EG4 3kW Drains Battery in AC Bypass Mode

[aznel]

I've been playing with a toy solar system using an EG4 3000EHV-48. I have a problem with the battery draining all evening/night when in AC bypass mode. This causes the battery to go into protect mode by the morning, and I need to "jump start" it with a dedicated charger before it can be charged again.

The battery is connected to an (externally powered) shunt. It shows that even when the EG4 inverter reports it is running in bypass mode, it draws about 0.3 amps from the battery until it hits ~45v and the battery goes into protect mode. If I turn off the inverter, the current draw drops to around 0.2 amps but doesn't stop. If I disconnect the battery from the inverter, the current draw goes to zero. I have verified that the current draw is real by removing the shut from the picture and using a multimeter to measure the current and voltage drop while the inverter says it is in bypass mode.

Perhaps related, even though the inverter is set to change only using solar, sometimes it decides to quickly charge the battery when it reaches ~46v up to around 47v (at ~6 amps which corresponds to the 2A max utility current rate setting).

The settings I believe are relevant are as follows:
5 - Battery Type - USE (User Defined)
11. Max Utility Charge Current - 2A
12. Back to Utility - 48v
13. Back to Battery - 50v
16. Charge Source Priority - OSO (Only Solar)
29. Low DC Cutoff - 46v

I've attached a battery voltage curve from a few days ago from the SmartESS app showing what a typical day looks like. Please help me determine if this is expected behavior, if I am doing something wrong, or if I have a defective unit. Thanks!

 

[Mattb4]

The unit runs off power from the battery. It will eventually drain the battery if not supplied with charging current either by PV or utility. You will see this referred to as idle draw. Some will take less power when in Energy saving mode (ECO) or when the power switch is off. But there is always some unless batteries are disconnected.

Say your idle draw is 50w. Over a 16 hour night til sun up that can add up to 800wh draw from your battery.

 

[rhino]

What is the size of your battery?

 

[aznel]

The unit runs off power from the battery. It will eventually drain the battery if not supplied with charging current either by PV or utility. You will see this referred to as idle draw. Some will take less power when in Energy saving mode (ECO) or when the power switch is off. But there is always some unless batteries are disconnected.

Say your idle draw is 50w. Over a 16 hour night til sun up that can add up to 800wh draw from your battery.

So what does the "Low DC Cutoff" setting do? Is it only effective in battery mode? This is somewhat strange because it means there is more battery draw when connected to AC than when not. Do I need to set up a smart-home outlet to disconnect the inverter from the grid when the battery level is below the DC cutoff?

Also, does every AIO exhibit this behavior? For example, the Growwatt SPF 3000TL LVM-ES can run without a battery at all -- does it also drain a connected battery when in bypass mode?

What is the size of your battery?

It's a relatively new 50AH Ecoworthy. On this note, should the battery BMA be kicking in at 45v? The specs say it can go down to 40v, which seems more typical as an absolute low level for a 16s Lifepo4 battery.

 

[Mattb4]

Low DC cutoff turns off the inverter from operating. It happens in any mode. It is my understanding that once that happens you can not even charge your battery from utility until voltage comes back above system minimum battery startup voltage. There might be a slight increased draw when in AC bypass due to the relay operating.

The batteryless inverters and how they operate when a battery is there, versus when one is not, I do not know what happens.

Most of the common AIO's require the battery in order to function and will have an idle draw. (Note: this is not the inverter efficiency which is often in the +90% range). You can read many Threads on the Forum about peoples dismay and attempted work arounds.

 

[aznel]

Low DC cutoff turns off the inverter from operating. It happens in any mode. It is my understanding that once that happens you can not even charge your battery from utility until voltage comes back above system minimum battery startup voltage. There might be a slight increased draw when in AC bypass due to the relay operating.

The batteryless inverters and how they operate when a battery is there, versus when one is not, I do not know what happens.

Most of the common AIO's require the battery in order to function and will have an idle draw. (Note: this is not the inverter efficiency which is often in the +90% range). You can read many Threads on the Forum about peoples dismay and attempted work arounds.

The inverter is not turning off when it goes below the DC cutoff. The inverter does not even turn off when the battery goes into protect mode -- when I wake up in the morning the inverter is still running fine. This is also true when I physically disconnect this battery. This calls into question the theory that the unit runs off battery power only.

Before this, I used a Growwatt SPF 3000TL LVM-48P (not connected to the grid). There was no (or negligible) power drawn from the battery when it was below the DC cutoff. If there was not enough solar to charge, the entire device would power down about 30 seconds after the inverter powered down. It would automatically come back on and charge when the sun came up.

 

[meetyg]

First, what is your output priority setting set to? (UTI/SOL/SUB/SBU etc...)
Second, did you check that the voltage the inverter is showing is really the battery voltage? It might not be properly calibrated and so it thinks your battery voltage is higher than it actually is.
After validating that, I would try to set the "back to battery" voltage a bit higher, see if it helps.

What are your bulk and floating voltages set to? Maybe your battery isn't getting enough charge in the first place... 50v for a 16s Lifepo4 is a bit on the low side of things...
That means that if you start the night with 50v, there isn't alot of capacity in the battery.

 

[Mattb4]

The inverter is not turning off when it goes below the DC cutoff. The inverter does not even turn off when the battery goes into protect mode -- when I wake up in the morning the inverter is still running fine. This is also true when I physically disconnect this battery. This calls into question the theory that the unit runs off battery power only.

Before this, I used a Growwatt SPF 3000TL LVM-48P (not connected to the grid). There was no (or negligible) power drawn from the battery when it was below the DC cutoff. If there was not enough solar to charge, the entire device would power down about 30 seconds after the inverter powered down. It would automatically come back on and charge when the sun came up.

Ok, whatever. Bye.

 

[aznel]

First, what is your output priority setting set to? (UTI/SOL/SUB/SBU etc...)
Second, did you check that the voltage the inverter is showing is really the battery voltage? It might not be properly calibrated and so it thinks your battery voltage is higher than it actually is.
After validating that, I would try to set the "back to battery" voltage a bit higher, see if it helps.

What are your bulk and floating voltages set to? Maybe your battery isn't getting enough charge in the first place... 50v for a 16s Lifepo4 is a bit on the low side of things...
That means that if you start the night with 50v, there isn't alot of capacity in the battery.

Output priority is SBU. I have checked that the inverter voltage readings accurately reflect the battery voltage. Bulk and Float are set to 58v. The shunt tells me I am putting ~50.6Ah into the battery to go from jump-starting to 58v.

The question this thread poses is why is any battery capacity needed overnight? I can manually disconnect the battery when the sun goes down and the inverter continues working fine (and powers inverter loads). Then I need to reconnect the battery in the morning to start charging. It seems the EG4 3000EHV-48 AIO could employ this same logic internally to prevent vampiring a battery down to potentially dangerous levels. I believe (but am not sure) that the Growatt SPF 3000TL LVM-48P did this correctly.

 

[meetyg]

I think it may be the logic in SBU mode. Try setting UTI for one night, just to check.
I agree that it shouldn't go below DC cutoff voltage. But it seems that your BMS is cutting out earlier than spec too. try setting that voltage a bit higher, to 47v, see if it matters.

My understanding of SBU mode is this: As long as voltage is above "back to battery", and grid is available, it uses solar and/or battery, down to "back to utility" voltage. The reason that it needs to use some power, is because is actually inverting DC to AC. It must be prepared to run your loads, so it's actively inverting. However, if grid isn't available, it will allow itself to go as low as "low voltage cutoff".

However, it seems like your inverter is not obeying these voltages for some reason. That's why I thought maybe voltage isn't calibrated.

So as I suggested, try to use UTI, see if it changes this odd behavior. If not, then I would suspect you either have a faulty device, or maybe one with a firmware bug (did you check if there are any FW updates for your inverter? ).