parasitic battery drain

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Princess Valiant

Princess Valiant

A.K.A. Rainy Day Auto
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ok, I know this is not really a concern for an older mopar with no accessories

but truthfully I am working on a later model car and it is draining the battery and I disconnected the battery on one terminal and put a test light between the post and cable end.....and I pulled fuses till the light went out and found it to be a dash light and accessory fuse.

problem is that im not convinced that it has a short even though the test light is on, I think it could be an older battery too.

so what I would like to do is measure how much of a parasitic load does it have exactly

so how do I measure the parasitic load with a millimeter?...I think it is connected in series between the battery post and terminal end .....but what to I put the settings on to accomplish this?

and what is a typical parasitic load for a car made in the mid 2000s ?
 
If the test light is "lit" consider this a drain

Just substitute your multimeter for the test light but BE CAREFUL

Before you do, make sure you have it set properly

If you can post a photo of the meter is best, or at least brand and model
 
Turn your multimeter to amps dc.
Key off and out of ignition
Disconnect the ground cable from battery
Hook the red lead to negative cable
Hook black lead to negative battery post

U should see less than 0.2 amps ( 200 miliamps)
It might be a lil high at first since the modules need to time out on newer vehicles
U might have to wait up to an hour

Your meter probably has a ten amp fuse so dont turn anything on or it will blow.

I always open the car door and then use a screwdriver to close the door latch so the car thinks the door is closed. Then u can pull fuses one by one till the draw goes away.
 
Most multimeters require that you put the leads in different terminals to measure current. Those are always fused, and it is easy to blow the fuse. That is a constant fuss if you teach a college physics lab (how would I know). I have read that mid 2000's cars have enough parasitic draw that the battery is often drawn down in a few weeks, even if everything is new. That keeps airport parking lot guys busy jumping cars. I use a Battery Brain on all my cars (don't ask, search on ebay). Mine is the little blue box in my 65 Dart avatar.
 
Above is true, EXCEPT

When measuring current, it's important to NOT overload the meter, because in the current scale you can blow the fuse --if so equipped, or damage the meter if not

It's important to find out whether the current to be measured is withing limits of the meter, and to start on the largest scale setting

Some "lesser" meters only have a 200 ma scale, so this ain't much headroom.
 
HOW much later model are you talking ??? You cannot isolate battery drain with test light on later model cars .....
Open all doors and lids and manually latch doors and lids so you can access fuse panels ...Turn key OFF and wait 20 minutes ,, now Set ammeter to highest scale ... now install INLINE ammeter as stated earlier ... Lock car with car with remotes .... and allow vehicle to sit for 15 -20 minutes while absorving ammeter ... ONCE you see parasitic drain stabilize ... then start pulling fuses 1 at a time and DO NOT reinsert fuses after pulling them ......spec stated earlier 200 milliamps ... TOO Much..... should be less than 30-40 millamps. Good luck .
 
:hello2:
 

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The bad thing about measuring Amps through your multimeter is that until you hook it up you don't know that it's too much untill it's too late. If the battery runs down after setting a couple weeks we are talking milliamps and not enough current to blow a fuse or melt your leads but if the battery runs down in a day or so you have a pretty good sized draw. The best tool to measure unknown draw is with a inductive pickup multimeter. Test lights in series will tell you there is a draw but it won't tell you how much. tmm
 
OK Rani, your "little red meter" is able to measure 10 amps, the Radio Shack as much as 30 amps

In the top right of that "little red" meter, the "green" section is "DCA" means "Direct Current Amps"

The smallest scale is 200 micro amps, and the largest is only 200 ma or milli amps. That is .2 amps, or 2 /10 of one amp. Not very much -- probably about what it takes to light your test lamp

BUT at the bottom right see the red bracketed setting which says "10A" You want to set your knob there, plug one probe into the "com" which means "common" and plug the other probe into the "10A" top jack. This will give you up to 10 amps of reading, so you start with that and see what you have

Now look at the RS meter..........

With the bottom knob set on the DC ma, you go by the brownish box on the upper knob, so the scales available are 3ma (milli amp), 30, and 300 ma (300 milli amp) which is only 100 ma larger than your red meter. These measurements are taken with the probes in the two right hand jacks

BUT notice that the top knob, all the way CCW, says 30A. That is 30 AMPS which is nearly as much as your factory A body dash ammeter can measure!!!

BUT..........

You must be very careful to get the two knobs properly set for 30 amp, IE the top knob at the 30A, and the bottom knob at "DC ma" AND THEN plug your probes into the LEFT two jacks on the meter, IE the far left being marked "30A"

Since you are "experimenting" I would try both meters and see what they say, then post back. If either reads more than 200ma or .2A then that is the limit of the smaller scales on the red meter. If either reads more than 300 or .3A then that is above the limit of the RS meter on the smaller scales.

By the way, my first digital meter I ever owned was that very model RS meter. Later I bought a much -hated B&K, until I found that Fluke worked so much better.

EDIT WARNING Be careful that when you have any meter set up for current readings that you do NOT connect the meter from a power source to "ground". Also attempt to determine if the current reading you wish to take is within range of the meter. This is why I suggest using a test lamp first, as you can get "some idea" of the current involved. If a large heavy lamp such as a dome, stop or tail lamp lights dimly, you don't have very heavy current there. With the same circuit, a "smaller" test lamp will light more brightly. But if a small test lamp lights fairly dimly as well, you can be assured there is not a large current flow. Most probably LESS (safe) that the 10A reading of your "little red" meter
 
67Dart all good info.... i am sure with all this good info... will help... BUT did he say what type of vehicle yet ?
 
it was starting to rain ...but this is what I got so far
 

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rrvolare said:
67Dart all good info.... i am sure with all this good info... will help... BUT did she say what type of vehicle yet ?
Click to expand...


fixed ^

and its a tortoise ......a 2006 ford Taurus ....its my adoptive mom's car ...but I am still using this to learn more about electrical ...I think the same method can be used on mopars with a drain somewhere and if someone has an aftermarket radio then it will have a parasitic drain.


The reason I used the red multi-meter ...I know a lot of people have the same meter, so if they are reading this thread ....now they know something new that their meter can do :D
 

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I think I read that under 0.1A parasitic draw is acceptable, for a vehicle that sees weekly use. A typical car battery is about 100 A-h, so after a week it would be down about 17%.

The 0.3A would be too much. That may be the load of a small lamp or a relay coil or two. Glove box, or trunk lights come to mind because when closed they cannot be seen as on. Another place to look is the fan relay, they often run with the ignition off. If the fan is inoperative, the relay may draw current with a defective temperature sensor.

Modern electronics should get the job done at much less, perhaps 20 mA or less. Owners manuals often call out a certain fuse to pull for extended storage.
 
this car is daily driven ....and the red battery is from another car and is known good but the yellow battery I had in there before was draining overnight. and most of the time it would start but with a weak "wirrrrrrrr ....wirrrrrrr click click wirrrrrrrrr vroom".....and the gauges would go crazy till it ran a little and then it would straighten out ....and a ten mile trip would charge it and it would start strong until night time again .....for the last week ....I didn't have time to spend with it so I would just pull the radio/dash lights/gauges /and dome light fuse and it made the test light shut off....then before leaveing in the morning ...put the fuse back in.

I didn't want to put a new battery without knowing if it was a problem with the car ....a new battery would mask the problem for some time but it wont go away till you get to the bottom of the problem
 
Knowing the fuse is a big help. Gauges and dash lights are typically key-on accessories. So that leaves the dome or other accessory lights. The radio is unlikely, if it still works, and takes the key to operate, the clock and setting memory take little power.

First thought would be a door, trunk, hood or glove box switch adjustment problem, that is keeping a light on, that is not visible. Sometimes the switches have plastic caps, when they fall off, the switches are no longer depressed enough, when panels are closed, to stay off.
 
I don't know how far away you are from a parts store, but if not to far, charge up the battery in question & take it & get it load tested if you can. However, if it drains it overnight with only .3a. draw that sure points to a weak/bad battery.

The draw does sound a tad high, How much draw does the alternator have?
 
I think .3A is a lot of draw. Hell I've got a 95 Olds which sometimes sits for 2-3 months at a time and IT doesn't go down. Maybe if I get ambitious I'll go see what the draw is on that thing.

Now if it was .03 (30 milliamps) I'd say, OK

I think you said you know what fuse this drain is on............so that might give you a clue.

Here's a couple of examples..............

The alternator output is always connected to the battery. Diodes can get "leaky" as well as many alternators have internal radio suppression caps (capacitor, condenser) which can get leaky

Radios / stereos may have the PA (power amplifier) transistors directly hooked to the battery line, and that may cause a drain when things "get leaky" or fail

There may be other stuff.........not sure what

Does this car have any aftermarket accessories you forgot to unplug, GPS, phone charger, etc?

How about aftermarket alarm, or "Lo jack" or other cell / tracking / etc. devices?
 
67Dart273 said:
I think .3A is a lot of draw. Hell I've got a 95 Olds which sometimes sits for 2-3 months at a time and IT doesn't go down. Maybe if I get ambitious I'll go see what the draw is on that thing.

Now if it was .03 (30 milliamps) I'd say, OK

I think you said you know what fuse this drain is on............so that might give you a clue.

Here's a couple of examples..............

The alternator output is always connected to the battery. Diodes can get "leaky" as well as many alternators have internal radio suppression caps (capacitor, condenser) which can get leaky

Radios / stereos may have the PA (power amplifier) transistors directly hooked to the battery line, and that may cause a drain when things "get leaky" or fail

There may be other stuff.........not sure what

Does this car have any aftermarket accessories you forgot to unplug, GPS, phone charger, etc?

How about aftermarket alarm, or "Lo jack" or other cell / tracking / etc. devices?
Click to expand...


nope ...I unplugged the phone charger in it and there is nothing else ....no alarms or anything silly like that...totally stock car
 
It doesn't have to be aftermarket radio to have a small draw. Factory radio memory, clock,, security systems, and more, are all common low amp draws. Newer the vehicle, more common these are. Even the ECU has a memory.
A battery can serve for start and run yet fail in amp storage.
 
I know I'm a little late on this but I would like to share how I check for draw and have done for years. Instead of measuring amps or milliamps at the risk of smoking a meter, I measure millivolts. Remember Ohms law. You are doing the same thing by looking at millivolts. I have a $5 little tool I made. It is nothing more than a 1.0ohm, 10 watt resister and a couple of alligator clips. Disconnect the neg. cable and hook up resister in line. Put your meter leads on either side of the resister and set your meter for DC millivolts or if it is an auto-ranging meter set to DC volts, it will measure millivolts automatically. I did a test on the '63. 0.0 millivolts just sitting with nothing on.(it has no radio or alarm, no nothing) Opened the door and 933 millivolts or .933 volts just from the dome light. I then tried it on my '08 Nissan frontier. 88 millivolts at rest. It has radio memory and a little red light that flashes on the dash like an alarm is armed.(it has no alarm). I then reached in and turned on the XM. 265 millivolts. Not a ton but enough to drain the battery. Tuned off the XM and then opened the door. Over 3,000 millivolts or 3 + volts. Dome and courtesy lights come on. Our rule of thumb at the shop was 100 millivolt draw or less was acceptable. The 10 watt resister was ok with the 933 mv draw from the Darts dome light but with the 3+ volt draw on the Nissan it started to get warm. But its like a sacrificial tool designed to protect your meter. You never run any amps through your meter. IMO, amp clamps are not very accurate at lower amps (milliamps) but work well with starters and alternators. This is just another way to skin a cat and what has worked for me. I am in no way dispelling any other input from this thread just sharing my experience's.
Larry
 

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To clarify what he is doing here, by using an external resistor, he is actually MAKING a low range current meter the same as is "in" your multimeter, except that by using an external resistor, it's almost impossible to damage the meter. "Good" meters are fuse protected

And to further clarify, when he says he measured "933 millivolts" because of the resistor, this translates directly to "933 milliamps" or .9 amps
 
67Dart273 said:
To clarify what he is doing here, by using an external resistor, he is actually MAKING a low range current meter the same as is "in" your multimeter, except that by using an external resistor, it's almost impossible to damage the meter. "Good" meters are fuse protected

And to further clarify, when he says he measured "933 millivolts" because of the resistor, this translates directly to "933 milliamps" or .9 amps
Click to expand...
Thanks for helping to clarify. I just wanted to throw out my approach. Both of my meters are fused or shunted, and like you said most "Good" ones are. But with this cheep set-up I don't have to worry about buying or replacing fuses. Works for me and maybe for someone else as well. Thanks 67Dart273! I was waiting to hear from you. :cheers:
Larry
 
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