Been playing around with the "Days Between Bulk" setting - aka Skip Days.
Here's my trouble ... if it is a problem I'll let you decide. I am using a Conext SW 4024 Inverter in AC Support mode. This mode allows for you to be grid connected but only use grid power when the battery falls below a user set threshold. (I assume not unlike Outback's GridZero idea).
The Issue with AC Support Mode is Two Fold:
1. AC Support Mode really only works well if your loads are perfectly balanced between L1 and L2, like a pump or water heater element on 240v. In normal operation of a Split-Phase system this is tough to do with 120v loads that vary constantly.
2. AC Support Mode requires that it use 2% from the grid at all times. This (according to Schneider) is to keep from back feeding the grid with power. How you define 2% is subjective, but what it works out to is about 200-250 watts that must be being pulled from the grid at all times.
But there is a relationship between point 1 and 2. If the loads are not balance, say you are using 400 watts on L1 and 50 watts on L2 you will not enter AC Support mode. You will pull all the loads off the grid and about 25 watts off the battery which occurs almost constantly in AC Support mode.
I was thinking of getting OutBack's Auto Transformer - the PSX-240. This might keep all 120 loads perfectly balanced at all times between L1 and L2. But a pricey "fix" for such little wattage savings from the grid.
Here's my trouble ... I only use about 150-500 watts an hour on and off at night unless the pump comes on (not very often and not very long). And then when we go to bed that load drops to between 60 and 150 watts an hour because of the fridge, so even if the load is balanced, it would not be enough for the SW to come off grid usage very often. And even then the grid would supply 200-250 watts while the batteries supplied 100-250 watts.
SO ... in AC support mode, my battery bank only discharges about 5-9% over night.
- Using the Skip Days setting for 2 days .... over night the battery drops to 93%, but then during the skip day, They Float Back to 100% and that is with a nice dump load of 1000 watts to heat water. So I generate about 4.5 kWh from the array.
- Go into the next night ... same thing. Loads drop the batteries to about 95%, The Float their way back to 100% the next skip day
- Of course this means there is decent weather and limited cloud cover.
I am running Skip Days to extend battery life so there are fewer cycles on the batteries. My goal is to save the batteries for when we really need them ... BUT ... Is it hard or bad for batteries to go thru these very shallow cycles?
- My thought is to perhaps do deeper 30-40% DOD once a week or so.
- But unless I get an Auto Transformer (expensive fix if it would even work well at low watts to perfectly balance the 120v loads) ...
- Or better balance my loads (which is kinda tough as they vary so much off and on) ...
- There is no real way get any DOD below 90%ish if I stay in AC Support Mode.
- And buying an Auto Transformer might be a waste of money anyway because even if the loads to balance, I am using so little power that pulling 100-150 watts an hour off the battery (and none at all after we go to bed) may not discharge them very much anyway.
So on the one hand I am trying to extend battery life by Skipping Days, but on the other hand, if I am not discharging the batteries below 90% each night, maybe that is doing more harm than good?? See the Dilemma? ??? :)
Thanks.
Mike
Hi Mike, a couple of quick thoughts ...
It is not good to recharge FLA batteries, frequently, when their ACTUAL SOC is above about 90%, you are correct, IMO.
As stated a number of times previously; the indicated SOC from any battery monitoring device is APPROXIMATE, NOT absolute. Even it your battery monitoring device says, that the batteries have been fully-charged from one day of recharge at Vflt, this is most likely, not the case. And successive days of Floating to "100%" will mean that this SOC indication becomes less, and less accurate for each Skipped day.
Will not try to address the way that Schneider inverters behave, etc. Thank goodness, have no experience with the modern SW line.
IMO, Skipping days is better for the batteries, than is recharging each day from SOCs that are above 90%. Fewer cycles, and less integrated battery heating should result from Skipping days, as long as the actual SOC is not depleted below about 65- 70%.
I would shoot for recharging your FLAs about twice per week, not, once.
All IMO, FWIW, Vic
Thanks Vic ... that is my goal, and yes I am aware of the vagueness of the % monitor. Kind of just a guage. Guess I need to go and check at the end of the day if indeed the batteries did return to fully charged from their 90%ish state, but I have every reason to believe they did based on Ah's returned and the actual charging current that seem to be being sued even in float. The current even in float is at times 3-13 amps. So they are charging all be it at 27 volts.
The issue seems to be, as long as I stay connected to the grid for support of the battery bank, I cannot seem to drift down to a lower SOC than 90% thru the night. And thus thru the next day ... even in float, the batteries appear to be (though as noted untested) but appear to be return to fully charged.
I guess I could set the float voltage to 25 or something, then they really would struggle to keep up and probably more just sit there while any loads where being supplied by the Array if there is sun light.
Maybe reducing the float voltage would help during skip days to allow a 2-3 day period to actually discharge the bank down to about 75%
As to the SW and me ... it is definitely a love - hate relationship. The inverter has several really nice features on paper that seem marginally thought thru by the engineers at best and so the implementation and actual function of those features is Meh at best.
Is there a way to set the CC during skip days so that not charging occurs, not even float, but loads are supplied by the solar array? I was able to slow down charging by setting the float voltage to 25.8v
Quote from: Matrix on April 04, 2018, 02:00:02 PM
Is there a way to set the CC during skip days so that not charging occurs, not even float, but loads are supplied by the solar array? I was able to slow down charging by setting the float voltage to 25.8v
No the skip day will go to Float
Quote from: Matrix on April 04, 2018, 02:00:02 PM
Is there a way to set the CC during skip days so that not charging occurs, not even float, but loads are supplied by the solar array? I was able to slow down charging by setting the float voltage to 25.8v
Mike,
I have also set the Vflt to a low voltage, in the early days of experimenting with Skip Days -- about 25 V equivalent, but then set it back to the normal Vflt.
Have always tried to keep Vflt as low as possible, as, even in Float, there is some positive plate erosion, particularly if much time is spent there.
As John mentioned, a Skip Day starts in Float MPPT, and will sit in Float as long as there is enough power to maintain Vflt (as you know).
I am happy that MidNite has added this great function, for those of us who have a bit too much battery capacity vs loads.
Your system has a lot of things going on, which probably make it difficult to stay on top of managing your battery bank.
I have little respect for Schneider as a company, as it seems that their Engineers are not permitted to Swing For The Stars. When something kinna starts working, they ship it. And their bug fixes often seem to be that they come out with a new model of that product, that kinna fixed one small thing, but may well have other bugs/flaws ... just my opinion.
Good luck with your system. Vic
Quote from: Vic on April 04, 2018, 04:20:06 PM
I have little respect for Schneider as a company, as it seems that their Engineers are not permitted to Swing For The Stars. When something kinna starts working, they ship it. And their bug fixes often seem to be that they come out with a new model of that product, that kinna fixed one small thing, but may well have other bugs/flaws ... just my opinion.
Good luck with your system. Vic
Well Said, I am right there with you. But I am kinda locked in now as I also have an E-Panel specifically made for the SW that ties it all together. The cost of changing how would not just be an inverter, but also an E-Panel and a lot more.
So I love to hate it. ;D
Beware of trying to balance the Grid with your small autotransformer. If the feed from the grid is not balanced, then your transformer will be overloaded.
If you are looking for more efficient than the PSX-240, here's a source for expensive toroidal versions
https://toroid.com/Products/Auto-Transformers
Quote from: mike90045 on April 05, 2018, 02:10:39 AM
Beware of trying to balance the Grid with your small autotransformer. If the feed from the grid is not balanced, then your transformer will be overloaded.
If you are looking for more efficient than the PSX-240, here's a source for expensive toroidal versions
https://toroid.com/Products/Auto-Transformers
Oh Mike now you've cooked my brain. I was thinking I was balancing the loads only coming off the inverter, but you are correct, these same loads are powered by the grid at least in a limited way.
My thought was the Grid power is going into the inverter same as the battery power and the all power is passing thru the inverter, but I think you are correct, grid power by-passes the inverter within the SW and is "blended" with inverter AC power. But you are saying that if the limited support grid power is not balanced it will over load the transformer? In what way am I looking for it to be balanced? Volts? My grid power is coming strait off my L1 and L2 from the Meter thru the main panel and to a 2 pole breaker and then to the E-Panel breaker to the Inverter.
Seems the AG Grid power voltage between L1 and L2 has about a 2-4 volt difference. Like L1 is at 121v and L2 is 123v but it swings. Other than that, I would not be exceeding total load wattage of the inverter (3400W) for my loads regardless of the source, either battery or grid.
This is an an interesting discussion...
As for how far to let the batteries discharge over a couple of days, I am not sure so I'll let that one go for now
except to say that I have heard (from "experts") that you want to discharge FLA (unsealed) to keep their
discharge capacity high and if you do NOT do this, that there is NO permanent damage (memory).
Matrix, when you say,
"I only use about 150-500 watts an hour on and off at night unless the pump comes on"
do you mean 150 to 500 "Watt-Hours" per night of energy ?
The 2% minimum from grid requirement, I assume, is per leg. Just a guess. But this is so that they
have time to react and stop supporting quickly when the consumption goes below 2% on either leg so
that they don't sell back on either leg for any length of time. I really do not know how all residential
power meters work when they phone home that you've been selling back power.
I would also assume that these power meters would have their own safety margin in them so that even
when you do sell back power above some threshold for some minimum amount of time, that it would
only then register that activity. After all, even when NOT selling back energy, some current can be
sent back to the grid every cycle when low power factor loads are connected. It's just not in-phase with
the voltage so it's not real power, just VARs.
The idea for Skip days and battery life is to just keep that higher voltage absorb cycle from happening
all the time... BUT you want it to happen once in a while. Maybe not even every other day but every
few days ? Maybe every situation is different ? I don't really know what is best. Just kind of a feeling.
I like the idea of lowering the float voltage but not too low. I would adjust that voltage to the minimum
SOC% battery voltage that you want the batteries to discharge to I guess. 50% maybe ?
I also question the use of ending-amps to stop an absorption charge, especially when using skip-days.
You really do want a full 2 or 3 hour (or ?) higher voltage absorb charge cycle once in a while to help
keep the sulfation away.
boB
Not knowing how your inverter is wired internally with the transfer switches, but my XW has 2 sets of switches, one for Generator Input, and one for Grid Input.
I know for sure the generator input switches to the inverter Load, and when the inverter is in Gen Support mode, I can make the generator howl by uneven loading of the L1 + L2 **
I think that in Grid Support, you also have Grid and Loads connected. So, do you have your own transformer on a pole in the yard, or do you share a transformer with a couple neighbors ? If just your own, you are in pretty good shape, but if you share a pole pig with several neighbors, your L1+2 balancing would be doing the whole neighborhood !!
**
A firmware upgrade from Xantrex added a mode GenSupport+ which activates the internal transformer in the inverter as a balancing transformer.
boB, so much to comment back that I will have to wait until later this evening when things slow down.
Quote from: mike90045 on April 05, 2018, 04:19:38 PM
Not knowing how your inverter is wired internally with the transfer switches, but my XW has 2 sets of switches, one for Generator Input, and one for Grid Input.
I know for sure the generator input switches to the inverter Load, and when the inverter is in Gen Support mode, I can make the generator howl by uneven loading of the L1 + L2 **
I think that in Grid Support, you also have Grid and Loads connected. So, do you have your own transformer on a pole in the yard, or do you share a transformer with a couple neighbors ? If just your own, you are in pretty good shape, but if you share a pole pig with several neighbors, your L1+2 balancing would be doing the whole neighborhood !!
**
A firmware upgrade from Xantrex added a mode GenSupport+ which activates the internal transformer in the inverter as a balancing transformer.
Easier to respond to
the SW has one AC L1 / L2 Neutral in and one L1 / L2 Neutral out. The user decides if that in is a Gen or AC Grid inside the SW.
All of my loads that come off the inverter are the only loads I would be trying to balancing. Not the loads of the whole house. The Auto Transformer would be put AFTER the inverter, not on the L1 and L2 coming in from the pole. It would be the L1 and L2 coming off the inverter. Not sure if that would matter based on what you re saying.
We share a pole transformer with one house next door.
But I am only trying to balance the loads coming off the inverter L1 / L2 and inverter neutral.
Outbacks Auto Transformer is used for Step up and Step down, but also for balancing the loads coming off of 2 Outback 120v inverters that are stacked and being used for 240v split-phase service.
My thought was that the SW would be similar to 2 inverters in one box. Because, even though the inverter is rated for 3400 watts continuous, the user is not supposed to use more than 1700 watts continuous per leg.
AC support mode in the SW does not work well unless the loads are in perfect balance
So my thought was to use the Auto Transformer from Outback similar to the way they describe using it with 2 120v inverters to balance loads between L1 and L2. It would look similar to this .... but with one Split-Phase L1 / L2 inverter and not 2 120v inverters. Perhaps it would not work at all as I anticipate. But I have been told it will but "ButchDeal" (another forum who first suggested it to me) and I also called Schneider who thought it was a great idea for AC support mode and that they had never thought of it. Which if Schneider knew (which they do know - they dont state it in the manual, but trust me ... they know) that AC support mode required such concise balance ... why didn't they build one in to the SW from the start????
I guess for the same reason they did not program little reasonable ideas into the SW like end amps for charging. Their Absorb time feature is useless. No mater where the user sets Battery Amp Hour (the program aspect that is supposed to control end amp if not time), Absorb ends at 7.8 amps, or 2% of my Battery Ah ... or about 30-45 minutes into Absorb. And my battery is only at 90% SG when their charger stops. And there is nothing I can do about it ... except increase charge volts to near EQ volts if I want the SW to fully charge the batteries.
Quote from: Matrix on April 05, 2018, 06:39:16 PM
.....
the SW has one AC L1 / L2 Neutral in and one L1 / L2 Neutral out. The user decides if that in is a Gen or AC Grid inside the SW.
All of my loads that come off the inverter are the only loads I would be trying to balancing. Not the loads of the whole house. The Auto Transformer would be put AFTER the inverter, not on the L1 and L2 coming in from the pole. .........
Right, but if there is a straight wire thru the inverter Loads to the Grid, your transformer is looking at the Grid too, not just your local loads.
If the inverter is powering your loads, AND backfeeding the grid at the same time, I think you have a straight through connection via transfer relay that disconnects the Grid if it fails.
I don't know if the outback transformer has been tested in a Load Shave configuration or only in Off Grid.
Anyone else ???
Quote from: mike90045 on April 05, 2018, 07:55:32 PM
Right, but if there is a straight wire thru the inverter Loads to the Grid, your transformer is looking at the Grid too, not just your local loads.
If the inverter is powering your loads, AND backfeeding the grid at the same time, I think you have a straight through connection via transfer relay that disconnects the Grid if it fails.
I don't know if the outback transformer has been tested in a Load Shave configuration or only in Off Grid.
Anyone else ???
yeah I dont know if the AC grid connection is straight thru the inverter or not. I guess I could go turn off AC Support AND turn off the inverter from within the software, but have AC grid connected and see if the house goes dark or if it continues to pass power thru.
But with the SW ... it is NEVER suppose to backfeed the grid as it is not a Hybrid in the since of a Grid-Tie / Off-Grid / Hybrid would be (as I think Outback has). It only receives grid power to support loads, It it was back feeding the grid at all ... I would be in trouble bc I don't have approval and an interconnect agreement to be injecting power back into the grid. Thus, there is no disconnect transfer in the inverter shutting it off if the grid fails like a grid-tie ... it just keeps on "invertering" and running off the batteries like nothing happened. But there is some kind of auto transfer switch in it ... because when I throw the breaker to turn on AC ... after 10 seconds the lights flash as the grid connection comes one.
I guess I'll power up the grid, turn off the inverter and see if I go dark. 8)
Here is the SW with Grid Connected and AC Support Mode on .... but loads are unbalance, so it is not drawing anything (but the smallest of constant 25w "signal") from the battery. All the loads are coming from the grid.
Even at this 370W load level ... if I turn on a 125W light bulb on L2 with the fridge on L1 it will balance the loads enough to start using 225W off the grid (which is the minimum required 2%) and will pull 145W off the battery. So I know balancing will get me there ... even kinda balanced as described above.
Here is the SW with AC support mode off ... I have no idea if it is passing AC grid thru, Inverter is still on and it is passing thru the inverter.
And here are my master settings for the inverter (see pic) .... Inverter is on, but as you can see from above there is nothing coming off the battery.
Now .... I will turn off the inverter from the controls and see if I am in the dark. (I will probably have to reset all my clocks. ::)) ... here goes ....
Hmmmm ... Inverter is off ... and I still have light. So I guess that answers the pass thru question. The SW continues to pass power right thru. BUT I know for certain, if I went out and switched off the 250 amp breaker from the battery to the inverter ... the house would go dark ... even though the AC grid is still live and connected to the inverter. So there is some kind of disconnect in the SW if it is shut off.
(I guess I could take it out of Operating mode and put it into stand by ... I think that would put me in the dark)
You might call Schneider Electric and see if they can help you out. I'm just asking questions and guessing at what the answers might be
Quote from: boB on April 05, 2018, 03:48:12 PM
This is an an interesting discussion...
As for how far to let the batteries discharge over a couple of days, I am not sure so I'll let that one go for now
except to say that I have heard (from "experts") that you want to discharge FLA (unsealed) to keep their
discharge capacity high and if you do NOT do this, that there is NO permanent damage (memory).
...
The idea for Skip days and battery life is to just keep that higher voltage absorb cycle from happening
all the time... BUT you want it to happen once in a while. Maybe not even every other day but every
few days ? Maybe every situation is different ? I don't really know what is best. Just kind of a feeling.
I like the idea of lowering the float voltage but not too low. I would adjust that voltage to the minimum
SOC% battery voltage that you want the batteries to discharge to I guess. 50% maybe ?
I also question the use of ending-amps to stop an absorption charge, especially when using skip-days.
You really do want a full 2 or 3 hour (or ?) higher voltage absorb charge cycle once in a while to help
keep the sulfation away.
boB
Hi boB,
I certainly am not a battery expert.
Agree that deeply discharging FLA batteries is good for them, on occasion. Personally, would not use Skip Days to do this. Usually do the deeper discharge by taking FLAs from about 80% SOC to about 55 - 60% SOC in one morning, then, fully charge them in that same day. We try to not let FLAs sit very long at a fairly low SOC. And avoid taking the main battery banks here, below 50% SOC ... but that is just me.
Agree with you about avoiding fully recharge of FLAs every day, unless the DOD justifies a full recharge every day. Personally would not want FLAs to spend very much time below 70 or 75% SOC, however ... all depends IMO.
In a simple off-grid system, we try to set Vflt to a voltage that just barely keeps a fully-charged battery, fully-charged. At least for systems with appreciable battery Capacity.
Regarding using EA to end Absorb with FLAs, this is all that I have ever used. First, it was CC EA with the venerable MX-60. Worked fine on systems with loads that were reasonably well-controlled near the end of Absorb (ie not a household full of teen-agers, ones with large water pumping demands, etc). Even without Shunt EA, FLAs allow one to actually measure SGs to see how well the battery is being charged, and changes can be made to EA settings that ensure fully battery charge.
Using Shunt EA (and that is all that we have ever used, since it first became available on the Classics), is even easier than CC EA was, on FLAs.
One can choose an EA value that is far out enough on the EA curve to ensure that one gets enough Absorb time to allow full-charge.
On the other hand, there are two slight things about even CC EA, that can trip up things;
One, is, that the ideal Shunt EA setting really somewhat depends upon just how deeply discharged the FLAs were discharged in the previous discharge cycle. A deep discharge seems to require a higher EA setting. So, there is a chance that the EA value for a customary fairly light discharge will never be reached, and the Classic (or other good CC), will hang in Absorb until the Absorb timer, times-out.
The other thing, is, for CCs which do NOT have battery voltage Sense leads, large opportunity loads, with attendant voltage drops can cause early termination to Absorb. [because this voltage drop decreases the Vabs that the battery sees, causing the measured battery charge current to be reduced. This can cause an early Abs termination]. Even a few tens of millivolts of drop in the CC output breaker, cables to the battery and in the RFI suppression chokes can cause an EA value that allows for a full battery charge under light CC output loading, to be reached considerably more quickly. This results in the battery not having its desirable Absorb that lasts some hours, and not receiving a full-charge IMO.
Regarding EA settings suggested by many FLA battery manufacturers, most of them have charge settings (including those for EA), based on a discharge down to the recommended minimum SOC. For EA, this is usually in the range 1.5 - 3% of 20 hour Capacity. For FLAs that are not cycled that deeply on each cycle, these EA values are far too high to allow an adequately long Absorb stage. This does result in an inadequate recharge, again IMO.
So, in summary, for the past 12+ years, we have used EA on the main banks here (ie, each battery bank is in its 13th year).
We began using the WbJr when it first became available, using Shunt EA on Classics.
When Skip Days first became available, we began using Skip Days with Shunt EA. One system usually uses 3 days Skipped, but sometimes this system is set to only Skip 2 days, depending upon A/C loads in the Summer. The other almost identical system has fewer Opportunity loads, and it usually Skips 3 days in Summer, and 4 in Winter, WX depending.
So, am no expert. Just have been running three battery banks, two of which have run EA, essentially since inception, with no observed issues. Some days, with light discharges, Abs time is about one hour. Other days, Abs is about four or so hours. These battery banks show full SGs on full-charge days using Shunt EA AND Skip days.
All of the above are simply my observations and opinions, obviously.
Thanks boB, for all of your fine work (and the work of the entire MN Team), over the decades, producing some very fine RE products, at a number of different companies. You and the entire team, really do Swing For the Stars!
The MX-60 is still a great CC, particularly given, that it was probably designed 16 or 17 years ago. Many of them are still going strong, after all of these years. GREAT WORK !! 73, Thanks, Vic
Quote from: boB on April 05, 2018, 03:48:12 PM
This is an an interesting discussion...
As for how far to let the batteries discharge over a couple of days, I am not sure so I'll let that one go for now
except to say that I have heard (from "experts") that you want to discharge FLA (unsealed) to keep their
discharge capacity high and if you do NOT do this, that there is NO permanent damage (memory).
Not sure i understand this... Seems like it says on the one hand you have to discharge FLAs to keep the capacity hi, But if you dont it does not mater ?? :o
Quote from: boB on April 05, 2018, 03:48:12 PM
Matrix, when you say,
"I only use about 150-500 watts an hour on and off at night unless the pump comes on"
do you mean 150 to 500 "Watt-Hours" per night of energy ?
I mean it will be that for about 3-5 hours until we go to bed. But in all reality, thru the waking hours of evening, it is really more like about 250 Watts per hour for 3-5 hours. It just varies from 150-450 off and on inside of any given hour depending on what we are doing. Then From 11:30pm (latest) on it is about 150 Watts or less for the rest of the night until charging starts again the next morning. I usually see a balance about 8am when there is enough light to make the 150 watts needed and the loads start to be supplied fully by the solar. Max thru the night Watt hours is around 2000 - 2400 Watt Hours.
Quote from: boB on April 05, 2018, 03:48:12 PM
The 2% minimum from grid requirement, I assume, is per leg. Just a guess. But this is so that they
have time to react and stop supporting quickly when the consumption goes below 2% on either leg so
that they don't sell back on either leg for any length of time. I really do not know how all residential
power meters work when they phone home that you've been selling back power.
I would also assume that these power meters would have their own safety margin in them so that even
when you do sell back power above some threshold for some minimum amount of time, that it would
only then register that activity. After all, even when NOT selling back energy, some current can be
sent back to the grid every cycle when low power factor loads are connected. It's just not in-phase with
the voltage so it's not real power, just VARs.
That is both legs, and I should have written 2 amps AC NOT 2%. But in practice it works out to be actually only about 240-300 watts total. When the loads are less than that the SW draws all current from the grid and nothing from the battery except 25 watts (all the time)
The SW does not sell back to the grid at all. It is not designed to, but I understand what you are getting at.
Quote from: boB on April 05, 2018, 03:48:12 PM
The idea for Skip days and battery life is to just keep that higher voltage absorb cycle from happening
all the time... BUT you want it to happen once in a while. Maybe not even every other day but every
few days ? Maybe every situation is different ? I don't really know what is best. Just kind of a feeling.
That is my feeling too.
Quote from: boB on April 05, 2018, 03:48:12 PM
I like the idea of lowering the float voltage but not too low. I would adjust that voltage to the minimum
SOC% battery voltage that you want the batteries to discharge to I guess. 50% maybe ?
Lowering float voltage has not worked out so well yet. I am still tinkering with it, but as of yet, I discharge down to 93% and thru the day I float back up to 100% even when i set it at 26.3v (for a 24v battery bank) on a fully sunny day. If I go much lower, the CC stops supplying (its like it limits) enough current to power the loads and they system will drop below the Waste Not Hi parameters, even though there is plenty of solar available to power the loads. Like the demand will be 1200 watts but if i set it to 26.3v the CC will only allow for 800, but if I set it to 27v, it powers all loads just fine.
So the lower you go in float voltage, the more the current seems to be limited not just for charging but also for loads even if the power is available .
Quote from: boB on April 05, 2018, 03:48:12 PM
I also question the use of ending-amps to stop an absorption charge, especially when using skip-days.
You really do want a full 2 or 3 hour (or ?) higher voltage absorb charge cycle once in a while to help
keep the sulfation away.
As to end amps, me and end amps never did get along. So many factors in charging its hard to keep up with it all, but the short version. I have to keep a higher than "normal" absorb voltage set (like 31.3v) or I never reach full charge even though I have tapered down to 1% of the battery amp hour. If I use 30.5v for absorb, I will get to 1% of Ah, but the batteries are not charged fully. If I turn off end amp and use time, I drop to below .5% battery Ah and still not charged and it just drowns on until the sun goes down. If it is a really good day, the batteries charge, but it takes all day. So the Volts go up ... up to 31.3v + for absorb, and the batteries reach fully charge at about 1% battery Ah or in my cast about 4.3 amps.
Why ?? I do not know. Has driven my crazy since installation, and I have given up and just live with it. I can never get a firm answer as to if the higher absorb volts harms the batteries ... not even from Trojan. (they actually said no it does not)
QuoteRegarding EA settings suggested by many FLA battery manufacturers, most of them have charge settings (including those for EA), based on a discharge down to the recommended minimum SOC. For EA, this is usually in the range 1.5 - 3% of 20 hour Capacity. For FLAs that are not cycled that deeply on each cycle, these EA values are far too high to allow an adequately long Absorb stage. This does result in an inadequate recharge, again IMO.
Thanks Vic, That about sums up what I see and really sheds some light on things from your vast experience.
Can I ask what battery life people are getting that advocate regular deep discharges and skipping days of charge?
When i moved into my house the previous owners had the generator come on at 80%SOC but in reality it was a lot sooner due to big loads like the drier forcing it to start. When i moved in I lowered the value to 70% however for most of the year our SOC rarely gets under 90% at night and batteries are fully charged by midday. A few times in winter the batteries will see 80% but again big loads normally kick the generator in (taken care of by older sMA inverter) before that.
My batteries (1,600 amp, 24v raylites) are now 12 years old and not showing any signs of wear. They get an equalise charge every 2 months or so but charged every day.
Quote from: jimbo on May 21, 2018, 06:47:15 PM
Can I ask what battery life people are getting that advocate regular deep discharges and skipping days of charge? ,,,
Just my opinions, but, to me, the main use for Skip Day charging, is for batteries that do NOT get sufficient discharge, on most days (and therefore are NOT seeing deep discharges regularly, without manual intervention). The banks, here that are on Skip Days, usually would not be discharged to less than 90% SOC on many days. Generally, it is best to discharge FLAs that are in regular cyclic (off grid) use below 90% SOC before recharge. This is the reason that we are using Skip Days.
The main banks here are Surrettes, and each in their 13th year of off-grid service.
An additional benefit of not recharging FLAs that have been lightly-cycled, is that there will be less heating of the battery bank, due to fewer Absorb cycles per given time.
Skipping days, might mean, that these FLAs might need a bit more EQing.
FWIW, Vic
Quote from: Matrix on April 08, 2018, 07:48:07 PM
Quote from: boB on April 05, 2018, 03:48:12 PM
This is an an interesting discussion...
As for how far to let the batteries discharge over a couple of days, I am not sure so I'll let that one go for now
except to say that I have heard (from "experts") that you want to discharge FLA (unsealed) to keep their
discharge capacity high and if you do NOT do this, that there is NO permanent damage (memory).
Not sure i understand this... Seems like it says on the one hand you have to discharge FLAs to keep the capacity hi, But if you dont it does not mater ?? :o
Right, sorta.... As I remember so see my statement of possible insanity below...
If you don't exercise the batteries to some depth of discharge all of the time, then they won't have that much depth of discharge
available until you work them down to that DOD level. This is what I heard and this MAY have just been some kind of
dream or nightmare, but if it was, then Steve Higgens from Rolls/Surrette battery was in that dream.
I have NOT seen this behavior myself !
boB
I have been told that short discharge means that the FLA battieres doesn't get much time to absorb and thus mix up the electrolyte.
Quote from: jimbo on May 22, 2018, 07:20:42 PM
I have been told that short discharge means that the FLA battieres doesn't get much time to absorb and thus mix up the electrolyte.
Ahhh ! YES ! This CAN be a problem with using only return amps to stop the absorb cycle.
The batteries must get a good "timed" absorb once in a while... Like at least once every week or two is what
I hear.
What would be best probably would be another timer that makes sure there is a timed absorb every so often.
When using Skip-Days, probably should use only timed absorb on those days there is an absorb. i.e. Set the ending
amps to zero and set Skip-Days to just a few days. Maybe even a bit longer time than usual for absorb ?
These are just suggestions to try of course and don't take over any hard instructions from the particular battery
manufacturer.
boB
boB,
What would be the logic in not using time to end absorb all the time? As opposed to say, end amps? If time is the better method, why use end amp at all?
I started at first, for the first 6 or so weeks after commissioning my batterues trying to use end amp and get that setting right.... But found after 2 months I was using no water at all, even though my end amp curve was flat at 1-1.5% of total bank amp hour. I found my batteries were very under charged. I was not using enough voltage.
Quote from: boB on May 23, 2018, 12:31:43 PM
Quote from: jimbo on May 22, 2018, 07:20:42 PM
I have been told that short discharge means that the FLA battieres doesn't get much time to absorb and thus mix up the electrolyte.
Ahhh ! YES ! This CAN be a problem with using only return amps to stop the absorb cycle.
The batteries must get a good "timed" absorb once in a while... Like at least once every week or two is what
I hear.
What would be best probably would be another timer that makes sure there is a timed absorb every so often.
When using Skip-Days, probably should use only timed absorb on those days there is an absorb. i.e. Set the ending
amps to zero and set Skip-Days to just a few days. Maybe even a bit longer time than usual for absorb ?
These are just suggestions to try of course and don't take over any hard instructions from the particular battery
manufacturer.
boB
Hi boB,
In my opinion, FLAs do not so much need a long Timed Absorb, as much as a sufficiently long Absorb to really fully charge the battery AND also allow enough mixing of the electrolyte.
Most "experts" say that taller batteries need longer Absorbs, or perhaps Absorbs at a somewhat higher voltage than might otherwise be required for a full-charge on less tall batteries.
If one chooses an Shunt EA value that is fairly far out on the curve of Rate-0f Change in battery charge current, this long Absorb time will be met, but still allow some time-variability in Absorb times, depending on the actual DOD of the battery. But, going out that far on the tail of the battery charge current to allow this long-ish Absorb, can mean that (as stated above) that other factors can disturb this finely tuned EA setting;
One of these factors, is large Opportunity loads that vary in intensity or duration from day-to-day. This can cause a large enough variation in voltage drop in the CC-to battery cables and breakers to cause an early Absorb termination.
AND another, is if there is a sufficiently greater discharge of the battery (to a lower SOC), from one full-charge day to the next (using Skip Days), Then there is some risk that the set EA value will not be reached, and the CC will hang in Absorb, when a long Absorb timer setting is used. (this is why folks like me have been asking for a WBSr, or similar device that will allow MN CCs to know actual battery voltage (measured at battery terminals -- Sense leads).
Certainly, using Shunt EA requires monitoring of actual Absorb times (this is one reason that some of us have been BEGGING for a stored Actual Absorb Time, after the CC has gone to Float), and monitoring of SGs with a Hydro (or Refractometer).
While not absolutely perfect, for off-grid FLA batteried systems, Shunt EA WITH Skip Days works quite well, and has been in continuous use with Classics, here, since it was available.
Thanks again boB, and all the MidNite team for all of the great products, each, with an array of important, innovative functions. There are simply NO other such products in the solar industry, today.
Thanks for taking the time to still keep us on track on this (and other) Forum/s.
73, GL, Vic
I was/am definitely in the "needs higher voltage" camp for my tall L16s. The trouble I was having with EA settings was before I set up my opportunity load AND before I upped my absorb charhing volts. I could probably flirt with EA again now that I have a better charging voltage.
The reason that you want to do a timed absorb (however long for the particular FLA battery) is so the batteries don't sulphate.
The reason you don't want to absorb every day (unnecessarily) is so that you don't prematurely wear the batteries out.
This is my understanding
boB
Quote from: boB on May 23, 2018, 06:16:45 PM
The reason that you want to do a timed absorb (however long for the particular FLA battery) is so the batteries don't sulphate.
The reason you don't want to absorb every day (unnecessarily) is so that you don't prematurely wear the batteries out.
This is my understanding
boB
Hi boB,
Just for my final beating of this poor horse ...
YES, an adequate Absorb time and voltage will return sulfates on the battery plates to the electrolyte, and thus, increase the electrolyte SG. This is an important thing for maintaining battery Capacity, and sulfates that are allowed to remain on the plates can harden, and can cause permanent loss of Capacity, if batteries are not fully charged on a regular basis. Agree with your statement (previously), that it IS better to overcharge (longer Abs time, and/or higher Vabs than really needed for a full-charge) batteries, than to under-charge them.
But, one of the important functions of using Return, or Ending Amps, is to terminate Absorb when that current reaches a point where the change in this current, essentially becomes zero, even when using Skip Days. Using Skip Days, might make finding an optimum EA setting a bit more difficult, vs, not skipping days.
With varying DOD, from one day, to the next, is the main reason that Shunt EA is used on the battery banks here. Deeper DODs require longer Absorbs, so EA is perfect for this situation verses using only a Timed Absorb.
There is no reason that using well-studied EA value would result in insufficient-long Absorb charge stage. Depending on DOD on our batteries, some Absorbs require less than two hours, and, some around four hours ... all depends.
We measure SGs frequently (at least on the Pilot Cells), and Skip Day Shunt EA does a wonderful job fully-charging the batteries, while not needing to resort to a Timed Absorb. With that variable DOD on these batteries, one would need to set an Absorb Time, that was always (or almost always) too long.
After using only CC EA, or Shunt EA for the 12.75 years of service of each of the two battery banks here, these batteries are doing fine. Have needed to increase Vabs somewhat to reach full-charge, starting about 2.5 years ago, as the batteries age. This increase in Vabs, required raising the EA value a bit (as one would expect).
I DO agree with your statement that deep-cycle batteries DO need to be cycled fairly deeply. But, we do not do this too frequently. The Surrette Battery Bulletin #614 used to council, that for their customers who are having problems maintaining Capacity, or those with Charge Acceptance issues, should consider cycling the battery bank down to about 1.83 Vpc (about 11 V, per 12 V equivalent), and then fully recharge them (without delay). This is just too extreme for me -- the deepest that we cycle the banks here, is to about 50% SOC, and recharge fully, immediately.
And, I would fully charge, daily, if the batteries were being cycled to/below about 80% SOC, or lower.
One other good reason for using Skip Days on off-grid FLAs, is, to help reduce battery heating, plus reduction on positive plate erosion, plus a couple of other things.
As an aside, have wondered, if some of the extremely high Vabs requirements for a number of the Trojan batter models, is that, perhaps they have some Calcium in the plates (many of these batteries, seem to need a Temperature Compensation value of -3mV/Cell/C -- a common value for lead-calcium batteries, vs -5mV for lead Antimony batts). Lead-calcium batteries Gas less vigorously, are used in Low Maintenance/Maintenance Free batteries, and this is probably the main reason for the use of lead-calcium batteries (reduced water electrolysis), IMO.
Give me Lead-Antimony batteries, please.
All FWIW, just opinions, but, based on experience, Vic
1.83 VPC? :o
Isnt that like lower than 10% SOC? I'd be afraid to do that even once.
QuoteAs an aside, have wondered, if some of the extremely high Vabs requirements for a number of the Trojan batter models, is that, perhaps they have some Calcium in the plates (many of these batteries, seem to need a Temperature Compensation value of -3mV/Cell/C -- a common value for lead-calcium batteries, vs -5mV for lead Antimony batts). Lead-calcium batteries Gas less vigorously, are used in Low Maintenance/Maintenance Free batteries, and this is probably the main reason for the use of lead-calcium batteries (reduced water electrolysis), IMO.
Might be a good catch:
Look at #4 under BATTERY SELECTION on this page. Seems Trojan does not admit using Lead-Calcium, but as my experience has shown, at "standard" absorb voltages (and per Trojan spec), charging at 2.46Vpc does NOT get the batteries to full charge. The EA is reached to a flat line, but the SG is off by about 10 points (or about 94% SOC). Cant really find anything one way or the other in reference to the use of lead-calcium.
https://www.trojanbattery.com/tech-support/faq/