Battery Absorb and Float Voltage Ranges

[finalman]

So basically some batteries as an example have absorb voltage range of say 14.4v to 14.8v and a float range of say 13.4v to 13.8v.

Obviously with the battery input voltage readings of charge controllers at the terminals are not always accurate so rather than say over charging I'm thinking maybe I should just use the mid range of those ranges and would like to know if there are any disadvantages of using the mid range voltage level instead of the max voltage level.

[Vic]

I forget (if you ever did state it) just what batteries that you are using,   perhaps they are Lead Acid ...

There are different flavors of Lead Acid (LA) batteries.   There can be differing charge voltage requirements,  depending on exactly what type of battery you are using.

We always recommend using the manufacturer's recommendations for charge parameters.

If your batteries are Flooded LA (FLA),   then you are in luck,   as you can actually measure the Specific Gravity of each cell to determine just how well the battery bank is being charged.

If your batteries are Sealed,   then,   they are usually very sensitive to exact charge voltage,  and Temperature Compensation,   and it is usually more difficult to determine how well they are being charged.

In general,   suggest that you use the lowest Absorb voltage that gets the battery fully charged on most days,   particularly if your system is a full-time off-grid system.

For FLA batteries,   choose the lowest Float voltage that just barely keeps a fully-charged battery,  fully-charged during Float.

A major cause of the Charge Controller (CC) is due to voltage drop between the CC's battery terminals and the battery terminals.

If you get the chance,   if you could describe your system in a Signature line,   that will help folks  give answers that more relative to your system ...   what brand,   model and type of batteries that your system uses?

Thanks,   Vic

[ClassicCrazy]

If the wiring is sized right the voltage at the charge controller terminals should be pretty much what the battery voltage is .
If the batteries are new start at the bottom of their range - you can raise it later as the batteries age or if you need to for some other reason.

Larry

[Vic]

If the wiring is sized right the voltage at the charge controller terminals should be pretty much what the battery voltage is   ...

Larry

Yea,   but at reasonably high output currents,   even the circuit breaker on the CC output has a significant voltage drop  --  At 60 A DC from one Classic,   the breaker drops about 37 mV.   This is not trivial,  especially when trying to use EA for Absorb termination,   with fairly heavy but variable (A/C)  Opportunity loads on the system.

Did eliminate the Common-Mode RFI reduction chokes on the CC output,   to help reduce the voltage drop  (Bifilar #6 AWG  wound on a stack of three Ferrite donut toroids).  One just cannot wind any larger wire on these cores,   and get many turns,  at all.

FWIW,   just my experience,    73,   Vic

[finalman]

I forget (if you ever did state it) just what batteries that you are using,   perhaps they are Lead Acid ...

There are different flavors of Lead Acid (LA) batteries.   There can be differing charge voltage requirements,  depending on exactly what type of battery you are using.

We always recommend using the manufacturer's recommendations for charge parameters.

If your batteries are Flooded LA (FLA),   then you are in luck,   as you can actually measure the Specific Gravity of each cell to determine just how well the battery bank is being charged.

If your batteries are Sealed,   then,   they are usually very sensitive to exact charge voltage,  and Temperature Compensation,   and it is usually more difficult to determine how well they are being charged.

In general,   suggest that you use the lowest Absorb voltage that gets the battery fully charged on most days,   particularly if your system is a full-time off-grid system.

For FLA batteries,   choose the lowest Float voltage that just barely keeps a fully-charged battery,  fully-charged during Float.

A major cause of the Charge Controller (CC) is due to voltage drop between the CC's battery terminals and the battery terminals.

If you get the chance,   if you could describe your system in a Signature line,   that will help folks  give answers that more relative to your system ...   what brand,   model and type of batteries that your system uses?

Thanks,   Vic

Batteries are "Giant Power" AGMs 280A capacity and four of them so 48v. Battery cable run is like 5 meters (one way) of 75mm2. Long cable run yes but usually only uses 2 Kilowatts overnight.

[Vic]

OK fm,   thanks for the info.

I am not an AGMer.   Many say that AGMs like      l   o     n      g      Absorb times.   Some AGM manufacturers look for very,   very small End Amp values to end Absorb.

Am not familiar with Giant AGMs,   but try to follow their recommendations.

FWIW,   Vic

[ClassicCrazy]

Vic - like you mentioned in another post - it would be nice if the controllers had sense wires.
I should probably check mine - I pretty much just plug and play and trust - maybe I should do more checking and not trust .
Larry

[Robin]

I have made voltage drop measurements many times over the years. Unless you are using too small of battery wire and too long or have huge DC loads, the voltage drop between the CC and the batteries is typically down in the mud. Charge controllers are not high accuracy devices when it comes to measuring voltage. Are you aware that some charge controllers when charging a 48V bank can only be adjusted to 0.4V increments! That really sucks. The Classic allows 0.1V increments. We have also tried hard to make the voltage measurements more accurate than what we designed years ago at other companies. That said, the B17 and Big Kid under development do have voltage sense terminals.

[Vic]

Hi Robin,

IMO,   the Classic and KID  CCs  are accurate enough,   and setpoint resolution finer than 0.1 volts is not really required.

AND,   I would NOT trade any of the Classics or KID CCs here for ANY other CC,  period.

Folks like me  just want it all,   everything possible.   But,  this is never possible.

The Classic has SO many great functions that are built-in  from the factory,   and no other CC even comes close to this.   Almost all of the other CCs that do have Sense terminals,   are completely stripped-down  --  essentially no other functions included,  compared to the Classic and KID.

It is just,   that even 0.1 V drop in the leads from the Classic to the battery can cause a 1 Amp nominal change in the battery charge current.   So,  near the end of Absorb,   this  "small" drop can make a 30 - 45 minute difference in when the Absorb ends.   Perhaps,  am a bit too far out on the curve of Finishing Current into the battery,   where small changes in measured battery current affects the length of Absorb.   We often Skip three days of full-charging,   and try to fully-charge on the fourth day,   so,   getting a good,   predictable full charge is important on those days.

End Amps is,  by far the best approach for ending Absorb IMO,   and even small voltage drops from Opportunity loads cause seemingly small changes in WbJr-measured battery current.   These small changes in Ibat can cause fairly long extensions of Absorb with unpredictable Opportunity loads,  like a fairly large A/C (that cools the power electronics and batteries,  here).

I do realize that there is essentially no room for any additional terminals (like those for Sense) in the Classic.

Just my observations.    Thanks,   always wanting MORE-Vic



It would be nice,   if the Comm accessory that you have mentioned might be in the works,   had Sense terminals,  and could communicate actual battery voltage to Classic  CCs.