float @ 90% SOC

dapago · December 2016

Hello,

My Classic is entering float with the batts not totally charged (90%/95%). Absorb time is set to 2 hours. Should I just add 30 mm more or are there other settings that need to be changed?

thank guys.

Estragon · December 2016

I would add to the absorb time. I think mine is set for 4 hours, but I have a whizbang jr and use ending amps as well.

dapago · December 2016

I have lot of sun here in my location and 2 hours absorb time set. I don't have wb jr. I just take the state gravity of my bank every day until I can reach a good setting for my Classic. During 8 month a year, sun is shinning every single day so it does help. On the other end I do not want to absorb more than necessary.

Estragon · December 2016

How much current is going into the batteries at the end of the 2 hrs? You could check Trojan specs but you likely want to stay in absorb until you get down to a couple of amps or so.

Note that you don' t necessarily have to do this every day. You can set the classic to skip X days. It's important to get the batteries fully charged with a long enough absorb once or twice a week, but you could just bulk and float for a couple of days and have it do a full absorb every third day for example.

dapago · December 2016

So you advise me to skip absorb let say 2 days with just bulk and float and full absorb for 1 day and so on? Does a full absorb every day damage the batts?

I haven't check the input voltage at the end of absorb. I understand that it should be around 2% of my 225ah batt (~ 5 Amps) so should I set absorb time on that basis? My load during the day is pretty stable.

mcgivor · December 2016

Seems strange to me to limit or skip absorbtion, my manual, not Midnight, states that absorbtion is the most important stage of charging. Is there not a default setting, usually the engineers who developed the controller have a pretty good idea of what a battery needs.

Photowhit · December 2016

mcgivor said:

Seems strange to me to limit or skip absorbtion, my manual, not Midnight, states that absorbtion is the most important stage of charging. Is there not a default setting, usually the engineers who developed the controller have a pretty good idea of what a battery needs.

They don't know what type or capacity battery you have.

mcgivor · December 2016

Photowhit said:

mcgivor said:

Seems strange to me to limit or skip absorbtion, my manual, not Midnight, states that absorbtion is the most important stage of charging. Is there not a default setting, usually the engineers who developed the controller have a pretty good idea of what a battery needs.

They don't know what type or capacity battery you have.

But they should have settings for various types, FLA, L16, AGM etc. Would this not be an accurate assumption?

mcgivor · December 2016

With regards to capacity, the current would be regulated according to the voltage during absorbtion, bulk is where you wouldn't want to over current, within reason. Is this not a reasonable statement ?

Estragon · December 2016

@mcgivor - it IS important to absorb to mix electrolyte and prevent sulfation, but the idea behind skip days is that it doesn't have to be done every single day. OP is concerned about too much absorb (positive plate corrosion, excessive gassing) and has good sun, so my suggestion would be to increase absorb time to be certain batteries are actually full a couple time a week and float otherwise.

Photowhit · December 2016

mcgivor said:

Photowhit said:

mcgivor said:

Seems strange to me to limit or skip absorbtion, my manual, not Midnight, states that absorbtion is the most important stage of charging. Is there not a default setting, usually the engineers who developed the controller have a pretty good idea of what a battery needs.

They don't know what type or capacity battery you have.

But they should have settings for various types, FLA, L16, AGM etc. Would this not be an accurate assumption?

There will be basic setting, AGM, FLA, ...

But think of all the different types of setups, You can have a 4K watt array feeding a lead acid battery! A weekend setup with a huge bank say 1200ah forklift battery, providing just a 5% charge rate, or a 400ah bank in a cloudy region. A finishing rate of 30 amps or 2-3% of a 1200 ah battery is charging rate for a small battery bank. Best to input a finishing rate perhaps more than a timed charging, and perhaps they might consider that at some point, but I think that varies by type as well. I mostly have had FLA.

Vic · December 2016

dapago,

Personally, would set the Absorb (called 'Bulk' by Trojan) voltage, as specified in the Data Sheet in the following Link -- 59.28 V, 59.3 should be fine:
http://www.trojanbattery.com/pdf/datasheets/T105RE_TrojanRE_Data_Sheets.pdf

Float is noted as 54.0 V, and EQ V is 64.8 V.

Target SG for full-charge is 1.277.

I, too, use Skip Days -- Skip three, and charge on the fourth day.
BUT. dapago probably needs to find settings that will bring the battery bank to full-charge, before Skipping Days.

Be certain to mount the BTS on one battery in the center of the battery bank.

The Temperature Compensation value is -- 5 mV/Cell/C. Would suggest setting Temp Comp EQ = YES.

As suggested elsewhere, would set the Charge voltages to those recommended by Trojan, and watch the SGs to see how they respond. If still not reaching 1.277 SGs, then try increasing the Absorb time by about 30 minutes, for a start:
http://kb1uas.com/mnsforum/index.php?topic=3560.0

The Classic Ending Amps function works great, when using the WBjr with a 50 mV 500 A Shunt. CC EA (without a WBjr) can work well, especially if there are no heavy loads that are present near the time when Absorb should be ending. Heavy loads that cycle every few minutes should not be an issue when using CC EA, as long as the heavy load is off for about five minutes or so. Used CC EA for about 5 - 6 years without any problems.

All FWIW, Vic

mcgivor · December 2016

Photowhit said:

mcgivor said:

Photowhit said:

mcgivor said:

Seems strange to me to limit or skip absorbtion, my manual, not Midnight, states that absorbtion is the most important stage of charging. Is there not a default setting, usually the engineers who developed the controller have a pretty good idea of what a battery needs.

They don't know what type or capacity battery you have.

But they should have settings for various types, FLA, L16, AGM etc. Would this not be an accurate assumption?

There will be basic setting, AGM, FLA, ...

But think of all the different types of setups, You can have a 4K watt array feeding a lead acid battery! A weekend setup with a huge bank say 1200ah forklift battery, providing just a 5% charge rate, or a 400ah bank in a cloudy region. A finishing rate of 30 amps or 2-3% of a 1200 ah battery is charging rate for a small battery bank. Best to input a finishing rate perhaps more than a timed charging, and perhaps they might consider that at some point, but I think that varies by type as well. I mostly have had FLA.

Vic said:

dapago,
Personally, would set the Absorb (called 'Bulk' by Trojan) voltage,   as specified in the Data Sheet in the following Link -- 59.28 V, 59.3 should be fine:
http://www.trojanbattery.com/pdf/datasheets/T105RE_TrojanRE_Data_Sheets.pdf
Float is noted as 54.0 V, and EQ V is 64.8 V.
Target SG for full-charge is 1.277.
I, too, use Skip Days -- Skip three, and charge on the fourth day.
BUT.   dapago probably needs to find settings that will bring the battery bank to full-charge, before Skipping Days.
Be certain to mount the BTS on one battery in the center of the battery bank.
The Temperature Compensation value is -- 5 mV/Cell/C.   Would suggest setting Temp Comp EQ = YES.
As suggested elsewhere, would set the Charge voltages to those recommended by Trojan, and watch the SGs to see how they respond. If still not reaching 1.277 SGs, then try increasing the Absorb time by about 30 minutes, for a start:
http://kb1uas.com/mnsforum/index.php?topic=3560.0
The Classic Ending Amps function works great, when using the WBjr with a 50 mV 500 A Shunt.   CC EA (without a WBjr) can work well,   especially if there are no heavy loads that are present near the time when Absorb should be ending.   Heavy loads that cycle every few minutes should not be an issue when using CC EA, as long as the heavy load is off for about five minutes or so. Used CC EA for about 5 - 6 years without any problems.

All FWIW,   Vic

Say for example you had a battery which has no loads and is fully charged at days end, overnight the self discharge is almost negligible, the next day sun up battery is at 99.9% charged, the controller sees the voltage and instead of doing a bulk charge goes immediately into absorbtion, after the time out of absorption, it switches into float.

Next night the battery is discharged to 80% SOC, following morning the controller reads the voltage and goes into bulk until the absorption setpoint is met, absorbtion takes place and times out, then float. This is using a standard algorithm without user input, would this not be a good starting point, to establish a base line from which to adjust setpoints and timed functions to suit particular needs of a system, if needed, wether it be a daily or weekend use, or specific battery requiments. Sometimes too many interventions can lead to problems and these can sneak up undetected and result in premature battery failure.
In the case of @dapago, it would seem his array is a little too large for the battery, 2480W for 225Ah, so if anything the bulk amperage may be on the high side, but once it goes into absorbtion, the current should drop as the level of charge increases. So if it is possible to limit the bulk charge current would this not be the prudent thing to do? The absorption stage would taper the current down to avoid gassing and terminate when the time has expired, then go into float, assuming there are no large loads which may prompt the controller into going back into bulk.

There seems to be different uses for the term bulk/absorbtion as @Vic stated so I copied the information from a Morningstar manual which are the terminologys as I understand them. So as @Estragon mentioned using absorbtion to mix the electrolyte, is this bulk being referred to as absorbtion, as bulk is more likely to do just that.

The TriStar MPPT 150V has a 4-stage battery charging algorithm for rapid, efficient, and safe

battery charging.

Bulk Charge Stage

In Bulk charging stage, the battery is not at 100% state of charge and battery voltage has not yet

charged to the Absorption voltage set-point. The controller will deliver 100% of available solar

power to recharge the battery.

Absorption Stage

When the battery has recharged to the Absorption voltage set-point, constant-voltage regulation

is used to maintain battery voltage at the Absorption set-point. This prevents heating and exces-

sive battery gasing. The battery is allowed to come to full state of charge at the Absorption volt-

age set-point. The green SOC LED will blink once per second during Absorption charging.

The battery must remain in the Absorption charging stage for a cumulative 120 - 150 minutes,

depending on battery type, before transition to the Float stage will occur. However, Absorption

time will be extended by 30 minutes if the battery discharges below 12.5 Volts (25 Volts @24 V,

50 Volts @48 V) the previous night.

The Absorption set-point is temperature compensated if the RTS is connected; otherwise,

voltages set-points are based on the reference of 25ºC.

.

Float Stage

After the battery is fully charged in the Absorption stage, the TriStar MPPT 150V reduces the

battery voltage to the Float voltage set-point. When the battery is fully recharged, there can be

no more chemical reactions and all the charging current is turned into heat and gasing. The float

stage provides a very low rate of maintenance charging while reducing the heating and gasing of

a fully charged battery. The purpose of float is to protect the battery from long-term overcharge.

The green SOC LED will blink once every two (2) seconds during Float charging.

Once in Float stage, loads can continue to draw power from the battery. In the event that the

system load(s) exceed the solar charge current, the controller will no longer be able to maintain

the battery at the Float set-point. Should the battery voltage remain below the Float set-point for

a cumulative 60 minute period, the controller will exit Float stage and return to Bulk charging.

The Float set-point is temperature compensated if the RTS is connected; otherwise, voltages

set-points are based on the reference of 25ºC.

Equalize Stage

Certain battery types benefit from a periodic boost charge to stir the electrolyte, level the cell

voltages, and complete the chemical reactions. Equalize charging raises the battery voltage

above the standard absorption voltage so that the electrolyte gases. The green SOC LED will

blink rapidly two (2) times per second during equalization charging.

The duration of the equalize charge is determined by the selected battery type. See table 4-1

in this section for more details. The Equalization Time is defined as time spent at the equalize

set-point. If there is insufficient charge current to reach the equalization voltage, the equalization

will terminate after an additional 60 minutes to avoid over gasing or heating the battery. If the

battery requires more time in equalization, an equalize can be requested using the TriStar Meter

or push-button to continue for one or more additional equalization cycles.

Estragon · December 2016

Mcivor - in your example above of a nearly full bank, cc will see voltage of ~12.8v at rest for a 12v bank. It will go into bulk sending available current to bank at whatever rate the bank will take until voltage reaches absorb setpoint (eg 14.7). If the bank was full, it will get to that voltage pretty quickly, but it still has a bulk stage. The controller will then hold voltage at the absorb voltage until either current drops to set value or timeout.

It might make some sense to limit bulk current, but I don't think it's a big issue unless batteries are hot.

As you and Vic have said, the main thing in this case is to get absorb set to fully charge batteries. OP says he checks sg regularly which should help get there.

Vic · December 2016

Hi mcgivor,

When you said,

"Say for example you had a battery which has no loads and is fully charged at days end, overnight the self discharge is almost negligible, the next day sun up battery is at 99.9% charged, the controller sees the voltage and instead of doing a bulk charge goes immediately into absorbtion, after the time out of absorption, it switches into float",

The above is the way that most CC behave now. There is generally NO Bulk voltage setting, because with PV charging, there is not enough current available to immediately reach the Absorb voltage, so maximum available charge current eventually allows the battery voltage to rise to the set Absorb voltage, and THEN, the Absorb stage begins.

If the only "load" on the battery was self-discharge, then the Bulk stage will be fairly short, as would be the required Absorb. But with a fixed Absorb time set in the CC, and Ending Amps was not being used, the Absorb, would most likely be much longer than necessary.

The Outback, and the MidNite CCs ALL have three stage charging, PLUS EQ. MorningStar IS a bit different, but they all have those "four stages".

Few other CC manufacturers have battery type settings, except for different NiCd, perhaps. Morningstar is the only manufacturer that I know of that has an L-16 setting. Much of this is a hold-over due to their very limited range of charge parameters, due to the use of DIP SWITCHES.

Later, Vic

dapago · December 2016

I just can not get my mind on that EA function.
What I understood at that point is that EA has priority on absorb time but how and when does EA know to limit the amp going into the batts?
Will EA:
- totally cut the charge and if so until when?
- if set to 1,5% of my batt capacity, limit the charge to 3.5A and if so until when?

mike95490 · December 2016

be able to read the battery end amps, the current sensor (shunt) has to be in only the battery leg, not the solar/inverter/battery wire,
That way, you are only reading the battery amps, not the solar-inverter amps

Photowhit · December 2016

dapago "...when does EA know to limit the amp going into the batts? "

End amps doesn't limit the amps going into the battery. It measures the amps going into the battery. as the battery approaches full it accepts less amps. When it reduces to your set limit, the charge controller lowers the voltage to the float level. At the float level the battery is basically treading water. (The voltage is just high enough to have a bit of a positive flow to the battery) While in the float mode, a load on the system will bring the voltage down, the charge controller will raised the level of current passing to compensate until the voltage is at the float level. In this manner the load will essentially be running off the array.

Estragon · December 2016

To clarify a bit, if you use a "whiz bang jr" with your classic end amps are measured at the battery. If you don't use a wbjr, you can still set end amps but current will be measured at the controller. At the controller current will be a combination of charging and loads, and the loads may prevent the controller from seeing end amps.

The second way can work okay and is probably better than nothing, but the wbjr and shunt aren't really expensive and is the better way to do end amps.

float @ 90% SOC

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