Float or higher charge voltage for value regulated sealed lead battery

mcgivor

Estragon said:

fratermus said:

Estragon said:

Personally, I wouldn't buy or use a controller that didn't have separate absorb and float voltage settings for off-grid use. Such a controller might be okay for a standby application, but not for regular daily cycling.

Dunno.   If I were cycling each day and had one setpoint I'd consider setting it to Vabs.  And watering regularly.  :-)

Regularly watering a valve regulated sealed battery might be a problem

Still got a hair trigger I see, good catch, pays to follow the thread.

Fabian

I currently have my battery bank (UPS/Telecom battery) configure at 12v @ 760Ah. It was recently discharged to 11.65v and was at that level resting for about  1 week before I started charging it back. Do you think the battery was permanently damage because of that low voltage level? It is the second time i bring it down so low. So it doesn't happen on a regular basis.

Also since then i had it charging from the grid constantly. So about 5 days has passed so far and it has been getting a constant 100watt from a power supply that i have running to my Charge controller. Currently the reading is now at 13.8v and I notice that the battery bank is warm to touch. I don't have a BMS install. I realize also that it is at this reading for a longtime even thou i set the CC to boost/bulk 14.4v and float at 13.7v. So I am wondering if because i am charging it from the grid which it is seeing  24/7 charging for several days would that eventually let it get a full charge at 13.8v?

With this in mind because the battery bank is getting a noticeable temperature would it be best to adjust the CC setting and just let it remain at this 13.8v for boost and then float at 13.7v and then after several 24/7 constant float charging it would eventually be fully charged at the float level 13.7v?

So basically when charging it from the grid with 24/7 charging for several days then charging it at the float level would be the ideal way to go?

BB.

Try setting float to 13.6 volts?

Very roughly, you are seeing:

• 100 Watts * 1/13.8 volts = 7.2 Amps
• 7.2 Amps / 760 AH battery bank = 0.009 rate of charge ~ 1%

That is pretty high for a continuous rate of charge/float. It should be dropping below that, especially on float.

And as a warning, 2% rate of charge or higher--The batteries should be replaced as there is a risk of "battery melt down" or fire (from what I have read).

-Bill

mcgivor

@Fabian What ambient  temperatures are you dealing with, it may, or may not be a factor but if greater than 30°C, voltages should be reduced, lead acid  batteries become excited at higher temperatures, if I'm not mistaken you are in a tropical location, yes/no? 

BB.

He is out of Jamaica.

-Bill

Fabian

I reduce the float voltage and now it is currently floating at 13.6v at about 5.3 amps. I assume the current will gradually decrease. So is this reading ok so far?
The battery bank is still warm which I assume will decrease after awhile.

I live in Jamaica. Tropical country.

BB.

It is better, but even 13.4 volts may be better for hot climate and reduce your charging current. Float current should not be very high if no loads and good batteries.

-.005 volts per cell per C (over 25C) * 6 cells = charging offset for temperature
-0.005 volts * (35C - 25C) * 6 cells = -0.3 volts reduction for 10C over 25C "room temperature" suggested for charging voltage

Some charge controllers have automatic temperature offset, others do not. Use you voltmeter to confirm float voltage at battery bank.

And as a rough estimate, 35C vs 25C room temperature (+10C) would expect the float current to be ~2x higher than that at 25C (every 10C over 25C, expect 2x higher float current and batteries to have 1/2 life--faster ageing).

-Bill

Fabian

About how many days float charging would it take to eventually full charge the battery seeing that it wasn't cycle up to the 14.4v boost voltage?

BB.

Fabian,

That is the $64,000 question... Think of filling a water tank that has a slight leak. At low flow rates (low charging current), the flow in equals the flow out. So no charging takes place.

So--What is the leakage vs what is the charging current. Try float charging at 13.4 volts and see what the float current drops too... Call that the "leakage current".

Then set the charging point at 14.0 volts (that would be a relatively slow charging current). Not great if you are actively/deeply cycling the battery bank.

Discharge/use the battery bank with 14.0 volt charging. If you used 10% of battery capacity (760 AH * 10% = 76 AH "consumed"). If you have charging at 14.0 volts and say 20 amps charging--Very roughly:

• 20 amps charging - 7 amps float current = 13 amps available for charging
• 76 AH / 13 amps = 5.8 hours (at 13 AH)...

I would assume that as the battery approaches ~90-100% state of charge, the 14.0 volt absorb charging will natural taper off (in theory to 1%). I would guess 2-3 days (using my completely made up numbers)... But it does show you how to evaluate the total current, charging current, and float/leakage current relationship.

-Bill

mcgivor

Fabian 

The temperature of the batteries will determine the charging voltage, if the ambient is 35°C the batteries will likely be higher due to inefficiencies in charging. With a 12V system for every 5°C over 25°C, the voltage should be reduced by 0.15V, therefore if the batteries are at 40°C the voltage would be reduced by 0.45V.

Most sealed batteries have a charging voltage in the range of 14-14.35V, so 14.4V without temperature compensation at 40°C battery temperature will cause overcharging, something sealed batteries cannot tolerate. The reason the voltage is not rising is because the self discharge rises with temperature so the current is producing heat which only manifests the problem.

My suggestion is first measure the battery temperature then lower the boost, bulk voltage to a more reasonable setpoint, if using the above example 40° battery temperature  13.55 to 13.9V range and float  12.95V.  Basically if the current doesn't taper down when the setpoint nears, the voltage is too high, at very similar temperatures my settings for flooded batteries are slightly higher 14V bulk, if I use 14.4V the batteries hiss all day and never reach float, but do get hotter. Being flooded I'm able to check the electrolyte specific gravity to verify they are fully charged, a luxury sealed batteries do not allow.

wellbuilt

I use a trace 40 amp unit for 3  years then it stoped working . 
The  manufacture  was no help all they can do is sell me a new one . 
 I can reboot the controller by turning off the power to it for a few minutes  and it would work for a day or two .
 I can’t say it was a total wast of money it did work 3 years .
 But in the end I just went back to my morning star PWM 25 amp unit I bought in the 80s 
  My battery’s are in there 4th year and I’ve abused them , I had to leave them discharged over the winter one year . 
  They have been under charged and over worked and I’m still pumping water with the system . 
 I use a small pump to move 300 gallons of water to a tank in my house it runs for a hour or so every other week . 
   I would get a better controller . 
 

Fabian

currently i am floating at 13.4v at around 1.5amp. If I leave it that setting for several days 24/7 will it eventually get a full charge without causing any overheating or overcharge or any other issue with my battery bank?

In other words is that setting and reading safe so far?

Estragon

If the bank is taking 1.5a on ~760ah, it's just about full, and the 1.5a is likely mostly offsetting self-discharge.  Note though that if you lowered the charging voltage, it may take some time (hours) for the battery voltage to drop to the new setting, and current could be misleading in the meantime.

BB.

1% or less current (~7.6 amps or less), you are not really charging your battery bank.

>2% rate of charge (~15 amps), you are charging, but very slowly (something like 1% per hour--rough guess). If your battery bank was discharged to 75% state of charge, it would take ~25 hours of "sun" to get somewhere close to full charge.

But you also have to watch the battery voltage... You do not want to have "full charging voltage" and unlimited time at >2% rate of charge--FLA batteries can still overheat if left for long periods of time on even a 2% rate of charge (1/2 day to days+).

More or less, at any reasonable float/charging voltage, >=2% rate of charge (does not drop below 2%) is a sign that the FLA/AGM/etc. lead acid batteries need to be replaced.

Too high of leakage current--gassing/loss of water/overheating (at float/charge voltage).

If you are EQing the battery (high voltage charging to "equalize" or balance the cells"... 2.5-5% rate of charge is "normal", but batteries need to be monitored for temperature. It is easy to overheat the battery after many hours of continuous EQ charging.

-Bill

Fabian

Estragon said:

If the bank is taking 1.5a on ~760ah, it's just about full, and the 1.5a is likely mostly offsetting self-discharge.  Note though that if you lowered the charging voltage, it may take some time (hours) for the battery voltage to drop to the new setting, and current could be misleading in the meantime.

When i lowered the charge voltage.It didn't take long before it was reading 13.4v and floating at that level drawing roughly 1.5amps.

So with this quick transmission to the lower voltage setting and quick reduction in charging current would that suggest that the bank is full?

The bank was still quite warm due to the fact that it was at the 13.8v setting for too long so after having it at 13.4v floating for several hours i remove the charger and now the battery has come down to 12.83v and is at that setting for couple hours so far so would this also suggest that the bank is full?

I feel like I definately have to get a battery temp sensor soon to attach to my Epever CC as i want to leave the SLA float charging 24/7 without any issues developing and in so doing would it be best to work with the manufacturer charging specs rite?

mcgivor

Floating at 13.4V, 1.5A for a 760Ah bank would indicate it is fully charged, there will always be some self discharge, more so at higher temperatures.

Estragon

After several hours with no loads or charging a 12v bank should have fully charged resting voltage of ~12.7-12.8.  If, after several hours, the bank is at 12.8x, that suggests to me the bank is full or nearly so. 

Fabian

currently now it is float charging between 13.4v -13.5v and the current is showing 1.5A - 2.7A sometimes but on a average it is showing 0.5amp basically less than 1 amp so is this a clear indication it is full and therefore i can let it stay on this setting permanently?

BB.

What is the "Absorb" charging setpoint for the charge controller?

Float voltage is fine for now.

-Bill

Fabian

i set it to boost at 13.8v and 13.6v for float. it has finish absorb and now floating.

BB.

13.8 volts is pretty low... I would probably be closer to at least 14.0 volts...

Monitor the charging current--That will tell you if the battery is being charged or not.

Letting batteries sit below ~75% State of Charge tends to accelerate sulfation--And since batteries sit overnight with solar charging, I would be a bit worried about a 5+ day charging cycle starting with a well discharged (down towards 50% state of charge) not being "good" for the battery bank...

-Bill "not a battery engineer" B.

Fabian

i set it to boost at 13.8v and 13.6v for float. it has finish absorb and now floating.

My charging is not tru solar. I am using a power supply connected to my CC so therefore I am leaving it for couple days charging 24/7 so leaving it floating at 13.5- 13.6v 24/7 it will eventually be full charged?