Hi all, We have two AC500 with one each B300S running in dual phase. The PV priority setting has worked like a charm for the past year. We expanded our system with one B300K per system and now it won’t switch to the grid. Last night, it bypassed the set SOC setting, and the system shut down. This morning, I isolated each battery, and all four said that the firmware is up to date.
I’ve tried everything that I’ve read to no avail. I believe it’s a firmware issue as all four batteries are recognized and charging. Please help as our system won’take it through the night nor through my work day on Monday. 
Hi @bviwahine, We truly care about the issue you’ve raised. Could you please share a screenshot of your UPS settings page, along with the SN code and firmware version of your AC500?
We’ll check to see if the issue can be resolved.
It won’t charge or recognize the grid in any configuration. I’ve tried single phase, dual phase, no solar connected, solar connected, nothing. The grid is not recognized.
I’ll have to send the ac500s firmware versions when I get home tonight as it appears the wifi needs updating.
Hi @bviwahine, We have applied to upgrade your BMS, our IT department will push the latest version of firmware to your machine in 24 hours. Please upgrade it tomorrow.
Please only connect 1 B300 with the AC500 each time, and do not load any device when upgrading it.
After that, please do a complete cycle of discharge and charge to correct the SOC. The problem will be resolved.
We also suggest you first set it to standard UPS mode and then try charging.
Additionally, you can also try disconnecting the connection and using solar panels to charge each B300 individually, which is also an emergency charging solution.
Please let us know if it does help.
Thank you! More than likely I will do the upgrade on Thursday when I more time. Please confirm that I should have only the one new B300K or the previous B300S hooked up while doing the upgrade (or does it matter)?
Hi @bviwahine, We have now pushed BMS v1022.14 and BMS v1067.13 to your two AC500 units.
Yes, each time please only connect one battery that needs BMS firmware upgrade during the upgrade process.
Hi,
I had no trouble with the upgrades. I did each battery individually and they were successful.
How should I do a complete cycle of discharge? I set the system to standard UPS, charged the batteries by solar, and let them deplete (the master depleted much quicker). The system still won’t charge from the grid. Please advise as to how to proceed or what I did wrong.
The system charges evenly from the grid, recognizes all four batteries but simply won’t charge from the grid.
Scottie
My suggestions:
- Disconnect PV completely
- Disconnect Grid completely
- Set AC500 to Standard UPS mode
- Discharge the complete System with a good load, e.g. an AC unit or a heater or sth else
- Discharge until all units shut off completely
- Connect grid to the units and let them charge until they are completely full
- Do not connect any load to the units until fully charged
- Set back your preferred UPS mode to the AC500 units
After that the units and the B300K’s should have 100%.
Now connect back PV and check all the settings.
Connect back your load and see if it worked.
If not you should repeat the cycle one more time to see if it makes a difference.
If that did not help you may have a support case.
Please note: sometimes you have to change all UPS settings more than once for the unit to accept them fully. I do not know why that is the case but I have experienced that several times.
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Hi @bviwahine, To help us better understand your parallel charging situation, could you clarify:
Were you previously able to charge via grid when the units were parallel-connected, or has this been attempted only with PV until recently?
Which AC500 is configured as the master unit versus the slave unit in your current setup?
For successful AC charging in parallel mode, you’ll need the dedicated AC charging cable for splite phase (standard AC cables won’t function in this configuration). This specialized cable ensures proper synchronization between units.
We’d also like to acknowledge @ftrueck’s helpful experience-sharing—such community contributions are invaluable for troubleshooting.
Hi,
Thank you, everyone, for your input.
Sorry, I disappeared for a bit. Yes, until the two new batteries I charged from solar and the grid. PV priority worked perfectly. So, while I wasn’t on the forum, we learned that the cable to the “slaved” AC500 appeared to have scorching at the connection. No idea why or when it happened. I turned one AC500 off at a time, and both the “main” and “slave” recognized the grid with the cable that wasn’t scorched. Ordered a new cable. No luck. When in dual phase, and the cable is plugged into the grid, it trips a 50-amp dual-phase breaker.
That’s where we stand, back at square one. Two new batteries and a tripped breaker if we try to charge from the grid. Yes, we do have the appropriate cable.
Any ideas? Super frustrated. 