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Limiter inverter with RS485 load setting
#56
The saga continues with this P.O.S., please excuse my french. So to quickly summarise what I have done so far to get this working:

The inverters would only work correctly for several hours before ignoring their output commands and start exporting a random amount to the grid (they never made it through a full day without breaking), so I presumed it was an issue with the external meter box. I tried everything to get it going including replacing the meter but couldn't get it fixed.

Then I removed the meter box as the control for the inverters and wrote some software that runs on a raspberry pi which takes a demand reading from my emonpi meter box and sends the required output command over a serial cable to the inverter. This also would only work for a while until the inverters decided to do whatever they like and output a random amount of power.

I connected a switching relay to my serial port cable chip (a max3232) because I found that if you unpowered the serial chip and powered it up again the systems would often respond properly again, so I thought the max3232 was crashing. The relay runs every 15 minutes and restarts the max3232 chip for a second but this still hasn't solved the problem.

I've written a loop that increments an outputted watt value every 0.5 seconds from 0 to 400 and I can see that the inverters do somewhat respond properly, the output draws a sawtooth waveform on my graphs as you would expect so the inverters are somewhat obeying my commands. It's the intermittent nature of this issue that makes it very hard to fix.


I'm starting to think that I might need to include a "ramp rate" feature in my software to get the inverters to better "track" what I am asking of them. For example, in my live system, if the demand goes from 400 to 800 watts perhaps I need to send output values along the lines of: 400, 450, 500, 550, 600, 650, 700, 750, 800 over the timespan of a second instead of what I currently do which is: 400, 800. 

I've also contacted SoyoSource on Aliexpress several times and they've "read" my message but have not replied. My opinion at this stage is unless there's a firmware update for this equipment I would really recommend against this product and would instead go for a Sunpower with limiter. I'm unsure if they make a 24 volt option which is what my system is based on but it will be something I will look into. 


@MasterTH I came across a slight error in your code:
Code:
            if bezug > 20:
                byte4 = int(bezug / 256)
                if byte4 < 0 or byte4 > 256:
                    byte4 = 0
                byte5 = int(bezug) - (byte4 * 256)
                if byte5 < 0 or byte5 > 256:
                    byte5 = 0
                byte7 = (264 - byte4 - byte5)
                if byte7 > 256:
                    byte7 = 8

Because you lack the <= and >= sign you will have values which are over 256 being sent to the wire at specific output values. This might or might not lock up your serial port.


To correct it, simply modify it to something like the following:

Code:
            byte4 = int(demand/256) ## (2 byte watts as short integer xaxb)
            if byte4 <= 0 or byte4 >= 256:
                byte4 = 0
            byte5 = int(demand)-(byte4 * 256) ## (2 byte watts as short integer xaxb)
            if byte5 <= 0 or byte5 >= 256:
                byte5 = 0
            byte7 = (264 - byte4 - byte5) #checksum calculation
            if byte7 >= 256:
                byte7 = 8

@completelycharged

I'm only getting around to re-reading your post now:

>This was part of the reason I ended up adding in a voltage detection and control override on the power output to prevent the unit from reaching battery cut-off. I ended up setting the cut-off voltage at near 0kWh (effectively emergency cut-off) and just control the output on/off purely with the separate code.

This is very interesting, my cut off is 22v and my startup is 23v, perhaps I will lower them and simply output zero when I get into the lower battery range because it does seem to happen more frequently at night and also early morning when the battery would be low . I'll report back in a few days.
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RE: Limiter inverter with RS485 load setting - by Cell-King - 07-22-2020, 12:49 PM

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