Curious whether others are experiencing .10v - . 20v voltage spikes and dips in absorption mode while charging with their Victron Multiplus II 12v 3000 2x120.
The distributor where we purchased our Multiplus has attempted to resolve this problem. They tested 2 other units in their warehouse and they both exhibited this same problem. It's possible this may not be an isolated problem with just my unit. To my knowledge, Victron was notified of the problem in early Oct 2023, and is supposedly working on a fix.
Here's how I replicate the problem quickly. Briefly discharge a fully charged 304ah 4s lifepo4 pack 3-4ah, then turn on the MP charger. It goes into bulk mode for a minute or two, followed by a quick transition to absorption mode a few minutes later. You can see this transition in the far left portion of the Victron shunt trend screenshot below. Current quickly ramps up to 60-65a, then quickly drops while transitioning to absorption mode. Absorption voltage for this particular test was set to 14.30v. No problems up to this point.
Unfortunately, the MP charger only maintains 14.30v for a few min. before it abruptly spikes to 14.48v. This particular time it spikes and dips, above and below 14.30v slowly (~14.40v to ~14.20v), 3 more times before "somewhat" stabilizing at 14.30v approx. 45 min. later. None of these voltage spikes and dips in absorption mode should be occurring.
Important to note, the BMS on our battery pack never goes into high-voltage disconnect (HVD) with the MP absorption voltage set to 14.30v. This same voltage spike occurs even if the pack is charged (carefully) without the BMS. My 10a DC power supply and 75a Powermax converter will both charge this same pack with zero voltage spikes or dips using any voltage from 14.20 - 14.50v.
There were no other loads or connections on the MP's 12vdc terminals except for the 304ah lifepo4 pack during this test. I might add, this problem does not occur the same way every time. Sometimes the .18v spike will happen quickly, sometimes it's delayed 5-10 min. Sometimes there's only the initial .18v spike followed a steady 10-20 min decline in voltage (to as low as 14.20v) before slowly ramping back up to approx. 14.30v 15-45 min. later. There are a number of different ways this voltage spike can present itself. Bottom line: The absorption mode voltage is not stable.
If the MP charger's absorption voltage is set higher than 14.40v, this voltage spike will activate the BMS's HVD. When the HVD activates another more severe voltage spike issue occurs. If there's very little load (<3a) on the MP charger output (with the battery offline due to the HVD), the voltage will pulsate up and down rapidly from ~13.9v to ~14.9v. The voltage will continue to pulsate until the BMS releases the HVD or a load greater than 2-3a is applied.
I've tried setting the Multiplus charger's absorption voltage at different values from 14.20v to 14.50v and even tried different battery chemistries---same results. All tests were accomplished using the latest firmware (v506).
Thoughts? Comments? Suggestions?
