battery temp compensation

[Vic]

fiddler..,

The Specific Gravity (SG) readings on your batteries seem a bit high.  I have not run the same brand GC2 as you have,  but,  would expect that the highest SG that would have been shipped with would be 1.277 - 1.280  (at 25 degrees C).  Perhaps,  even 1.265.

SO,  your batteries may well need some Distilled Water added, given the high SGs,  IMHO,  given that the temps that your report are very,  very close to standard rating temperatures.

FWIW     YMMV,    Vic

[fiddlerkelly]

Vic all of the batteries have at least 1/2 inch of battery acid over the tops of lead plates. I had brought the batteries back upto cabin inn truck and roa going in is rough in spots so for sure acid was shaken up but I never checked the batteries till next day , if that makes any difference in SG. 

[Vic]

fiddler ..,

OK,  then,  perhaps your Hydrometer just reads a bit high.

Forget if this has been mentioned,   but Hydrometers need to be rinsed,  several times  with Distilled Water after each measuring session.   If not rinsed,  the Hydro gets a sticky residue built up inside.   This residue can allow air bubbles to stick to the float and inside the tube.   These bubbles cause false readings,  often high readings.

The plastic Hydros seem to have floats that can be eaten by the electrolyte.   This seems to cause ever-increasing readings despite the actual SG of the electrolyte.

All FWIW.  Vic

[vtmaps]

The plastic Hydros seem to have floats that can be eaten by the electrolyte.   This seems to cause ever-increasing readings despite the actual SG of the electrolyte.

Does that statement apply to the Hydrovolt that Midnite sells?   --vtMaps

[Vic]

vtMaps,

I should have done a better job describing just which "plastic" Hydrometers that seem to have that malady.

Some of the Hydrometers that appear to have this issue are those that have a plastic body,  and a plastic float that is also the pointer to the SG scale.   Often the SG scale is colored and may not even have any  SG numbers on it,  just something like "Charged" ..  "Discharged",  "Good" ...  "Low"  or similar subjective terms.

On the above type Hydrometers,  it appears that the electrolyte can attack the plastic of the pointer,  and erode it,  causing a permanent change in buoyancy,  and therefore a permanent change in accuracy.  This problem would probably not exist IF THE HYDROMETER WAS RINSED SEVERAL TIMES AFTER EACH MEASURING SESSION  --  This rinsing is very important for any Hydrometer!

These are often $7.00 Auto Store type Hydrometers.

Have NO reason to believe that the HydroVolt Hydrometer has any of these issues.  It appears to be very well constructed,  easy to read,  accurate and generally,   repeatable,  if the reservoir is fully filled when the reading is taken.  The HydroVolt is a very good Hydrometer.

Sorry for the lack of precision in the description of the problematic class of Hydros.   Thanks,   Vic

[fiddlerkelly]

Yeah Vic my hydrometer is all glass along with the actual float and shows both the colors from weak to strong and a numerical scale. Bought mine at canadian tire. Just need to do temp com each time as the hydrometer does not have built in temp comp and yeah I do clean mine with distilled water after as just recently I broke the float in one and when I got a new one I notice and dark spot on inside of glass tube at about where the battery acid level would be when measuring SG. Will have to pay more attention to the cleaning.

[TomW]

I finally got tired of all the fooling about with float style hydrometers and got a Robinaire refractory type:

http://www.amazon.com/Robinair-75240-Coolant-Battery-Refractometer/dp/B000HTNODE/ref=sr_1_1?ie=UTF8&qid=1387201098&sr=8-1&keywords=robinair+refractometer

Looks like this:



It has gone up in price since I got mine but it is great.

No temperature compensation, no sticking floats and only uses a drop of fluid. Easy to calibrate against distilled water. Works for battery fluid or coolant. 

Tom

[vtmaps]

No temperature compensation, no sticking floats and only uses a drop of fluid. Easy to calibrate against distilled water. Works for battery fluid or coolant. 

Most installers around here do prefer refractometers to hydrometers.

Most of the ones I've seen have built-in automatic temp compensation... are you sure yours has no temp compensation?

Also, you should calibrate it against battery acid of known concentration... distilled water is too far out of its range to trust for calibration.

--vtMaps

[TomW]

No temperature compensation, no sticking floats and only uses a drop of fluid. Easy to calibrate against distilled water. Works for battery fluid or coolant. 

Most installers around here do prefer refractometers to hydrometers.

Most of the ones I've seen have built-in automatic temp compensation... are you sure yours has no temp compensation?

Also, you should calibrate it against battery acid of known concentration... distilled water is too far out of its range to trust for calibration.

--vtMaps

I should have said "no temperature compensation needed". The tiny bit of fluid takes on the temp of the tester so I guess it is "automatic". Or that is my understanding.

You are probably right about the calibration. I just used the method in the instruction manual it came with. Seems OK if you lack a fluid with a known S.G. in the proper range?

I only speak 2 languages. English and Bad English so any confusion is my doing!

Tom

[fiddlerkelly]

Well actually on the packaging of the hydrometer it doesn't  say it does temp comp and at 8 dollars Canadian I assumed it doesn't.

[fiddlerkelly]

Rather than start another subject I thought I ask this here as already under battery.

Lets say you have a system. 12 volt as example with 12 -  6 volt batteries , 2 a piece in series and then all parallel from there and you have 300 amps of panels on roof.  Lets say you use it for 8 hours one evening drawing 2 amps an hour for total of 16 amps that evening. So that night you burned 960 watts of energy.  Okay next day it is charging it is sunny but takes two days of sun to fully recharge, would a system with 6 -6volt batteries recharge faster or slower all other things being the same considering that that 960 watts is being consumed from a smaller bank in one case and a bigger in another case.

Feedback appreciated and why or  if one is faster than the other.

[vtmaps]

I can't even read this without fixing it...

Lets say you have a system. 12 volt as example with 12 -  6 volt batteries , 2 a piece in series and then all parallel from there and you have 300 amps of panels what does this mean? on roof.  Lets say you use it for 8 hours one evening drawing 2 amps an hour I think you mean 2 amps for total of 16 amps I think you mean 16 amphours that evening. So that night you burned 960 watts I think you mean 960 watthours of energy.  Okay next day it is charging it is sunny but takes two days of sun to fully recharge, would a system with 6 -6volt batteries recharge faster or slower all other things being the same considering that that 960 watts I think you mean 960 watthours is being consumed from a smaller bank in one case and a bigger in another case.

Feedback appreciated and why or  if one is faster than the other.

The answer to your question depends on whether there are limiting factors on the charger or the wiring or the battery.

In either case you are removing 960 watthours of energy from a battery.  With the smaller battery bank, the discharge takes you to a lower SOC just because the 960 watthours is a greater percentage of total capacity of the smaller bank.  However, the higher currents involved in drawing current from the smaller bank means there will be greater Peukert losses of the battery, and I²R losses in the wiring.  Thus the SOC will be disproportionately lower in the smaller battery bank

Therefore you need to replace more watthours in the smaller bank. 

Another factor that is very important is where your SOC is on the charge efficiency curve... charging from 50% to 60% SOC is more efficient and takes less time than charging from 85% to 95%.  With a larger bank you may need to spend more time in the slower, less efficient range.

Another issue in the timing of the charge cycle is charger limitations... how many amps of bulk charging current can your panels and controller produce as a function of the battery capacity?  It is likely a different number for each different battery bank. 

--mapmaker

[fiddlerkelly]

Thanks vtmaps for picking me up on my errors. 300 amps panels was suppose of course to say 300 watts . Regarding what you are saying about charging from 50-60 SOC is more efficient than from 85-90 % SOC. So are you saying that if your battery bank is discharged to 50-60% that this is better for a battery bank than just to discharge to 85-90% SOC. The reason I ask that question is when first reading about solar power  and battery banks that you should only use approximately 20 % of the battery bank capacity as this will maximize the life of the batteries /battery bank. Am I misunderstanding what I had read or am misinformed.

Thanks again for your assistance.

[vtmaps]

The reason I ask that question is when first reading about solar power  and battery banks that you should only use approximately 20 % of the battery bank capacity as this will maximize the life of the batteries /battery bank. Am I misunderstanding what I had read or am misinformed.

The shallower the cycle, the more cycles you get.  You batteries will last more days with 20% cycles than with 40% cycles... but that is assuming daily cycles.  You want to avoid very shallow cycles (less than 10%) because you may get lead dioxide clumping on the positive plate.

Suppose you have 40% daily discharges with a particular battery bank.  If you double the bank you would have daily 20% discharges.  So with a double sized battery bank you spend twice as much money and it lasts almost twice as long as the single sized bank.

If you have a big battery you can skip charging until you get down to 40% DOD (= 60% SOC).  Then you have deeper cycles, but each cycle last two days, so your battery may last twice as long because it has half as many cycles per week or month or year.

There is one other consideration... if you create the big bank by paralleling smaller batteries (rather than using big batteries) you are shortening the life of the bank and reducing its safety (fire, thermal runaway) because of all the issues with parallel banks.

--vtMaps

[fiddlerkelly]

Vtmaps, right now have my system parralled as is, 2 - in series  6 volt batteries, but am just waiting for new panels to arrive and will be connecting my panels as 24 volts . Plan is to get the midnite as I said before . Even though I connect my new panels in sets for total of 24 volts and join all in a combiner box can I still have the battery bank set up as 48 volt. Is there a feature in the midnite that gives me this option or do I have to stick with arranging my batteries as 24 volt system.


If you have a big battery you can skip charging until you get down to 40% DOD (= 60% SOC).  Then you have deeper cycles, but each cycle last two days, so your battery may last twice as long because it has half as many cycles per week or month or year.


so the big battery you refer to can either be as you said one big battery or several connected in series as one, right.?

Thanks