Victron Multiplus never gets out of Absorb mode

[jscrews]

Hello all, I'm a new user to the forum and been reading for a few weeks trying to learn about diy batteries and Victron equipment. I installed a Victron Multiplus 2 2x120 in my 5th wheel this week. I have the Victron Power In (I thought I was ordering the DC distribution), but it appeared the only difference was the ability to monitor it on the Victron network, and the missing bolts to hold the fuses. I put in my own bolts and connected batteries and MP2 and that seems to be working okay. I don't have a smart shunt, but I put VenusOs on a Raspberry Pi3 and installed the dbus-serialbattery drivers to use as my battery monitor. This all seems to be working.

I have a 2P4S configuration of EVE 280ah cells using JDB 150a BMS, one for each 4 cells. I top balanced them a few weeks ago and they have been sitting until I received and installed the equipment. I don't yet have solar, so I am just charging with 30amp shore power or my Honda eu2200i generator for now. When I first hooked up the batteries, I connected to 1 bank and let the MP2 charge, then I connected to the other bank, let it charge, then I put them in parallel. I guess didn't wait long enough with them resting to check the voltage, so they are off by about .17V between the banks. Within each battery the cells are only .05 off roughly. All cables are pretty short and mostly even length. The one exception is the pos cable from the battery to the Power In is maybe 6" longer than the neg cable.

So life is good, until I try to charge. I set Absorption to 14.2v, Float to 13.6 and Absorption time to 1 hour. I turn on MP2 and it starts at Bulk. When it gets to around 13.5v it goes into Absorb, and it stays there putting in around 5amps and tapers off to 0. The voltage never got above 13.65 I see in most discussions that Absorb should be really short. I found one post that described this was the point the BMS was balancing and it seems their suggestion was long was okay with low current in. So I let it stay in absorb almost 12 hours yesterday. It never stopped charging in absorb. After about 7 hours, I turned on all my 12v lights for about 30 minutes and it dropped the voltage to 13.26 and then went back to Bulk. After about 30 minutes it was back to Absorb. This time it went up to 13.8v until I shut everything down overnight.

So what am I missing? Is the .17V difference between the banks causing this? dbus-serialbattery can only show 1 bank to the victron as a battery monitor, and it is using the one that it thinks is most charged. I'm trying to get some help from the vendor I purchased from, but so far they are busy and no return calls.

What should I check or change? Thanks for the help.
Jeff

 

[svsagres]

So in your case, the voltage settings don't really matter as the entire thing is being controlled by your BMS. The BMS is telling VenusOS what it wants in terms of voltage and/or current, and that in turn is controlling your MultiPlus.

As long as the voltage/current on the system is satisfying what the BMS wants, then it's pretty much irrelevant what the lights on the MultiPlus say. The Bulk/Absorbtion/Float stages are really only there for when the charger is operating in dumb open-loop voltage control. You have a closed loop system.

 

[HRTKD]

You have a 4s2p battery configuration, not 2p4s.

I don't know anything about your dbus-serialbattery. I'm using the 120 amp 4s JBD BMS and it does not communicate with anything except the app on my phone. It sounds like you have an issue if your device is looking at only one battery. That's not an ideal situation.

In my 4s2p system the batteries are staying well balanced between each other and my Multiplus 12/3000 charges them just fine. However, since I have solar, I'm rarely using the charging feature of the Multiplus.

 

[jscrews]

So in your case, the voltage settings don't really matter as the entire thing is being controlled by your BMS. The BMS is telling VenusOS what it wants in terms of voltage and/or current, and that in turn is controlling your MultiPlus.

As long as the voltage/current on the system is satisfying what the BMS wants, then it's pretty much irrelevant what the lights on the MultiPlus say. The Bulk/Absorbtion/Float stages are really only there for when the charger is operating in dumb open-loop voltage control. You have a closed loop system.

That makes sense. I've not seen anyone else with dbus-serialdriver setup talk about this behavior. It seems that this will never use a Float voltage, it will always try to keep the batteries at a high charge. I guess when connect to shore power I just have to turn off the charger when batteries are sufficiently charged. It will just be more manual than I expected.

 

[jscrews]

You have a 4s2p battery configuration, not 2p4s.

I don't know anything about your dbus-serialbattery. I'm using the 120 amp 4s JBD BMS and it does not communicate with anything except the app on my phone. It sounds like you have an issue if your device is looking at only one battery. That's not an ideal situation.

In my 4s2p system the batteries are staying well balanced between each other and my Multiplus 12/3000 charges them just fine. However, since I have solar, I'm rarely using the charging feature of the Multiplus.

I said I was new. Thanks for correcting me.

 

[svsagres]

That makes sense. I've not seen anyone else with dbus-serialdriver setup talk about this behavior. It seems that this will never use a Float voltage, it will always try to keep the batteries at a high charge. I guess when connect to shore power I just have to turn off the charger when batteries are sufficiently charged. It will just be more manual than I expected.

It will keep the voltage at whatever the BMS requests. Assuming you have DVCC turned on, which you should, the BMS is going to be driving the entire process and setting the voltage/current limits. In this kind of situation, you can more or less forget about the whole Bulk/Absorb/Float thing; the MultiPlus is just doing what the BMS commands.

On my system, if I'm charging up from a low enough SoC, the BMS is going to ask for 14.5V, and taper the requested current down as the system approaches that 14.5. It will eventually hit 14.5, and then quickly drop the voltage request down to 13.8V. At that point, the MultiPlus more or less turns off until the system bleeds down to 13.8.

When I leave the boat, I'll set the DVCC override and drop the system voltage down to 13.3v. The system then settles down over the next week, before the MultiPlus starts maintaining 13.3v (around 55% SoC). If I'm going to be heading out on an overrnight, I'll log in remotely remove that limit, and let the system go back up to 100%.

In your case, don't look at what the MultiPlus settings are (other than ensuring they're safe for your system) and instead focus on what the BMS is requesting. If the BMS is requesting 13.8, then that's what the MultiPlus is going to do. If it's requesting 14.5, again that's what the MultiPlus is going to do. If your BMS isn't all that smart about these kinds of things, you might want to investigate something that is better at it.

 

[jscrews]

When I leave the boat, I'll set the DVCC override and drop the system voltage down to 13.3v. The system then settles down over the next week, before the MultiPlus starts maintaining 13.3v (around 55% SoC). If I'm going to be heading out on an overrnight, I'll log in remotely remove that limit, and let the system go back up to 100%.

Thanks for this explanation. It helps a lot. I've been scratching my head for a few days trying to figure why all the victron settings are ignored. I knew it was reading the BMS but thought the limits still applied. Makes perfect sense now. I just set the upper limit on my BMS to 14.20.

I'm curious about the DVCC override you mentioned. Is this where you're setting the 13.3? I have DVCC on but with all the defaults.

 

[svsagres]

Thanks for this explanation. It helps a lot. I've been scratching my head for a few days trying to figure why all the victron settings are ignored. I knew it was reading the BMS but thought the limits still applied. Makes perfect sense now. I just set the upper limit on my BMS to 14.20.

I'm curious about the DVCC override you mentioned. Is this where you're setting the 13.3? I have DVCC on but with all the defaults.

View attachment 107687

That’s it exactly. Been running like that for about a month now, and it works well. My solar is barely enough to keep up with my idle load, so most of the time I have the inverter off, but will turn in on (and that DVCC setting off) the day before I go on an overnight trip.