New Multiplus Goes Crazy in Absorption With New LiFePO4 Battery

DIY
, , ,
1

Hi All,

I’ve owned a number of Multiplus 12/3000/120 inverter/chargers since 2003 and have a lot of experience using them with regular flooded and AGM batteries. I even worked with Victron back in 2004 to help them test and debug the Multiplus PowerAssist function to work with the Honda EU-2000 which ended up working great and Victron subsequently advertised it extensively. However, I recently encountered a very strange problem with a Multiplus after upgrading my Lagoon catamaran from 840AH of worn-out Lifeline AGMs to a single 460AH Li Time LiFePO4 battery (I did the original install 10 years ago).

This was my first experience with LiFePO4 so there was a learning curve. The upgrade required a number of changes, including two new Renogy DC-DC chargers, a Victron BlueSolar100/50 charge controller, and a lot of rewiring. The Renogy and BlueSolar chargers worked perfectly all the way to float so I figured a few minutes with VE Configure changing to LiFePO4 and Li Time’s recommended settings would have my 10-year-old Multiplus also working fine but that was not the case.

The bulk phase worked well but only charged at 75-80 amps instead of the specified 92 amps (.2C). However, the moment it reached absorption voltage, it went “crazy”. Instead of holding constant voltage with current gradually reducing to tail current (9.2 amps) as expected, the voltage varied dramatically – spiking to the high 14 volt range and then dropping into the 13s over about 5 minutes. The current was even more bizarre – quickly dropping to zero amps, slowly climbing back to 55-60 amps, and then quickly back to zero in the same 5-minute cycle. Both patterns repeated indefinitely and the unit never reached float. I wondered if Li Time’s recommended absorption voltage (14.6 volts) was too high and causing a BMS disconnect so I changed to Victron’s default LI absorption voltage (14.2 volts) but that made no difference. So I finally came to the conclusion that my old Multiplus was too old to work with LiFePO4 and I needed an upgrade.

When I looked into buying my fourth Multiplus, I discovered that Inverters-R-Us sold them through Amazon for the same price as everybody else plus their “experts” would pre-configure it and provide “expert” technical support so I ordered from them. Fast forward a week and the new Multiplus was installed and operational. Unfortunately, it displays the EXACT same symptoms in absorption as my older Multiplus! I called Inverters-R-Us’ “expert” tech support and soon found they knew less about the Multiplus than I do. After carefully preserving their “expert” settings file, I reviewed the VE Configure options and found there are very few changes in the last ten years. The only change I made was to accept Victron’s default LiFePO4 voltages. I installed a VE.Bus Smart Dongle to see if I could get any insight from Victron Connect but learned nothing new. I also verified that the Multiplus has the current firmware version. At this point, I’m stumped!

The Li Time 460AH battery works GREAT and has more usable capacity than my previous 840AH of Lifeline AGMs did when they were new. As I said before, the other chargers, including the Victron BlueSolar, work perfectly - only the Multiplus has issues. Has anybody else experienced and, hopefuly, resolved these symptoms with a Multiplus working with LiFePO4? If so, I would GREATLY appreciate any help you can provide!

Thanks!
Glen

2

Does the battery have Bluetooth and an app to look what the battery is doing?

My guess is that the battery is disconnecting due to a high cell voltage.

Try to reduce the charging current to give the BMS time to balance the cells.

14.6V is pretty high, I would also recommend to set that to 14.2V

1 Like
3

Hi Mathias,

Unfortunately, the battery doesn’t have Bluetooth capability.

Regarding your suggestions, I completely agree with you! In fact, I said in my post that "
I wondered if Li Time’s recommended absorption voltage (14.6 volts) was too high and causing a BMS disconnect so I changed to Victron’s default LI absorption voltage (14.2 volts) but that made no difference. "

I’m not aware of any way to control charge current in the absorption phase.

The symptoms I’m experiencing are baffling! What am I missing?

Thanks,
Glen

4

If you have a GX device you can reduce the charging current with DVCC.
If not you have to reduce the current in the settings of the MultiPlus with VE.config.

5

I don’t have a GX device. I know Victron has a lot of cool new stuff but I only have what I stated in my original post.

The only current setting I’m aware of in VE Configure is bulk charge current which is set at the battery manufacturer’s recommended 0.2C (92 amps). I have no problem with bulk.

By definition, the absorption phase is constant voltage which is set at the default 14.2V and current should slowly decline - but that’s not what I’m seeing. What am I missing?

6

Probably the battery being new is still a little unbalanced.
Try for a while a smaller voltage, e.g. 14V (3.5V per cell) or even less, 13.8V (3.45V per cell).
Choose the voltage that will not generate those symptoms.
Set the desired voltage for all voltages: bulk, absorption, float.
In this way you’ll prevent some cells to hit the overvoltage trigger and allow the BMS to balance the cells.

7

Reduce that current to less than 0.1C and charge the battery slowly to give the BMS time to balance the cells.

Going into absorption can be a side effect of the battery blocking the charging current during bulk.

8

As long as the voltage is left to a higher value, a 46A (0.1C) or even 20-30A current is more than enough for the “happy” cells to overshot, because balancing is done with less than 2A. It’s an overvoltage, not an overcurrent, trigger.
And once the (lower) voltage limit will be hit, the current will fall anyway.
Remember, Victron recommended in DVCC to limit the charging voltage, not charging current, for reducing HV alarms… :wink:

Or even better, reduce both current - for slow charging - and voltage - for avoiding HV charging disconnects.

9

Hi Alex,

That’s an excellent suggestion and worth trying. Recall this a 460AH battery and it technically isn’t new anymore as this problem first came up several months ago. I’ve been successfully charging it with solar and the DC-DC chargers so wouldn’t the cells be balanced by now? I need to get the Multiplus working for when I need a faster charge rate and I only recently discovered this forum.

Thanks,
Glen