Battery & charger advice please?

[superjonnyboy]

Hi all,

I have just clocked up 1000miles on my converted hardtail MTB and have noticed some changes with the battery and charger behaviour.

Now, here's the tricky bit. I don't know what the battery chemistry or cell count is. I know the first piece of advice to be offered will be to tear the battery down and find out but that's going to be a mammoth task given the installation and I'm not sure I want to go down that route. I wonder if anyone can make any deductions based on the following information?

1. The kit was sold a "1500W Electric Bike Kit including 60V 18ah Battery".

2. When the kit was new, I recall the battery charging to about 71.4V, however, now it only holds 69.2V.

When the charger has finished bulk charging and the BMS is balancing, the voltage does briefly pulse up to 71-72V, but it would appear the cells cant quite hold it there, like when new. Not a major change but in my previous experience with RC LiPo batteries, a cell not holding full charge was not a good sign. This may be perfectly normal with Li-ion though, I don't know so require educating

I have also read that it could be the charger drifting away from nominal and adjusting one of the internal poti's to a higher cut off voltage may help, but not sure if this is a good idea? There are 3 poti's inside that aren't labelled.

Is it possible to comment on this information as to what chemistry the battery is "likely" to be? At 71.4V fully charged (new), my guess would be 17S Li-ion.

The reason I'm trying to work this out is that I need another charger. I'm commuting on the bike and not doing much pedalling to be honest, so a top up in work would be handy. I'm thinking of keeping the supplied 5A charger in work and buying maybe a 2A charger for overnight at home.

I see lots of chargers for sale and 60V seems to be commonly quoted, would this be the right spec? What I mean is do the chargers quote nominal battery voltage in their specs, as opposed to fully charged voltage, for example? What's confusing is that I also see 71.4V 17S chargers listed, so there seems not to be a norm for the labelling.

Thanks all,
Jon

 

[superjonnyboy]

For what it's worth, here's a few pics of the battery and some detail on the controller label. Also a stock image of what the charger looks like.

 

[vfr400]

Can you show us a photo of the charger's label?
It's normal for a LiFePO4 battery to drift down after charging. The normal charging voltage for a 20 cell one would be 73v.

 

[superjonnyboy]

Can you show us a photo of the charger's label?
It's normal for a LiFePO4 battery to drift down after charging. The normal charging voltage for a 20 cell one would be 73v.

I can do later when I get home...if my battery gets me there

What I can say is that the label has lots of specs listed on it. Various input & output voltages and charge rates, similar to the attached image.

There's ink dabs on 240V, 60V & 5A respectively.

But, battery chemistry is not listed. I wonder if that's even important - does the charger just supply CC & CV stages and the BMS control the cut-off voltage?

 

[Nealh]

Some sellers list charge voltage as nominal for battery or as max voltage.
You can check the charger output voltage if it is 71.4v then it should be fine and any fault is likely within the pack.

 

[vfr400]

Life isn't inked, so it must be a normal li-ion one. 71.4v is 17 cells. It's probably a bit out of balance and what you're seeing is the bleeding off of the high cells.

 

[superjonnyboy]

Some sellers list charge voltage as nominal for battery or as max voltage.
You can check the charger output voltage if it is 71.4v then it should be fine and any fault is likely within the pack.

Yes, I'm seeing this now. Seems like there isn't a standard practise for listing specs.

Life isn't inked, so it must be a normal li-ion one. 71.4v is 17 cells. It's probably a bit out of balance and what you're seeing is the bleeding off of the high cells.

Makes sense, I have suspected a low cell or two. I've never been a fan of the stock charger putting 5A in, despite being a large capacity battery. I'd rather a lower charge rate to allow the BMS more time to balance - probably psychological though and in reality makes no difference.

I think I'll check the plug pin configuration tonight and look for a 2A charger. If a new charger gets the pack back up to 71.4V, then I can consider tweaking the cut-off voltage of the old one.

 

[Nealh]

Tweaking charge cut off voltage will lead to what you are experiencing currently unless a smart bms (uart/Bluetooth) is fitted, std bms use top balance when voltage is near the end with less then 5% to go ( 4.15 - 4.2v per cell group).

 

[superjonnyboy]

Tweaking charge cut off voltage will lead to what you are experiencing currently unless a smart bms (uart/Bluetooth) is fitted, std bms use top balance when voltage is near the end with less then 5% to go ( 4.15 - 4.2v per cell group).

That's interesting info, thanks. I only intend to tweak the charge cut-off voltage if it has drifted below 71.4 V (to be measured). I have read this can happen on some Luna Cycle chargers in this thread...

How to adjust the Luna charger (mini and advanced) - Electricbike.com Ebike Forum

https://www.youtube.com/watch?v=taNI-7x5BoY&feature=youtu.be Charger fine tuning basics https://www.youtube.com/watch?v=H9ENLcYFn54&feature=youtu.be Example of adjusting a charger How to adjust the Luna charger They all have 3 potentiometers in them, we will call...

electricbike.com

Having re-read the article, actually I wonder if it's the charge current cut off that's out, based on this paragraph...

"To Adjust P3, the current cutoff.

The only reason I see that you should play with this one is that you have adjusted the P1, and the cells are balanced and you still don't get the 100% you wished for... The charger is maybe cutting too soon in the CV phase... not charging long enough at low amps.

I found that my older advanced 300W shifted a bit and was cutting at 0.6amps (over the 10%) So I set it back to 5% current (0.25amp) and charging took a couple minutes longer but actually got the 58.8V."

This may explain the rapid on/off charging I see when the pack is near full. The BMS wants a few milliamps to top the cells up but the charger supplies too much?

 

[Nealh]

That's interesting info, thanks. I only intend to tweak the charge cut-off voltage if it has drifted below 71.4 V (to be measured). I have read this can happen on some Luna Cycle chargers in this thread...
to-adjust-the-luna-charger-mini-and-advanced[/URL]

Argh thanks for clarifying , I misunderstood your intentions.
I regularly check my chargers for drifting and adjust the V pot if need be.
I had a pair of 36v Sans that both drifted to 42.6v and brought them back down to 42v.

 

[superjonnyboy]

The challenge now is to find out which of the blue pots adjust CC, CV and current cut-off in my charger. General concensus from other forums is that the max volts poti is the one on it's own near the edge of the board (bottom right). I may have to make a breakout cable to measure charging current (will tune it down a bit from 5A) and to identify the current cut-off poti.

Unless anyone knows for sure which is which?

 

[Nealh]

The current pot will be one of the pair by the shunt and the voltage next to the CAP at C1.

 

[Andy-Mat]

Hi all,

I have just clocked up 1000miles on my converted hardtail MTB and have noticed some changes with the battery and charger behaviour.

Now, here's the tricky bit. I don't know what the battery chemistry or cell count is. I know the first piece of advice to be offered will be to tear the battery down and find out but that's going to be a mammoth task given the installation and I'm not sure I want to go down that route. I wonder if anyone can make any deductions based on the following information?

1. The kit was sold a "1500W Electric Bike Kit including 60V 18ah Battery".

2. When the kit was new, I recall the battery charging to about 71.4V, however, now it only holds 69.2V.

When the charger has finished bulk charging and the BMS is balancing, the voltage does briefly pulse up to 71-72V, but it would appear the cells cant quite hold it there, like when new. Not a major change but in my previous experience with RC LiPo batteries, a cell not holding full charge was not a good sign. This may be perfectly normal with Li-ion though, I don't know so require educating

I have also read that it could be the charger drifting away from nominal and adjusting one of the internal poti's to a higher cut off voltage may help, but not sure if this is a good idea? There are 3 poti's inside that aren't labelled.

Is it possible to comment on this information as to what chemistry the battery is "likely" to be? At 71.4V fully charged (new), my guess would be 17S Li-ion.

The reason I'm trying to work this out is that I need another charger. I'm commuting on the bike and not doing much pedalling to be honest, so a top up in work would be handy. I'm thinking of keeping the supplied 5A charger in work and buying maybe a 2A charger for overnight at home.

I see lots of chargers for sale and 60V seems to be commonly quoted, would this be the right spec? What I mean is do the chargers quote nominal battery voltage in their specs, as opposed to fully charged voltage, for example? What's confusing is that I also see 71.4V 17S chargers listed, so there seems not to be a norm for the labelling.

Thanks all,
Jon

I probably cannot answer all your queries on the strange behaviour of the Battery/voltage/charger sadly, as I have never seen anything like it myself. Hopefully someone else has and can assist!
I would imagine that you have 18650 Li-ion cells, thats usual nowadays. They are available everywhere, but stick to good makes if you eventually re-cell. My personal recommendation is Panasonic cells, but they are the only ones I have ever used!!
I can only imagine that the problem is for some reason, some cell(s) are not working as well as they should!
I stress, that is a guess only.
And they are screwing up the BMS in its operation, again guessing only.
It may help you to understand that usually, when speaking about any battery, the "nominal voltage" is quoted, as that saves misunderstandings.
In your case, that appears to be 60 Volts.
The battery fully charged will have a higher voltage, and when discharged (when the built in electronics refuses to supply more power), a lower voltage.
I have a 36 volt bike, and the charger will charge to a max of 42 volts. The lowest point of the battery discharge will be about 29-30 volts.
Much lower than this, which can be caused by forgetting to recharge, may cause the electronics to refuse a charge.
The correct usage of a so called "Zer0 Volt Charger", can usually recover the battery again, but not always.
Plus I personally have not seen one for a 60 Volt battery, but a good bike shop should be able to help, for a fee of course.
Extrapolating those values to a 60 volt battery, should give around these values, assuming that I have not made a mistake:-
Fully charged 71.4 volts (as you saw previously), and around 50 volts fully discharged.
If you still have guarantee, I would take it back to where you bought it from. Any DIY repair will remove that guarantee usually.
If you have no guarantee, try to find someone with good knowledge to have a look.
Do not forget that these batteries can under certain circumstances, burst into flame, and they are difficult to extinguish. Not good for your Office/house/garage! Make sure that you have an active smoke alarm where you charge any battery. On something made of metal or concrete, and that you are covered with the correct insurance!
I am sure you get the idea.
I wish you well and hope for some better ideas from others here....
regards
Andy

 

[vfr400]

I wouldn't mess with the charger. I guarantee that it won't solve your problem. Just leave the charger on for a long time after you get the green light to rebalance the battery.

 

[superjonnyboy]

I wouldn't mess with the charger. I guarantee that it won't solve your problem. Just leave the charger on for a long time after you get the green light to rebalance the battery.

I do. Left it overnight last night and still it wouldn't come up to the full 71.4V so it would appear that either the cut-off voltage is too low or cut-off current too high.

Having said that, there's lots of posts suggesting not to charge to 4.2V/cell for longer battery life, instead only charge to 4.1V/cell. Well, that's where I'm at now so perhaps it's no bad thing.

Maybe these chargers really are "smart" and it's doing me a favour

 

[Nealh]

Have you yet checked the charger out put with a meter and if it is 71.4v ?

This is what I eluded to in #8, 4.1v will cause cells to go out of balance as their is nothing in place to balance them. In the long run you will create more issues then there is to solve, the bms carries out balancing not the charger for lion.

Lion chargers are mostly dumb and a different set up to the more technical lipo balance ones. With lion the only way to balance at a lower voltage is to treat them like lipo (no BMS) a faff or install a smart BMS which are adjustable via BT/ uart.

 

[vfr400]

You can measure the voltage directly on the charger connector. Do not set your charger to lower than 4.2v per cell (71.4) or your battery will definitely go out of balance.

 

[superjonnyboy]

Have you yet checked the charger out put with a meter and if it is 71.4v ?

This is what I eluded to in #8, 4.1v will cause cells to go out of balance as their is nothing in place to balance them. In the long run you will create more issues then there is to solve, the bms carries out balancing not the charger for lion.

Lion chargers are dumb and a different set up to the more technical lipo balance ones. With lion the only way to balance at a lower voltage is to treat them like lipo a faff or install a smart BMS which are adjustable via BT/ uart.

You can measure the voltage directly on the charger connector. Do not set your charger to lower than 4.2v per cell (71.4) or your battery will definitely go out of balance.

OK so wise to go full 4.2V/cell to enable the BMS to balance. Of course, I am used to LiPo chargers that do the balancing. I'll check the charger voltage this evening, if it's drifted low, I'll tweak it back up.

If that doesn't work then I'll investigate lowering the cut-off current which will enable the bms to balance at lower milliamps after bulk charging. Coincidentally, with my LiPo charger I get a better balance after charging at lower rate, it just lets those last few wiggly amps sneak in to finish the job off.

I think I'm clear on what needs doing now, I'll report back with my findings.

 

[Andy-Mat]

I do. Left it overnight last night and still it wouldn't come up to the full 71.4V so it would appear that either the cut-off voltage is too low or cut-off current too high.

Having said that, there's lots of posts suggesting not to charge to 4.2V/cell for longer battery life, instead only charge to 4.1V/cell. Well, that's where I'm at now so perhaps it's no bad thing.

Maybe these chargers really are "smart" and it's doing me a favour

Have you checked your meter against a known good meter, or two?
Just a thought!
Andy

 

[superjonnyboy]

Have you checked your meter against a known good meter, or two?
Just a thought!
Andy

I haven't even measured anything yet with my meter, the voltage readings I've mentioned above are all from the KT3LCD display.

I have no reason to doubt my meter but fortunately I do have regulated benchtop power supplies and calibrated meters in work, so I can try that out tomorrow. I measured the battery voltage with a calibrated works Fluke this afternoon and there was a 0.15V discrepancy with the display which was reading higher so yes, worth bearing in mind!