question

agroventuresperu avatar image
agroventuresperu asked

Batteries Now Only Charge to 88%

I've had my system set up for a year now. No problems. Using CerboGX with Touch50, Smart Solar 250/100, Multiplus 48/5000 and a battery bank of 4 Pylontech US3000.

Looks like I've encountered my first hiccup. I have the touch screen display for my cerboGX, and check it every so often. Today I noticed the MPPT was not sending any more electricity to the batteries. It seemed to be treating 88% charged as if it were 100%. I confirmed this by running a pump in the house. The sun was shining outside. When the pump was on, I could read the (-) amp draw from the battery bank, and when the pump cycled off, the MPPT compensated accordingly and sent an equivalent amount back to the batteries, until it reached a full 88% charge again. Battery health on the monitor states 99%.

I certainly haven't changed any settings lately. Actually, I haven't made any modifications since the installation one year ago. The only thing I can think of that might be causing this is about a week ago, I was moving a floor fan in the room, and the back of it accidentally touched the switch on the inverter, which turned it off. I turned it back on promptly. Maybe I've been having this problem since then, but can't say, because today was the first day I payed attention to the display since then.

What do you think is causing the system to treat 88% charged as if it were 100% charged? It will not go above 88%. The six LED charging indicator lights on the front of the batteries also only show 5/6 lights illuminated.

Pylontechsmart solar charging behaviourmultipus
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4 Answers
snoobler avatar image
snoobler answered ·

Hello from DIY solar forum.


Can you view the cell data on your Pylontech batteries? Are any of them engaging high voltage protection?


Is your absorption voltage sufficiently high to push batteries to 100%?


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Hi Snoobler, Yes the absorption voltage is the same as its always been. I had a solid year of this system charging to 100% before these batteries decided it was time to throttle down to 88%, and now 87%. I called the engineer at my distributor and he had me update the firmware on the cerbogx and the smart solar mppt. This didn't fix it. The third battery in the stack was noticeably a little more charged (based on the green led indicator lights on the front of the batteries).


I can't view the individual cell data of each battery module. What would I need for that?


What would be the indication for high voltage protection?


A couple days ago, the third battery in the stack had a red alarm light, and the Touch50/cerbo showed that it was a low battery temperature warning wich kicked in at about 23 celcius and stayed on all night to a low of 20 celcius. Since then, I have not seen the alarm, but the batteries still won't charge past 87%



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snoobler avatar image
snoobler answered ·

concerning cell voltages, I don't know how to access individual cell data. I don't believe this is possible without physical access.


concerning over-voltage protection, I would expect, but can't confirm, the GX device would show an alarm.


This flavor of battery is susceptible to cell imbalance as many are reporting on DIY Solar.


Recommend the following troubleshooting steps:

  1. Set absorption voltage to 3.45V/cell.
  2. Set float voltage to 3.40V/cell.
  3. Set fixed 7 hour absorption time.

The above parameters will permit 98%+ SoC charges.



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Thanks. Did you read this quote I posted over on the DIY Solar Forum taken from the Victron-Pylontech compatibility manual published by Victron?

When DVCC is enabled, the battery (via the CAN-bms) is responsible for the charge voltage. The Pylontech battery requests a charge voltage of 53.2V. We have however found that in practice this is too high. The Pylontech battery has 15 cells in series, so 53.2V equates to 3.55V per cell. This is very highly charged and makes the system prone to go overvoltage. It should also be noted that a LiFePO4 cell stores very little additional energy above 3.45V. For this reason we opted to override the BMS and cap the voltage at 52.4V. This sacrifices almost none of the capacity and greatly improves the stability of the system.


I will try your suggestions next. The absorption voltage would be 51.75V. I'm not sure if VeConfigure or VictronConnect has a way to set a customized duration for a fixed absorption time. Can anyone else confirm this?


P.s. What do you mean by flavor of battery?

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snoobler avatar image snoobler agroventuresperu ·
Missed it.


Charge voltages depend highly on current. "stores very little additional energy above 3.45V" is not accurate without context. If you're talking low charge currents - 0.15 to 0.2C, then a large portion of capacity is taken on below 3.45V. Faster charge rates need much longer absorption periods when charging at 3.45V. Hence my recommendation for a 7 hour absorption time.


Depending on context, 3.55V is not too high. If you experience over-volt, it's because the cells are imbalanced, and they trigger over-volt protection.


Regardless, it appears you have essentially implemented my suggestions at a slightly higher absorption voltage. If you can live with that solution, I'd stick with it for now.


"Flavor" = GILL/BYD/Pylon/EG4 server rack batteries.

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I have not implemented your suggestions yet. Just waiting for a day that starts out sunny so I can get a jump start on the seven hour absorption time window. The days here are always only 12 hours long at the equator.
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I finally tried your three troubleshooting steps this morning. It looks like they didn't make a difference.
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nickdb avatar image
nickdb answered ·

Pylon setup is perfectly documented on the battery page. It works, There are thousands of installs.

Follow the guide and check your settings.

You can access detailed data with a cable and battery view software but this is not necessary as the gx will trigger alarms - accessible from the pylon tab on the gx main page.

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Pylontech said I would need the laptop debugging cables if I want to view the individual cell voltage levels via BatteryView software. The only alarm that has been triggered (now only two days over the past month or so since this started) has been a low battery temperature alarm, which was weird because the alarm came on with battery temps registering 20-24 centigrade, which is far from a low temperature. That's the only info I get from the CerboGX.


Well, I think one year of flawless operation indicates a proper installation was done, so I'd assume this is a glitch with one of the batteries in the stack.

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ponzoa avatar image ponzoa agroventuresperu ·
Perhaps your Master battery has a faulty temperature indicator causing low readings and hence is cutting charge with low temperature. This would be correct behaviour if the temp was truely low.


Have you tried swapping your master with another battery? If this solves the problem, you know you need to take the previous master in for a warranty claim on the temp sensor.

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I'm not sure my comprehension is correct. The master battery would be the one with the CAN cable going to the cerbo? In my case, it is the battery in the top of the stack. Two batteries down from that battery is the battery that is generating the alarm light. Wouldn't the temperature sensor be faulty in that third battery in the stack as opposed to the master, which doesn't show any alarm light ever?

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agroventuresperu avatar image
agroventuresperu answered ·

From what I can gather, there are two issues:

1) The third battery in the battery bank is preventing the entire battery bank from charging to full capacity.

2) This battery has a red alarm light that comes on once or twice a week. The cerbogx states this is a low battery temperature alarm even when the temperature is 25C (77F). I'm thinking the cerbogx is just misidentifying/mislabelling the actual problem.

Hypothetically speaking, if you could somehow get just one battery in your stack to reach dangerous low temperatures, would that cause the entire battery bank to stop charging when in the 84-89% range?

Yes, my batteries now will not even get above 84% SOC!

The low temperature alarm may or may not be the root cause of this issue. If there's a faulty temperature sensor, then why would it cause the batteries to limit capacity even when no alarm is triggered? As I said, the low temperature alarm is only triggered randomly a couple times per week at most.

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