Discharged Duracell Energy Bank 2

[Waynefb]

Good afternoon from Tasmania,

Not exactly a DIY battery but I am trying to DIY a fix for a discharged battery. I bought a property which has a Duracell Energy Bank installed which was left to discharege below the level the BMS would allow for re-charging (excuse my ignorance; I'm new to this).

The Duracell Energy Bank is a 6 module 14.4kWh battery. Each module has 10 cells and is 2.4kWh with a rated voltage of 32V and Operating Voltage Range of 28-36 Volts.

I have been advised to recharge the modules to 34 volts using a workbench power supply. Because the power supply is only rated to 30 Volts I was told to charge 5 cells at a time to 17 V.

I am using the power supply on a constant current until it reaches the desired voltage, and then constant voltage and decreasing current. I have two questions: should I set the constant voltage to a setting on the power supply that will allow the battery to reach 17 volts measured at it's terminals, or set the voltage on the power supply to 17 volts? Secondly at what point do I switch off the power supply - what is the bottom limit for the current where I turn off?

Many thanks for any input.
Cheers.

 

[crossy]

How long has the beast been left in the over-discharged state??

I assume you have access to the individual cells in each group. Check all the cell voltages, any that are below about 2V may have suffered permanent damage

If all the cells are over 2V set your power supply to 17V with it disconnected, do NOT adjust the voltage again. Connect it up to a group of 5 and wind the current to maximum.

Since you won't have the protection of the BMS you will need to watch the cell voltages to ensure none go over 3.6V or so.

In reality you don't need to fully charge the cells, just get them to a voltage (3V or so) where the BMS will actually allow charge. Then the normal charger should do the job.

 

[Waynefb]

Thanks very muc for your reply, I am most grateful.

How long has the beast been left in the over-discharged state??

Approximately 2 years or thereabouts.

I assume you have access to the individual cells in each group. Check all the cell voltages, any that are below about 2V may have suffered permanent damage

Yes I have the module open and they are accessible. I did measure the voltage of the modules earlier and they were all around 11 volts or less, so definitely less than 2 V per cell (10 cells in each module)

If all the cells are over 2V set your power supply to 17V with it disconnected, do NOT adjust the voltage again. Connect it up to a group of 5 and wind the current to maximum.

Since you won't have the protection of the BMS you will need to watch the cell voltages to ensure none go over 3.6V or so.

In reality you don't need to fully charge the cells, just get them to a voltage (3V or so) where the BMS will actually allow charge. Then the normal charger should do the job.

OK, I am doing that now. The power supply is set to not go over the constant voltage of 17V which it has reached and this translates to a cell voltage of ~3.3V. Current is now reducing while the voltage remains constant. I have read that I should not let the current below 0.02C which I have calculated to be 3.75 A. (2.4kWhx1000/32 = 75Ah; 75Ahx0.02=3.75) I hope I've understood that correctly. Any advice would be most helpful.

 

[crossy]

Can you measure the individual cell voltages? You really need to keep a close eye on them in case you have a completely dead cell!

EDIT My internet is playing silly-beggars at present and it's not even raining

 

[Waynefb]

Can you measure the individual cell voltages? You really need to keep a close eye on them in case you have a completely dead cell!

EDIT My internet is playing silly-beggars at present and it's not even raining

Yes, each cell is showing 3.3V. I'm watching them.

 

[crossy]

If they stay at that level when you kill the charge you could move on to the next group.

If you've got all 10 cells at that level each the BMS "should" come alive. Maybe!

 

[Stevie Rae]

Can anyone help me with a Duracell Energy Bank 2. It keeps going offline and not showing any errors on a daily bases. Rendering the system useless. When I bought it I wasn't provided any monitoring or diagnostic software which I need to.