Batteries not charging

solosol · June 2010

System: 10 x Kyocera KD135 panels on two Deger TopTrakers, Outback VFX3024, FM60 and Exide OPzS 1320 Ah (C120) batteries 24V. Location Spain, loads of sun.

Absorption set point is currently 30V, it was increased at the recommendation of the battery supplier. Absorption time is 2 hours, again increased to try and get the batteries to charge.

System has been in for about 3 months, I noticed that the batteries ‘appeared’ not to be charging early on. Looking at the FM log you could see the batteries were going onto float every day, but the specific gravity was very low. I installed a simple Kwh meter, typical daily usage is 4kWh. I have changed the FM60, but this made no difference.

It appears that the batteries are reaching the Absorb set point before the Specific Gravity has reached the correct value, or maybe the acid density is not correct?

All obvious stuff tried, equalizing etc, connections all checked, voltage at charge controller matched voltage on battery terminals, etc.

When absorbing the batteries gas quite happily, all seems to be working well, but the batteries simply are not charging.

I took these SG readings after the FM had just indicated the Absorption has finished:

1.21
1.215
1.215
1.22
1.21
1.21
1.215
1.21
1.21
1.21
1.215
1.215

Has anybody seen a similar problem?

BB. · June 2010

Re: Batteries not charging

solosol,

I am not sure you have any problem... According to this document (PDF Download--by the way, download and save this manual to your computer--I am not sure it will stay where it is) the specific gravity your cells were filled with should be 1.22 kg/l at 20° C (if BLOCK) or 1.24 kg/l (if SOLAR). Or sg of 1.22 / 1.24. All +/- 0.01 accuracy.

Once the battery is "charged" for commissioning, they want 1.21 (BLOCK) or 1.23 (SOLAR) specific gravity.

So I guess the first question is what specific gravity acid were the batteries filled with?

When charging, have you monitored the specific gravity while under at least 5% or so rated charge current? Does the SG continue to rise, or it is "stuck" at the measured value while the cells are vigorously bubbling?

Are you charging at 2.35 to 2.40 volts per cell (28.2 to 28.8 volts--yours is set to 30.0 volts--should be OK) as measured with a known accurate meter at the battery itself?

What is the wire size / length between the Charge Controller and the battery bank (are you getting too much voltage drop between the charge controller and the battery bank at full current)?

Do you have the Remote Battery Temperature Sensor option for your Outback? (Don't think lack of RBTS is causing you any issues at the moment).

Incorrect wiring and/or no RBTS can cause the battery to take longer to charge or not fully charge--but if you are at 30.0 volts at the battery--then neither of these are causing you this charging issue you are asking about.

Everything sounds fine otherwise. As I understand battery chemistry (not much)--a slightly lower specific gravity fill can give you longer battery life--but less absolute capacity (higher sg will give you more available energy but shorter life).

-Bill

niel · June 2010

Re: Batteries not charging

there could actually be a problem here with too low of a charge %. the kc135s are series/parallel so for 24v you are getting 7.63a x 5 strings = 28.15a. dividing this into 1320ah of battery capacity gives about a 2.14% charge rate. this is too low. to reach the 5% area would mean it must be at least .05 x 1320 = 66a at 24v.

solosol · June 2010

Re: Batteries not charging

Thanks for the quick replies.

I’m using an Outback FM60 MPPT charge controller, so the charge current theoretically can go beyond the nominal charge current of the panels. The batteries are 1320Ah at C120, a more realistic design value would be C10, which brings them down to 940Ah.

Ralph Day · June 2010

Re: Batteries not charging

Han (solo)
You will reach the absorb setpoint long before you reach full state of charge on the electrolyte because absorb is reacting to a voltage...soc is reflected by specific gravity reading. Once your system has bulked and reached the absorb point it just means you've reached the arbitrary voltage point, not completely charged the batteries.

My solution is/was to set a long absorb time and check the sg every hour or so. If it reaches your expected level (full soc) before the time is up, just reduce the absorb time. If not reached by the end of the time put the float voltage up to match the absorb voltage and continue. Don't forget and leave in this configuration because you'd use too much water.

Just remember, absorb setpoint and time doesn't mean full state of charge...sg readings do. Use the former to achieve the latter.

Ralph

Dave Angelini · June 2010

Re: Batteries not charging

A different appraoch as I do not know this battery. What is your early AM voltage before sun hits the trackers? With a 4 KWH usage over night I would thing your voltage would be above 24.6V. Maybe as Bill says there is not a problem.

niel · June 2010

Re: Batteries not charging

the wattage in may work out with the wattage used on sunny days, but that charge % is still low. allowing for a constant 10% mppt action this will round it up to about 31a. i look at the extra from mppt as just that, extra, for the base current is what is 100% reliable. no matter as assuming you get this extra current and dividing this 31a into the 940ah capacity for 20hr that you indicate shows the charge % at about 3.3%. this is a bare minimal area and if you consistently use that 4kwh every day even when the sun is not prominent then it could be deficit charged at that point as it never reached full charge and possibly lost some capacity due to sulfation.

GreenPowerManiac · June 2010

Re: Batteries not charging

Almost sounds like there is a controller setting issue. Dip switch setting ? Try raising or lowering the voltage setting with the dip switch settings as an experiment. My controller will not allow the system to float, absorb or otherwise until my voltage is in excess of what is set by these switches. I'll loose power in one way or another: Voltage too low to maintain a float stage or too high of a setting to allow it to do its charging stages.

Considered a different SG gauge ? A misreading or low electrolyte SG in the batteries themselves ? I'd contact the manufacturer and notify them of your situation immediately.

Normally a battery will draw the current it needs to charge itself fully. Bad batteries or fully charged batteries draw too much or nearly nothing at all. Apparently a low current is being drawn under the circumstances. Bad batteries ?

Dave Angelini · June 2010

Re: Batteries not charging

niel wrote: »

the wattage in may work out with the wattage used on sunny days, but that charge % is still low. allowing for a constant 10% mppt action this will round it up to about 31a. i look at the extra from mppt as just that, extra, for the base current is what is 100% reliable. no matter as assuming you get this extra current and dividing this 31a into the 940ah capacity for 20hr that you indicate shows the charge % at about 3.3%. this is a bare minimal area and if you consistently use that 4kwh every day even when the sun is not prominent then it could be deficit charged at that point as it never reached full charge and possibly lost some capacity due to sulfation.

Your point may be right but in practice most offgrid people only do what you advise in a very small percentage of cases. Most start small and add on as they go. In this case the battery is capable of 11.2KWH at 50% discharge. With 4KWH of usage and tracked arrays that will gather 30% more energy than a fixed I would say the OP's problem is not related to your point. I tend to think as your esteemed colleague that there is not a problem. I certainly do not understand the SG readings of this battery.;)

niel · June 2010

Re: Batteries not charging

Dave Sparks wrote: »

Your point may be right but in practice most offgrid people only do what you advise in a very small percentage of cases. Most start small and add on as they go. In this case the battery is capable of 11.2KWH at 50% discharge. With 4KWH of usage and tracked arrays that will gather 30% more energy than a fixed I would say the OP's problem is not related to your point. I tend to think as your esteemed colleague that there is not a problem. I certainly do not understand the SG readings of this battery.;)

understood and if the batteries are fine right now as you and bb believe they are, they could be in trouble in the near future for the reason i stated and was the reason why i stressed that there still is a problem.

Dave Angelini · June 2010

Re: Batteries not charging

niel wrote: »

understood and if the batteries are fine right now as you and bb believe they are, they could be in trouble in the near future for the reason i stated and was the reason why i stressed that there still is a problem.

The wolf is always at the door! It takes a very disciplined user to avoid the problem you are referring to. But it can be done and avoiding "voltage creep" as I call it is the key to batteries lasting 10 to 15 years. It would be nice if the OP would come back with his early am unloaded voltage as it is another way to go.

65DegN · June 2010

Re: Batteries not charging

How many KWH does the system generate in a month? You stated consumption but not generation.
What is battery temperature?
A battery that is too hot will not retain a charge.
On the point about SG, the reference to 1.22 kg/l, I'm not sure that this equates to an SG of 1.22. I would want to establish this fact through the manufacturer not the dealer or distributor. If they are telling you to extend absorb time then something does not compute.
Also I would want to get the 'finish current' for the absorb cycle. I have found that using 'finish current' instead of 'absorb time' is a better way to completely charge a battery, particularly since the charge current and loads in an RE system often vary. Seems to me that would make using absorb time a rather random indication of a completely charged battery and disregards battery internal resistance.
Subtracting load current from the absorb current and using this number as the finish current will give a more reliable indication because when the battery internal resistance decreases to a certain level it will require a certain current to maintain the absorb set point voltage and indicate a full charge.
In other words when fully charged the battery internal resistance should always be about the same. Hence the current to keep the battery at the absorb set point when it is fully charged should also always be about the same.

BB. · June 2010

Re: Batteries not charging

65DegN wrote: »

the reference to 1.22 kg/l, I'm not sure that this equates to an SG of 1.22

1.00 kg/L is the specific gravity of water (at standard temperature and pressure--at least as I understand it). In the US, Specific Gravity is a ratio referenced to pure water so that 1.00 SG equals 1.00 kg/L, and 1.22 SG should equal 1.22 kg/L...

-Bill

65DegN · June 2010

Re: Batteries not charging

Thanks for that info Bill. That is a very unusual SG.
I would want to hear the mfg tell me that 1.22 is what they ship them with just for the record.

solosol · July 2010

Re: Batteries not charging

I have tried adjusting the Absorb time to up to 3 hours, this does not help with the SG problem, the batteries go onto float every day, and show a full ‘voltage’ charge, not SG! Within 45 minutes of the charge controller going to sleep the battery voltage is down to 24.8, reflecting the low SG.

Having read the user guide for Exide Opzs, kindly submitted from the forum, it states that if the batteries have been left for more than 3 months in storage they need a ‘refreshing’ charge, I suspect that because the general business slow down here in Spain, these batteries have been in the back of a warehouse for a while! The refresh charge needs to be constant current and constant voltage for up to 72 hours, this can’t be done from the FM60, and I’m not sure about the Outback VFX3024 inverter charger, the battery supplier has agreed to lend me a suitable charger to try!

On the point of 'refreshing charge' I have noticed it is freely interchanged with 'Equalizing Charge' on the internet, not sure if it is the same thing, I'm hoping not as you cannot fix the Amps on an equalizing charge on the FM60? A refreshing needs a fixed voltage, fixed current charge.

Just for information, I have used the 1320 batteries with similar setups in systems for the past 5 years, and no problems.

The FM60 also has a setting for return Amps, this seems to be a much better way of charging, rather the Absorb time. Does anyone have any values for typical return Amps. Batteries are Exide OpZs Solar a320 Ah (C120)

Thanks Tim

Dave Angelini · July 2010

Re: Batteries not charging

I think you are being overloaded and missing the obvious. You have not done an EQ yet correct? I would perform a generic EQ at 31V for 2 hours! Is there a change for the better?

What is the early AM voltage and SG compared to the Sunset voltage and SG?
What is your energy usage?

solosol · July 2010

Re: Batteries not charging

Hi Dave I have posted this on the Outback forum as well, improve my chances of a solution, I think I have already responded but here it is anyway:

I have done many equalizing charges, at 31v as you also suggest, but all I can do is get a marginal increase, and more recently no increase in SG.

Voltage in AM is 24.6 / 24.8 and 24.8 1 hour after sunset. I have installed an electricity meter to monitor consumption, so I'm confident that the usage is 2kWh overnight, and the voltage drop for that usage is ok.

Only problem is I can not get the SG up to the value stamped on the batteries.

I have had no joy contacting Exide, typical large company!

Any thoughts on the refreshing charge, constant current / constant voltage, this is different from an equalizing charge where the voltage is constant but the current tapers?

Regards

Tim

Vic · July 2010

Re: Batteries not charging

Hi solosol,

I have no knowledge of this specific battery.

From the link that BB provided, it appears that this battery may be shipped to the distributor or dealer dry, and would need commissioning there. This is usually a many hour process, which needs to be fairly cafrefullly monitored. Perhaps your batteries have not been fully 'activated'.

What method are you using to measure the SGs ? Are you certain that it is accurate ? Some of your SG readings appear to be to 3 decimal places, so it may be a refractometer ??

A constant Voltage, constant Current charge is DIFFERENT than an EQ charge -- the Equalization is constant voltage charge, where the current diminishes as the EQ proceeds.

I am most familiar with Surrette batteries. With the Surretes, End-Of-Charge current, where the bank is considered to be fully charged, is: between 1% and 2% of the 20-hour capacity. This is ONLY the current into the battery -- ie, minus any loads on the bank (like an inverter).

Probably, the people that supplied the batteries to you will have more direct communication with Exide. Since this is a new system, the supplier of the batteries owes you some very direct support. Exide must have some applications or technical support persons who can help, if you can communicate with them. Keep asking the people who sold you the battery bank for support. This is their problem to help you solve.

Good Luck, let us know of your progress. Vic

Dave Angelini · July 2010

Re: Batteries not charging

Tim,
OK, it sounds like the only thing left beside what you suggest (refresh charge) is to do a load test and test the capacity.

I would take them down to 22V with a controlled load over 20 hours. Probably use a 1500 watt heater adjusted for what you would expect. Do the math! Make sure you have a generator or something large to bring them back in 8 hours or so. Remember not to charge at a rate higher than 10% of the battery capacity. Record the data and analyze! Good Luck!

65DegN · April 2011

Re: Batteries not charging

Dave is right, the bottom line is AH capacity. There's no arguing with that number in hand.
I have found that it is very important to check specific gravity immediately upon receipt of the batteries. Check every cell and record it. This arms you with valuable information that can be extremely important if you have problems with new batteries.
Note the cell with the lowest SG and use this as a monitor cell for the bank. That way you don't have to check every cell to get a good idea of the SG every time the SG is tested.

Also the idea of charging with constant current and voltage for a refreshing charge makes little sense to me.
The battery internal resistance changes as the battery becomes charged and will consequently draw less and less current. You can not force it to draw more (or constantly the same) current without increasing the charge voltage.
If what they mean by 'constant current' is the available current, then this does not differ from typical charge power supplied by a generator.

BB. · April 2011

Re: Batteries not charging

Solosol has not been back since July of last year... I hope that means all is OK.

From the mfg information (manual), it would appear that the batteries are pretty much at their designed / as filled SG. Within margin of error.

Low SG levels can give the battery bank a longer life (operating years)--So, there is a good reason for lower SG levels.

Hopefully, we will hear back someday and the OP will still be happy with the operation of his bank.

-Bill

Batteries not charging

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