Whens the best time to do specific gravity test

[Mobilesport]

After batteries rested? 
Or
Affter batteries have been charged?

 

[poncho62]

I was trained in this many years ago, but am a bit foggy......If I remember right, the test should be done after disconnecting and before charging. Also, if water needs to be added, it should be after charging to prevent boiling it over.

 

[Mobilesport]

Would the alternator be considered charging ?
I just got done driving about 12 miles.

 

[poncho62]

I would let it rest for a few hours and then test.......I would think recently charging it would give a false reading. My training was on electric fork lift batteries

 

[Mobilesport]

Thanks

 

[Optimistic Paranoid]

If you are using a voltmeter, you will definitely get a false reading right after charging.  The plates hold a "surface charge" that needs to dissipate before you can read an accurate voltage.

I'm not sure a specific gravity reading is similar - I don't believe it's too high after charging and needs time to drop back to "normal".

On the other hand, if you have to add water after charging, you will definitely get an inaccurate reading because the water won't mix with the electrolyte already in the cell.

Why not conduct your own experiment?  Take readings right after charging, and compare them to what you get after the battery has rested several hours?

 

[SternWake]

The reason to test specific gravity is to see if the battery is fully charged or NOT, or if some cells are lagging while others are OK. 

  Some battery manufacturers  will equate a SG reading with a % of charge.


I tested SG when my solar said the battery is full and 95% of the time the SG proved the solar controller needed to hold absorption voltage for longer, and I would then adjust it.

Ideally, one would have a specific gravity reading taken when the batteries were new and fully charged, and then all subsequent readings can use this as a setpoint for what is indeed full on that specific battery as SG readings will vary among manufacturers and whether it was a battery sold for a warm or cold climate.

Usually some cells will read low, and always read low, and these low cells can be the only ones dipped from there if one is worried about the time consumed to do so.

When performing an Equalization charge, a hydrometer is basically necessary.  

After the Specific gravity on all cells stops rising when the battery is held at 16v, accounting for rising electrolyte temperature, then the battery can be considered fully charged.  Hopefully the SG readings are all close to each other and 1.275 or higher.  

If this freshly EQ's battery had 1.275 on all cells, and were left to sit overnight without any discharging going on, the SG might rise to 1.278 in the morning. So there is some SG lag, but not enough to really matter.  I've actually never noticed it When i'd check the rested battery the next day,  but people smarter than me says SG lag is a reality.

Do NOT initialte 16v EQ charges until the battery has spent several hours at 14.8v and is otherwise 'fully' charged.


The SG will read lower after filling battery with distilled water, and read a bit higher when the level is just above the plates.  One should take this into account.  Only fill the battery before charging if plates are exposed to air, and only fill enough to cover the plates. After fully charging then one can top off, and this means a few mm below the arms which hang into the cells.

Keep in mind cells in the middle of the battery get warmer than the outside cells when charging.  Hotter electrolyte is less dense and will read lower SG on the float.

You can take SG readings anytime, just protect your eyes if the battery is still charging and be careful to not let anything drop into the cells.  Clean the battery top before removing caps and make sure nothing falls inside.  Rinse the hydrometer after use and make sure no bubbles stick to the float when taking readings.



Back when I was cycling a flooded battery I made a chart with 6 columns, 1 for each cell.  I'd record temperature, SG reading the date and an estimation of the electrolyte level.

Some cells used more water, Some cells always read higher than others, Sometimes they behaved and another cell decided to be petulant.  I;d record how long it took at 16V for SG to max out, and how many amps the battery was requiring to be held at 16v when SG maxed out

it got to the point where i could dip one cell, say 45 minutes at 16V should do it.

Later on I just knew it had been 10 or 14 cycles and an EQ was required and would just bump voltage to 16v for X amount of time, but this was only after I had figured out what the specific  battery wanted in my usage to maximize capacity retention.
Each battery, even of the same manfacturer and date will be slightly different.

Now i cycle an AGM and use amperage at absorption voltage to detemine when it is full.  But it also occassionally needs the high amp recharge to keep the time span for amps to taper to a certain number at absV, to an acceptable level.

 

[Mobilesport]

All where 12.37 , well there was 2 that were slightly higher but not by much

 

[SternWake]

Those EZ red hydrometers are kind of a joke. They are both inaccurate and imprecise, and inconsistent.

This tool is much better:

https://www.amazon.com/OTC-4619-Pro...=UTF8&qid=1477012375&sr=1-1&keywords=otc+4619

Absolute top of the line:
http://www.freasglass.com/

Find somewhere to plug into the grid and recharge at 14.8v until amps are about 2.5 then bump voltage upto 16v from the meanwell. See how high you can get the SG to go. You are hoping for 1.275.

If you can get the batteries up there, they will have a batterygasm

 

[BradKW]

I guess it's time to buy a hydrometer...which is considered best and most convenient for mobile life?

I see a few different flavors:

[img=300x300]https://images-na.ssl-images-amazon.com/images/I/51B3PxScfaL._SL1000_.jpg[/img]    ATV Battery Rapid Hydrometer

[img=200x200]https://images-na.ssl-images-amazon.com/images/I/516V4c-fw7L._SL1000_.jpg[/img]   Automotives Battery Hydrometer Tester


And then this one which is 4x the price of others:

[img=200x200]https://images-na.ssl-images-amazon.com/images/I/71obqg44twL._SL1500_.jpg[/img]    DURAC 1.150/1.300 Battery Hydrometer with Siphon Set

 

[BradKW]

hmm, I posted that apparently as you two were posting pics and links

 

[SternWake]

You keeping those Trojan L-16's topped up?

The OTC4619 is perhaps not as accurate as the freas, but when testing against itself it is fine, just make sure no bubbles stick to the float, and they seem to like to do that more the lower the SG number is.,

Keep the plastic container it comes shipped in. Do not lose the little foam piece to immobilize the float in the glass tube for storage, and do not push it too deep in the tube...

1.280+

Batterygasm

 

[BradKW]

thanks...Trojans haven't moved since I bought them...thinking electric is next project after 'fridge/AC enclosure...

 

[SternWake]

Batteries can self discharge 15% a month in 75F ambients. KW gone under 75F yet this fall?

Top them up.

 

[BradKW]

heh, I wish we would hit 75...looks like a cold spell is coming and might dip down to a low of 74F next week   :O

Getting my battery boxes made went sideways on me a couple times and I've been delaying purchase of cabling till I had placed them. Looks like it's on track now...friend just picked up the metal for me on the mainland.  I wanted 1/4" plate for $200, and ended up with 1/4" Diamond plate for same price...he texted me this pic:

[img=300x300]http://i465.photobucket.com/albums/...Uploads/0161014_161341_zpskgaa40ui.jpeg[/img]
 
Now I just need to get them welded up...hopefully he does it this weekend.  There will be two identical boxes about like this:

[img=250x325]http://i465.photobucket.com/albums/...ads/IMG_20160904_121253_zps1t9lv6gb.jpg[/img]

 

[SternWake]

While batteries are supposed to leave the factory fully charged, that takes time and electricity, and both are money.

my Recommendation is to make sure those L-16s are top charged while they wait to be put into service.

Pair them up for 12v and put a regular battery charger on them. They do not like sitting at 80% charged. That lead sulfate starts getting hard and can forever impact capacity if left for too long.

Specific gravity readings will also prove the Voltmeter is a liar. 12.8v means fully charged in a lot of minds, incorrectly.

A specific Gravity of 1.275+ is the the goal, the Hydrometer is the battery polygraph.
Voltmeters are the national enquirer of deductive tools.

 

[SternWake]

BTW, here is a Specific gravity chart for a new healthy battery.

An abused battery will not really follow this chart very closely, but one can get a general Idea.

the more data one has for comparison, the better, if one cares.

 

[Optimistic Paranoid]

One other thing that Stern didn't mention.  The Trojan Technical Manual says that "If a battery has a specific gravity variation of more than 0.030 between cells, equalize it."

 

[SternWake]

One other thing that Stern didn't mention.  The Trojan Technical Manual says that "If a battery has a specific gravity variation of more than 0.030 between cells, equalize it."

good catch.

Equalizing and specific gravity readings go hand in hand.

How often  EQ charge is required can only be definitively determined by a Hydrometer, but one who watches their voltmeter and whose overnight loads are always similar, can certainly notice a lower morning voltage and guess that a normal 'full' charge is really not quite full and the batteries appear to have lost capacity.

And after an EQ session would notice a higher morning voltage.

EQ charges are not so easy to perform, as most charging sources will not allow 16v. Some solar charge controllers can be reprogrammed to allow 16v, but the battery needs to be mostly full before trying, and one will require strong cloud free sunlight and a few hours of it, with all loads turned off.  Basically, one needs 5 amps per 100Ah of capacity to get a fully charged battery to 16v, where as it might only require 1.2 amps to hold this fully charged battery at 14.8v.

They can do wonders for morning voltage and they can make it easier to fully charge the battery to full, as well as allow it to charge faster to ~80%, if the charging amps are there to take advantage of the depleted battery's ability to accept large currents

Generally the better the battery is recharged each deep cycle the less often and necessary EQ charges become, but it does not entirely eliminate their benefits.

Though of course many flooded/wet batteries give perfectly adequate lifespans without ever having an EQ charger performed.

In a van dwelling scenario, discharging 7 nights a week, the battery can really take a beating, and the Eq charge more beneficial.

Trojan recently upper their recommended EQ voltage from 15.5 to 16.2v.  Many DC items will not like voltages this high, so disconnecting them when performing an EQ is called for.  I was reluctant to goto 16v and went from 15.5 to 15.7v but found that 16v could do in 45 minutes what took 15.5v 4 hours to achieve. 

Also note that only lifeline AGM's say you can equalize them, but they call it a reconditioning charge, but the process is similar, absent the checking  of SG.  No other AGM manufacturer 'recommends' an EQ charge.

EQ charges are hard on a battery, but not as hard as continuing to cycle the battery deeply when an EQ is sorely needed.

Also note that progresssive Dynamics converters claim to have an Equalization stage.  Contemptible Marketing mumbo jumbo.  Their EQ stage is a 15 minute bump to 14.4v every 16 hours when the unit has been floating the batteries at 13.2.  This 14.4v blast on an already fully charged battery causes some gassing/bubbling and destratifies the electrolyte, as the denser stronger acid will tend to seek the bottom of the battery and eat the plates down there faster.

On that note, when taking a SG reading on a well rested battery, one might only be pulling the less dense acid on top of the cell and it will read low.  One can use the bulb to mix the electrolyte in the cell somewhat, or just do the 14.4 gassing voltage thing for a while to mix up the electrolyte for a more accurate reading

 

[ccbreder]

I could justify the cost of the Freas Hydrometer, but I had much to much difficulty finding one to buy. I was ready to drive to Philadelphia. Then as we walked through Sears, I checked things in the battery area and found a very nice hydrometer with a thermometer combined. It is made in Taiwan, marketed by East Penn. (Deka) It is well made and I'm happy. The turkey baster for filling cells, that came with it is junk and it has been tossed. The tested fluid temperature is used to adjust true SG. It does not matter if rested or after charging. Only must be before adding water. The little floating ball or similar, don't allow temperature adjustment.