Hi to all,
This is my first post and first foray into Arduino.
I need to be able to remotely test the Specific Gravity of an array of Lead Acid Batteries used as the power source / storage from my Solar Panels and Wind Turbine.
Can anyone please advise me as to how to either make or where to purchase a hydrometer sensor from?
Thanks to all.
Kind regards,
jB 8)
Most important indicator is a voltage meter. As lead accus are up to 25Volt (or even maybe higher) you must use a voltage divider (see wikipedia) to be able to connect it to the analog in of an Arduino. An Arduino can handle 5V max so the voltage divider needs to be 1 in 5 at least.
Can anyone please advise me as to how to either make or where to purchase a hydrometer sensor from?
Have you checked instructables.com yet?
Battery voltage is not as useful a guide to state of charge than the specific gravity, since the concentration of sulphate ions is intimately related to the amount of current discharged. Battery voltage depends on state of charge certainly, but also on temperature, whether charging of discharging, contaminants in the electrolyte and polarisation and suplhation of the plates.
Normally you would keep the batteries sealed between taking measurements - so I guess you want a hydrometer that screws in as replacement for a cell cap? Erm, good luck.
Suggest you ask the same question at www.navitron.org.uk/forum where you'll find a wealth of knowledge on your application
Hi,
Thanks to all those that have pointed me further down the long road.
Seems I always choose the tougher projects in any new environment.
I would have thought by now someone would have developed a commercial hydrometer sensor.
Maybe if I manage it, I could get rich beyond my wildest dreams?
Kind regards,
jB 8)
PS The 8) is not coz I'm cool it's coz I'm partially sighted and the icon looks like me...
Every cell has to be separate, so you ideally need 6 sensors for each 12V LA...
Seems I always choose the tougher projects in any new environment.
Thats the right spirit 
All you need is one good quality hydrometer, which will be used to calibrate the ones you make.
It should be of the glass bulb type that's usually weighted with a bunch of BBs embedded in wax.
Then, get a pack of clear polyethylene drinking straws, run a clothes iron over the final 1/2" of all the straws you need (protect the ends with aluminum foil so iron does not stick - wait until straw is cool to peel off foil).
DO NOT PUT ANY FOIL INTO THE BATTERIES!!!
Experiment with different amounts of sand or snips of tin/lead solder snips in the straws ... the straws will float higher or lower in the acid depending on specific gravity (and of course, battery acid level!).
Presto(ne) , instant hydrometers AND fluid level indicators.
If you put all the straws in a row, one laser can look at all the straw tops ... use black construction paper and a hole punch to make a shutter for each straw.
You have just built one humongous optical AND gate, once you add a phototransistor to pick up the laser beam.
If you build this, I want a PICTURE!!!
Overnight the cogs whirred and churned out a totally electronic sensor solution to measuring specific gravity.
Sensor design is what I do for a living.
How many sensors do you need?
I can make them for about $1 apiece (100s) ... a single excitation circuit and some multiplexers would be needed to scan all the sensors at the rate of about 1 sensor per second.
Specific gravity shouldn't change very quickly ...
What are you doing about battery voltage and fluid LEVEL?
Hi,
I have 2 banks of (12 x 2V DC = 24V DC) 1200ah Lead Acid Batteries as produced by Isofoton etc. They are solid plate, electrolyte activated. They are about 10cm square by about 100 cm high.
They are directly fed by a 3.5 Kv Wind Turbine (24V via a DC regulator)
I have 10 Solar Panels producing 1Kv which is fed into a Victron Blue 5000Kv 24V 50Hz Inverter Charger.
I have an 11Kv Kubuta Generator which is used when domestic drain is above certain tolerance such as Dish Washer, Power Showers. Additionally it is used to boil the batteries once a month to equalize them, therefore each battery is fitted with a gas recycling cap rather than the standard screw cap.
I had therefore thought that for initial trials I would use a standard screw cap to allow access t / from the hydrometer. Once proof of concept was shown I would move on to using the recycle caps which a fairly expensive.
I had also initially thought that maybe 1 sensor in each bank would suffice, but if the economics was correct ideally each battery should report its condition.
Which would also include its fluid level and current temperature.
A friend of mine is a big installer of domestic off grid systems and if I approached him with a product I am sure he would be able to sell these by the bucket load, especially if there was also a front-end solution, which was my ultimate aim. I wanted to produce a web based solution that would inform me about the overall condition of the batteries both individually and collectively, which could be accessed by both the end user and the off-site installer, maintainer...
So anything you can develop would be wonderful, bearing in mind I am an Arduino virgin...
Kind regards,
jB
This is becoming very interesting!
I live in the United States (Boston Massachusetts), have done a bit of research on other uses for such a sensor and there seem to be MANY.
Over the next week, I'll fabricate a few prototype sensors, test them, choose the best design, use it in the lead/acid 12v battery I use for my main computer's UPS and generate some power failures.
I'll dedicate a sub-domain on my website to make the progress data (video, pix, schematic, spreadsheet log) available to you and all viewing this thread.
My goal will be to get 1 sensor and the excitation circuit running, delivering an analog voltage between 0.0 and 3.3 volts scaled to specific gravity (1.0 volts = dead or sulfated cell?), which can be fed to the Arduino.
The standard SG of distilled H2O is 1.0000 (?temperature?) ... if SG goes below that you've got a dry cell or the sensor failed ... and someone's got to look at it.
One byte (8 bits) of data will give us 256 levels available to encode SG, more than enough I would think, which will make the Arduino data easier manage. We might be able to encode multiple SG values within that byte depending on what SG resolution is needed (this isn't for a laboratory so we shouldn't need much).
In the meantime, maybe you can find/write the code necessary to read that voltage range using one of the Arduinos analog converters? I've seen something like it on this site I believe.
You could simulate the output of my sensor using a pot (10k linear taper is good) tied from Vcc of the Arduino to ground, with the wiper going to one of the Arduino analog converters.
Monitor the wiper with a digital voltmeter before you conect to an Arduino pin.
MAKE SURE the wiper voltage never gets above the Arduino power supply voltage if you are using a separate voltage source to energize the 10k pot (it'll blow out the anti-static protection diodes inside the Arduino). It wouldn't hurt to put a 100k fixed resistor between the pot wiper and the Arduino pin, limiting current to the protection diode inside the Arduino.
Brief me on your electronics experience level so I can skip unnecessary details, and let me know what Arduino part you will be using! 
Once that's working, we can get the system reading all the cells on one battery, and then multiplex more sensors to other batteries.
Fluid level and temperature are trivial ... my main concern is making sure bubbles don't foul the the SG sensors ... which would cause the sensor to read SG too low, which is fail-safe (would report inadequate SG when it was actually ok, a false alarm).
I need a number for maximum SG, and I am assuming H2SO4 for the electrolyte as the only species.
Just remember, while designing those sensors, that you are working around highly corrosive sulfuric acid and that any moving parts that are potentially exposed to fumes are going to turn into corroded crud.
JSA Photonics has a solution, but it suffers from fouling caused by crud floating in the electrolyte. No one else has a solution, that I know of. If you come up with something, I'll buy a few hundred dollars worth, provided you've got some test results that show they work and don't turn to crud within weeks of installation.
FWIW, I have clients with around 1MW DC of installed solar production, so I'm very interested.
As I said, this is becoming more interesting as time goes by ...
Thanks for the info about the crud floating around ... already considered the corrosion problem and have chosen materials accordingly ... does the crud come from sulfation, plates and separators disintegrating over time or do people pour crud in while they're topping off the cells?
Prototype is almost finished ... it's a small cylinder approx. 1 cm x 4 cm (1/4" x 1", could call it a capsule), has no moving parts.
A vent at each end of the capsule (allowing electrolyte diffusion) is protected inside by filter material.
The capsule is designed to rest submerged in electrolyte, doesn't move around, just sits there measuring filtered electrolyte.
Teflon spaghetti tubing will protect signal conduit coming from the sensor, up through the electrolyte, leaving the battery and connecting to the excitation module.
Hi,
Totally agree this is great.
I have as yet not purchased a board or considered coding as I was investigating the possibilities before investing time and money.
I am disabled and partially sighted so have to regulate time on the PC for my eyes sake and also disability pensions sake on purchasing frivalous boys toys. 
I believe I mentioned earlier that normally about once a month I "boil" the batteries. This is, that I take the batteries up to 32-34V DC to "burn" off all of the sulphates and realign the system. This is called equalization. Normally the process flows in this fashion.
Stages 1 & obviously 4 produce the most crud and as I use gas recycle caps I think it would be most prudent to remove the sensors during these phases, where possible. Gas recycling caps, reduces the amount of acid gas pushed out of the batteries which is quite noxious and flamable. I would have to experiment with the durability of sensors attached to a gas cap.
It would be great if the capsule could also contain a temperature, amperage and min / max depth guage.
Not sure how to attach photos of a battery and gas gap but will try during the day.
Kind regards to all,
jB 8)
Before finding this post I was pretty satisfied with how much I understood about how lead acid batteries worked.
Could you be more specific about any sight / manual dexterity limitations you have? It will be easier to design around them if I know what they are. To me, one of the most interesting applications for sensor technology is the augmentation of human perception, especially for people who have lost or never had one or more abilities the rest of us take for granted.
Also, I've been accused of having a dark sense of humor, so if any of it slips out, please don't be offended ... I mean no harm.
For example, the first thing that came to my mind when you mentioned being handicapped was that this post was actually about maintaining batteries for a limousine sized wheelchair ... which would only motivate me more!
In any case, this project has quite a few possible applications, especially at the dark end of the spectrum.
Has everyone heard that the Columbians have built at least one submarine to ship contraband autonomously! 8)
As they say (whoever they are) "If you can't stand the heat stay out of the kitchen".
Being ex military I too have a very dark sense of humour and the limo sounds like a great idea, except there would be room for the wife and kids and grand kids so can we leave that project until next month...
I have about 30% vision in 1 eye, nothing in the other. I tire very easily and often cannot get out of bed which was a primary consideration for this system for me.
My body is attacking itself so sometimes due to the pain my fingers are useless other times when the morphine kicks in I think I could run a marathon. It is all very hit and miss.
I want to do something like this project for my sanity and confidence, I admit to being an arduino virgin and am aware of electonics but have ordered a couple of books to bring me back up to speed. I forget things quickly but can remember trivia instantly.
So to start programming again I will need a manual by my side. Ten minutes later it will all come flooding back and off I go. The next day I have to think hard before I start again.
There you have me in a nutshell.
Dark, thick and slow. (Don't you dare call me Treacle, I can still remember some dirty tricks from the Army)... :0
Kind regards,
jB 8)
Was there any further followup to this thread? I'd be very interested to know if the sensors were ever built and whether or not they were successful.
Hi,
Did you ever get some hydrometer sensors, or did anyone develop sensors for this purpose? I also need to monitor a battery bank, remotely, via an arduino and would appreciate if someone can point me into the right direction to purchase some sensors.