Configuration for a MUST Inverter

[roboza]

Hi ,

 

First post here. I have recently had a system installed at my house. Nothing fancy but something to allow me to work when we have no power. So far the system does what I need but I have a question on configuration.

I have 2 major options when configuration the inverter.

Output source priority selection

1. SbU. Solar energy provides power to the loads as first priority. Solar and battery will provide power to the load. When the batter drops below a configured voltage it will switch to grid.

2. Uti. Solar use used when the grid is not available. Grid charges the battery.

Using the SbU mode:

The problem with this and I found it out the other day. During the day it worked perfectly. We hit 7pm Sun was gone and the battery started to get used. At 8am load shedding hit and by that stage the battery was around 20%. The utility would only charge once the voltage was low enough on the batteries. What happened though was the battery hit 10% during load shedding and then the utility was not able to charge the batteries and we had to wait for load shedding to finish.

Using Uti mode:

This works fine. I have configured the inverter to charge the batteries with solar however, if there is excess solar the inverter still uses utility to power the load. The only time solar is used is when there is no Utility power available.

I did some tests and set the voltage on the battery in the inverter to not go below 26.5V so the SbU mode works and then if the battery goes below 26.5V Utility power kicks in to charge it and serve the current load. During the day the battery and load are both served from the Solar power.

Does anyone know of a better way if possible to do this.

I am using a MUST Inverter PV1800 3kw

 

[suds7162]

I'm considering purchasing a similar model for my own backup needs (Specifically the PV18-3024VPM). I've been studying the user manual as part of my research.

I interpret the "output source priority" options as follows:

• SUB = solar - utility - battery
• SBU = solar - battery - utility
• SOL = solar only
• UTI = utility only

Based on this, I reckon you actually want SUB - since you don't want to use battery if the grid is available? SUB should use solar first, if that's not available, go to utility, and if that's not available then battery. My interpretation of the SUB setting description is that it'll draw as much solar as it can, if the loads is more than what solar can give, it'll draw from the grid, and if the grid is not available then it'll draw from the battery. This way you will always use your panels to provide power to the home when the sun's out.

In addition to the above, you have two other important settings:

"Solar Supply Priority" (05)

I reckon for this one, you need to set it to LBU (load-battery-utility). If the battery level is lower than the setpoint in setting 20, then use solar to charge the battery. I interpret "If the battery voltage is higher than the setting point in program 20, the solar energy will supply to the load or recharge the battery." to mean that it'll charge the battery at whatever amperage it needs, and the rest will go to the load.

In addition to this, I think you can change setting 20 to something higher than default. Set it to maybe 70% of your battery SOC voltage? That way, you will never drain the battery below 70% IFF the grid is available and you have no sun. You'll only dip into your reserves if the grid is not available during loadshedding.

"Charger Source Priority" (10)

Here I think SNU (solar-and-utility). You will charge the battery using both solar and grid (same as setting 05). 

 

I think bottom line is the battery is there for a backup. Not to be used as part of your regular daily usage. Our grid is unpredictable, and you want to make sure you have battery available when you need it, and not draw from the batteries when you can avoid it (when the grid is available).

[roboza]

17 hours ago, suds7162 said:

• SUB = solar - utility - battery
• SBU = solar - battery - utility
• SOL = solar only
• UTI = utility only

Thank you for your input. I 100% agree with you on your interpretation however my inverter does not have the SUB option. Only the other 3 options.

[An3s.]

SBU and SOL both work just check what works for you

Settings 20 try 26.5v

 

[Veronica1946]

I have recently had the same MUST 3kw inverter installed. I get the impression the installer (qualified registered electrician) is still on a learning curve, but I am starting from zero and trying to get the menu settings right. Twice the battery has overloaded (error 3) and once has been completely flat -0%. Surely this is damaging the battery. How to I set it not to go above or below a certain capacity? 
My inverter is only connected to certain circuits on the DB board (all the lights) and a few specially installed electric sockets, supposed to keep the fridge and house alarm going every day during load shedding, plus one or two small loads eg TV. 
The solar panels have been very successfully charging the battery every sunny day, but at night, between load shedding, the grid doesn’t kick in to recharge the battery. There must be some incorrect setting on the inverter menu. 
Please help this not -electrically-knowledgeable senior lady. 

[SilverFoxza]

I've got the same 3kw inverter and recently got panels installed, also went for gel to a lithium battery. 

I setup the output source priority to SOL. I set program 20 to 26V and default on program 21.

So my system seems to be behaving, the grid disconnects when the panels can handle the load. If it does not, it connects battery. If the battery voltage falls to 26V the grid kicks in and charges everything. So far most of the day I'm drawing 0 from the grid. 

I did test the SBU option but I didn't set the parameters of the program 20 and 21 properly and drained the batteries through the night over a stage 6 load shedding. 

Using Uti I'm not saving during the day with the panels and constantly charges. So I've ruled this setting out for my setup.

I would say that this system has saved us endless power outage hassles, but I do feel I should have gone with a 5KW inverter instead just to handle loads a bit better from multiple appliances. 

However, I've been quite happy and would appreciate any advice or changes that work for you on this MUST inverter.

[Matt3]

SilverFox, is it the 1800-3024VPM you have? I have that and it doesnt behave as yours does. If grid is available it will always be on bypass while solar charges the battery.

I'm on SOL mode now, but have tried UTI and SbU.

For Setting 5 I've tried both LBU (solar goes to loads and then batteries if excess power) and BLU (solar priority to charge batteries). Both cases Utility should be last resort.

Setting 20 is at 26.1V

Setting 21 is at 27.2V (whats the default I don't feel like resetting right now?) Could this be the problem for me?

Veronica there are definitely some settings you can change to help - although I feel some of these inverters have some bugs and you may have a dud. Some will reach float voltage and not continue charging. Some may behave like mine and not use solar on a sunny day when grid is available. Try changing setting 14 to USE, 17 to 28.6 and 18 to 26.7. This should be fine for LiFePO4 batts. If you battery capacity is 2.5kWh or below I'd recommend setting 11 to "25", and 13 to "20". This is charge current.