Charging with Sol-Ark 15k question

[SunDave]

Hi all,
Anyone have experience with similar equipment that can chime in and let me know if this is normal?

I have a sol-ark 15k and 30kWh of Pytes 48100r batteries. Previously I was running my battery down to about 40%, then getting whatever sun I get, but since I have bumped up the low-end of the battery % before going to grid to get a fuller charge. I have a starter 2kW array in until I get the full 19kW array installed soon.

When I charged say from 40-55% during a day, the charge went up by about 1% every 15 mins of good sun. Basically it went up in steps, like you would imagine it would. Now when charging today from 83% and going up from there, it seems to sit around 90% for a long time. Today, in good sun with a steady 1kW+ going to the battery for over 5 hours, it barely budged the % charged. Started off going up, then sat at 90% for 4 hours.

Normal or no? Is there some kind of change in charging procedures at around 90%? If it charged that long and the battery voltage didn't change much for hours, and the battery keeps taking the full 1kW where is the power going? Just a sensor or algorithm in the Sol-Ark that is still learning the battery bank?

I have full coms on CanBus with the Pytes batteries and their BMS says the same thing. Wattage going in, but SOC and voltage not changing much over many hours.

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So to anyone with a similar setup. Ideas? Normal? Not enough wattage to get past a certain point in the charge cycle (absorb?). I don't want to change settings or call support unless it is an issue. I can give it a couple days too to see if it is a consistent thing.

Thanks!

 

[Spunky]

I'm not sure what instructions are being sent to the inverter from the BMS, but it's not unusual for it to taper the amperage. This would be when changing from absorption to float.

A graph like this might help to see.

 

[BentleyJ]

As the battery charges its internal voltage increases thus creating "back pressure" and reducing current flow at a given Constant Voltage setting.
If you wish to analyze an apparent problem you need to keep track of current and voltage over a period of time to determine how many kWhrs actually went in. This is common complaint regarding BMS SoC readings, they are often not very accurate if using voltage as an estimate of SoC rather than coulomb counting.

 

[SunDave]

Thank you both. I have some charts here. Doesn't seem anything cut back on amperage. It was basically PV minus the load that went to the battery. SOC just didn't move much this afternoon. I have my Sol-Ark set to percentage SOC, and not voltage.

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As you can see, it showed decent charge in the AM with even less amperage going to the batteries, then in the full sun, it slowed way down.

 

[SunDave]

Now that I look at a charge I did a few days ago using the grid, up to 100%, it sat at 90% for 1/2 hour even with 6kW going to the batteries. So it must be a BMS thing? Possibly normal? I hope so!

Still very new to this. Setup less than a few weeks old.

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One other thought edited in here. According to just the stats I have, I put 7.5kWh into charging the battery today, and it went from 83% to 90%. So one way or another the stats are a bit skewed. Not accounting for loss, in a perfect world 7.5kWh would add over 24% to my 30.74kWh battery.

When I charge from say 60-80% this behavior doesn't show up that I have seen.

 

[RCinFLA]

It can do this if BMS Columb counter is off. First find out what full charge level is required for your Columb counter reset.

Many BMS's require the stupid condition of a cell overvoltage charge shutdown to reset Columb counter to 'full' fresh reference point.

Some BMS's allow you to set the battery voltage and/or charge current taper off level to reset Columb counter to 'full' reference.

It is normal for Columb counter to accumulate errors over time due to current measurement inaccuracy. This is why they need to periodically be given a full charge 'full' reference reset to wash out accumulated errors.

 

[SunDave]

Thank you RC. I'll just try a full grid charge this evening, and let it sit there for several hours to see if that straightens out the counter.

 

[Spunky]

I have 19.36Kw of panels (they don't all get direct sun at the same time). I have Pace BMSes, so what my Sol-Ark 15k does in closed loop (BMS directing the inverter's charge parameters) and yours does will probably be different. Yours seems to be pushing a fixed voltage?

Here's a pic of mine on a sunny day.

 

[SunDave]

Thanks Spunky. Seeing your charge curve, I think it may just be slow on that part of the charge due to the 2kW array.

I did charge it back to 100% just now, and it only took about an hour to get there from the 86% I started from. I have the charge set to only use up to 8000 watts. It started there, but went almost linearly to 60 watts meaning that it took just over 4000 watts to get that 14% which works out math wise. Why the solar can't do the same thing, only slower is yet to be seen. I'll try a charge near the top end again during the next sunny day. The BMS may just not have enough amperage to work with for that much battery until I get a bigger array.

Just a guess at this point. The good news is that the batteries seem fine. We will see if this full charge, and holding it there for many hours will reset the BMS counter (RC's idea).

Thanks for all the insight.

 

[SunDave]

I did a charge from grid this evening, since I wanted to get the batteries topped off again once. It took 25kWh to charge the 6 pytes batteries (30.72kWh total) from 50% to 100%. It could have been that the SOC was WAY off from 2 weeks of not being charged to 100%, or who knows what.

For those familiar with Powerview, do you ever get this stuck at 90% for a long time when charging behavior? Some kind of absorb mode on Pytes? I started charging at 4kW but bumped it up after it seemed "stuck" on 90% forever. Seems the voltage doesn't really take off unless it is fed good amperage. Thanks all.

A

 

[Rodney L]

Looking over my data it appears the pytes take the fixed voltage and Max current until 90% SOC then limits the current. Mine went from 90+ amps to 10 when the SOC hit 90%

 

[Lt.Dan]

Looking over my data it appears the pytes take the fixed voltage and Max current until 90% SOC then limits the current. Mine went from 90+ amps to 10 when the SOC hit 90%

It's probably seeing a cell imbalance, and telling the inverter to slow down so the balancer can keep up before a cell hits HVD. Very common in some BMS's.

 

[SunDave]

I'm not seeing any amperage drop on mine when at 90%. It just stays there a long time and soaks up amps. See the graph shows 4kW going to battery from about 13:00 to 17:20, then I even bumped up up charge wattage to about 8kW. It still charged for another 30-40 minutes at "90%" before it went up from there.

Could be that I am only getting a full charge every couple weeks, could be something else. Not sure right now. If I knew that it wasn't even a real problem, just wacky SOC and the system will still stay on the rails and work fine, that ok. But if there is a way to dial it in better by changing a charge efficiency setting or something like that, I would be happier.

Thanks for the info.

 

[SunDave]

Looking over my data it appears the pytes take the fixed voltage and Max current until 90% SOC then limits the current. Mine went from 90+ amps to 10 when the SOC hit 90%

Similar here, but it took a long time to pass 90%, then it started to throttle down amps at 94-95%.

 

[SunDave]

Steady state at about 53.7v full charge. Sound about right on the Pytes 48100r?

Weird that the BMS temp reports as 20.9F. It is over 50F in the garage at all times. Battery temp stays accurate, but "BMS" temp reports low. Is your BMS temp reporting correctly Rodney?

 

[Rodney L]

Yes, I built a 8x8 shed I insulated well. To verify the BMS was reporting temp. Accurately I bought a unni device for the house with the sensor in the shed. Top reading is Solar shed. My probe is on the floor next to the batteries.

Oops I read your post wrong...sorry.
No, mine is way off too. Lt Dan is most likely right. They got their Celsius and F confused.

 

[Lt.Dan]

Weird that the BMS temp reports as 20.9F. It is over 50F in the garage at all times

More than likely this is 20*C, not F. My batteries are almost always in the 18-22*C when the garage is in the 50's*F

 

[SunDave]

Yes, I built a 8x8 shed I insulated well. To verify the BMS was reporting temp. Accurately I bought a unni device for the house with the sensor in the shed. Top reading is Solar shed. My probe is on the floor next to the batteries.

Oops I read your post wrong...sorry.
No, mine is way off too. I read in the Sol-Ark manual the 15k doesn't have a DC temp. Sensor so that most likely why the App reports what it does?

Thanks Rodney,
That's likely not a problem then. I saw the same thing, that the DC temp doesn't work, but the BMS temp seems to come from the battery. But yes, if that was in C, it would be very similar to the F. reading of the battery at the moment.

These little quirks make it harder to know exactly what is going on.

Looks like your battery voltage will be pretty close to 53.7 at100% as well. Good to see a similar setup. We should keep each other in the loop on performance over time.

 

[Rodney L]

Sure thing!

 

[Rodney L]

Thanks Rodney,
That's likely not a problem then. I saw the same thing, that the DC temp doesn't work, but the BMS temp seems to come from the battery. But yes, if that was in C, it would be very similar to the F. reading of the battery at the moment.

These little quirks make it harder to know exactly what is going on.

Looks like your battery voltage will be pretty close to 53.7 at100% as well. Good to see a similar setup. We should keep each other in the loop on performance over time.

The fog burnt off and we are getting a bit of ? Here's a few screen shots of what my system is doing today