Hello All. My setup: 2 x 314Ah 12V Smart Bluetooth WattCycle batteries, parallel/bussbar 2/0 cable supplying my 30A RV power circuits and a Victron Multiplus 12/3000/120. Battery chargins is via 540W of solar PV and the Multiplus 12/3000/120. I’m having difficulty finishing charging two paralled 314Ah Smart batteries using a Victron Multiplus 12/3000/120. Bulk proceeds okay. I’ve varied bulk current from 15A to 75A to the paralleled pair. However …
When absorption voltage at 13.9V (or higher) is reached, sometimes the WattCycle 314 will block further charging, I think because the voltage might spike at the transition causing “Charge” to turn off. I often see OVP codes.
Sometimes absorption at 13.9V will proceed and the battteries will throw an OVP code at the point where absorption is finished.
I understand why the BMS is invoking the OVP protection. When the WattCycle OVP code shut “Charge” off, the Victron Multiplus continues to attemp to supply current to the battery, then stops, then begins again. This cycle is repeated until I shut the Victron Multiplus charger off. This pattern doesn’t happen when I use a Victron MPPT Smart Solar controller or a Victron IP65 15A Blue Smart Charger.
What are the correct charging parameters for the pair of paralleled 314Ah smart batteries? The Multiplus does not detect the charge current is not going into the battery and keeps trying over and over. I suspect I have an incorrect setting, perhaps tail current, in the Multiplus 12/3000/120 program.
WattCycle suggests these parameters for a Multiplus charger:
If you plan to use our battery with the Victron system, we recommend setting the voltage as the following:
Absorption voltage: 14.2V–14.4V
Bulk charging voltage : (Not set separately)
Float voltage: Disable or ≤13.4V
Storage voltage: 12.8-13.2V
Our battery is equipped with a Battery Management System (BMS) that is designed for low-temperature operation.
Charging: The battery will not allow charging at temperatures below 32°F (0°C).
Discharging: It can continue to discharge down to -4°F (-20°C).
Please note that charging must occur at or above 32°F.
Best regards,
Wattcycle Service Team
I’ve attached a few pictures of the Multiplus 12/3000/120 trend history. The transition from bulk to absorption is shown. Also shown is the repeated voltage/amperage cycling the Multiplus charger does as it attempts to re-establish absorption to the battery.
I solved this with my 12 V system using a combination of batteries, inverter charging, and solar. If you set up a Venus OS system on a Raspberry Pi or Cerbo GX, you can use the large image with Node-RED and DVCC to automatically limit the charge current as voltage increases.
I’ve created a Node-RED flow that scales the charge current based on battery voltage — here’s what it looks like on a chart. The internal charger works alongside the DVCC setting to support the solar charger and maintain around 50 A of charge until the battery voltage rises, at which point the current is gradually reduced.
This is one of the problems with “3rd party badged” manufactured batteries, and a company who do not put full specifications on their website.
As you are getting Over Voltage Protection errors, the best practice is to reduce the Absorption voltage by 0.5V, charge again to see if you are getting the error, and to then either increase or decrease the absorption voltage in 0.1V steps until you just don’t get the error any more. The Multi will not be happy with a battery that keeps disconnecting. Float charging from Solar does help, as these will cope better with battery disconnection.
Yuo probably have a cell out of balance which is causing this problem.
That workaround is impressive. It’s actually what I was thinking needed to be done. I’m not at all familiar with coding the controllers that would interface with the charger. That would take me some time to learn but I’m not against learning if you could suggest tutorials. Back in the 90’s I worked with integrators to sense and interpret similar curves generated by FID detectors in gas chromatography. The tail current sensitivity would determine how many data points were taken as the slope changed. This setting would catch the change in slope so small changes where quickly identified and recorded. It seems you solution is similar. Thank you.
I’ve watched cell voltages stabilize over a few months. What I’ve observed is at the point where the Multiplus transitions from bulk to absorption, there’s a voltage spike. The WattCycle BMS reacts quickly too this spike and shuts off charging. Increasing absorption voltage slowly is how I got to this point. I have monitored cell voltage via the app as the batteries approach the bulk/absorption inflexion point. At that time, cell voltages between the 4 differ by several millivolts. Is this an acceptable difference?
Originally in 2020, the Multiplus was programmed by the company in Reno NV that I bought it from. I informed them of the two Renogy 170Ah Li batteries that powered my system. After 6 years of use, one of them lost about half of its capacity. The failed batter was the lead negative in the parallel system. I suspect it was charging related stress, but I have no real way of determining that. This lead me to purchasing 2 of the WattCycle 314 Minis.
After installing the Mini, I purchased the MK3 USBC dongle. I followed directions offered by this fellow. The main changes were in the Charge profile but I did change one setting. I did not take note of what section this was in and I failed to save the setting prior to this. Since I’ve been using the Multiplus to charge the WattCycle batteries I have varied the bulk current and absorption voltage and time in an attempt to find the sweet spot that results in a 100% SoC without the OVP code.
an acceptable difference for Lithium is anything less than 30mV - though this varies between manufacturers. If the battery impedance is low enough, then the Multi should not produce a Voltage spike changing from Bulk to absorption. There is no actual transition at this point, it’s just that the charger has reached the Abs voltage and comes out of constant current mode. This should not produce either a voltage or current spike. The voltage spike is possibly caused by the first battery getting to the disconnect point. Back off the voltage a little from where you are now and the problem should disappear, whilst still maintaining full charge.
… The voltage spike is possibly caused by the first battery getting to the disconnect point. Back off the voltage a little from where you are now and the problem should disappear, whilst still maintaining full charge.
Are you referring to backing off the absorption voltage? It happened last time at 13.9V absorption. One of the two batteries always finishes first and that battery is less likely to throw an OVP code. Once the OVP occurs, the Charge FET shuts off. The impedance at this time would be what, high or infinity? From my BMV screen shots, it appears immeasurable amperage is occurring when the voltage cycles.
When I next charge the pair, I will watch for this to occur again. At that point I’ll shut off the other battery via the app. I can also switch off the ‘full’ battery but that might create a spike in itself. I am using a Blue Sea Systems 6007 4 position battery switch to join the two batteries.
if one battery ‘finishes first (balancing / charging?)’ it looks like it quietly disconnects from the bus. The other then causes the oscillation as the charge fet cycles on and off. when both charge fets are off then the batteries are open circuit, presenting very high impedance, and the Multi’s charger has no load and will overshoot. Current will be zero at this point. You would need a more sensitive clamp meter on each battery to check exactly what is happening.
However, a reduction in charge (Abs) voltage of 0.1 - 0.4V should stop this from happening without loosing effective capacity.
I’ve added what I think is happening. The green arrow shows where you should transition from Absorption to float charging. One battery disconnects at this point, causing small ossilations as it periodically reconnects. at the end of the graph, the larger oscillations are caused by the other battery also going into disconnect/reconnect mode. Reducing the charge voltage at the indicated point will eliminate this behavior.
Remember NOT to charge the batteries to the manufacture’s maximum ratings, but keep the Abs and Float voltages below this. You want to transition to Float charging at about 6 - 8A tail current.
I would start from scratch. Remove both batteries. Charge them fully with a bench charger if you have one(a victron blue smart is a great investment all around). Parallel connect the batteries for 12-24 hrs so the cells balance(sometimes unnecessary but a good measure). Then reprogram the multi correctly to the battery specs. Remember specifically your “charged voltage” needs to be .2 lower than your absorption setting in a 12v system. I have seen incorrect charged voltage settings not let batteries charge completely lots of times. Finally make sure both batteries are installed so they get charged and discharged at the same rate(i.e. equal length, correctly sized cables, and/or paralleled to a common bus bar).
I set this up for my 12 V battery bank, which totals about 10 kWh and includes batteries ranging from 340 Ah down to 50 Ah. They all charge at different rates and use different types of balancing.
Some have passive charge balancing, which pulls down the highest cell only when there’s charge current. A few use active balancing, which continuously redistributes charge once a cell rises above a set voltage. Others rely on passive static balancing, which only activates when there’s no current flow and a cell is too high — these tend to cause the most issues, since in a live system the battery rarely stays at a constant high voltage long enough for balancing to occur effectively.
I’ve tuned the charge curve to hold a steady 14.0 V for about 2–3 hours before rising to the absorption voltage at 14.2 V. This gives each type of balancer enough time to do its job properly.
There’s plenty of information on Node-RED if you want to try automating your setup. All you need is a Raspberry Pi to get started — and fair warning, once you start using Node-RED, you’ll never stop.
Your explanation is very plausible. Thank you very much. I recall while charging both batteries observing the small oscillations you’ve labeled “1 bat off” and Indeed, the first battery had stopped charging without an OVP. At that point I intervened and stopped Multiplus charging. The battery that finishes first doesn’t usually show OVP and your explanation of periodically reconnecting fits well with the scenario.
I will follow your recommendation, thank you. I’ll do individual capacity tests and drain both down before. I’ll remove them from the system and charge them with my Victron IP65 Smart Blue, parallel balance the pair and go from there. WattCycle states to charge at 14.2V, however I’ve only managed to get them to 14.1 while charging them individually with the IP65 15A, never with the Multiplus. They don’t get past 13.9V before OVP happens charge them with the Multiplus when they’re paralleled. I’ll see how they perform after the reset you suggest.
Ideally, you want them connected to a bus like you have, but you might be able to try series connecting the cables like this. This is what I do with a new battery that needs to start its new life. What this will do is raise the voltage and force absorption before the bank is full. It might help to keep the end battery charge MOSFET open.
Ah, you have a point there, thank you. I wasn’t aware that ‘series’ method would possibly have that effect on the MOSFET. The usual what I call string-parallel connection is recommended by WattCycle, perhaps for a similar reason you’ve mentioned. I will try it to see if the results are different, but first I’ll individually drain, check capacity and recharge each battery. A friend had tried the typical parallel scheme with his two WattCycle batteries and had a similar to mine and he returned them.. His pair were not as well balanced as mine are.
You don’t need to drain the batteries to top balance them. You can leave the system running on one battery — just pull the fuse from the one you want to work on.
First, figure out how the battery balances. Most don’t have an active balancer; they’re usually charge-balanced or static-balanced. You can tell which type it is by charging it until it disconnects, then turning the charger off and watching the voltage. If it stays around 13.9 V and doesn’t drop, it’s likely a charge balancer, meaning it only balances when current is flowing. If it slowly drops, it’s probably a static balancer, which balances when the voltage is high but there’s no current.
You’ll need to balance each type differently. For a charge balancer, cycle the voltage between 13.6 V and the disconnect point. If it’s working, you’ll see the voltage gradually rise over time. For a static balancer, set bulk, absorption, and float to about 14.2 V and leave it connected for a couple of days.
Keep in mind the balancing current is very small usually around 200 mA so a large 300 Ah battery can take a long time to balance. If it’s a charge-balancing type, you’ll need to cycle it under load. A work light works well for this: turn the charger off and let the work light discharge the battery down to 13.6 V, then turn the charger back on. Using the lowest current setting on your charger will also help the process.
Thanks for that info, it explains what I see when I leave batteries on my bench system. The WattCycle voltage slowly settles, so static balance. I’ll postpone the capacity test at this time. I first need to find if the changes I made in the 702 BMV and the charge settings in the Multiplus will settle the charger oscillation issue. I might need to lengthen the charge detection time.
MikeD, is your recommended 6-8A tail current per each batter or the paralleled pair? I’ve reset the 702 BMV to reflect 1.3% or 8.2A for the paralleled pair ofo 628Ah. Thanks in advance for clarifying this point.
