question

chrisb13 avatar image

Discharge Current Limit in Multiplus-ii with Pylontech and Cerbo

Hi, I have a question around the behaviour of the Multiplus-ii when connected to Cerbo GX with DVCC on under the control of Pylontech US3000.

The US3000 manual has the following current limits:
Recommend Charge/Discharge Current (A) 37
Max. Charge/Discharge Current (A) 74
Peak Charge/Discharge Current (A) 100A@15sec

The Cerbo DVCC Discharge Current Limit is set to 37A since plugging in the Pylontech cable to the Cerbo. What will happen when the load on the Multiplus causes DC current to exceed 37A? Will it just shut down or alarm, or something else?

I really need it to allow the Multiplus to operate within the specification of the battery, to allow for short-term high load scenarios as this is an entirely off-grid install with solar and backup generator.

Thanks, Chris.

PylontechDVCC
2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
chrisb13 avatar image
chrisb13 answered ·

So, a terrible generator meant that we got to try this out:

When AC Load on MP causes DC Current draw to exceed Max Dishcharge Limit communicated from Pylontech Battery to DVCC, nothing happens!

In the scenario that occcurred:

Setup:

Cheap 3300W AVR Generator as sole AC source to....

Multiplus-ii 3000/48 configured to charge...

Pylontech US3000 also charged by...

1680W of PV in 3s2p configuration via SmartSolar 150/35...

all under DVCC control of Cerbo GX.

Details:

AC Load (all on output of MP) = ~1600W (Washing Machine heating)

Generator managed to supply ~1400W before becoming unstable, remainder supplied by Multiplus inverting from minimal solar output and remainder from US3000 battery.

Whilst adjusting AC Input Limit on Multiplus to find max stable generator output, AC Input disconnected automatically several times due to instability - this left the total load supplied by the DC bus at approx 45A.

The most useful generator settings were to accept wide input frequency, turn off UPS, disable loss of mains detection (this caused total havoc with generator) and turn off Weak AC (this allowed us to increase AC Input Limit a little when charging).

Conclusion: A proper generator is required! However, until that issue has been resolved, it is not a problem to utilise full capability of Pylontech battery output power capability.

2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

albert-vd-westhuizen avatar image
albert-vd-westhuizen answered ·

@ChrisB13 In off-grid situation with no AC source connected to AC in, my understanding is the following: MP will always try to meet the load demand on it's output. If the demand exceeds the rating of the MP it will shut down on Overload. If load does not exceed MP rating but exceeds battery max current rating (and no solar to support) the battery will shut down. The MP cannot be set to limit this demand from the battery when no AC source available on AC in. If AC in power source, grid or generator, available, excess will come from this source to supplement any shortage from the DC bus. Your options are: 1) Control demand to below battery max rating on MP AC out using load control switchgear 2) Increase battery size so inverter becomes limiting factor and not battery

2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.