Testing Batteries with Hydrometer

[Spaceman Spiff]

Now that my electrical system is together, and my charge controller has been in float mode most of today (9/22), I decided to check the specific gravity of the electrolite. You can really tell that I am new to this; not going well :-/ I'd like to get the solar charging setup checked out before it becomes less accessible.

Questions:

1. How does one go about checking the cells without making a mess (dripping electrolite all over)?

2. What variance can I expect in readings? Three measurements taken on the same cell gives reading 12.5 to 12.9. This seems way too much. Either my method is wrong, my hydrometer is very inaccurate, or ??

3. What variability between cells is acceptable?

4. Do you flush hydrometer out between cells?

5. How and were do you store your hydrometer? This thing is wet and could make a mess if there is any residual sulfuric acid left in it.

System is: 200 W solar into TS-45 charge controller into 2 x 6 V, 205 AH golf cart batteries. Charge controller says batteries are above 80%, for whatever that is worth. Trimetric hasn't been set up yet, as I have to tell it when batteries are at 100%.

-- Spiff

 

[SternWake]

What Hydrometer did you get?
First, do not get confused with a SG reading of 1.290 and a voltage of 12.90.

It really depends on teh battery as to how high the SG will read. in general batteries sold int he far north will see 1.300 where as tropical batteries will have weaker electrolyte and max out at 1.270.

Also as electrolyte levels get lower, SG will read higher.

The plastic ones are not really very good. Poor repeatability, poor precision. I've tested a plastic Napa one next to a Glass turkey baster one side by side and often the plastic one was way out and i could not get it to read inline with the Glass one, and on th next cell I could, then i'd go back and test again and it would be fine, then the next cell it would be whacked out again. I still have it, but I should have just crushed the thing with a hammer, or find someone i don;t like and give it to them.

Lots of times, bubbles stick to the float, and make readings appear higher than they should be.

If the battery has not been charging, then the electrolyte can be stratified, so a bunch of bulb squeezes can help mix things up, and help the bubble situation too.

Generally when cells are more than 0.015 apart from each other the battery should be equalized, but sometimes one or two cells will always read higher, or perhaps lower so having a record or a good memory can keep one from abusing the battery trying to even out all the cells.

To minimize the mess, after draining the hydrometer, hold the spout over the cell and let gravity work for you. Slowly allow air into it, and expel it faster to help blowout the extra.

Do not rinse out the Hydrometer between cells. you will dilute the acid and readings will be thrown off until all the water is flushed out of the hydrometer. Always rinse afterward. If you have a plastic model, it is near impossible to dry it out completely as the bulb is not removeable.

The Glass turkey baster ones are generally a much much better tool than the plastic ones. they are not that hard to keep from breaking, just keep the plastic container it was purchased in and take extra caution.care of the glass float.


Since you are trying to determine full so as to zero your trimetric, you need to find maximum specific gravity, and this basically requires an Equalization charge, and you need 15.3v minimum for this. I find my battery that 16volts allows the SG to max out in around an hour, where as at 15.7 it will take 2.5 hours, and 15.3, well I've never maxed out SG at 15.3 unless it is super hot out and I used little battery the night before and it was at Absv before noon.


Please use eye protection when taking readings, especially when charging/ Equalizing. Having some baking soda mixed in some water nearby is handy. Wear wool or junky clothes as sulfuric acid likes to eat moth holes in Cotton/synthetic fibers. Wool is immune to it.

It helps to have a little chart so you can keep track of which cells always read a bit higher or lower, and also some cells use more water than others. Older/aging batteries will start using water faster too. So this is another metric to try and plan for when to replace, as opposed to being stuck buying the first battery you can get whenever the battery does fail to meet one's capacity requirements.

I generally rinse out my glass turkey baster, remove the bulb, remove the float , wipe that off and and set aside, then roll up a napkin and insert it into the glass tube , then stick the foam protected glass float back in the baster( not too deep), return the bulb in a twisting motion, Wipe the end of the tester which goes in the cells with the used napkins, and return it to the case it was shipped to me in.

http://www.amazon.com/OTC-4619-Professional-Battery-Hydrometer/dp/B0050SFVHO

 

[Zil]

Don't forget, temperature has a big effect on specific gravity.

 

[Spaceman Spiff]

Thanks guys,

I have the OTC 4619 'Professional Battery Hydrometer' from amazon.

Batteries are from Sam's Club, Energizer 6V Golf Cart batteries manufactured in June 2014 and purchased in late August. Charged them up with my Munkie Wards 6 amp battery charger 'til down to 1 amp and let them sit until now, when I got the solar charging system on line. Thinking after I posted last night before sleep (usually my best 'thinking' time) that the batteries were stratified and needed mixing up. Will see if I can find a good charger, else use the equilizer function on the TS-45.

One problem I was having was that the hydrometer would dribble acid as I brought it up to eye level. I had to get a glass to 'plug' the spout to keep from making a mess. Hard for me to get down to the level of the batteries.

Eye protection is always a must. As I have gotten older, I am more aware of safety stuff.

I didn't think about taking the hydrometer apart to dry. I'll have to remember to save the float protector.

The plastic tray is a little flimsy, I will try to find a small box for it to reside in. MaineSail talks about the grungy hydrometers he finds laying about in sailboat engine rooms and I am concerned about contamination of the electrolite.

Zil - thanks, the hydrometer has a thermometer built in, marked with the conversion factor.

--Spiff

 

[SternWake]

Afraid you pretty much need to keep the hydrometer in the cell to keep the acid in the cell. Lifting it out to read it is a recipe for sulfuric acid drops everywhere. You also don't want to be pulling acid from the cells, when they need refilling with distilled or deionized water, and you do so, the acid will be somewhat weaker, and you will notice lower voltages under the same use. But pretty much every refill will make the battery appear to be weaker after refilling if watched close enough, and especially when the battery is aged and has lost capacity.

Also note that while and after charging, the cells in the center of the battery will be warmer than the outer cells, so keep the thermometer reading in mind when reading the float on each cell. Also during equalization, i have seen the readings on the float lower to my surprise, but then seen that the thermometer had risen significantly indicating the SG was still rising.

Kind of hard to get a true full charge with a 6 amp automatic charger. GC batteries vary but you should be hoping for at least 14.6v for a while before the charger declares good enough and goes to float.

Also keep in mind healthy flooded batteries can self discharge 15% per month at 75F.

Most every automatic battery charger out there cuts the charging cycle short for fear of overcharging and lawyers. the programmable solar controller is the solution, when programmed correctly for the batteries under its care, and enough sunlight for the capacity removed the night before.

I've been falling short on Sunlight lately, have only been getting to ~10 AH from full, and I can easily notice this by the voltage held right now. Another day of this and I will need to significantly reduce consumption or employ another charging source.

Make sure to twist and pull the bulb off the glass tube for cleaning/drying, and twist and push it back on. The glass float is the only real fragile portion. The body of mine has taken some unintentional abuse in stride.

I moved my flooded battery to my engine compartment so I could take SG readings easier. I used to have to climb inside my electrical cabinet on my stomach with a head lamp and a mirror to read the SG before, or check the levels,and this was such a task, it caused me to put it off too long, and 2 sets of Crown group 27 batteries had slightly exposed plates from not watering them in time. One set was killed pretty much instantly, the next set were just capacity compromised until premature failure.

This time I went with a single group 31 instead of 2 27's, as I never needed that much capacity. The higher solar wattage / battery capacity rate, and the easier checking of SG has this single battery performing well despite deeper discharges nightly. I am closing in on 300 cycles with little detectable performance loss.

 

[RogueRV2]

Hi SternWake,

Thank you for those voltages. I'll be getting a user adjustable charge controller as you suggested next month and will use those numbers. For those who live in colder climates and do not have a temperature compensation thermometer built-in to their hydrometer, here is an on-line compensation calculator. It's good to play with as well.

Hydrometer Temperature Adjustment Calculator | Brewer's Friend




And here's a downloadable chart in a PDF:


http://www.thermcoproducts.com/documents/Correction Table for Specific Gravity Hydrometers.pdf

What Hydrometer did you get?
First, do not get confused with a SG reading of 1.290 and a voltage of 12.90.

It really depends on teh battery as to how high the SG will read. in general batteries sold int he far north will see 1.300 where as tropical batteries will have weaker electrolyte and max out at 1.270.

Also as electrolyte levels get lower, SG will read higher.

The plastic ones are not really very good. Poor repeatability, poor precision. I've tested a plastic Napa one next to a Glass turkey baster one side by side and often the plastic one was way out and i could not get it to read inline with the Glass one, and on th next cell I could, then i'd go back and test again and it would be fine, then the next cell it would be whacked out again. I still have it, but I should have just crushed the thing with a hammer, or find someone i don;t like and give it to them.

Lots of times, bubbles stick to the float, and make readings appear higher than they should be.

If the battery has not been charging, then the electrolyte can be stratified, so a bunch of bulb squeezes can help mix things up, and help the bubble situation too.

Generally when cells are more than 0.015 apart from each other the battery should be equalized, but sometimes one or two cells will always read higher, or perhaps lower so having a record or a good memory can keep one from abusing the battery trying to even out all the cells.

To minimize the mess, after draining the hydrometer, hold the spout over the cell and let gravity work for you. Slowly allow air into it, and expel it faster to help blowout the extra.

Do not rinse out the Hydrometer between cells. you will dilute the acid and readings will be thrown off until all the water is flushed out of the hydrometer. Always rinse afterward. If you have a plastic model, it is near impossible to dry it out completely as the bulb is not removeable.

The Glass turkey baster ones are generally a much much better tool than the plastic ones. they are not that hard to keep from breaking, just keep the plastic container it was purchased in and take extra caution.care of the glass float.


Since you are trying to determine full so as to zero your trimetric, you need to find maximum specific gravity, and this basically requires an Equalization charge, and you need 15.3v minimum for this. I find my battery that 16volts allows the SG to max out in around an hour, where as at 15.7 it will take 2.5 hours, and 15.3, well I've never maxed out SG at 15.3 unless it is super hot out and I used little battery the night before and it was at Absv before noon.


Please use eye protection when taking readings, especially when charging/ Equalizing. Having some baking soda mixed in some water nearby is handy. Wear wool or junky clothes as sulfuric acid likes to eat moth holes in Cotton/synthetic fibers. Wool is immune to it.

It helps to have a little chart so you can keep track of which cells always read a bit higher or lower, and also some cells use more water than others. Older/aging batteries will start using water faster too. So this is another metric to try and plan for when to replace, as opposed to being stuck buying the first battery you can get whenever the battery does fail to meet one's capacity requirements.

I generally rinse out my glass turkey baster, remove the bulb, remove the float , wipe that off and and set aside, then roll up a napkin and insert it into the glass tube , then stick the foam protected glass float back in the baster( not too deep), return the bulb in a twisting motion, Wipe the end of the tester which goes in the cells with the used napkins, and return it to the case it was shipped to me in.

http://www.amazon.com/OTC-4619-Professional-Battery-Hydrometer/dp/B0050SFVHO

---

Hello Spaceman Spiff,

A 1 1/4 or 1 1/2 inch pvc pipe with caps works well as protection for the glass tube and float. The bulb and other rubber are removed and stored along side in a metal crush proof box.

 

[SternWake]

The voltages I use on my 12v USbattery group 31 are abnormally high. I wound not recommend them on GC batteries. I would not recommend them on other 12v batteries. Even the larger Trojan T 1275 (150 A/H) does not need daily 15.3v finish, but it does need 15v for the topping charge when cycled deeply.

Finding the manufacturer of the battery and their recommended abs and F voltages is the best place to start. These relabelled GC batteries make the task of finding them a bit more difficult, and if say they are made by Johnson Controls, or USbattery or Exide, or Crown, there is no guarantee they are made to the same specifications.

This link can help one figure out who made what, but it is not always clear cut:
http://jgdarden.com/batteryfaq/batbrand.htm.

Emailing the corporations and asking, might go nowhere either.

Note that while the common charging stages are bulk, absorption and float, I am using Float as a "finishing/topping" charge, at 15.3v. I'll let it hold 14.9v for 2.5 hours or so, then 15.3v finish usually gets the SG up near the maximum. When i am not cycling the battery deeply, then I will lower absorption voltage and duration and set a common float voltage, but daily cycles, I set the float as a 'finish/topping' charge and set the voltage higher than Absorption voltage. Not all solar controllers will allow float to be higher than Absorption/Acceptance voltage.



From all reports i have read these GC batteries do not need the extreme voltages that these large 12 volts jars require to maximize specific gravity.

Many people report that 14.4v will get their Sams club or Costco GC's to Max SG others say 14.6, soe others say 14.8, and i think some say whatever just to say something. If I could not do 14.9 absv and 15.3v finish, my group 31 would be recycled by now, instead of performing well, considering I am cycling it to near 50% almost each and every night.

But Now, I am also lagging on solar wattage for my usage. days being shorter, nights longer, and more shading morning and evening. I could really use another 50 watts, or just conserve more. Can't fit 50 more watts so options are limited.

The hydrometer is the tool you use to figure out the lowest voltages you can get away with that will get the SG within .005 on a good day. if you only need 2 hours at 14.8v, then 2 hours at 14.9v is somewhat abusive to the battery. Sure 14.9v is more likely to get the job done, but at the cost of increased positive plate erosion. It is kind of a high wire act, the goal is to get as close as possible to maximum SG, without being abusive in getting there, but having enough daylight to hold it there for 2 hours or so, and perhaps another hour or 2 at higher voltages too. Again each battery will be different, and it will be different under different discharge and recharge cycles, and it will change as the battery ages too.

I was reluctant to push the voltages as high as I have done, but the hydrometer allowed me, with enough experimentation and monitoring, to figure out how to get the best performance from this battery.

It is now changing. Yesterday I was able to get max SG at 15.3 volts, but I assisted the solar with 8 amps of a AC switching power supply/ charger( my new toy, (MeanWell RSP-500-15). This power supply/ charger will allow me to select upto 19.3 volts, and I did a little 16v and even a experimental smidge of 16.5v But it was not really required. Mostly curiosity to see how much power supply current would be required to force battery voltages that high, but the SG reading surprised me a little too, and I'm glad I checked, as my expectations were wrong.

Temperature not only effects SG readings, it also effects the chemical reaction that occurs as the battery charges. While I have determined that I need 14.9v and 15.3 when charged only by solar, these numbers get a bit skewed when other larger charging sources are implemented. I can also achieve higher Max SGs when hot and it is easier to get them up there, so during hot weather i will reduce voltages and durations, and this is where a solar controller with a battery temperature sensor excels. I really regret not spending that extra 35$ back in 2007 for the model with a BTS

That is the great thing about flooded batteries. With AGMs there is no definitive way to test to see how the charging sources are doing.

With flooded batteries, the hydrometer is the true polygraph. Amp hour counters are useful tools, enlightening tools, learning tools, but the hydrometer has the final say, and it WILL disagree with the battery monitor at some point, or at a lot of points, and you cannot choose to believe the battery monitor just because it cost 20x more money and has buttons, flashing lights and numbers displayed on it.

 

[ccbreder]

This link is for a device to measure SOC for lead acid batteries, including sealed.
http://www.pbase.com/mainecruising/smart_gauge
This link is also relevant.
http://www.pbase.com/mainecruising/battery_state_of_charge

 

[RogueRV2]

SternWake,

Again, thanks for the clarification and elaboration. Very interesting. Knowing from hard data and field experience wat works and watt is marginal is a good thang. It's good to investigate and verify that the charge controller is indeed up to the basic task. Less expensive, el cheapo Chinese charge controllers may function, yet are set up for a particular climate and a generic one size fits all approach that proves inadequate for a significant percentage of applications. Even reputable name brand charge controllers have models represented in a vague way and lead one to purchase a quality item that is not appropriate for their application, and this is a dis-service to the customer as their system operates sub-par. The Morningstar SK-12 is great CC, yet it's bulk rate is set at 14.1vdc, appropriate for only a gel cell, and not the typical flooded battery that need 14.4 or more. Bummer once again I bot one of those some years back. Fortunately I'm learning. I just got off the phone and found that my new prospective CC is still a good choice for me, but it is not what is apparently is represented by the business. The devil is in fact in the details, and the buyer should beware. The Morningstar Sun Saver Duo 25 amp does not have a built in temperature sensor, so the RTS must be purchased separately. Charging times and voltages may not be altered via a PC. The dual battery charging option, the durability, as well as the RTS are the big attractions for myself. I may not have the chance to buy another one, so I'm trying to get it right. The batteries should last longer as a result, and those in the future, could be very expensive.

 

[RogueRV2]

I've had to quote myself as a correction is in order. After several phone calls to verify, finally, I may have the correct information. The Morningstar Sun Saver Duo DOES have a built in temperature sensor, and the voltage and other options CAN be customized via a PC connection.



" The Morningstar Sun Saver Duo 25 amp does not have a built in temperature sensor, so the RTS must be purchased separately. Charging times and voltages may not be altered via a PC. The dual battery charging option, the durability, as well as the RTS are the big attractions for myself. I may not have the chance to buy another one, so I'm trying to get it right. "

SternWake,

Again, thanks for the clarification and elaboration. Very interesting. Knowing from hard data and field experience wat works and watt is marginal is a good thang. It's good to investigate and verify that the charge controller is indeed up to the basic task. Less expensive, el cheapo Chinese charge controllers may function, yet are set up for a particular climate and a generic one size fits all approach that proves inadequate for a significant percentage of applications. Even reputable name brand charge controllers have models represented in a vague way and lead one to purchase a quality item that is not appropriate for their application, and this is a dis-service to the customer as their system operates sub-par. The Morningstar SK-12 is great CC, yet it's bulk rate is set at 14.1vdc, appropriate for only a gel cell, and not the typical flooded battery that need 14.4 or more. Bummer once again I bot one of those some years back. Fortunately I'm learning. I just got off the phone and found that my new prospective CC is still a good choice for me, but it is not what is apparently is represented by the business. The devil is in fact in the details, and the buyer should beware. The Morningstar Sun Saver Duo 25 amp does not have a built in temperature sensor, so the RTS must be purchased separately. Charging times and voltages may not be altered via a PC. The dual battery charging option, the durability, as well as the RTS are the big attractions for myself. I may not have the chance to buy another one, so I'm trying to get it right. The batteries should last longer as a result, and those in the future, could be very expensive.

 

[SternWake]

A remote temp sensor mounted on the battery, despite the extra cost, is superior to an ambient temperature sensor. especially if there is a big difference in mounting locations between controller and batteries.

I have my AGM under the body, and my controller in ventilated cabinet. I just took a temperature reading on battery body and on Controller's steel mounting box in which it resides, and there is a 17 degree difference, the controller being hotter.

I am not familiar with MorningStar products. But with other chinese controllers which make various claims, beware of what can be lost in translation to chinglish and outright deception. Some controllers might have overtemperature protection, like if they are overheated due to surpassing their rating with too much solar, but they might not alter charging voltages with temperature differences.

In temperature extremes these self adjusting controllers based on actual battery temperature, can have huge effects on how well the battery gets charged, and with AGM's, if the battery is hotter than the controller, then the temp compensation can keep the vents from blowing, or the AGM from going into thermal runaway.

http://www.cdtechno.com/pdf/ref/41_7944_0712.pdf

 

[RogueRV2]

Hi Stern Wake,
I believe you may have once again saved me the experience of learning the hard way. I put my order in just today, but will now order the remote temperature sensor. Your field test 'rang true' to life. The differences in temperatures is significant. My CC will be 4 feet higher than the batteries. As you probably are aware, there is a voltage adjustment for every 1 degree F, the voltage is increased or decreased .017 volts. A 17 degree difference would require a change in voltage of .289. A lead acid battery could not be fully charged should there be .3 volts less. Thank you.

A remote temp sensor mounted on the battery, despite the extra cost, is superior to an ambient temperature sensor. especially if there is a big difference in mounting locations between controller and batteries.

I have my AGM under the body, and my controller in ventilated cabinet. I just took a temperature reading on battery body and on Controller's steel mounting box in which it resides, and there is a 17 degree difference, the controller being hotter.

I am not familiar with MorningStar products. But with other chinese controllers which make various claims, beware of what can be lost in translation to chinglish and outright deception. Some controllers might have overtemperature protection, like if they are overheated due to surpassing their rating with too much solar, but they might not alter charging voltages with temperature differences.

In temperature extremes these self adjusting controllers based on actual battery temperature, can have huge effects on how well the battery gets charged, and with AGM's, if the battery is hotter than the controller, then the temp compensation can keep the vents from blowing, or the AGM from going into thermal runaway.

http://www.cdtechno.com/pdf/ref/41_7944_0712.pdf

 

[RogueRV2]

SW,
The cost of shipping almost doubles the price of the RTS, so it would be about $39. I'll probably relocated the CC within a few inches of the batteries instead. Sometimes my penchant for penny pinching hurts!

Hi Stern Wake,
I believe you may have once again saved me the experience of learning the hard way. I put my order in just today, but will now order the remote temperature sensor. Your field test 'rang true' to life. The differences in temperatures is significant. My CC will be 4 feet higher than the batteries. As you probably are aware, there is a voltage adjustment for every 1 degree F, the voltage is increased or decreased .017 volts. A 17 degree difference would require a change in voltage of .289. A lead acid battery could not be fully charged should there be .3 volts less. Thank you.

 

[SternWake]

If the batteries are flooded, do not put the controller that close in the same compartment. The gassing fumes are corrosive as well as explosive, and there is a likely a spark producing relay in the charge controller that engages when the sunlight is strong enough and disengages when not, and there will be a very small spark. Perhaps fully contained, but either way, Solar controller is to be close to the batteries over short thick cable, but not in the same compartment.

PaY the extra for the remote temp sensor. Or at least put it in the future plans. and make accommodations for its addition at a later date.

 

[RogueRV2]

Relocating the CC within 1 foot electrically will also be an improvement over my original install, by eliminating voltage line loss of .12 volts. With the RTS and relocation, it will be a much better system. With the standard 30 amp Renology CC, during the average winter day up here in Montana, the batteries would have be deprived of about 1.12 volts!!!



L

SW,
The cost of shipping almost doubles the price of the RTS, so it would be about $39. I'll probably relocated the CC within a few inches of the batteries instead. Sometimes my penchant for penny pinching hurts!

 

[RogueRV2]

A valid concern. Fortunately it will be mounted near, but not with the batteries, and not in a seal compartment where gasses can accumulate. Also, the controller is sealed in epoxy that affords it extra protection.

 

[Spaceman Spiff]

Follow-up on battery testing:

Took a few days to find someone with a battery charger that will do equalizations. Removed batteries to bench (better to see you with, my hydrometer) and removed caps. Charged batteries for 20 minutes (per charger instructions), then hit the equilization button. Worked for ~2 hours, then dropped to float voltage. Checked voltage a couple of times with DVM at 15.2V (I don't have a clamp on ammeter).

Results for batteries after sitting ~24 hours unconnected (no load).

Hydrometer readings ±.001 (temperature corrected, 62° ambient)
Battery 1: 1.297, 1.292, 1.292; 6.44 volts
Battery 2: 1.292, 1.292, 1.287; 6.45 volts

Samples are repeatable (twice), so I am happy with the results.

Thank you everyone for your help. Cleaned and dried the hydrometer and found a nice place to store it between battery box and wall.

-- Spiff