A number of lead acid
batteries were tested using low rate discharge tests in an attempt to
identify their capacities and as a relative measure of improvement
during sulphation treatments.
Of the batteries tested,
four were suspected of having low electrolyte levels for some time and
as such were thought to be partially sulphated, that is, with
sulphation occurring at the top portion of the plates. They were
observed to have a reduction in terminal voltage and capacity. The
batteries were three 100AH Century N70T deep cycle batteries (labelled
1,3,4) and a 100AH Trojan 27TMX deep cycle battery (labelled 2). A new N70T (labelled 10) was also tested as a reference.
Following restoration of electrolyte levels, the batteries were tested with low rate discharges at 4A and 9A.
- Battery 3 was treated with MgSO4 according to the recommended method, replacing the electrolyte with a MgSO4 solution, charging the battery, then replacing the solution with fresh electrolyte.
The battery recovered some capacity, however it isn't clear if the
fresh electrolyte added at full concentration had any role the observed recovery.
- Battery 4 was treated with a CdSO4
additive and charged at high voltage (15.5V rather than the recommended
14.4V) over three weeks. The battery recovered almost to full capacity.
- Battery 1 was later treated with a CdSO4 additive and charged at 15.5V.
- Battery 2 was not treated, but recovered most of its capacity without any intervention.
These cases will be discussed in further detail below.
Tests were carried out on
batteries after restoration of electrolyte levels and before any
treatment was applied. This involved discharge at 4A followed by
recharge. Graphs are provided for a 7 hour period to allow direct
comparison. Early discharge tests were carried out over a three hour
period, while later tests were allowed to run until the battery voltage
fell to 11.15V. This point was used for a comparative capacity measure.
An attempt to measure
capacity by coulomb counting of discharge current plus equilibrium
terminal voltage measurements showed that the new and recovered
batteries had a capacity of around 50AH to 60AH, rather less than the
100AH specified. This is not a particularly reliable way of measuring
capacity. The new battery 10 was incidentally (due to equipment
failure) run down to a very low charge level during the last
discharge test. Coulomb counting over the entire time of its discharge
also gave a capacity of 60AH and is probably reasonably accurate.
The CdSO4 treatment was effective in recovering capacity to almost that of a new battery in the case of two of the batteries. The MgSO4
treatment initially did not appear to make a significant difference,
but after high voltage charging for four days the capacity also
recovered markedly to almost that of a new battery. It is not possible
to draw definitive conclusions without further testing.
These tests were not carried
out in a controlled scientific way and the conclusions need to be
considered carefully. All batteries experienced slightly different
conditions. Batteries 1 and 3 were both in an operational installation for
about 12 months while battery 2 was used in the same installation but
for a longer period. This installation subjected the batteries to
temperatures close to 50oC on occasions (although charging
was suspended over 45oC). Battery 4 was in a different installation. Battery 2 is
a more expensive battery with a different construction (using
mysterious "technologies" promoted by the manufacturer), which may possibly have contributed to its better survival.
The MgSO4 treatment was modified to use conditions similar to the CdSO4 treatment by charging at a higher voltage for a period of time following the chemical treatment. Although the MgSO4 electrolyte was removed and replaced with fresh MgSO4 electrolyte, some of the MgSO4 may
have remained behind. It is possible that the higher voltage treatment
alone would have been sufficient to restore capacity given that the
plates were most likely only lightly sulphated.
Battery 1 Century N70T 100AH capacity and terminal voltage low
This battery initially had no treatment applied apart from a restoration of electrolyte levels, and was used as a reference. The tests show slight but insignificant changes in voltage or capacity since the restoration of electrolyte levels. The test that was run just before the CdSO4
treatment was applied lasted for 5:50 hours before the terminal voltage
fell to 11.15V. Capacity measurements showed around 30AH ± 5AH, about
half that of the new battery 10.
A CdSO4 treatment
was applied and the battery was charged at high voltage (15.50V) for 21
days as suggested in various descriptions of this treatment. The test that was done immediately following this treatment lasted for 11:10 hours before the terminal voltage fell to 11.15V. The battery voltage and capacity increased dramatically as shown in the graph below. The capacity measurements showed 47AH, close to that of battery 10.
Battery 2 Trojan 27TMX 100AH
This battery had no
treatment applied apart from a restoration of electrolyte levels, but
appeared to recover its capacity. The latest test lasted
for 9:10 hours before the terminal voltage fell to 11.15V, very close to that of the new battery.
Capacity measurements were initially very variable, but later showed
values around 50AH ± 10AH, also close to that of the new battery 10.
Battery 3 Century N70T 100AH capacity and terminal voltage low
This battery was treated by
replacing the electrolyte with a magnesium sulphate solution,
recharging and replacing the sulphuric acid electrolyte at full
strength. The battery
gradually recovered some capacity but not as much as might have
been hoped. The test lasted for 6:45 hours before the terminal voltage fell to 11.15V, slightly more than the reference battery 1 without treatment. Capacity measurements were
very variable, but after treatment showed values around 45AH ± 10AH.
The above plots shows some
recovery of the battery voltage and capacity after electrolyte levels
were restored but before treatment. These are very similar to the early
discharge tests for battery 1 which is of the same type and experienced
identical conditions as battery 3.
After the MgSO4
treatment (yellow 31/08/2017*) these show some recovery over time compared to the first discharge test (light blue 11/08/2017). Initially
the voltage levels increased markedly, possibly as a result of replacement of fresh
(and hence more concentrated) sulphuric acid electrolyte. In subsequent tests the voltage level
dropped but the slope of the discharge curve also dropped allowing the
battery to last longer during discharge. Unfortunately early tests were
stopped after 3 hours so it isn't possible to determine the overall
lifetime of the battery at those stages.
Following these tests, the battery was placed on charge at elevated voltage as recommended for CdSO4 treatments but without further chemical treatment.
After four days it was removed due to overheating. The curves below
show the results of load tests soon after the treatment and again after
three weeks of normal use. These are compared with the original curve
of the untreated battery and that for the battery immediately after the
treatment. The terminal voltage is now significantly elevated and the
load test lasted for 8:52 hours at 4A before the terminal voltage fell
to 11.15V. This is now quite close to that of the new battery 10.
Battery 4 Century N70T 100AH capacity and terminal voltage low
This battery was treated by addition of cadmium sulphate and then some days later by charging at high voltage over 21 days. The battery recovered capacity quite substantially. The test lasted
for 9:00 hours before the terminal voltage fell to 11.15V, close to that of the new battery.
Capacity measurements initially showed values around 25AH ± 5AH. After
the final high voltage treatment, tests showed values of around 44AH ± 2AH.
These show the initial discharge curve (green 12/8/17) followed by treatment with CdSO4
(yellow 1/9/17*). There followed only very small improvement in capacity
until after the battery had been placed on overcharge at 15.5V for three weeks.
The final curve (brown 24/10/17**) shows a very significant improvement
Battery 10 Century N70T 100AH new
This battery was new and was
tested as a reference to determine how well the treated batteries had
recovered their capacity. The battery voltage dropped over the time of
the tests, possibly a settling period as suggested by the manufacturers as being
needed for the battery to gain its full capacity. In the last test the
battery lasted for 9:55 hours before the terminal voltage fell to 11.15V. Capacity was about 60AH as discussed above.