Parasitic Drain - Bulb Trick

Just wanted to ask:

Is the "light bulb" test (putting a 12v bulb in series with the battery
circuit) an accurate test for a parasitic drain? My ammeter only goes
up to 0.25A, and I don't want to risk overloading the meter.

How bright should the bulb light up, if it should at all, for a
"normal" drain? (clock, ECU, radio memory)

Thanks!

 

See the relevant page at Bill Darden's excellent Battery FAQ:
http://www.uuhome.de/william.darden/carfaq10.htm

 

See the relevant page at Bill Darden's excellent Battery FAQ:
http://www.uuhome.de/william.darden/carfaq10.htm

 

sure, but it depends on the bulb and the drain!!! if you describe your
problem, maybe we can address that question better?

 

sure, but it depends on the bulb and the drain!!! if you describe your
problem, maybe we can address that question better?

 

I had a light bulb that was a parasitic drain, once.
I thought I just had a dying battery. It was a little sluggish starting
sometimes, and dead if I didn't drive it every day.
I bought a new battery, and that made things much better, and then it was
dead again after it sat for a few days.
I charged it up, got in, and noticed a strange glow on the floor. At first
I thought it was a street light, then I realized that the glove box light
was on. The switch had gotten knocked out of it's mounting. I didn't see
the dim light under daytime conditions, and only happened to notice it at
night.

I would say that a dual filament 1157 bulb should glow dimly. If it is at
all bright, that is a pretty good load. At full brightness:

bright filament: 12.8V, 26.9W, 2.10A (R=V/I=12.8/2.1=6.1 ohms)
dim filament: 14.0V, 8.3W, 0.59A (R=24 ohms)

 

I had a light bulb that was a parasitic drain, once.
I thought I just had a dying battery. It was a little sluggish starting
sometimes, and dead if I didn't drive it every day.
I bought a new battery, and that made things much better, and then it was
dead again after it sat for a few days.
I charged it up, got in, and noticed a strange glow on the floor. At first
I thought it was a street light, then I realized that the glove box light
was on. The switch had gotten knocked out of it's mounting. I didn't see
the dim light under daytime conditions, and only happened to notice it at
night.

I would say that a dual filament 1157 bulb should glow dimly. If it is at
all bright, that is a pretty good load. At full brightness:

bright filament: 12.8V, 26.9W, 2.10A (R=V/I=12.8/2.1=6.1 ohms)
dim filament: 14.0V, 8.3W, 0.59A (R=24 ohms)

 

Sure, jim. And thanks.

Last week, the battery drained overnight on my '95 Civic 1.6L. I took
the battery to be recharged at a shop, and we found that the water
level was low. But I suspected a "ground" somewhere, because I had just
sprayed the engine with a degreaser and rinsed it (low pressure garden
hose).

Since my ammeter only goes up to 0.25A (250 mA), and I read on some
posts that the current could go over 1A, I tried the bulb trick first.
I don't know the exact rating of the bulb (aftermarket dome/trunk
light), but it glowed brightly. (All doors/trunk was closed, key off)

I tried pulling underhood fuses and even disconnecting the alternator,
with no result. Then I tried pulling the cabin fuses, and I found that
it was the Pioneer head unit that was pulling most of the power (for
the preset memory, I guess).

When I disconnected the radio, the bulb was finally very dim. I tried
the ammeter and expected less than 80 mA (from the battery FAQ link,
thanks to TeGGer). But I still got 170 mA or so. I've checked all the
possible bulbs, and I think a bulb would pull more than that.

I finally concluded that there was no parasitic drain at all, but I'm
puzzled as to what could be making that extra load.

 

Sure, jim. And thanks.

Last week, the battery drained overnight on my '95 Civic 1.6L. I took
the battery to be recharged at a shop, and we found that the water
level was low. But I suspected a "ground" somewhere, because I had just
sprayed the engine with a degreaser and rinsed it (low pressure garden
hose).

Since my ammeter only goes up to 0.25A (250 mA), and I read on some
posts that the current could go over 1A, I tried the bulb trick first.
I don't know the exact rating of the bulb (aftermarket dome/trunk
light), but it glowed brightly. (All doors/trunk was closed, key off)

I tried pulling underhood fuses and even disconnecting the alternator,
with no result. Then I tried pulling the cabin fuses, and I found that
it was the Pioneer head unit that was pulling most of the power (for
the preset memory, I guess).

When I disconnected the radio, the bulb was finally very dim. I tried
the ammeter and expected less than 80 mA (from the battery FAQ link,
thanks to TeGGer). But I still got 170 mA or so. I've checked all the
possible bulbs, and I think a bulb would pull more than that.

I finally concluded that there was no parasitic drain at all, but I'm
puzzled as to what could be making that extra load.

 

Maybe the Pioneer is wired wrong. It shouldn't take that much current for
the presets.

Earle

 

well, first, you have to eliminate the battery as a problem - if it's
draining itself, it's no good.

after that, 170mA is a 2W bulb at 12V [hence bulb glow]. that drain
seems high for the ecu memory [what you'd have left after disconnecting
the audio.] i'd continue looking for leakage. check both sets of fuses
pulling each one individually and connect the meter probes between the
slots.

 

well, first, you have to eliminate the battery as a problem - if it's
draining itself, it's no good.

after that, 170mA is a 2W bulb at 12V [hence bulb glow]. that drain
seems high for the ecu memory [what you'd have left after disconnecting
the audio.] i'd continue looking for leakage. check both sets of fuses
pulling each one individually and connect the meter probes between the
slots.

 

Ok. Thanks for the heads-up.

 

Ok. Thanks for the heads-up.

 

That might be a low wattage lamp, and glow brightly at a low current draw.
A stoplight bulb is a better choice, perhaps. I could look at autozone.com
to find the dome light bulb number, and then sylvania.com for the bulb
specs, but I think you found your culprit.

I think you are indicating that 170mA made the bulb glow dimly, and the
Pioneer made it bright. That's not good. The pioneer should only draw a
few milliamps in standby. There should be a figure in the manual.
There should also be a standby control on the Pioneer.

A voltage supplied to the Pioneer that is always on is expected to be a
heavy current feed for the amplifier, that also draws a tiny amount of
power in standby. There should be another switched control that comes on
with the radio or ignition that cause the Pioneer to turn on its
amplifiers. I think yours is switched on all the time.

Or maybe not... ;-) Check the manual for some specs on the Pioneer.

 

That might be a low wattage lamp, and glow brightly at a low current draw.
A stoplight bulb is a better choice, perhaps. I could look at autozone.com
to find the dome light bulb number, and then sylvania.com for the bulb
specs, but I think you found your culprit.

I think you are indicating that 170mA made the bulb glow dimly, and the
Pioneer made it bright. That's not good. The pioneer should only draw a
few milliamps in standby. There should be a figure in the manual.
There should also be a standby control on the Pioneer.

A voltage supplied to the Pioneer that is always on is expected to be a
heavy current feed for the amplifier, that also draws a tiny amount of
power in standby. There should be another switched control that comes on
with the radio or ignition that cause the Pioneer to turn on its
amplifiers. I think yours is switched on all the time.

Or maybe not... ;-) Check the manual for some specs on the Pioneer.

 

but the 170mA is /after/ the audio is disconnected! yes, the audio
needs to be addressed, but there's still unusually high residual drain.

 

but the 170mA is /after/ the audio is disconnected! yes, the audio
needs to be addressed, but there's still unusually high residual drain.

 

The obvious question is - can you see the Pioneer front panel lit up?

 

The obvious question is - can you see the Pioneer front panel lit up?