Curious how to test for a parasitic draw.

[sugarwood]

I know incorrectly installed things like aftermarket alarms and stereos can cause issues. My car works fine, and does not have a drain issue. But, I'd like to learn how to try doing this test.

How and where do I measure actual current draw?
I believe 25mA is an acceptable range.

Then, I'd like to disconnect something and note a difference in the current draw.
Should I just disconnect my stereo? Pull a certain fuse?

Then I remeasure current draw and see the difference.

When there is an actual unknown culprit, do you just repeat this test for each fuse in the fuse box?

[RSTarga]

Connect multi tester between your battery ground and chassis ground. That will give you total draw. Then pull fuse by fuse to narrow down the culprit.

[timmy2]

Install a DC ammeter (on the 10amp range) in line with the negative cable (remove cable, connect leads to cable and negative post) so power has to flow through the meter.
Take a reading. Remove one fuse at a time and see if the reading changes. When it changes you have found the circuit drawing current. Hood lamp should be disabled as it will draw current when on.

[sugarwood]

Thanks for the explicit directions.

I will set my multimeter to DC and 10amps range.

How do you disable the hood lamp?

[timmy2]

Not sure on your year. I just pulled the bulb when I was doing the same test on my car.
Only thing I found was the clock cicuit on mine, so it was all good.

[gliding_serpent]

I am a big fan of a test light. Same result, just less fiddling

[billybek]

With some electronics like stereo components and alarm systems you may have to sneak up on the problem. You can run amps through the meter so the leads are carrying the current. This is easy if you have a battery disconnect switch on the negative post, you just place the leads across the switch and then open it to read inline amps through the meter.
If not, you can pull the negative post with the meter across the post to the clamp and do the same thing.
I had an alarm system in one of the cars that I had to do this with. If I had simply disconnected the negative post it would reset the problem in the module and would not show a pull down problem.
You have to watch how much current your meter can carry. I believe my old Fluke 22 was fused for 300 ma and 10 amps.

[911pcars]

More results from a Google search on this forum:
https://www.google.com/?gws_rd=ssl#q=pelicanparts+parasitic+current+drain

Sherwood

[sugarwood]

Billybek,
My multimeter has 2 ports for the black lead. 10A and 200mA. I think I can use either since normal draw is 25mA

Just set it to Vdc at 200mA?

.http://m.craftsman.com/craftsman-multimeter-digital-with-8-functions-and-20/p-03482141000P

[911pcars]

Originally Posted by sugarwood

Billybek,
My multimeter has 2 ports for the black lead. 10A and 200mA. I think I can use either since normal draw is 25mA

Just set it to Vdc at 200mA?

.http://m.craftsman.com/craftsman-multimeter-digital-with-8-functions-and-20/p-03482141000P

On some voltmeters, measuring current higher than the max. current measuring range can damage the meter and/or blow the internal fuse. Typical handheld multimeters can measure up to 10A - should be safe for typical parasitic current loss. BTW, a direct short to ground at 10A will let out the smoke.

Sherwood

[sugarwood]

Originally Posted by 911pcars

BTW, a direct short to ground at 10A will let out the smoke.

Whoa, I'm going to hold off on this test until I figure out what that means.

[911pcars]

Originally Posted by sugarwood

Whoa, I'm going to hold off on this test until I figure out what that means.

Sorry to hang you up with my "smoke" warning.

If you connect the multimeter to the elec. system as described, worst case is that the internal meter fuse will blow to protect the electronics.

The warning is to NOT ground a circuit without a load (electric motor, bulb, etc.) in the circuit or to bypass the load circuit path to ground with test wires. Most automotive electrical circuits are protected with fuses; a few circuits on some 911s aren't, but that's just a general precaution when circuit testing. Didn't mean to put the orange alert out there.

Sherwood

[mattC2993]

I bought a multimeter with a clamp on DC ammeter (inductive?) just for this purpose. I haven't used it yet so can't report on how well it works.

[gregoryp]

You can also just put a test light between the negative cable and the negative battery terminal and pull fuses until the light goes out.

[billybek]

Select amps and place the lead in the highest amp socket first and give it a try. If you are getting a very small reading, select the m/a scale and give it another try.
A big pull down over 10 amps would indeed take the fuse out of the meter. In this case, you would probably be aware that you have a problem already but it is possible.
Fluke meters are very well fused with very expensive fuses! I am not sure what type of fusing a Craftsman meter would have so be careful.
Amp clamps may not show too much for a small current draw. You can make multiple winds of the wire through the clamp for smaller current draws then divide the reading by the number of turns.

[Mike80911]

Originally Posted by gregoryp

You can also just put a test light between the negative cable and the negative battery terminal and pull fuses until the light goes out.

This is definitely the easiest most fool proof test to use on our older cars. A multi meter is only really needed on newer cars as there are many different electronics that draw when car is off but they have acceptable levels of draw. So you need to test the levels to make sure they are within within spec.

[sugarwood]

Originally Posted by 911pcars

The warning is to NOT ground a circuit without a load (electric motor, bulb, etc.) in the circuit or to bypass the load circuit path to ground with test wires.
Sherwood

To which I PM'ed:

I am an electrical N00b, so I don't understand what this means. Can you translate it explain to your wife or mother?

My "safe" plan:
1) Detach negative terminal cable.
1b) Disconnect hood lamp bulb
2) Connect black probe/lead to negative battery post
3) Connect red probe/lead to the negative terminal cable.
4) Read measurement
5) Re-connect hood lamp bulb
6) Read measurement

Can you explain what to do to create the problem you described?

Meter connection to observe parasitic current drain is correct. You can leave the bulb in place.
If the meter displays more than ~160 Ma (milli-amps), excessive current is flowing in the electrical system, maybe not enought to blow the fuse, but enough to drain the battery overnight.

The next step is to temporarily remove each fuse from the fuse box in turn while observing the current display. If the current level decreases, you have partially identified the offending electrical branch circuit. That particular fuse could protect a series of branch circuits, powering several loads (accessories; e.g. cigarette lighter, glove box, dome light, etc.).

Once you've identified the circuit causing the excess current draw (fuse # X, you must refer to the electrical schematic diagram and identify the circuit/load(s) protected by fuse X). It may be the circuits providing electricity to the cig. lighter as well as the blower motor, etc.).

Make a copy of the circuit, then with a transparent marker, highlight the circuit wires and branch circuits leading away from fuse X all the way to ground (return path of electricity to battery).

For example, let's say you have identified that removing fuse X changes the current reading on the current meter and fuse X protects the branch circuit(s) that provide electricity (current) to the cig. lighter and glove box. One of these loads is causing the abnormal current drain. Here's how to isolate which load is causing the excessive current drain.

While observing the meter, disconnect the source wire to the cig. lighter. Does the meter change (reduced current)? If so, you have identified the source of the parasitic current draw. If not, reconnect, then disconnect the source wire to the glove box bulb and observe the meter.

This identify and isolation procedure is the same for any circuit protected by a fuse. Obviously, if the current drain is high enough, current flow will cause excessive heat and cause the fuse to melt (blow) and thus opening the circuit to prevent continuous current flow. Parasitic current flow isn't normal nor is it high high enough to flow the fuse. It will, however, slowly drain the battery, similar to leaving the dome light ON overnight.

Here's a source that illustrates a "short circuit".
Short Circuit (Series)

Suggest reading about basic DC electricity to understand the elements that allow electricity to perform work. The link above provides more pages you can read. Electrical malfunctions begin here: DC CIRCUIT FAULTS

BTW, removing and replacing the bulb (load) won't reveal a short circuit. Excessive current with switch off typically indicates a malfunction somewhere in the circuit path that bypasses the normal load (bulb, in this case).

[sugarwood]

When I put the multimeter in line with the negative ground, I was reading a full 12V, and not the expected 25mA.
If I put the setting on 200mA, I got (-1). When I put it on 20, I got 12.08
It is reading the voltage, not the current. Need to learn the difference.

[MetalDoc]

Hi, You should post a picture of your DVM. It is a pretty simple measurement. If you read your instruction manual it will tell you how to make the measurement. There are probably some videos on you tube if you search. In current mode the two wires are connected to a resistor that is called a shunt. You can think of this as a flow meter, the current flows down one lead, through the shunt and out the other wire. The meter reads the voltage drop across the shunt and converts the reading to current. There are two shunts in the meter, a high current and low current. Both of these are fused. If you pass to much current through the low scale one, a fuse will blow. Again the manual will tell you what kind of fuse you are going to need and how to take apart the meter to change it. Reading on the high current mode will display the lower currents, the resolution of the meter is just lower.

[sugarwood]

Note, to read current, you must set the dial to Amm (DC), and not Volts (DC)
At first, it read 125, then after a few seconds it dropped down to 8.
Anyone know what this means?

Also, my hood light does not light up with the DVM in the circuit.
Everyone implied the hood light would still be on.
Any clue what is going on?