Simple Emergency Power Supply - How Do I Build? - Page 3

 

Hydrometer to measure the specific gravity of the acid solution. This tells
you the charge on the batteries, not the health of the battery or it's
capacity but just the relative charge.


systems

panels are

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Christian M. Mericle wrote:

Christian, while John is almost correct, it is more correct that a
hydrometer is useful to determine the health of a battery.

Batteries are not, as some would have you believe, boxes full of
electricity. A battery is, in reality, a box of chemicals that that have
the potential, though chemical reaction, to cause electrons to flow
through a circuit.

When discharging lead acid batteries produce electricity when the
negative (lead) plate reacts with sulphuric acid and forms lead
sulphate. At the same time the positive plate (lead dioxide) is also
converted to lead sulphate.

When being charged, the reverse reactions occur.

A fully charged cell should have a specific gravity of around 1.25 - 1.28

If after charging all day you find a cell that has a SG of 1.11 while
all the other cell have a SG of 1.23 then it is a good bet that you have
a dud cell.

This is somewhat more accurate than measuring the voltage in that the
electrolyte is separate from all other cells while the voltage is
measured as part of a circuit which may cause a false reading as the
other cells are trying to charge the dead cell.

 

wrote:
<snip>

Okay, I thought it might be something like that. I gather that the
hydrometer is not permanently attached but is used periodically
(regularly?) to check the charge and health of the battery. Is that
correct?

-- Christian

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Christian M. Mericle wrote:

http://donate.wvus.org/OA_HTML/xxwvibeCCtpItmDspRte.jsp?section 025&item72182

Pretty much. To be honest I only check the SG of my batteries a few
times a year. OTOH I check the voltage of of the bank 3 - 4 times a day
as well as the charge going in and every morning I check the previous
days consumption. It's just a push of a button so it is easy. Small
problems don't get a chance to become big problems.

 



      I am worse than that.  I check my AGM batteries with an automotive load
checker every year just before storm season.  I look at the display lights on my
charge controller when I happen to be out there.  Because of the design of my
controller, as long as my yard lights keep coming on every night, I know that my
battery must have an adequate charge.

     It has worked for me so far.

Vaughn