HamzaH
New Member
Sounds like you're doing the right things. I haven't used SI with lithium, but others here have.
How many kW of PV and Sunny Boy do you have?
I have 2 SB 1x 3000TL-20 (with 2.8kw panels) & 1x5000TL-20 (with 2.5kw panels)
I have the battery charging amps set at 190ah (from memory the SI recommended 210ah when I did the setup . but i lowered it to 190ah ) but in reality the maximum charging current my panels will generate will not exceed 115 ah (5500w/48v = 115ah) which makes it around 0.3C of the 400ah battery capacity
How many kWh of battery? (400 Ah) Correct
I have oversize PV array compared to battery, and default charge rate of about 0.6C would never occur if sized according to SMA recommendations.
I reduced charge rate to 0.2C for my AGM.
Reduced charge current may help with the issue.
Does BMS report what it disconnected for? Maybe a cell that was a runner? It doesn't disconnect completely
on my BMS monitoring app I have notices that at full charge that I have a difference of 0.3v in the lifepo4 cells voltage, so one cell would be 3.7v and another 3.4v , and it takes a while before the balancer is able to equalize the voltage down to a difference of 0.03v .
please note that the bms only disconnects the charging but keeps the discharging open (like a diode allowing current to go in one direction only).
How much "absorption" time is it set for? I think holding within a voltage range allows BMS to rebalance. Maybe yours are drifting apart? Check cell voltages while fully charged. From memory it was still default at 120min
Your SI should raise frequency when battery isn't accepting all the power at voltage setpoint. But there is a delay, some seconds to frequency shift.
Reduced charge current could help with that, except in the "load dump" case when a large load suddenly turns off.
Is ramp-down supposed to be 100% at 51 Hz to 0% at 52 Hz? Could reduce that closer to 50 Hz & 51 Hz to save time on ramping down. I am not sure if I can control these in my SB as I purchased these second-hand, one of them I can access the settings on it, the other one is locked with a password that I wasn't able to get) and both the SB were used in a grid tie connection. my setup is an offgrid one
Thank you for your reply,Are you sure SB ramps down voltage in response to frequency? That takes a setting, either something like our newer "Rule 21" frequency-watts, or "Island", or "backup" for grid connected systems. Do you have a DMM with "Hz" range? I can see the frequency shift. When it works, my frequency hovers between 61 and 62 Hz. When it doesn't, runs to 64 Hz and disconnects. I am not sure , Is there a way I can check if this setting is activated?
What model SB? Some don't do frequency-watts as intended. have 2 SB 1x 3000TL-20 (with 2.8kw panels) & 1x5000TL-20 (with 2.5kw panels)
Please check my reply above in BOLD :