New Sunny Island and JK PB BMS set up - problem and solution.

[Calvin98]

And the basic idea here with upstream/downstream is to connect the AC1 of the downstream Sunny Island to the AC2 input of the upstream Sunny Island? Or the other way around? You might also have to fiddle with the generator setting so is to not exceed the capability of the AC1 56 A on the one Sunny Island set up?

Just basically pretend the downstream Sunny Island system is acting as the generator for the upstream Sunny Island and set the generator settings in the upstream Sunny Island appropriately?

 

[Calvin98]

I’ve been trying to figure out a failsafe scheme for BMS comms, because loss of comms means SI goes into deep sleep, requiring DC disconnect and cap drain to bring online again. I’ve thought about a dedicated battery backup for my “fake BMS”, and even a 2nd unit to eavesdrop and take over in case of loss of

I’ve been thinking about a similar way to avoid a problem. I recently had an F605 error message on one Sunny Island and when that happens, it goes off-line, leaving the other three inverters online. If you have a heavy load that could be problematic. It certainly easy to restart The Sunny Island after the error message, but you have to physically be there and press enter to start it up again. Wondering what sort of thing I could set up as a sort of a fail safe if that happens. You could be using some heavy loads like EV charging, water pumps, and ovens all at the same time and if you lose 25% of your power, that could be problematic and then everything could shut down because of overloading.

 

[Consumerbot3418]

And the basic idea here with upstream/downstream is to connect the AC1 of the downstream Sunny Island to the AC2 input of the upstream Sunny Island? Or the other way around? You might also have to fiddle with the generator setting so is to not exceed the capability of the AC1 56 A on the one Sunny Island set up?

Just basically pretend the downstream Sunny Island system is acting as the generator for the upstream Sunny Island and set the generator settings in the upstream Sunny Island appropriately?

Well, if @Hedges and I are on the same page, it's the other way around. "Waterfall" meaning that upstream feeds downstream, so upstream is acting as a grid or generator. Hopefully this will work:

+-----------+          +---------------+          +----------------+          +-------+
|           |          | UPSTREAM SI   |          | DOWNSTREAM SI  |          |       |
| GENERATOR |----------|AC2         AC1|----------|AC2          AC1|----------| LOADS |
|           |          |               |          |                |          |       |
+-----------+          +---------------+          +----------------+          +-------+

Idea is to set up downstream in VRLA mode, always charged and connected to "grid", which is actually the upstream SI.

I've been operating in this waterfall mode for quite a while, but with LFP (Li-Ion BMS mode) on the downstream. Seems to work a treat, passes through the power from upstream just fine, and even helps out when heavy loads switch on and off, i.e. if frequency droops or spikes, it briefly contributes or sinks power.

It certainly easy to restart The Sunny Island after the error message, but you have to physically be there and press enter to start it up again. Wondering what sort of thing I could set up as a sort of a fail safe if that happens.

I doubt this idea/solution would be useful for that scenario. There is a possibility to command SI to go to standby or come out of standby via CAN, but I'm not sure if it would bypass the need for you to press enter at a fault code... May be worth a try.

 

[Hedges]

But that’s very complicated, compared to your plan of using downstream SI in VRLA mode, which ought to be rock-solid.

Not just "mode", but VRLA itself (so no BMS).

I've got 20kWh of SunXtender AGM. Robust, won't trip for over-current, no pre-charge needed. But cycle life about 650, 70% DoD.

I should hope switchover glitch doesn't upset anything. Especially when it is snap off by upstream SI, vs. slow brownout. SMA writes about that. However, with SB connected to upstream SI, I suppose other voltage and possibly frequency characteristics might occur.

Yeah, any man in the middle needs to be reliable.
My telecom equipment is 12V, so considering AGM with AC charger + SCC. Possibly 12V linear regulator on output diode-paralleled with OEM wall-wart. Might use LAN cable to also send power to smoke alarms.

 

[Hedges]

I’ve been thinking about a similar way to avoid a problem. I recently had an F605 error message on one Sunny Island and when that happens, it goes off-line, leaving the other three inverters online. If you have a heavy load that could be problematic. It certainly easy to restart The Sunny Island after the error message, but you have to physically be there and press enter to start it up again. Wondering what sort of thing I could set up as a sort of a fail safe if that happens. You could be using some heavy loads like EV charging, water pumps, and ovens all at the same time and if you lose 25% of your power, that could be problematic and then everything could shut down because of overloading.

SI has 3 second surge capability.
Enough time to release a load-shed relay?
If your control system is aware.

There is a "Derating" status for signaling relays. Is there "Overload"?
Or do we need to use one that says "operating"?

 

[Calvin98]

SI has 3 second surge capability.
Enough time to release a load-shed relay?
If your control system is aware.

There is a "Derating" status for signaling relays. Is there "Overload"?
Or do we need to use one that says "operating"?

Not sure. Need to think what’s the best way to go. Three seconds is kind of a short period of time for a relay to act. I would imagine it could be possible, but you would know better than me.

So far the F605 error message has not been a problem, but I imagine it could be. This could happen to any of the other inverters also and it would be good to have some sort of plan in place should that happen.

I have my home assistant set to give me a notification when the slave has a 0.0 kW output for more than 5 minutes. So far that’s not a reliable indicator that this F605 message has happened because there are times in the afternoon when the batteries are full and the sun is going down and the inverters are still producing when the sunny islands are basically putting out no power and the sunny boys are handling all the loads.

 

[Calvin98]

Well, if @Hedges and I are on the same page, it's the other way around. "Waterfall" meaning that upstream feeds downstream, so upstream is acting as a grid or generator. Hopefully this will work:

+-----------+          +---------------+          +----------------+          +-------+
|           |          | UPSTREAM SI   |          | DOWNSTREAM SI  |          |       |
| GENERATOR |----------|AC2         AC1|----------|AC2          AC1|----------| LOADS |
|           |          |               |          |                |          |       |
+-----------+          +---------------+          +----------------+          +-------+

Idea is to set up downstream in VRLA mode, always charged and connected to "grid", which is actually the upstream SI.

I've been operating in this waterfall mode for quite a while, but with LFP (Li-Ion BMS mode) on the downstream. Seems to work a treat, passes through the power from upstream just fine, and even helps out when heavy loads switch on and off, i.e. if frequency droops or spikes, it briefly contributes or sinks power.


I doubt this idea/solution would be useful for that scenario. There is a possibility to command SI to go to standby or come out of standby via CAN, but I'm not sure if it would bypass the need for you to press enter at a fault code... May be worth a try.

Thanks. I just had the terminology mixed up. But yeah, that’s the idea as I understand it.

 

[Hedges]

Relays respond in about 1 millisecond or a bit longer.
Easy for hardware e.g. CT measurement.
Possible for software but only if it isn't distracted.
uP firmware could be used for this purpose.

I want frequency monitoring, so if SI swings frequency, dump loads turn on and off.

 

[Calvin98]

OK right. Have to figure out what to use as the trigger though. Even when the slave shuts down, there’s still voltage on AC1 from the other inverter. So looking for 0 V wouldn’t work. The slave could also be on even with zero current going through so current wouldn’t necessarily work either. Would there be a way to capture an error message on the Sunny Island and use that to turn a relay on or off?

The home assistant is set for frequency monitoring right now. I have the sunny boys ported into it and monitor the frequency through that.

 

[Hedges]

Four CT, one per SI AC1 "L" output. Any > ~50A for > 1 second triggers load shed?
Bit of analog circuitry required. Maybe RC circuit and comparator.
Time delay or hysteresis to re-enable?
Software to re-enable would be fine. Only disconnect has to be fast.

 

[Consumerbot3418]

I have my home assistant set to give me a notification when the slave has a 0.0 kW output for more than 5 minutes.

What is your source of the energy data? You have RS485 comms working?

I want frequency monitoring, so if SI swings frequency, dump loads turn on and off.

Seems like this shouldn't be all that difficult to implement, but I haven't yet seen an affordable integrated solution. Shelly has ability to measure frequency, but I got noisy readings.

I do capture SI reported frequency on the CAN messages, but sometimes seconds elapse between messages. Could be my software needs optimization. There is a $20 modules available that has integrated CAN and two relays, able to run ESPHome. I could pretty easily tweak my "fake BMS" ESPHome software to simply spy on the CAN messages from SI, and switch relays off/on based on frequency thresholds. Those relays could probably trigger more powerful relays or contactors for your dump loads. I think this all depends on being in Li-Ion BMS mode, but possibly also possible in VRLA mode. I wish I had some time to see.

 

[Consumerbot3418]

Would there be a way to capture an error message on the Sunny Island and use that to turn a relay on or off?

As per my previous post, I'm successfully decoding CAN traffic from SI in Li-Ion mode. This includes error messages. The $20 device I mentioned has a CAN module and relays included, and it should be fairly simply to control its on-board relays using error messages. I've yet to drive them, as I haven't had a personal need to do so.

I've got a binary bit status for overload, but I've yet to see it trigger. Maybe if I charge my EV, turn on the oven, and the hot water heater element...?

In the post I made with the schematic, at the bottom, I mentioned that you can trigger standby/wake via CAN, as well. Not sure if you saw that, you replied so fast!

 

[Hedges]

Seems like this shouldn't be all that difficult to implement, but I haven't yet seen an affordable integrated solution. Shelly has ability to measure frequency, but I got noisy readings.

For a uP approach, AC voltage stepped down (resistor divider), LPF (capacitor), rectified and clamped to power rails. That gives "1" = positive, "0" = negative.

Running count of cycles in 10 seconds, update every cycle or every 1/10th second to a new 10 second count. (two moving pointers in circular buffer, add "1" as they appear at the front, subtract "1" as they disappear to the rear. "600" count is nominal frequency of 60 Hz. (only increment for transition from "0" to "1", not state of "1"!

This gives a slow responding (~ 10 seconds) loop to gradually add or subtract loads.
SI will run a faster loop to ramp SB up and down.

It could be used to control a continuously variable load, or switch in/out various discrete load steps.

There might be other simple analog frequency to voltage controls, or ICs designed to do it.

Maybe faster frequency measurement would be desirable, and of course is possible with time per cycle instead of cycles per time. Then control a slow PID loop.

 

[Calvin98]

Four CT, one per SI AC1 "L" output. Any > ~50A for > 1 second triggers load shed?
Bit of analog circuitry required. Maybe RC circuit and comparator.
Time delay or hysteresis to re-enable?
Software to re-enable would be fine. Only disconnect has to be fast.

Yes, that could work. We should talk about how to design a circuit for that. Or maybe come up with a drawing? I think this would only be a problem at night. During the days the sunny boys could handle the load and as long as the frequency shifting reacts fast enough, they could take care of any big surgeons also. The problem would be if the air happens at night or in the evening. Just having had the error message come up. I figured it might be good to take some proactive action so if it ever happens in the future, you’re ready. And I guess that goes for anybody with a Sunny Island also.

 

[Consumerbot3418]

Yes, that could work. We should talk about how to design a circuit for that. Or maybe come up with a drawing? I think this would only be a problem at night. During the days the sunny boys could handle the load and as long as the frequency shifting reacts fast enough, they could take care of any big surgeons also. The problem would be if the air happens at night or in the evening. Just having had the error message come up. I figured it might be good to take some proactive action so if it ever happens in the future, you’re ready. And I guess that goes for anybody with a Sunny Island also.

Feel silly asking, but have you considered using the multifunction relays (241.01/241.02)? They can be programmed to switch in overload condition or error state.

I don’t have any experience with it, so I don’t know what the hysteresis is like.

 

[Hedges]

Yes, if they do signal overload, that could work. Will it work if signal relay is in the SI that just crapped out? Not sure.
It's hysteresis is likely overload vs. not with a bit added in.
We would like to widen that enough to not reconnect load unless enough headroom.

There is a derating function (for hot weather). I figured an added analog thermometer (e.g. NTC) on heatsink could give better control.
Not for this sudden overload, just for overheating.

 

[Calvin98]

I had help with it, but we set up a raspberry pie and get the data via the can cable from the Sunny Island and send it to Home assistant. We also have the sunny boys imported there.

Still need to go over all these things carefully. And come up with a solution.

I do know about the multifunction relays, but I haven’t put them to use yet. This might be a good opportunity to do something. Gonna take a while to figure it out though.