Conext 4024, dc over voltage with charger enabled

bigbill

Hi,

Long time forum stalker, first time posting. I have a conext 4024, (vintage 2015 ish) that is giving a dc over voltage fault.  It only happens with the charger enabled. I've adjusted the hvco value to max, tried with and without the bts. Charging voltage is set at 28.4v... charging a lithium bank, and it is currently night time. There is no voltage coming from the charge controller. Interestingly the battery bms (Daly) has not gone into high voltage protect mode (set at 29.2v)

Battery back is sitting at 25.9 volts, it is inverting fine. A/C input voltage was 238v and being passed through fine.  

The moment I select to enable the charger with the scp, the system hard reboots three times with nice chunking noise and returns the fault. 

All my system settings are unchanged from last winter,  everything has been running fine in this configuration with the LiPo bank for 2 years. Has anyone else seen this sort of behavior or error with with the context units? Any suggestions? I do have a backup unit that I'll probably swap tomorrow... 

I appreciate all the tips I've gleaned from this forum the past decade!

Bill

P.s. this older conext unit doesn't seem like a perfect match for newer lithium banks. Any recommendations for it's eventual replacement that can make 240v? 

Dave Angelini

Are you sure all charge settings for the charger are maxed? 

You could use an external charger and stop the problem.

I like Midnite. Not sure if they are 24v. I think your problem here is 24v. You really should be 48. I have a CSW 4048 that is fine. Your firmware good? 

bigbill

For anyone that reads this, the light of morning brings a solution. Not the inverters fault. 

The thermostat responsible for warming my batteries failed. The BMS low temp condition was triggered. Apparently if the inverter tries to charge a battery and it refuses the current, the dc over voltage fault occurs. 

Compounding confusion, the BMS Bluetooth app doesn't work on my new phone. I had to dig out an old one to get accurate data. 

For anyone interested, that app generally sucks, but the Daly 200a BMS itself has been working very well for 2 years and cells have always  been  balanced well. I've had zero issues until now, and am pleased that the low temp cutoff worked. Using Prismatic Cells from Docan Amy. 

Also for anyone interested, I keep the batteries warm in winter with a gun safe dehumidifier driven by an ink bird heating thermostat. All in a foam insulated wooden box. It's the inkbird that failed after 2 years. 

Conext sw 4024 inverter bought from NAWS almost a decade ago, still going strong. 

bigbill

I updated the firmware when I made the switch from lead acid to Lithium. Inverter has been pretty good.
My only current gripe is I'd like to be able to set a charging voltage below 28.4. It simply refuses to accept any lower value, despite the manual saying it should. The custom battery low voltage option has an apparent low limit of 28.8. Never figured out why...  

Agree about 48v. This is the largest practical system for 24v, it has served us well. Whenever i need to upgrade, I'll go 48v for sure. But... this inverter has run fine for years and I have an unused spare sitting on a shelf, so probably/hopefully going to be a while!

Dave Angelini

I hope you are right! There often is freeze damage to LFP that shows up later. 

Others, do not let this happen, ever! 

Crossing fingers for you Bill !

bigbill

Final comment for future people that may find it helpful. Issue confirmed. Daly BMS when in protect mode with charging disabled will result in over voltage errors on all charging sources, every time. I am able to replicate the issue by manually turning  off the charging within the BMS app. It tripped up the conext inverter, as well as Morningstar charge controllers. I'm not exactly sure how that little voltage spike happens when the BMS shuts it's charging FETs, but it does. Whatever the voltage spike is, it is above 36v. 

If you get over voltage errors and are running with a Daly BMS, make sure the BMS isn't in charging protect mode first before blaming the inverter and wasting time. 

In the end, everything is ok, I think.  I had the low temp cutoff on the Daly BMS set at 32 F. I replaced the thermostat and upgraded the heating element. I switched important loads to grid as soon as the first fault occured. Let the batteries warm up slowly for 3 days before re-engaging the loads. As far as I can see, there is no ill effect. 

This system has been powering our workshop and critical farm loads for over a decade. Aside from one incident where energy hungry in-laws plugged their RV into it, this squirrel induced failure has been our only hiccup. 

Switched to lithium 2 years ago, for the most part finding that a 7 kwh pack in lithium does the same job that 20kwh of Trojans did, and the Daly BMS (300a model) works well, though the app is complete garbage. I did not trust it until months had passed and it just worked. I could not understand it's behavior with the data from the app, but it keeps the cells balanced and the protections do work. 

Just don't let squirrels chew your thermostat wires.