Connecting Pure Sine Wave off-grid inverter to home office on grid

[matttelz]

So new issue...

I finally was able to reach full charge on my 100Ah battery with the new MPPT controller. Yes, it is about 30% more efficient on the full range of charging, cloudy days I can get like 35-45W and full sun in Feb I've been able to get up to 292W which is pretty good for 3-100W panels...
So the issue is once I hit the cutoff voltage of my controller...it doesn't seem to reconnect and recharge and any particular voltage... I was at 13.2V this AM and the controller wasn't charging yet...so it was still disconnected. I'm not sure what setting I need to look for, reconnect voltage? I have it set for the standard lifepo4 4 cell setting but I'd think it'd reconnect shortly after once the voltage drops but it hasn't done so yet...kinda disappointed and I'll need to do some additional trouble shooting...

 

[GXMnow]

What charge controller are you using? Can you post a link to the manual?

Both my BougeRV and Victron charge controllers have no trouble going back into "Bulk" charge if the batteries drained down a bit when there was still sun available. When the batteries stay at full charge, they go into "Float" and hold the voltage while matching the load current. The PV input voltage rises in this mode as it is not pulling full current from the panels. On the BougeRV controller, the battery voltage had to drop 0.4 volts (on a 48 volts system, it would be just 0.1 volts on a 12 volt system) before it would go back into Bulk charge. The Victron only needs a 0.02 volt drop, even at 48 volts, and it goes back to Bulk. It has a whole lot of settings to tailor it to the batteries.

What is the input voltage limit of your MPPT charge controller? If it can handle the 3 panels in series, it might work a lot better, especially in low sun conditions. But only if you don't have shadows. Most MPPT controllers need the PV voltage to be at least 5 volts above the battery voltage.

Another issue could be the BMS is going into a cell over voltage protection mode. My BMS units act like a diode when this happens. You can still pull current out of the battery to discharge it, but it won't take any charge current. Can you easily monitor the individual cell voltages?

 

[matttelz]

What charge controller are you using? Can you post a link to the manual?

Both my BougeRV and Victron charge controllers have no trouble going back into "Bulk" charge if the batteries drained down a bit when there was still sun available. When the batteries stay at full charge, they go into "Float" and hold the voltage while matching the load current. The PV input voltage rises in this mode as it is not pulling full current from the panels. On the BougeRV controller, the battery voltage had to drop 0.4 volts (on a 48 volts system, it would be just 0.1 volts on a 12 volt system) before it would go back into Bulk charge. The Victron only needs a 0.02 volt drop, even at 48 volts, and it goes back to Bulk. It has a whole lot of settings to tailor it to the batteries.

What is the input voltage limit of your MPPT charge controller? If it can handle the 3 panels in series, it might work a lot better, especially in low sun conditions. But only if you don't have shadows. Most MPPT controllers need the PV voltage to be at least 5 volts above the battery voltage.

Another issue could be the BMS is going into a cell over voltage protection mode. My BMS units act like a diode when this happens. You can still pull current out of the battery to discharge it, but it won't take any charge current. Can you easily monitor the individual cell voltages?

Here's the manual - https://cdn.shopify.com/s/files/1/0...-b8fb-44af-b705-ef13f9c0da9e.pdf?v=1686640659

I have no issue pulling current. I'm not tripping the battery bms. I was down to like 13.3v and it still wouldn't turn on charging... I'll try and investigate in the menu system today. It's a really complicated menu too...
If I get a 4th panel I'll likely do 2 in series for like 50v open circuit.

Something is definitely screwy with it...just can't figure out what...

Ok so the charger is charging now... I think it had to get down to 13V but I'm not entirely sure. I reset the controller from AUTO voltage to 12V. I'm not sure on the lifepo4 setting if there's a float/resume charge setting to alter here...I think that might be my issue but not sure... I think its just I'm unfamiliar with the terminology and settings of the controller... but I'm glad its charging again at least...

Ok figured it out.... its called the "Resume charge" voltage and its in the settings and its currently set to 13.0V which makes sense. Now I just don't know how to change the value... I'll have to reach out to them to see.

Edit: Ok so I wasn't able to adjust the resume charge voltage in the LIFEPO4 battery type so I switched it to manual and I was able to adjust the battery to the correct resume charge voltage...I set the max charge to 14.4 and resume to 14.3v. It looks like I'm unable to adjust the equalization charge which is 14.6V so I'm hoping that's ok with Lifepo4....

 

[matttelz]

I should be getting another 100ah battery this week along with an additional 100w panel. I plan to go from 3 panels in parrallel to 2 in series and 2 in parallel for the increase in voltage to support 400w.

 

[underdog5004]

Edit: Ok so I wasn't able to adjust the resume charge voltage in the LIFEPO4 battery type so I switched it to manual and I was able to adjust the battery to the correct resume charge voltage...I set the max charge to 14.4 and resume to 14.3v. It looks like I'm unable to adjust the equalization charge which is 14.6V so I'm hoping that's ok with Lifepo4....

I'd be worried about those charge voltages. 14.4 volts is 3.6 volts per cell which is pretty high. Generally bringing the cells up to 3.45 volts and holding at that point until amps drop off is sufficient. I bring my batteries up to about 3.5 volts and hold it for an hour and a half which gives the batteries time to balance the internal cells at that higher voltage. equalization charge voltage of 14.6 volts is equivalent to 3.65 volts per cell. This is acceptable as long as all the cells are equally balanced, which they never are. 3.65 volts per cell is the absolute maximum you should bring them up to, and if the cells aren't balanced you might have a 3.5 volt cell and a 3.8 volt cell averaging 3.65 volts per cell. This might damage the Cell at 3.8 volts. I would try to reduce the charge voltage down to 14 volts and disable Equalization or set it to 14 volts as well.