Data logging

I also had another problem today with msb overload. I have 1200W of panels on each but one msb was reporting up to 1400W for brief moments before faulting. Cooler and overcast weather today. Panels are 2s3p so have reduced to 2s2p for 800W.

I left the system running while I was away for 4 weeks so no idea what faults/issues popped up during that time. Was all good when I returned.

Make Sky Blue  is on ebay  Now  and 132 dollars  for the v118 .    Each of my MSB  is 2S for 600w only .    

Hi,

thanks for your work to read data from MSB, could somebody post code please for esp8266 oder esp32?  With mqtt-pub-feature would per perfect or collecting code on a github repo would be great too. I think a lot of people are willing to use the datafeature for grafana but they are not good enough in coding to do it on their own. Me too 🙂

Esp8266 code should be very similar to esp32. I used Grafana in the past but just copied what I found on the web. No personal knowledge on mqtt. I now just use Home Assistant/Esphome which I find much simpler.

I am also using HA/ESPhome with a custom module.

Disaster! Inverter shut down just after noon which I was advised thru Tuya. Get home to find both MSB's dead along with esp32. So far have only found a popped 200V capacitor.

Batteries were full so a few cells causing BMS to trip on HV. The MSB's were both set to 28V max but the data shows them hitting 29V. I knew from early use that 28V was a safe level to stop nuisance BMS trips. The MSB's have poor voltage limiting at higher power it would appear. It shouldn't be an issue but suspect the on/off's from the BMS has fried them.

Doubt if I will persist with the MSB's. Time to try Warpspeed's analog SCC's using parts from the MSB's. 

that part alone should tell you something pretty significant!  It takes a LOT of energy to blow an electrolytic cap out!

Honestly, those abrupt battery BMS "disconnects" are the absolute worst for every single piece of equipment connected to them (except the battery).  I liken it to effectively throwing your equipment off a cliff--which easily explains why such disconnect activities usually result in blown equipment.

In short, almost any DC power conversion appliance will utilize inductors/transformers for power conversion.  (The MSB MPPT uses inductors.)  Power conversion at a most basic principle generally functions by repeatedly "charging" the inductor with "input power", and then "letting the inductor go" and gating the resulting "kick" of power into the "output" circuitry.

The reason this is a problem, is because inductors are just pieces of wire wrapped around a suitable ferromagnetic core.  They have no concept of "maximum output voltage" or anything of the sort.  From an oversimplified perspective, an inductor's "kick back" voltage is limited only by the power finding "somewhere to go."  Under normal operations, this is the battery.

But when the battery is abruptly disconnected (by the BMS), suddenly there is nowhere for the "kick" to go.  With nowhere to go, the voltage will easily exceed several hundred volts (kilovolts are technically possible, especially when kilowatts of power are involved!)--often until appliance internal components break down and blow out.

LF inverters (GS included) have a slightly similar problem with being cut loose by a BMS.  With a full-bridge drive on the transformer, any "excess" power (especially on the falling edge of the AC waveform, when the transformer magnetics need pulled back in line) gets gated back to the batteries.  But when that battery instantly "vanishes" (due to the BMS disconnecting), suddenly there's no place for the "excess power" to go--and the inverter's DC bus voltage will easily exceed several hundred volts in a few milliseconds, blowing out any parts that weren't designed to handle that unexpected voltage.

Glanced through that thread over on DIYSolarForums...yes, it's a clever idea.  I see one caveat to be aware of...and also one significant strength to note.

The caveat is that the maximum power point is adjusted by a potentiometer.  Especially in "four season" environments where ambient temps can reasonably be expected to range from 0F to 110F, this can result in some notable power losses: solar panel voltages are significantly affected by their junction temperature.  For example, my SW245 Mono array in a 3S config has a 23v expected swing across the expected temperature range (i.e. 106v to 129v), or ~8v/panel.

The strength is that it was observed that the MSBs have very slow regulation response times--and this likely plays heavily into why the MSB blew.  A direct-feedback analog regulation circuit should have a considerably quicker response time to the BMS abruptly disconnecting the battery--maybe even fast enough to not blow itself out.  (It only takes a fraction of a second to blow a FET or chip out with overvoltage.)

A possible solution would be to get a bunch of 5kw TVS diodes at the proper voltage spec to put across every single appliance downstream of the treacherous BMS.  The risk here is that TVS diodes' maximum clamping voltage is considerably higher than their "nominal" rating. 

For example, I'm using 64v TVS diodes in the new-design GS inverters.  That's lower than I'd like--but their "peak clamp voltage" is 103v...3v past the absolute max of several parts.  (Obviously, if there's a lower "spike", the clamp voltage will be lower.)

That's a bummer..  What was your cell deviation? Have you top balanced recently?  I have mine set also to 28V. (well 56V equiv for my battery)

I generally don't go into absorption with the MSB.  I'll have to watch carefully as we are getting more sun and I will soon be able to fully charge and watch as the MSB goes into absorption to see if it goes over 56V...

Makes me think I might want to get some high current zeners to act as a safety bridge..

also known as TVS diodes (transient voltage suppressors).

One thing to keep in mind about zener diodes: the higher the voltage rating, the wider the "clamp" voltage range--and by "wider", I mean easily exceeding 5-10v.  Zeners by themselves are anything but precision devices!  (They can be used for relative accuracy in some cases, but that's generally in a constant-current circuit intended specifically for accuracy.)

No record of the cell deviation but it's been pretty good. Like I said, I found 28V was a good max setting on the MSB to prevent nuisance trips. That was with my crappy panels pushing 500W max. Now with 1200W on the MSB it's just not regulating the max voltage accurately. They were holding the battery at 29V when they blew. Just using the 40A unit with 400W of panels to keep things operating.

I understand the limitations of a fixed voltage SCC but I don't need to extract every watt from the panels. I like the simplicity and repairability of the design. It's all a learning curve but would prefer to learn on the cheap!

I just was glancing at my voltages today with the battery full...

Now I wasn't at full sun today..  But I was near full battery voltage.  I never saw it go over 56V.  It just kept bouncing around

55.2 -> 56.  And the reported mode kept bouncing between 4 and 3.  4 is normal MPPT and I think 3 is absorption mode.  I have the float voltage set to 55.8 so with it bouncing around I think it just jumps between MPPT and Absorption.

My system has been operating with the same settings for over a year without issue but only ~1kW max in solar for 2 MSB's. For 6 weeks it's been operating with 1.2kW on 1 MSB. Soon as I added another 1.2kW on a 2nd MSB nothing but issues.

23v swing * 7.37Ampp on my panels is 167W, more than half of one entire panel.  But yes, a lot of things are all about acceptable compromise--and reliability often is more important than even efficiency!

Worth noting, if you're having issues with "voltage swing" on the MSBs, you definitely don't want to try the Epever Tracer MPPTs.  They're VERY slow and will HUGELY over-regulate.  But they will do their rated power amounts...with no fan.

"Surviving" on 400W thru the MSB 40A. I know I am not maxing the Watts but look at the curve. No interference and you can see when the tree comes into play at the end of the day. At the same wattage the 60A units were corrupting the data and wifi. Very hot yesterday so 300W from 400W 2nd hand panels I think is good.

Now that I have to rely on the 40A MSB my opinion is it's a better unit than the 60A. 400W of solar is not enough so I doubled that to 800W in the morning. Another hot day so maxing at 650W but the MSB performed faultlessly.

This unit doesn't generate the RF noise of the 60A so the data and wifi link to the esp32 was stable all day. Also connected another esp32 to the 3 batteries and alao no issues with data. Seems to be some bad design choices when they made the higher amp versions. I'll still make some analog units as I have all these parts and quite a few spare panels.