Charger strange behaviour (53.5V)

Recently I've acquired 10.4Ah 48V LG M26 pack from Unit Pack Power together with 2A charger.

The battery was removed from the bike, the switch is in off position and it's connected to the charger.
When the charging was over, indicated by the led, switching from red to green, I've disconnected it, turned on the battery and measured the voltage on the battery connector where the motor is connecting. Voltage is 53.5V. This means cells are charged to 4.11V, not 4.20V.

If I connect charger again but switch the battery to on, it will start charging. If the battery is in off position charger is reporting battery is full.

Any idea what's happening here?

What's the charger voltage ?

999zip999 said:

What's the charger voltage ?

Click to expand...

Without load, 54.2V.

On a charger it says "model: XVE-5460200"

It's this one: http://www.jinxinyupower.com/en/c2410.html

13 in series x4.2 is 54.6.

Just under that is a bit better for longevity, but with such a low charge rate, just stopping at 4.2V is a good strategy, rather than holding Absorb / CV stage for too long.

Voltage always drops once charge stops, perfectly normal.

Put a slight low-amp load on the pack for a few seconds, then rest it will drop a bit more.

3.6-3.7Vpc working range is still very high SoC, depending on the load.

Measure the V / A of the charge cycle while it's active to see what's specifically happening but afaic all is well.

john61ct said:

13 in series x4.2 is 54.6.

Just under that is a bit better for longevity, but with such a low charge rate, just stopping at 4.2V is a good strategy, rather than holding Absorb / CV stage for too long.

Voltage always drops once charge stops, perfectly normal.

Put a slight low-amp load on the pack for a few seconds, then rest it will drop a bit more.

3.6-3.7Vpc working range is still very high SoC, depending on the load.

Measure the V / A of the charge cycle while it's active to see what's specifically happening but afaic all is well.

Click to expand...

So to recap what happened.
When charging battery while turned off, end voltage is 53.5V, charger stopped at this voltage.
When charging battery while turned on, end voltage is 54.1V.
I don't have a problem with this only if BMS did the balancing.
I planned anyway to use m604 circuit to stop charging at 4.05V per cell (52.65V), then every week or so do the full charge.
How can I know if BMS did the balancing of the cell groups?

The charger will be a simple dumb charger it only supplies charge voltage if the BMS allows it to,the charger doesn't dictate the charging it just responds to the BMS which will or will not except a charge voltage.

The switch is linked to the balance side of the BMS and typically the balance occurs above 4.15v per cell.
Unless you have away of monitoring cell groups then you have little option but to trust the BMS and allow full balance charge each time. If short charging or charging with switch off you run the risk of unbalance with a BMS .

Issue with only charging to 52.65v is assuming all cells are at 4.05v and they charge evenly which might not be the case, the case could be you end up with more unbalance and cell groups could be out by as much as 0.5v low to high. You can only know for sure if you can monitor all 13 groups.

hefest said:

I planned anyway to use m604 circuit to stop charging at 4.05V per cell (52.65V), then every week or so do the full charge.

Click to expand...

Interesting, have you got a link to a detailed datasheet?

Good experience with the reliability / longevity of this board?

Up to how many charging amps can it tolerate?

Or does the on/off relay actually control the AC input to the charger, or integrate with a remote switch port of the charger or something else?

> How can I know if BMS did the balancing of the cell groups?

Don't you have the ability to measure / monitor the cell voltages? Or at least the paralleled groups?

But really, for that level of precision do not trust anything but a known-good calibrated DMM.

Also a link to the BMS manual, or at least a tech specs datasheet would be helpful.

For now you need to know at what voltage it starts the balancing process, and how many amps (or more likely mA) per cell balancing current is available.

What would be nice to know is the state of charge.
1. 4.15
2. 4.01
3. 4.20v


13. Xxx volt

hemo said:

The charger will be a simple dumb charger it only supplies charge voltage if the BMS allows it to,the charger doesn't dictate the charging it just responds to the BMS which will or will not except a charge voltage.

The switch is linked to the balance side of the BMS and typically the balance occurs above 4.15v per cell.
Unless you have away of monitoring cell groups then you have little option but to trust the BMS and allow full balance charge each time. If short charging or charging with switch off you run the risk of unbalance with a BMS .

Issue with only charging to 52.65v is assuming all cells are at 4.05v and they charge evenly which might not be the case, the case could be you end up with more unbalance and cell groups could be out by as much as 0.5v low to high. You can only know for sure if you can monitor all 13 groups.

Click to expand...

Great info, thanks.

So it's not the charger that stops charging once the voltage of battery gets to a certain level, but it's actually chargers response to the BMS stopping the charging process. Did I get this right?

My understanding was that charging battery full every time is going to reduce it's lifetime. What I gathered from various sources is that charging usually up to 80-90% is extending battery life and now and then to 100% to balance it. Is this wrong or should I just let the charger and BMS charge it to full every time, which in my case is 4.11V per cell?

john61ct said:

hefest said:

I planned anyway to use m604 circuit to stop charging at 4.05V per cell (52.65V), then every week or so do the full charge.

Click to expand...

Interesting, have you got a link to a detailed datasheet?

Good experience with the reliability / longevity of this board?

Up to how many charging amps can it tolerate?

Or does the on/off relay actually control the AC input to the charger, or integrate with a remote switch port of the charger or something else?

> How can I know if BMS did the balancing of the cell groups?

Don't you have the ability to measure / monitor the cell voltages? Or at least the paralleled groups?

But really, for that level of precision do not trust anything but a known-good calibrated DMM.

Also a link to the BMS manual, or at least a tech specs datasheet would be helpful.

For now you need to know at what voltage it starts the balancing process, and how many amps (or more likely mA) per cell balancing current is available.

Click to expand...

I think xh-m604 is DC relay that cuts out charger after battery reached certain voltage.
Maximum current is not specified but because it's relay I think it can handle my 2A easily.

I don't have a way to monitor the cell groups unless I open the case and measure it myself (which I'll probably do at some point). Battery is pre-built one with who knows what BMS from Unit Pack Power.

http://www.icstation.com/mobile/m604-charge-control-module-battery-protection-board-controller-lithiumlead-acid-battery-p-11314.html

hefest said:

So it's not the charger that stops charging once the voltage of battery gets to a certain level, but it's actually chargers response to the BMS stopping the charging process. Did I get this right?

Click to expand...

There are many possible permutations.

Personally I wouldn't pull the trigger until I learned exactly how the prospective pack worked, in detail.

Most cheap BMS just bleed off incoming charge - at a crazy silly slow amp rate - from the higher cells while waiting for the lower ones to rise.

And most do not start this process until the voltage is already higher than what is good for longevity.

Thus balancing can take a very long time if imbalances are significant, especially as the pack ages.

Which will happen more quickly if that's the sort of BMS they use.

But for sure it will last through their warranty period

999zip999 said:

What would be nice to know is the state of charge.
1. 4.15
2. 4.01
3. 4.20v
13. Xxx volt

Click to expand...

13S pack, 53.5V just after charger shuts down, so not quite at rest?

4.12V right?

john61ct said:

999zip999 said:

What would be nice to know is the state of charge.
1. 4.15
2. 4.01
3. 4.20v
13. Xxx volt

Click to expand...

13S pack, 53.5V just after charger shuts down, so not quite at rest?

4.12V right?

Click to expand...

Not sure what you are asking.
Charger went from red to green on 53.5V, meaning it stopped the charging process. On one of the sites that sell this charger i read that once it goes to green, current charger is supplying is minimal. All this is with battery switch in OFF position.

When battery switch is in ON position, it chargers to 54.1-54.2V.

In the mean time UPP that sold me the battery responded to my question suggesting that battery switch should be in ON position while charging.

john61ct said:

hefest said:

So it's not the charger that stops charging once the voltage of battery gets to a certain level, but it's actually chargers response to the BMS stopping the charging process. Did I get this right?

Click to expand...

There are many possible permutations.

Personally I wouldn't pull the trigger until I learned exactly how the prospective pack worked, in detail.

Most cheap BMS just bleed off incoming charge - at a crazy silly slow amp rate - from the higher cells while waiting for the lower ones to rise.

And most do not start this process until the voltage is already higher than what is good for longevity.

Thus balancing can take a very long time if imbalances are significant, especially as the pack ages.

Which will happen more quickly if that's the sort of BMS they use.

But for sure it will last through their warranty period

Click to expand...

Oh well, so I should probably open up the battery and measure the voltage of each cell group periodically to be sure.

Another option would be to replace existing BMS with something else.

Yes, some batteries need to be "on" when charging. My 52vdc 11.5 AH Li Ion bottle battery is another example.

It's been mentioned, but a high quality multi-meter that reads accurately is a must when testing batteries and chargers.

I have a different take on a chargers duties though... As you will see in the thread below of a typical good quality charger operation is that it does not depend on the safety features of the battery's BMS to shut off. Which in my opinion would be terrible. The charger shuts off at a predetermined low current setpoint which should be about 5% of your charger's amperage output. (at full voltage...)The Battery's BMS should just be functioning as a last ditch effort to protect the battery's cells. Not as a means of charger shut-off control. Except in the balancing function of course. :wink:

Link as mentioned... https://electricbike.com/forum/foru...-to-adjust-the-luna-charger-mini-and-advanced

In your charger's description it makes it sound like your charger will continue charging even after your light turns green, at a reduced current. I would verify this to see if it's true. And also to see at what current it shuts off at.
A 48 volt nominal Li Ion battery should be charging to 54.6 volts for 100% charge. I would do this occasionally to allow the BMS to balance the cells. But do not leave it at 100% charge for long. For other charges, using your battery at mid range State Of Charge would allow the longest life of your expensive battery as shown in this chart...





Being just 4 tenths of a volt shy of 100% voltage charge and having normal range and operation would not compel me to open up my pack to check individual cells. Although down the road may be a good troubleshooting path. But I would check the charger over as per the link above for proper operation. And to allow time for balance charging over several charges.


Regards,
T.C.

I would not change the BMS unless for a good reason.

Adding the ability to see group voltages does not require that.

A picture of the BMS and were the 14 wires plug into it would be helpful that way we'd tell you if you have easy or good enough access to put the probes in and measure individual voltage. State of charge.

I'll leave it be for now, but not knowing the state of charge of the cells is making me nervous.
I'm used to balance charging LiPo/LifePo RC packs with enough information on my more advanced charger to know what's the state of the pack,
and I know how easy is to damage the cells if you over-charge/discharge.

In some time when I decide to open the pack, I'll probably see how tricky would it be to sometimes balance-charge it with my 8S 150W hobby charger.

Well you can measure the pack level voltage.

You know it's a 13S pack.

You measured 53.5V just after the charger stopped charging down, isn't that correct?

If so, 4.12V is a very good definition of Full.

The only uncertainty is the degree to which the cells are balanced.