Frequently Asked Questions
Interacter
LS, PS and ICS
If you have a technical question relating
to Battery Chargers for Lead acid or
Safety and liability issues - please read this first.
Return to Interacter Home Page
Absolutely not! We recommend that, where
possible, you leave the charger plugged in and switched on, with the batteries
connected, until you next need the battery for use. There are several reasons
for this. At the end of the charge cycle, when the green ready light is on, the
charger is trickle charging the battery in constant voltage float/standby mode,
nominally at 2.3 Volts per cell. This is the same charge method used for
batteries in standby applications such as alarm panels or emergency lighting,
where the battery is intended to be charged 24 hours a day, every day. At this
voltage, the battery will not be gassing so loss of electrolyte is minimal. The
charge current drops exponentially to a very low level, sufficient to maintain
the battery in a fully charged state and to compensate for any self discharge.
Over time this low rate of charge will tend to equalise charge imbalance
between the cells, which can extend the battery life. By leaving the charger
switched on, you will prevent any risk of damage to the battery from sulphation
(which can be caused by allowing the battery to stand in the discharged state).
The energy consumed in standby mode is minimal, typically about
Well, the lower cost charger may be fine
for some applications. But, if you are using a battery in a demanding
application where performance and battery lifetime are important, you might
find that saving money on the battery charger is not cost effective in the long
term. If the battery is overcharged or undercharged then your product will not
perform as well as it could, and the battery will not give the lifetime, in
terms of cycles of discharge and standby time, and so will need to be replaced
more frequently than you, or your customers, were expecting. Batteries can fail
within the warranty period, and the battery manufacturer may decline warranty
claims for replacement batteries where incorrect charging has contributed to
the problem. This is why it's advisable to test your system carefully using the
exact battery, charger and load in a simulation of actual use. Also, the system
designer should ensure that the cyclic and float voltage settings of the
charger are within the ranges specified by the battery manufacturer. Our
chargers are designed to offer the best battery performance and lifetime with
features such as three stage charging, precise voltage regulation, proportional
timing, overrun timer, low start voltage, and low parasitic loading. Some of
our regular customers started using our product only after they had experienced
a problem. Don't find this out the hard way - there is much more to the
specification of a battery charger than the Voltage, Current rating, and price.
Back to top.
A battery charger is a type of DC Power
supply (PSU) which is specifically designed for charging batteries. While any
DC Power supply can be used to charge batteries, there are serious potential
pitfalls to using a generic power supply as a battery charger. For example, a
DC Power supply may include regulation circuits, which may be damaged if a
battery is connected to the output, before the AC Power supply is switched on.
The regulation circuit in a power supply is not designed to reduce parasitic
load and so may draw power from the battery if left connected when AC power is
switched off. These two issues can be addressed by adding a blocking diode, but
then the volt drop of the diode (which is temperature dependant) needs to be
allowed for. Generic power supplies do not provide multiple stage charging with
different voltage limits, or temperature compensation of the charge voltage, or
reverse battery connection protection. In general, it?s better to use a battery
charger that was designed for the job, rather than a general purpose DC power
supply, for battery charging. If using our chargers, there is no need to fit
any external blocking diode or contactor to prevent current flow from the
battery back into the charger, when the AC supply is off, as may be required
with some generic power supplies.
No, we don't offer that type of charge
termination. We use an alternative technique called proportional timing, which
does the same thing, but does it better. We have done extensive testing on
different types and sizes of batteries to reach this conclusion. Many
competitors multi stage chargers use a current comparator to determine when to
switch from bulk charge (constant voltage at the cyclic voltage limit)to
float/standby mode (constant voltage at the float voltage limit). This method,
although widely used, has some drawbacks. The problem is that the current at
end of charge varies with a number of parameters external to the charger, such
as the temperature, the age of the battery, and the size of the battery. In a
constant voltage charge system, the charge current falls off exponentially as
the battery EMF increases and the charger voltage is held constant. At the end
of the charge, where the determination of switch to float has to be made, the
slope of the current against time graph is quite flat, so a small change in the
current setting can make a wide difference to the charge time. When a battery approaches
the end of it?s life it tends to draw a higher self discharge current due to
sludge accumulation increasing electrical leakage between the plates, so if a
current comparator is used the charger may never switch down to the
float/standby voltage, resulting in overcharge, gas emission, and premature
battery replacement. Our chargers use proportional timing where the switch to
float is timed optimally, eliminating the need for sensing low currents, and
eliminating adjustments to the charge termination controller to match the
Amp-hour size of the specific battery.
Probably not. Our chargers feature short
circuit and reverse polarity shutdown, so they don't produce any output voltage
unless they are actually connected to a battery. The charger waits to
"sense" the battery voltage on the output before it starts producing
voltage, so you cannot test for DC output with a volt meter or test lamp, when
there is no battery connected to the charger output. Try switching the AC
supply to the charger off and on, the Led indicators should show the power on
test sequence (Green-Yellow-Red, each for about a half second) each time the AC
power is applied. If there is no Led test indication, check that AC input power
is getting to the charger, and the AC Power input fuse is intact. If the Led
power-on indication is OK, try connecting the charger to a known good battery
(of the correct voltage, but almost any size will do for testing), the yellow
charge indicator should come on, and the battery voltage should rise to around
2.4 Volts/Cell. If this happens, the charger is producing output. If the yellow
charge Led does not come on, when the battery and AC power are connected, check
carefully that your connections from the charger to the battery are sound and
that the battery is wired the correct way around (Red lead from charger to the battery
Positive). If the battery is very excessively discharged (to less than 1 or 2
Volts DC in total) then the charger may not start because it can't detect that
the battery is there. If this happens, try removing the DC load to allow the
battery voltage to recover, or connect another battery in parallel momentarily
to provide starting bias. Note that batteries discharged to zero voltage are
liable to be damaged by sulphation if allowed to remain in a discharged state
for more than a few hours.
SCR controlled chargers have un-smoothed
output, so the DC output to the battery is in the form of a pulse of current
each half cycle of the AC supply. During the time when the AC input is crossing
zero, in between pulses of output, there is no current flowing in the cables
from the charger to the battery. We take advantage of that, by using a sample-and-hold
circuit to measure the battery voltage at mains zero crossing, so that the
charger can monitor the battery voltage without errors that would otherwise be
caused by volt drop on the DC cables. When in Constant Voltage mode, the
charger will maintain a constant voltage at the battery terminals, by
increasing the voltage at the charger end of the cable if needed to compensate
for volt drop in the cable. In some applications, especially when using long DC
cables, this feature can improve performance and eliminate the requirement to
run separate voltage sensing leads. This feature does not apply to switch mode
or other smoothed output chargers.
The override (sometimes called overrun)
timer is a software timer, which starts at each beginning of each charge, and
runs until the green "Ready" light comes on. There is a fixed maximum
time allowed for completion of each charge cycle, the default setting is 18
hours, but this setting can be modified if required by changing the software.
If the override timer times out before the "Ready" LED comes on, the
unit enters "fault mode" and shuts down, producing no further output.
The fault mode is indicated by a continuous rapid flashing of the Green
"Ready" LED. The fault mode can be cleared by either switching the AC
supply off and on, or by disconnecting from the battery. Note that, providing
the charge cycle completes normally, the charger will normally remain in
float/standby mode with the green Led on, and 2.3V/Cell constant voltage
output, indefinitely because the override timer is stopped when the green
"Ready" Led comes on. The override timer is intended to prevent continuous
charging (and possibly overcharging) under fault conditions, such as a shorted
cell in the battery, or a charger fault causing low output current, or a
voltage sensing failure. For very unusual applications, if a charger is used on
a disproportionately large battery (such as sometimes used in a float/standby
application) where the charger may normally take over 18 hours to reach the end
of the charge cycle, we can supply a modified control chip with the override
timer disabled (-NT option). Normally, even in float/standby applications, the
charger current rating should be selected so that it is large enough to fully
recharge the battery in less than 18 hours, so the override timer will never
terminate the charge under normal conditions.
Parasitic loading means the DC current
that flows into the charger from the battery when there is no AC power supply
to the charger. In some competitors units the control circuits in the charger
are powered from the DC output circuit, so that the charger may
"leak" several tens of milliamps (or sometimes more) back out of the
battery, if it?s left connected when there is no AC power, or when it's
switched off. This can cause a problem in applications where the charger is
normally, or may be, left wired to the battery, when the AC input power is
switched off or the supply fails. A load of just 50mA will discharge the
battery by 1.2 Ah every 20 Hours, and by 8.4 Ah in a week. If , over time, the
battery becomes over-discharged, that can lead to sulphation, or excessively
low voltage, so that when the AC power is restored, the battery will not
recharge even though power is available. Ideally, the charger should be
specified so that the parasitic loading is less than, or comparable to, the
battery self discharge rate. Our chargers typically have a parasitic load spec
of less than 300 micro Amps, or 0.3 mA, which is low enough to be insignificant
in normal applications. No series isolation diode between charger and battery
is needed when using chargers with a low parasitic load current.
This could be due to a number of things,
because the battery, the load, and the charger have to work together as a
system, so a problem in any one of them may result in sub-optimal performance.
First, review answer to ?How long will my battery support my load, how can I
calculate the expected runtime? below and check the expected runtime of the
load current against the size of the battery. Measure the actual load current
and verify that it is as expected. Check the Cyclic Voltage Limit and
Float/Standby Voltage Limit settings of the charger are correct per the
recommendations of the manufacturer of your battery. For details on how to
check these voltage settings, see answer "How does one check and adjust
the Voltage settings of my battery charger?" below. If the voltage
settings are OK, try leaving the battery on charge for an extended period (for
example, over the weekend) to make sure it's as fully charged as possible. Also
see answer to "How does one check and adjust the Current Limit setting of
my battery charger?" to confirm that the current output of the charger is
up to specification. In the cables from the charger to the battery, check that
there are no excessively long cables, thin wiring, or badly connected terminals
causing power loss in the cable run, verify the charge current flowing using an
Amp meter connected in series with the battery terminal under the actual
conditions of typical charging. If the charger voltage or current values are
not correct, either adjust them or return the charger for repair. Consider
having the battery capacity tested using a constant current test load, if you
have access to one, typically a good battery will run a 1xC rate discharge for
30 minutes to 1.5V/Cell, for example, a 32Amp-hour battery, discharged at 32
Amps, should run for 30 minutes before the battery terminal voltage drops to
below 9 Volts. The runtime of the battery drops over time, a good quality
equipment battery will typically provide 200 cycles of discharge, to 100% depth
of discharge, before needing replacement. These figures are typical, check the
published spec from the battery manufacturer for the exact type of battery you
are using.
This can be due to a number of things. If
the battery has a faulty cell, then it's on charge voltage will not reach the
charger set point to switch to Constant Voltage Mode, which results in
overcharging of the remaining cells, until the overrun timer terminates charge
after 18 hours. If there's a fault in the charger which causes the voltage
setting to drift upwards, or if the charger is not set for the correct battery type,
that can cause overcharging. In any case, the appropriate test, is to measure
the battery voltage when in the constant voltage charge stage, and confirm that
the voltage is correct per the specification of the battery. To do this, switch
the charger off and on to reset it, and then wait until the "charge"
light starts to flash (or, on some units, until the "80%" led comes
on. The charger is now in the constant voltage mode. Measure the battery
voltage using an accurate digital volt meter, measuring at the battery
terminals. If the voltage is too high (for example, more than about 14.7V on a
12V, absorbed electrolyte sealed battery, then the charger is faulty or needs
adjustment. In some very unusual applications, if the AC power supply is
unreliable (frequent supply interruptions) that may result in overcharging,
because the proportional timer always holds the battery at the cyclic charge
voltage limit for a minimum of one hour before switching back to float/standby.
If the battery is supporting a load while charging, and the nature of the load
is regular, high current demand pulses (greater than the charger current
rating),that may reset the proportional timer and cause overcharging. In this
case, the charger can be modified to eliminate the 1 hour minimum time offset,
contact the factory if this modification is needed in your application.
Yes, but there are a few points to watch for.
Firstly, the load will be subjected to the on-charge voltage of the battery,
which is of necessity somewhat higher than the battery's normal on load
voltage. For example, a 24 Volt battery system will normally be held at about
29 Volts DC for several hours during the Constant Voltage charge stage, so you
should check that your DC load is specified to be OK at the higher voltage,
including some allowance for voltage overshoot and charger adjustment
tolerance. If it looks like there might be a problem, consider lowering the
charger cyclic voltage adjustment setting (this will result in a longer
recharge time but will reduce the stress on the load). Or consider using a
voltage regulator, or voltage reducer, between the battery and the load.
Secondly, any load current drawn from the battery while charging, will reduce
the effective charge current and so extend the recharge time. It's best to keep
the average level of DC load current to not more than about 20% of the charger
current rating, for this reason. Thirdly, if the charger is an un-smoothed SCR
type, it will cause superimposed AC ripple on the battery DC output, which can
upset sensitive electronic loads, for example causing a background hum noise on
radios. This can be reduced by keeping the charger cables and the load cables
separate if possible, run the charger cables (both Positive and Negative)
directly to the battery terminals, separate from any other wiring. Alternately,
a DC filter circuit can be added to the charger output.
Charging more than one battery, or
battery pack, from a single charger, is something of a compromise and should be
avoided if possible. It's much better to use two smaller chargers, one for each
battery. We also offer 5 bank chargers which include several independent
charging circuits. If the batteries are not equally discharged, that is if they
support different loads, then it's not possible to charge them optimally using
one charger, because the timing of the stages of charging should be matched to
the battery depth of discharge for optimal charging performance. But, this is
often done, for example in a boat or RV/caravan application where there is a
"starting" battery and a "house" battery, and it's desired
to charge both from a single battery charger. A common arrangement is to use a
"diode splitter" to divide the charger output between the two
batteries, while maintaining isolation between the batteries, so that, for
example if the "house" battery gets discharged, the vehicle can still
be started. Our chargers are designed to be connected directly to the battery,
they will not operate correctly, if there is a diode splitter fitted between
the charger and the battery, because the diode does not allow reverse current
flow from the battery to the charger so the charger cannot measure the battery
voltage accurately. To get around this, we suggest fitting a 1K Ohm, half watt,
resistor across each of the diodes. This is a readily available component, and
it will allow enough current to pass through the diode to allow the charger to
operate normally. If more than one battery is connected, it's advisable to try
to make the lengths and thickness of the cable to each battery about the same
so as to avoid unequal resistances. Even so, the charger will measure the
battery voltage as halfway between the two actual voltages, if they are
different, and so the charging will not be as optimal as it should be. This is
a fundamental problem and the best solution is to fit a separate charger for
each battery bank. Charging batteries of multiple cells, either in series or in
parallel, to make a higher voltage or Amp-hour rating, is acceptable, providing
the batteries are of the exact same type, capacity, and age, and are connected
in series or parallel at all times so that there is no unequal load. A common
error, is to charge two 12V batteries in series with a 24V charger, and then to
tap a 12V supply from the centre connection, this always results in one battery
overcharged and the other undercharged which shortens the life of both
batteries, and so should be avoided. It's much better to use two 12V chargers,
if there is any load driven from the connection between the batteries.
There are three preset pots on the PCB
inside the charger, these are marked as V-LIM1, V-LIM2/STBY, and I-LIM. Some
chargers also have a DIP switch for setting the battery type. In any case, to
check and adjust the charger voltage limits, proceed as follows. First, connect
the charger to a fully charged battery. The battery used for this test can be a
small one, or it can be the battery normally used with the charger, but it must
be in good condition, fully charged and of the correct number of cells (for
example, 12 cells for a 24 Volt charger, or 6 cells for a 12 V charger, and so
on. The test battery does not have to be exactly the same type as the actual
battery used in the application. Connect a calibrated accurate digital volt
meter or multi-meter in parallel with the battery terminals. The volt meter
should be connected directly to the battery terminals if possible. Switch the
charger on and observe the green-yellow-red Led indication (Power on self
check) showing the circuit board appears to be working OK. Then the Charging
(usually yellow) Led should come on, indicating that a battery is connected to
the charger. After a few seconds, the charger should reach the voltage limit
and enter the constant voltage stage of charge. This is indicated, either by
the yellow charging Led starting to flash off and on about once per second, or
by the "80% Charged" led coming on, if fitted. (Some non standard
chargers do not flash the yellow charging Led to indicate when the voltage
limit is reached, but those are very unusual). When the charger is in constant
voltage mode, observe the volt meter reading. The reading should be correct per
the "Cyclic charge voltage limit" for the type of battery being used.
The default setting, which works OK with most batteries, is 14.5V (2.42 Volts
per Cell). If the voltage is more than 0.1 Volt wrong, adjust the preset marked
V-LIM 1 to get the correct voltage. Next, locate the test point link on the
PCB. On PCB?s with a 3-pin header, the test point is the 2 pins nearest the
rear of the unit. On PCB?s with a 2-pin header marked "test", that is
the test point. Bridge the test point pins momentarily using a small flat blade
screw driver, and observe that the green "ready" Led comes on and
stays on. When the green Led is on, allow the battery voltage to settle for a
few seconds, then check the reading which should be 13.8V on a 12V battery, or
2.3 Volts per cell. If necessary, adjust using the preset pot marked as either
"V-LIM 2" or "STBY" (Standby). Note that, if the charger is
fitted with temperature compensation (usually there is a thermistor sticking
out the side or rear in a pigtail bush if this is fitted), then the voltage
setting should be adjusted to allow for the temp comp at the actual ambient
temperature at time of adjustment, if it is significantly different to 20
degrees C. The temp comp adjustment is 0.004 Volts per cell per degree C
difference from 20C. For example a 12V (6 Cell) battery, if adjusted at 30C
ambient temperature, should be set to 0.24 Volts below the nominal setting, so
the float voltage would be 13.56V instead of 13.8V.
The current limit setting is adjusted
using the preset pot marked I-LIM (short for Current Limit). It is set when the
charger is made and does not normally need to be re adjusted. The current limit
is a little more difficult to check and adjust than the voltage limit, because
the amp meter has to be connected in series, and a load is required to hold the
battery voltage down. If you do need to check and adjust it, proceed as
follows. Connect the charger, either to a recently discharged battery in good
condition, or to any battery with a DC load in parallel that is draws more
current than the charger's current rating. For example, for adjusting a 10 Amp
charger, a 12 Amp DC Load would be suitable. A good current load for small 12V
chargers, is a car battery with the car headlamps switched on, or a battery
with a resistive or lamp load connected across it. Connect an amp meter in
series with the charger output. Switch the charger on, observe the current reading.
It should correspond with the charger nominal current rating. If the current is
too high, adjust the I-Lim preset to correct it. If the current is too low, and
will not adjust to the correct value, confirm that the AC input voltage is
within spec, and that the battery voltage when charging is around 2.1 Volts per
cell (approximately 12.6V on a 12V battery). The charger must be in current
limit when adjusting the I-Lim preset, or the adjustment will have no effect.
Note that the amp meter must be connected in series with the charger output in
such a way that it does not add any significant amount of resistance, for
example if using a digital multi meter, the standard set of meter probes should
not be used because they are relatively long and thin, and may give a falsely
low current reading. A pair of substantial thick and short test leads with 4mm
plugs to plug directly into the amp meter should be used instead. A DC reading
clamp meter is ideal, if available. A moving pointer type of meter is best because
it reads arithmetic mean value, digital meters may not give the correct reading
when measuring un-smoothed DC current. Meters which read RMS values should be
avoided because the arithmetic mean value corresponds to battery charging time,
and this can be significantly lower than the RMS or equivalent heating effect
current, if there is superimposed AC ripple present.
On chargers that are fitted with a
Battery Type DIP switch inside on the PC Board, the charger can be quickly
configured for use with either gel cell, sealed lead acid, or liquid
electrolyte battery types. The difference is the cyclic voltage limit setting
(This is the first voltage limit, where the charger changes to constant voltage
mode, which happens when the battery reaches about 80% level of charge). The
DIP switch setting also has a small effect on the float/standby voltage. If in
doubt, we suggest use of the default normal setting, as that will give
satisfactory performance with most battery types, with a voltage limit of 14.5V
(per 6 cells). The sealed lead acid or normal setting is appropriate for
absorbed electrolyte or AGM batteries. The two switch levers are marked on the
PCB next to the switch, as N for normal and G for gel. The default (factory)
setting, unless otherwise specified, is the "
To a first approximation, to calculate
how long the battery will run the load, just measure or calculate the current
that the load will draw when running, and divide the battery Amp-Hour (Ah)
capacity rating by the load current, to give runtime in hours. This will be the
runtime to 100% depth of discharge (DOD) and should be de-rated by 20% to avoid
over discharge. Note that the battery capacity is expressed in Amp Hours (Ah),
this is not the same as any figure in Amps which is a unit of current flow. If
a battery supplier offers you a 100 Amp
This can be calculated approximately as
follows. The recharge time in hours equals the battery capacity in Ah,
multiplied by the Depth of Discharge in %, multiplied by 0.8, multiplied by
1.5, divided by 100 times the charger current rating in Amps, plus one hour.
For example, a 55Ah battery, discharged to 80%, on a 6-Amp charger, would take
about 9.8 hours. A 110 Ah battery, discharged to 50%, on a 10 Amp charger,
would take about7.6 Hours. The battery reaches 80% recharge relatively quickly,
the last 20% of the charge is done in constant voltage mode where the current
is dropping exponentially, so it is charging more slowly, this is the reason
for the 1.5 factor and the plus one hour constant. Our chargers usually provide
an indication when the 80% level and switch to CV mode has been reached (either
an indicator Led marked 80%, or the Charge Led starts to flash) showing that
the battery could be used at this point, with some loss of run time. At the end
of the charge cycle, the Green Ready Led will show that the battery is ready
for use. It?s recommended to leave the charger connected and switched on, if
possible, even after the green Led shows, as the charger is still supplying a
small current in standby mode, which tops off the charging process. The heating
effect on the battery is proportional to the square of the charge current,
while the recharge time is inversely proportional to the linear value of the
charge current.
These are many different types of
Lead-Acid rechargeable battery, and there is some confusion. Quite often
customers refer to a battery as a "Gel Cell", when in fact it's
another type of
These
FAQ notes are intended for use of suitably qualified persons only. This page is
provided for free, in good faith, on an "as-is" basis, by and on
behalf of INTERACTER INC. The answers given are BASED UPON EXPERIENCE AND ARE
EFFECTIVE, to the best of our belief. However, the reader is responsible
for verifying these points, by checking with the battery charger
manufacturer, and the
Copyright (C) 2000 Phil Hutchings.