Float or higher charge voltage for value regulated sealed lead battery

Fabian · July 2017

I am using a 24v system and I have (4) EnerSys PowerSafe 12V190F 180Ah valve regulated sealed lead acid battery which I connect in series and parallel so my battery bank is 24v at 380Ah. I am trying to figure out what is the correct max charge voltage it is suppose to get. The specs on each of the batteries says max float charge voltage per cell is 2.29v which works out to be 13.74v per battery and when you double for 24v that works out to be 27.48v.

So should I set the max charge voltage to be always 27.48v on my charge controller?

What if I run down the battery to 23.3v or slightly below 24v sometimes should it still charge up to 27.48v or do I need to go a bit higher sometimes because of the lower discharge?

Does this battery bank require equalization charge sometimes and if yes how often should it be applied and what is the max charge voltage I should use for equalization charge and how long should it remain on equalization charge?

littleharbor2 · July 2017

Many of the AGM batteries out there are designed for UPS/float service. They aren't made for daily cycle service. This may be why you aren't seeing a bulk charge voltage on the label. A lot of people get decent performance with these batteries in part time systems where say in a cabin or RV you don't cycle them on a regular basis.

Typically AGM batteries don't want as high a charging voltage as a flooded battery wants because they have to recombine the hydrogen gasses back into the electrolyte. If charged at too high a voltage they cant recombine the gas fast enough and will vent and lose electrolyte which cannot be replaced. They all vary in bulk/absorb voltage allowances but usually about 14.4 to 14.6 is safe per 12 volt battery. Gel batteries are even worse as the gas bubbles will become trapped in the gel electrolyte so they will max out at about 14.2 volts max.

Generally speaking sealed batteries shouldn't get equalized for the aforementioned reasons. Some Mfg. will call for a periodic slightly higher voltage, "Freshening charge".

mcgivor · July 2017

From what I can gather these batteries are designed for telecomm or UPS service, not for cyclical use, the float voltage is not the charge voltage, on a 24V nominal system the bulk/ absorb voltage would be in the neighborhood of 28.8V, float would be around 27V, as far as equalization is concerned, they should not be equalized, unless the manufacturer recommends to do so. If you are experiencing low voltage on discharge it is more than likely because they are not being fully charged, just a speculation as I've no idea of the loads,

Fabian · July 2017

My charge controller does not allows you to set bulk/absorb then set float voltage. It just allows you to set the pv cut off voltage and whatever voltage you set it at that's where the charge voltage doesn't pass. It will remain at that voltage sending high current into the battery until the current drops down to a small amount and will start to float at that same voltage. So in my case If i set it at the 27.4v will the battery get a full charge? Also what would be the float current going into the battery that would suggest my battery bank is fully charged? My bank is 380Ah so what current or percentage of the 380Ah going into the battery at 27.4v would suggest it is fully charged?

Estragon · July 2017

The bank will eventually charge at float voltage, but off-grid we don't generally have time for that (sun goes down, etc.). I consider between 1-2% of capacity at absorb voltage to be fully charged, at which point the controllers go to float voltage.

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.

littleharbor2 · July 2017

Raise your setting to 28.8. This will get you closer to full charge. When your controller transitions to float and batteries drop their surface charge voltage, like hours after dark with no load, you should see what your float voltage is.

Solray · July 2017

You cannot get 380 ah out of any configuration using a 180 ah battery. You are limited to numbers that are divisible by 180. ie. 180, 360, 540, 720, etc.

Horsefly · July 2017

Solray said:

You cannot get 380 ah out of any configuration using a 180 ah battery. You are limited to numbers that are divisible by 180. ie. 180, 360, 540, 720, etc.

It was a typo. The batteries the OP mentioned are 190AH.

Estragon · July 2017

> @Solray said:
> You cannot get 380 ah out of any configuration using a 180 ah battery. You are limited to numbers that are divisible by 180. ie. 180, 360, 540, 720, etc.

I'm guessing it's a simple arithmetic error or typo in the OP, but strictly speaking you could get 380ah from a 180ah battery. Just have to warm it up some.

mcgivor · July 2017

Fabian said:

My charge controller does not allows you to set bulk/absorb then set float voltage. It just allows you to set the pv cut off voltage and whatever voltage you set it at that's where the charge voltage doesn't pass. It will remain at that voltage sending high current into the battery until the current drops down to a small
amount and will start to float at that same voltage. So in my case If i set it at the 27.4v will the battery get a full charge? Also what would be the float current going into the battery that would suggest my battery bank is fully charged? My bank is 380Ah so what current or percentage of the 380Ah going into the battery at 27.4v would suggest it is fully charged?

A setting of 27.4V is unlikely to get the battery fully charged in an off grid cyclical application, this low setting intended for standby use, UPS/telecom, which relies on the fact that grid power is available 24 hours, the next discharge may be days,weeks or months away, thus allowing a full charge overy time. Discharging on a daily basis, coupled with a limited window of opportunity, sunlight, may lead to problems related to insufficient charging, the amount of discharge, load, is a critical factor, not mentioned, but if the load is light and the voltage drops below 24V, the capacity is ~50% or less. A voltage in the range of 28.2 to 28.8V @25°C, would seem more appropriate. Could you show your controller and list the loads including PV array size, this would help everyone determine what exactly it is you are dealing with.

Solray · July 2017

190 ah will get you a 380ah bank wired correctly. There are ways of getting odd ah ratings from a bank, but many of them are unsafe and can cause a fire so they are not recommended.

Fabian · July 2017

it was typo. I didn't even realize until now. I meant 360ah of course. So basically if I set my controller to 28.8v is it safe to float charge my value regulated battery at that voltage once the battery temp is @25°C or below?

mcgivor · July 2017

Because there are only so many hours of useful sunlight the current would taper down to almost nothing, probably in a pulse width modulation, at the higher voltage, there would be no float perse, the voltage would drop as the sun sets until it settles, usually around 25.4V, without load.

littleharbor2 · July 2017

As mentioned, that setting is the bulk/absorb voltage., Not float voltage.

westbranch · July 2017

Read this document abut AGM charging... http://www.cdtechno.com/pdf/ref/41_2128_0212.pdf lots of good info , just have to reread it as it is up to you based on usage and temps and make...

I use 28.8 in summer and 28.9 in winter...

littleharbor2 · July 2017

Here's some info I pulled from a seller on ebay for your brand of controller. It should be self explanatory as to the charging parameters. You have different voltages for different types of batteries and also user settable voltages from 9 - 17 volts. Model	Tracer1210A	Tracer2210A	Tracer3210A	Tracer4210A

Nominal system voltage	12/24VDC auto work
Rated charge current	10A	20A	30A	40A
Rated discharge current	10A	20A	30A	40A
Battery input voltage	8~32V
Max. PV / open circuit voltage	100V(at minimum operating environment temperature) 92V(at 25℃ environment temperature)
MPP voltage range	VBAT+2V～ 72V
Max. PV input power	130W(12V) 260W(24V)	260W(12V) 520W(24V)	390W(12V) 780W(24V)	520W(12V) 1040W(24V)
Equalize charging voltage	Sealed: 14.6V, Flooded: 14.8V
Boost charging voltage	Gel: 14.2V, Sealed: 14.6V, Flooded: 14.8V
Float charging voltage	13.8V
Low voltage reconnect voltage	12.6V
Low voltage disconnect voltage	11.1V
Self-consumption	≤20mA/12V; ≤16mA/24V
Temperature compensation coefficient	-3mV/ ºC/2V(25 ºC)
Working temperature	-25 ºC ～+45 ºC
Enclosure	IP30
Overall dimension	172x139x44mm	220x154x52mm	228x164x55mm	252x180x63mm
Power terminals	12AWG(4mm2)	6AWG(16mm2)	6AWG(16mm2)	6AWG(16mm2)
Net weight	0.6kg	1.1kg	1.2kg	1.9kg

Battery Voltage Parameters (parameters is in 12V system at 25 °C, please use double value in 24V.)Battery charging setting

Sealed

Gel

Flooded

User

Over Voltage Disconnect Voltage

16.0V

9~17V

Charging Limit Voltage

15.0V

9~17V

Over Voltage Reconnect Voltage

15.0V

9~17V

Equalize Charging Voltage

14.6V

——

14.8V

9~17V

Boost Charging Voltage

14.4V

14.2V

14.6V

9~17V

Float Charging Voltage

13.8V

9~17V

Boost Reconnect Charging Voltage

13.2V

9~17V

Low Voltage Reconnect Voltage

12.6V

9~17V

Under Voltage Warning Reconnect Voltage

12.2V

9~17V

Under Volt. Warning Volt.

12.0V

9~17V

Low Volt. Disconnect Volt.

11.1V

9~17V

Discharging Limit Voltage

10.6V

9~17V

Equalize Duration (min.)

120

——

120

0~180

Boost Duration (min.)

120

10~180

bsolar · July 2017

Fabian said:

it was typo. I didn't even realize until now. I meant 360ah of course. So basically if I set my controller to 28.8v is it safe to float charge my value regulated battery at that voltage once the battery temp is @25°C or below?

it will be safe but it wont hurt to lower the value and thats what i would do since it sounds like your controller is a diverter or cutoff type .. i would shoot for a value of 13.4v or even 13.2v per battery, you will lose very little in usable capacity and they will last longer ... to equalize simply add a volt ( per battery) .. only other contingency would be if you have a giant array and no real way to regulate amps, in that case buy a better controller, you could afford the panels so get a 3 stage controller/s ...

jonr · July 2017

You can set "Charging Limit Voltage" to 14.4V and "Float" to 13.2V. Adjust as needed for batteries in series.

Fabian · July 2017

Would anyone of these charge controller appropriate to use?

http://www.ebay.com/itm/60A-MPPT-solar-charge-controller-regulator-12v-24v-48v-3200w-monitoring-PCM60X-/161615675225?hash=item25a10b7f59:g:K6UAAOSwm8VUygAw

Image: http://i.ebayimg.com/images/g/K6UAAOSwm8VUygAw/s-l1600.jpg

http://www.ebay.com/itm/EPEVER-1210A-2210A-3210A-4210A-MPPT-Solar-Charge-Controller-Regulator-OR-MT50-MT-/311660954363?var=&hash=item489070c2fb:m:mG7121Dtm3XtuoGkUt8o9qA

Image: http://i.ebayimg.com/images/g/grgAAOSwepZXSSbP/s-l1600.jpg

Fabian · August 2017

still waiting on an answer someone please.

littleharbor2 · August 2017

Fabian said:

still waiting on an answer someone please.

Fabian,
You would have better luck getting an answer if you started a new thread instead of jumping into someone else's thread. Also your question is impossible to answer because there is no way to judge appropriateness of a charge controller without more information.
The way it usually works is you need to know your load over the course of a 24 hour period as well as peak load. Then you figure out an appropriate size battery. Battery size and load dictates charging requirements. Peak load will determine inverter size, if using an inverter. From there you figure how much solar and what size charge controller you need.

Fabian · September 2017

Charging my current battery bank with my regular PWM charge controller how long should I let the battery bank stay at the bulk/ absorb voltage of 28.8v before I cut it down to 27v for float charge?

Estragon · September 2017

Many(most/all?) PWM controllers will terminate absorb when the duty cycle (number/length of pulses over a given time period) falls to a predetermined level. The manual should have details.

With no other loads, 3 hours or so of absorb would be typical.

Fabian · September 2017

Regular(most) pwm controllers will terminate the Pv cutoff voltage that you set for eg.28.8v and then switch to a lower voltage setting automatically for eg.27.4v and then commence float charging at that lower voltage or will still maintain the high voltage setting that you set but then switch to a lower current charging?

My controller just has one setting in which i set the cutoff voltage and whenever it reaches that voltage setting it remains at that voltage setting and then the current decrease gradually as the battery starts to get closer to the full charge level so in my case the controller won't decrease the high voltage setting once the battery gets full charge and then switch to a float charge voltage for eg. 27.4v. It just has one cutoff setting which it floats at that same setting.
Is there a way for me to let the controller automatically switch from that high bulk charge/absorb voltage after a certain length of time and then switch to a lower voltage setting to float charge with?
Or suppose i use a temp sensor (BTS) which attaches to the battery bank will the regular pwm controller ignore the voltage setting that i set and auto adjust the voltage/current once the battery starts to get too warm or too hot or pass the safe temp range?

Estragon · September 2017

It's normal for current to drop off as the battery gets full at absorb voltage. It's not a matter of the controller reducing the current, it's just that the battery takes less current at a given voltage as it gets full.

There definitely should be some way to get the controller to go to a lower float voltage when (if) the battery gets close to full.

A couple of things come to mind:

1. It may be that the controller doesn't know the battery is full. For example, you may have loads besides charging which prevent the duty cycle from dropping low enough for long enough for the controller to know to go to float.
2. There may be a duty cycle setting that is set too low, or a time at that duty cycle setting that's too long.

A temperature sensor should adjust voltage. It will lower voltage for higher temps, and vice versa. I don't know that it's directly related to the transition to float issue, but generally a good idea anyway.

Fabian · September 2017

If i install a BTS between my current VRLA battery bank which are factory default to float at 27.4v and set my one setting controller to cut the bulk charge at 28.8v which it will begin to float at that same voltage, will the BTS prevent the battery from getting too warm or pass the safe temp range by reducing the current or the voltage or both to a very minimal amount that will prevent the battery from gassing too much and prevent water loss or go into thermal runnaway at that 28.8v setting?

My controller has a Temp compensation of 4mV/Cell/'C does that indicate that once a certain battery temp is reach, the controller will decrease the charging voltage according to the temp reading and it will even reduce it more if the temp increase again?

Estragon · September 2017

Yes, the controller should reduce voltage as temp rises on the RTS. IIRC the compensation is typically from 25°C. Current is affected only indirectly, as the battery will accept less current when voltage is reduced.

If ambient temps are significantly different than battery temps, you may want to cover the sensor part that sticks onto the battery with a bit of insulation.

fratermus · September 2017

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. :-)

Fabian · October 2017

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

what is Vabs?

littleharbor2 · October 2017

The point at which your controller transitions from Bulk to Absorb . While in absorb mode the voltage is held at that setpoint until the battery is done absorbing current. from there the controller transitions to float mode.

Estragon · October 2017

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

Float or higher charge voltage for value regulated sealed lead battery

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Battery Voltage Parameters (parameters is in 12V system at 25 °C, please use double value in 24V.)Battery charging setting

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