question

Bruno M avatar image
Bruno M asked

IP22 charger cycling between BULK and ABSORPTION too quickly

Hi,

I'm charging a 250 AH li-ion batterie equipped with an internal BMS.

When connected to mains, the charger start in BULK charging at 30A, and quickly switches to ABS (around 3A, which is correct).

But a few dozen of seconds later, it goes back to BULK charging at 30A, and a minute later back to ABS, and cycles like this.

Load on the battery is light at this time (around 10W), and from my understanding, ABS should maintain a fixed voltage and provide the current absorbed by the battery (+load). No reason to switch back to BULK charging.

I see alternating BULK (buzzing) /ABS (silent) every minute. I'm providing four screenshots of the app with phone's time to illustrate.

screenshot-20210309-155930.jpg

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screenshot-20210309-160103.jpg
screenshot-20210309-160254.jpg


Any idea on what could be causing this ?

Thank you !

battery charging
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3 Answers
Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

Hi @Bruno Bruno,

I have the same charger and no such problems. The reason the IP22 returns back to bulk might be a loose connection between charger and battery or a high voltage cell that causes your BMS to cut off charging. From your screenshots it's obvious that battery voltage (output) falls back to around 13.1V. Enough for the charger to start bulk again.

What do your battery settings look like in VictronConnect?
Did you check all cables going in and out of the charger?

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Bruno M avatar image
Bruno M answered ·

Thank you for your feedback.

Cables look fine, but I'm going to try again with a direct and short connection to the battery.

As this battery is a Chinese Li-ion setup from AliExpress, I suspect the BMS to cause such things. Maybe it should be balanced, bavause of an unbalanced cell like you're explaining but I don't know if/how this will be done with this BMS (no Bluetooth).


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Mark avatar image
Mark answered ·

Hi Bruno,

See section 4.3 in the online manual - with standard settings (no re-bulk current configured) a new charge cycle will commence if the charger output current increases to the maximum charge current for four seconds.

In your case, the likely scenario is what Stefanie suggested:

  • The charger operates in bulk stage and at max output current
  • The batteries internal BMS goes open circuit (likely due to cell over-voltage)
  • The charger moves into absorption stage and only powers the loads (since the battery is disconnected)
  • When the BMS goes closed circuit again, then the charge current increases to the maximum charge current and 4 seconds later a new charge cycle commences (the charger goes back into bulk state)

If your battery/battery bank has some out of balance cells, assuming it also has an internal balancer, then you need to charge at a very low charge current to a) prevent the high cells from going over-voltage and b) allow time for the cells to balance (which can take >24h at low current).

The IP22 charger has a 'low current' mode that will reduce the max output to 15A (for the 30A model) - try this setting, as it will help, but it may not be enough. If the BMS keeps triggering (even with the charger in low current mode), then try to manually reduce the absorption voltage set-point to ~13.0V, and when the output current (going to the batteries, not batteries + loads) finally decreases to less than ~5A, then increase the absorption voltage set-point in ~0.2V steps and repeat the process until you are back at 14.2V and the cells have balanced (at which time you can also change back to normal/full current mode).

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Bruno M avatar image Bruno M commented ·

Thank you Mark for this awesome explanation.

I'm going to try what you suggest to rebalance the cells with a low current by increasing the abs voltage. This seems a clever way to do it.

I'll take care of disconnecting the loads during this process (I have a BatteryProtect that can be easily disabled).

After this I'll come back here to update everyone with the outcome.

Thank you!

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