EZRED hydrometer

Stuart

Are the EZRED hydrometers accurate. 

mcgivor

For the purpose of accurately measuring the SG, no they are not, a quality glass tube type which has been calibrated, kept clean by rincing after use,  is a far superior tool, at best the EZ red will provide, at best, a vague indication as to state of charge.

BB.

Just an FYI:

http://www.ezred.com/product/battery-hydrometer/



-Bill

Stuart

Thank you Mcgivor.  I will purchase a glass bulb. But would you say that although the exact SG reading is not accurate the general green good area, yellow fair, etc. is valid?

BB.

In your other thread, I posted a bunch of battery links. Take a look through those.

More or less, recharge a battery that is <75% state of charge to >90% state of charge if you are going to store the battery (below ~75% state of charge and not cycling, the Lead Acid batteries tend to sulfate quicker).

Reach >90% state of charge once or twice a week. Do not try for 100% SoC every day--That is pretty hard on Lead Acid batteries (gassing batteries erode plates, oxidize positive grid/plates, lose water/electrolyte, run the batteries hotter--shorter life, etc.).

There is a an alternative mode of cycling batteries between 50% and 80% state of charge and going to >90% SoC once a week. Some vendors recommend Equalization once per month, others when cells are >0.015 to 0.030 difference between high/low SG cells in a bank. Flooded Lead Acid batteries are very efficient when cycled below 80% SoC.

Equalization is hard on a battery bank. Do not over equalize (generally ~5% rate of charge, 2.5% minimum of bank 20 Hour capacity... I.e., 100 AH bank, 2.5 to 5 amps charging). Hot batteries age faster (every 10C over ~25C, batteries age 2x faster). Equalization is nearly 0% efficient (most energy goes into heat and gassing).

When equalizing, you want all cells fizzing about equally (not a rolling "boil"). Fill battery water space above plates about 1/2 full before equalization. Check electrolyte levels (and top off as needed) after equalization (hot battery, electrolyte expands, gases are trapped under plates/between plates and can drive electrolyte out top of "full cells").

A DC current clamp meter (DMM--Digital Multi Meter) can make running parallel strings easier (check that strings are sharing charging/discharging currents, debugging DC circuitry, etc.):

http://www.sears.com/craftsman-digital-clamp-on-ammeter/p-03482369000P (good enough for our needs $60)
https://www.amazon.com/Klein-Tools-CL800-Auto-Ranging-Digital/dp/B019CY4FB4 (~$105)

-Bill

Stuart

Bill,

Thank you very much for helpful information

jonr

> Reach >90% state of charge once or twice a week. Do not try for 100% SoC every day

I'm curious how this is implemented without excessive manual effort?   A shortened daily absorb time and then a light equalization scheduled weekly?   Then a manually triggered true equalization when indicated by cell imbalance?

Dave Angelini

I never do that either. I design for reaching the manufacturers SG at full daily. In winter it can happen occasionally and less if you are in a location that can support not having generator and over design on the solar. Most of the systems get very long battery life if taken care of.

mcgivor

Reaching 100% every day is my goal, but realistically that doesn't happen, so for the few days that 100% is achieved, makes up for the days when clouds get in the way, so 90%, or less, happens every so often, without intervention, just went through a spell of low production due to storms, so 100% looks good, until the next storm arrives.

BB.

Just adjusting the Absorb voltage to get >90%. Not cranking it up to get 100% every day. Lead Acid batteries do better if not subjected to high charging currents/excessive charging voltages.

When you get into winter (fewer hours of sun per day, shading by hills/mountains/trees)--Sometimes you have to up the absorb voltage to make up for lack of hours of sun/charging per day.

From what I have read/understand--I am, definitely, not a battery expert.

-Bill

Vic

In addition to the above,

The MidNite Classic does have a Skip Day function,  that allows a settable fixed number of days to Skip the Absorb stage (up to 32 days,  IIRC).

So on a Skip day,  the CC begins charging in Float-MPPT,  until the Float voltage setpoint is reached,  and spends the entire day trying to maintain that Float voltage.

BUT,  still try for 100% charge on non-Skip days.   All of the Surrette banks here are approaching 12 years of service.   The battery efficiency has certainly dropped with advancing age,  necessitating a bit of an increase in Vabs,  and attendant increase in the EA settings,   but these batteries seem to be doing fairly well ...   knock on wood.

FWIW,   Vic

jonr

> on a Skip day,  the CC begins charging in Float-MPPT

In the case of batteries seeing significant daily use (ie, going below 90%), I can understand the theory behind (but no support for) purposely skipping most daily absorb cycles.  But skipping daily bulk sounds like a bad idea.   BTW, I can't find any documentation of this Midnite Classic function.

Estragon

The skip won't generally happen on normally cycling batteries. They end up bulking on the reduction in voltage.

It's mostly useful for when not being actively used - eg during the week or over winter at a cabin (my use), or a standby system, that really just needs to float most of the time. I set mine for 4 days over the winter.

Vic

First,   most all things regarding our systems and batteries seem to be relative.

Have never used the ReBulk function in MN,   or OB CCs.   This is the voltage setting where the CC  will perform a,  or a new Bulk.

Would say that lightly-cycled banks can benefit from Skipping Days  --  due to Summer heat,   and the lack of cool nights,  have gone from Skipping 3 days,   and completely charging on the fourth (with the Classics),  to Skipping only one day.

Here,  the goal is to try to get the bank down to about 85% SOC,   or a bit lower.  The main banks have a nominal Capacity of 1280 Ah.   Need the available Capacity at times,   but not daily,   so the Skip function works great:
http://forum.solar-electric.com/discussion/23052/quick-question-for-midnite-classic-owners

jonr,  here is a Link to an old Discussion here on the Skip Days,   beginning with Post #11.   Believe that the Skip Day function may not be in the latest Classic Manual,   but it is easily setup in the Classic Charge>Advanced menu page.

And I DID say that the Classic can Skip Absorb,   I should have said Skip Bulk & Absorb.   Skipping Bulk and Absorb seems to work fine.   On an Ah returned to the battery basis,  even when using the historic Surrette-recommended relatively low Vflt of 52.4 V (about 2.18 Vpc)  one can return 50-60% of the Ah removed in the previous discharge (roughly ....   depending upon a number of variables),   and seldom do any of the battery banks here get below 75% SOC.

We all have our beliefs about battery behavior,   AND  there really seem to be few absolutes,  regarding battery behavior,   and the "best"  thing to do in some certain situation   ...   IMO.

FWIW,   YMMV,  so on,     Vic

jonr

Thanks, just trying to clearly understand your situation and procedures that have led to your good results.    

Evidently charging past bulk causes positive plate corrosion and time below 100% SOC causes negative plate sulfation.  The latter starts to become permanent somewhere in the few days to 1 week range (shortening significantly with increased temperatures).  Maybe some other issues are also involved - stratification?

Vic

IMO,  once Gassing Voltage reached,  Positive Plate corrosion has begun,   but Stratification starts to lessen.   Just my opinion,   but Sulfation is quite reversible within a few days,  unless the SOC has been reduced to somewhere around 70% SOC.   The lower the SOC has been taken,  the greater the difficulty there is in removing Sulfation by simply going through a normal charge cycle ...   these things are relative to exactly what is the construction of the battery,   and so on ...   just my read on things.

Many years ago,  like most off-gridders,  I did strive to try to reach 100% SOC each day.   Now,  not so much.

As has been stated by BB Bill,  NOT looking to do a complete recharge each day really does reduce the amount of heating that the battery experiences,   heat is not good,   and,   of course almost all of heating from recharge occurs at/above the Gassing Voltage.

Even during heavy Bulk charging,   have only noted a 1 - 1.5 degree C temp rise of the battery,  even at about 18%  of C.   There is probably some lag in the heat soaking out to the BTSes,  but still,   almost all of the battery heating occurs from about Vgas and above,   as one would expect ...   (relative to an earlier wonderment you noted, [ Estragon ] ...

Just "throwing the dice" to see what happens.   My read on things,    Vic

jonr

I'm still not clear as to the possible advantage of ever skipping bulk.   As you say, bulk doesn't cause much heating/gassing.   So why not get the charge back in as soon as possible and reduce sulfation, even if it should be reversible?    Sure, some charging will occur even at float voltages, but that's much slower and less effective than going all the way up to peak bulk voltage.  Maybe the answer is simply "Midnite doesn't have that function".

Trojan says "Batteries should be fully charged after each use. “Use” is defined as at least 30 minutes of runtime".  I interpret that as a goal of 100% SOC every day, except for standby or near standby applications.

BB.

Absorb (voltage set point regulation) with lead acid batteries occurs when the battery bank is over approximately 80-90% state of charge (high rate charging would be >80% SoC or >90% SoC for low rate of charge).

Skipping bulk not really the issue, it is skipping charging completely until the battery bank is below 85% SoC or so.

- Bill

Vic

Two things;

It is a very good thing to not recharge an FLA unless the SOC is below (approximately) 90%.   On some daily-used off grid systems,  this will require more than one typical day's use.

Bulk does little heating,  and very little Gassing.   Avoiding Bulk and Absorb still allows a significant number of Ah to be returned to the battery (during the all-day Float,  even at relatively low Vflt).   This still counts as charging.

These things are all a matter of opinion.   There are many,  many opinions around,   particularly regarding batteries.

The above  comments from yours truly are just my opinions,  which have evolved a bit over the years.

All of this is in the context of having about four typical days of Autonomy for these battery banks.   Folks with relatively heavier discharge of their batteries,  daily,  will certainly have a different perspective.

Much of the generator run-time on systems here,   are mostly just to exercise the gensets.   And that was one of the goals of the design of these systems ...   many other people will have completely differing perspectives.

FWIW,   Vic

jonr

OK, that makes sense - if you don't skip charging when SOC is < ~85%, then there is no difference.   Bulk is skipped either way.

Vic

SOMETIMES,   we Skip charging when the approximate SOC IS below 85%.   When this is done,  it is because a genset needs exercising.

Occasional deeper discharges are good for Flooded batteries,  perhaps to about 60% SOC.    Here,  these are intentional discharges,   that usually result from shutting off the PV input,   and sometimes running electric heaters,  so that the battery does not spend much time at this lower SOC.   Then,  the genset recharges the battery into the Absorb stage,   and the PV finishes recharge to 100% SOC,  nominal.

This is just the way that it is done here,   there are many ways to run off grid systems,   and most every system is at least a bit different from most others ...   and so on.

Vic

Estragon

> @jonr said:
> OK, that makes sense - if you don't skip charging when SOC is < ~85%, then there is no difference.   Bulk is skipped either way.

If the SOC is much under that, and the system is being used, it won't skip unless rebulk is set really low. My 48v system is set for 4 day skip, but it bulk/absorbs daily when I'm at the cabin.