Parasitic
Draw
The term Parasitic Draw refers to electrical devices that
continue to use or draw current after the ignition switch is
turned off. This small amount of continuous battery
draw is expressed in milliamps (mA). On Ford Motor Co.
and General Motors vehicles produced after 1980 MY, a typical
Parasitic Load should be no more than 50mA.
I’m going out on a limb and say my limit is 85mA on
newer beyond 2000 MY, to 100mA on beyond 2010 MY,
assuming you find nothing to attribute it too. Vehicles
produced
since 1980 have memory devices that draw current with ignition
off for as long as 20 minutes, on older MY’s, to two hours, on
newer MY’s, before shutting down the
Parasitic Drain. When Parasitic Load exceeds normal
specifications, the vehicle battery will go dead, overnight,
or in a few days, depending on the size of the drain.
The key to long life for any battery is to make sure battery
voltage doesn’t drop below 12.4 volts. The combination of a
significant parasitic draw and long periods of
non-use can easily cause voltage to drop below 12.4 volts.
When that happens, sulfation begins to diminish both capacity
and performance. If you have an 85-milliamp
draw in a car with a single 50Ah battery, as is the case in
most vehicles, your battery will be completely discharged from
a full state of charge in just over three weeks.
If the vehicle is going to sit for long periods of non
use, disconnect the battery. Pay close attention to the
battery top, if it appears wet and dirty, give it a good wipe,
that accumulation will also slowly discharge the battery.
Use of NoCo oil based battery terminal protectors will
help keep corrosion to a minimum is a good practice.
TEST PROCEDURE USING TEST SWITCH
Draw
The term Parasitic Draw refers to electrical devices that
continue to use or draw current after the ignition switch is
turned off. This small amount of continuous battery
draw is expressed in milliamps (mA). On Ford Motor Co.
and General Motors vehicles produced after 1980 MY, a typical
Parasitic Load should be no more than 50mA.
I’m going out on a limb and say my limit is 85mA on
newer beyond 2000 MY, to 100mA on beyond 2010 MY,
assuming you find nothing to attribute it too. Vehicles
produced
since 1980 have memory devices that draw current with ignition
off for as long as 20 minutes, on older MY’s, to two hours, on
newer MY’s, before shutting down the
Parasitic Drain. When Parasitic Load exceeds normal
specifications, the vehicle battery will go dead, overnight,
or in a few days, depending on the size of the drain.
The key to long life for any battery is to make sure battery
voltage doesn’t drop below 12.4 volts. The combination of a
significant parasitic draw and long periods of
non-use can easily cause voltage to drop below 12.4 volts.
When that happens, sulfation begins to diminish both capacity
and performance. If you have an 85-milliamp
draw in a car with a single 50Ah battery, as is the case in
most vehicles, your battery will be completely discharged from
a full state of charge in just over three weeks.
If the vehicle is going to sit for long periods of non
use, disconnect the battery. Pay close attention to the
battery top, if it appears wet and dirty, give it a good wipe,
that accumulation will also slowly discharge the battery.
Use of NoCo oil based battery terminal protectors will
help keep corrosion to a minimum is a good practice.
TEST PROCEDURE USING TEST SWITCH
Fig. 1
Check battery
voltage, make sure its at least 12.4v, remove negative
battery cable terminal,*
install disconnect tool, (J-38758) test switch male end to negative battery
cable, turn test switch knob to OFF position, install
negative battery cable to the female end of test switch,
turn test switch knob to ON position, (current through
switch), make sure ignition switch is in LOCKED position and
remove key, and fob from the vehicle, connect ammeter (I’m
not crazy about using inductive probes, see why) terminals to test switch terminals, see Fig. 1, select the highest amp
scale, turn off all electrical accessories, turn off
interior lights, under hood lamp, trunk light, illuminated
entry, etc, to avoid damaging ammeter or obtaining a false
meter reading, all accessories must be off and
time allowed for all systems to enter sleep mode (I
allow a minimum two hours on late MY’s to make sure) before
turning test switch knob to OFF position, (I recommend a
fused 5 – 8A test lead to protect your DMM fuse) turn test
switch knob to OFF position to allow current to flow through
ammeter, observe current reading, If reading is less than 2
amps, turn test switch to ON position to keep electrical
circuits powered-up, select low amp scale, turn test switch
to OFF position and compare results to normal current draw,
If current draw is unusually high for the vehicle’s overall
electrical system, give the car a good visual look, is the
dome on, could be a door ajar switch, is the trunk shut,
there are all kind of things to look at, the two things I
found most, visor lights, and glove
box lights, after this, check and see if the alternator may
be causing the draw by disconnecting it totally from the
system and recheck, if the draw still exists, connect it
back up and continue to the main maxi fuses (if equipped),
you are only going to check the ones that have battery
volts on them, not the ones that would power up
with the key on, and check for any voltage drop across
them (voltage
drop charts) (make sure there is no under hood lamp or
hood ajar switch) Any reading here in drop would point to
where you go next by looking at a diagram for the
application your working on, now you will know what fuses to
check to narrow it down, fuses with out test points will be
a problem, so replace them with fuses with test points
before you start your testing.
Why couldn’t you use a test light to check for an indication
of a draw? Why not? If you have one of those with the fuse
style bulb, that only requires 150ma to light up, which
would be about where you would go looking for an excessive
draw, you just connect the test light the same way you would
your ammeter, if the light is on, its at least enough to
turn the light on. you could still check the fuses for
voltage drop, or you could just pull fuses one at a time, to
see if the light goes out.
*You could save
the connection to the battery by using a jumper
battery, then remove the ground terminal, then
connect the ammeter, then disconnect the jumper
battery, this would negate the need for the
disconnect switch.
voltage, make sure its at least 12.4v, remove negative
battery cable terminal,*
install disconnect tool, (J-38758) test switch male end to negative battery
cable, turn test switch knob to OFF position, install
negative battery cable to the female end of test switch,
turn test switch knob to ON position, (current through
switch), make sure ignition switch is in LOCKED position and
remove key, and fob from the vehicle, connect ammeter (I’m
not crazy about using inductive probes, see why) terminals to test switch terminals, see Fig. 1, select the highest amp
scale, turn off all electrical accessories, turn off
interior lights, under hood lamp, trunk light, illuminated
entry, etc, to avoid damaging ammeter or obtaining a false
meter reading, all accessories must be off and
time allowed for all systems to enter sleep mode (I
allow a minimum two hours on late MY’s to make sure) before
turning test switch knob to OFF position, (I recommend a
fused 5 – 8A test lead to protect your DMM fuse) turn test
switch knob to OFF position to allow current to flow through
ammeter, observe current reading, If reading is less than 2
amps, turn test switch to ON position to keep electrical
circuits powered-up, select low amp scale, turn test switch
to OFF position and compare results to normal current draw,
If current draw is unusually high for the vehicle’s overall
electrical system, give the car a good visual look, is the
dome on, could be a door ajar switch, is the trunk shut,
there are all kind of things to look at, the two things I
found most, visor lights, and glove
box lights, after this, check and see if the alternator may
be causing the draw by disconnecting it totally from the
system and recheck, if the draw still exists, connect it
back up and continue to the main maxi fuses (if equipped),
you are only going to check the ones that have battery
volts on them, not the ones that would power up
with the key on, and check for any voltage drop across
them (voltage
drop charts) (make sure there is no under hood lamp or
hood ajar switch) Any reading here in drop would point to
where you go next by looking at a diagram for the
application your working on, now you will know what fuses to
check to narrow it down, fuses with out test points will be
a problem, so replace them with fuses with test points
before you start your testing.
Why couldn’t you use a test light to check for an indication
of a draw? Why not? If you have one of those with the fuse
style bulb, that only requires 150ma to light up, which
would be about where you would go looking for an excessive
draw, you just connect the test light the same way you would
your ammeter, if the light is on, its at least enough to
turn the light on. you could still check the fuses for
voltage drop, or you could just pull fuses one at a time, to
see if the light goes out.
*You could save
the connection to the battery by using a jumper
battery, then remove the ground terminal, then
connect the ammeter, then disconnect the jumper
battery, this would negate the need for the
disconnect switch.
When is it safe to use a bigger fuse?
NEVER!
Never ever use a fuse of higher value than
is specified, it could possibly burn the vehicle to the
ground!
OHM’S
LAW
Ohm’s law is
helpful when you need to determine a value that you
need, use the formula’s in the chart above, for
example
if we want the battery volts in the waveforms, I did
resistance checks on the injectors before, and the one
on the left was
8 ohms, the one on the right was 7.1 ohms. Using the
formula to determine volts, E=IxR 1.74 x 8 is
13.92 volts, and the other
one is 1.92 x 7.1 is 13.62 volts, you just need to
know two of the values, to determine the one in
question, good to know.
LAW
Ohm’s law is
helpful when you need to determine a value that you
need, use the formula’s in the chart above, for
example
if we want the battery volts in the waveforms, I did
resistance checks on the injectors before, and the one
on the left was
8 ohms, the one on the right was 7.1 ohms. Using the
formula to determine volts, E=IxR 1.74 x 8 is
13.92 volts, and the other
one is 1.92 x 7.1 is 13.62 volts, you just need to
know two of the values, to determine the one in
question, good to know.
Fuse Voltage Drop Chart *
When
you are checking voltage drop on fuses to determine if an
excess draw exists, the chart above gives you
the conversion from volts to amps based on the value of
the fuse, higher amp fuses allow more current to pass
through the element, and will show a higher amperage draw.
For example, lets say you drop test a fuse, and
*This
chart figures mA by dividing the
voltage drop by the resistance of
the fuse, to determine the
resistance of the fuse, for
example: a 2amp fuse flowing at 1mV
.0001 / .019mA 19mA = 5.2mOhms
.005263Ohms would be the
resistance across the
fuse, a 3amp fuse flowing at 1mV
.0001 / .032mA 32mA = 3.1mOhms
.003215Ohms would be the resistance
across the fuse.
you get a reading
of 1.5mV on a 15A fuse, that shows 313mA flowing through
the fuse, which may not be the
exact amount of draw from your parasitic value, but it
should be close. Lets say you come to the PCM battery
volts fuse, and you see a value of .1mv that means on a
10A fuse its drawing 13mA, I’m guessing here but I’m
just using it as an example of whats possible, (the
disadvantage of being retired) it would be interesting to
see.
2008
Hyundai Veracruz, after doing a parasitic draw test, total
draw found was 210 mA, after checking voltage drop on the
main
fuses, the I/P B+2 50A fuse was showing a 4mV reading, and
based on the fuse drop chart, for a 50A cartridge fuse
should be
167mA, this value minus the 210mA would net 43mA total
draw which I would consider normal, all other fuses showed
nothing.
Now we look at the fuses that are powered by the 50A
main fuse, and looking at the legend for the fuses, there
are several areas
it goes to, now we need a diagram to help show us what
needs to be looked at, keep in mind, this is B+ volts.
The fuse we found with current flow has
several fuses in question powered up, looks like
seven total fuses in all to various items,
now we need to start looking at fuses in the I/P
fuse box, and check them for any voltage drop, the
legend will tell which ones
are powered up and need to be checked for any
voltage drop, and after checking them, all were
good with the exception of the
15A ROOM LP fuse was reading 8mV, based on the
chart for the 15A fuse and based on the drop
chart, its the same value, 167mA,
after looking at the diagrams for whats on that
fuse, there are several items the fuse powers, so
its going to be a pain in the rear.
you are checking voltage drop on fuses to determine if an
excess draw exists, the chart above gives you
the conversion from volts to amps based on the value of
the fuse, higher amp fuses allow more current to pass
through the element, and will show a higher amperage draw.
For example, lets say you drop test a fuse, and
*This
chart figures mA by dividing the
voltage drop by the resistance of
the fuse, to determine the
resistance of the fuse, for
example: a 2amp fuse flowing at 1mV
.0001 / .019mA 19mA = 5.2mOhms
.005263Ohms would be the
resistance across the
fuse, a 3amp fuse flowing at 1mV
.0001 / .032mA 32mA = 3.1mOhms
.003215Ohms would be the resistance
across the fuse.
you get a reading
of 1.5mV on a 15A fuse, that shows 313mA flowing through
the fuse, which may not be the
exact amount of draw from your parasitic value, but it
should be close. Lets say you come to the PCM battery
volts fuse, and you see a value of .1mv that means on a
10A fuse its drawing 13mA, I’m guessing here but I’m
just using it as an example of whats possible, (the
disadvantage of being retired) it would be interesting to
see.
2008Hyundai Veracruz, after doing a parasitic draw test, total
draw found was 210 mA, after checking voltage drop on the
main
fuses, the I/P B+2 50A fuse was showing a 4mV reading, and
based on the fuse drop chart, for a 50A cartridge fuse
should be
167mA, this value minus the 210mA would net 43mA total
draw which I would consider normal, all other fuses showed
nothing.
Now we look at the fuses that are powered by the 50A
main fuse, and looking at the legend for the fuses, there
are several areas
it goes to, now we need a diagram to help show us what
needs to be looked at, keep in mind, this is B+ volts.
The fuse we found with current flow hasseveral fuses in question powered up, looks like
seven total fuses in all to various items,
now we need to start looking at fuses in the I/P
fuse box, and check them for any voltage drop, the
legend will tell which ones
are powered up and need to be checked for any
voltage drop, and after checking them, all were
good with the exception of the
15A ROOM LP fuse was reading 8mV, based on the
chart for the 15A fuse and based on the drop
chart, its the same value, 167mA,
after looking at the diagrams for whats on that
fuse, there are several items the fuse powers, so
its going to be a pain in the rear.
The diagram below shows all the components on
the fuse, a total of four legs off the fuse, so how to
make this easier than going
to each component and disconnect them and where do you
start? If you are observant, you will notice each leg
from the junction
box is through a connector, if you can easily, (or not),
get to the back of it, you can remove the connector from
it and voltage drop
each leg until you find a draw, that will lessen what
you have to go and find to disconnect from the circuit
looking for the draw. One
connector has two legs through the connector, I/P-E
number 3, and 10, so find those circuits on the
connector and voltage drop test
each circuit at the connector, do you know how? Just
hookup your voltmeter to see volts, between the bat+ and
each circuit looking
for a voltage drop reading like you were looking at
fuses for a reading, your essentially doing the same
thing, just not across the
fuses, when you find the circuit flowing current showing
a voltage drop, you have found your draw, now you’ve
narrowed it down.
Make sure you check every thing connected and powered up
by the fuse, in our case the room lamp fuse, number 3
Sheesh!
Now you know how important doing and learning voltage drop tests can be
of help in your diagnostic endeavors.
the fuse, a total of four legs off the fuse, so how to
make this easier than going
to each component and disconnect them and where do you
start? If you are observant, you will notice each leg
from the junction
box is through a connector, if you can easily, (or not),
get to the back of it, you can remove the connector from
it and voltage drop
each leg until you find a draw, that will lessen what
you have to go and find to disconnect from the circuit
looking for the draw. One
connector has two legs through the connector, I/P-E
number 3, and 10, so find those circuits on the
connector and voltage drop test
each circuit at the connector, do you know how? Just
hookup your voltmeter to see volts, between the bat+ and
each circuit looking
for a voltage drop reading like you were looking at
fuses for a reading, your essentially doing the same
thing, just not across the
fuses, when you find the circuit flowing current showing
a voltage drop, you have found your draw, now you’ve
narrowed it down.
Make sure you check every thing connected and powered up
by the fuse, in our case the room lamp fuse, number 3
Sheesh!
Now you know how important doing and learning voltage drop tests can be
of help in your diagnostic endeavors.
After
checking each leg at the connector, the draw was found on
leg I/P-E #10 circuit, mostly lighting inside the vehicle,
most
everything was good, but the cargo lamp was unsure, since
there was 40 tons of personal belongings in the area,
after 10 minutes
clearing it out, the cargo lamp was on and lying out of
where it would snap in, evidently all the junk jumping
around in the back
turned it on at the switch as well as knocked it out of
it’s receptacle, isn’t it funny how such a simple thing
can be a nightmare?
It’s
a good idea to look at the diagrams for each component to
show you how its arranged, like the connection to the
power
window switches, from the connector circuit at the
junction box, you can see where it branches off to the
other switch.
