Battery health help

[Ianb84]

hi guys,
my first post here and i'm looking for some help/advice.
I've been using a 1000W ebike kit with 48V13.5ah battery for my 11 mile commute to work - when i arrive i charge battery for my cycle home as there's 20% left. I've covered almost 2000 miles and the battery seems to be draining a little faster which i expected, just maybe not this soon.
I've read charging to 80 or 90% can extend battery life, does anyone know if it sounds too late to start doing this? And, with having only 20% left when i arrive , would a partial charge do more harm than good as it would be below 20% if not fully charge to begin with?
Perhaps i just a bigger battery altogether,
any suggestions would be great,
thanks ,
Ian.

 

[vfr400]

Always charge to 100% to avoid any problems. The charging system can't complete all its functions if you partially charge.

1000w controllers and motors tend to wear out batteries like yours pretty quickly regardless of how you treat them.

 

[Ianb84]

thanks for reply,
do you know of any reason why my battery seems to be dying quicker after around 200 charges? i was expecting more 500-600?

 

[vfr400]

You're taking a much higher current from it that what's the norm. Do you know what cells are in it and how many amps the controller has written on the label?

 

[Andy-Mat]

hi guys,
my first post here and i'm looking for some help/advice.
I've been using a 1000W ebike kit with 48V13.5ah battery for my 11 mile commute to work - when i arrive i charge battery for my cycle home as there's 20% left. I've covered almost 2000 miles and the battery seems to be draining a little faster which i expected, just maybe not this soon.
I've read charging to 80 or 90% can extend battery life, does anyone know if it sounds too late to start doing this? And, with having only 20% left when i arrive , would a partial charge do more harm than good as it would be below 20% if not fully charge to begin with?
Perhaps i just a bigger battery altogether,
any suggestions would be great,
thanks ,
Ian.

According to what I have understood from some good links on the net, the upper 10% and the lower 30% are considered by a good charging system to not to be used.
The charger voltage should stop at the upper limit, and the battery safety electronics will stop at the lower limit.
You can charge your battery and measure the voltage across the battery when the LED (generally) goes green to say that charging is stopped.
The voltage you should should be seeing is 4.2 volts x the number of cells or cell groups. For 48 volt nominal Li-ion batteryies, that should be 13 in series. I reckon that to be 54.6 volts max for safety.
My battery for example is a nominal 36 volt and I see exactly 42 volts when charging is finished (Not a micro volt more) and the battery is fully charged, so mine is 10 cells in series.
How many are in parallel for the 10 groups, depends on the maximum current needed.
I have two chargers and both show exactly the same "end voltage" of 42 volts.
But I have read here of chargers that "over charge" which will significantly impact the life of a battery. Not seen any myself, but I try always to err on the side of quality and safety.....
What some here do not believe is that leaving a charger connected for periods AFTER full charge is achieved, can be very detrimental to the batteries life. You also see it on any products that use such batteries such as laptops! People forget to only partially charge the battery, and remove it from the laptop,when running on the mains. They are surprised when the battery dies early!!
So I modified a very cheap electro mechanical time switch, so when the set time is reached, it not only completely removes mains power to the charger, it also switches itself off completely.
All you need to know is how long a charge takes approximately and set that on the timer!
Its a tiny bit "hit and miss", but still better than nothing!
I use such things whenever I charge ANY type of battery.....
It allowed my last e-bike to achieve over 6 years of usage, and the bike was given away still fully working, and no noticeable drop in capacity.
Though of course some loss was probably there, but I never ever needed to test very exactly! It still did the miles I needed each day....
Over 30,000 Kms in all....
I keep telling myself that I should build an electronic switch, that senses when the battery is fully charged EXACTLY and remove the mains completely and not reapplying it!
I did it for a LA charger for my caravan some years ago and that works (still very) well, and its quite simple to do really!!
That battery is 15 years old and still going, but is LA not Li-ion!! Different chemistry!!
If I can help further, just ask.
Andy

 

[Ianb84]

You're taking a much higher current from it that what's the norm. Do you know what cells are in it and how many amps the controller has written on the label?

i think they are panasonic cells or claim to be at least, and 18650 type - amps on controller is 26

 

[Ianb84]

According to what I have understood from some good links on the net, the upper 10% and the lower 30% are considered by a good charging system to not to be used.
The charger voltage should stop at the upper limit, and the battery safety electronics will stop at the lower limit.
You can charge your battery and measure the voltage across the battery when the LED (generally) goes green to say that charging is stopped.
The voltage you should should be seeing is 4.2 volts x the number of cells or cell groups. For 48 volt nominal Li-ion batteryies, that should be 13 in series. I reckon that to be 54.6 volts max for safety.
My battery for example is a nominal 36 volt and I see exactly 42 volts when charging is finished (Not a micro volt more) and the battery is fully charged, so mine is 10 cells in series.
How many are in parallel for the 10 groups, depends on the maximum current needed.
I have two chargers and both show exactly the same "end voltage" of 42 volts.
But I have read here of chargers that "over charge" which will significantly impact the life of a battery. Not seen any myself, but I try always to err on the side of quality and safety.....
What some here do not believe is that leaving a charger connected for periods AFTER full charge is achieved, can be very detrimental to the batteries life. You also see it on any products that use such batteries such as laptops! People forget to only partially charge the battery, and remove it from the laptop,when running on the mains. They are surprised when the battery dies early!!
So I modified a very cheap electro mechanical time switch, so when the set time is reached, it not only completely removes mains power to the charger, it also switches itself off completely.
All you need to know is how long a charge takes approximately and set that on the timer!
Its a tiny bit "hit and miss", but still better than nothing!
I use such things whenever I charge ANY type of battery.....
It allowed my last e-bike to achieve over 6 years of usage, and the bike was given away still fully working, and no noticeable drop in capacity.
Though of course some loss was probably there, but I never ever needed to test very exactly! It still did the miles I needed each day....
Over 30,000 Kms in all....
I keep telling myself that I should build an electronic switch, that senses when the battery is fully charged EXACTLY and remove the mains completely and not reapplying it!
I did it for a LA charger for my caravan some years ago and that works (still very) well, and its quite simple to do really!!
That battery is 15 years old and still going, but is LA not Li-ion!! Different chemistry!!
If I can help further, just ask.
Andy

thanks for reply -

so just to confirm , when my battery life shows 20% does that actually mean ive got that 20% plus the 'unused' 20%?

AND - i was thinking about a hive smart plug, to just set to turn off after say 5 hours give or take , so think i'll get one as theres times ive had to leave on all night as it wasnt fully charged by bed time and need for next morning....

 

[soundwave]

at 26a that is a big ask from a small batt like that imo you want one double that size to get a longer life out of it.

 

[Andy-Mat]

thanks for reply -

so just to confirm , when my battery life shows 20% does that actually mean ive got that 20% plus the 'unused' 20%?

AND - i was thinking about a hive smart plug, to just set to turn off after say 5 hours give or take , so think i'll get one as theres times ive had to leave on all night as it wasnt fully charged by bed time and need for next morning....

I believe the "lower" 30% is not used in a well set up system, though I have not worked out the math myself.
In total, you cannot use 40% as I understand it.....
Your 20% is/should be above the unusable bottom 30%.
Eg. You still have 20% before power is cut off by the electronics in the battery. Or should be.
Another poster had a good question about how many cells were in parallel. A very good question as this is part of the maximum current set up....If you know how many cells in total, simply divide by 13 and then you know how many in each set.
Then you add up the maximum current allowed from each battery in one set, I would set the controller to a slightly lower value myself....Just to be safe. But its an area that I have never adjusted.....Too many things can go wrong, big time....Fire and explosion.......
Best wishes
Andy

 

[Ianb84]

at 26a that is a big ask from a small batt like that imo you want one double that size to get a longer life out of it.

ok perfect, so double the AH ?

 

[Ianb84]

I believe the "lower" 30% is not used in a well set up system, though I have not worked out the math myself.
In total, you cannot use 40% as I understand it.....
Your 20% is/should be above the unusable bottom 30%.
Eg. You still have 20% before power is cut off by the electronics in the battery. Or should be.
Another poster had a good question about how many cells were in parallel. A very good question as this is part of the maximum current set up....If you know how many cells in total, simply divide by 13 and then you know how many in each set.
Then you add up the maximum current allowed from each battery in one set, I would set the controller to a slightly lower value myself....Just to be safe. But its an area that I have never adjusted.....Too many things can go wrong, big time....Fire and explosion.......
Best wishes
Andy

i dont know how many cells but will try and fond out,
thanks again,
Ian.

 

[soundwave]

ok perfect, so double the AH ?

if you are pulling lots of amps then a bigger pack the better for it to last longer as less stress on the hole pack.

thats what is left of his bike after he tried to pull 90a from a normal small frame batt and it vaporised in to a fire ball 6ft high pmsl.

 

[vfr400]

It's the type of cells that are important. Panasonic make many different types with different capabilties. My guess is that they're the 3400mAh ones, which are supposed to be rated at 6A each, but in my experience, 4A is more like it, so with 4 in parallel, your battery is good for 16A. That's aĺ based on a guess though. Without knowing exa tly what you have, I can't be sure.

When they test the 500 cycles, that would be at a much lower current. The higher the current, the faster they wear out and a high speed direct drive motor like yours draws the maximum current a lot of the time.

If you replace the battery, you can use a 52 cell battery as long as the cells are rated at 20 amps. A 65 cell battery with the same 20A cells would be better.

 

[jokskot]

I'm not sure I understand what is meant by 80% capacity.
Taking as an example a 36v battery which will be fully charged at 42v and which will be unusable when the voltage, controlled by the BMS, drops to 30v or so.
Is the 80% of 42v (ie about34v) or 80% of {42-30} + 30 (ie about40v)?

 

[vfr400]

We normally refer to the capacity of a battery as being the charge between the low cutoff and the high cutoff. That's 100% capacity.

Say you had a 10Ah battery or a 400Wh one, 80% would be after it was down 2Ah and 80Wh respectively from fully charged. 20% would be 8Ah and 320Wh down. You'd have to measure those values with a wattmeter and see at which voltage those points occur. You can't scale the voltage because it's not linear. It goes down rapidly at first, then for the larger part is a ramp, then it starts to accelerate downwards towards the end. If you scaledthe voltage to 80% and 20%, it would be equivalent to capacities of around 90% and 7%.

It's all academic because you should only chage an ebike battery to 100%, i.e. to when the charger gives the green light.

By using the 80% 20% rule, you not only kill your battery, but you give up 40% of its capacity or effectively increase your mass per amp-hour by 40%, in which case, it would be much better to get a LiFePO4 battery, which will last four times as long for the same cost and weight without all the messing about.

 

[Andy-Mat]

I'm not sure I understand what is meant by 80% capacity.
Taking as an example a 36v battery which will be fully charged at 42v and which will be unusable when the voltage, controlled by the BMS, drops to 30v or so.
Is the 80% of 42v (ie about34v) or 80% of {42-30} + 30 (ie about40v)?

As I understand it, neither.
The 42 volts of a 36 volt battery, is the theoretical point, that is in fact 10 % below the "absolute" full. But it wears the batteries out really rapidly, so good electronics does not even charge above 42 volts (or 4.2 volts per cell). The 30 volt level is the last 30% of the remaining capacity, 0 volts is 0 % of capacity. But discharging below this 30 volts will seriously damage the battery.
So good battery or controller electronics prevents going below this value.
This is still above the point at which a battery "refuses" to charge anymore. That is that it shows a green LED as in full, but is actually very empty! Below 28 volts on a 36 volt battery.
Good bike shops have a special "0 Volt" charger, that will breath life back into the battery if it refuses a charge for that reason alone, but the normal charger will not charge till the battery achieves above a certain safety level, close to 30 volts.
But the battery will be a little bit damaged from that low voltage, depending upon how long it was very low....
Some bike shops will not do such a charge, they will only try and sell you a new battery.....
Remember, to try and give a buyer the opinion that a bike can go further than others, some charging systems over charge, but thereby reduce battery life dramatically....
Short battery guarantee times are an indication of such things IMHO!!
regards
Andy

 

[Ianb84]

It's the type of cells that are important. Panasonic make many different types with different capabilties. My guess is that they're the 3400mAh ones, which are supposed to be rated at 6A each, but in my experience, 4A is more like it, so with 4 in parallel, your battery is good for 16A. That's aĺ based on a guess though. Without knowing exa tly what you have, I can't be sure.

When they test the 500 cycles, that would be at a much lower current. The higher the current, the faster they wear out and a high speed direct drive motor like yours draws the maximum current a lot of the time.

If you replace the battery, you can use a 52 cell battery as long as the cells are rated at 20 amps. A 65 cell battery with the same 20A cells would be better.

Ok thats great - i dont quite understand the 52 / 65 cells part, is this still or a 48V battery, better yet if you can point me in right direction where to get one
Also i was reading a 52V battery would get more speed and i se these with 20ah, would that be worth it if im changing battery anyway?

thanks again,
Ian.

 

[soundwave]

https://ebikebatteries.co.uk/

they can make custom packs any size you want

 

[vfr400]

48v is 13 groups of 18650s in series. You can have 2, 3, 4, 5, etc cells in each group., so 4 x 13 would be 52 cells and 5 x 13 would be 65 cells. The current is shared between the cells in the group, so in a 52 cell battery at 24 amps, each cell has to give 6 amps. In a 65 cell one, each cell has to give 4.2 amps approx. You can tell how many cells you have by the weight. 52 cells is around 3.5 kg and 65 is over 4kg.

52v 20Ah would probably 7cells in the group and 14 in series , so 98 cells total, which will weigh well over 5kg. Where are you going to put it?

 

[Ianb84]

48v is 13 groups of 18650s in series. You can have 2, 3, 4, 5, etc cells in each group., so 4 x 13 would be 52 cells and 5 x 13 would be 65 cells. The current is shared between the cells in the group, so in a 52 cell battery at 24 amps, each cell has to give 6 amps. In a 65 cell one, each cell has to give 4.2 amps approx. You can tell how many cells you have by the weight. 52 cells is around 3.5 kg and 65 is over 4kg.

52v 20Ah would probably 7cells in the group and 14 in series , so 98 cells total, which will weigh well over 5kg. Where are you going to put it?

hmmm looks like they can be strapped in the triangle, i'm guessing this is a bad idea? Too much weight for velcro straps to hold?