Author Topic: Wet lead acid batteries - electrolyte level - how to observe  (Read 24084 times)

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David HK

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Wet lead acid batteries - electrolyte level - how to observe
« on: April 10, 2010, 07:34:00 PM »
Many readers will be familiar with automotive wet lead acid batteries which normally have two lines showing the Mimimum and Maximum electrolyte levels.

The problem I find is trying to observe the electrolyte level through the sides of the battery.

Is there any mechanical way of checking it? I have tried a 12 volt bulb shining light from one side to the other and it does not work.

Some sort of two pin stainless steel prong with a simple LED circuit attached to it springs to mind as an idea.

David in HK


DanG

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #1 on: April 11, 2010, 09:16:49 AM »
Best I could think of is a liquid crystal film strip that could/would highlight temperature change -

TomW

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #2 on: April 11, 2010, 09:39:33 AM »
Best I could think of is a liquid crystal film strip that could/would highlight temperature change -

DanG;

I cannot sort out how temperature will help monitor electrolyte level? I doubt the change from liquid to air inside will be a sharp line through the case?

I just figure if I can see the plates they definitely need water. I use an LED flashlight to look into the holes but then my battery is in a metal can and the cells are black plastic anyway.

My battery vendor offered some sensor option that monitored this and also had a system that could keep them topped off. The keeping them topped off bit would be trivial. a tube from a sealed tank of distilled water that had its lower end at the min level you wanted it kept.

No valves or gizmos just gravity and vacum to do the job.

Might be some gotchas but stock waterers have been done this way forever.

Just a thought.

Tom
« Last Edit: April 11, 2010, 09:43:44 AM by TomW »

ghurd

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #3 on: April 11, 2010, 09:46:12 AM »

I cannot sort out how temperature will help monitor electrolyte level?


I figure it may be like those propane tank things.
They monitor the level based on the temp of the metal and the difference between the part touching or not touching propane on the other side, which metal disperses heat pretty well, so it could work better on plastic?

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RP

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #4 on: April 11, 2010, 03:48:34 PM »
My battery vendor offered some sensor option that monitored this and also had a system that could keep them topped off. The keeping them topped off bit would be trivial. a tube from a sealed tank of distilled water that had its lower end at the min level you wanted it kept.

No valves or gizmos just gravity and vacum to do the job.

Might be some gotchas but stock waterers have been done this way forever.

I think the big gotcha would be diffusion of sulfuric acid up into the tube and of course water into the electrolyte.  You might be able to stop this with a restriction of some kind but then the "auto fill" bubble action may not work when the level fall below the tube.  I'd be worried that over time you'd dilute the electrolyte down

Just my two cents.  Maybe there is a way around it...

DanG

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #5 on: April 11, 2010, 05:26:20 PM »
Of course there is always a dip tube, glass pipe is best - open cell cap, lightly drop tube in, cover open end with thumb, withdraw tube and check level of electrolyte held in tube, remove thumb to dump liquid back in cell and move to next cell...  scribe min & max onto pipe walls and keep it clean it should last forever...

On the liquid crystal film - Y'all are spot on about displaying the differences between plastic case with and without electrolyte behind it - okay, it may require wiping with a cool wet rag to really 'see' the thermal mass of the electrolyte but that is the only non-contact quick check method I can think of.


wpowokal

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #6 on: April 12, 2010, 04:14:05 AM »
This is handy.

allan
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David HK

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #7 on: April 12, 2010, 08:49:48 PM »
I did some Google research and came up with these two interesting sites that offer commecial electrolyte level checking devices.

http://www.rvtechstop.com/articles/batmon.pdf

http://www.vandapower.be/PDF/BEST%20Sensors%20v.1106.pdf

Can anyone offer any comments on the first item as the circuit is very easy to construct.

Is it dangerous?

Thanks for comments so far.

David in Hong Kong

Ungrounded Lightning Rod

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #8 on: April 12, 2010, 09:02:50 PM »
I think the big gotcha would be diffusion of sulfuric acid up into the tube and of course water into the electrolyte.  You might be able to stop this with a restriction of some kind but then the "auto fill" bubble action may not work when the level fall below the tube.  I'd be worried that over time you'd dilute the electrolyte down

Diffusion in still liquid in a pipe narrow enough to avoid thermal convection cells passing each other is on the order of inches per decade or inches per century.  (Chemistry building at the U of Michigan used to have a demo in a display case in a hallway using yard-long sealed tubes of distilled water with a potassium iodide crystal on the bottom coloring the water.  They'd add a new tube ever decade or so and the purple hadn't gotten very far in the ancient one.)  Given the one-way nature of the refill flow and the low conductivity of distilled water I'd bet that's how the auto-waterers keep from shorting the battery out.

I imagine you'd want to have reasonably long paths to the place where the individual cells' pipes join, though, so the electric field from the voltage differences between cells doesn't pump ions through the liquid.

Ungrounded Lightning Rod

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #9 on: April 12, 2010, 09:16:06 PM »
I did some Google research and came up with these two interesting sites that offer commecial electrolyte level checking devices.

http://www.rvtechstop.com/articles/batmon.pdf

http://www.vandapower.be/PDF/BEST%20Sensors%20v.1106.pdf

Can anyone offer any comments on the first item as the circuit is very easy to construct.

Is it dangerous?

The first circuit looks fine to me.  But you really want lead or a mostly-lead alloy for the probe.  Since the article it may be hard to find - at least here in the US and places that share the supply chain.  Lead solder has been banned for plumbing and is being phased out in electronics.

Dangerous:  Main risk I can think of is if the probe breaks circuit in a gas bubble during equalization.  You might explode the battery.  Shorting it out could make it melt through and spark, ditto.  Soldering the resistor on just outside the cap and covering it (and the exposed probe wire) with heat-shrink tubing should mitigate both risks, by limiting the probe current to a couple milliamps.

I imagine a thick lead coating on a regular copper wire would work for a probe, too.  Like by thick-tinning the whole length of one wire of a fresh resistor, solvent-cleaning off any rosin flux, and then covering the place it enters the resistor body with "liquid electrical tape" potting compound, to avoid galvanic corrosion if a little of the copper ends up exposed there.

ghurd

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #10 on: April 13, 2010, 09:39:27 AM »

The first circuit looks fine to me... ...limiting the probe current to a couple milliamps.


Seems like the same thing could be done with few microamps and 2 logic level fets (2N7000).

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ghurd

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #11 on: April 13, 2010, 10:10:02 AM »
I could do my taxes, or make a sketch.
I made a sketch.   ::)

Entire circuit in standard operation uses only 0.15ma.
With the LED On it uses about 3ma.

No clue if this is a good idea,
G-

« Last Edit: April 13, 2010, 10:32:06 AM by ghurd »
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DamonHD

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #12 on: April 13, 2010, 10:15:53 AM »
Doing your taxes needn't be taxing...

Rgds

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TomW

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #13 on: April 13, 2010, 10:34:51 AM »
I could do my taxes, or make a sketch.
I made a sketch.   ::)

Entire circuit in standard operation uses only 0.15ma.
With the LED On it uses about 3ma.

No clue if this is a good idea,
G-



G;

WRT the sketch label..

Picking the nits here but aren't most cells 2 volt [or thereabouts?]

Tom

ghurd

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #14 on: April 13, 2010, 10:48:26 AM »
WRT the sketch label..

Picking the nits here but aren't most cells 2 volt [or thereabouts?]

Tom

Yup.  I debated about calling it the 3rd or 4th cell.  Or a cell showing 6 or 8V relative to Negative.
Maybe "Probe in THE 6V or 8V Cell"?

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David HK

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #15 on: April 17, 2010, 11:52:32 PM »
Made up a circuit based on Ghurd's drawing and achieved the following result:-

Negative post cell - LED will not extinguish
Second cell LED extinguishes
Third cell LED extinguishes
Fourth cell LED extinguishes
Fifth cell LED extinguishes
Positive post cell - LED extinguishes

12 Volt motorcycle and car batteries produce the same result.

Any ideas for a solution?

ghurd

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #16 on: April 18, 2010, 10:29:09 AM »
Hi David,

I assumed you wanted to use 1 circuit per battery, monitoring the 3rd (6V) or 4th (8V) cell, as they did in one of the pdfs above.

The 1st cell has only 2V.  It is not enough voltage to reach the threshold of the 1st mosfet.

I can modify the circuit for use in the 1st cell.  It will require a 2N2222, 2N7000, and different resistor values.
I may be able to post it later today.
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ghurd

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #17 on: April 18, 2010, 11:50:08 AM »
I think this will work.

If it does or does not, let me know either way!
G-


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David HK

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #18 on: April 19, 2010, 03:42:24 AM »
Ghurd - your new circuit works a treat!  ;D

The LED is dimmer than before - is it okay to change the 3.3 K resistor to 1 K without upsetting the circuit?

This week i will arrange with a friend to machine up some nylon discs so that I can push a stainless steel probe into each one at the  maximum electrolyte level from the top edge of the screw plug common to all cells in which ever battery I wish to measure. I only have two types of wet cell batteries at the moment hence two probes adjusted for each one.

I will put up some photographs later in the week.

David in HK

ghurd

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #19 on: April 19, 2010, 08:37:21 AM »
Changing the 3.3K (3K) to a lower value would not fix the problem with the circuit.
Or it could be that particular LED is dimmer than the others?

First, change the 1M to 10M and test, if you have not changed it already.

Next change 270K to 240K and test.
If 240K does not work correctly, try 220K.  (No lower than 220K)

Before changing anything, if you have a chance,
I would like to know a voltage from the circuit for the 1st cell (2V).
With the probe NOT in the acid, the LED is On but not bright, what is the voltage on the 2N7000 Gate?

It could be that particular 2N2222 leaks more than most, or that particular 2N7000 has a higher threshold than most,
or something I have not thought of.   :-[

After measuring the Gate voltage, go ahead and make the changes.

Also, changing the LED resistor to 1.5K or 1K would be fine.
Indicator type LEDs tend to not appear much brighter with 20ma than 8ma.
3.3K will put about 3.5ma through the LED.

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David HK

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #20 on: April 21, 2010, 06:28:03 PM »
Ghurd,

Thanks for the advice.

I regret that I cannot give you the reading over a 2 volt cell because my batteries are automotive and the linking straps are within the battery case.

I have built your second circuit and used a 1 M resistor and not the 10M. It actually works well, so the idea of a brighter LED is desirable but not essential. The probes are half made and I may be able to put up a photograph over the weekend.

David in HK

David HK

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #21 on: April 28, 2010, 08:39:16 PM »
I now have the Mark I version of Ghurd's circuit built and the probe consists of a stainless steel rod inserted through a piece of nylon. The probe is a press fit and can be adjusted to suit the depth from the cell plug hole to the maximum level shown for the electrolyte.

I have a Mark II version under construction which will consist of the same adjustable probe slightly offset on the nylon disc. Adjacent to it will be a stainless pipe which will not touch the electrolyte level and this is connected via pipe to an electrolyte top up bottle. Therefore when testing a cell, if the LED does not extinguish, it means the level is below the bench mark and a simple squeeze will send in topping up electrolyte until the LED extinguishes.

Can anyone see problem with this>


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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #22 on: April 29, 2010, 11:30:00 PM »
I now have the Mark I version of Ghurd's circuit built and the probe consists of a stainless steel rod inserted through a piece of nylon. ...
Can anyone see problem with this>



Yes.

If the probe is just about any metal but lead you'll contaminate your battery.  (That's why a resistor lead heavily tinned with tin/lead solder was recommended.)

David HK

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #23 on: April 30, 2010, 05:54:37 PM »
ULR,

Thanks for making the observation.

In the ordinary course of events you are right about contamination, however, I am minded to think that a momentary dip of one second or thereabouts once or perhaps twice a month would not cause any significant effect sufficient to ruin a battery.

If the stainless steel was left in situ - partly in the cell electrolyte - all day and every day, then yes there would undoubtedly be a reaction.

Comments please from anybody.

Dave in HK

Ungrounded Lightning Rod

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #24 on: May 03, 2010, 03:10:41 PM »
In the ordinary course of events you are right about contamination, however, I am minded to think that a momentary dip of one second or thereabouts once or perhaps twice a month would not cause any significant effect sufficient to ruin a battery.

If the stainless steel was left in situ - partly in the cell electrolyte - all day and every day, then yes there would undoubtedly be a reaction.

Agree there.  But a) I thought we were talking about a modified cap to make a permanent monitor and b) why not use a lead wire even if it's only as a probe?

David HK

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #25 on: May 03, 2010, 06:22:03 PM »
ULR,

Thanks for your note. The test plug is definitely not a substitute for the manufacturers screw in plug. I shall certainly have a go at your lead probe if it can be machined and fit the test disc satisfactorily.

David

ghurd

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #26 on: May 03, 2010, 07:07:07 PM »
Looks good to me David.

Honestly, I thought you were going to build one for every cell of every battery!
And I thought you must drink too much coffee, or be very bored.   :D
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frackers

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #27 on: May 03, 2010, 10:20:42 PM »
Yes.

If the probe is just about any metal but lead you'll contaminate your battery.  (That's why a resistor lead heavily tinned with tin/lead solder was recommended.)

Might I suggest the carbon rod out of a D size dry cell? Non-metalic, conductive, pretty inert chemically (at least at room temperature!!). Or even the graphite core out of a wood workers pencil (the big chunky ones). You get a wooden carrier for free then that can be whittled, glued or whatever to fit to your nylon 'stop'.
Robin Down Under (Or Are You Up Over)

DanG

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #28 on: May 04, 2010, 08:17:49 AM »
95% Platinum / 5% Iridium wire is going for $20 an inch on ebay...

jlt

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #29 on: May 04, 2010, 09:22:20 AM »
I have a moisture tester that i got from harbor freight . don't know if it works in battery acid 

Tinbendr

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #30 on: May 04, 2010, 06:56:08 PM »
David,
You could just use something like this.
Nothing is foolproof because fools are so ingenious!

David HK

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #31 on: May 04, 2010, 07:21:49 PM »
My thanks to Frackers and Tinmbendr for your interesting suggestions.

For the time being simplicity rules and I shall try to pursue the lead probe in favour of stainless steel.


David in HK

Ungrounded Lightning Rod

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Re: Wet lead acid batteries - electrolyte level - how to observe
« Reply #32 on: May 04, 2010, 07:59:43 PM »
95% Platinum / 5% Iridium wire is going for $20 an inch on ebay...

And when you equalize your battery and start putting out Brown's Gas, a platinum/iridium wire will probably catalyze the ignition of the hydrogen/oxygen mixture, causing an explosion.

Platinum is GREAT at adsorbing hydrogen atoms and then catalyzing their exothermic reactions with other materials.  And I understand there used to be a cigarette lighter consisting solely of a screen made with platinum wire running one way and palladium the other.  Touch to the end of the cigarette and inhale and you catalyzed enough combustion to produce enough heat to light the coffin nail.