Absorb Times & Float Voltage ??

[epsgunner]

Um..

I need a recommended Absorb min/max TIME for when I get the Midnite Classic 150 in next weekend..

I'll be doing 14.4 Absorb Voltage.. the battery bank will be starting at 440ah worth of FLOODED battery.. (4 * 6v GC2 220ah types).. wired 2 in series then 2 in parallel..

So is 30 mins and 2 hours the standard numbers to plug in here?? I saw a Midnite video showing those numbers as default..

Also, What should be my FLOAT voltage?? is that 14.5??

I figure I will set the Equalize to 15.3 volts..

Suggestions??

[Westbranch]

I would highly recommend you go the GC battery manufacturers site and dig through it to find the correct settings for YOUR battery model.  Don't guess here or you will eventually end up with 4 lumps of lead...sooner or later...

[epsgunner]

Found old numbers in my old manuals.. 14.4 Absorb and 13.6 Float..

Trojan says 14.8 Absorb.. (off another forum)..

Yeah.. that would normally work.. but I'll be testing on a single cheapy battery 1st.. so numbers aren't easy to get from Wallyworld (aka JohnS Controls)..

Just need a tip on the Absorb min/max times now.. 30 mins and 2 hours sound ok??

[plongson]

What do I know, and I might (probably) get corrected by the gang, but...

If you set a wide spread like you are suggesting, then it falls into the realm of Ending Amps, and you have to determine what you want your EA to be. It has been suggested here at 10% your bank capacity, plus your parasitic draw is a good starting point for EA.

I think if you had a wide spread with a low EA, it would just continue to Absorb until the max time is reached.

If you set the absorb time tight, like 2hrs/58 minutes minimum and 3 hours max with a low EA like around say 4 amps it will simply absorb for a set time, essentially 3 hours.

It all depends on getting the SG correct at the end of the day, and believe me, that has been my biggest challenge which I believe I have won.

Anyway, this is my understanding and I'm sure you will see more reply's if I'm wrong. Hope this all makes sense...

Paul

[epsgunner]

I thought I read online 1/2 hour per 100ah of battery bank for absorb time..

Can anyone confirm that as a general rule of thumb..

Between that and setting my EA to say 2 (for a 200ah battery banK)

Anyone else got simple tips..

[boB]

I thought I read online 1/2 hour per 100ah of battery bank for absorb time..

Can anyone confirm that as a general rule of thumb..

Between that and setting my EA to say 2 (for a 200ah battery banK)

Anyone else got simple tips..

I don't know if I have heard that exact rule of thumb, but it sounds OK I think.  In the ball park at least.
Will have to think about that a bit more but I kind of like it.

boB

[Vic]

Al,

The time needed in Absorption is heavily dependant the SOC at beh beginning of the charge cycle.

It is for this reason that I like EA,  which is usually set between 1 and 2% of 20 hr capacity for FLA batteries.   EA is fairly consistant irrespective of DOD.   But there is the proviso is that heavy loads on Inverters appear to be charge current to a CC,  so consistant heavy loads,  or random intermittant loads need to be accounted for and considered.

Since you are and will be using FLA batteries,  the good news iis that you can actually measure how you are doing with either EA or timed Absorption.

It is a good idea to get a good glass float type Hydrometer for this  purpose.   I have not used a Refractometer,  but appears that thre inexpensive refractometers.   Good Luck,  Vic

[boB]

Al,

The time needed in Absorption is heavily dependant the SOC at beh beginning of the charge cycle.

This is definitely true but in past charge controllers where the SOC is not known or ending amps cannot be used, time is the way it has been done with success.  For instance,  the old Trace C40/C60 and all of the Trace inverter/chargers did it this way and worked well.

The  only real downfall of using time as the end of charge deciding factor is that it may be too long some times and so you have to watch the electrolyte (water) level more often so it does not run the battery dry.

boB

[Vic]

Hi boB,

1.  You and your crew have much more experience with solar than I.

2.  Yes,  know that this  has been the case for a decade or more  -- using timed Absorption stage,  perhaps with Absorption time equaling Bulk time.  With the cost of batteries having increased more than 200% in the past few years,  have adopted a personal strategy of attempting to avoid any "overcharging" if at all possible.  Many systems have fairly consistant DOD,  so it is simple to get fixed charge times set correctly.

With the more common use of A/C in off grid settings,  much larger homes  and kids each running TVs, computers  and such, all at the sane time  etc,  have noticed that DOD can/does vary significantly from day-to-day.
Have wondered if this variability has become more common,  and therefore a more precise method of ending recharge would be in order.

To me,  overcharge cannot be good for batteries,  even FLAs.  The battery banks here,  when overcharged exhibit high SG levels  (up to 1.300 with correct water fill levels, where 1.265 is the target),  this cannot be good.  just opinions,   whatta I know?!   Vic

[vtmaps]

Overcharging causes positive grid corrosion.  Undercharging causes sulfation.  Therefore, it is good to get the absorb time right. 

End amps is probably the best way, but very few systems support it (Outback does, if you have their FNDC, hub, mate, and controller).   Even if you do have a system that supports it, you have to know what EA setting to use.

My advice is to learn what EA your batteries want, and then try to set your time to give them that EA at least a couple of times per week.

To learn what your batteries want, you need to know how much current they are being charged with.  You can do this with a shunt type battery monitor, or by using your Classic's meter with all loads and other charging sources disconnected from the system. 

First step is to set absorb time to 'forever'.  Once you get to absorb voltage, monitor the charging amps.  The current will taper down with time.  Record the current every 15 minutes.  When the current is no longer decreasing that is your EA.  (note: you should redo this every year or so... EA changes as a battery ages).  Record the length of time you spent in absorb.

Now you need to figure out how to achieve that EA on a daily basis.  Using the EA function of the Classic is the best way, but unfortunately it is not reliable if there are any loads or other charging sources in the system.  Most of us make do by setting the absorb time. 

Unfortunately, setting a fixed absorb time will not result in achieving the desired EA every day.  The required time is a function of the battery SOC and the battery charging current during bulk stage. 

My EA is 2.5 amps (less than 1% of my 375 AH batteries).  In the summer, starting the day with 85% SOC, I find that an absorb time of 80 minutes will get me to 2.5 amps.  If we have a rainy day, the next sunny day (starting at 70% SOC) might typically get my charging current down to only 4 amps after 80 minutes.  When we have 2 sunny days in a row, the 80 minutes almost always gets me down to 2.5 amps.

In the winter, I find that a daily absorb time of 2 hours will get me down to 2.5 amps at least twice a week.

--vtMaps

[boB]

Overcharging causes positive grid corrosion.  Undercharging causes sulfation.  Therefore, it is good to get the absorb time right. 

End amps is probably the best way, but very few systems support it (Outback does, if you have their FNDC, hub, mate, and controller).   Even if you do have a system that supports it, you have to know what EA setting to use.

My advice is to learn what EA your batteries want, and then try to set your time to give them that EA at least a couple of times per week.

To learn what your batteries want, you need to know how much current they are being charged with.  You can do this with a shunt type battery monitor, or by using your Classic's meter with all loads and other charging sources disconnected from the system. 

First step is to set absorb time to 'forever'.  Once you get to absorb voltage, monitor the charging amps.  The current will taper down with time.  Record the current every 15 minutes.  When the current is no longer decreasing that is your EA.  (note: you should redo this every year or so... EA changes as a battery ages).  Record the length of time you spent in absorb.

Now you need to figure out how to achieve that EA on a daily basis.  Using the EA function of the Classic is the best way, but unfortunately it is not reliable if there are any loads or other charging sources in the system.  Most of us make do by setting the absorb time. 

Unfortunately, setting a fixed absorb time will not result in achieving the desired EA every day.  The required time is a function of the battery SOC and the battery charging current during bulk stage. 

My EA is 2.5 amps (less than 1% of my 375 AH batteries).  In the summer, starting the day with 85% SOC, I find that an absorb time of 80 minutes will get me to 2.5 amps.  If we have a rainy day, the next sunny day (starting at 70% SOC) might typically get my charging current down to only 4 amps after 80 minutes.  When we have 2 sunny days in a row, the 80 minutes almost always gets me down to 2.5 amps.

In the winter, I find that a daily absorb time of 2 hours will get me down to 2.5 amps at least twice a week.

--vtMaps

Which happens faster ?  Sulfation or  positive grid corrosion ?   I'm thinking that sulfation is quicker because I have seen that much more often that I know of.

Learning the EA would be a very simple algorithm that could be done fairly easily.  Obviously, the battery monitor will be necessary for best results.

Thanks !
boB

[Vic]

vt,

A few more points...

Have seen the EA determination method that you noted above.  Believe that Julie -- tallgirl -- has mentioned this previously.  Believe that this method is best for AGM battery banks, as it omits the mention of measuring SG.  For my banks of FLAs,  this method would probably represent overcharge.

For FLA banks,  there is an important additional instrument that will quickly add additional clarity -- the Hydrometer.  Actually measuring SGs is a great way to measure just how well the chosen EA value is working.

Second,  some DC Conduit boxes include a Shunt in the Neg lead of the batteries,  which allows one to use a DMM to measure the actual battery charge current,  without needing a BM,  although,  on small battery banks,  the resolution on many/most DMMs may be great enough.  A 500A 50 Mv shunt sells for about $35,  so for some folks,  this may be the only additional hardware giblet required to measure actual charge current.

Having some downstream loads,  on inverters for example,  is not a huge detriment to using EA.  Even cyclic loads should not be a problem,  unless they are large or run for extended periods,  randomly.

Believe that using EA settings in a CC have been generally given a bad rap  by those saying that there must be "NO loads on inverters or battery bank"  My experience shows that this is generally false.  Opinions,   Vic

[boB]

Believe that using EA settings in a CC have been generally given a bad rap  by those saying that there must be "NO loads on inverters or battery bank"  My experience shows that this is generally false.  Opinions,   Vic

Yes, you're right.  Of course EA in the CC will work exactly the same as if there were no loads, IF those loads are constant enough to just be used as an offset.   Of course there doesn't have to be NO loads !  What a silly statement.   It's just that if there are NO loads, then
you don't have to  take them into account when setting the EA in the CC.

SG IS the best way to find the ending amps, but not always easy to do.

I still believe it is better to overcharge and watch the electrolyte level than to undercharge....  That is, to err on the side of
overcharging...   If you have only those 2 choices.

boB

[vtmaps]

Have seen the EA determination method that you noted above.
<snip> 
For my banks of FLAs,  this method would probably represent overcharge.

Very interesting... so you think that I may be routinely overcharging?

I admit that if I check SG during absorb, I can't see a change in SG as my charging current falls from about 5 amps to 2.5 amps (about 20-30 minutes). 

I have always assumed that measuring current was more sensitive than measuring SG, but I could be wrong about that. 

Why do you think that Julie's method would result in overcharging your batteries?  Is it just a matter of faith that SG is a better measure than current?  Perhaps we should call it 'end SG' rather than 'end amps'.

--vtMaps

[Vic]

Hi vt,

I do not know about your battery bank,  just speaking of the ones here,  which are the batteries that I pay the closest attention to.  These banks are routinely lightly cycled,  which probably affects the slope of the charge current curve  near the end of Absorption.

And,  when these banks are cycled into the 80-85% SOC range,  the batts are just a bit undercharged at my selected EA value,  but catch up the next day.  Part of this is the result of Bulk recharge rates at or very near 10% of 20 hr capacity.

EDIT:  The reason that I mentioned that the method noted would result in overcharge is that the charge current is still tapering at my selected EA value ... perhaps If I chose a lower Vabsorb  it would be a bit more to formula.  Here,  measure SG at the beginning of Float,  and it is stable.  I have not chosen a lower EA value and watched for any increase in SG,  as I really hate to charge more than needed,  but still do EQ the bank.

I'm too obsessive about this stuff,  and as you noted previously,  things need to average over a period of a few days.  And FLAs are tolerant,  within reason.

boB,  I agree,  I'd rather slightly overcharge than undercharge,  altho,  am wondering if I should no longer try to get the Pilot cell to rated 1.265 on each chcle,  and settle for about 1.260 or 1.262,  which would be a bit easier on the remaining cells.  Good thing that nothing needs to be perfect!  Thanks,  and,  sorry Al  for derailing your thread - hope that you got a satisfactory answer earlier in the thread.   Vic