Conext MPPT80 exiting absorb early?

Rossman · February 2016

G'day all,

I have two MPPT80 charge controllers charging my battery bank, but I notice that they will sometimes exit absorb early. I have absorb set to 240 minutes right now and noticed that today they got to absorb, charged for an hour, and exited absorb. It's a solid sunny day so there is plenty of power incoming. The battery SG's were all checked a week or so ago after a full charge and were all around 1.265.

Any thoughts? I don't see any setting in the MPPT80 to exit absorb based on current or anything like that, just the absorb timer.

Thanks,
mark

Vic · February 2016

Hi Rossman,

The old, original manual for these MPPT80-600s that I have state that,

The unit transitions to the float stage if either of two conditions are met: • The charge current allowed by the batteries falls below the exit current threshold, which is equal to 2% of the programmed battery capacity (for a 500 amp-hour battery bank, this would be 10 amps), for one minute. • The unit has been in absorption for the programmed maximum absorption time limit. The default is three hours, but the time limit is programmable from one minute to eight hours.

So, it looks like the End (Exit) Amps function may be always on. If this is so, then you might need to massage the AH Capacity entry in the setup for these CCs. These CCs are hardwired to use 2% of the battery Capacity that you have entered ... You might be able to make the CC use your time setting, only, by setting the C to zero ... dunno.There really should be a way of disabling this EA function, although I have always used EA, and it works well for trhe FLA batteries here.That is just one drive-by thought. Good Luck, Vic

Rossman · February 2016

Thanks Vic, it's weird, my bank is 1445Ah and they seem to exit absorb still pushing 40A's, give or take. It it was the exit amps triggering it should continue on to 29A or so? Maybe I will reboot one of them and see if it makes a difference.

When I run my gennie with the XW charging it will push all the way through the absorb time to completion (with a final EA close to 2%).

Vic · February 2016

Hi again Rossman,

Another question, is, since you have two of these XW MPPTs, presumably each with its own PV array, charging the same battery ...

I assume that you have both of these CCs Networked, in some fashion, and wired as recommended by Schneider/Xantres, such that both of these CCs will share the charge stages(?).

Furthermore, I assume that there must be a Shunt in the negative battery lead that allows the brains of the system to know just what IS the battery charge current, and correctly use the EA INTO the batteries, and so on(?).

Perhaps verifying all of the charge parameters/settings in the CCs, and whatever is the brains might be in order.

Have there been any changes in the system -- additions, deletions, FW Updates etc -- recently that might explain this?

Just guessing ... more later, Thanks, Vic

Dave Angelini · February 2016

The XW system knows the amps into the battery without a shunt BTW, it always has. One of the first to do this.
The screen on SCP shows
battery, amps, and voltage. The same on the combox. Charging I x V = W + load W equals power in + loss.

Good advice on setting the capacity to much smaller than actual to set the end amps lower.

The other common problem that plagues many CC's this time of year is that the system on solar can be fooled by clouds,
absorb set-point starts the timer. This is a winter problem with clouds and just forcing a bulk may show you that your 3 hour? absorb got fooled by clouds/loads. This tends not to happen to large solar systems or south of 40 degrees latitude.

Use your hydrometer goes without saying. Good Luck!

zoneblue · February 2016

So youre saying that Scheider "understands" battery current by taking the CC output and subtracting the inverter load?

Interesting. Assuming they measure inverter load accurately, this will break down the minute you add any kind of DC load. Or other (non networked) charging source. Or... the mind boggles.

And you also saying that Schneider has EA permanently on set to 2%, you cant alter the percent, or disable it. And that its based on this creative battery amps value?

If so 10 points for effort, but really....

Dave Angelini · February 2016

Yes the XW system always has understood battery current. It needs an XW or new SW inverter/ charger, an XW Mppt or generator and a SCP or COMBOX.

The reason the OP is doing fine with the Genny is he is not letting his absorb voltage fall as with the solar. He has clouds and loads.
He can look at the battery screen on the combox and will see the picture/log of his solar absorb voltage dropping due to clouds or loads.

The XW system can alter the 2% end amp setting by entering in a smaller battery capacity as stated before. This has been in the manual since 2006.

The only problem is that without the shunt the XW system does not log power after sundown/generator shutdown. There are workarounds to this though without needing a shunt. I do not use shunts with an XW system.

Blackcherry04 · February 2016

The EA is 2% of the set amp hr capacity of the battery bank. By raising or lowering the capacity you can change the EA. All the old Traces and Xanterx's were the same. Thats the only thing that uses the capacity setting.

I'd take a guess and say there is a hall sensor somewhere on the boards.

Vic · February 2016

Blackcherry04 said:

The EA is 2% of the set amp hr capacity of the battery bank. By raising or lowering the capacity you can change the EA. All the old Traces and Xanterx's were the same. Thats the only thing that uses the capacity setting.

I'd take a guess and say there is a hall sensor somewhere on the boards.

YES, Bco4, believe that each CC has a shunt, perhaps in the negative lead of the PV IN, this saves some money.

There is NOT a separate Shunt in the negative lead of the battery on these systems, unless it is used by some other accessory, like a real Battery Monitoring device.

Just more guesses. Vic

Dave Angelini · February 2016

Yep that is a guess Vic. The system needs the Inverter/charger to accurately measure AC loads and communicate thru Xanbus. Otherwise the DC out of the CC would not be accurate in end amps.
They do sell the battery monitor with the shunt but it really is just more stuff and not needed. It can be useful for AGM batteries and their protection.

The Traces and old SW's did not do this and that is why they were often fooled in end-amps. No communication bus on any of them for inverter loads.

Rossman · February 2016

Pretty sure not due to clouds, we entered absorb before noon and it was perfectly clear and sunny all day. We were drawing ~1000-1200W and pulling in around (or over) our full rated capacity ~6500W+. For context the gennie is an EU7000 and I have it set to deliver max 5000W (less than we can get from the array).

Just to recap my system, in Ontario Canada (near Ottawa):
XW6048
2x MPPT80 (13 250W panels on each, in series...6500W total)
SCP
Conext Battery Monitor with DC shuntu
Combox
AGS (not yet wired in)
48V - 24x 2V surrette 4500's (1445Ah)

Everything is networked up internal communications and I've not observed any other issues, except we had a combox failure in december and had to replace it under warranty (january). Feel like I have reviewed all settings several times (that combox makes it pretty easy), but have attached them in case it helps.

Thanks again for the comments!

Image: https://us.v-cdn.net/6024911/uploads/editor/gi/rooh18zc4um5.png

Dave Angelini · February 2016

Look at your battery bank daily summary plot on COMBOX for the day you are questioning.
Does the absorb voltage stay steady at 59.8 for 4 hours or is it being pulled down by loads/clouds?

I know you said there were not clouds but the point is something is causing you to not duplicate the gen run for full charge!
At about 29 amps into the battery it will go to float.

Rossman · February 2016

The absorb voltage stays steady during the absorb, but it just appears to run for an 60 not 240 minutes. I will watch it some more and see what happens, cloudy today so will wait for next full sun day and see. Thanks!!

YehoshuaAgapao · February 2016

I lower absorb exit current by lying to the system and telling it the battery bank is only 300ah instead of 800ah. It then exits absorption at 6A instead of 16A. DUring the summer the batteries do indeed absorb down to 6A. Its very hot in AZ.

Dave Angelini · February 2016

Image: https://us.v-cdn.net/6024911/uploads/editor/0c/d6yi7v9umv8y.png

Dave Angelini · February 2016

An example above of the absorb voltage being pulled down slightly. Running 2 Mini-Splits Heatpumps on full heating.

Rossman · February 2016

Thanks Dave. We had clouds today and another two days of crappy weather predicted

In my case i still had like 4000W give or take pushing into the batteries. Anyway I will try and get a good example of it from my graphs next sunny day!

Vic · February 2016

Dave Angelini said:

The XW system knows the amps into the battery without a shunt BTW, it always has. One of the first to do this.
The screen on SCP shows
battery, amps, and voltage. The same on the combox. Charging I x V = W + load W equals power in + loss.

Good advice on setting the capacity to much smaller than actual to set the end amps lower.

The other common problem that plagues many CC's this time of year is that the system on solar can be fooled by clouds,
absorb set-point starts the timer. This is a winter problem with clouds and just forcing a bulk may show you that your 3 hour? absorb got fooled by clouds/loads. This tends not to happen to large solar systems or south of 40 degrees latitude.

Use your hydrometer goes without saying. Good Luck!

Dave,

Do not understand the logic in the above;

YES, the Absorb timer should start when the CC enters Absorb. IF there is insufficient PV power available, or too many loads on the system to maintain the Absorb voltage, the CC should revert to Bulk, and the Absorb timer should STOP, or in the case of some CCs, even begin counting up the remaining Absorb time, rather than counting it down.

There should be none of cloudy/loadie confusion in a CC that is well designed.

Certainly hope that the XW CCs do not confuse themselves when clouds come by, or when there are loads on the system that mean that the CCs cannot maintain Absorb voltage ... this would be truly demented behavior.

IMO. FWIW, Vic

Dave Angelini · February 2016

I am not really sure what his system did and he said he would come back.
I have never had any problems like this but weird things can happen and running solar way up north is always a challenge.
The screen I told him to watch shows an excellent graph of absorb and all battery data over a 24 hour day.
There is also more data, graphs, logs than a human needs to see from COMBOX.

He did say that he only saw an hour of absorb, to me that is an indication that the 2% amps ended absorb because his battery was charged. Maybe he ran the generator the night before and did not use much energy overnight?

If the XW devices do not show float time for the day, you are warned by reading the display, or it can e-mail, text, cell/land phone, and probably be available on your web page. That does not sound demented to me.

Rossman · February 2016

Had a lovely sunny day today and from watching my CC's/combox I can only guess that it is, indeed, the End Amps terminating the absorb. I've attached a graph from today - entered absorb approx 11:00am and then exit absorb/into float about 1:10pm. The XW system is great, certainly the only thing demented is perhaps myself

I find it interesting that the XW itself seems to push down to a lower End Amps and usually will get all the way through an absorb without exiting.

Image: https://us.v-cdn.net/6024911/uploads/editor/jp/2afmy308p56y.png

Dave Angelini · February 2016

That looks good ! It could be in your system settings that the "cascading" is not enabled. Cascading allows all devices to share all the data which may be why you are getting a longer absorb with the generator. You just will have to watch it.

The point here for others is that using your hydrometer is how you calibrate this and with the XW/SW you may have to enter a smaller number in the battery capacity to really get to a full SG.

Your display does not show bat temp or am I reading it wrong. Your Battery SOC on the graph, is it connected? Why is it not going to float voltage in the display at 1:30 or is this a gen run? Dementia is never great but it is survivable.....

Rossman · February 2016

I turned off the battery temps as that data seemed irrelevant

I have battery sensors on all applicable units (XW, CC's, battery monitor).

I think my battery SoC needs to be re-synced, this wasn't a gen run (though a ran the generator for an hour or so in the morning just to push things up quicker). I'll double check the settings again for the cascading stuff

Thanks!

Dave Angelini · February 2016

I have seen people accidentally select (no float) on the solar CC menu. The graph looks like that to me. Definitely always want float offgrid.

Rossman · February 2016

They are all set for three stage charging, the reason the graph doesn't look like it went into float is because it only went into float for a little bit then my wife pulled a bunch of power doing chores and it went back to bulk again. The small rise in current and voltage just before 4pm is it back in bulk trying to charge again, but we ran out of sun (short days this time of year)

Conext MPPT80 exiting absorb early?

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