Newbie here. I have a 24v system. Multiplus 3000/24, lynx shunt, lynx bus, cerbo and 5500 onan. Li Time 230ah 24 lifepo4
Everything charges fine until the battery SOC gets to 88% (28.8 is full charge). At that point weird stuff starts to happen:
The multiplus switches between absorption and inverter every 10 seconds or so. AC1 is stable from the genny (118-120vac). This will go on for about 5 - 10 mins and the genny eventually shuts off. There is no Genny start/stop installed.
Everything runs great until it reaches the 88% soc state. The genny runs smoothly and the batteries are pulling about 65 amps steadily.
My victron distributor said he logged into the system remotely and changed a few settings but he said it’s the genny and not the multiplus causing the problem with the genny shutting down. I don’t buy it. I think there is something going on with the multiplus that’s affecting the genny’s capability to supply the current in a stable fashion. Or a config setting is wrong. Odd thing is it worked fine for about a year. I am not on the latest firmware for Cerbo or mplus. I’m a little worried to upgrade the firmware on the multiplus because it sounds confusing since I don’t want to lose any settings.
I am dry camping for another month so I cannot hook up to a pedestal to test anything.
Any ideas or some tests I can run to see what’s going on?
Hi Rich,
If your genset has no control wiring to the system, then it’s stopping of it’s own accord. Unless there’s something in it’s design that’s causing it to stop under certain conditions?, it may be faulty.
The first thing to do when looking at an SOC value is learn not to trust it until you know where it’s coming from. Then whether it’s been set up correctly. It’s likely the shunt, but make sure.
Your batteries are probably drop-ins with no creeping up to full charge. So maybe just shutting off charge when they’re full. You could take a look at what V is doing when this is happening. VRM is 1 minute sampling at best, so maybe you could rig up VictronConnect to monitor the shunt to see what’s happening at 1 sec intervals.
Look at Volts particularly, what it’s reaching as an upper value, then what’s happening to V and A if it’s shutting off. You may be able to soften the intensity of that by lowering the V setpoint, but how low you can go is the unknown.
Check your battery for alarms - this can happen if you have one cell that is hitting a cell high voltage alarm and the BMS is then telling the MP to back off, then the cell recovers, and repeat
As JohnC mentioned, the whole pack might be already at full voltage, and going into alarm or turning off the charge FETs.
Check in the console, what is set as the battery monitor - if its the BMS, you might have a mis-calibrated shunt in the battery. If its the Lynx, you might have something that is not being accounted for (by additional wires on the wrong side of the shunt) but this would typically result in an SOC higher than the true SOC.
You are charing at 0.3C - pretty mild, but still a fair charge rate at the top end of the charge. Try a run where the gen cuts out, then restart it but have the battery charge rate at 0.1C - if it continues a fair way, you are pushing too hard.
Watch your charge current, or graph it on the VRM/Advanced panel, “AC Input Voltage and Current” will give you the actual power coming from the gen, and compare to the requested current - i think this is a custom widget, with your MP selected, then choose “AC Input 1 Current Limit”, but i’m not sure of this, someone with more experience can say. Might turn up something interesting.
Does the gen have a feature where you can signal it to turn off by momentarily not drawing any load?
I upgraded the firmware on Cerbo and multiplus II to the latest version which gave me the opportunity to review settings. I tweaked a few things.
I have a Question though:
In the screenshot below, the battery tile shows Charging with 10.1 amps and the MPII tile shows Discharging with -12.2 Amps. Why is that? I could swear that before upgrading firmware the amps and mode in both tiles were the same.
Any ideas?
I will run the genny tonight and see if it cuts out or not.
I upgraded the firmware and all went well. Before upgrading the firmware I noticed the charge voltage jump to over 30 volts occasionally on my 24v/230ah battery which obviously is bad, so after the firmware upgrade I set an overvoltage alarm and lynx shutdown to 29.2 volts. Sure enough as you see in the chart, it just jumped up to over 30v and the lynx shut down as expected.
What’s the deal? Why would the voltage jump so high? When the lynx shut down so did my genny a min or so later.
@Richpetr
Good pic. It appears that the batts are accepting a 30A charge right to the end. The high V likely just overshoot from having the batteries ‘slam the gate shut’. The internal batt cells shouldn’t see that V, they’re on the other side of the gate.
The fairly steady V for a while, then the increasingly steep climb in V suggests they’re close to full (way past 88% SOC).
You could try lowering the Absorb setpoint to where this savage shutoff is avoided, the difficulty then is knowing if the V is enough to balance the cells. How the Amps taper off might be a clue to that. But they’re not getting much balancing done if they’re completely isolated from the charge.
I agree with JohnC - the BMS is protecting the cells by throwing a high voltage back at the source to get it to back off.
Multiple reasons for this;
One cell is over voltage
The pack is over voltage
The cell difference (highest minus lowest) has exceeded a threshold.
pack temperature is too high (not likely in your case)
some other alarm state.
You need to prevent the charging source from fire-hosing the power in - its like filling a bucket without spilling any water, you can start fast, but you have to finish slowly.
Do you have any software and cable to look at the BMS details on that battery? This is how you will see which alarm condition is triggering the issue
Thanks again for the advice. It’s a 24v li time 230ah battery. I think I’m the bms turned off at 27.2. Unfortunately I don’t have any bms software or cables. I’m not too keen on cutting the battery open to do any balancing lol.
Is there a way to balance all the cells without opening the battery?
I can try lowering the absorption set point. What should I lower it to? What should the charged voltage and float be if I lower absorption?
I decided to try the preset Lithium default settings instead of the manufacturer settings which had the absorption at 28.8 which I think is way too high.
Absolutely : You just hold the voltage high (about 3.4v to 3.6v per cell) with modest current. This allows the BMS to turn on balancing.
In a lead acid battery, you balance the cells by boiling the crap out of the cells - the theory is that an over-voltage lead cell will gas (turn water into H2 and O2), but still allow current to pass, which allows the low cells to carry on charging to reach full - kind of like the fastest runners being held at the finish line for the slower runners to catch up.
In a lithium battery, you would destroy the cells in about 10 cycles going over-voltage like that. Instead, there are fine wires that run to the junction between each pair of cells, and very small currents can be pulled or pushed on these wires, something like 50 to 300mA is typical. When a bunch of rules are met (typically: Cell must be above 3.35v, difference between highest and lowers must be >65mV, temp must be normal) the BMS enters the balancing phase.
High cells might be pulled down, or low cells pushed up - depends on the architecture of the BMS.
This is called “top balancing”, and most BMS’s top balance.
Some BMS’s bottom balance - same theory, but its done when the cells are low.
Some BMS’s can balance at any time - but there are experts that claim this is pointless.
Your battery might be trying to balance, but because your gen is thumping 65A into it, the amount of time spent in balancing (ie the rules are met, but you haven’t hit any cell over-voltage alarms) might be only a few seconds or minutes. You probably need about 20 min each time you reach 100% for your battery to maintain balance, but your battery might need to do that a number of times to get from where you currently are, into balance.
Some BMS will only balance for a set period, others will balance until the balance threshold is met, maybe cell diff has to get below 50mV.
Our batteries, with good cells, and getting a chance to balance regularly, are often cycling with less than 5mV difference.
Great info thanks!!! Can I do that with a lithium battery charger or do I need something special? If so what do I need?
Also, I’m such a newbie, sorry…
I don’t see my mppt on the monitor screen in VRM or in the device list of remote concise all the sudden. I’ve tried rebooting everything. Mppt has owner and the current from solar is shown to be charging my batteries (I have current going in with no genny or pedestal), it just doesn’t show the mppt device as a tike on the screen.
Is that because my battery is at 99% SOC right now? It’s odd not to see it on the monitor screen in the VRM portal.
From the Victron Lithium NG 25.6v battery manual, on the topic of balancing a 12v LiFePO4 battery;
In this section they are talking about a battery with very poor balance (one cell is 100Ah below the other cells which are at 200Ah), and ways to get the battery to stay in the balancing phase for long enough to finish the job. One way, with Victron charger that has a BMS (in some Victron batteries the BMS and the battery are separate - in most other brands the BMS is inside the battery), and is configured for Lithium, you might have to restart the charger many many times, so that it goes through the balancing phase again and again, and spend at least 55 hours in the rebalancing phase. They they say this;
The equivalent of 14.2 for you would be 53.25v (14.2/4cells = 3.55v, times 15s = 53.25v)
By lowering the Absorption set point to 28.25 I was able to get the system to stay running without the genny cutting out! At least it’s working now without the 31v spike when the bms turns off like it was doing before.
Those are your shunt settings. Useful for tuning that SOC before you can trust it. Time to read the manual there.
I think your batteries are ‘drop-in’, standalones with no real comms to the Victron side. If you can’t see them listed in Device List then that’s the case. All you can really do is treat them as the maker recommends.
Ok - so the only way to see your cell diff is the manufacturer’s software and a laptop, or a phone app if your battery has bluetooth.
Otherwise, don’t worry about it - if you frequently get your battery to 100%, and the last 30min is slow, your battery should do its thing and manage itself.
