Battery charging anomalies

[Jodel]

A bit of a puzzle for those more electrically / electronically knowledgable than myself. I have Woosh DWG22C kits fitted to two of my bikes. Both have 48 volt 12Ah batteries and both have worked very well since their installation and continue to do so. I monitor battery charge cycles / voltages on a spreadsheet and have noticed a couple of anomalies of late.

Battery 1 is about 18 months old and would previously charge up to around 54.3 volts fresh off the charger.

Battery 2 is about 1 year old and normally charged up to around 53.8 volts fresh off the charger.

On both my kits, I rarely use more than assistance level 3 (of 5) and more often only use up to level 2. I can easily get 50 miles range so I don’t think the batteries are being particularly stressed. I have only ever used the supplied ‘Sans’ charger which has an output rated at 54.6 volts / 2 amps.

Within the last month, battery 1 now charges up to 54.8 volts, battery 2 charges to 54.3 volts.

In the case of battery 1, I didn’t think these 48 volt batteries could accept a charge beyond 54.6 volts, so I’m a bit confused. I’ve checked the voltage readings with two different DVMs and get the same readings. I’ve tried to check the output of the charger itself by using probes on the output plug, but I don’t get a constant voltage reading – it fluctuates considerably.

I don’t want to damage the batteries by overcharging, so my query is really around asking the forum members if they can offer any explanation for the increase in voltage reading from a freshly charged battery? Is is possible that the charger may be on the way out?

I’d rather buy a new charger than risk ‘cooking’ two perfectly good batteries.

Any comments or observations would be appreciated.

 

[flecc]

A bit of a puzzle for those more electrically / electronically knowledgable than myself. I have Woosh DWG22C kits fitted to two of my bikes. Both have 48 volt 12Ah batteries and both have worked very well since their installation and continue to do so. I monitor battery charge cycles / voltages on a spreadsheet and have noticed a couple of anomalies of late.

Battery 1 is about 18 months old and would previously charge up to around 54.3 volts fresh off the charger.

Battery 2 is about 1 year old and normally charged up to around 53.8 volts fresh off the charger.

On both my kits, I rarely use more than assistance level 3 (of 5) and more often only use up to level 2. I can easily get 50 miles range so I don’t think the batteries are being particularly stressed. I have only ever used the supplied ‘Sans’ charger which has an output rated at 54.6 volts / 2 amps.

Within the last month, battery 1 now charges up to 54.8 volts, battery 2 charges to 54.3 volts.

In the case of battery 1, I didn’t think these 48 volt batteries could accept a charge beyond 54.6 volts, so I’m a bit confused. I’ve checked the voltage readings with two different DVMs and get the same readings. I’ve tried to check the output of the charger itself by using probes on the output plug, but I don’t get a constant voltage reading – it fluctuates considerably.

I don’t want to damage the batteries by overcharging, so my query is really around asking the forum members if they can offer any explanation for the increase in voltage reading from a freshly charged battery? Is is possible that the charger may be on the way out?

I’d rather buy a new charger than risk ‘cooking’ two perfectly good batteries.

Any comments or observations would be appreciated.

I doubt you have anything to worry about, the fully charged voltage difference between the two batteries has remained consistent at 0.5 volts and the 0.2 volts peak rise is unlikely to cause any damage.

The identical small change on both batteries suggests you are simply experiencing mains voltage fluctuations, something which becomes more common with the colder weather as the grid tries to cope with rising demand.
.

 

[Woosh]

you have two chargers, swap them to see if the difference comes from the chargers.

 

[Jodel]

Thanks for the responses.

flecc - my first thought was also potential variations in the mains supply, but the charger can accept an input voltage range from 180 volts to 240 volts so I thought it should be able to accommodate minor fluctuations in the mains.

Woosh - I only have the one charger as it didn't seem necessary to buy another when I got my 2nd kit.

I'll continue to monitor the fully charged voltages on the batteries and if they keep increasing, will probably buy another charger to hopefully resolve the issue.

 

[StuartsProjects]

the charger can accept an input voltage range from 180 volts to 240 volts so I thought it should be able to accommodate minor fluctuations in the mains.

My chargers accept a voltage from 100v to 240v and a lot of laptop supplies are the same.

They design them this way so that the same product can be used the World over, just use a different plug. You would then expect that a small variation in mains voltage would have no readily measurable affect on the charger output.

 

[vidtek]

The mains supply is pretty well regulated here in the UK, compared with many other countries. I have rarely seen the supply drop below 220v and never seen it go above 250v.
The vast majority of the time it will be rock steady at between 230-240v. There will be larger variations outside urban areas, but even then I have never measured it to be below 220v.

Your charger will be a SMPS (switched-mode power supply) as used in 99% of chargers for whatever appliance you have. A mains transformer with simple rectification is an extreme rarity these days as they are vastly more expensive to produce and much heavier.

SMPS provide an extremely well regulated supply and it is very unlikely that is your issue unless you have a faulty one. How they work is the incoming mains supply is converted to a dc output by a high frequency oscillator which can then be calibrated to a very fine degree by circuitry with feedback loops and protection circiutry which dynamically alters the position on the rising waveform to account for fluctuations. This is all done by generic ic's and a few well-chosen peripheral components. In most circuits well over 60% of all components are for protection against things like possible thermal runaway of active components.

 

[Woosh]

You only have one charger:
One battery charges up to 54.3V the other up to to 54.8V
that's about 1% variation, both are within the normal range of fully charged cells.
Usually the older battery has lower voltage when full due to small loss of capacity over time.
Don't worry about it.

 

[Jodel]

vidtek - I spoke with a friend who studied electronics at Uni and has worked on (Industrial) electric motor control systems for many years. He pretty much stated the same things as you have above.

Woosh - I wasn't overly concerned, but am one of those irritating people who likes to understand things . Electronics have always been a bit of a mystery to me and my ageing brain cells were struggling to comprehend why the fully charged voltage readings from the batteries should have started to increase (rather than decrease) after being used for 18 months / 12 months respectively.

I'll just keep an eye on things and see how it goes.

 

[hussin]

A bit of a puzzle for those more electrically / electronically knowledgable than myself. I have Woosh DWG22C kits fitted to two of my bikes. Both have 48 volt 12Ah batteries and both have worked very well since their installation and continue to do so. I monitor battery charge cycles / voltages on a spreadsheet and have noticed a couple of anomalies of late.

Battery 1 is about 18 months old and would previously charge up to around 54.3 volts fresh off the charger.

Battery 2 is about 1 year old and normally charged up to around 53.8 volts fresh off the charger.

On both my kits, I rarely use more than assistance level 3 (of 5) and more often only use up to level 2. I can easily get 50 miles range so I don’t think the batteries are being particularly stressed. I have only ever used the supplied ‘Sans’ charger which has an output rated at 54.6 volts / 2 amps.

Within the last month, battery 1 now charges up to 54.8 volts, battery 2 charges to 54.3 volts.

In the case of battery 1, I didn’t think these 48 volt batteries could accept a charge beyond 54.6 volts, so I’m a bit confused. I’ve checked the voltage readings with two different DVMs and get the same readings. I’ve tried to check the output of the charger itself by using probes on the output plug, but I don’t get a constant voltage reading – it fluctuates considerably.

I don’t want to damage the batteries by overcharging, so my query is really around asking the forum members if they can offer any explanation for the increase in voltage reading from a freshly charged battery? Is is possible that the charger may be on the way out?

I’d rather buy a new charger than risk ‘cooking’ two perfectly good batteries.

Any comments or observations would be appreciated.

Unbalance group cells can you open and charge the group alone uses charger 4.2v

 

[harrys]

I am surprised that you cannot verify the open circuit output voltage on your charger, I suspect it's drifted upward a little.

If the BMS is working right, it should limit each of the 13 groups in the battery to a max of 4.2V. If it were me, I would probably get nervous about the 54.8 and look inside. If four groups were .05V high, that;s no big thing. If one group was at 4.4V though, I'd be worried. That'swhy I look.

One time,. I had installed a new BMS and it failed and let 3 banks of cells hit 4.5V. Now I always test after a new BMS goes on. Oh, I binned those three bank. Fifteen cells scrapped. Don't trust batteries.

 

[Woosh]

I am surprised that you cannot verify the open circuit output voltage on your charger, I suspect it's drifted upward a little.

If the BMS is working right, it should limit each of the 13 groups in the battery to a max of 4.2V. If it were me, I would probably get nervous about the 54.8 and look inside. If four groups were .05V high, that;s no big thing. If one group was at 4.4V though, I'd be worried. That'swhy I look.

One time,. I had installed a new BMS and it failed and let 3 banks of cells hit 4.5V. Now I always test after a new BMS goes on. Oh, I binned those three bank. Fifteen cells scrapped. Don't trust batteries.

54.8V / 13 = 4.21V
It's perfectly acceptable.
when the charger's output has noload, the voltage you may read on its output terminals can be anything because it's in protected mode so if you want to measure the charger's output voltage, measure at the battery's output terminals.
There is also roughly about 0.25V voltage drop through the charging FET.