Hydrometer readings

kansas · October 2014

Just checked my SOC for the first time since startup with a new Hydro Volt hydrometer. The batteries are two US 6 volt wired in series with AH of 242. The manufacturer says the SG should be 1.27 minimum. US says the batteries won't reach full capacity until 30 cycles or so. These have cycled 5 times at most with no deep (below 80%) discharges.

The system was in float mode at 13.6 volts, .6 amps, 100% battery according to the Trimetric meter, just before I shut down the charge and output prior to using the hydrometer. I waited about 15 minutes before taking the SG readings at which time the voltage measured 13.2 volts on my multimeter. The CC is a Morningstar 30 that equalizes every 25 days and has not yet, from what I can tell, gone through an equalizing charge.

I got what seemed to me, a guy with no experience, inconsistent results from the Hydro Volt, which sometimes "shot up" to a high reading, then hold there, then drop a lot lower, then lower still as it dripped a little. The it might go up a bit, etc. Every cell and reading was a little different. The following are the results of three tests of each cell, somewhat "stable" readings after the ups and downs. After the first tests, I rinsed with distilled water between tests and cells. The first two readings on cells 1 and 2 were solid.

Cell 1 - 1.28, 1.25, 1.25
Cell 2 - 1.28, 1.25, 1.25
Cell 3 - 1.25, 1.20, 1.23
Cell 4 - 1.26, 1.22, 1.26
Cell 5 - 1.27, 1.26, 1.23
Cell 6 - 1.20, 1.26, 1.25

Are these normal readings for new batteries?

Should I take the third tests as definitive?

Does "reaching full capacity after 30 cycles" mean full AH, or full SG/ charge, or both?

Is this proper functioning for the Hydro Volt?

Are the varying readings due to the unsettled status of the battery after being on float mode just before testing?

Thanks a million - Bill

Blackcherry04 · October 2014

Re: Hydrometer readings

I have used the Hydro Volt for over a year and find the readings fairly consistent, None of them are perfect. I don't consider it to be exact. I'll usually let it fill and give it a little tap on the top of the well. As the wheels temperature compensate you'll get a little drift one way or the other. Also if your distilled water is not the temperature of the electrolyte you'll get some drift.

On Battery cycles, until the plates fully form you will get funky readings. I would call 30 cycles a minimum to start seeing some stability in the readings. Also 15 minute rest is really not long enough, my Surrettes take overnight to get accurate readings.

BB. · October 2014

Re: Hydrometer readings

If you have not equalized the batteries--You probably want to do that too... More or less, any SG readings farther than 0.015 to 0.030 from each other (depending on who you read) should be equalized.

Also, remember to rise your hydrometer with distilled water a couple of times before you put it away--They can build up a sticky scum inside if the electrolyte is left to dry out.

-Bill

kansas · October 2014

Re: Hydrometer readings

Thanks, Bill. I would like to equalize now, but have no way straight forward way to do that. The CC is on an automatic cycle that won't come due for 20 days . I have a generator I'm thinking of integrating for backup but haven't done that so have no charger for that. I do have a tractor starter/ charger that I'm sure would put out the necessary current, but the timer is broken and I wouldn't have anyway to be sure of the voltage (except my multimeter, I suppose). I've got a clear idea of how to equalize from your earlier response to one of my threads For the sake of fleshing out this thread, I'll copy here your recommendations for testing and equalizing a new battery bank:

So--New bank:

0. mark battery(ies) and cell #'s so you can keep track of data in log book.
1. Check electrolyte levels (no exposed plates, no cracks/leaks/spills from shipping)
2. check/log as received specific gravity of each cell. (should be >75% state of charge)
3. log as received voltage of each battery (or each cell, if possible) for all batteries. (should be >75% state of charge)
4. Assuming 0-3 are OK... Then start charging to ~100% SOC. Log specific gravity readings for each cell.
5. If the SG differences are more than 0.015 to 0.030 or greater, then "equalize" battery bank (~15 volts or 2.5 to 5% rate of charge for 30 minutes at a time).
6. Check SG every 30-60 minutes. When SG stop rising. Log final SG readings (temperature corrected). This is your bank's 100% state of charge. If battery bank gets too hot--Stop equalizing to let bank cool.
7. Start running battery bank. Pick a pilot cell, and monitor SG readings (daily, weekly, as needed, etc.) until you understand how your system is performing.
8. Do a electrolyte level check/all cell SG log once a month (first few months), check battery/cell voltages--Looking for "differences" that may indicate problems.

One thing I will do is take another series of SG tests after the system has been off for 2 hrs and see how consistent those are.

Question: will the SG rise as the batteries cycles and "capacity increases?" will the AHs increase toward the rated number, in this case 242, as the batteries cycle?

Blackcherry04 · October 2014

Re: Hydrometer readings

Question: will the SG rise as the batteries cycles and "capacity increases?" will the AHs increase toward the rated number, in this case 242, as the batteries cycle?

Yes, as more of the plate becomes formed and active the pores in the lead become active then the sulfate will be driven off the plates more evenly and Sulfuric acid will fully recombine in the electrolyte and you'll get more consistent readings.

Again , if you do not use a resting period. You'll still have a mixing period where you still get a rise in the SG level. it's not unusual for me to stop a EQ at 1.250 and find them at 1.265 the next day.

kansas · October 2014

Re: Hydrometer readings

I've averaged the results listed above. Cell 1 - 1.26; 2 - 1.26; 3 - 1.23; 4 - 1.25; 5 - 1.24; 6 - 1.24. Not too bad, on average, if .03 is taken to be the standard for the maximum variance before equalizing, but cell 3 does look weak.

Blackcherry04 · October 2014

Re: Hydrometer readings

kansas wrote: »

I've averaged the results listed above. Cell 1 - 1.26; 2 - 1.26; 3 - 1.23; 4 - 1.25; 5 - 1.24; 6 - 1.24. Not too bad, on average, if .03 is taken to be the standard for the maximum variance before equalizing, but cell 3 does look weak.

Yeah, a little weak, but they are all a little different in how they develop. Give them another 20 days and then you'll know if you have to take more action on it.

kansas · October 2014

Re: Hydrometer readings

Thanks Blackcherry, Bill

BB. · October 2014

Re: Hydrometer readings

Remember it is not the "average SG", you are concerned about specific SG for EACH CELL. Essentially, the cell with the lowest SG in the series string is the "weak link"/lowest AH capacity in the string.

If all cells are at 100% except one at 75% state of charge--That string will only have 75% useful AH capacity (I.e., weak cell will "go dead" before the rest of the cells). Taking a Lead Acid Cell battery to zero (or worse yet, to "reverse charge") is very hard on the cell--And may destroy it.

-Bill

kansas · October 2014

Re: Hydrometer readings

That's why I was averaging each cell, to even out the hydrometer readings. Even then cell 3 looks weak. Hopefully the equalizing charge will help. Thanks, Bill

vtmaps · October 2014

Re: Hydrometer readings

kansas wrote: »

I would like to equalize now, but have no way straight forward way to do that. The CC is on an automatic cycle that won't come due for 20 days .

kansas wrote: »

Even then cell 3 looks weak. Hopefully the equalizing charge will help.

You need to go deep into the specs on your charge controller to know what this automatic EQ cycle is. What CC is it?

The term "equalization" has many different meanings and is used in many different ways. It is almost always a controlled overcharging of a battery.

"Corrective EQ" is a controlled overcharge that is applied to a battery when the cells do not have uniform SG. On the other hand, "routine" equalization is just that... a routine part of a battery's maintenance schedule.

Many battery manufacturers recommend "routine" EQ every week or so. There are different reasons for this. One reason is to avoid the "99.9%" trap. There are several ways to know when your battery is 100% charged, but they are not so precise that you can tell 99.9% SOC from 100% SOC.

If you achieve 99.9% every day, after a while the 99.9% becomes your new 100%. Charging to 99.9% of 99.9% of 99.9% etc for awhile is what we call slow deficit charging. Doing a routine EQ can break this cycle.

So if you decide to do a routine or corrective EQ, what is it that you are doing? That has no consistent meaning in the industry. For many chargers and controllers, it means holding the battery voltage a bit higher than the usual daily charging voltage, for a period of time. But not all... for example Iota battery chargers do an automatic weekly EQ if the battery is being held in float, but their EQ is really just a regular bulk/absorb cycle at the usual bulk/absorb voltages. Its purpose is to periodically stir the electrolyte of a flooded battery to prevent stratification and sulfation from building up.

When charging batteries, the lower the voltage (within limits), the longer it takes to charge the battery. Also, the lower the voltage (within limits), the better it is for the long term health of the battery. And also, the lower the voltage (within limits) the more efficient the battery charging is.

When you set your daily absorb charging voltage, you are playing off time against battery health... you need to get the voltage high enough to finish the charge in a reasonable amount of time, but the sooner you finish the charge, the worse it is for the battery.

Some folks lower their absorb voltage and/or absorb time... and intentionally deficit charge on a daily basis, but then do a weekly routine EQ. The theory being that it's better to go easy on the battery every day, and then hammer the battery once a week.

I mention all of this because you seem to have your hopes pinned on EQ... but do you even know what EQ means on your CC? What CC is it? (hint: put some details of your equipment in your signature line). You can achieve the same results as a high voltage EQ by increasing the (usually lower voltage) absorb time... If you can't raise the voltage for an EQ, just run the absorb longer. Raising the voltage speeds up charging... that's true anywhere in the range of absorb through EQ voltages. (although as mentioned, some manufacturers have EQ voltage = absorb voltage.

I will finish this post with a stochastic view of battery charging. Suppose a battery manufacturer produces battery cells that have the following characteristics:
99.5% of the cells will be fully charged with a voltage of 2.37 volts (14.2 volts in a 12 volt system).
99.95% of the cells will be fully charged with a voltage of 2.43 volts (14.6 in a 12 volt system).

If they recommend a charging voltage of 14.2, a half percent of their cells will fail during warranty, but that means almost 3% of their 12 volt batteries will fail (6 cells per battery). On the other hand, if they recommend charging at 14.6, only 0.3% of the 12 volt batteries will fail. If you buy that 12 volt battery, what charging voltage will you use? There is a 97% chance that if you use the lower voltage your battery will last longer.

You are lucky that you have flooded cells... you can use a hydrometer to tune your charging voltages and time to what works for your battery in your system in your environment. In all likelihood you can (if you have adjustable chargers and controllers) use less time and voltage than the manufacturer recommends and extend the life of your bank.

--vtMaps

Plowman · October 2014

Re: Hydrometer readings

My Hydro-Volt is pretty consistent, though I do sometimes have to shake it around a bit to get it to stabilize at a single reading. I fill it and empty it 3 times before I take a reading to mix the electrolyte a bit. I also don't bother to let my batteries rest since they're pretty much always in a state of charge/discharge.

Doesn't look like your Prostar 30 has a manual equalization option (my Tristar 45 does). Also appears that it equalizes at 15.1V, which is on the low side.

You might consider getting an Iota battery charger for your generator and adjusting its potentiometer to whatever your battery manufacturer specifies for equalization. I wouldn't bother with the IQ4 feature if you're just using the charger to bulk and equalize with a generator.

kansas · October 2014

Re: Hydrometer readings

Battery literature asks for an equalization charge of 2.55 volts/ cell ( I think this would be 15.3 volts for my string) for 1 to 3 hours, every 30 days. CC literature promises equalization charge of 14.9 volts, for 1 hour, every 25 days. The way I read the Prostar literature, a 15.1 volt equalization that lasts for 2 hours takes place only if the battery has discharged below 11.7 volts. So far as I can tell the Prostar is not adjustable. If there are specs for the CC other than these, I need to be enlightened. Based on these specs for battery and CC, the equalization charge of the Prostar appears deficient.

I have been considering a 55 amp Iota charger as backup for PV, especially since I already have a 3000 watt Honda generator. Using it for a corrective EQ would be an additional benefit. So far, however, use of the system has been less than the design wattage and the batteries have not discharged below 92%. This will no doubt change as winter comes and we become more free with our usage, but I doubt there will ever be anything like the 40% DOD I planned on, save an accidental discharge, i.e. forgetting to turn off the lights, etc. The Iota for PV backup is therefore probably not needed. Moreover, the price of the Iota ($200) approaches the cost of the batteries ($300). At this point it doesn't seem worth it.

So, I guess I am depending on the Prostar equalization, having no other cost effective options. Perhaps someone will suggest going directly from the panels to the batteries, in a controlled way. Obviously there is adequate voltage coming from the panels to boil the batteries. I suspect that is a far fetched idea.

Thanks for all the ideas and in depth explanations. I really do appreciate it. I've edited (created) a signature. I hope it appears when I post this reply. Bill

kansas · October 2014

Re: Hydrometer readings

No signature. Any tips on how to get it to appear?

kansas · October 2014

Re: Hydrometer readings

Voila! There's he answer.

Plowman · October 2014

Re: Hydrometer readings

kansas wrote: »

The Iota for PV backup is therefore probably not needed. Moreover, the price of the Iota ($200) approaches the cost of the batteries ($300). At this point it doesn't seem worth it.

Depends on if you're dependent on your off-grid system and your local conditions. I live off grid year round with no option of charging the batteries on the grid short of schleping them to a friend's barn. So I need a generator and charger for winter, when we can go well over a week (often two or three) with overcast, drizzly weather.

With 242 Ah of battery, you could go with an Iota DLS-30, which is <$130 shipped. This would give you a 12.4% charge rate. An Iota DLS-55 would give you 22.7%, which is on the high side.

Or even better, an Iota DLS-45 for $145 shipped. 18.6% charge rate, which I think is OK for occasional bulking with a generator, though others may disagree. There's a trade off between running the generator longer and stressing your batteries with a high charge rate. But since my generator is worth a lot more than my batteries, I've gone with a higher charge rate.

You could also replace the charge controller with something better, say a Midnite Kid. I can't say as I'm fully satisfied with my Morningstar charge controller, thinking about selling it and buying a Kid.

gww1 · October 2014

Re: Hydrometer readings

I don't leave my battery overnight after eq. I do concur that the one or two times I did that the sg went up. I thought it was probly temp change as I don't temp comp my readings athough I do try to pay attention to temps while checking best I can. My sgs have been all over the board. I have seen as high as 1.300 while 1.275 was high on others. I have one cell that never gets above 1.272 while my high one gets to 1.290/1295.

I have a couple other that set somewhere between. I no longer check all cells but do use the records to decide which ones to spot check. Funny thing. I did see the low cell hit 1.285 one time in my life but it had to be some sort of fluke. I quit worrying as the cells seem to consistantly and always end up in the same place. I feel I could be over charging a bit as the way I eq now is go till the high and the low get to their to sg, with the low being 1.272. When it hasn't risen or has went down for a one and half or two hour period I quit. I used to go till it dropped every time.

The battery just went over a year. The sgs are easyer to get to their max now then in the beginning. I use almost eq voltage for absorb. The manufatuer insistent that I eq once a month but I still wonder if my sgs arn't really gaining but just staying where they were if it is nessasary. In the beginning it was 16 to 20 hour eq's now it is 3 or so to check if the sg's are raising or not.

I hope my selfish post fits this thread and if so any advice.
Thanks
gww

kansas · October 2014

Re: Hydrometer readings

The literature for the Iota DLS-45 says it will charge at a rate of 13.6 or 14.2 volts. Will that be enough to equalize my batteries? US Battery asks for an equalization rate of 15.3 volts.

kansas · October 2014

Re: Hydrometer readings

Thanks, vtMaps - I just re-read your response and have a much better understanding of your points. As for my query below concerning the charge rate of an Iota charger, your advice indicates I can equalize by charging loner rather than at a higher rate. Bill

Blackcherry04 · October 2014

Re: Hydrometer readings

kansas wrote: »

The literature for the Iota DLS-45 says it will charge at a rate of 13.6 or 14.2 volts. Will that be enough to equalize my batteries? US Battery asks for an equalization rate of 15.3 volts.

You have to open the charger case, on the fan end left side there is a 10-20 turn potentiometer that you can crank up the voltage to about 15.5v with the plug in the jack. If your only going to dedicate it to EQ's then leave it or cut it back to the voltage you want when finished.

14.2v is pretty low to start with , even with IQ-4 it runs the voltage to 14.8 and drops to 14.2 v for absorb. I usually set my voltage to 14.6 and it will taper in absorb and then disconnect it. Since all the voltages are a ratio to each other it does mess up the float voltage unless you reset it.

Hydrometer readings

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