Sunny Island/Rolls 530-S charging question

Cariboocoot · November 2012

Re: Sunny Island/Rolls 530-S charging question

palausystem wrote: »

So if skipping bulk/absorb for a few days is not good on an off-grid, what is the best scenario? Full charge it every day? Why does the Sunny Island charging scenario make it better for grid-tied?

In its native form the SI would keep the batteries in Float waiting for a power outage. Under those circumstances it isn't necessary to even try Bulk/Absorb every day because it's not expecting any power to be used. Off-grid expects a daily discharge and recovery, so doing Bulk/Absorb/Float every day is more or less standard. Two different usage expectations result in two different recharging scenarios.

I do have the shunt,tri-metric, but it's also based on Ah capacity...but I think it might have a setting for checking cumulative Ah in and out, not sure...the hydrometer will be coming out more often now.

At this point I would rely only on a hydrometer reading to determine SOC. It's as close to infallible as you can get, save perhaps a refractometer. If there's anything wrong with capacity or charging efficiency the Trimetric will be inaccurate.

What is the 0.52 efficiency figure? Is that temperature compensation and inverter efficiency and...?

Over-all system efficiency from nameplate rating of panels to end AC power: 3000 Watts * 4 hours good equivalent sun * 0.52 efficiency = 6240 Watt hours per day. You lose a lot because of having batteries at all; once they are charged the panels could harvest more energy but there's no place for it to go unless you have "opportunity loads" available.

So as far as the 12v Iota charger goes, how would you do the EQ with that? Two batts at a time I guess? The maximum amp safe-limit for the S530 is 44. I think Rolls actually recommended 30 amps for EQ So would I get a 12v 75 amp charger and do two 6v batteries at once? Would that work?

It's a pain, but you'd have to detach half the batteries (one string of 8 ). Then you take them two at a time (12 Volt sections) and charge 'em. This is in one way better than a whole string EQ because it does not subject 'good' cells to as much stress. By the same token it can't even out the lot, but it can bring them closer so that a full string EQ will work better.

EQ does not depend on Amps, but charging does. If Rolls recommends no more than 44 Amps to the battery (understandable) then the 45 Amp Iota 12 Volt would definitely charge a pair of these in series. If they don't need that much current they shouldn't be taking it (batteries are to a degree self-limiting in this respect). The EQ is a matter of holding the higher than Absorb Voltage on them to try and force as much sulphor off the plates and back into the electrolyte as possible. Again the hydrometer is invaluable here as it will tell you the condition before you EQ, show if it is having any affect, and indicate when things are no longer improving. At that point it's time to quit: you can do nothing more. If the SG isn't proper then, it never will be.

You were right to readjust the charge Voltages to Surrette's recommended levels. Now it's a question of "were you in time to save them?"

Photowhit · November 2012

Re: Sunny Island/Rolls 530-S charging question

niel wrote: »

i think we agree on the batteries as suspect, but ripple is the artificial induced ac (actually pulsed dc) by a huge variable load to an inverter that is straining the batteries which would be undersized for the loads for whatever reason. sulfation can lower the battery bank capacity that would create large ripples under large loads and throw things off, but i think we agree that reduced capacity alone may be a problem even if not severe enough to cause the ripples to be too large for the inverter.

Thanks Niel,

Curious if the SOC readings you've been giving us are from the Trimetric?

stephendv · November 2012

Re: Sunny Island/Rolls 530-S charging question

palausystem wrote: »

So if skipping bulk/absorb for a few days is not good on an off-grid, what is the best scenario? Full charge it every day? Why does the Sunny Island charging scenario make it better for grid-tied?

The Sunny Island was designed from the start to be a 100% off-grid inverter. And this charging method they use is unique in the industry and was designed to prolong battery life. In fact, Midnite solar is working on modifying their off-grid charge controller so that it can integrate with the Sunny Island and follow the SI's charging pattern. Here is a brochure on why they've chosen to use this charging method: http://files.sma.de/dl/3491/TECHBATT-AEN114414.pdf

Just because most other chargers use a less sophisticated charging algorithm which everyone is familiar with, doesn't mean it's the best one. This is the main reason I was considering switching over to a sunny boy for my system, so that I didn't have to use the "dumb" charging algorithm of my charge controller and could instead use this better system implemented in the SI.

One reason the SoC of the SI could be out is that it isn't reaching the full charge characteristics so it's error is increasing. In the battery section it should also give you a SoC error %, check that to see whether it's becoming too large. If the battery never completes the "full" charging parameters then the SoC meter will never be reset to 100% and the error in SoC can start to accumulate.

Another reason could be that the battery size was not entered correctly in the first place. You can also check this in the battery settings menu, the size should be set in C10 not C20. So your S530s should be set as a 680Ah battery.

I also see sudden changes in my SoC every now and then, but not huge jumps. If the two things I mentioned above are set correctly and your SoC error isn't too big then it may be worth contacting SMA directly. You could also use a hydrometer to check the batteries actual state of charge and then correlate that with the SoC on the SI to see what the real difference is.
Here's a graph showing my SoC and the SoC error as a blue band around the soc value and a sudden dip from 91 to 89%.
Attachment not found.

palausystem wrote: »

So as far as the 12v Iota charger goes, how would you do the EQ with that? Two batts at a time I guess? The maximum amp safe-limit for the S530 is 44. I think Rolls actually recommended 30 amps for EQ So would I get a 12v 75 amp charger and do two 6v batteries at once? Would that work?

What's the point of buying another charger?? You already have an extremely sophisticated 100A charger available in the SI. Rolls recommend a maximum of 15% charge during bulk charging, which is 120A for your battery as a maximum for both your strings. 100A is more than enough.

stephendv · November 2012

Re: Sunny Island/Rolls 530-S charging question

The best way to set the Absorb time for a "full" charge is to do it experimentally. Set the time to something very long, e.g. 10 hours, then on a good day, start the gen and let it get up to absorb voltage early in the morning. Then every 30 minutes write down the following 4 values:
- Time
- The SG of the pilot cell (just pick a cell and keep measuring that one)
- The amps going into the battery, which you'll see in the battery menu
- The SoC of the SI.

When the SG stops changing over a 2 hour period, then the batteries are fully charged. Now go through the list of values you have and see when was the earliest you reached that SG value. That is your new "full" absorb time, and you also know what the charging amps going into the battery at that time are. This is useful as a fallback value to determine when your batts are at 100% without having to measure the SG. You can now also check how far off the SI SoC measurement is and whether this falls within the SoC error % stated in the battery menu.

vtmaps · November 2012

Re: Sunny Island/Rolls 530-S charging question

Cariboocoot wrote: »

6kW hours AC daily is about 140 Amp hours @ 48 Volts. That's a 280 Amp hour 48 Volt battery bank minimum. On 400 Amp hours that would be only 35% DOD.
You don't really need 800 Amp hours of battery.

Part of your problem (with the SOC jumping around) may be having two parallel battery strings. As the strings diverge (with age and use) in their electrical characteristics, you get to the point where, after charging, one string may be discharging into the other. A DC current clamp meter may help you diagnose that, but the solution is to use just one string.
read: http://forum.solar-electric.com/showthread.php?14674

--vtMaps

Cariboocoot · November 2012

Re: Sunny Island/Rolls 530-S charging question

The point of getting the stand-alone charger is that this so-called "better" charging system in the SI is not working for him and he needs to try and salvage the batteries before they are completely scrap if possible. Since this system obviously does not work as it needs to there is no point in claiming it is good when it isn't. Repeatedly telling someone something that does not work is all right is not helpful.

stephendv · November 2012

Re: Sunny Island/Rolls 530-S charging question

Cariboocoot wrote: »

The point of getting the stand-alone charger is that this so-called "better" charging system in the SI is not working for him and he needs to try and salvage the batteries before they are completely scrap if possible. Since this system obviously does not work as it needs to there is no point in claiming it is good when it isn't.

Firstly, lets establish what his problem actually is. So far the only thing he has reported is a sudden jump in SoC as reported by the Sunny Island. This could be the result of undercharging or it could be the result of problem with SI's soc measurement. Lets see if he can first confirm that the battery size is correctly set in the SI, or if the SoC measurement is out because it never reaches the full charging set points.

Secondly, if it is actually the SI's charging algorithm that is the problem then it can simply be changed by setting the "full" charge interval to 1 day. Then it will act just like every other charger on the market, (with consequent battery over or undercharging).

It's equally unhelpful to say that his system is 'crackers' and that he should go out and buy more equipment or sell what he has just because it's unfamiliar to you.

Photowhit · November 2012

Re: Sunny Island/Rolls 530-S charging question

Before you get to heated, we could use the information from his Trimetric meter for some good info, like amps in and out. It's a pretty simple install so even if someone suspects the installer, it sould be installed correctly...

Cariboocoot · November 2012

Re: Sunny Island/Rolls 530-S charging question

Photowhit wrote: »

Before you guys get to heated, we could all use info from the trimetric, I believe he should be able to give us Amps in and out of the battery, might be nice to know!

At this point I wouldn't trust the info from the Trimetric. They rely on programming being fed accurate info. If the battery capacity has diminished and/or the efficiency is wrong then the Trimetric will be reporting incorrectly.

As I said before, the hydrometer is your friend. The first thing that has to be done is the batteries check and salvaged.

Then we can worry about correcting the charge problem as much as possible.

As I've already pointed out, this system's array is marginal for the amount of power used daily and undersized for charging that much battery bank given the OP's location. Ignoring these facts isn't going to help.

He's spent a lot of money on this system and it's a shame the installer clearly didn't know what he was doing. None of the installer members on this forum would have walked away without knowing it was working properly. Certainly none of them would have had to be dismissed from the job!

I have never said there's anything wrong with SMA equipment. But this system is crackers; it is not suited for the job it's trying to do. The best we can do now is help him pick up the pieces and try to get it to work. That starts with the battery bank. If it is no longer viable no amount of fiddling with the controls will help.

palausystem · November 2012

Re: Sunny Island/Rolls 530-S charging question

Another reason could be that the battery size was not entered correctly in the first place. You can also check this in the battery settings menu, the size should be set in C10 not C20. So your S530s should be set as a 680Ah battery.

Where did you get that information? I have them set at the C/20 (800Ah)

What's the point of buying another charger?? You already have an extremely sophisticated 100A charger available in the SI. Rolls recommend a maximum of 15% charge during bulk charging, which is 120A for your battery as a maximum for both your strings. 100A is more than enough.

Are you talking about the Iota 12v charger suggestion? I think that was just about being able to do an aggressive EQ on a couple batteries at a time rather than the whole string which might work better in some cases if highly sulfated? Dunno.

Ok, so let me try to narrow down what the issues seem to be:
1. - jumps and drops in SI meter soc % and faster than usual battery drain. I cured this at least temporarily by doing a good full charge. Last year I cured it by doing a proper EQ It hasn't happened in days. I'll be doing a proper EQ this weekend.

2.Why did things get screwed up? The absorption time was set too low. The voltages were set too high. Proper EQ's didn't take place. The PV capacity is on the low side for this size battery so extra vigilance needed. I need to up the absorption times, EQ more frequently, test the cells, etc.

3.There is some talk about making sure the EQ is effective, and so I will monitor the SG during EQ to see how far I am able to improve things. I know last time I did the EQ, the SG still wasn't up to snuff after 10 hrs per string, so I will either have to do it longer, or consider cabricoot's method of a 12 volt charger on 2 batteries at a time

So I wouldn't go so far as to say the SI isn't working for us. If the basic absorption time has been set at 2hrs instead of at 6 hrs or more, then you can't blame that on the SI. The batteries have been abused from improper charge settings on the installer's part and ignorance on my part.

Thanks, stephendv for the link, I'll check that out.
This just in from SMA: "For the US inverters (Sunny Islands ending in "U") the C20 rate is used. For all other SIs, the C10 rate is used."
Darn.

I appreciate everyone's input and will post back after the EQ

Cheers!

stephendv · November 2012

Re: Sunny Island/Rolls 530-S charging question

palausystem wrote: »

This just in from SMA: "For the US inverters (Sunny Islands ending in "U") the C20 rate is used. For all other SIs, the C10 rate is used."

Aha! Good catch, mine uses the C10.

palausystem · November 2012

Re: Sunny Island/Rolls 530-S charging question

Stephendv,
sounds like you have some experience with the Sunny Island...
"Boost" mode eludes me. I'm waiting for a recommendation from Rolls on what to set the duration for. I don't know if they really know either. I wonder if the default settings in the SI could give me a clue: for FLA's: Boost - 2.55v for 90 min. Full - 2.5v for 5 hrs. That's a difference of 2/3rds. So, the Rolls charging formula says that my ideal Full absorb time would be 8.4 hrs of PV. Subtract 2/3 and that would be about 3 hrs for Boost. How does that logic sound?
And regarding those default voltage settings: I'm wondering why the .05v higher for Boost. From Rolls there's just the generic 2.4v for Bulk/absorption.
I understand in a very limited sense that Boost is there to prevent overcharging...but their literature still seems vague.

Please ignore the attachment - I don't know how to delete it

[I do; that's what we're here for. ]

palausystem · November 2012

Re: Sunny Island/Rolls 530-S charging question

This just in from Rolls tech re my question about Boost absorb time:

For the Sunny Island because the SI looks at return current if you leave it in the default settings the SI will "learn" the correct time and adjust the time for every single charge depending on the current SOC of the battery.

That's just not true. You have to manually set the Boost time. Where did he get that?! Ugh.

stephendv · November 2012

Re: Sunny Island/Rolls 530-S charging question

This is how I understand the charging works, it's not all 100% clear to me, because as you've found they are a bit vague about it:

Float: If SoC is above 80%(ish) then charger stays in float mode all day. There appears to be a time limit to this, so it'll do a boost after 3-4 consecutive float days (I don't know what the exact number for this is). The point of this is to not overcharge the batts if they're already nearly full.
Boost: On good solar days, you could be doing a boost charge every 4 days. On bad days, maybe every second day. The main purpose of this is to bring the battery up to 90+% SoC. If the battery has been floating for a few days without reaching the gassing voltage (around 2.37V) then stratification of the electrolyte is more of an issue. I'd speculate that this could be reason why the default setting is higher than 2.4V, so that it causes some good gassing in the battery to break the stratification and charges in a short amount of time.
Full: The interval programmed overrides all other settings, so if it's 1 day interval then it'll do a full charge every day. With the previous two settings you could have the battery hovering at 90+% SoC for a few days, this setting ensures that they reach 100% SoC. This will mean that you overcharge them slightly, but it doesn't happen every day so not as bad as a daily overcharge to ensure 100% SoC. Open to debate how often this should be performed. Victron have released a paper where they suggest once a month: http://www.victronenergy.com/orderbook/ seems a bit long to me, but maybe rolls have a better idea.
EQ: Also overrides other settings, think it'll override Full as well. Depending on what values you used for boost and full, you might be able to extend the EQ interval. E.g. if boost takes the batts up to 2.5V every 4 days and full ensures a full charge (i.e. an overcharge) then IMO there's less need for frequent EQ. If however you boost at 2.4V and you do a full charge at 2.4V then you might need to do an EQ more often to mix electrolyte and correct cell imbalance.

If you have Rolls tech support handy then it might be easier for them to answer more non-SI-specific questions, I'd definitely be interested in what they suggest, e.g.:
The more open ended question:
- My charger does a float charge if SoC is above 80% by default. It then supports 3 independent constant voltage charge settings: "boost", "full" and "eq". Every 2-4 days it does a "boost" charge, the 2-4 day interval is not adjustable. At adjustable intervals it can do a "full" and an "EQ" charge. All of these constant voltage charging modes ("boost","full" and "eq") can have their own voltage and time limits. What do you recommend for each of these values for the longest battery life?

Or you could go with more leading questions:

- If the batteries have been under float charge for 3 days at > 80% SoC, how long and at what voltage would you suggest the absorb charge should be on day 4?
- If the batteries are kept under float charge for 3 days and then boosted to > 90% SoC every 4 days, how often would I need to bring them to 100% SoC?
- During this "100% SoC" charging process, what do you recommend for absorb voltage and time?
- If I could program the charger to do 2 different types of EQ cycles (independent absorb voltage and time) at 2 different intervals, would you recommend a more frequent but shorter EQ at lower voltage as well as a longer EQ at higher voltage but more infrequently? E.g. a 2.5V EQ for 2 hours performed weekly and then a 2.65V 4 hour EQ performed every 4 months? What would be the optimal settings for the longest life?

palausystem · November 2012

Re: Sunny Island/Rolls 530-S charging question

Yes,
thanks for those non-SI-specific questions. And your descriptions of charging were very helpful. I'll wait a few days and maybe someone else will be at the Rolls support desk.
The SOH of the Batteries is at 86% right now, and I'm hoping to bring most of that back with EQ and proper Full charges.
You've probably read this before, but... this from the SI v.4 manual:

The Sunny Island remains in this (float) phase until either more than 30 % of the nominal capacity has been used (all discharges are
added up) or the state of charge is below 70 %.

So It looks like after we use 240Ah of our 800Ah, (adjust for SOH number) it will go into Boost.

Every 14 days (the default) or 8 nominal charge throughputs, the Sunny Island automatically initiates a full charge

For us, since we dip lightly into our large battery, the 14 day default would apply. I think I will start with that interval.

SolaRevolution · November 2012

Re: Sunny Island/Rolls 530-S charging question

Please, please, please! Get a Specific Gravity reading for all cells!

The erratic SOC readings and charge algorithms could be due to "unexpected" return current and low voltage conditions caused by a bad cell or two. Bad or corroded cable connections could be a problem too. The other "good cells" could be getting tortured by getting recharged over and over while they are already at a high SOC.

-Alex

palausystem · November 2012

Re: Sunny Island/Rolls 530-S charging question

Yes! Yes!
I'm at the site only on weekends, so that is the first thing I will do and will post back ASAP. In the meantime I'm trying to learn as much about the SI as I can.
Thanks everyone.

palausystem · November 2012

Re: Sunny Island/Rolls 530-S charging question

More from SMA tech support on SI charging behavior:

Technically, the absorption phase time that the SI counts down when charging the batteries can vary (it does this automatically).

Short answer, but part of the puzzle anyway.

palausystem · November 2012

Re: Sunny Island/Rolls 530-S charging question

So I'm in the midst of the EQ and have a question about charging amps.
Rolls says in their documentation to EQ at 5A per 100Ah capacity.
I'm doing one 400Ah string at a time. If I set the max amps for 20 the batt volts drop below the 62v set point, which is the minimum for EQ.
I was told by Rolls guy that 44A is safe max for this battery.
So I set it at 35. But even here, I'm only getting 61.2 into the batteries, currently.
I'm wondering if I should bump it up to 40, which would be twice the recommended rate...?

inetdog · November 2012

Re: Sunny Island/Rolls 530-S charging question

palausystem wrote: »

So I'm in the midst of the EQ and have a question about charging amps.
Rolls says in their documentation to EQ at 5A per 100Ah capacity.
I'm doing one 400Ah string at a time. If I set the max amps for 20 the batt volts drop below the 62v set point, which is the minimum for EQ.
I was told by Rolls guy that 44A is safe max for this battery.
So I set it at 35. But even here, I'm only getting 61.2 into the batteries, currently.
I'm wondering if I should bump it up to 40, which would be twice the recommended rate...?

The EQ part really only starts once your batteries are fully charged. So if you cannot get up anywhere near the recommended EQ voltage at the recommended EQ current, your batteries are just not fully charged yet. Check the SG with a hydrometer and/or measure the resting voltage of the batteries after 3-4 hours without either charge or discharge.
Also check for uniformity from cell to cell.
If you have one or more bad cells, the whole voltage to State Of Charge relationship for the series string breaks down!

palausystem · November 2012

Re: Sunny Island/Rolls 530-S charging question

I was at the EQ setpoint voltage this morning. I believe the reason the voltage wants to keep creeping down is because the batteries have been abused... and so I'm wondering if more amps is a good thing in this situation.
Just to recap my situation - we believe a lot of deficit cycling has been taking place. Now I'm trying to deal with seeing how much battery I have left, how much is gone. The SG has been very slowly creeping up from 1.220 to 1.229. We want to see at least 1.255 for a "good" battery.

Blackcherry04 · November 2012

Re: Sunny Island/Rolls 530-S charging question

palausystem wrote: »

I was at the EQ setpoint voltage this morning. I believe the reason the voltage wants to keep creeping down is because the batteries have been abused... and so I'm wondering if more amps is a good thing in this situation.
Just to recap my situation - we believe a lot of deficit cycling has been taking place. Now I'm trying to deal with seeing how much battery I have left, how much is gone. The SG has been very slowly creeping up from 1.220 to 1.229. We want to see at least 1.255 for a "good" battery.

Your doing ok, just keep a eye on the temperatures and keep them below 115-120 or so. I have a digital thermometer with the probe built into a cap I use, but anything will do. Check the SG's every 30 minutes or so, as long as they are rising your doing what you need to. If you have to stop and wait till they cool off it's ok. It will take a while to get back up to voltage, as far as the current goes, the batteries will kind of limit that on what they will accept.

palausystem · November 2012

Re: Sunny Island/Rolls 530-S charging question

That's the thing -
I'm artificially limiting my amps because of what a Rolls tech told me. 44 Amps is maximum "safe limit" for that battery. Now, I am EQ'ing 8 400Ah batteries. So am I wrong in assuming that the limit he mentioned is for the entire string?
That is the question. If my charger is feeding 40 amps to an 8 battery string, then each battery is only getting 5 Amps?
That is what I need to know. Someone set me straight here.

Cariboocoot · November 2012

Re: Sunny Island/Rolls 530-S charging question

When you connect batteries in series to increase Voltage the Amp hours stay the same. Therefor if you have a manufacturer's current limit of 44 Amps for a battery it is the same for eight in series as for the one individual battery.

BB. · November 2012

Re: Sunny Island/Rolls 530-S charging question

Sometimes you have to re-ask the questions of the factory support people. I would pray they know more about their batteries than I ever will.

We try to give people rules of thumbs so that they are, at least, not doing something really dangerous or cause series battery degradation.

Flooded cell batteries tend to be very efficient (most charging energy goes into chemical processes to store electricity) from 0 to ~80-90% State of Charge.

As the State of Charge goes from 80-90% and up to 100% SOC--More energy goes into creating Hydrogen and Oxygen gases (which is hard on the battery bank--but also can be good because it mixes the electrolyte and "scrubs the plate" a bit) and more energy goes into making the batteries hot.

(just guessing but it appears that a flooded cell battery is >90% efficient when charging up to around 80-90% SOC, and much less than 80% efficient for the last 10-20% charging points).

Which, more or less, for our rule of thumbs (with many hammer hits and bandages) works out to ~25% maximum rate of charge (short periods, temperature monitoring, possibly active battery cooling with fans). ~C/8 or 13% rate of charge for unmonitored maximum charging. And 5% as the maximum rate for equalization (when a larger amount of battery charging energy is simply turned into heat/gases).

Equalization is, more or less, talking about series connected cells (6 cells in a 12 volt battery or 24 cells in a 48 volt battery connected in series). Most cells are "full" charged and a few cells are not (self discharge, other issues)... And you are "over charging" most of the cells (bad) to get some extra charging current into the cells that are not fully charge ("good"-- AKA equalization charging). So the next time, all cells can perform at near 100% of their expected abilities.

There are alternatives... Use a "2 volt" charger on individual cells (there are multi port chargers like this for large systems--basically charge each series connected cell). Or use cell top charge controllers that can "by pass current" when the cell is fully charged (stop cell from getting even more charging current--Typically used in high tech batteries like Li Ion cells although I have seen ads in the past for use with lead acid batteries--gets expensive and wiring gets complicated).

-Bill

stephendv · November 2012

Re: Sunny Island/Rolls 530-S charging question

Rolls' EQ current limit is the same as most other lead acid batteries: 5A for every 100Ah of capacity. This limit only applies once you're above the gassing voltage of around 2.4Vpc, so while you're under the gassing voltage you can use a lot more current (15A/100Ah if I remember correctly).
400Ah string = 20A current limit for EQ phase.

http://support.rollsbattery.com/solution/categories/692/folders/1399/articles/430-corrective-equalization-instructions as they note, if the batts are very sulfated it may take a very long time of constant EQ to get them back up to good condition. As Blackcherry mentioned, you have to watch the temp even with the reduced current limit.

inetdog · November 2012

Re: Sunny Island/Rolls 530-S charging question

palausystem wrote: »

That's the thing -
I'm artificially limiting my amps because of what a Rolls tech told me. 44 Amps is maximum "safe limit" for that battery. Now, I am EQ'ing 8 400Ah batteries. So am I wrong in assuming that the limit he mentioned is for the entire string?
That is the question. If my charger is feeding 40 amps to an 8 battery string, then each battery is only getting 5 Amps?
That is what I need to know. Someone set me straight here.

Just like in drawing current from a group of batteries:
When they are in parallel, the voltage stays the same and the current is the sum of the current to/from each battery.
When you put batteries in series, the same current flows through all of the batteries, and the voltage is the sum of the voltages for each battery.

Feeding 40 amps at 48 volts into a string of 8 six-volt batteries looks the same to each battery as feeding 320 amps at 12 volts into a parallel set of 8 batteries with each one getting 40 amps Except that will batteries in parallel it gets very hard to force the current to divide equally.

So in your case 40 amps into the string is 40 amps into each battery. Do not try to increase the current just because you have more batteries. You have taken care of that already by increasing the voltage.

Volvo Farmer · November 2012

Re: Sunny Island/Rolls 530-S charging question

palausystem wrote: »

So I'm in the midst of the EQ and have a question about charging amps.
Rolls says in their documentation to EQ at 5A per 100Ah capacity.
I'm doing one 400Ah string at a time. If I set the max amps for 20 the batt volts drop below the 62v set point, which is the minimum for EQ.
I was told by Rolls guy that 44A is safe max for this battery.
So I set it at 35. But even here, I'm only getting 61.2 into the batteries, currently.
I'm wondering if I should bump it up to 40, which would be twice the recommended rate...?

Do the batteries initially reach 62V and then creep down over the course of the EQ? Or are you unable to get the batteries to 62V at all?

ChrisOlson · November 2012

Re: Sunny Island/Rolls 530-S charging question

I didn't read this whole thread (I probably should have). I read the first couple of pages then jumped to the end. But I'll add my 2 cents anyway because I have seen this story with Surrette batteries repeated too many times.

From the specs given on the system by the OP, considering the size of the bank, size of the charging capacity, and the voltages being used, the bank has been deficit charged since new and is probably severely hard sulfated. The chances of bringing it back from the dead are not good. I caught this problem with my Surrette's in the first the three months that we owned them and got right on the phone with tech support at Surrette to get it fixed. Because my hydrometer showed that even though I was doing everything right, my bank was not getting fully charged.

With the specs given, this 800 ah bank would have to absorbed for 8-10 hours at the voltages used. That's simply not going to happen with 3 kW of solar available to get it done. After three months from new, and being deficit charged for the whole three months, it took me a month to finally get the SG's in my Surrette's up to 1.255. I followed Surrette's advice and have absorbed them at 31.0 (on our old 24 volt system, and now 62.0 on our 48 volt system). They have been fine ever since and when absorb is done (using normal absorb times) they are at 1.255 SG.

From experience with badly sulfated Surrette's, do not underestimate how much power it's going to take to get the voltage up to where it should be to get the job done. By splitting the bank in half you might be able to get it there with 3 kW of solar. But you'll probably have to use the generator to help out. The reason your voltage creeps down when you get up to absorb (EQ at the voltages you're using) setpoint is because the plates start to shed sulfate and they take more amps. Meaning you're going to need more power to get the job done. Been There Done It.
--
Chris

palausystem · November 2012

Re: Sunny Island/Rolls 530-S charging question

ChrisOlson,
can you tell me what you did for that month to get the SG back up to 1.255? How many amps, EQ's?, etc.
My new Rolls tech support guy says don't worry about a 44 amp limit for that battery. You can go to 60. But then, why should I trust him either?

I'm doing single string, I'm using the generator, my target is 63v. Which I am at now.
The amps have gone from 25 to 33 over an hour and a half period. I set a limit of 50a for the battery.
Did your Rolls helpers ever mention a max amps for your battery?

VolvoFarmer - it reaches the setpoint and then creeps down if I've limited the amps. If I raise the amp limit, it creeps up.

StephenDV - My rolls tech guy seems to not agree with the rolls documents that talk about the 5A per 100Ah when doing an EQ. So I'm a bit addled. I don't want to run the gen for 10 hours with a voltage of 2.54 and less, when the minimum EQ voltage they specify is 2.58, when I can get to the proper setpoint if I don't limit the amps so much.

Sunny Island/Rolls 530-S charging question

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