Hydrometer

dongringo

I use 5 105amp batteries on a small 12 v solar system (400 watt panels,  5 105amp batteries, 50 amp controller ) less than a year old.
I use the same battery (Home Depot Marine deep  cycle, made by EXIDE)  in my truck.
All seem to charge and discharge ok.
Yesterday morning I checkedt the batteries: 12.40 digital volt meter: 11.75 hydrometer.  
In the afternoon I bought an additional battery and a new hydrometer: 12.61 volt meter, 12.60 hydrometer, 
This morning I checked the  old batteries: 12.42 volt meter, 11.75 hydrometer
So I checked everything with the old hydrometer, same result.
Then I verified the new battery , same result.
The I checked my truck battery:12.61 volt meter, 11.75 hydrometer.
Obviously I am frustrated.
The hydrometer  reads the new battery ok, but not the old ones.
My truck starts fine, but would not with a specific gravity of 11.75.

The only difference may be the battery composition or acid. I use suposedly distilled water  sold by the the only local gas station (I live in the boonies in Mexico)

Or of course the two hydrometers are bewitched.

Any suggestion? Thanks

mvas

First the hydrometer values are:
1.175, not 11.75
1.261, not 12.61

Yes ...
12.40 volts could be 1.175 SG ( not fully charged or is sulfated )
12.61 volts could be 1.260 SG ( nearly 100% SOC )

Voltage is not a good measure of State-Of-Charge.
SG is a reliable measure of SOC - ( although bubbles stuck to the float can give false readings )
There can be a "false" Surface Charge that needs to be removed before before measuring the voltage.
Both Voltage and SG changes with temperature.

Did you buy a Float type Hydrometer ?
https://www.solar-electric.com/brin1bahy.html

Or the kind with a Pointer and Scale ?
http://www.quickcable.com/images/display_images/d_tools_battery_pointer-hydrometer_3.png

Estragon

A few thoughts -

Before and after each session using the hydrometer, rinse it 2-3 times by sucking in distilled water. This prevents buildups that can cause sticking and bad readings.

Check cells a with a number of sucessive readings.

If possible, do the check after a complete charge cycle, including a full absorb. The electrolyte can stratify, with the stronger, denser acid at the bottom. You end up reading the weaker, less dense acid at the top. The repeated readings can help at bit as it mixes some as you put the acid from the previous reading back, but the bubbling during the latter part of absorb is better.

"Marine deep cycle" batteries typically aren't really deep cycle. If they're in a hot place, they may be halfway through life at a year old. When the time comes to replace, you might want to ask Costco if they have or can get 6v golf cart batteries. They're likely around the same price per watt hour as the marine ones, but are better suited for deep cycle applications.

dongringo

Did you buy a Float type Hydrometer ? yes. cheapo Home Depot, only one available locally And you aree correct. Instead of 11.75  I should have said .1175. Now can you please explain the correct  readings on my new battery? and the uniform 5 bad readings?

Photowhit

Ever think they might not be bad readings?
Have you lost noticeable capacity in the old battery bank?
Did you disconnect the battery bank from the solar array before taking measurements? You might be reading 12.42 volts going into a battery bank that is 60% discharged (or what ever 1.175 represents) I can't look things up right now, but I believe 12 volts is represents roughly a 1/2 capacity for a battery at rest. When charging the voltage would be higher to allow flow into the battery bank.

dongringo said:

and the uniform 5 bad readings?

I guess you have been told about the problems with so many batteries in parallel as well as most marine batteries are NOT true deep cycle batteries. In fact if they start your truck, I'd suggest they likely are some type of compromise battery and not true deep cycle.

Estragon

In warmish weather, even a true deep cycle battery in decent shape would probably start the truck okay. I've used bagged out golf carts to start the boat diesel at times (starting battery died faster).

Assuming the truck wasn't running at the time, charging voltage wouldn't be a factor in that reading. OP didn't say if the morning voltage was resting though, so could be a factor.

Most (all?) hydrometers are float type, and need to be rinsed to prevent sticking. Multiple readings help too, as sometimes a bit of crud gets sucked in and makes the float stick. There are spectrometer meters for checking SG, but aside from the cost, I'm a klutz and the notion of holding acid up to my eye doesn't appeal.

My guess is the SG readings aren't reflecting the real SOC. If the readings are still low after trying to get electrolyte mixed properly, there may be other issues. In the meantime, I would focus on getting it mixed.

dongringo

Vic

Hello Don,

It has pretty much all been said in earlier posts.

Here is a good article on measuring SGs from Surrette battery.  The Chart in the article is relative to batteries with 1.265  SG for full charge at 25 degrees C,  but,  the process is well written:
http://support.rollsbattery.com/support/solutions/articles/4347-measuring-specific-gravity

Also,  as has been stated,   RINSE,  RINSE,     RINSE  after measuring SGs is essential to keep your Hydrometer accurate.  It is best to use only Steam Distilled water for rinsing and adding to batteries.   Personally,  would not allow the Hydro to sit around for more than one  hour before rinsing  (that's just me).

Try to find a Hydro that has a glass outer tube,   with a glass float.   AVOID Hydros that are plastic,  and/or those with floating balls.

There is a relatively large effect of battery temperature on battery voltage readings.  Warm/hot batteries will read a lower voltage at full charge than ones that are at the Reference Temperature  (usually 25 - 27 C,  about 77 - 80 F).

Also  when trying to use battery voltage as an indicator of State Of Charge (SOC),   the battery needs to be Rested.   A Rested battery needs to have had NO  charge OR discharge in the previous 6 - 12 hours,   and have the voltage reading compensated  at about  -- 0.018  volts for every degree C that the battery temperature varies from the 25 C Reference temperature for your probable 12 V batteries.   This compensation value means that if your battery temperature is 5 degrees C warmer than 25 C,   that you would need to add about  0.11 volts to the Rested battery voltage reading from your ACCURATE  volt meter,   to approximate the SOC of the battery,  using the voltage table that you listed.

One other variable in the compensation noted above,   is that some batteries need a compensation value of --3 mV per cell per degree C (this is what was used above),   and others need -- 5 mV?C,   and sometimes some need --4 mV.  Lead Acid batteries have cells that are 2 volts each (nominal).  A 12 V lead acid battery has 6 cells.

If one knows one's system well,  after watching battery voltage verses measured SG over a long period of time,   voltage can be a more meaningful indicator of SOC.

FWIW,   Vic

dongringo

it all makes sense. EXCEPT the hydro measures the new battery correctly,  and basically tells me my other batteries are dead, 12,41 volts, 7 am,  80f, after discharging 12 hours- I'm gonna throw these freakometers in the trash before I pull out the rest of my hair

Estragon

The hydro MAY be telling you the older batteries are stratifying. Mix the electrolyte by fully charging and retest.

BB.

Mix electrolyte is equalizing charge (about 5% rate of charging current at 15-16 volts typical for 12 volt bank). The cells should be bubbling to mix electrolyte.

A few people have mixed there batteries by loading them on a pickup or trailer and driving over rough roads.

- Bill

mcgivor

When taking a sample it's generally a good idea not to take the reading on the first pull, suck and discharge 3 times read the fourth, gets things stirred up, the first one usually has a lower reading, especially if they have been sitting for a while without being on charge. Also give the hydrometer a little shake to allow the float to free itself from sticking to the sides of the tube.

Blayd

I only use hydrometer to verify bad cells in any given jug.  My battery bank is never at rest.  My current L16 RE B's are pretty much worn out.  Right now they are just fine with the current heat wave we are having (day time 105°f-night time 75-80°f).  I know full well the minute those batteries experience cold winter weather that I will be getting a new set.

My banks are pretty much cycled to death, and even with the best of care, heat and cycles do them in.  Four years with the current set, which will go to the spare emergency system just in case.

 Like a fine wine, no battery gets recycled before it's time ~

Dead cells will mean rapid charge of a flat battery, wont hold a charge, and will get quite warm (or have run-away thermal reaction).

Worn out jugs will just sit there looking sad, wont take much of a charge, and have nothing to give.

I only watch depth of discharge and keep electrolite levels to proper level, and clean connections.

jonr

...have the voltage reading compensated  at about  -- 0.018  volts for every degree C that the battery temperature varies from the 25 C Reference temperature for your probable 12 V batteries.  

.018V is typical for charging compensation, but rested, open circuit voltage compensation is much lower (closer to 1/10 of the above).

http://jgdarden.com/batteryfaq/SoC.xls

WaterWheel

Blayd said:

I only watch depth of discharge and keep electrolite levels to proper level, and clean connections.

I did that for the first 8 months (plus a monthly 1hr EQ) I had the batteries only to discover that even when the SOC meter said 100% the SGs were saying 75-85%.         You really need to check SGs occasionally and use the SG readings to fine tune your controller.

Aguarancher

      You really need to check SGs occasionally and use the SG readings to fine tune your controller.

+1

Thom

I would Equalize charge them and c if the sg goes up. 

Thom

Lumisol

'c' or 'see' ?

Blayd

WaterWheel said:

Blayd said:

I only watch depth of discharge and keep electrolite levels to proper level, and clean connections.

I did that for the first 8 months (plus a monthly 1hr EQ) I had the batteries only to discover that even when the SOC meter said 100% the SGs were saying 75-85%.         You really need to check SGs occasionally and use the SG readings to fine tune your controller.

I have to do seasonal changes to the controllers due to the wide range of temperatures involved.  Thankfully the newest controller is state-of-the-art FlexMax80 with a lot more options than the old stuff that only allowed float adjustment.  My answer for longer battery life was to add extra panels and watch depth of discharge. When the current set of Trojan L16RE B's goes into semi-retirement they will have well over the rated 1500 cycle life which isn't too bad considering 100°f summer temps which certainly have a negative impact on them.  Hopefully the next set will last a lot longer with reduced depth of discharge and better charging acheived with new equipment and additional panels that were only added less than a year ago.  The new controller will also do EQ, which I have disabled. The upgrades are paying off.  Longer battery life, and almost no generator run time ($200.00usd annual savings in gasoline).

Agreed that for most folks, checking SG once in a while is best practice.  In my case seat-of-pants observations and water usage are good indicators as well keeping tabs on voltage levels.  My equipment is in plain sight next to the fridge, so I know voltage status at a glance.

davemac

I use the Pro Hydrovolt HYDRO VOLT Lead Acid Battery Hydrometer Electrolyte Tester. Has a simple suction chamber system with temp calibration built in to the float reading. I check every 3 months at night at sunset after an equalization has settled down. Found the SG's of my T105's has improved over the first 12 months, how about that? Still in optimal range.