How to accurately determine H2So4 Acid Levels in an Auto Battery

You are trying to measure the distance from top of cover to top of acid too accurately. There are too many other variables to consider if you need a volume that accurate. The end cells of the case bow out slightly, the top lead is not uniform cell to cell, the plates are not that consistant. When I used to do it we used glass rods about 3/16" thick with the nice rounded end. You can see through the glass when it makes contact with the acid surface (it will darken). Then hold your thumb nail there and measure using a 6" scale to your best guess in 32nds of an inch.

If you want info on water loss in the battery then use weight of the entire battery and average over the 6 cells. There are significant differences in performance cell to cell in a battery due to manufacturing tolerances and the stronger cells will lose water faster. Keep in mind the whole time you are basically losing water. There is very, very little sulfuric acid that is lost over time, it is almost totally water that is cooked off or evaporates.

Hi Metman,

I think that measuring the density of the acid solution inisde the battery will help you.

Try this link: http://www.alibaba.com/product-gs/50553208/battery_densitometer.html

Regards

Ernesto

As PaulB says it looks as if you are trying to be too accurate,

would capacitive sensing through the cell wall give you a sufficiently accurate figure.

many mfrs make capacitive proximity sensors. select for the sensitivity needed or, i think i have sen some that can be adjusted

good luck

Chas

Hello PaulB & Chas .. Thank you for your comprehensive answers

Perhaps I should have been more specific in respect of tolerance. The Acid Level is controlled to 150mm from Cell Base ± 1,0mm so that gives us 2mm field, bringing us to the type of measuring equipment we may use as I do believe the resolution would have to be within 10% of the given product tolerance field, i.e. 0,200mm. The objective is to acertain the Levels for R&R and CmK studies so we are compelled to utilise a fairly accurate method of verification. You are of course correct in stating that we will encounter some "Swelling" on the end Cells after formation though this condition is also controlled as we apply a permissable "Outward Bowing" tolerance. Capacitive Sensing through the Cell Wall sounds like a viable proposition, but concerned again owing to the Acid possibly "climbing" up the Cell wall to some degree. Envisioned taking a direct measurement from above the Battery into the Vent Plug onto the Acid surface via some Laser bounce-back technique. Your glass rod intrigues so I'm off to the Lab to pick one up and play around a little Let you know the outcome, Enjoy Your Days,

Best Regards, Metman.