Edited to remove irrelevant waffle

 

[awol]

You mention a programmable bms. Is there one model that stands out as the one to get

My favorite programmable BMS is my Neptune15. You can set the charge/balance and discharge to whatever you want within range. It also tells you over bluetooth in real time everything you would ever need to know about what is going on with your cells but as Nealh says programmable BMS are not cheap.
https://www.speedict.com/