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Discussion Starter · #1 ·
Parasitic drain is the current that continues to be drawn from the battery after the car is shut down. The New Beetle will continue to draw about 50 milliamps of current from the battery while the engine is off. If something goes wrong this can increase to the point where after a few hours the battery will no longer start the engine.

I will describe how to test the parasitic draw. The method I describe uses a resistor connected in series with the battery and a voltmeter to measure the voltage across the resistor. Since the resistor that I choose is 1 ohm the voltage across the resistor will equal the current flowing through it. This is safer than measuring the current with the meter directly since if the current happens to go up dramatically it is the resistor and jumper wires that will experience the overcurrent and not the meter. The maximum safe current through the 1 ohm 10 watt resistor is 3 amps so if you see the meter exceed 3 volts during the test you should remove the jumper between the battery and the resistor to prevent it from overheating.

I describe attaching wires to the positive side of the battery. While this is convenient to do using the alligator clip jumper wires, be aware that all the wires will be "hot" and must not touch anything metal that is attached to the chassis of the car or the battery will discharge directly through the jumper. I spread a packing blanket over the engine to provide an insulated working space while I did this.


Equipment needed:

Multimeter that has a millivolt scale

Jumper wires (Radio Shack Catalog #: 278-1157 or similar) 24" (60.9cm) Insulated Test/Jumper Leads - RadioShack.com

1 ohm, 10 watt resistor (Radio Shack Catalog #: 55050123 or similar) 10W1D0 1 Ohm Cermet Power Wirewound Resistor : Resistors | RadioShack.com


Step 1: Open and close the driver's door. This will cycle the fuel pump and make it less likely that it will run again during the battery drain test. Do not put the key in the ignition during the test as turning the key to "run" will cause an excessive current to flow through the 1 ohm resistor.

Step 2: Open the fuse panel above the battery and connect one jumper wire to any terminal in the panel. It doesn't matter which one you choose.

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Step 3: Open the top of the battery box and connect another jumper wire to the positive battery terminal.

Auto part Automotive wheel system Bolt cutter Suspension Wire

Step 4: Connect the other ends of the two jumper wires to the leads of the 1 ohm resistor.

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Step 5: Use a 10 mm wrench to remove the cable going from the battery positive terminal to the fuse panel. Be sure the wrench doesn't touch the negative battery post or anything else metal or it will short out the battery. By disconnecting this after the jumpers are in place, the power to the car will always be maintained.

Suspension Auto part Wire

Step 6: Use jumpers to connect the multimeter to the two resistor leads. Turn the meter to the 20 volt scale. Remember, you will be reading volts and the number of volts will be equal to the current flow in amps.

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If the reading is above 3 volts (or below -3 volts), then disconnect the jumper going between the battery and the resistor. The parasitic draw is over 3 amps and will overheat the resistor. You will need to proceed to the troubleshooting phase and only connect the jumper to the battery momentarily when checking for current draw.

If the meter reading is negative you can reverse the meter lead connections to the resistor if you like. There is no harm in leaving it, though. The sign on the reading can be ignored.

Step 7: If the reading is less than 2 volts you can turn the meter to the 2 volt (2000 mV) scale. With the doors closed and unlocked my indication was 56 millivolts, or a 56 milliamp current draw. This is normal. Opening the driver's door increased the reading to 650 mV (0.65 amps). This was with the interior lights turned off (one over each door and one in the rear view mirror). After closing the door again the reading quickly went back to 56 mV.

Step 8: If your voltage is much above 56 mV with the door closed then chances are you have a parasitic draw somewhere. You can search for the cause of the draw by removing fuses one at a time until you find the circuit with the offending item on it. The fuse panel is behind the driver's door.

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The door for the fuse panel can be removed and this will make it easier since you will need to open and close the driver's door often as you track down the parasitic drain. The general procedure is:

a) Remove one of the fuses from the fuse box.
b) Close the driver's door and check the multimeter reading.
c) Open the driver's door and replace the fuse.
d) Keep repeating until you find the circuit with the excessive draw.

Some fuses where problems are commonly found are #42 (radio system), #5 (comfort system) or #14 (interior lights). With the radio the problem will often be the Monsoon amplifier, if equipped.

Once the offending fuse is found, start disconnecting the items powered through the fuse until you find the source of the parasitic drain.

Step 9: When done, reattach the cable between the battery positive terminal and the battery-top fuses that was removed in step 5. Tighten the nut securely with the 10 mm wrench. Again, be careful not to touch the wrench to anything else as you tighten the connection. Remove all the jumper wires.
 

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Great write up.

A few additional comments to add for others looking at trying to measure and troubleshoot a battery draw.

Most all Multimeters have 10 Amp current measurement capabilities. This means the meter has a large shunt and is usually fused with a slow blow 10 or 12 Amp fuse. So as long as you do note exceed the fuse value you will not have any problems, if you exceed the fuse valve the fuse will blow in the meter and you will have to replace the fuse in the meter.

Most multimeter that support a 10 Amp current measurement scale require you to move the red test lead to a different spot in the meter that is usually marked as 10 Amp.

The other option is to use an inductive current clamp or inductive Amp probe. The issue is DC inductive Amp probes or clamp meters are a bit hard to find, it is usually easier to find either an AC/DC or a DC inductive current clamp.

If you have a really tough batter draw problem, you should consider a multimeter with a computer interface for logging. This will allow you to see exactly how high the current draw will get and how long the draw will last and when the draw starts after the car is turned off.

RadioShack 46-Range Digital Multimeter w/ PC Interface : Multimeters | RadioShack.com

Only issue with this meter is I believe it still only has a RS232 port?? Or at least be careful as the original meter only had a RS232 interface and you need to watch out for old stock in stores. It appears the newer model may in fact have a USB inteface. You can get a RS232 to USB adapter and make it work. No idea is the software will work with anything newer that Windows XP, I own 3 of these meters and have used them for data gathering and even used them with a USB to dual RS232 adapter to allow 2 meters to be connected to a single computer at the same time.

Reference this post with the VW Bulletin regarding parasitic current draw - http://newbeetle.org/forums/1-8-lit...draining-overnight-02-turbo-s.html#post836574

In general any load above about 50 mA is not good. Be prepared for the load to be higher than 50 mA for the first 20 minutes of testing as many cars have modules that need to go to "sleep" once the car has been turned off. Usually about 20 minutes until "sleep" mode starts is pretty typical.
 

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Discussion Starter · #4 ·
Most all Multimeters have 10 Amp current measurement capabilities. This means the meter has a large shunt and is usually fused with a slow blow 10 or 12 Amp fuse. So as long as you do note exceed the fuse value you will not have any problems, if you exceed the fuse valve the fuse will blow in the meter and you will have to replace the fuse in the meter.
Thanks for your comments, jfoj.

The big advantage of using the resistor and voltmeter is that it is not possible to damage a digital meter this way. Only the resistor and jumpers can be damaged. (An analog meter could be damaged if you are not careful about not letting it go overscale with the voltages.)

My meter says right on the face "unfused" for the 10 A connection. I think that a fuse adds resistance to the circuit and therefore affects the accuracy of the current reading. I'm not sure what the safe limit is on the lower current scales, but with this method I don't need to risk finding out.
 

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If the meter states it is unfused, the easy solution is to just put an external fuse in series with what you are measuring.

You can likely find an external fuse and holder easier than a resistor.

Even if the meter is internally fused, you can still add an external series fuse holder and fuse to save you opening the meter.

I would not worry about the fuse casing a Voltage drop, it really will not, but if it does you can make a correction factor to adjust your measurements.

Put a load on the meter between 4-8 Amps with and without the fuse and see if there is a difference in the measurements.

If there is, just adjust for it.
 

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Parasitic drain on aftermarket ipod kit.

Hi guys,
I may have a parasitic draw from an aftermarket iPod kit that connects directly to the AUX port on the back of my stock head unit (non-Monsoon). It is made by Dension. I loose cranking power after three days after a full recharge with my trickled charger. So I'd like to try this method but am no electrician but oddly have a Multimeter sitting around for hobby robotics. Can I use a 12V accessory fuse that came with my trickle charger's alligator clip? Not sure rating...also is there any special reason to hook up to the clip to the 3rd bolt on the Battery top fuse tray?

I'll probably proceed anyway when I top up the battery again but input and guidance would be appreciated.
 

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Discussion Starter · #7 ·
Can I use a 12V accessory fuse that came with my trickle charger's alligator clip? Not sure rating...also is there any special reason to hook up to the clip to the 3rd bolt on the Battery top fuse tray?
If you have a cable with alligator clips that has a fuse built into it that should be fine as long as the fuse rating is greater than your parasitic drain current. Otherwise the fuse will blow.

There is no special reason that I chose the third bolt in the first photo. Any exposed metal surface in the fuse box will work as they are all connected together.
 

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Great

Great little write up...............and you beat me to it I was going to make a diy like that but have been real busy with my cars and the new house I just bought.....it's Hectic every weekend. Anyways, GOOD JOB DUDE. :goodjob:
 

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https://www.youtube.com/watch?v=KF1gijj03_0

What are your thoughts about using the negative terminal to test the draw?

Also, is there anything that may be drawing on the battery that does not flow through either of the fuse boxes? In my case, my girlfriend's 2001 1.8 GLS Beetle has a 3 amp draw when it's off. I ran the test to similar to the youtube video with the negative terminal and was not able to bring down the draw to from 3 amps. I did not use clamps, so I might be engaging the ECU every time I'm testing, but not sure :confused:

Any wisdom that you guys would like to bestow? I was hoping it was going to be related to the monsoon issues that are prevalent with these models.:(

Great post BTW!
 

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Discussion Starter · #15 ·
Removing the negative terminal is safer if you are using an ammeter to do the test. I use the positive terminal because it is convenient to attach the test leads that way. My method has two main advantages. First, the power to the car is always maintained so no loss of clock, radio or ECU memory. Second, you can't destroy the meter by putting too large a current through it. You can only burn up the resistor. Notice in the video all the cautions that he gives about putting too large a current through the meter.

If you remove the connection on the positive battery post that I circled in the fourth picture and still get a current draw, the only thing left that is connected is the starter motor. Everything else in the car including the alternator goes through that fuse panel on top of the battery.
 

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Great article, but I am still stumped

This is a great article. I looked up general testing and then thought I would try looking up something specific for our beetle and found this.

I didn't feel like going to the hardware store to get a resistor so I put my DMM inline with the negative battery post and negative cable.

Surprisingly, I got 4.6 amps! No wonder the battery keeps dying. I gave it 5 minutes to see if it would drop and it bounced around 4.4A and 4.5A.

So, I began systematically removing each fuse. Nope, nothing changed. Not happy about that.

So, I looked at the fuse panel, and pulled all three 30 amp fuses. Still draining. So, I took off the red jumper from the fuse panel to the positive post. No drain. So, what does that leave? It is getting dark, so I think I will call it a day.
 

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Sometimes diodes in the alternator can actually have a problem where they can partially short and cause a drain.

4 Amps is HUGE assume you are reading this correctly.

Try to isolate the alternator feed and see if the draw is directly from the alternator output wire, if so, you have a bad diode(s) in the alternator.
 

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Discussion Starter · #18 ·
If you remove the 3 30 amp fuses from the battery fuse panel and all the red wires that go out to the car, the only thing left will be the alternator. (Keep the connection at the battery positive post. When you disconnect this the only thing left is the starter.) The first large, black wire on the panel goes to the alternator.
 

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Oops

Turns out I did have my meter hooked up incorrectly. I guess I am pretty lucky I didn't smoke it.

Hooked up correctly and letting the car settle it is reading about 20 milliamps.

Turns out my battery is good. Apparently, my battery charger wasn't correctly charging my dead battery. I had left the lights on and completely drained the battery.

The auto parts guy told me that "smart" chargers will not charge a battery unless they detect a minimum voltage. Mine seemed to give the battery a surface charge and then quit. I would read 12.4V on the battery but it really didn't have a charge.

After 4 hours charging at the parts store, I was able to finish it off with my charger and now everything is working fine.

Thanks for the help. Great thread. Just had some user error on my part. :D
 

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Some of the "smart" chargers will not properly charge very low batteries. Also you cannot use a Battery Tender or smaller Amperage wallwart to actually "charge" a battery that is very low.

I have 2 older "analog" battery chargers that I love because I can put these on a fully discharged battery and they will bring them up to a proper charge assuming the battery is in fact good.

Do not feel bad about improper measuring with a meter, happens all the time, this is why I often ask for pictures and ask a lot of questions when the values seem way out of the ballpark.
 
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