Just a question about PV assistant being installed on a stand alone 3000w/24v Multiplus but NO micro inverters hooked up to the AC output.
24v 12kWh lithium battery pack with internal BMS, but no communication to the Multiplus.
Will the Multiplus vary the output frequency based on the battery voltage getting close to full charge from the ‘external’ DC sources even though there are NO micro inverters sourcing the load? (System has an MPPT controller, plus an external battery charger.)
Does the frequency swinging response require the Multiplus to have ‘figured out’ that there is an external source of AC power FIRST and be using that ‘extra’ energy to charge the battery pack before the frequency shift to throttle kicks in?
Thanks,
Steve
Ok, just tested the Multiplus by charging the batteries from the MPPT and an external power supply and NO micro inverters.
Multiplus charger is set for:
Lithium Batteries
Absorption @27.95
Float @ 27.70
Charge Current 70a
Curve Adaptive
Repeated Absorption time .25 hour
Repeated Absorption interval 45 days
Max Absorption Time 1 hr.
I just accepted the PV assistant defaults:
Solar converter will:
Start Reducing output at 60.2Hz
Output power will reduce to minimum at 62.7Hz
Converter will disconnect over 63Hz
(I have NO IDEA what the frequency vs output defaults actually are on the DS3 at this point, and I’m waiting for a 3kva 120v/240 transformer to show up so I can actually try it with my 120v Multiplus.)
Multiplus Freq shift on output, while Slowly Raising Voltage from the point where the Multiplus is outputting 60Hz.
Volts Hz
27.97 60.3
27.98 61.0
=======
Multiplus Freq shift on output, while Dropping the Voltage from the point where the Multiplus is outputting 62.8Hz.
27.94 62.4 Slowly Dropping from a higher voltage value
27.92 61.8 Slowly Dropping from a higher voltage value
27.91 60.5 Slowly Dropping from a higher voltage value
It appears that the frequency shift is exaggerated if the voltage overshoots and it is on the way back down.
Once the transformer gets here, I can actually test the DS3 and see how it acts.
Hi @Brownian_Motion I have an AC coupled SunnyBoy inverter. I presume that all your load devices expect 60 Hz?
I have experimented with the settings in the PV Assistant and I think you are setting the frequencies too high.
My batteries are 48v and base AC frequency is 50 Hz and I have these settings working mostly well:
*) Restart PV Inverters when the (temperature compensated) battery voltage becomes lower than 55.00 V.
*) The solar converter will start reducing its output power at 50.20 Hz.
Output power will be reduced to minimum when the frequency is 51.30 Hz.
The converter will disconnect when the frequency is higher than 51.40 Hz.
*) Total installed PV inverter power is 3000 Watts.
Total installed PV panel power is 3000 Watts.
When I had the minimum and disconnect frequencies higher, my AC load appliances like the washing machine would glitch.
These settings seem to be what the SunnyBoy “expects”. SunnyBoy calls this behaviour “Frequency Shift Power Control” but I know other inverter manufacturers do something similar with a different name eg “Demand Response Mode” and there are international standards which they all probably conform to: AS/NZS 4777.2:2015 sec 7.6 in Australia and NZ, IEEE 1547-2018 or UL 1741 SA may be more widely recgnised.
The problem I am having is that the Multiplus II keeps the AC frequency high when the battery voltage has dropped below the set point of 55V.
Hope this helps,
Graham
I’ve seen that behavior as well. It always takes time for the freq shift to drop back to normal, even with the voltage back down. It’s like it has some internal slope it follows, and is dependent more on elapsed time after the voltage normalizes than what the voltage actually is.
I was hoping it had more of a proportional response as the voltage headed back down to normal.
I’m not sure why these issues exist in the Multiplus line. I had voltage sense issues, and the local dealer wanted to swap. I told them to test the BRAND NEW UNBOXED unit before I would swap. Yep same issue. They sent off theirs for depot repair, and then made them test it again upon return. Only then, did I swap. I’ve since discovered, that when the Multiplus is in “Support Mode” and set for, say, 26.2v, the unit will push about 5a to the batteries, (expected,) but the voltage gradually increases to about 26.5v before the current throttles back.
C’mon Victron…
Power supply control systems routinely keep voltages within several HUNDREDTHS of a volt without issue.
Victrons’ MPPT controllers do it accurately all day long.
Why won’t the Multiplus product line do the same?
In my case, when the Multiplus is in that mode it can stay there for a very long time- long after battery voltage has dropped (I’m usually slow charging an EV or two while the sun is out), wasting valuable solar radiation.
The only solution I have found is to “Restart VEbus System” via the console- which is not a great solution for me.