Schneider xw pro 6848 not powering up with eg4 lithium battery

[Koldsimer]

My first post, read a lot more than I talk.

I have a Schneider XW6848, running on a small Lead Acid bank. I'm waiting on 3 of these EXACT EG4 LifePower4 batteries to ship from Signature Solar to me. So this thread is timely and concerning to me.

I did pre-charge my inverter using a light bulb while hooking it up to the lead acid batteries. It glowed for a bit, so they do pull some to charge up.

I'm not sure how the batteries built in PRE-CHARGE resister works, but I assume it must be a timer or something initiated by battery turn on.

I suggest you shut ALL battery breakers OFF, and hook the battery buss to the inverter, turning all other breakers ON between inverter and buss bars. Then with the batteries connected to inverter turn battery breaker on. That should initiate a pre-charge of the circuit using the built in battery pre-charge resistor. It should be ok to turn them all on at same time, as long as they are going from an OFF to ON state while hooked to the inverter inputs.

I tried exactly that today with no luck.

I'm interested to see what your inverter does with the eg4's.

Hopefully, you will have better luck than me.

 

[Koldsimer]

@MrM1 @SpongeboB Sinewave @Hedges @Horsefly @RCinFLA

Could y'all please make some recommendations on exactly what size/type resistor i need to pre-charge the inverter? I've seen lots of suggestions and I guess I was going to try the 50 ohm 100 watt unit with a push button switch since i need something permanent.

Honestly, I'm hesitant to even try this, based on what MrM1 has to say in his thread about wiring his pre-charge system but I feel like I don't have any other good options at this point.

I'm going to order what's needed tonight so i can try this later.

Thanks in advance

 

[Rustic]

Excellent information, thanks. I noticed they recommend to close dc breaker before turning on batteries. Would that somehow limit inrush current?

Of course, all the batteries listed with that recommendation are linked to the inverter via bms and I am not so I don't know how applicable that would be to my situation.

The startup procedure is different depending on manufacture. You won’t know unless you try.

 

[Hedges]

Could y'all please make some recommendations on exactly what size/type resistor i need to pre-charge the inverter? I've seen lots of suggestions and I guess I was going to try the 50 ohm 100 watt unit with a push button switch since i need something permanent.

50V/50 ohm = 1A, 50V^2/100 ohm = 25W, probably works fine for precharge.

Say 5V drop (leaving 45V to power inverter) divide by 50 ohm = 0.1A, 45V x 0.1A = 4.5W, not enough to keep inverter up with standby draw.
You'll need to close switch fast enough to supply inverter before it starts inverting.

Consider 100A, 50V. That's 0.5 ohms. 400A would be 0.125 ohms. Look for a piece of wire in that range, and heavy enough to carry a couple amps or more. That would precharge capacitor without exceeding BMS limit, and carry 100W or more of idle consumption. 12 awg is 0.16 ohms per 100'. Have a 100' or 250' coil of Romex? About 0.3 ohms or 0.75 ohms round trip. Put a wire nut on white & black at one end. use other end as precharge resistor. That should limit current to 75 or a couple hundred amps and power up the inverter.

 

[Horsefly]

@MrM1 @SpongeboB Sinewave @Hedges @Horsefly @RCinFLA

Could y'all please make some recommendations on exactly what size/type resistor i need to pre-charge the inverter? I've seen lots of suggestions and I guess I was going to try the 50 ohm 100 watt unit with a push button switch since i need something permanent.

Honestly, I'm hesitant to even try this, based on what MrM1 has to say in his thread about wiring his pre-charge system but I feel like I don't have any other good options at this point.

I'm going to order what's needed tonight so i can try this later.

Thanks in advance

First of all, don't be too afraid. The current through the pre-charge resistor can be a fair amount, but it is for such a fraction of a second that it doesn't really matter. A 50 ohm 100 watt is fine. I use a 10 ohm 50 watt on my 24V system, and it works great. Don't be scared!

The problem: When the capacitors on the front-end of an inverter are completely depleted (after a couple of minutes of no power), the capacitors appear as a dead short to any DC source connected to the Inverter. So when you connect up a bank of LiFePO4 batteries, they are presented a dead-short, so there is the potential (with LFP batteries) for 1000's of amps. Thing is, that dead-short goes away really quickly. The capacitors charge back up and balance is achieved. Problem is, during that fraction of a second your BMS sees a ton of current, and after the BMS cuts off current the Inverter sees no voltage. No one is happy.

The math is pretty simple. If you have say 53V and a 50 ohm resistor, if the capacitors look like a dead short the current is only 53/50 = a bit over 1 amp, which is only 53W of power. Remembering that this rush of current is very brief, it probably makes more sense to go with something like 10 ohms, which means you have a bit over 5A of current, and maybe 250W of power. BUT, since the rush is so short, you don't need to size the resistor for 250W. 100W (or even lower) will do.

If you use a larger resistor, you - strictly speaking - need to allow the pre-charge to go for longer. In practice, I'm not sure this matters. Humans won't notice much difference between a 5/100's of a second and 3/4's of a second.

@FilterGuy wrote up a good resource on the pre-charge, and you might want to look at that. I think he was way too conservative on the current, ratings of the resistor, etc., but I guess it's better to be too conservative on such things than to just wing it.

 

[FilterGuy]

Here is the resource

Inverter Disconnect Switch with Precharge

To get the paper, click on the orange button at the top of this page. This circuit is designed as a disconnect switch that allows the user to pre-charge the inverter capacitors before turning the switch completely on. 26 June 2020 update: At...

diysolarforum.com

It is big and clunky compared to a pushbutton, but I like it because it is very hard for the operator to get it wrong.

 

[Koldsimer]

Ordered the 50ohm 100watt resistor, should be here tomorrow evening.

My Schneider insight didn't get delivered yesterday, should be here today. Will update firmware asap.

Gonna get battery readings this afternoon after my fla's float.

 

[Mr-Sandman]

I got a notice my batteries shipped today. I should have them by Friday. I'll let you know how they work for me hooked to my XW 6848 Pro.

 

[Koldsimer]

I got a notice my batteries shipped today. I should have them by Friday. I'll let you know how they work for me hooked to my XW 6848 Pro.

Thanks. Very curious to hear what happens in your case.

Some updates-

-got the latest firmware version downloaded into my xw6848

- Signature Solar said not to parallel batteries of different chemistries in an effort to make the inverter start.

- Ordered 50ohm 100watt resistor and switch to install tomorrow evening and try.

 

[Horsefly]

Signature Solar said not to parallel batteries of different chemistries in an effort to make the inverter start.

I'm not surprised they would say that. I personally don't think it is a good idea to have FLA and LiFePO4 wired together in parallel permanently, but I think it would be a useful experiment to try in your case, just to see if the XW started up OK.

There are many folks here who seem to think putting FLA (or AGM - same diff) in parallel with LiFePO4 is fine. See this thread:
https://diysolarforum.com/threads/t...p-battery-banks-in-parallel.31202/post-377349

 

[Mr-Sandman]

I would like to understand how the EG4 LifePower4 batteries PRE-CHARGE feature works.

I looked thru the manual they just updated and uploaded but no where in it does it talk about pre-charge feature or pre-charge resister being in place. Anyone know how it configured to work? Maybe it uses the resister when breaker is flipped on until BMS boots up? I think that detail might shed some light on this issue.

My XW Pro would do as you described yours does "start booting up, clicking, then after fans cycled reboot" when I had it pre-charging on the lead acid. I then tried again, moving quickly to the battery after a couple seconds of precharge and it finished coming online. I don't think it was getting enough power thru the pre-charge to come online.

 

[Koldsimer]

I'm not surprised they would say that. I personally don't think it is a good idea to have FLA and LiFePO4 wired together in parallel permanently, but I think it would be a useful experiment to try in your case, just to see if the XW started up OK.

There are many folks here who seem to think putting FLA (or AGM - same diff) in parallel with LiFePO4 is fine. See this thread:
https://diysolarforum.com/threads/t...p-battery-banks-in-parallel.31202/post-377349

Yeah, i thought it was just an issue with charging but i'm not surprised they didn't recommend it.

If the pre-charge resistor idea doesn't work, i guess i'm going to return these batteries and find something else that will work.

Signature doesn't seem to have any ideas to offer besides seeing if the resistor works. I'm beyond disappointed with them. They don't seem to be proactively helping at all. Just seeing what I can figure out on my own is what it feels like.

 

[Mr-Sandman]

If the pre-charge resistor idea doesn't work, i guess i'm going to return these batteries and find something else that will work.

Signature doesn't seem to have any ideas to offer besides seeing if the resistor works. I'm beyond disappointed with them. They don't seem to be proactively helping at all. Just seeing what I can figure out on my own is what it feels like.

They will be getting more than yours back if I have the same problem. DIY is their customer base, they MUST support their customer base, as WE talk, a LOT...

 

[Koldsimer]

Ok, so i tried again this afternoon after the firmware update.

With everything off, i switched to the eg4's and still won't start.

With my dvm, i measured 52.8 at the dc breaker before connection. As breaker was switched on, voltage immediately dropped to 13v and slowly (over about 3 seconds) rose to 33-34v and hovered there. Inverter clicked and fan pulsed but nothing would turn on. I considered adjusted inverter minimum input voltage to say 30v but its minimum voltage input is 40v i believe.

System started right back up with fla.

 

[MrM1]

Well there's Ur problem right there. The battery voltage is falling through the floor and not recovering.

It has absolutely NOTHING to do with Ur XW or firmware or that u need to use a resistor.

That said, just watched @Will Prowse quick tear down of that battery he released today. After watching that I'd suspect something in that built in pre charge resistor in the battery or the BMS

 

[MrM1]

How does the batteries built in pre charge resistor even work? What makes voltage "decide" to stop flowing thru it. I bet if you opened up the battery and bypassed that resistor they would work

 

[Horsefly]

Ok, so i tried again this afternoon after the firmware update.

With everything off, i switched to the eg4's and still won't start.

With my dvm, i measured 52.8 at the dc breaker before connection. As breaker was switched on, voltage immediately dropped to 13v and slowly (over about 3 seconds) rose to 33-34v and hovered there. Inverter clicked and fan pulsed but nothing would turn on. I considered adjusted inverter minimum input voltage to say 30v but its lvco minimum is 44 i believe.

System started right back up with fla.

I suppose it could be other things, but it certainly still sounds like the inrush current to the inverter is causing the eg4's BMS sees it like a short and cuts off the power. Pre-charge would fix that.

I've kinda lost some of the details, but... Did you try this with only one EG4 instead of all 4? I think @RCinFLA said that the EG4 BMS probably has some pre-charge like thing if the power is turned on at the BMS, rather than at your main switch. So this is something else to try:

• Disconnect all but one of the EG4's to your bus bars
• Turn off the discharge from the EG4 via the BMS control app
• Turn on the power disconnect between the EG4 and the Inverter
• Now turn on the discharge from the EG4 via the BMS

If @RCinFLA is right about this BMS having a pre-charge, this should turn on the power from the EG4 with a pre-charge.

 

[Mr-Sandman]

That sounds like the Pre-Charge in the battery packs not delivering enough power during startup, causing a failed start on the inverter.

We need to know how the pre-charge operates in these batteries.

 

[MrM1]

For anyone interested who has not actually seen the internals of these batteries , here's @Will Prowse video from today. I'm guessing this is Ur battery

 

[MrM1]

I suppose it could be other things, but it certainly still sounds like the inrush current to the inverter is causing the eg4's BMS sees it like a short and cuts off the power. Pre-charge would fix that.

The battery has a built in pre charge resistor