Charger Stops before Charging is complete

MrM1 · March 2018

I have a small system with both an AC charger and solar charge controller (classic 150).   The battery bank is 6v x 4 = 24v 435ah.    The manufacture SG for these batteries is 1.277.   Their rated absorb charge voltage is 29.6.

No matter which charger I use, unless i set the absorb volts to 31.6 for absorb, The batteries only get about 90% charged before the charger goes into float.    I have the absorb timers effectively set to off or max minutes.   In the classic I have the end amp set to 4 amps and in the AC charger I have the battery Ah set to 50 ah which is supposed to end the charge a 2% of the set Ah, but it goes into float at about 7 amps. But neither charger will fully charge the battery bank to 1.277 SG unless I set the absorb volts to 31.6v

I have 3 hydrometers that are temp compensated and they all are repeatable and agree within 5 points of each other.

Why would I have to charge batteries that are 5 months old with about 125 cycles on them at such a hi voltage - 2.63v per cell. The temps so far at this rate never go above 31C. But the outside temp has not been much above 85F since they were put into service either. Is this a resistance issue ? A charger Issue (odd if so because it is occurring with 2 diff chargers)?   Temperature? (it has been winter but the battery temp at charge is between 19c and 29c depending on the day) OR what else?

If the batteries are not overly heating up, am i doing any damage to them by charging at a voltage that is 2 v higher than the manufacture 29.6v?   I have the current set to limit at 54 amps.

Photowhit · March 2018

Are you using a battery temperature sensor? During winters I've seen adjustments around 31 volts from my preset 29.6 on my Classic 150.

Here's a chart showing the relationship between temps and charging setting;

Image: https://us.v-cdn.net/6024911/uploads/editor/0t/6ehu94z9vqzc.jpg

From this site;
http://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures

I guess you have tried these things one at a time? Or have you done end amps and 4 hours at absorb...

MrM1 said:

MrM1 · March 2018

Yes tried one at a time. And I have my absorb times set at 6 1/2 hrs in the classic and 7 1/2 hrs in my AC charger. So its not that the chargers are running out of time.

mike95490 · March 2018

Where does the classic get its power, that it can run Absorb for 6.5 hrs ?

MrM1 · March 2018

Its not that its getting 6.5hrs, that is where I have it set. I realize that the classic would stop charging if it ran out of solar power, but the AC charger should keep charging until the batteries are full. But it does not if set to 2.46v /cell. The batteries only reach 1.277 SG if either charger is set up around 2.63v /cell.

Solar Array size is 2565 watts going to this 24v battery bank thru the Classic.

MrM1 · March 2018

If i look at the curve for the Whiz Bang Jr amps in MyMidNite, I can see that toward the end of absorb with the classic there is a leveling off of amps at about 4.3 +/-. This will occur at either 2.46v / cell or 2.63v /cell, but at the lower charge voltage the batteries SG are only at 1.260. Having the voltage set to 2.63v /cell leaves either charger in bulk longer and so the current stays toward the higher end longer.

MrM1 · March 2018

Please note: nothing i am saying here is an Argument (I don't know enough to make a case for anything), just observations. Wondering why I cannot charge at 2.46v /cell as the manufacture recommends?

mcgivor · March 2018

What SG readings are you actually getting when the transition to float occurs? Did you perform an equalization or commissioning charge when first installed? How deeply are the batteries discharged on a regular basis, morning voltage is a rough guide ? Have you performed an EQ after they reach float? Were the SG readings good when the batteries were new?

Rationale behind the questions is to establish a base line, sometimes it takes time to break down minor sulfation which may have occurred over time, which can't be achieved when the batteries are discharged between charging cycles. Corrective equalization can take several days without any loads, difficult when relying on the system. Given time, with recommended voltage settings, my guess is the SG will recover, this was my observation with a bank that was too small for the loads, it was reassigned to light duty and recovered over time.
Fooling the controller by setting Ah capacity lower than actual, along with raising voltage setpoints is much the same as performing an EQ, but it can get out of hand, better to use the EQ function as designed, if at all possible use another source such as a generator to support loads for a few days to allow time for a recovery process using EQ without any cycling, this would be the fast way, not nesesarally the best way. All speculation at this point, without knowing details.

mike95490 · March 2018

your batteries need to charge at about 45A for the bulk portion of the charge (10% of capacity) If your solar cannot provide this much, your batteries WILL suffer. This high current is needed to accomplish some chemical changes in the battery plates.

What has water usage been like, a little added every couple months? A pint monthly?

Photowhit · March 2018

So do you have the batteries charging using the battery temperature sensor to adjust the voltage? What are the temps you have been having?

Estragon · March 2018

Have you measured voltage at both the output terminal of the classic (and ac charger), and at the bank +/- posts while in bulk at max current? If so, what is the difference between the two? It's possible an undersized or defective wire or connection is causing voltage drop under load, so the actual voltage is lower than the classic/charger thinks, leading to premature transistion to absorb and float.

At 29°C, charging voltage should be reduced slightly vs recommended. If using the classic local app, you should be able to see temp compensated target voltage, battery temp, battery voltage offset, battery current, and the absorb timer. I would confirm and sanity check these values as much as possible (for example by measuring battery temp with an ir thermometer to see if it agrees with local app).

MrM1 · March 2018

mcgivor said:

What SG readings are you actually getting when the transition to float occurs? Did you perform an equalization or commissioning charge when first installed? How deeply are the batteries discharged on a regular basis, morning voltage is a rough guide ? Have you performed an EQ after they reach float? Were the SG readings good when the batteries were new?

The SG from float to absorb if I use the recommended 29.6v is right at about 1.260 with a 5-10 point margin depending on the cell.

EQ Commissioning charge. No I did not. My bad. Novice mistake. But at commissioning the sg in all cells was pretty close to 1.277

Daily DOD is between 15-30%

Todays voltage on each battery

- at 11pm SOC was 92%

- after doing a topping charge last night at 31.6v for 1 hour at 11pm, AC charger went into float.

- then running at float for the next 8 hrs at 30v at between 1amp and 3.5 amps

- Total Amp hours returned to batteries was 447 ah 8 hours later (battery AH is 435)

- Voltage on each battery disconnected from each other after 2 hours is: 6.58 / 6.57 / 6.58 / 6.58 - No Load at all

- Temp never exceeded 29C during charging

- SG ranged from 1.284 to 1.305 using a Hydro Volt which I have determined is consistently 5 points too hi based on my glass hydro and refractometer. So those readings would be -5 points.

I have preformed EQ's probably every 3 weeks to a month. And yes the SG was good in all cells when new.

MrM1 · March 2018

mike95490 said:

your batteries need to charge at about 45A for the bulk portion of the charge (10% of capacity) If your solar cannot provide this much, your batteries WILL suffer. This high current is needed to accomplish some chemical changes in the battery plates.

What has water usage been like, a little added every couple months? A pint monthly?

solar does this with ease, And lasts until SOC is about 88-92%. From solar I can get upwards of 64 amps. And I have set my AC charger to max at 56 which is just slightly higher than C/8 (435ah battery bank)

I have had to add water 2 times in the 5 months. The first time very very little. the second time the water level was about 1/4" to 3/8" from the full ring. I would guess yes, about a pint or more. This was about 3 weeks ago. So IMO not using much water.

MrM1 · March 2018

Estragon said:

Have you measured voltage at both the output terminal of the classic (and ac charger), and at the bank +/- posts while in bulk at max current? If so, what is the difference between the two? It's possible an undersized or defective wire or connection is causing voltage drop under load, so the actual voltage is lower than the classic/charger thinks, leading to premature transistion to absorb and float.

At 29°C, charging voltage should be reduced slightly vs recommended. If using the classic local app, you should be able to see temp compensated target voltage, battery temp, battery voltage offset, battery current, and the absorb timer. I would confirm and sanity check these values as much as possible (for example by measuring battery temp with an ir thermometer to see if it agrees with local app).

As to wire size, using 4/0 and the terminals are all machine hydraulic pressed. I have good connection at all serial connections and main posts as well as at the inverter / shunt connections. Tested with a temp gun, all connections are almost the same temp at 45 amps.

I will check to see if the temps at the posts agree with temps i am getting from the 2 sensors I have connected. one for the classic and one for my AC controller, which vary about 1-1.5C between the 2.

I am using temp comp on both chargers, and yes voltage is reduced at 29C

MrM1 · March 2018

Here is the graph from last night. Beginning at 9:30pm and Ending at 10am. You can see the bump charge that started at 93% SOC and started charging in bulk at 55amps. 45 minutes later system switched over to absorb at 97% SOC and the current was reduced until it went to float about an hour later. the system was then reading 3.7amps. At this point I had returned an extra 5 Ah to the batteries above 435. From they until 10 am the system received an additional 7 Ah. I set the Float voltage to 29.6 and went to bed.

All of this was done with the AC charger and recorded thru the Classic using the Whiz Bang JR at the Shunt. Battery temp never exceeded 28C and reached max at the end of absorb. Battery box was open and the outside air temp was 71F at midnite

Image: https://us.v-cdn.net/6024911/uploads/editor/6z/su2cb1tk0x7u.jpg

mike95490 · March 2018

MrM1 said:.....
I have had to add water 2 times in the 5 months. The first time very very little. the second time the water level was about 1/4" to 3/8" from the full ring. I would guess yes, about a pint or more. This was about 3 weeks ago. So IMO not using much water.

Then I would add an hour to your absorb timer, and see what things look like after a few days. Then add time in 15 min increments till batteries are happy. If temps start going more than 10F over ambient, stop adding time till batteries recover some baseline charge

Not adding much water = not fully charging batteries.

MrM1 · March 2018

mike95490 said:

MrM1 said:.....
I have had to add water 2 times in the 5 months. The first time very very little. the second time the water level was about 1/4" to 3/8" from the full ring. I would guess yes, about a pint or more. This was about 3 weeks ago. So IMO not using much water.

Then I would add an hour to your absorb timer, and see what things look like after a few days. Then add time in 15 min increments till batteries are happy. If temps start going more than 10F over ambient, stop adding time till batteries recover some baseline charge

Not adding much water = not fully charging batteries.

But there in lies my problem Mr Mike,   my absorb timers are set to the max times, But the charger stops charging long before the timers of either the classic or the AC charger ever reach the end of they absorb times.   Charge stops due to amps. And if I use 2.46v /cell, the batteries when they go into float are not full according to SG.    They are at about 1.260 ... or 90%.   So I turn up the voltage little by little, charge after charge, until I find the voltage that gets me to 1.277 fully charged SG or more. And (in the case of the classic) I also tinker with lowering the end amp setting to 4.3 give or take, until I hit a balance.

I can lower the charge volts, and set the end amp of the classic to 2, but then I run out of day light- But the charger never goes out of absorb.    The AC charger, even though I set the user battery size setting of 50 ah and this is supposed to be 1amp for end amp, it usually stops charging at about 7amps. So I have to use near EQ voltages in both chargers to get a good full charge.

The timers in either charger seem to be pointless as the chargers would stop before any timer time is reached.   This is what has me stumped.

I looked at this data .... and on page 3 it says

"It only requires between 107% and 115% of the ampere hours energy removed from a lead acid battery to be restored to achieve a fully charged system capable of delivering 100% of its rated capacity. "

But I am returning about 7-15 extra AH's according to my charge controllers Control panels.   I do not really know what to make of that statement above, But if those percentages are correct , I should be returning at lest 30 extra amp hours.

Needless to say, the only way I am getting my batteries to charge to anywhere near full seems to be to charge them at 31.6v or 2.63v /cell.   But with that, I do realize I am not at that hi a voltage the whole charge, just usually the last 10% in absorb. But still it seems hi and I am trying to get to the bottom of why I have to use such a hi voltage in the first place.    I do not think it is the chargers, because I get similar results for both.

MrM1 · March 2018

On a battery temp note, I did open up 2 more 18" x 2.5" vents in the top of my battery box AND also cut a 4" hole in the bottom back with a 18" PVC pipe leads under my house so that the battery box can draw cooler air from under the house. And from the vantage point of the PVC pipe, it would be easy to install a computer fan if needed to push air into the box.

westbranch · March 2018

Have you contacted the maker or googled other batteries that they make for the target SG of the other batteries? Is an SG of 1.277 abnormal? If that is correct then carry on....
BUT first do a series of EQ's , and know that the process can take days at the start, not hours...
How about the MidNite Solar Forum? Post your issue there, lots of good advice.
Have you thought of increasing the Ah rating to fool the CC into a longer charge?

MrM1 · March 2018

westbranch said:

Have you contacted the maker or googled other batteries that they make for the target SG of the other batteries? Is an SG of 1.277 abnormal? If that is correct then carry on....
BUT first do a series of EQ's , and know that the process can take days at the start, not hours...
How about the MidNite Solar Forum? Post your issue there, lots of good advice.
Have you thought of increasing the Ah rating to fool the CC into a longer charge?

Yes to the battery manufacture. They said "no problem at 31.5v, our golf cart batteries are charged at voltages higher than that every night at golf courses." While that may be true, it was not sure if that was an attempt to sell me more batteries knowing it would shorten their life.

1.277 is the normal SG for Trojan L16 H AC batteries and other batteries in the same family.

A series of EQs. I will do that. But with EQ,
- When I do EQ, I will have some cells that rise to 1.300, lowest cells will be 1.288.
- Do I then assume that those higher SG numbers, Higher than 1.277 are actually the fully charged SG numbers?
- Or do I continue to target 1.277 for normal daily charging?

Will try the Midnite forum too.

As to increasing the AH of the battery in the Classic 150 ... so that would force it to charge longer? If so ... perfect. I like that idea. But does that mean it will also use a higher charge current at the beginning? No real problem. Just need to tinker with it to not let it get too hi.

Vic · March 2018

Mr. M1 said, "As to increasing the AH of the battery in the Classic 150 ... so that would force it to charge longer? If so ... perfect. I like that idea. But does that mean it will also use a higher charge current at the beginning?"

No, the Ah Capacity setting in the Classic is used only for Remaining Ah and SOC calcs, and should have NO effect on the Rate of charge (unlike some Schneider Inverter/Chargers and CCs.

The OP IS on the MN Forum ...

Why not give your batteries a few deeper-cycles? Later, good luck, Vic

mike95490 · March 2018

MrM1 said:

But there in lies my problem Mr Mike, my absorb timers are set to the max times, But the charger stops charging long before the timers of either the classic or the AC charger ever reach the end of they absorb times. Charge stops due to amps. ............................................

Then you have configured something really wrong. I regularly get absorb times over 2 hours with my classic. Disable using the whiz-bang Jr.

What is your AC charger, and a link to it's manual. I know of few AC chargers that monitor end amps

Vic · March 2018

Mike, I am NOT MR.M1, but, would bet that it is the, "Conext SW 4024 Inverter/Charger" if memory serves ... Vic

MrM1 · March 2018

That is correct Vic. Here looking for different eyes than the MidNite solar classic exclusive eyes.

Mike, it is indeed the SW 4024 ... here is the PDF Link.

MrM1 · March 2018

mike95490 said:

MrM1 said:

But there in lies my problem Mr Mike, my absorb timers are set to the max times, But the charger stops charging long before the timers of either the classic or the AC charger ever reach the end of they absorb times. Charge stops due to amps. ............................................

Then you have configured something really wrong. I regularly get absorb times over 2 hours with my classic. Disable using the whiz-bang Jr.

What is your AC charger, and a link to it's manual. I know of few AC chargers that monitor end amps

Mike I get 2 hours of absorb if my SOC is down to 70%-65% ... but unless the Absorb volts are set hi, i do not get but only 1.260 give or take SG.

Here are my Classic settings:

mike95490 · March 2018

Them's some strange settings. Did you set up with a default 24V setting and modify or what? Rebulk of 8V ??

Did you set this with a Local App or the Graphics Panel ?

Vic · March 2018

mike95490 said:

Them's some strange settings. Did you set up with a default 24V setting and modify or what? Rebulk of 8V ??
Did you set this with a Local App or the Graphics Panel ?

Mr.M1, no issue with you looking for additional advice here, we often recommend those on other Forums to indeed come here ...

Mike, I do not know anyone who needs to use ReBulk. 8V is the Default, and that means that it is not ever used.

You probably know all of this. Later, Vic

MrM1 · March 2018

mike95490 said:

Them's some strange settings. Did you set up with a default 24V setting and modify or what? Rebulk of 8V ??
Did you set this with a Local App or the Graphics Panel ?

Yes defaults and then a few tweak mods to absorb time and Volts / I tinker with AUX 1 a good bit as it controls my dump load / Some of the Battery Eff settings / End amps / and at present I am not using Reset for Net AHs at 100% ... but rebulk is default.

Any suggestions would be welcome.

mcgivor · March 2018

@MrM1
Increasing the absorption voltage to a value greater than the manufacturers recommendations will probably be benificial in an offgrid application, the voltage specifications were determined in controlled conditions with unlimited time, unlike the 4 hours give or take available using PV. There is however a limit where the voltage is approaching EQ values, which could be potentially damaging through plate erosion. Below is en except from Home Power Magazine which I found particularly interesting

Battery management and maintenance are significant concerns in off-grid PV systems.

Many of the user problems associated with these systems can be traced to improper treatment and misunderstanding of battery performance.

Modern battery chargers use three charging stages— bulk, finish (absorption), and float. Bulk brings the

batteries up to the high voltage regulation point; finish holds it at this high voltage regulation point based on

time. In the absorption stage, the voltage is constant, and the current tapers off as the batteries are filled.

Float trickle charges the battery to a lower, userdetermined voltage to keep it full.

From my experience, the most common battery problem is undercharging, leading to sulfation, loss of storage

capacity, and shortened service life. Sandia National Laboratories recently published “PV Hybrid Battery

Tests on L-16 Batteries” (see Access). Their tests represent several years of systematic testing of a PVgenerator

(hybrid) system. The 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. Tests were repeated so that the data represents good averages, and the conclusions are based on good data and methodology.

The study has four conclusions:

1. The finish voltage (sometimes called the absorptionvoltage) 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.

2. Finish charge time should be at least 3 hours and often longer.

3. The maximum interval between finish charges should be about five days.

4. Not all brands of L-16s are the same (though the report names no names).

The general conclusions of the Sandia report are consistent with the number one problem experienced in

off-grid PV systems—undercharged batteries. Richard Perez has for many years advocated higher finish

voltages for PV-engine generator systems. As he says, “I like to run them hot.” Home Power technical editor Joe Schwartz adds some good advice regarding flooded lead-acid batteries: • Higher finish charge rates result in significantly more gassing and potential for hydrogen buildup. Before you crank up the finish voltage to 15.3 VDC (for a nominal 12 volt system), make sure that the battery containment is well ventilated. The use of powered

battery vents is recommended.

• Batteries charged to a high finish voltage produce a significant amount of waste heat. Depending on the

type and location of the battery containment, in warm climates or seasons active ventilation may be required

to keep battery temperature in check. Optimal operating temperature for lead-acid batteries is 78°F

(25°C). Higher battery temperatures (90°F plus; 32°C) result in increased self-discharge. Temperatures over

120°F (49°C) can damage lead-acid batteries. • Batteries charged to a high finish voltage consume a

lot of water. Compared to charging at the traditional 14.4 VDC finish voltage, the time period between

battery watering can easily be cut in half. Automatic battery watering systems greatly simplify the process.

Use temperature compensation on all charge controllers and inverter/chargers. Finish Charging Is Inefficient

There is one significant downside to the battery management strategy presented in the Sandia report.

Due to battery charging characteristics, efficiency is very low during the finish charge phase. Very long

engine generator run times were reported, sometimes from 6 to 20 hours. These long run times were required

to completely refill the batteries to the manufacturers’ stated ampere-hour capacity.

The state of charge (SOC) of a battery is most accurately measured with a hydrometer, and is

indicated as specific gravity (SG). Most RE users rely on amp-hour meters to provide convenient (although

slightly less accurate) battery SOC information. During the Sandia tests, full batteries had a SG in the range of

1.290. The long, engine generator run times needed to achieve this SG translate into dollars and pollution (both

audio and atmospheric). Perhaps there is a “middle way” that preserves the lifetime of the batteries while

reducing the time and cost of engine generator finish charging.

Revisit the Assumptions

The batteries tested at Sandia were discharged by 60 percent of capacity (to 40% SOC) and then charged

back to rated capacity. In these tests, the rated capacities were determined empirically, and in most

cases were close to the manufacturer’s stated value (in the range of 350 AH for an L-16).

These two points require comment. First, this depth of discharge is not typical of most well-designed, standalone

PV systems. This point is clearly stated by the author of the study. Most stand-alone PV systems, by

design, cycle batteries by about 25 percent daily, not 60 percent.

Second, the manufacturer’s rated battery capacity and the way it is determined should be understood. All

manufacturers recharge batteries on the grid. Using the grid, they can finish charge the batteries for long periods

(on the order of 8 to 12 hours), cramming maximum ampere-hours into them. For a manufacturer, this

method makes sense because it results in greater AH capacity figures for their product.

The long engine generator run times required by PV hybrid systems must mimic the finish charge conditions

the manufacturers use to rate the battery’s capacity. Perhaps batteries should be rated based on their

application. For instance, a battery used in a standby application (such as utility backup system with grid

recharging) might specify a full charge SG of 1.290. The same battery used in an application that regularly

cycles the batteries (such as a PV system with engine generator backup) might have a recommended SG of

1.250 to be considered full. It is true that a battery with a SG of 1.290 holds more

charge than the same battery with a SG of 1.250.

However, the shorter finish charge time required to achieve the lower SG reduces the engine generator runtime.

Estragon · March 2018

> @MrM1 said

> A series of EQs. I will do that. But with EQ,
> - When I do EQ, I will have some cells that rise to 1.300, lowest cells will be 1.288.
> - Do I then assume that those higher SG numbers, Higher than 1.277 are actually the fully charged SG numbers?
> - Or do I continue to target 1.277 for normal daily charging?
>

EQ is short for equalize. A hydrometer may not read absolute value correctly if not calibrated, but if readings are done correctly, they should be consistently high or low. Ideally, you want to EQ until all cells are equal SG, and no longer rising at EQ voltage. Realistically, if low cells are at 1.288 vs high one at 1.30, and the low cells aren't rising much over a half-hour reading interval, I'd call it a day. Doing this over the course of several days can sometimes get them closer, but I certainly wouldn't run the generator all night to get them closer than .01

mike95490 · March 2018

Run the generator in the morning to bulk the cells, and figure how to ignore the whizbang and get yourself a 3 or 4 hour solar absorb, you are undercharging batteries and slowly killing them.

As I understand rebulk, it gets used a lot on my system on cloudy days, I get 3 min of absorb, clouds roll in and w/out rebulk, absorb won't continue. Even rebulking a 12V battery at 8V, the battery is already destroyed from the low voltage

You cannot make the SG rise beyond factory fill specs by extended charging, if you have one cell hitting 1.3 and the others are lower, the others have suffered a bit of sulfation and may never come back. If factory acid is 1.3 you can never make it climb over 1.3, and any lower indicates sulfur is locked onto cell plates and not coming back into solution.

Charger Stops before Charging is complete

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