Well, I'm kind of stumped. I'm trying to measure a phantom draw on my daughter's car by using a clamp on Sears AC/DC ammeter at the car battery.I can only get the readout of OL (Open limit?) on the 0-40 amps DC range, no matter what I do. On the 0-400 DC amps range, I can get it to read about zero when I press the "zero" button on the meter, but I think that's the wrong range to measure what I am trying to determine.It is a sears model 82369, clamp type meter. It also has leads, which I have disconnected for this purpose.Thanks for any assistance. I know there are a lot of electricity savvy guys on this forum.

Did you put the clamp around a single wire? Can't put it around multiple wires or cables.

I put it around only one wire, but no change.

Hit the zero button on 0 to 40 . It's got to be around a hot lead I believe maybe to small to measure.

Orcadrvr wrote:I put it around only one wire, but no change.With it on the positive or negative battery cable, turn on the headlights, parking lights and radio and see what you get there. If you are using it correctly, it should show a large draw. Once you know it's working, start turning things off.

Phantom draw will be very low, probably <50mA range or lower. Then after the car sits "idle" for awhile (no activity through the computer for 10- 30 min) it will be even go lower than that. I'm not sure you will be able to see such small ranges on that meter.Be sure to zero the meter with the jaws closed, and not around a wire. Then try the lowest range 0-20A to see if it can detect that small current. Clamp on meters don't do well when there isn't much magnetic field built up around a conductor unless they have an external sample loop.Yes, try the experiment suggested by Drycamper11 to see if the meter will indicate a higher current. Headlights should be fine at the 0-20A scale.

Use of clamp on dc ammeter | Good Sam Community

wa8yxm
Explorer III
Dec 15, 2013
There are a few things in a car that draw power all the time

The radio needs power to maintain the station memory and to run the clock
The Engine Control Computer also has a memory that needs to be powered.
ON-Star/On-Guard transponders need full time power.
On some cars even the dome light is always poweres.. My 2001 Neon is like that, a small current flows even with the doors closed and it is computer controlled!!

(How do I know this.. Well the lamp was missing when I got the car used so I installed an LED, it has a very tiny glow all the time, you have to look to see it, but it's there)
bukzin
Explorer
Dec 15, 2013
RJsfishin wrote:
60-75 AHs if the battery is full charged. But the fact is most cars seldom ever see full charge, except if driven at least 30-50 miles a day. Cars that live in town, never see full charge, unless placed on a charger once a month or so.
The few cars that do see full charge quite often, those are the batteries that last 8-10 years like they should.
Living near town,I drive mostly short trips. And I overnite charge at least once, sometimes twice a month. And seldom is the readout higher than 80% at start.

Which model charger are you using?

Can you adjust the voltage output?
RJsfishin
Explorer
Dec 14, 2013
60-75 AHs if the battery is full charged. But the fact is most cars seldom ever see full charge, except if driven at least 30-50 miles a day. Cars that live in town, never see full charge, unless placed on a charger once a month or so.
The few cars that do see full charge quite often, those are the batteries that last 8-10 years like they should.
Living near town,I drive mostly short trips. And I overnite charge at least once, sometimes twice a month. And seldom is the readout higher than 80% at start.
jake2250
Explorer
Dec 14, 2013
Does the car have "OnStar or an Alarm"? Just replaced the battery in my '08 Impala SS and it was dead three days later,, charged it up and it was back down in two day,,, Car sits for up to a week with out being driven... Read on other forums that OnStar stays on and is a drain on the system,, also a car alarm is a drain..
bukzin
Explorer
Dec 14, 2013
Instead of the cost of a replacement radio a simple switch to kill
its incoming 12volts would be much cheaper.
wa8yxm
Explorer III
Dec 02, 2013
1.5 amps times 10 hours is 15 amp hours.

A Group 24 only has about 75 amp hours. 1500/75 = 6 2/3 percent

That should not kill it, if the battery is smaller than G-24, or old and tired, however it might.

However I would not trust the clamp on at very low current, (Basically less than 4 amps) even on the 40 amp range.

I also have one of those sitting beside me by the way.. it just figured out my main GC-2 battery bank is toast.. Oh the joy.
pianotuna
Nomad III
Dec 02, 2013
Hi,

Most cars now keep the radio and other items powered for about ten minutes after the key is switched off. Check to see if other items are turning on and off at random.
Orcadrvr
Explorer
Dec 02, 2013
The car was sitting for at least five days. It apparently constantly turns on and off by itself, which we just happened to notice one night. It never occurred to me that it might be draining the battery, or I would have checked it sooner.

I have pulled the radio fuse, and we are going to see how the battery holds up with the radio disconnected.
MrWizard
Moderator
Dec 02, 2013
1.5 amps should NOT kill a good battery overnight
even 18hrs would only be around/slightly above 24ampHrs of power drain
how big is the car battery

BUT if the radio turns on ... the increased power draw could do it

measure power with radio ON at Her Normal listening volume

which is most likely to be set at, when it self powers on
SaltiDawg
Explorer
Dec 02, 2013
Orcadrvr,

Back in the day - 1940s - car radios had vacuum tubes and drew a lot of current to heat the tube filaments. Also, they commonly were not connected so as to turn off with the ignition switch... or power switch.

I had an uncle that apparently adored me... until I sat in his parked Olds listening to the radio. I did not turn it off, apparently, and next morning he went out to find a dead battery.

Ah, the good old days.

PS I ceased being his favorite nephew that day!

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