Using my new Hydrovolt sp.grav. meter

MarkC

Questions using the Hydrovolt sp.grav. meter

Background;
My on-grid system is supplemented with two sets of 4 golf cart type batteries (48 volts) that are combined in parallel to power an APC UPS - SUA3000 (high reliability, pure sine wave, line interactive UPS). This UPS is 120 volt nominal output. One set of batteries are Interstates that are over 4 years old. New Trojans are a few months old. Both are ~ 150 AH/20HR

The SUA3000 output is connected to my "off-grid/emergency" users which consists of two ceiling fans, medium size refrigerator, total of 6 CFL lights and a medium screen TV. The system will hopefully get us through the aftermath of a hurricane type event with some level of comfort.

Using the hydrovolt to check battery sp.grav.;
When fully charged, the largest spread of any one battery's cells was .02. However all gravities were very high - 1.28 to 1.31. This was the case for both the new Trojans and the older Interstates. All batteries had been on a 50 watt desulfator/charger for two weeks while we were vacationing. I do the bulk of charging with the golf cart (smart?) charger with the Trojans in parallel to the Interstates. I did a "light" usage test of the SUA3000 for 5 hours powering two ceiling fans, refrigerator, LCD TV, few lights, etc. The average sp.grav. drop was ~.03 points with quite a bit of variability. I found that getting consistent readings with the hydrovolt was a challenge. It seemed that "flushing" the unit several times on each cell would settle the readings down. Beginning to think the acid might not be well mixed? Also, as all readings seem so high, I'm not sure how to estimate the change in SOC - but my estimate was in the 10-20% range. The power used during the test (from the SUA3000 data logger) calculated to be 1700-1800 watt-hrs (~15000 watt-hr total battery capacity).

The test did seem to go well - no glitches with any equipment.
Has anyone had such experience with high gravity issues? I believe the hydrovolt was working properly - it is very quick and efficient - no evidence of any bubbles of any type - highly recommended based on it's ease of use. I do wonder, based on the design of the hydrovolt, whether or not it might not be calibrated correctly. The ambient temps are quite high in the storage shed - sometimes at 100 degrees F, average around 85 degrees.

vtmaps

Abnormally high SG can be caused by loss of water from evaporation or gassing. One other thing... many reliable forum members have reported that equalization may raise SG above normal for a few hours. After resting the battery the SG drops a bit. I don't doubt the phenomenon, but i can't explain it. By definition, when all the sulfur is off the plates and in solution, the SG is back to the factory specs... you can't get more sulfuric acid than what the manufacturer starts with. One possible explanation is that overcharging a battery puts something other than sulfuric acid into the solution. Remember that you are measuring SG, not sulfuric acid concentration. if you ASSUME that the electrolyte is only water and sulfuric acid, then SG does correspond to sulfuric acid concentration.

MarkC wrote: »

The ambient temps are quite high in the storage shed - sometimes at 100 degrees F, average around 85 degrees.

Are you using a remote battery temperature sensor with your battery charger and controller? If not, you are likely equalizing the battery every time you do an absorb charge.

--vtMaps

MarkC

The "off-grid" system is really on over-statement. It is basically a set of (old) working golf cart batteries and a new spare set housed in a vented enclosure wired in parallel to the golf cart via an anderson connector. The combined sets (via the proprietary "blue" anderson connector), feed an old APC SUA3000 that then feeds both L1 an L2 legs of my emergency power panel (120V). Recharge is by the SPS on my on-grid system (SMA Sunny Boy) - seems well balanced in that regard.

Since the "old" batteries seem to have done very well using the OEM Club Car 48 V charger (4+ years old and still seem excellent). I simply recharge all 8 batteries by keeping the new batteries connected. When I leave the property (quite remote - and for several weeks at a time), I hookup the 50 watt desulfator/charger. Don't really have any monitors of any type. Being in a metal shed in South Texas, it is going to be quite hot on all equipment - don't really have any options there. FYI, I probably do keep the electrolyte level on the low side in the golf cart - it seems to "spill" less during the (off road) usage and also during the copious gassing during the bulk charging of the OEM charger. So I keep the level ~1/8 " above the plates - when settled down.

Is it possible that the desulfator/charger might actually overcharge both sets of batteries? Also, a rough approximation of the average gravity drop during the test run used to estimate the actual power extracted, seemed to be close at the actual calculated.

Next trip to the property, I am going to measure the actual voltage at each battery that is being supplied by the desulfator/charger after several days/weeks of charging - which is basically a "trickle" for this many batteries!

Vic

Hi MakC,

First, YES, one should draw and return two or three samples of electrolyte with the Hydrometer, and take the measurement on the following draw. Here is Surrette Battery's write-up on using a Hydrometer on Flooded batteries, it is a good general overview:
http://support.rollsbattery.com/support/solutions/articles/4347-measuring-specific-gravity

Be certain to rinse the any Hydrometer three or more times with Distilled Water, after the measuring session -- this is very important with the Hydrovolt, as it has a lot of internal surface area that is wetted with electrolyte (IMO). The Hydrovolt Hydrometer is said to be temperature compensated. Warm/hot electrolyte should read as a lower SG (if not compensated), as the electrolyte is less dense when warm/hot. The Hydrovolt appears to be a very good Hydro, IMO.

Keeping electrolyte level low in the cart would allow the SGs in those batteries to rise. However spilling of electrolyte should reduce the SG of the electrolyte, because when you eventually add water, the electrolyte is diluted.

You really must use temperature-compensated charging of batteries, essentially always, and especially when the batteries are very warm/hot or cool/cold. Cannot speak to the use of Desulfators, other than ... WHY (??) !!

All FWIW, Vic

MarkC

Vic - good inputs. However, until I make a decision on a good MPPT charge controller (putting this off for a number of reasons - actually sold a Kid after keeping it in storage for a year!), I'm not going to have a reasonable way to temperature compensate. That is unless someone has a suggestion that uses the OEM golf cart charger. Again, I use the SPS (120 v) outlet on my Sunny Boy to drive the golf cart charger, which works amazing well - not the most efficient, but works with my equipment. The 48 volt desulfator/charger was, frankly, an experiment to see if the life of the old batteries might be extended by switching the OEM charger to the "trickle" charger during the extended times I'm away from the property. Got to say, these old batteries seem to match the new Trojans - at least on the lightly loaded "test".

You hit the nail on the head about spilling vrs low levels in the old golf cart batteries - but then the new Trojans measured essentially the same and discharged to essentially the same (Voltages - on average) during the "test" run. That is what seems odd. Next trip, I'm going to use the cart, recharge with the OEM (to get gassing), let them sit overnight, flush the hydrovolt several times and see what I get.

inetdog

You are quite right to force gassing before measuring SG, especially if the last charge started from a low SG. Alternatively (as if....), you could shake the batteries vigorously without spilling to get more acid mixing.
Stratification will always cause an SG reading that is lower than the actual average SG of the electrolyte as long as you are filling the hydrometer from the top layer of the electrolyte. Sulfation of the plates will take some of the sulfate ions out of the picture, preventing building the SG back up to the normal maximum level. And it will change the SG versus SOC correlation, but will not have as great and effect on SG versus remaining capacity.

Vic

MarkC wrote: »

...
I probably do keep the electrolyte level on the low side in the golf cart - it seems to "spill" less during the (off road) usage and also during the copious gassing during the bulk charging of the OEM charger. So I keep the level ~1/8 " above the plates - when settled down ...

Hi Mark,

Should have mentioned this before, but forgot;

The Water Miser caps might help reduce the spillage of electrolyte in your cart:

http://www.solar-electric.com/batteries-meters-accessories/batteries/baacma/batwatmiscap.html

FWIW, good Luck, Vic

MarkC

Update - checked gravities again after a week on the OEM charger (only). Seems they have come down about .01 - still high on both old and new batteries, but below the 1.3 level. Going to do another "exercise" of the batteries soon with auto-data dumping to a spreadsheet that calculates total energy expended with an alarm when KWH reached a preset level - as soon as I can get my local area Wifi set up.

Thanks Vic - I found that by keeping the levels about 1/8" above the plates, I don't seem to have any spillage. The Interstates come with the quick release (three at a time) caps that are very convenient. Wish Trojan would adopt them.

Is there a "calibrated" acid that can be used to check the hydrovolt? I can buy a quart of replacement acid, but don't know how controlled their concentrations are?

BB.

From here:

http://support.rollsbattery.com/support/solutions/articles/4347-measuring-specific-gravity

[h=4]Checking Calibration[/h]
As with all measuring equipment drawing conclusions from the results is not worth the effort if the equipment is not calibrated.
The correct way to check the calibration of a hydrometer is to test the hydrometer against a known master that is accurate to one more decimal point. These hydrometers are; however, very expensive ($100-150 USD) and can be easily broken.
The simplest and cheapest way, when facilities exist, is to measure out a volume of acid and weigh it. A small graduated cylinder and an electronic balance are perfect. The specific gravity is then calculated as follows:
SG = Mass (g) / Volume (ml)
The metric units must be used to convert to the specific gravity scale based on water. The hydrometer is calibrated if it agrees with the sample within its manufacturing tolerance.

Get a bottle of pre-mixed electrolyte from a battery distributor? Double check electrolyte solution (or make your own with sulfuric acid and distilled water--Add acid to water, not water to acid) with a scale+graduated measuring cup (may be more errors from this vs just getting a bottle of electrolyte from a battery distributor).

-Bill