Charging parameters never met

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Charging parameters never met

Postby JohnGourlay on Sun Apr 08, 2018 12:05 pm

I have a relatively new system, grid-tied with battery backup, that I'm still trying to understand fully. The system overall seems to be working well, but the FLEXnet DC has not reported that the charging parameters have been met for over a month. The last time the parameters were met was shortly after an eight-hour interruption in grid power. The FLEXnet DC does consistently report states of charge of 98%--100% and the battery voltage overnight when charging is not going on shows a good-sounding 52 V or so, so I'm pretty sure the batteries are well-charged. The charging settings throughout the system are correct to the best of my knowledge. Is this behavior to be expected? If not, what information would you like me to provide to help understand what's going on?

I have a SystemEdge SE-420GH with a 4.48 kW PV array and an additional Flexmax 60 charge controller. The battery bank contains 8 200GH batteries.
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Re: Charging parameters never met

Postby Mike Curran on Mon Apr 09, 2018 9:24 am

Hey John - Take a look at this app note on the FNDC: http://outbackpower.com/downloads/docum ... p_note.pdf
In particular, the section on charge parameters. Also note, it says set the charged voltage (page 3) 0.4 volts lower than absorb voltage (48V system) to insure your system reaches it.

I have a 24 volt system but fyi, here are the battery charging setpoints on my FNDC:
Screenshot_20180409-122019.jpg

HTH - Mike
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Re: Charging parameters never met

Postby JohnGourlay on Tue Apr 10, 2018 8:16 am

Thanks, Mike. I used the app note along with the FNDC user manual and the spec. sheet for the batteries to come up with my settings. Here are the numbers I'm using in the FNDC:

Battery Ah: 380
Charged Voltage: 57.2
Charged Time: 3 minutes
Charge Factor: 94 percent
Charged Return Amps: 7.6

For the GS4048A inverter:

EQ Voltage: 60
Absorb Voltage: 57.6
Rebulk Voltage: 48
Float Voltage: 54.4
Re-float Voltage: 50
EQ Time: 3 hours
Absorb Time: 2 hours
Float Time: 2 hours

For the FM60 and FM80 charge controllers the settings are the same as the inverter except:

Absorb Voltage: 58
JohnGourlay
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Re: Charging parameters never met

Postby Kurt Lundquist on Tue Apr 10, 2018 8:56 am

Hi John,

I suggest you bump Absorb Time up to 4 hours. The Absorb Time is the maximum time for the Absorb cycle, it is not a minimum. If you are in Grid-Tied mode and your grid is stable I wouldn't expect the system to spend very much time in Absorb each day.

It is hard to keep the FN-DC calibrated to the battery SoC in a Grid-Tied system because the batteries are not really changing in SoC but the FN-DC is seeing a lot of current flow on the DC bus. I wouldn't stress about the FN-DC SoC too much in your application.

Thanks,

-Kurt
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Re: Charging parameters never met

Postby JohnGourlay on Tue Apr 10, 2018 7:36 pm

Thanks, Kurt. I'll change the float time to 4 hours, but should I expect this to affect when the FNDC decides that the charging parameters have been met? This is what I'm really asking about. Looking through the OpticsRE event log I see that the system rarely goes into float charging state. It happened just twice during April so far, once for about 5 hours and then later for about 2.5 hours. Mostly it spends its time bulk charging (no charging at night), going into absorb charging occasionally but only for a minute at a time.
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Re: Charging parameters never met

Postby Mike Curran on Wed Apr 11, 2018 4:59 am

Hey John - Mine never goes into float either. With a grid-tied system, you want it to sell whenever you have excess PV. The grid-tie mode setting on your charge controller insures this by raising the float voltage setting to absorb, otherwise if you're in float, you won't be selling. For this to work it's important to set your sell voltage about 0.4 volts (48 volt system, I use 0.2 volts for my 24 volt system) lower than your float voltage, if your CC sees float before it reaches sell, it'll never sell.

In case I'm not explaining this well, here's an excerpt from the Mate3 manual:
Screenshot_20180411-074130.jpg
I think you only see absorb briefly due to your 3 minute charged time setting on your FNDC. That's okay, since you don't normally deep discharge your batteries, they don't need a "normal" absorb time. If you have a grid outage and discharge your batteries below rebulk, you'll see a prolonged (3-4 hour, depending on your setting) absorb time with your batteries at the absorb voltage setting - sell will be disabled until this absorb cycle completes.

At least, that's my understanding O:) - Mike
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Re: Charging parameters never met

Postby Kurt Lundquist on Wed Apr 11, 2018 8:13 am

JohnGourlay wrote:...but should I expect this to affect when the FNDC decides that the charging parameters have been met?


Since you are Grid-Tied the answer is yes and no. When battery charging with grid power after a grid outage the extra Absorb time will help you meet charging parameters. When in normal Grid-Tied operation the extra Absorb time will not help because your battery bank should not drop low enough to cause the inverter to go through a bulk charge cycle. You would need to enable "Auto Grid-Tie Control" in the Mate3 FN-DC Advanced Control menu to ensure the battery bank meets charge parameters before the system sells. This feature turns selling off at night and only re-enables selling after charge parameters are met.

For you GH style batteries I would say the Grid-Tie Control feature is not necessary. If this were my system and the grid only has a few outages per year I would set my Sell voltage to 54.4 so the system keeps the battery at Float during the day while selling. I would set my Charge controller Float target to something like 56V and make sure Grid-Tied mode was enabled.

Thanks,

-Kurt
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Re: Charging parameters never met

Postby JohnGourlay on Thu Apr 12, 2018 7:00 am

Kurt and Mike,

Below are a few more settings in my system. Mike, Is the Sell Voltage too low? It's more than .4 V below the inverter's Float Foltage. Kurt, do you know where I can learn more about the Auto Grid-Tie Control feature. That one has been a mystery to me. It's disabled because the setup wizard set it that way.

GS4048A
AC Input
Sell Voltage: 53.6
Grid-Tie: ON
Battery Charging
Float Voltage: 54.4

Mate 3S
Global Charge
Auto Grid-Tie Control: Disabled
JohnGourlay
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Re: Charging parameters never met

Postby Kurt Lundquist on Thu Apr 12, 2018 7:29 am

Hi John,

Page 39 of the Mate3s programming guide has the following information about Auto Grid-Tie Control:

FNDC_Auto_Grid_Control.JPG
FNDC Auto Grid-Tie Control


Remember that you have a battery style that loves to sit at float. This is why I suggest you set Sell to the battery float voltage. I'm assuming that your inverter can sell more power than your PV can produce so the battery bank will sit at float voltage all day. For this to work you have to set the charge controller float target higher than the manufacturer recommended battery float voltage. The charge controller will fight to grab every last electron from the PV array to push the batteries to the charge target while the inverter happily diverts any charge current that would bring the battery bank past the sell voltage.

Thanks,

-Kurt
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Re: Charging parameters never met

Postby JohnGourlay on Sat Apr 14, 2018 6:01 pm

I had another grid power failure and at about the same time the FNDC finally decided after more than a month that its charge parameters had been met. This is the second time I've seen the charge parameters being met in correlation with a power failure. What's the connection? It was a brief power failure, not one that significantly lowered the battery voltage. The failure occurred during a bright sunny day.
JohnGourlay
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Re: Charging parameters never met

Postby raysun on Sat Apr 14, 2018 9:19 pm

Not sure if it works differently, but on my off-grid system when the battery becomes fully charged, FNDC will read 100% but not indicate Charged Parameters Met until the system draws current from the battery for a period of time - 3 minutes in my case. On a sunny day, my battery may sit at 100% SOC for hours until very late in the afternoon at which point current is drawn from the battery and FNDC indicates at that time that the charge parameters have been met.

Is it possible that until there's a grid failure there isn't charge drawn off the battery so FNDC never sees the Charge Time satisfied?

The Charge Time can be set via the Mate and defaults to 1 minute. I believe the Charge Time may be set to 0 and the FNDC won't use the metric.
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Re: Charging parameters never met

Postby Mike Curran on Sun Apr 15, 2018 8:06 am

JohnGourlay wrote:I had another grid power failure and at about the same time the FNDC finally decided after more than a month that its charge parameters had been met. This is the second time I've seen the charge parameters being met in correlation with a power failure. What's the connection? It was a brief power failure, not one that significantly lowered the battery voltage. The failure occurred during a bright sunny day.

The connection is that each time there's a grid outage, your inverters go through an absorb cycle. However, on a daily basis with no grid outages, your system will not go through an absorb cycle unless you have auto grid tie control enabled. Why not? Because your sell voltage setting prevents battery voltage from reaching the absorb voltage setpoint.

Kurt suggested you don't need to enable auto grid tie control because the nature of your system and specifically, your batteries don't need a daily absorb cycle. However, I believe that if you enable auto grid tie control, you'll see charge parameters met on a daily basis. Not to sound snarky or anything, but my system (with FLA batteries, different from yours, but with auto grid tie control enabled) does achieve charge parameters met daily, unless it's cloudy all day. - Mike
Screenshot_20180415-105138.jpg
PS - This all assumes you don't have auto grid tie control enabled. If you do and you're still not achieving parameters met on sunny days, then there's some other problem.
Mike Curran
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Posts: 607
Joined: Sat Aug 28, 2004 6:28 pm
Location: Chagrin Falls, Ohio
My RE system: Outback:
- 8 (2x4) Evergreen 180's into one MX60
- 6 (2×3) ALEO S79-300's into one FM80
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
- 12 Surrette/Rolls 2V x 1766Ah
- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar:
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied.

Re: Charging parameters never met

Postby JohnGourlay on Sun Apr 15, 2018 9:05 am

Thanks for clarifying, Mike. I don't have auto grid tie enabled, and I didn't understand until now that you do. I'll give it a try. I did make the other changes (float time and sell voltage) that you and Kurt suggested and they don't seem to make the FDNC see its charging parameters met.
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My RE system: SystemEdge SE-420GH grid tied/battery backup system with an additional FM-60 charge controller and a 4.48 kW array.

Re: Charging parameters never met

Postby JohnGourlay on Tue Apr 17, 2018 7:00 pm

Kurt, I'm beginning to see the wisdom of your suggestion not to use auto grid tie. In Michigan we've been having some really dark, snowy days lately, and after two days with auto grid tie enabled I see that I'm not selling nearly as much power as I had been when auto grid tie was disabled. The first day it took two hours of daylight (we haven't seen the sun in a long time) before the charge parameters were met, and no selling occurred until then. The second day the charge parameters were not met at all. The absorb time ran out and the charge controllers dropped the battery voltage to the float voltage, but selling didn't start. I'm not sure I why.

If I disable auto grid tie and keep the batteries around the float voltage during the day as you suggest, I guess I can trust that the batteries will remain fully charged while the grid is up. When the grid goes down, however, the charge controllers will try to float the batteries at a voltage that's a little bit too high. Will this harm the batteries? Alternatively, I could keep the batteries at a voltage slightly lower than float while the grid is up, and use the manufacturer's recommended float voltage in the charge controllers. I'm thinking this could also harm the batteries by leaving them slightly under charged while the grid is up. To solve this problem is there a way manually to initiate an absorb cycle once in a while to top the batteries off?
JohnGourlay
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My RE system: SystemEdge SE-420GH grid tied/battery backup system with an additional FM-60 charge controller and a 4.48 kW array.

Re: Charging parameters never met

Postby Kurt Lundquist on Wed Apr 18, 2018 8:58 am

Hi John,

JohnGourlay wrote:When the grid goes down, however, the charge controllers will try to float the batteries at a voltage that's a little bit too high. Will this harm the batteries


The elevated float voltage is still less than the absorb voltage so it should not damage the battery if it happens on occasion. The grid would have to drop while the PV array is producing more power than your critical loads. That scenario is way too convenient so in reality it probably never happen.

JohnGourlay wrote:To solve this problem is there a way manually to initiate an absorb cycle once in a while to top the batteries off?


On the Mate3 press the Charger button then press Bulk Charge then Start Bulk. Your system will probably not spend very much time in absorb. I think the battery bank voltage has to drop below the re-bulk voltage for the absorb charge timer to add time to the absorb cycle.

Thanks,

-Kurt
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Re: Charging parameters never met

Postby JohnGourlay on Wed Apr 18, 2018 11:53 am

I think I've got it. Thanks for your help, all of you.
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