EG4 24v throws errors when starting inverter

MTBioGuy

New Member
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Mar 9, 2021
Messages
45
Location
Montana
I've been trying to install my new EG4 LifePower4 24v battery pack in my RV and have hit a wall. I certainly hope that you have an easy solution. This one is stumping me.

1) I'm simply attempting to replace my existing 12v FLA battery pack with my new EG4 24v pack.

2) I'm also replacing my existing 12v inverter with a new 24v inverter.
Here it is...
- 24v Aeliussine 2000 watt Pure Sine Wave Inverter
- https://www.amazon.com/gp/product/B08CMK1941/

3) It's a very simple install... only two cables... directly from the EG4 to the inverter... same cables as with the old 12v, perfectly functioning, system. I've temporarily removed the battery and inverter from the RV so no other circuits are involved. My Epever charge controller is NOT connected.

4) The problem is that I have a simple switch in the positive line so as to isolate the inverter. It's the same switch that I've used for years with my old 12v battery / inverter system. Here it is...
- 24V Battery Isolator Switch
- https://www.amazon.com/gp/product/B09J25P42X/
I've tried replacing the switch with another brand... same problem.

5) The problem is that the instant I flip that switch to connect the inverter the BMS throws 3 errors and cuts the circuit. The errors are:
- "Charging MOS off"
- "Discharging MOS off"
- "Short Circuit protection"

6) If I remove the switch entirely, connecting battery and inverter directly, and use the main breaker on the front of the EG4 as the isolator switch (just as a test) the battery boots up and plays just fine with the inverter. I don't want it to remove the isolator switch because I seldom use the inverter in my RV and don't want it running all the time due to parasitic drain issues.

7) I just don't see HOW a short circuit could occur... it's just two cables! I never observe any sparking when connecting the positive cable if that's a clue. I assume that the EG4 must have some sort of pre-charge capacitor to prevent that annoying event.

8) I know the EG4 is programmed to expect to be connecting to a Growatt controller/inverter unit... which I don't have. Perhaps there is a BMS setting that would prevent this but I'm unable to access the BMS parameters (no password).

Suggestions anyone?
Thanks
 

robby

Photon Vampire
Joined
May 1, 2021
Messages
1,738
The EG4 has a precharge circuit that limits the current going to Inverter for several seconds when it is switched on.
I suspect that turning on the load after the battery has gone through the PreCharge time is what is causing the problem. I think @RichardfromEG4 can probably help you figure out in more detail what is going on.
 

RichardfromEG4

The "Do-What's-Needed" Solar Guy
Joined
Dec 23, 2021
Messages
837
Location
Sulphur Springs, TX
Hey there I’ll do some research tomorrow. Very odd situation. Have you tried any other switches for testing? PM me or @ me tomorrow to remind me, it’s late here so I’ll likely forget I even posted here haha!
 

MTBioGuy

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Joined
Mar 9, 2021
Messages
45
Location
Montana
Hi Robby @robby - @RichardfromEG4 https://diysolarforum.com/members/43351/
I think you may be on to something. Another poster, JoeHam, sent me a link to a solacity.com article that discusses this very problem. The only doubt I have is that at 2,000 watts my inverter is not what you'd call "large". That said, perhaps the EG4 battery BMS just has a hair-trigger surge shut down setting... I good thing... I guess.

Here's the salient paragraph:
Battery Shut Down When Starting A Large Inverter -
"Inverters have input capacitors on the battery side, to smooth out and handle surges in output power on the AC side. Large inverters have large input capacitors, and large capacitors cause very large currents to flow when they are connected to the battery. For large inverters, around 3 kW and up, this can easily reach in the hundreds of Amps!

While most lithium-ion batteries have a large limit for brief surges, this capacitor charge-up current can still exceed that limit, causing the BMS to switch the battery off.

To make it possible to even connect these large inverters, the input capacitors need a chance to slowly charge up, and to do that a 4.7 kOhm 5 Watt 5% Axial resistor can be connected over a switch or breaker in line with the positive wire between battery bank and inverter. The resistor makes it so a little current flows into the inverter, slowly charging the capacitors, and by the time the switch or breaker is moved to the “on” position they are already charged up and there is no large current surge."
Source: https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/

What I'm trying to get my head around is whether I would now require TWO switches... activated in this order:
- Switch #1)
to turn ON a small line (running from the battery to the inverter) that contains the 4.7 KOhm resistor. This would pre-charge the inverter input capacitors.
- This would be then followed by flipping switch #2) which is the big one I currently have installed, that connects the battery, via 2/0 AWG cable, to the inverter itself.

By having switch #1 I'd be able to completely cut off all power to the inverter when it's not needed... which is most of the time... so I wouldn't have problems with parasitic power drain issues. I just wonder how large the resister wire would have to be... with 4.7 KOhms of resistance I wouldn't think I'd need a very large gauge wire. Yes?

Richard... what would your team think of this as a solution?
 

MTBioGuy

New Member
Joined
Mar 9, 2021
Messages
45
Location
Montana
How heavy is that inverter?
It's only a 2,000 watt 24v inverter.
Well... after much experimenting...
I'd recommend that you tell EG4 owners who are experiencing this problem, that an easy fix is a parallel pre-charge circuit using (in my case) a 25w / 40 ohm wire wrapped resistor between the EG4 battery and a momentary "on" switch that by-passes any existing (and problematic) master inverter "kill" switch. The required button-press charging period might be less than my 20 seconds but that would depend upon your choice of resistor and how large your inverter is. Just be sure to turn on the master switch while still holding down the by-pass switch. Others have told me that I don't need to hold it down for more than about 5 seconds. I've never tested less than 20 seconds and so far, I've never had the BMS object with it's usual "short circuit" shut down.
 

MTBioGuy

New Member
Joined
Mar 9, 2021
Messages
45
Location
Montana
Now that my EG4 to Inverter problem appears to be solved I'm hoping you might be able to help me on one other question. It should be pretty easy.

My Epever 50A SCC has a set of "Rules" that I have to follow when setting up my solar charge profile in order to ensure that it will play nice with my EG4 24v battery. I've attached a screen shot of those rules below.

Notice that I've also penciled in the numbers that I have currently entered into the SCC. Yes, they are a bit conservative but I'm trying to play it safe until I can get a handle on how this system handles my 600w of PV input and how it hands it off to my EG4... only then will I try to fine tune the settings for maximum capacity. My needs in this RV are pretty minimal and I suspect that I won't need to maintain a very high SOC... I don't see much need for maximizing the voltage in order to constantly be top balancing my cells. That seems to take place nicely even with my existing lower voltages.

The problem is that there are two spots in this set of Epever rules that require knowledge of the existing (unchangeable) settings within the EG4 BMS. You should be able to see them below the two red question marks. Part of the problem is that Epever uses (sometimes) a non-standard set of terms that I just don't understand... meaning that I can't seem to find the equivalent terms within the EG4 BMS. For example I just can't fathom what the difference might be between the "low voltage" and "under voltage" terms you see used below. That's where I'm hoping you might be able to help?

Epever SCC Rules.jpg

Please tell me what those two RED numbers should be... and will they work with the penciled in numbers I've already listed?


Thanks a bunch! I'm almost ready to "flip the switch" on this project!
Cheers!
- Dan
 
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