(https://dl.dropboxusercontent.com/u/69165939/attachments/solar/boostgraph.jpg)(https://dl.dropboxusercontent.com/u/69165939/attachments/solar/boostmode.jpg)
Here is a screen shot from my Schneider SCP showing the charge controller setup for "boost mode" :
The first hour of absorption, the XW tries to take the batteries to 31V (t.comp'd) and then for the rest of the Absorption time it goes back to 29.2V. I have found this to be quite good at getting the batteries up to 1.275+ SG with less water usage than what I used to do before (with my morningstar TS-60 MPPT) which was to run Absorption @ 31v (t.comp'd) for the whole absorption period.
Something the Classic could benefit from?
Here is an excerpt from the XW Manual :
Boost charging allows for better utilization of flooded lead acid batteries under moderate cycling in off grid applications. Boost charging encourages a short duration charging voltage - above the gassing voltage - at the beginning of the absorption charge state. Testing has shown that boost charging improves battery performance by providing a regular mixing of the liquid electrolyte. Boost charging specifically discourages capacity-robbing acid stratification and plate sulfation.
Boost mode charging can be enabled by selecting 'custom' battery type and by setting the bulk voltage higher than the absorption voltage. The multi-stage charge algorithm then attempts to use the higher bulk voltage for the first hour of the absorption stage - unless interrupted by the max absorption timer or exit current threshold.
You can do this with the Morningstar Tristar controllers by using the custom configuration tool to set up the absorption extension.
FYI, if your XW controllers have V01.05.00-0006 firmware you can also set the Bulk voltage to normal Absorb V and set Absorb to the finish stage voltage recommended by your battery manufacturer for two-stage absorb with finish. US Battery and Trojan both recommend three-stage, bulk/absorb/finish charge profile. The XW controller is currently one of only two controllers on the market that can do it - the other is Ralph Hiesey's new SC-2030 solar charger that communicates with and is controlled by the new TriMetric TM-2030 battery monitor.
There are other schools of thought about this. SMA and Surrette strongly disagree with this method.
Ryan or boB may want to chime in here. I will probably get it wrong, but this is a good place to discuss this.
Quote from: Robin on May 04, 2014, 02:21:02 AM
There are other schools of thought about this. SMA and Surrette strongly disagree with this method.
Disagree with what? Boost charging, or three-stage bulk/absorb/finish? Just about all industrial chargers (forklift, floor maintenance machines, etc) use IUI charge profile. I don't know about SMA, but Rolls' published charging specs are based on the use of a IUI constant-current charger, not voltage-based chargers like we have in the RE world. Steve Higgins has been busy rewriting their tech support stuff to reflect the use of RE voltage-based chargers because too many people have been using the published Absorb V spec for IUI profile, and ending up with badly sulfated batteries.
Rolls doesn't actually publish the recommended profile, but US Battery does:
(https://lh4.googleusercontent.com/-MBk3_YUr8nY/U2XlYF1eH-I/AAAAAAAAIHY/nukjueIu2tg/w640-h463-no/AVPageView+442014+85254+PM.jpg)
Quote from: ChrisOlson on May 04, 2014, 03:00:43 AM
Just about all industrial chargers (forklift, floor maintenance machines, etc) use IUI charge profile. I don't know about SMA, but Rolls' published charging specs are based on the use of a IUI constant-current charger, not voltage-based chargers like we have in the RE world.
Yes, but... I think these industrial IUI profiles are used in systems where there is NOT a lot of PSOC cycling (partial state of charge). Some (most?) forklift battery manufacturers recommend against partial charging and partial discharging. I think this has to do with the buildup of stratification (in tall batteries) during both partial charge and partial discharge. Also, the cycle-life charts of these batteries often indicate that the best ratio of kwh throughput to dollars is at deep discharges.
It's not obvious to me that IUI profile is the best way to charge batteries in a RE system.
DISCLAIMER: very few things about batteries are obvious to me.
--vtMaps
Rolls has issued a bulletin for RE applications:
I have attached the pdf here:
Quote from: vtmaps on May 04, 2014, 04:40:01 AM
It's not obvious to me that IUI profile is the best way to charge batteries in a RE system.
It's actually impossible to charge batteries with IUI in a RE system. Well, I guess I should say darn near impossible without throwing excess solar capacity at the problem. The Schneider Conext XW controllers do it in a sort of roundabout way that works. But they use Bulk (maximum current available), Absorb (constant voltage), Finish (constant voltage). We use 2.40 VPC for Absorb and 2.58 VPC Finish here and it works very well.
What the XW controller does is is charge during Bulk until the voltage hits Finish voltage, then the controller "throttles" the voltage back to the Absorb setting for one hour. This limits the current to the battery when it is at lower SOC during gassing, which keeps its internal temperatures down. After one hour it then increases the voltage to Finish stage voltage and exits at 2% C/20.
I tried for months to get the Classics to do this by using AutoEQ for the Finish stage. But it didn't work because the Classic has a flaw in that it will not fully absorb the battery before it jumps into EQ. So it got the batteries hotter than blazes when the AutoEQ kicked in because they were not ready for it yet. So I finally gave up on it because it boiled way too much water off.
Ralph Hiesey has done one better than Schneider with his SC-2030. It does not use constant current bulk, but instead uses all available power. Then it does a constant voltage absorb and a constant current finish stage with current held at 2% C/20 until finish voltage is reached. The controller itself is "dumb". The charge profile is actually controlled and communicated to the charger by the TM-2030 TriMetric over serial link. Ralph is a brilliant engineer.
Quote from: DMJ72 on May 04, 2014, 09:04:00 AM
Rolls has issued a bulletin for RE applications:
I have attached the pdf here:
That's some of Steve's work. I've told people this very thing for years on various forums, that have ended up with sulfated Surrettes. Invariably somebody always comes out of the woodwork with their published Absorb V spec that is way too low for RE systems and proclaims that if you use higher voltage you're going to wreck your batteries. Well, Steve and I got together on this long ago when we initially had problems with ours and that's why I've been trying to tell other folks to crank those controllers up. Glad to see Steve finally got around to getting this in print.
Quote from: ChrisOlson on May 04, 2014, 11:27:59 AM
Quote from: DMJ72 on May 04, 2014, 09:04:00 AM
Rolls has issued a bulletin for RE applications:
I have attached the pdf here:
That's some of Steve's work.
<snip>
Glad to see Steve finally got around to getting this in print.
Huh? I don't think Steve can take credit for that document... he hasn't been at Rolls that long. That document has been around since at least 2008. I downloaded it a few years ago from here:
http://forum.solar-electric.com/showthread.php?p=21460#post21460
--vtMaps
They used to have a lot of PDF downloads of various bulletins and whatnot, and it appears they are going to more HTML based bulletins that you can search on their support pages to make it easier to find
http://support.rollsbattery.com/support/search
So if that WAS in print as early as 2008 very few people were paying attention to it, and still using the 2.4VPC Absorb V for RE systems. Steve said it was his job to make sure this is better understood for folks using their batteries in RE applications, and to get the manuals rewritten. That link to where that evidently used to be on Rolls' website is long gone.
Would a way to offer either/both of these two charge profiles on the classic, would be to have absorb1 and absorb 2, both with adjustable setpoints? Absorb 2 follows after absorb 1. Use both or disable one...
Quote from: zoneblue on May 04, 2014, 05:23:16 PM
Would a way to offer either/both of these two charge profiles on the classic, would be to have absorb1 and absorb 2, both with adjustable setpoints? Absorb 2 follows after absorb 1. Use both or disable one...
Yep, I like that.
BULK-->>ABSORB1-Voltage---for time T>>ABSORB2-Voltage for rest of Absorb time or until End Amps>>Float.
Quote from: DMJ72 on May 04, 2014, 05:59:55 PM
BULK-->>ABSORB1-Voltage---for time T>>ABSORB2-Voltage for rest of Absorb time or until End Amps>>Float.
Actually, that's Schneider's method using a timed first Absorb stage. And it's not ideal. Ideally, the controller should stay in that first Absorb stage until ending amps is reached, THEN increase the voltage to finish voltage. I would call the stages Bulk, Absorb, Finish as that is the terminology used in the industrial world. And I believe that the terminology that Ralph Hiesey is using for his SC-2030 as well.
I don't know that a true constant current finish stage is absolutely necessary. Ralph did it with the SC-2030. But I really think the method that the Schneider Conext XW controller (and the XW inverters) use is just as good. It simply bumps the voltage up to finish voltage and exits at 2% C/20. In the RE world where you may be running out of power to complete the finish stage late in the day, the constant current method might not get the job done because it won't be able to hold the current at 2% C/20 for long enough to complete it. That finish stage here can take up to an hour with a cycle every 2-3 days, and 3 hours if the cycle has gone 7 days or more.
Quote from: ChrisOlson on May 04, 2014, 02:26:56 PM
So if that WAS in print as early as 2008 very few people were paying attention to it, and still using the 2.4VPC Absorb V for RE systems.
I think a lot of folks were influenced by Sandia research that was reported in this HP article from 2002:
http://www.homepower.com/view/?file=HP89_pg120_IPP
QuoteThe Sandia report is very thorough. Four different brands of batteries were tested. They were all flooded, L-16 type batteries, the most common battery used in residential-scale RE systems.
The study has four conclusions:
- The finish voltage (sometimes called the absorption voltage) for a flooded lead-acid battery operating at 12 VDC nominal should be about 15.3 volts (2.55 per cell) rather than the customary 14.4 volts.
- Finish charge time should be at least 3 hours and often longer.
- The maximum interval between finish charges should be about five days.
- Not all brands of L-16s are the same (though the report names no names).
--vtMaps
The main advantage I've seen here with three-stage charging (bulk/absorb/finish) is that once the battery reaches gassing voltage (absorb stage), limiting the amps to the battery during the first part of it cuts water use and keeps the battery's temperature down. It still needs the higher voltage to properly desulfate it, and that's what the finish stage does. The overall charging time is longer using three-stage. But it's more efficient. Our cycle efficiency is in the 92-93% range with three stage charging (according to the TriMetric). With just regular bulk/absorb charging the cycle efficiency is around 88%.
ChrisO, can you say more about why adapting auto EQ didnt work? If the "finish" stage was just timed, i would have thought it would work. I know that manual EQ doest wait for absorb to finish, and i do find that strange aswell.
Quote from: zoneblue on May 05, 2014, 06:45:01 PM
ChrisO, can you say more about why adapting auto EQ didnt work? If the "finish" stage was just timed, i would have thought it would work. I know that manual EQ doest wait for absorb to finish, and i do find that strange aswell.
It's probably because EQ always goes to Float if it ends when the timer expires. It may have done what he
wanted if instead of going to Float, it would go to Absorb first for its time or ending amps.
That may happen eventually, which might be a decent work-around as long as it can do it every so often instead of havint to happen every single day. OR, happen below a preset SOC% maybe.
Quote from: zoneblue on May 05, 2014, 06:45:01 PM
ChrisO, can you say more about why adapting auto EQ didnt work? If the "finish" stage was just timed, i would have thought it would work. I know that manual EQ doest wait for absorb to finish, and i do find that strange aswell.
boB, what it did for me was that when the auto EQ activated it would not absorb the battery first, but instead it just kept charging at full power until the EQ voltage was reached, totally skipping the absorb stage. So it wouldn't actually do a two-stage absorb (or absorb/finish) like I wanted it to. The only way I could get it to work was to sort of monitor it and when absorb was getting close to done, then manually force the EQ.
The result using the auto EQ was that the battery was at way too high of voltage for its SOC so it got hot from taking on too many amps, as it wasn't absorbed yet.
I haven't tried it now for about a year because after we put in the XW system here we got XW controllers to go with our system. And the Classics only do wind now. So maybe this was all changed in later firmware? If the Classic can absorb to 2% C/20, and when it exits absorb have auto EQ kick in with the EQ voltage set to the proper finish voltage recommend for a three-stage charge profile, the Classic is already capable of three-stage (bulk/absorb/finish) charging. Just set the EQ timer for what the battery needs for finish charge. That's what I was trying to get to work a year ago.
One of the nice side effects about bulk/absorb/finish charging is that it eliminates periodic equalization charges because the higher voltage finish stage fully desulfates the battery and keeps it healthier. No need to abuse your battery for long periods at high voltage doing EQ every month because the bulk/absorb/finish charging keeps the SG's (at least in our batteries) within 15-20 points between cells.
I gotta get me one of those Whizbang Jr and try this again. The firmware updates for the Whizbang probably "fixed" a lot of the problems I had when I was experimenting with it (for one, end amps actually works properly with the Whizbang, which is a key factor).
Not fixed yet Chris. I happened to try it the other day since I had never used it and was surprised to see it in EQ MPPT at 7am in the morning. So you are correct NO ABSORB stage with Auto Equalize.
Darn, that's what it did for me too. I had Follow Me set up with one controller that initiated the auto EQ. I was not around to watch it when it happened the first time, and caught it when the batteries were taking on 150 amps from two controllers at finish stage voltage. So I halted the whole process and forced a bulk charge, and the battery was already up to 41C.
The second time I watched it and it totally skipped over the absorb stage again. That's when I decided it don't work.
Hm I would think you would want it that way so the battery gets to EQ voltage quicker? You are saying you prefer to complete an absorb cycle and then complete an EQ cycle? In my case there would not be enough sun for a 5hr absorb cycle and a 2-3hr EQ. I can say that going straight to EQ and staying there for 2-3 hrs always gets my specific gravity where it needs to be?
Quote from: Halfcrazy on May 06, 2014, 08:20:52 AM
You are saying you prefer to complete an absorb cycle and then complete an EQ cycle?
He said earlier that going straight to EQ without stopping at absorb voltage for awhile makes his batteries get too hot.
fwiw, most battery FAQs I've seen on the internet say to only EQ a fully charged battery... none of them say why.
--vtMaps
I don't know. On our system it pushes way too many amps early in what should be the absorb stage if the battery isn't fully absorbed first. And the batteries get really hot. Our XW controllers, and inverter, will refuse to do any equalizing until absorb is complete. You can push the button and the inverter will flash that EQ is pending (and the controllers too). But they will not start EQ until absorb is done.
I don't know of any battery manufacturers that recommend doing an EQ unless the battery is charged as much as possible beforehand.
Quote from: ChrisOlson on May 06, 2014, 08:52:26 AMOur XW controllers, and inverter, will refuse to do any equalizing until absorb is complete. You can push the button and the inverter will flash that EQ is pending (and the controllers too). But they will not start EQ until absorb is done.
Found that out on a friends XW invertor. I tried to get it to equalize and could not figure out why I could not force an equalize. Dug out the manual and found out it had to complete the time absorb cycle and then it would equalize. :o
Quote from: Resthome on May 06, 2014, 01:13:08 PM
Found that out on a friends XW invertor. I tried to get it to equalize and could not figure out why I could not force an equalize. Dug out the manual and found out it had to complete the time absorb cycle and then it would equalize. :o
Equalizing without fully charging the battery first is a good way to cause a thermal runaway on a bank that has some sulfated cells. As the hardened sulfate comes off the negative plates, internal resistance drops and causes amps to actually increase for a time as the cells even out. You don't want to be doing that kind of stuff when you're pushing > C/10 amps into the battery at EQ voltage. On a system where the amps is limited by available solar capacity, you can probably get by with it. But IMO it's still best for the charge controller to make sure the battery is ready for an EQ before attempting it.
Quote from: ChrisOlson on May 06, 2014, 01:47:05 PM
Quote from: Resthome on May 06, 2014, 01:13:08 PM
Found that out on a friends XW inverter. I tried to get it to equalize and could not figure out why I could not force an equalize. Dug out the manual and found out it had to complete the time absorb cycle and then it would equalize. :o
Equalizing without fully charging the battery first is a good way to cause a thermal runaway on a bank that has some sulfated cells. As the hardened sulfate comes off the negative plates, internal resistance drops and causes amps to actually increase for a time as the cells even out. You don't want to be doing that kind of stuff when you're pushing > C/10 amps into the battery at EQ voltage. On a system where the amps is limited by available solar capacity, you can probably get by with it. But IMO it's still best for the charge controller to make sure the battery is ready for an EQ before attempting it.
I agree with you Chris. It was over a year ago and I though it had already completed an absorb cycle but had not been set to equalize. Too long ago to get all the fact correct. And I probably remember it wrong. Just remember it had to do an absorb first.
So with your XW inverter, if once you have completed an absorb and no equalize was pending you can go to equalize without going through another absorb?
Quote from: Resthome on May 06, 2014, 02:39:47 PM
So with your XW inverter, if once you have completed an absorb and no equalize was pending you can go to equalize without going through another absorb?
Nope. If absorb is completed and you press the EQ button the controllers say Equalize Pending on them and the inverter flashes its red light for EQ Pending. The whole system goes to absorb and verifies that the amps to the battery are less than 2% of what you have entered into the system for the battery amp-hour capacity. It takes it 60 seconds to verify that, then the whole system goes to EQ.
If there's not enough power to maintain EQ voltage the system aborts it. It will allow 60 seconds below EQ voltage before it aborts it. The red light on the SCP starts flashing and there's a warning message on the screen that says it was aborted due to insufficient available power. All you have to do is acknowledge the warning by pressing the Exit button and the warning message goes away and the red light stops flashing. But the system saves it and will attempt the EQ again the next day after absorb is complete.
Quote from: ChrisOlson on May 06, 2014, 09:42:25 PM
Quote from: Resthome on May 06, 2014, 02:39:47 PM
So with your XW inverter, if once you have completed an absorb and no equalize was pending you can go to equalize without going through another absorb?
Nope. If absorb is completed and you press the EQ button the controllers say Equalize Pending on them and the inverter flashes its red light for EQ Pending. The whole system goes to absorb and verifies that the amps to the battery are less than 2% of what you have entered into the system for the battery amp-hour capacity. It takes it 60 seconds to verify that, then the whole system goes to EQ.
If there's not enough power to maintain EQ voltage the system aborts it. It will allow 60 seconds below EQ voltage before it aborts it. The red light on the SCP starts flashing and there's a warning message on the screen that says it was aborted due to insufficient available power. All you have to do is acknowledge the warning by pressing the Exit button and the warning message goes away and the red light stops flashing. But the system saves it and will attempt the EQ again the next day after absorb is complete.
Thanks for the explanation Chris.
Quote from: ChrisOlson on May 06, 2014, 09:42:25 PM
The whole system goes to absorb and verifies that the amps to the battery are less than 2% of what you have entered into the system for the battery amp-hour capacity.
Does your XW system know what is going into the battery ?
Why don't they just limit the current and thus the rise to EQ voltage by looking at the battery temperature ?
That might work pretty good.
Since you don't do a manual EQ very often, you could just manually do it after you've done an absorb.
Quote from: boB on May 07, 2014, 01:09:09 AM
Does your XW system know what is going into the battery ?
Yes, it displays battery net amps on the SCP. Even though it does not measure it with a shunt it agrees with our TriMetric within +/- 0.5A
Quote
Why don't they just limit the current and thus the rise to EQ voltage by looking at the battery temperature ?
That might work pretty good.
Because there is no need to make something more complicated than it has to be.
Manually doing an equalize is fine if you're around to do it. The idea was to use the auto EQ to simulate three-stage bulk/absorb/finish charging. Unfortunately, auto EQ in the Classic does not work properly. Or at least not according to the charging recommendations from any battery manufacturer I have ever encountered. That was the issue.
Quote from: ChrisOlson on May 07, 2014, 07:43:59 AM
Quote from: boB on May 07, 2014, 01:09:09 AM
Does your XW system know what is going into the battery ?
Yes, it displays battery net amps on the SCP. Even though it does not measure it with a shunt it agrees with our TriMetric within +/- 0.5A
How does it know the battery current aside from other DC loads without its own shunt or sensor ?
How does it take into account the current coming from the wind system for example ?
Quote from: boB on May 07, 2014, 07:16:03 PM
How does it know the battery current aside from other DC loads without its own shunt or sensor ?
How does it take into account the current coming from the wind system for example ?
The controllers have shunts on their outputs so each one is measured. The XW inverter has a hall effect sensor mounted on the main processor board in the upper right of the DC section of the inverter. It measures DC current in or out of the inverter. The whole system communicates what they're doing over Xanbus and either the SCP or the ComBox does the calculations to determine net current and reports the results back to the devices. So they all know what battery current is (along with other information that they communicate with each other).
It does not communicate with the wind system. During absorb charging our RD-1 Relay Driver shuts the wind system down so it doesn't interfere with the XW system measuring its end amps, and the battery gets charged correctly. The wind is not needed at that point anyway when there's adequate solar to charge the battery and carry loads. If the voltage "sags" more than 0.5V below the Absorb V setting, either due to excessive loads on the system or solar insolation dropping off, then the RD-1 lets the wind system start back up.
The XW System's method of measuring end amps is pretty accurate. It agrees with the TriMetric +/-0.5A during finish stage near end amps for charging. At higher amp draws the XW system is a little more off compared to what the TriMetric says - like at 100A actual current draw by the inverter (as shown by the TriMetric) the XW system says 104-105A. With the inverter overloaded at 200A draw on the battery as shown by the TriMetric, the XW system says 218-220A.
Oooh.. can't wait for this new feature in the Classic. (and KID)
Two absorb stages so that pre-absorb boost or post-absorb boost or neither can be selected
I assume this would need to be part of the follow-me logic where there are two or more Classics charging the battery bank.
And of course configuarable by the local app :D
dgd
Quote from: dgd on May 07, 2014, 10:36:17 PM
Oooh.. can't wait for this new feature in the Classic. (and KID)
Two absorb stages so that pre-absorb boost or post-absorb boost or neither can be selected
I assume this would need to be part of the follow-me logic where there are two or more Classics charging the battery bank.
And of course configuarable by the local app :D
dgd
Sounds good. 8)
pre-absorb boost charging is not recommended by any battery manufacturers that I know of. It only works on batteries that have been moderately cycled where it can be used to take advantage of peak solar conditions at solar noon, and without excessive heating of the battery. For batteries that have been discharged to 50% SOC it will get your battery way too hot by forcing too many amps into it at the higher boost voltage for the first hour.
Finish charging (delayed boost) is different. It is an algorithm designed to limit current to the battery to no more than C/10 to prevent excessive water use and heating of the battery. And at the same time provide a high voltage finish stage that fully desulfates the negative plates. It is now almost the industry standard recommend charge profile (Trojan, US Battery, Surrette, and all industrial forklift/floor maintenance, locomotive and marine batteries). Industrial grid-powered forklift/floor maintenance and marine chargers have used it for years (IUIa with no float). Currently there are only two RE chargers that I know of that can do it - the XW from Schneider and the SC-2030 from Bogart. Of the two, only the Bogart SC-2030 does it correctly.
Quote from: ChrisOlson on May 09, 2014, 12:24:37 PM
pre-absorb boost charging is not recommended by any battery manufacturers that I know of. It only works on batteries that have been moderately cycled where it can be used to take advantage of peak solar conditions at solar noon, and without excessive heating of the battery. For batteries that have been discharged to 50% SOC it will get your battery way too hot by forcing too many amps into it at the higher boost voltage for the first hour.
There does not seem to be too many battery manufacturers who recommend their deep cycle batteries are only partially discharged then recharged as seems to occur in many RE systems.
My own 1025Ah bank gets to about 20% dod maximum but more often 10 to 15% daily.
40 to 60% dod very very occasionally when weather turns to custard, maybe once every 2 years.
This is where I though a pre-absorb boost would be of advantage and reduce stratification before absorb. A fixed one hour time I don't like so a configurable time up to an hour would be nice.
Finish charging boost where PV is the charging source may be wishful thinking as end day PV input diminishes.
Quote
Finish charging (delayed boost) is different. It is an algorithm designed to limit current to the battery to no more than C/10 to prevent excessive water use and heating of the battery. And at the same time provide a high voltage finish stage that fully desulfates the negative plates. It is now almost the industry standard recommend charge profile (Trojan, US Battery, Surrette, and all industrial forklift/floor maintenance, locomotive and marine batteries). Industrial grid-powered forklift/floor maintenance and marine chargers have used it for years (IUIa with no float). Currently there are only two RE chargers that I know of that can do it - the XW from Schneider and the SC-2030 from Bogart. Of the two, only the Bogart SC-2030 does it correctly.
Ok, but what is the difference for desulfating purposes to just doing a regular EQ cycle?
Is it more efficient or better for the batteries to do a finish stage and perhaps not bother with a float stage? I'm thinking RE not very deep dod system here.
dgd
Quote from: dgd on May 13, 2014, 06:21:27 PM
Ok, but what is the difference for desulfating purposes to just doing a regular EQ cycle?
Is it more efficient or better for the batteries to do a finish stage and perhaps not bother with a float stage? I'm thinking RE not very deep dod system here.
The only reason industrial chargers use IUIa (no float) is because it's more efficient and doesn't waste power floating batteries that are going back to work during the next shift.
The finish stage is different than EQ. It is a constant-current stage designed to fully de-sulfate the battery as part of the normal charging process instead of relying on periodic EQ charges that severely abuse the battery. During EQ the battery is held at high voltage for a long period of time. Finish charging with IUI holds the battery at a constant current and lets the voltage rise above Absorb V until it reaches the recommended finish voltage at the constant current. Then the charger shuts off.
Quote from: ChrisOlson on May 13, 2014, 09:53:19 PM
Finish charging with IUI holds the battery at a constant current and lets the voltage rise above Absorb V until it reaches the recommended finish voltage at the constant current. Then the charger shuts off.
What voltage and current is that though ?
The stage will most likely stay at a high voltage at a high current very long unless the voltage is VERY high.
I would think that battery temperature would also play a role but voltage times current together kind of do
relate to temperature after the battery has been fully charged.
Also, chargers for fork lifts etc are normally plugged into the grid so they will have a lot of energy available whereas off grid may not be so lucky.
But if it's only every so often (week or two) then it's probably OK to let them cook, but watch the battery temperature as well as voltage and current.
Quote from: boB on May 16, 2014, 06:07:14 PM
What voltage and current is that though ?
Good question... in a few battery specs that I have looked at, the Vboost, Veq and Vfinish are often the same or within a few tenths of volt. I think the whole rationale for any of these high voltages is to stir the electrolyte.
Makes me wonder about other ways to achieve the same ends with a flooded LA battery. Maybe shorter, but wider batteries that are less prone to stratification. I think with an electrolyte circulation system there is no need to exceed gassing voltage.
--vtMaps
Quote from: boB on May 16, 2014, 06:07:14 PM
What voltage and current is that though ?
For our batteries, after absorb is complete at 2.45 VPC, the recommended current for finish stage is 2% C/20 and held at that current until voltage rises to 2.58 VPC. Different battery manufacturers have different recs. For instance, US Battery recommends 2.40 VPC absorb and 3% C/20 to 2.58 VPC
(https://lh4.googleusercontent.com/-MBk3_YUr8nY/U2XlYF1eH-I/AAAAAAAAIHY/nukjueIu2tg/w640-h463-no/AVPageView+442014+85254+PM.jpg)
Quote from: ChrisOlson on May 16, 2014, 11:08:07 PM
Quote from: boB on May 16, 2014, 06:07:14 PM
What voltage and current is that though ?
For our batteries, after absorb is complete at 2.45 VPC, the recommended current for finish stage is 2% C/20 and held at that current until voltage rises to 2.58 VPC. Different battery manufacturers have different recs. For instance, US Battery recommends 2.40 VPC absorb and 3% C/20 to 2.58 VPC
OK, so in your case it's 58.8V up to 61.92 volts. That makes sense.
So, how long does it take to go from, say, 60V to 61.92 volts ?
I wouldn't think it would be there long enough to do much good but, maybe...
Quote from: boB on May 17, 2014, 03:02:49 AM
So, how long does it take to go from, say, 60V to 61.92 volts ?
I wouldn't think it would be there long enough to do much good but, maybe...
boB, it depends on depth and length of cycle. On shallow cycles like down to 20-30% DoD where the battery is being charged every day the finish stage will be done in about 20 minutes usually. If the battery has been cycled below 50% DoD and hasn't been fully charged in a week I have seen the finish stage take 2-3 hours.
BUT - our XW controllers do not do IUI correctly. They are IUU. The things have a timed 1 hour absorb stage, then they transition to finish stage with constant voltage instead of constant current. This seems to work fine, and I don't know what the difference is between using IUI as recommended, vs IUU like our XW controllers do.
I have told Schneider that instead of the timed 1 hour absorb the controller SHOULD stay at absorb voltage until current falls to 2% C/20, THEN go to 2.58VPC finish and again exit at 2% C/20. The XW algorithm (according to Schneider engineering) is designed to make maximum use of peak solar insolation during the day with the assumption that there may not be enough solar later in the day to complete the finish stage. And they may be right, as in most cases there is not going to be enough hours of solar to do a true IUI charging.
Ralph Hiesey's SC-2030 does true IUI, but I have not heard any results on how that matches available solar insolation to get the charging done before the solar runs out for the day. My gut feeling is that doing true IUI is going to be touch and go in most cases, because unlike grid-powered chargers for industrial batteries, solar does not have a flat power curve during the day. With RE charging using solar I think you have to "push" the battery as hard as feasible early while you got decent insolation to get the job done. And that seems to be the algorithm that Schneider has chosen for the XW systems.
This all being said, the one hour absorb before transition to finish voltage (with our XW system) does help keep amps down to the battery when it's still "hungry", and thereby keep its temperature and water use down for the whole charge cycle. And it makes pretty good use of available solar capacity. But without a whole bunch of experimenting with this, I don't know who's right. It's easy enough to implement IUI charging with a solar controller (according to Ralph Heisey). But whether or not it works time after time in the world of RE remains to be seen.
Hi Chris,
This may be common notation in this forum, but the way you are using "C/20" seems a little strange to me and potentially confusing to others.
To me the letter C represents the amp hour capacity of the battery or battery bank. But by itself, as characterized in Peukert's Law, that does not actually specify a characteristic of the battery. You have to add a specification of the time period at constant current over which you perform the discharge.
For RE, the standard is the 20 hour rate, and that is usually written C20, or for the typographically challenged C20 or C(20).
A current which is some fraction of the amp hour capacity of the battery would then be something like 5C or C/5.
I think you are using C/20 to indicate C20, yes?
Otherwise for a 100AH battery a finish current of 2% C/20 would be .1A instead of 2A. A very big difference!
PS: Fortunately this and most other forums do allow you to enter subscripts and superscripts, even though in some you have to go into Advanced entry mode first.
Quote from: inetdog on May 28, 2014, 05:31:03 PM
Fortunately this and most other forums ...
Hi Dave, Welcome to the Midnite forum... I'm really glad to see you here!
--vtMaps (aka mapmaker on that forum you moderate)
Quote from: vtmaps on May 28, 2014, 05:57:54 PM
Quote from: inetdog on May 28, 2014, 05:31:03 PM
Fortunately this and most other forums ...
Hi Dave, Welcome to the Midnite forum... I'm really glad to see you here!
--vtMaps (aka mapmaker on that forum you moderate)
I totally agree ! Another techie type. We need all we can get !
I was just admiring one of your posts on the NAWS forum
Discussion on this kind of stuff is great.
I would think that C/20 would naturally mean "battery capacity divided by 20" though and C20 or 20C would
mean "Capacity times 20" (algebraically speaking)
C/20 would also agree with Wikipedia...
http://en.wikipedia.org/wiki/Battery_%28electricity%29#C_rate
They have also done a bit of discussion about this in the "talk" section of that article.
I can usually tell what someone means either way.
What about those AGMs that can be charged at like, 4 times capacity of current ? How would you
designate that ?
Great to see you here !
boB
Quote from: inetdog on May 28, 2014, 05:31:03 PM
A current which is some fraction of the amp hour capacity of the battery would then be something like 5C or C/5.
I think you are using C/20 to indicate C20, yes?
Yes, I meant that to mean C divided by 20, which is the amp-hours of the battery (C) divided by 20, which gives you the 20hr rate of discharge in amps.
Ah, I see what inetdog is talking about I guess. When I am talking about ending amps of 2% of the battery capacity at the 20hr rate of discharge I should probably use something like 2% C(20hr) or similar. 2% of C/20 would be very little amps.
Quote from: ChrisOlson on May 28, 2014, 11:36:00 PM
Ah, I see what inetdog is talking about I guess. When I am talking about ending amps of 2% of the battery capacity at the 20hr rate of discharge I should probably use something like 2% C(20hr) or similar. 2% of C/20 would be very little amps.
I'm pretty sure that the 2% means 2% of the 20 hour capacity which should be close to the nameplate capacity
unless the battery is rated at some ungawdly hourly rate.
Quote from: boB on May 29, 2014, 05:58:59 PM
I'm pretty sure that the 2% means 2% of the 20 hour capacity which should be close to the nameplate capacity
unless the battery is rated at some ungawdly hourly rate.
Yeah, a person could probably just say 2% C. I don't remember seeing any battery manufacturers that provide the amp-hour rating of the battery at anything other than the 20 hour discharge rate.
Hi vtmaps,
Nice to visit.
I may not spend much time here but I will try to drop in from time to time.
Quote from: boB on May 28, 2014, 07:44:02 PM
...
What about those AGMs that can be charged at like, 4 times capacity of current ? How would you
designate that ?
Great to see you here !
boB
Thanks boB!
I would just write 4C. If I had to worry about an environment where other than 20 hour capacity was often quoted, I would write 4C
20.