Hi All

I have been having some intermittent trouble with my migration from AGM to lithium. I have recently purchased a single Narada 48npfc100 to run on a quietish Axpert 5kw inverter that powers my home along with 2kw of canadian solar panels. 

The new lithium battery has been going into protection (short circuit by my recent investigations .. thanks rs485) a few times a day, which due to my model of inverter, results in a power outage in my home, till I restart the batteries with an AGM 48v jump start to the inverter. I manage my loads with a homebrewed raspberry pi app that I wrote that monitors the inverter over serial, and turns off loads like my heat pump and pool pump if my inverter use goes over 2.5kw, so it VERY rarely exceeds 3.5kw and if so, only for seconds at a time and this sends the draw back to utility for a few minutes until the offending kettle or iron use is over.

So I suspect, unless I can find a way to limit the current draw to 100A, the intermittent ms surges, will continue to drive me mad.. so I have a few options, and I'd love some additional opinions

- Buy a newer inverter with a softer start

- Buy more batteries to limit the draw per battery (not 100% sure this will solve my problem .. not sure how many I would need to be sure it would work ?)

- find a way to limit current and rather brown out the inverter, than draw too much current

Thoughts ?

8 hours ago, jetlee said:

- Buy more batteries to limit the draw per battery

I think that's the best solution. One 100Ah battery module is a bit light for a 5kW inverter. The Narada seems to have a hard and fast 100A limit (1C), and you'll never be able to drop loads fast enough to beat that. One extra module should be plenty. 

6 hours ago, Coulomb said:

I think that's the best solution. One 100Ah battery module is a bit light for a 5kW inverter. The Narada seems to have a hard and fast 100A limit (1C), and you'll never be able to drop loads fast enough to beat that. One extra module should be plenty. 

Hi Coulomb

Thanks for the advice, I have read MANY of your responses on this forum, and appreciate that you took the time to reply, I'm sure you spend many hours helping people on this forum.

I have a follow up question / comment that could use some clarity.

I have yet to update my firmware (current - 74.31) and I know there is an updated version (if I recall 74.40 with the lithium slant), I assume that has no extra bits to soften the cutover? Additionally, there are no settings I can tweak to force the capacitors to stay "more charged" when switching back to battery? This is a little frustrating when I spent 4 years running flawlessly on 100ah of AGM, and after spending the cash, now need to spend more .. so just trying to exhaust as many options as possible, before selling my soul for another Narada 😉

Again, thanks for your reply

16 hours ago, jetlee said:

Buy more batteries to limit the draw per battery (not 100% sure this will solve my problem .. not sure how many I would need to be sure it would work ?

I strongly agree with @Coulomb. More batteries will bring even more benefits, such as being able to harvest more solar energy for night use. One can never have too much battery capacity. I started with an Axpert/Synerji MKS 5K (5kW) and 2 10048 packs, total 200Ah. It worked well and later I doubled the installation to adapt to the need.

17 hours ago, jetlee said:

74.40 with the lithium slant), I assume that has no extra bits to soften the cutover?

No, there is nothing that firmware can do to "soften" a sudden increase in battery load.

Patched firmware version 74.40e does have KettleKomp™, which will make it switch to bypass mode less often, and for a shorter period of time when it does (conditions allowing). But it looks like that won't help your present situation.

I feel like maybe I havent been very clear, so just to be super clear.. I am not exceeding the 100A draw .. I havent ever gone over about 60A according to my logs. BUt when the inverter switches between battery / utility / solar, its sometimes going into protection mode with a short circuit protection, which I am assuming is due to the capacitors suddenly requiring current when switching.

I just want it to be clear, that I am not getting close to 100A yet .. but once or twice a day, even at lowish loads, I can see the battery behave as if it detects a short.

No need to answer if thats been understood, I just got the feeling from the replies that there was an assumption that I was getting over the 100A limit on occasion

I was under the impression that you were getting spikes of battery current that exceed 100A, e.g. starting a motor. These are very brief in duration (less than a second), and logging software typically doesn't capture it (often sampling the current many seconds apart). But the BMS might well consider these to be an overload, reporting them as a short circuit.

I have noticed spikes of battery current occasionally when switching to or from bypass mode. I don't know why that happens. If your problem is premature switching to bypass mode, fully patched firmware such as 74.40e featuring KettleKomp™ could well help (if set up properly, follow the instructions). 

After following this topic some inputs. Initially the OP was not sure if the 100A limit might be exceeded. Further if the heat pump is not inverter start and it and pool pump would start at the same time the OP will for sure exceed 100A. May be even the pool pump on its own. Also stated that at times the load is up to 3.5 kW. In such a case even when a normal fridge would start the peak power used by a 150W motor can equate to as high as 1.8kW. This will exceed 100A from 48V. This I measured by using a high fps video and reading on the DC side during a start of my one fridge. Digital multimeters tend to be too slow to read the fast peaks in current.

Initially the thought of changing the inverter to one with soft start. This the inverter will never do. One has to take care of it as the inverter MUST at all times provide the full AC output.

With the old betteries being in use for years there was no BMS and as indicated this battery has a fast BMS to trip once 100A is exceeded.

Edited August 28, 20223 yr by Scorp007

4 hours ago, Scorp007 said:

even when a normal fridge would start the peak power used by a 150W motor can equate to as high as 1.8kW.

Never 1.8kW, if anything like then 1.8kVA. The difference is that kVA is not real power but apparent power. That means it does not draw all of it from the battery but part from the capacitors inside the inverter. The Axpert MKS 5K claims capability of twice nominal current during a few seconds. That's 10kVA short circuit power.

Normal induction motors, such as used in fridges and pumps, are known to start with up to 5 times nominal current.

53 minutes ago, Beat said:

Never 1.8kW, if anything like then 1.8kVA. The difference is that kVA is not real power but apparent power. That means it does not draw all of it from the battery but part from the capacitors inside the inverter. The Axpert MKS 5K claims capability of twice nominal current during a few seconds. That's 10kVA short circuit power.

Normal induction motors, such as used in fridges and pumps, are known to start with up to 5 times nominal current.

In order to get away from PF I used a 12V battery with car running and battery at 14V. The power was even higher as the DC clamp meter in the video had a peak of 140A. Not guessing. I used my 12V 3kw portable inverter.

22 hours ago, Scorp007 said:

After following this topic some inputs. Initially the OP was not sure if the 100A limit might be exceeded. Further if the heat pump is not inverter start and it and pool pump would start at the same time the OP will for sure exceed 100A. May be even the pool pump on its own. Also stated that at times the load is up to 3.5 kW. In such a case even when a normal fridge would start the peak power used by a 150W motor can equate to as high as 1.8kW. This will exceed 100A from 48V. This I measured by using a high fps video and reading on the DC side during a start of my one fridge. Digital multimeters tend to be too slow to read the fast peaks in current.

Initially the thought of changing the inverter to one with soft start. This the inverter will never do. One has to take care of it as the inverter MUST at all times provide the full AC output.

With the old betteries being in use for years there was no BMS and as indicated this battery has a fast BMS to trip once 100A is exceeded.

Thanks for this.

I just want to comment here. I am not off-grid, I (mostly) have a grid (bar loadshedding, which is not when I am experiencing this problem). In the event that I have a utility failure, I agree 100%, the inverter must supply, and should the demand exceed the 100A limit on the battery, yes, I expect a trip or some sort of drama. But, my expectation when utility is available is not the same, and perhaps this is where I am off with my expectation. If I have a fully functional grid, my expectation is that when the inverter is asked for more than its rated power (5kw / 100A at 48v), it should ask from utility, not try to pull the additional load from the battery, and that switch should be handled gracefully.

On 2022/08/28 at 4:14 AM, Coulomb said:

I was under the impression that you were getting spikes of battery current that exceed 100A, e.g. starting a motor. These are very brief in duration (less than a second), and logging software typically doesn't capture it (often sampling the current many seconds apart). But the BMS might well consider these to be an overload, reporting them as a short circuit.

I have noticed spikes of battery current occasionally when switching to or from bypass mode. I don't know why that happens. If your problem is premature switching to bypass mode, fully patched firmware such as 74.40e featuring KettleKomp™ could well help (if set up properly, follow the instructions). 

Thanks

Ill give a firmware update a bash, and monitor for a bit. I was hopeful this was a more common problem with a simpler solution like an inverter setting, but it appears a new battery will be in my near future.

3 hours ago, jetlee said:

If I have a fully functional grid, my expectation is that when the inverter is asked for more than its rated power (5kw / 100A at 48v), it should ask from utility, not try to pull the additional load from the battery, and that switch should be handled gracefully.

It depends on the exact model and the output source priority. To do what you expect, I think you'd have to be using SUB output source priority, where AC-in is connected to AC-out so if there is a sudden big demand, it will come instantly from AC-in rather than the battery. Some inverter models don't have an SUB output source priority option.

If you're in battery mode, the inverter possibly can't switch fast enough to bypass or other modes to prevent the battery current from being excessive for very short periods of time. I'm guessing that it is a very short term overload that you don't even see in your logs that is upsetting the battery.

3 hours ago, jetlee said:

I just want to comment here. I am not off-grid,

On 2022/08/26 at 8:55 AM, jetlee said:

have yet to update my firmware (current - 74.31) and I know there is an updated version (if I recall 74.40 with the lithium slant),

Isn't that a contradiction? In my understanding the 74.xx firmware are on off grid inverters. I got 74.40. These inverters in SbU mode switch to utility bypass only if max power is exceeded for a couple of seconds or if battery voltage goes below the setting 12. They never mix inverter output with utility input.

4 hours ago, jetlee said:

Thanks for this.

If I have a fully functional grid, my expectation is that when the inverter is asked for more than its rated power (5kw / 100A at 48v), it should ask from utility, not try to pull the additional load from the battery, and that switch should be handled gracefully.

May be I have it wrong but the inverter can only provide 5kW output even if you have grid. If you want loads to draw more than 5kW those loads should get it from utility. The Sunsynk / Deye and others do have a much higher bypass. Just refer to the AC input cable size. 4sq mm for Kodak 5.6OGS which does have SUB. The output at 2x is only for 5sec and 110-150% rating for 10 sec. So even on the blending type you must stay within the rating of the inverter otherwise the thermal trip unit will switch it off.

Thus you cannot expect the inverter to supply 5kW and ask it to provide 5kW on the bypass side directly from the grid.

If I have it wrong please correct my understanding.

2 hours ago, Scorp007 said:

May be I have it wrong but the inverter can only provide 5kW output even if you have grid. If you want loads to draw more than 5kW those loads should get it from utility. The Sunsynk / Deye and others do have a much higher bypass. Just refer to the AC input cable size. 4sq mm for Kodak 5.6OGS which does have SUB. The output at 2x is only for 5sec and 110-150% rating for 10 sec. So even on the blending type you must stay within the rating of the inverter otherwise the thermal trip unit will switch it off.

Thus you cannot expect the inverter to supply 5kW and ask it to provide 5kW on the bypass side directly from the grid.

If I have it wrong please correct my understanding.

The inverter will surge to utility, in short tests, I have seen it go to 8kw.. I haven't tried much higher than that, and do not intend to. It moans a bit by beeping, but it will do it. I feel like we are debating semantics though. My inverter very seldom even gets to 3.5kw, and if it does, its there for a few seconds and then back to a regular load of around 500w. My statement is really just, that while the inverter is under 5kw (its rated load), it SHOULD be able to handle switching between solar / utility / batt without asking the battery for more than 100A, which it appears is not 100% the case.

16 minutes ago, jetlee said:

My statement is really just, that while the inverter is under 5kw (its rated load), it SHOULD be able to handle switching between solar / utility / batt without asking the battery for more than 100A, which it appears is not 100% the case.

Since you mentioned main firmware version 74.xx, that tells me that you have an Axpert MKS model (like mine, but mine are much older). These models don't attempt to blend AC-in and solar/battery. When overloaded, they merely pull more current from the battery for a short time, then switch over to bypass mode if the overload persists. In bypass mode, AC-in takes over the entire load, not just the excess. For the duration of the overload (when the load is higher than the inverter's continuous rating), the battery will be supplying well over 100 A.

On 2022/08/27 at 4:41 PM, jetlee said:

No need to answer if thats been understood, I just got the feeling from the replies that there was an assumption that I was getting over the 100A limit on occasion

You may well have spikes over 100A, that the logging side isn't picking up, but the BMS is, there's no reason for the battery to behave as it does, otherwise, that I can think of, but presumably the short term current surge is so short in duration that it isn't picked up otherwise...

12 hours ago, Coulomb said:

It depends on the exact model and the output source priority. To do what you expect, I think you'd have to be using SUB output source priority, where AC-in is connected to AC-out so if there is a sudden big demand, it will come instantly from AC-in rather than the battery. Some inverter models don't have an SUB output source priority option.

If you're in battery mode, the inverter possibly can't switch fast enough to bypass or other modes to prevent the battery current from being excessive for very short periods of time. I'm guessing that it is a very short term overload that you don't even see in your logs that is upsetting the battery.

 

8 hours ago, jetlee said:

The inverter will surge to utility, in short tests, I have seen it go to 8kw.. I haven't tried much higher than that, and do not intend to. It moans a bit by beeping, but it will do it. I feel like we are debating semantics though. My inverter very seldom even gets to 3.5kw, and if it does, its there for a few seconds and then back to a regular load of around 500w. My statement is really just, that while the inverter is under 5kw (its rated load), it SHOULD be able to handle switching between solar / utility / batt without asking the battery for more than 100A, which it appears is not 100% the case.

As indicated not knowing the model or at least the rating details on the right hand side we are all just trying to assist in the dark. If the output source priority is SBU then it will draw from the battery even when you have grid as grid is only used after the battery has been discharged to the level set in setting 12. The battery can still supply 100A before reaching this level. SBU doesn't know you don't want to use battery.

Edited August 29, 20223 yr by Scorp007

Jetlee

 

A year or so late. I solved the priblem by bringing setting 12 down to 46/47 volt