EG4-Lifepower4 Short Circuit Protection

Shimmy

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So, is this statement of theirs about needing an inverter that's less than 80% of the battery bank have any electrical reasons behind it?
The BMS can only handle 100-150A momentarily. The pre-charge resistor should address the initial surge, but might not be sufficient for the short-duration overload requirement.
Does any other inverter and/or battery manufacturer make such a statement? I mean, it doesn't make sense to me. Their 6.5kW inverter's not always going to start up with full load on it, maybe it won't have any load on it, and may never get close to full load, so then it would meet their <80% requirement. It seems like they're just making it up as they go along.
I know eFlex has a similar statement-- the minimum number of modules required for specific inverters. For the one I was interested in (XW-Pro 6848) it was 3 modules minimum.

The issue is that the startup power is roughly equal to the nameplate of the inverter.

I am a little torn on how to look at this. I don't know why there isn't better logic on operating the pre-charge resistor, but at the same time, why isn't there better information from the inverters on pre-charge requirements and start-up procedures that provide sufficient start-up delay that pre-charge resistors are disengaged?
 

Subdood

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The BMS can only handle 100-150A momentarily. The pre-charge resistor should address the initial surge, but might not be sufficient for the short-duration overload requirement.

I know eFlex has a similar statement-- the minimum number of modules required for specific inverters. For the one I was interested in (XW-Pro 6848) it was 3 modules minimum.

The issue is that the startup power is roughly equal to the nameplate of the inverter.

I am a little torn on how to look at this. I don't know why there isn't better logic on operating the pre-charge resistor, but at the same time, why isn't there better information from the inverters on pre-charge requirements and start-up procedures that provide sufficient start-up delay that pre-charge resistors are disengaged?
Is it because the surge of the capacitor banks in larger inverters, i.e. at startup the caps act almost like a short circuit? But like you said the pre-charge resistor should take care of that?

Now that I've done some math, I could see how starting up the inverter and one battery with a load of around 70% on the inverter could trip the overcurrent on the BMS. Considering the inverter (battery DC to AC output) efficiency is around 90%, about 4400W on the loads would pull about 100A out of one battery at 48VDC. Of course this excludes any PV input, which would help power more if not all of the loads.
 

Shimmy

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Is it because the surge of the capacitor banks in larger inverters, i.e. at startup the caps act almost like a short circuit? But like you said the pre-charge resistor should take care of that?
Yes, charging the capacitors is essentially a dead short. (Failure mode 1) The pre-charge resistor acts to limit current, but it is disengaged by a timer only on the EG4. The inverter doesn't know about the pre-charge resistor status. Pre-charge is not the same as startup-- it is just providing voltage to the capacitors. There is no guarantee that the capacitors will be fully charged at the end of the timer setting. (Failure mode 2) Some inverters will start up automatically, which poses the biggest challenge as far as I can tell. If they start up too quickly, the pre-charge resistor might still be engaged. Low-frequency inverters with large transformers can cause magnetizing inrush current. (Failure mode 3) Finally, once the startup is completed, the inverter will begin inverting and supporting load. You can see some inrush from loads starting at this point. (Failure mode 4)

So, pre-charge addresses faiure mode 1, but it might not be enough with a single battery. Switching on a second battery cuts the resistance in half and allows for 2x the current.

The second battery can also help with faiure mode 2, as it is switched on slightly later than the first, so the pre-charge resistors disengage at different times.

To avoid failure mode 3 you need additional capacity. Inrush on low-frequency units can be 6-20x the rating of the transformer, but the way it ends up working it might be 3x your inverter's nominal capacity. Most BMSs can handle the additional inrush for a short-term overload (IIRC), but this is the difference between needing 2 and 3 batteries for a ~6.8kW inverter. Again, if the pre-charge resistor is somehow still engaged, it will be overloaded at this point.

And, for failure mode 4... make sure the inverter starts up with zero load.
 

ncsolarelectric

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So, is this statement of theirs about needing an inverter that's less than 80% of the battery bank have any electrical reasons behind it? Does any other inverter and/or battery manufacturer make such a statement? I mean, it doesn't make sense to me. Their 6.5kW inverter's not always going to start up with full load on it, maybe it won't have any load on it, and may never get close to full load, so then it would meet their <80% requirement. It seems like they're just making it up as they go along.

I actually was in Texas last week visiting some friends and was going to pick up one of these Lifepower4 48v batts from their facility on the way back home. But, they were out of stock despite one of their salespersons kind of intimating that they did have them available. I had ordered it on-line from them, but had to cancel the order, as I wasn't going to pay $300 shipping it here, when I could've picked it up for free (after sales tax). They're on back order and won't be in until the middle of July, and the inverter won't be available until early August.

I've really wanted to get a system installed for our place using their battery and inverter, but these issues I seen regarding this battery have got me a bit gun shy.
I agree, as stated, the statement doesn't make sense. However, what he is referring to is that the BMS must be capable of supplying the Maximum current, at the Maximum output power at the Minium voltage input. For the 6500W inverter, we're looking at,

(6500W/39) x 1.075% for efficiency loses, = 179.2A. The SUM of the circuit breakers on the battery bank AND the main fuse/CB to the Inverter DC input should be rated at a minimum, of 179.2A x 1.25 = 225A. 179A is 80% of 225A. That's where he gets the 80% from, I think.
 

Kornbread

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The BMS can only handle 100-150A momentarily. The pre-charge resistor should address the initial surge, but might not be sufficient for the short-duration overload requirement.
100a max continuous, 30amp recommended ... umm, kornfusing.
1657318279617.png
 

Subdood

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I agree, as stated, the statement doesn't make sense. However, what he is referring to is that the BMS must be capable of supplying the Maximum current, at the Maximum output power at the Minium voltage input. For the 6500W inverter, we're looking at,

(6500W/39) x 1.075% for efficiency loses, = 179.2A. The SUM of the circuit breakers on the battery bank AND the main fuse/CB to the Inverter DC input should be rated at a minimum, of 179.2A x 1.25 = 225A. 179A is 80% of 225A. That's where he gets the 80% from, I think.
Yes, I understand one battery can't handle full load on their 6.5kw inverter. I guess what I don't understand is this- are they (SS) inferring you need two batteries to start up this inverter? Maybe they're not and I'm making a wrong assumption.

For reference, they have several vids on youtube that show their batts starting up various inverters. In particular, they show a single Lifepower4 batt starting a Solark 12K, and a Schneider 6.8K inverter. But, then they need 2 batts to start up a 8k Outback Radian.
 
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ncsolarelectric

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Yes, I understand one battery can't handle full load on their 6.5kw inverter. I guess what I don't understand is this- are they (SS) inferring you need two batteries to start up this inverter? Maybe they're not and I'm making a wrong assumption.

For reference, they have several vids on youtube that show their batts starting up various inverters. In particular, they show a single Lifepower4 batt starting a Solark 12K, and a Schneider 6.8K inverter.
I doubt it. If there is no load on the inverter, there is an idle power of about 70W. If the battery can deliver 70W at 48V without collapsing, it will start and run. It's when it's loaded, especially with things like AC units, motors, compressors, power tools, then the battery needs to be able to provide the surge amps.
What surprised me was how low the continuous amps are from the battery. Basically, those batteries are rated for 1500W continuous, ~ 50V x 30A. You can size the number of battery banks based on this and your load requirements. If your continuous load is only 1500W, you can get away with 1 battery. Just don't hit it with more load than that until you add more batteries.
It would be the same running off solar-only with too few panels. If there are only 1500W of solar panels, the inverter can't pull 6500W from the solar input.
 

Subdood

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I doubt it. If there is no load on the inverter, there is an idle power of about 70W. If the battery can deliver 70W at 48V without collapsing, it will start and run. It's when it's loaded, especially with things like AC units, motors, compressors, power tools, then the battery needs to be able to provide the surge amps.
What surprised me was how low the continuous amps are from the battery. Basically, those batteries are rated for 1500W continuous, ~ 50V x 30A. You can size the number of battery banks based on this and your load requirements. If your continuous load is only 1500W, you can get away with 1 battery. Just don't hit it with more load than that until you add more batteries.
It would be the same running off solar-only with too few panels. If there are only 1500W of solar panels, the inverter can't pull 6500W from the solar input.
Why then would they need two batts to start an 8k Outback Radian?

Maybe I'm missing something, but shouldn't a battery rated at 5.12kwh run a load(s) at 100A (being that 100A is the max rating) and ~50V for an hour without a problem? Like Korn, I don't get the 30A recommended current.

Unless they're talking about 30A/120VAC (3600W) load? But that's not consistent. Their data sheet says 100A DC max, but 30A AC recommended?? Dang, I'm getting Kornfused too..
 
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ncsolarelectric

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Why then would they need two batts to start an 8k Outback Radian?

Maybe I'm missing something, but shouldn't a battery rated at 5.12kwh run a load(s) at 100A (being that 100A is the max rating) and ~50V for an hour without a problem? Like Korn, I don't get the 30A recommended current.
According to the 8k OB Radian spec, it requires 34 Watts idle power. There must have been a load on the Radian at the time, it wasn't simply idling.
 

Kornbread

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I doubt it. If there is no load on the inverter, there is an idle power of about 70W. If the battery can deliver 70W at 48V without collapsing, it will start and run. It's when it's loaded, especially with things like AC units, motors, compressors, power tools, then the battery needs to be able to provide the surge amps.
What surprised me was how low the continuous amps are from the battery. Basically, those batteries are rated for 1500W continuous, ~ 50V x 30A. You can size the number of battery banks based on this and your load requirements. If your continuous load is only 1500W, you can get away with 1 battery. Just don't hit it with more load than that until you add more batteries.
It would be the same running off solar-only with too few panels. If there are only 1500W of solar panels, the inverter can't pull 6500W from the solar input.
What I gather from other posts on other threads; it is the inrush current at initial inverter startup that causes the basic eg4 to enter short circuit protection mode. So yes, it may be they are recommending multiple batteries just to cover startup inrush, not max inverter output, or for that matter, any amount of inverter output. This seems counterintuitive as the basic eg4 has a precharge resistor. As many people have stated, I also believed that the recommendation for multiple batteries was only if you desired max output from the inverter, not just to turn it on.

With the hit and miss nature of issues with the eg4, I have to question what SigSolar is doing as far as guaranteeing they are receiving and passing on to their customer a known consistent high-quality product. If a reseller did not have effective quality control in place, it would not be that hard for a manufacturer to slip in their seconds.
 

robby

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Wow! You need 6 battery packs to run 6500W continuously. I wonder if you only had 2 battery packs and ran it at 6500W if the fact that it will run out of juice before they are damaged is sufficient?
Don't you mean more like 4 Packs?
4 Packs should handle 6000W. It is still is a lot of batteries for the load.
 

Shimmy

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Don't you mean more like 4 Packs?
4 Packs should handle 6000W. It is still is a lot of batteries for the load.
I read the specs as don't do a continuous discharge at more than .3C. Considering most inverters are going to be loaded an average of 30% I think you would be fine with the minimum of 2, but ideally 3 modules.
 

Subdood

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I read the specs as don't do a continuous discharge at more than .3C. Considering most inverters are going to be loaded an average of 30% I think you would be fine with the minimum of 2, but ideally 3 modules.
Okay, now that makes sense. So, that means at 1500W continuous load, the battery would last about 3.3 hours?

What would be the consequence be if you discharged it at 1C? Would that affect the longevity of the battery? I read somewhere that a LiFePo4 batt should be max charged at 1C and max discharged at 0.5C, or maybe it's the other way around?
 

Shimmy

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Okay, now that makes sense. So, that means at 1500W continuous load, the battery would last about 3.3 hours?

What would be the consequence be if you discharged it at 1C? Would that affect the longevity of the battery? I read somewhere that a LiFePo4 batt should be max charged at 1C and max discharged at 0.5C, or maybe it's the other way around?
That's a better question for EG4. I am only guessing, but I doubt you can discharge over 0.8C for more than a few hours. It does reduce life; there are fairly standardized life vs DoD and discharge rate graphs-- maybe a 50% reduction in total cycles?
 
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