Daily charging parameters

herodotus · July 2016

Hi all,

I've recently commissioned our new solar system (details in sig) and I'm a bit unsure about the results I'm getting from daily charging. When I first turned everything on a couple of weeks ago, I gave the bank a really good boil, and got all my SGs to between 1270 and 1280 - so I'm happy that the batteries started in a reasonable state.

Since then, I've been trying to tweak the settings to get things running reasonably smoothly, and I'm finding that I'm not getting my SGs high enough with any reasonable "return amps" value. Today I even tried putting the value right down to 1% of the C20 capacity - i.e. 4.7A, and my charge still only finished at an SG of 1250-60.

Up until today I've been running with return amps set to more like 2% - i.e. about 9A, and my "charged" SGs appear to have drifted down to 1240-50 across the bank, which seems on the low side.

My charging voltages are all configured as specified by Rolls - i.e. a 60V absorb (which generally translates to about 59.6 at the moment after temperature compensation)

Am I being unrealistic in my expectations? What sort of SG should I be aiming for from a daily charge? I don't want to shorten the life of the batteries by routinely overcharging them, but I also don't want to end up sulphating them by undercharging them either. What reasons might there be for the battery current dropping off before they are charged? I thought that was generally a sign of sulphation, but I'm not quite sure how these batteries could have ended up particularly sulphated given where they started from a couple of weeks ago and the level of use/charging they've had. At worst they really only should have been a tiny bit undercharged - but perhaps I'm missing something here. Should I be thinking about increasing my absorb voltage?

Cheers,

BB. · July 2016

I am not sure how well Ending Amps (EA) works with the Outback FNDC system... You may be better off just running a timer for now (you can try setting EA to 1% of battery bank 20 Hour capacity rating).

Next--You really only need to be >90% state of charge once or twice a week. And avoid going below 50% state of charge very often.

Do not try to hit 100% SOC every day (or even several times a week). That is not needed and can actually be a bit hard on the battery bank (you are, more or less, starting to equalize the battery bank--Which erodes plates, oxidizes positive plates/grid, uses water, and heats batteries up).

For equalization, once per month is usually often enough... Some battery vendors suggest equalization only if 0.015 to 0.030 difference between high and low SG cells in your bank. Getting a little bubbling/equalization helps for "tall cased" batteries to mix electrolyte (high SG electrolyte tends to sink, low tends to rise--Stratification layers are "mixed" by gassing during final charging/equalization).

There is an alternative method of running a battery bank... Some folks will run 50% to 80% state of charge and reach >90% State of Charge once per week. The batteries will not sulfate if they are being actively cycled (charged/discharged) even if below ~75% State of Charge.

-Bill

herodotus · July 2016

Hi Bill,

Thanks for the response. In ideal world, I was hoping to get the system running without me needing to intervene beyond a monthly checkup/maintenance session, where I review the charging data, record SGs, run an EQ if necessary. As such, I don't really want to be manually fiddling with settings each week to adjust how the batteries are charging.

At the moment, our house is only partially set up and we're waiting on permissions to go further. As a result, we're using a lot less power than the system is designed for. It being summer, we're going into float by mid morning most days. I guess the only way I can achieve what you're suggesting is to manually change either the end amps or the absorb timer once a week - which seems to slightly defeat the point of having spent $$$ on all the fancy outback monitoring gear, which I'd hoped would help me automate the system more...

SolarMusher · July 2016

What's your absorb time? Rolls needs a long absorb time and 2% EA is too short.
Rolls serie 4000 should be 1.265SG when at 100% SOC, 1.260 with 1% end amp is not that bad.
End current can be as low as 0.5% (and below) on new Rolls batteries, set your absorb time to 3-4hrs and check your end current before it goes to float. I would set them to 59.2V for 3hrs as you're a bit overpaneled with 70/75A to the batteries.
EQ every 2-3 monthes and you should be ok. Don't know much about the FNDC, I'm on Midnite.
A+,
Erik

BB. · July 2016

More or less, I am telling you to not worry unless you don't hit >90% SoC once or twice a week... You can adjust your settings to meet this (EA, absorb time, etc.).

Do not fret that you are not reaching >99% SoC daily/weekly. Just a once a month full charge + equalize is usually enough.

Monitoring one cell SG daily until you understand that all is working well is usually a good double check on your battery bank.

Taking a battery bank--accidentally--And under charging, is probably the number one cause of early battery bank death... But over charging is probably the number two cause for early death.

You may want to try a voltage based monitor too--Just a belt and suspender solution (easy for everyone to read, and can give you information if other parts of your system are not working/programmed correctly):

MidNite Solar MNBCM Battery Capacity Meter
http://smartgauge.co.uk/smartgauge.html

Note: I have not used either of the above meters (I am grid tied), and have only read here, a few threads, about the Midnite meter being used on the forums (and happy with the results). Just some links to look at. The Midnite is not much more than a DMM.

Be careful of "full automation"... The more automation, the more wild and wonderful ways things can fail. I am not knocking the Outback FNDC--I just do not know anything about it.

Shunt based systems have the capabilities of being more accurate and giving you more data (actual current/power/energy usage/recharging)--However, they can also "drift" in normal use (usually, they "reset" to 100% full when the battery voltage is held to Absorb for 2+ hours or so). Voltage based systems are less accurate--But can let you know if basic stuff is not happening (for example, the Midnite Meter will warn you if the battery has not been fully charged in the last 7/14 days).

Do not trust one piece of your kit's battery monitoring with off grid solar... Reading S.G. is the "gold standard" with flooded cell batteries--But even hydrometers stick/crack/fail (and nobody likes reading/logging 24+ cells on a daily cycle).

-Bill

Vic · July 2016

... DANG, just lost another Post, by erroneously trying to add a Link by Right-Clicking, instead of Ctrl Ving ...

A number of FNDC users are disappointed that it ends Absorb too soon, in error ... read this Topic on the OB Forum:
http://www.outbackpower.com/forum/viewforum.php?f=28

FWIW, Vic

herodotus · July 2016

Thanks for all the input. Some thoughts:

Sounds like I just need to chill out - I'll keep an eye on the SGs regularly but as long as I'm getting into the 1250-60 range a few times a week and then perhaps equalising once a month I should be ok.
I'll try turning the end amps down to 0 and setting the absorb time according to Rolls' recommendations and seeing what the final current is. I confess that the idea of an "absorb time" has always struck me as a bit odd. If the batteries are at 90% SOC they will surely need a shorter absorb cycle than if they start at 60%? At the moment I actually have to work at it to drop my SOC below 90% because the system is overspecified for our current loads, so a full absorb cycle almost invariably ends up being an overcharge.
I'm surprised to hear someone suggest we're overpaneled - 470ah x 60V charge voltage / 0.77 derating * 0.1 charge rate = 3662W - which is almost exactly what we have. Have I got the maths wrong here? In practice for reasons that aren't entirely clear to me yet (still some poking around to do on this) we're actually struggling to pull more than 2.5k from the panels at the moment so I don't think there's any call to drop the absorb voltage at this stage.
Vic, I don't believe we have the FNDC "float mode" problem - I read that thread previously. Charging is ending exactly when I'd expect it to based on the parameters I've configured; the "problem" is that the batteries are not responding quite as I'd expect - but by the sounds of it, my expectations may well be the problem here.
I'm not sure what an additional voltage meter is going to achieve - the system already records the battery voltage over time, but it's not enormously interesting since I hit the absorb voltage without breaking a sweat every morning anyway.
I'm not aiming for full automation - I'm aware that keeping tabs on SGs and reviewing the charging history is extremely important; but there's a big difference for me between "monitoring and tweaking" to prevent drift/compensate for inaccuracies/battery aging etc and having to manually set the charge parameters regularly every week as part of the basic operation of the system. I paid thousands of euros for a high-end system with sophisticated capabilities, and I expect it to be able to run day-to-day without manual intervention - just a little "guidance" once in a while to keep it on track.

vtmaps · July 2016

herodotus said:
I'm surprised to hear someone suggest we're overpaneled - 470ah x 60V charge voltage / 0.77 derating * 0.1 charge rate = 3662W - which is almost exactly what we have. Have I got the maths wrong here?

Math looks OK.

herodotus said:
In practice for reasons that aren't entirely clear to me yet (still some poking around to do on this) we're actually struggling to pull more than 2.5k from the panels at the moment

You have 3750 watts of array. With a 0.77 derate you should expect to see 2887 watts.

herodotus said:
I actually have to work at it to drop my SOC below 90%

Repeated shallow discharges are actually bad for the battery... lead dioxide clumps form on the positive plates. Maybe you should only charge the battery every other day.

--vtMaps

westbranch · July 2016

Solar Musher did not mention, as he has noted elsewhere before, the fact that there is a break-in period for most FLA batteries and it ,apparently, can take a few months or more to achieve, since it may take up to 50 CYCLES to finish the break-in period...
we are in a similar situation of construction plus being currently over-pamslle, and at 1680W STC.and a 24v 900Ah AGM battery, with the fridge and \net connection running 24/7 March to Nov are only using 1.8Kwh / ~10% a day and power tools only add another 500-1000Whr of consumption
so I redirect 1/3 of my panels to a standby (redundant) battery to keep it happy... More PV to put up too...
hth...

BB. · July 2016

Second quick and easy display (honey, the red light is on, anything wrong?) for family and friends, if you are not there.

-Bill

herodotus · July 2016

BB. said:

Second quick and easy display (honey, the red light is on, anything wrong?) for family and friends, if you are not there.

-Bill

Bwahahaha. Sorry, I'm just laughing at the idea that I might ever get a chance to go on holiday again

If we ever did manage to leave here for more than a day, the continued operation of the solar system would be the least of my worries, somewhere way down below all the animal care and irrigation.

If it ever happens I can always spy on things using OpticsRE anyway/write my own remote monitor and stick it on a Raspberry PI.

Does anyone have any insight into how deep a daily discharge is enough (on average) to keep the batteries healthy? If I get it down to 85% SOC most days, and then maybe once every few weeks I turn the panels off and let it drop to 50%, is that good enough?

westbranch said:

so I redirect 1/3 of my panels to a standby (redundant) battery to keep it happy... More PV to put up too...
hth...

When you say "redirect", how are you achieving that? Do you have another charge controller?

I do have each string of the array on a separate breaker, so I guess I could just turn off 1/3rd of the array, but I'm not sure how helpful that would really be. The problem is not really that we're over-panelled, but that the whole system is too big. If I turn off part of the array I'm not really addressing the problem that the batteries aren't getting cycled deeply enough by our usage, I'm just slowing the recharge rate.

Probably the best thing is for me to just flip the main panel breaker every couple of days to take the batteries a bit lower... or to get on with buying some electric water heating to dump more of that free energy somewhere useful!

Cheers,

herodotus · July 2016

vtmaps said:

herodotus said:
In practice for reasons that aren't entirely clear to me yet (still some poking around to do on this) we're actually struggling to pull more than 2.5k from the panels at the moment
You have 3750 watts of array. With a 0.77 derate you should expect to see 2887 watts.

Yeah. And the 0.77 derate is obviously just an average for use in specifying a system. At the moment I'm hunting around for explanations of where *specifically* I'm losing all of that extra right now. I can account for some of it with temperature (although lacking an IR thermometer I'm not sure exactly how much I should really expect to be losing there), panel tilt (I'm at 40 degrees and solar normal is about 13 here at this time of year) and a bit of cable loss (~1.5%), but unless my cell temperatures are ~75C (nominal is 47C at 20C ambient with a light breeze) there's something else going on... but that's another question that I'm working on separately!

SolarMusher · July 2016

herodotus said:

Thanks for all the input. Some thoughts:
Sounds like I just need to chill out - I'll keep an eye on the SGs regularly but as long as I'm getting into the 1250-60 range a few times a week and then perhaps equalising once a month I should be ok.
I'll try turning the end amps down to 0 and setting the absorb time according to Rolls' recommendations and seeing what the final current is. I confess that the idea of an "absorb time" has always struck me as a bit odd. If the batteries are at 90% SOC they will surely need a shorter absorb cycle than if they start at 60%? At the moment I actually have to work at it to drop my SOC below 90% because the system is overspecified for our current loads, so a full absorb cycle almost invariably ends up being an overcharge.
I'm surprised to hear someone suggest we're overpaneled - 470ah x 60V charge voltage / 0.77 derating * 0.1 charge rate = 3662W - which is almost exactly what we have. Have I got the maths wrong here? In practice for reasons that aren't entirely clear to me yet (still some poking around to do on this) we're actually struggling to pull more than 2.5k from the panels at the moment so I don't think there's any call to drop the absorb voltage at this stage.
Vic, I don't believe we have the FNDC "float mode" problem - I read that thread previously. Charging is ending exactly when I'd expect it to based on the parameters I've configured; the "problem" is that the batteries are not responding quite as I'd expect - but by the sounds of it, my expectations may well be the problem here.
I'm not sure what an additional voltage meter is going to achieve - the system already records the battery voltage over time, but it's not enormously interesting since I hit the absorb voltage without breaking a sweat every morning anyway.
I'm not aiming for full automation - I'm aware that keeping tabs on SGs and reviewing the charging history is extremely important; but there's a big difference for me between "monitoring and tweaking" to prevent drift/compensate for inaccuracies/battery aging etc and having to manually set the charge parameters regularly every week as part of the basic operation of the system. I paid thousands of euros for a high-end system with sophisticated capabilities, and I expect it to be able to run day-to-day without manual intervention - just a little "guidance" once in a while to keep it on track.

2) The last time I talked with Steve from Rolls, he told me that for residential systems a full absorb cycle is finally a "matter of water" only.
As Westbranch said, new batteries have a break-in period and you need to be patient for the first monthes of use. I would be curious to know where your real end current is. A common mistake is to set your controller to 1% EA with new batteries, if you take the time to check your end current, you will note that it could be far below when new. My Rolls bank is at 0.3% right now and is 6 monthes old (my old interstate bank was around 1% before it began to die). To me, end current is still the best way to avoid overcharging with low/daily discharges (90% SOC) in summer but it needs to be really accurate and I'm in doubt that the Outback can do it well. 60V is in the high range and you can have the same result with lower charge voltages and longer absorb time which would be better for your batteries in time. Anyway they're yours.
3) I'm in Canada and this 0.77 rule does apply to me only 2 monthes a year, I can see frequently 3kw output from my old 3.2kw array (roof mounted) in summer and more than 3.2kw for the rest of the year. It's all depend on your location and system design. One of my clients is doing 3.5kw regularly with his 3kw pole mounted array.
A+
Erik

vtmaps · July 2016

herodotus said:

And the 0.77 derate is obviously just an average for use in specifying a system. At the moment I'm hunting around for explanations of where *specifically* I'm losing all of that extra right now. I can account for some of it with temperature (although lacking an IR thermometer I'm not sure exactly how much I should really expect to be losing there), panel tilt (I'm at 40 degrees and solar normal is about 13 here at this time of year) and a bit of cable loss (~1.5%), but unless my cell temperatures are ~75C (nominal is 47C at 20C ambient with a light breeze) there's something else going on... but that's another question that I'm working on separately!

The 0.77 also includes controller losses.

--vtMaps

BB. · July 2016

Solar panels are rated at "room temperature" under a "flash tester" (sunlight for a very short time to electrically test the panels at the end of production). In real life, Vmp (voltage maximum power) falls as the cell temperatures rise. And, on a warm day/sunny/roof, the panels will be at ~81% of Rated Vmp @ Standard Conditions (also include some dust on the panels and wiring loss). And assume that the charge controller is ~95% efficiency, the overall average output (from rated panel Pmp=Vmp*Imp under full sun) will be:

0.81 * 0.95 = 0.77 overall "average" maximum power

In cold weather, you can see more. At higher elevations you can get more power too (less haze). If you have below freezing daytime temperatures during winter, better output too. But, for a quick set of calculations, we use this numbers to get a system that will (for most people) perform to predicted output over most of the year.

-Bill

herodotus · July 2016

2) The last time I talked with Steve from Rolls, he told me that for residential systems a full absorb cycle is finally a "matter of water" only.
As Westbranch said, new batteries have a break-in period and you need to be patient for the first monthes of use. I would be curious to know where your real end current is. A common mistake is to set your controller to 1% EA with new batteries, if you take the time to check your end current, you will note that it could be far below when new. My Rolls bank is at 0.3% right now and is 6 monthes old (my old interstate bank was around 1% before it began to die). To me, end current is still the best way to avoid overcharging with low/daily discharges (90% SOC) in summer but it needs to be really accurate and I'm in doubt that the Outback can do it well. 60V is in the high range and you can have the same result with lower charge voltages and longer absorb time which would be better for your batteries in time. Anyway they're yours.

What do you mean "a matter of water only"? I don't really understand you, sorry. :-/

I'm not sure why the Outback system would be particularly inaccurate in this regard? It's measuring using two shunts (one on the inverter and one on the CC) and a FlexNet DC (dedicated battery monitor); as far as I am aware, the resolution of the voltage measurement is pretty high. There are various known problems with the FNDC but as far as I am aware the accuracy of its current measurements isn't one of them.

I chose 60V because that's what Rolls specify for off-grid systems; are you suggesting a lower voltage because I'm not cycling them very deeply at the moment?

herodotus · July 2016

Thanks to those who have commented on the lower output problem. I understand the factors involved - but at the moment I'm only seeing 66% of nominal and I can't make the numbers add up, so more digging is called for. I have friends locally who are currently seeing more like 75-80% with similarly configured arrays. In theory the Vmpp of my panels should be about 93V, but the CC is settling on about 70V at solar noon most days. According to Munchen's specs, Vmpp drops by 0.35% for every degree C that the cells rise above 25; and the cells should operate at about 47C on a 20C day with a light breeze.

I'm losing about a volt on the round trip from the panels to the CC which puts the panels at 71V, but that's still 22V lower than the ideal. Accounting for that with temperature alone would put the cells at nearly 90C which seems unlikely. Are there any other factors that would reduce Vmpp? I had a cursory poke around with a voltmeter the other day and couldn't see any evidence of any obvious losses across connections/cabling within the array (it's all put together properly with MC4s), but this is my main target for further investigation at the moment.

Interestingly, Voc is 97.2 vs a nominal of 111. The thermal coefficient of Voc is 0.33% / degree, which would put the cells at 62.5C, which is a bit high but a lot more believable then 90C. In the absence of any other possible reasons (what other reasons are there for Vmpp to move dramatically other than temperature?), it *sounds* like I'm looking for a stray resistance somewhere - e.g. bad connection. But so far I haven't found anything untoward.

SolarMusher · July 2016

herodotus said:

2) The last time I talked with Steve from Rolls, he told me that for residential systems a full absorb cycle is finally a "matter of water" only.
As Westbranch said, new batteries have a break-in period and you need to be patient for the first monthes of use. I would be curious to know where your real end current is. A common mistake is to set your controller to 1% EA with new batteries, if you take the time to check your end current, you will note that it could be far below when new. My Rolls bank is at 0.3% right now and is 6 monthes old (my old interstate bank was around 1% before it began to die). To me, end current is still the best way to avoid overcharging with low/daily discharges (90% SOC) in summer but it needs to be really accurate and I'm in doubt that the Outback can do it well. 60V is in the high range and you can have the same result with lower charge voltages and longer absorb time which would be better for your batteries in time. Anyway they're yours.

What do you mean "a matter of water only"? I don't really understand you, sorry. :-/

I'm not sure why the Outback system would be particularly inaccurate in this regard? It's measuring using two shunts (one on the inverter and one on the CC) and a FlexNet DC (dedicated battery monitor); as far as I am aware, the resolution of the voltage measurement is pretty high. There are various known problems with the FNDC but as far as I am aware the accuracy of its current measurements isn't one of them.

I chose 60V because that's what Rolls specify for off-grid systems; are you suggesting a lower voltage because I'm not cycling them very deeply at the moment?

You are right in saying that low discharges need a shorter absorb time than deeper ones, it was also one of my concerns. What Steve said is that in your case for example, it doesn't matter if your absorb time is a bit too long because of low discharges (90% SOC), it just uses a bit more water, that's it. You should not worry about that as long as your voltage is correct and your current is pretty small at the end of the absorb (0.5-1%). Rolls have modified their specifications recently, one year ago absorb voltage was 58.8V for temperature compensated systems. Once again, I don't know where you are located and what are your loads, but with a 3750 watts array, your 470Ah bank shouldn't be discharged too deeply day by day and a lower voltage/longer absorb would be better. If you follow 470Ah : 70A x 0.42,
I think that a 3hrs/59.2V absorb time should be enough to get your SG to 1.265 (you don't want this SG to go higher for longevity), no matter how deep they are discharged.
I would keep this 60V for really hard cycled systems and/or for winter when you'll need to charge as much as you can in short days.
A+
Erik

BB. · July 2016

Charging a lead acid battery near 100% state of charge is taking most of the current and generating Hydrogen+Oxygen+Heat... So, trying to get >90% state of charge daily just causes, mostly, loss of water (very little extra charge capacity and does not help the battery last longer). So, instead of needing to add some water ~every two months, you could be adding a lot of water every 1 month or less (cost of distilled water).

In practice, when charging a lead acid battery bank and gassing--Oxygen gas is produced by electrolysis on the positive plates--Causing oxidation of the plates and support grid. In addition, gassing can cause plate erosion too. Lastly, heat is produced during electrolysis--A good rule of thumb is for every 10C (18F) above room temperature, the battery will age 2x faster. Even a 2% rate of charge (basically equalization voltage) can cause the battery bank to run hot--So, overall, I would humbly suggest that folks avoid trying to reach >>90% state of charge as a matter.

What ratings of the Vmp/Imp ratings of the panels and what is the series/parallel configuration of the array?

It sort of sounds like you have a bad panel??? The array voltages do not make sense. It is possible that the MPPT controller is miss-programed or failed--But I don't think that is the problem.

-Bill

SolarMusher · July 2016

herodotus said:

Thanks to those who have commented on the lower output problem. I understand the factors involved - but at the moment I'm only seeing 66% of nominal and I can't make the numbers add up, so more digging is called for. I have friends locally who are currently seeing more like 75-80% with similarly configured arrays. In theory the Vmpp of my panels should be about 93V, but the CC is settling on about 70V at solar noon most days. According to Munchen's specs, Vmpp drops by 0.35% for every degree C that the cells rise above 25; and the cells should operate at about 47C on a 20C day with a light breeze.

I'm losing about a volt on the round trip from the panels to the CC which puts the panels at 71V, but that's still 22V lower than the ideal. Accounting for that with temperature alone would put the cells at nearly 90C which seems unlikely. Are there any other factors that would reduce Vmpp? I had a cursory poke around with a voltmeter the other day and couldn't see any evidence of any obvious losses across connections/cabling within the array (it's all put together properly with MC4s), but this is my main target for further investigation at the moment.

Interestingly, Voc is 97.2 vs a nominal of 111. The thermal coefficient of Voc is 0.33% / degree, which would put the cells at 62.5C, which is a bit high but a lot more believable then 90C. In the absence of any other possible reasons (what other reasons are there for Vmpp to move dramatically other than temperature?), it *sounds* like I'm looking for a stray resistance somewhere - e.g. bad connection. But so far I haven't found anything untoward.

Have you shut off the array and tested voltage string by string to find a culprit?

westbranch · July 2016

yes I do...When you say "redirect", how are you achieving that? Do you have another charge controller?

I also have a marine battery selection switch and some other rewiring that allows me to move it to either battery in less than a minute

herodotus · July 2016

Ok, so I think:

Theoretically speaking, I think I should be setting my end amps to a lower level, and probably bumping my absorb voltage down. A full absorb for me is probably about 4 hours (470/47A * 0.42). This accords with what Erik has been saying.
However, I hear what Bill is saying, and have heard other experts saying similar things; really I don't *want* to be charging the batteries right up all the time. So I'm in a bit of a quandary; I want the system to stop short of charging fully every day; but I also don't want to lie to the battery monitor and skew my data. So I guess what I probably need to do is to leave the return amps settings where they are, but tweak the absorb time to curtail the charge until we've got some bigger loads that will slow things down more usefully. Periodically I can then whack the absorb time up to 8 hours or something and let the system charge the batteries until the end amps reaches the appropriate level. It's not as automated as I'd like, but then again, I really don't want to be buying new batteries for a *long* time, so I guess I just have to suck that up.
On the underperforming array: I think it's unlikely to be a problem with the charge controller - I've watched it tracking and I can see that it is picking the maximum output that it finds. I will try and play with some settings but I'd be surprised if it makes any difference. The array is 5 strings of 3 250W panels. Spec sheet is here. I have done a bit of playing with turning individual strings off, but so far I haven't found anything particularly enlightening by doing so. I'm pretty sure that the problem is that the voltage is lower than it ought to be - I just need to find out why! I'll do some more systematic investigation tomorrow - so far I've been a little unstructured in my debugging!

BB. · July 2016

Backing off on set points (absorb, EA, timers) so that you get >90% (via SG) is good. I believe that newer Midnite firmware supports a "don't to a full recharge cycle until battery is taken to under 80% state of charge--Or whatever you program).

And with the 250 Watt panels (your link):

@ 25C	Per panel	Per 3x string	Est. @ 47C
Module efficiency	15.4
Voltage at Pmax	31.02	93.06	85.89438
Current at Pmax	8.06	24.18
Open circuit voltage	36.99	110.97	102.42531
Short circuit current	8.62	25.86

Use your current clamp meter to measure per string current for each 3x panel string... Nice thing about having three identical strings of panels, it usually is very easy to see if one string is under performing the other two (You can also do a similar test, if you have 3x circuit breakers (one per string), just turn on one string at a time and see what the Vmp-array and Imp-array readings are).

-Bill

Vic · July 2016

Herodotus,

You mentioned in the first Post, " ... My charging voltages are all configured as specified by Rolls - i.e. a 60V absorb (which generally translates to about 59.6 at the moment after temperature compensation) ... "

Unless Surrette just changed the recommended Absorb voltage (Vabs), it should be 58.8 (2.45 VPC).

It is good that you know that the FNDC is not causing the issue, as many seem disappointed with the FNDC, generally having lower than expected SGs

The Surrette banks here are 11 years, or so old. Had previously been running at about 0.93 % of actual 20-hour Capacity, with Vabs at about 57.5-ish volts. In the past nine months or so, have needed to increase the Vabs to about 58.4 V on one bank, and, now up to 58.8 V on the other largish bank. EA is now up to 1.4% of C. (am using a 5% reduced C, as C is speced for 1.280 SG, not the actual SG of 1.265).

So, you have actually watched or looked at log charges to see that you are actually getting down to the EA that you have set in the system??

The Classic CC does have in the latest FW versions, the ability to Skip Charge days, where the number of days to be skipped is entered by the user. On Skip days, the CC begins in FloatMPPT, and stays in Float all day, until the day after the Skip number has been satisfied. We Skip three days on both of the larger systems here, and recharge on the fourth day ... FWIW. Vic

SolarMusher · July 2016

Hey Vic!
Rolls has changed its absorb voltage for 60V at 25°C, not a small step!
Maybe, too much warranty issues at lower voltages.
http://support.rollsbattery.com/support/solutions/articles/428-state-of-charge-charging-flooded-lead-acid-batteries
A+
Erik

vtmaps · July 2016

SolarMusher said:

Rolls have modified their specifications recently, one year ago absorb voltage was 58.8V for temperature compensated systems.

Vic said:

Unless Surrette just changed the recommended Absorb voltage (Vabs), it should be 58.8 (2.45 VPC).

Herodotus, I may have missed it in this thread, but just how discharged is your battery at solar noon when you find lower than expected voltage from your array?

--vtMaps

herodotus · July 2016

Herodotus, I may have missed it in this thread, but just how discharged is your battery at solar noon when you find lower than expected voltage from your array?

--vtMaps

Hi,

So I've tested this two different ways - a couple of times just running a bunch of appliances while in float to see how much I can pull in from the array, and on another occasion turning off the array for a day or so to get the bank down to a level where it needed a decent bulk charge (I'm afraid I'm not sure what the exact SOC % was) and monitoring then. Obviously the voltage I'm talking about is the input voltage to the CC rather than the battery voltage...

Either way, the results are the same - I can't seem to pull more than about 2.5k max from the panels.

Cheers,

herodotus · July 2016

Vic said:
(am using a 5% reduced C, as C is speced for 1.280 SG, not the actual SG of 1.265).

Hmm, that's interesting. I didn't think of discounting the value of C in my calculations according to the target SG. That makes sense.

So, you have actually watched or looked at log charges to see that you are actually getting down to the EA that you have set in the system??

Yeah, I've watched it get down to the return amps value that I've configured for the FNDC (CC End Amps is set to 0 to avoid conflicts) and then terminate the charge. In fact, I've fiddled with the value and bumped it back into absorb and then watched it charge a bit more until it gets down to the new value. All seems to be working fine

The Classic CC does have in the latest FW versions, the ability to Skip Charge days, where the number of days to be skipped is entered by the user. On Skip days, the CC begins in FloatMPPT, and stays in Float all day, until the day after the Skip number has been satisfied. We Skip three days on both of the larger systems here, and recharge on the fourth day ... FWIW. Vic

Interesting, I don't think that feature exists on the Outback FM80, sadly. That would be super useful. I wonder if it's possible for me to program that behaviour from a remote PC (I know the OpticsRE platform can control various behaviours of the system, so perhaps it's possible...)

Vic · July 2016

SolarMusher said:

Hey Vic!
Rolls has changed its absorb voltage for 60V at 25°C, not a small step!
Maybe, too much warranty issues at lower voltages.
http://support.rollsbattery.com/support/solutions/articles/428-state-of-charge-charging-flooded-lead-acid-batteries
A+
Erik

Lovely, my mouse touched the Quote above, and now everything looks like it is inside the Quote ...   love it ... perhaps need to Delete the Post and start over ...

Here are Vic's comments:

Hey Erik,   WOW, news to me.   Downloaded the "latest" Battery Manual from Surrette in May, 2016, and this new regime was not there.   Great that Surrette is doing a very good job, updating their Docs,   believe that this mostly under Steve Higgins' direction. Very good!   Hope that they will soon place some Revision Control on the Battery Manual, so users can/will know when there have been some changes, or at least know when a previously downloaded Manual has been superseded.

Thanks.   We do not really do PSOC, as, we really do try to fully charge the batteries every four days ...

OK thanks for the news,   Vic

Vic · July 2016

And, hero..,

Good that EA is actually working on your system, when you want it to ... perhaps OB has actually fixed a few of those annoying FNDC bugs, let's hope.

And am sorry that I misstated the Surrette recommendations for Vabs ... we do not do real PSOC, but sure have never needed anything close to 60 V Absorb.

And also agree with Erik (believe it was), that 30 - 50, or even more cycles are needed for these batteries to build full Capacity and stabilize. These cycles probably need to be down to about 75% SOC, or even a bit lower (as measured with your Hydrometer).

Forget, you DO have a Hydrometer, or Refractometer don't you ??

Have Fun with the new system, Vic

herodotus · July 2016

Hey Vic,

Yeah, I have a hydrovolt hydrometer that I have been using to measure SGs. I did the whole bank a couple of times at the start and now I'm testing a couple of test cells each time. I've got my panels switched off for the moment so I can get a good deep cycle on the batteries. The FNDC battery monitor will probably wind up reading about 85% SOC, but I suspect the SGs will say otherwise - presumably because my batteries are actually lower capacity right now than they will be once they are "broken in".

Cheers,,

Daily charging parameters

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