Battery life

[guerney]

One doesn't need to mess with many parameters , only a few programmable parameters are the necessary ones.

Balance range adjustment 3.3v - 4.2v .
Over voltage 3.6v - 4.3v.
LVC 2v - 3.3v.
Over current & temperature.

With a large battery capacity if one has the needs to carry a so much weight and range then 4 - 4.05v balance will likely suffice , with a smaller capacity battery then 4.1v will be ok. The top end 0.1v of a charge carries little mah capacity and for most ebike batteries only equates to 1- 1.5 miles in range.

A monster pack of plus 30ah one could opt for less then 4v, though it is dependant how one uses that capacity vs discharge current used.

I'm suddenly nervous of continuing this line of enquiry, because it could lead to my soldering a smart BMS to a battery pack... which could go well, or catastrophic. I wouldn't do it to my existing battery, maybe to a Yose or something.

 

[StuartsProjects]

I power my battery charger via a timer as the general advice is to NOT leave batteries connected to the charger permanently (or longer than necessary).

I have seen this mentioned a few times, so what is the exact issue (apart from a waste of energy) of leaving the charger connected longer than necessary ?

 

[matthewslack]

I have seen this mentioned a few times, so what is the exact issue (apart from a waste of energy) of leaving the charger connected longer than necessary ?

Fire, either by a fault in the charger, or a fault in the BMS.

Should not be an issue with top end brands, although I have no statistics to offer in support of that, but disconnecting the mains supply takes the charger out of the picture, and means the BMS has no input power, so some faults can't happen.

 

[Bikes4two]

I have seen this mentioned a few times, so what is the exact issue (apart from a waste of energy) of leaving the charger connected longer than necessary ?

In addition to post #83, another issue is overcharging (a function of your charger) in that unless you have a calibrated DVM to measure the final charge voltage, you might be over charging your battery which will shorten the service life (discharge cycles) of the battery. In the absence of a calibrated DVM, it seems to me a sensible precaution to disconnect the charger once charging and balancing is complete just in case the final charge voltage is too high (a bit belts and braces I guess, but I'd venture it is good practice to switch off if no longer needed).

This paper here by Battery Universe (initially referenced by @WheezyRider in post #24) is worth a read, specifically around this bit -

and from this graph at the same source you can more clearly appreciate the effects of over charging on service life.

 

[StuartsProjects]

Fire, either by a fault in the charger, or a fault in the BMS.

Really ?

Failures in a lot of electronics stuff is often due to the physical stress when things switch on an heat up or switch off and cool down etc.

Something that has warmed up and is temperature stable, like a charger thats been on for a while is not that likely to fail. Electronic stuff tends not to 'wear out' so if you want it to last leave it switched on when its got to a stable temperature.

An exception would be moveable stuff, like fans in chargers, which can of course mechanically wear out.

 

[StuartsProjects]

In addition to post #83, another issue is overcharging (a function of your charger)

For sure you dont want to overchage a battery.

But if the charger has a cut-off voltage of 4.2v say, it cuts off charge when the batteries reach that point.

So how would leaving the charger connected cause overcharge, if you continue to apply charge after the 4.2V point, the battery voltage would continue to rise, implying that the charger is faulty and has not actually cut off charge at all.

 

[Bikes4two]

Re post #85 - I would mostly agree with you @StuartsProjects but failures outside of the scenarios you mention can happen, as unlikley as it might seem.

Let's say you've put your battery on charge in the bike shed - it's a fairly warm time of the year but the charger's fan is coping - but then the sun comes out, the ambient shed temperature rises AND the fan fails. It might be that the charger just overheats and fails passively - but maybe not.

Electrolytic capacitors dry out over time - who is to say what effect the failue of such a component may have on the charger.

Me, I am probably overly risk avers, so I switch my charger off when not needed, especially as like the ebike battery, it is unbranded and tested to undeclared standards.

Each to their own of course

 

[Bikes4two]

For sure you dont want to overchage a battery.

But if the charger has a cut-off voltage of 4.2v say, it cuts off charge when the batteries reach that point.

What I'm saying is, how confident can you be, in the absence of a calibrated DVM, that the cut-off voltage (and enabling circuitry) is correct?

 

[StuartsProjects]

Electrolytic capacitors dry out over time - who is to say what effect the failue of such a component may have on the charger.

Oh, indeed they do. But in general thats only a significant issue if there left unused for long periods, the chemical film that is the insulator breaks down with age and can get shorts (and explosions) at switch on.

I have to switch on my 1940s valve radio that I have in my workshop (great for listening to the cricket on LW) every few months, just to make sure I the electrolytics dont degrade.

 

[StuartsProjects]

What I'm saying is, how confident can you be, in the absence of a calibrated DVM, that the cut-off voltage (and enabling circuitry) is correct?

You cannot of course, without checking, but if the charger takes the batteries above the safe limit during 'normal' operation, the damage is already done.

 

[soundwave]

 

[WheezyRider]

For sure you dont want to overchage a battery.

But if the charger has a cut-off voltage of 4.2v say, it cuts off charge when the batteries reach that point.

So how would leaving the charger connected cause overcharge, if you continue to apply charge after the 4.2V point, the battery voltage would continue to rise, implying that the charger is faulty and has not actually cut off charge at all.

Most chargers do not cut off and stop applying power at 4.2 V. All that happens is that there is a sensor circuit detecting when the charging current drops below a preset value. Typically, this is about 150mA for a 10s string of cells. When this happens, the LED changes from red or orange to green. When the green light comes on, it does not mean charging is complete at this point. Gradually, the current will drop down to less than 10 mA and charging is complete.

The issue is that if the charger is then left connected, the battery is not being allowed to relax from its maximum potential point of 4.2V, it is pinned there by the charger. It is the voltage, not the current that is the issue. Reactions at the interfaces depend on electrode potentials. When the charger is disconnected, the battery voltage will relax and drop slightly, reducing the strain on the electrode interfaces.

 

[soundwave]

 

[guerney]

Electrolytic capacitors dry out over time - who is to say what effect the failue of such a component may have on the charger.

These have caused many a failure in computer motherboards and driver boards for LED monitors I have owned - suddenly I am very determined to measure the voltage of my charger before every battery charge! And to open the charger to look for capacitor puffiness every so often, and perhaps buy a new charger every couple of years as a precaution.

 

[WheezyRider]

These have caused many a failure in computer motherboards and driver boards for LED monitors I have owned - suddenly I am very determined to measure the voltage of my charger before every battery charge! And to open the charger to look for capacitor puffiness every so often, and perhaps buy a new charger every couple of years as a precaution.

I wouldn't worry too much, quite often I find in a lot of chargers the large electrolytics are not soldered into the board properly in the first place...

If you are worried, buy some known brand quality electrolytics and solder them in.

 

[guerney]

I wouldn't worry too much, quite often I find in a lot of chargers the large electrolytics are not soldered into the board properly in the first place...

Well that's just marvellous, isn't it? A knock or small drop away from ebike battery fire...

If you are worried, buy some known brand quality electrolytics and solder them in.

My charger is now two years old: many a LED monitor driver board would be failing around now, like the one in the monitor I'm using right at this very moment - time to be nervous and buy a new charger methinks, and look into replacing caps in the old one.

Electrolytic capacitors dry out over time - who is to say what effect the failue of such a component may have on the charger.

Thank you - I have found this to be quite triggering.

 

[WheezyRider]

Well that's just marvellous, isn't it? A knock or small drop away from ebike battery fire...



My charger is now two years old: many a LED monitor driver board would be failing around now, like the one in the monitor I'm using right at this very moment - time to be nervous and buy a new charger methinks, and look into replacing caps in the old one.



Thank you - I have found this to be quite triggering.

I wouldn't throw it away, I'm using laptop chargers that are more than 10 years old. Several of my ebike chargers are years old. They all still work.

Modern electrolytics don't die because of drying out. It's usually because the electrolyte hasn't been formulated properly. Then the protective oxide layer breaks down, you get electrolysis occurring, gas builds up and the can ruptures, or you get significant conduction through the oxide layer and in effect a short, which leads to rapid failure.

If you are worried, open up the charger and have a look at the PCB and components.

 

[WheezyRider]

The water ingress problem is really interesting. Probably should dismantle a pack once a year to check the internals...

Also, the Bluetooth BMS draining the pack is interesting. Glad I put ports on mine for manual measurement.

 

[guerney]

I wouldn't throw it away, I'm using laptop chargers that are more than 10 years old. Several of my ebike chargers are years old. They all still work.

After throwing away older laptops, I think the oldest laptop and charger I have left is a Toshiba made in 1998, and it still works. I have increasing low confidence in modern electronic products, which I believe are designed to fail far quicker - particularly the cheap ones.

If you are worried, open up the charger and have a look at the PCB and components.

My last charge was a couple of days ago, caps will be empty by now. I'll have a good nosey around...

 

[guerney]

dont buy any bms with Bluetooth it will drain the pack flat my bike light does this if the pack is connected even turned off as constantly searching for the remote.

Also, the Bluetooth BMS draining the pack is interesting.

Can't that be prevented by adding a physical switch to the bluetooth module's power wire? Or would the smart BMS detect it's apparent absence after powering on, and report an error and/or not function?