Strange voltages and parasitic load ?
- Thread starter eljefino
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After being a mechanic for years, and owning older BMWs, I've come to the conclusion that their wiring is marginal.
So, clean all the power and ground cable ends [not just the battery]. I'd put in a larger diameter cable for the main ground and alt. power lead.
Make sure that your fuses are clean and tight.
I'll bet you'll see an improvement.
So, clean all the power and ground cable ends [not just the battery]. I'd put in a larger diameter cable for the main ground and alt. power lead.
Make sure that your fuses are clean and tight.
I'll bet you'll see an improvement.
Not sure it adds anything here, but I once had a problem where my tach was fluctuating with the instrument panel dimmer switch. Manufacturer said radio frequenty interference and recommended I run the ground for the tach directly to the battery. It worked. Apparently the dashboard metal understructure was not a good ground. But does a BMW use the frame and body for the electrical circuits or do they like the Japaneese run two wires to everything?
I fought electrical problems in my truck for most of the 29 years I have owned it. Even while still fairly new, some things were flaky, the gages in particular. It also tended to die at times. It was getting worse and worse a few years ago. Finally, I let it set and idle until it quit. Then I started gently probing the electrical connections. I found I had voltage going into the fuse box, but not at fuse holders, not even the hot side. The fuse holders were riveted to the buss the wire from the battery was connected to. I took everything apart and soldered all the connections. It has run better since then than it has for a long time. Perhaps the infamous Honda main relay is the same sort of a problem.
So look for any riveted or crimped connections and solder them.
So look for any riveted or crimped connections and solder them.
As a general rule, a 50mA draw is considered the upper end of "normal". I would not worry about a 50mA draw as long as the battery is in good shape.
EDIT: Forgot to mention- Cars with electronic modules don't like to have their power interrupted. It can take as long a 15 minutes for certain modules to sleep. Checking power draw immediately after restoring power (via your ammeter) is sometimes misleading.
EDIT: Forgot to mention- Cars with electronic modules don't like to have their power interrupted. It can take as long a 15 minutes for certain modules to sleep. Checking power draw immediately after restoring power (via your ammeter) is sometimes misleading.
My 1988 Ford Mustang draws 25mA--it has a Sirius tuner and a trip computer from an '83 T-bird in it, as well as the EEC-IV backup memory and an AM/FM/CD player from a Mazda Protege (it fit and matched the dash lighting).
If you don't drive the car much, get a solar charger. Look on Ebay for the VW ones--they put out about 2.5 watts.
If you don't drive the car much, get a solar charger. Look on Ebay for the VW ones--they put out about 2.5 watts.
JHZR2
Staff member
The ammeter readings were afer the car sat overnight.
uggh, I did start it for some reason, but shut it right off... Maybe it was before I did the test (?) anyway, thanks for the replies!
Things must have slept or something, as what was 1.04V right after shutoff was 0.55V after ovrnght...
Thanks again!
JMH
uggh, I did start it for some reason, but shut it right off... Maybe it was before I did the test (?) anyway, thanks for the replies!
Things must have slept or something, as what was 1.04V right after shutoff was 0.55V after ovrnght...
Thanks again!
JMH
The thing's 15 years old ... it's like an old dog; if it gets too sick, you take it out behind the barn and shoot it !!
P.B.
P.B.
JHZR2
Staff member
Hi,
My 91 BMW 318i has an issue with its service interval computer, that caused my tach and MPG meter to stop working. Ill be fixing it soon, but it prompted me to look a bit more into the electrical system.
I checked voltage at the battery, and with the key off, had 12.39V, and with it on, 12.13V. This is a bit too low, right? I know it is charging properly, as with the car on, I get 13.68V.
The strange thing is that at a number of fuses, I got 1.04 V (and when I checked them again today, noted that I had 0.55V at them). I thought this was a potential issue, but did a parasitic load test and found that it is not an issue that these voltages are liek that. All the same, why would I have a very low voltage at a few circuits, which then go to the proper 12.xxV when the car is on?
OK, now, parasitics... how much parasitic load is considered normal?
I found that my car has 50.4 mA parasitic load w/ trunk light disconnected, and everything off (the battery is in the trunk, thus why I had to disconnect that light). I found the following:
-Amp draw @ battery = 50.4 mA
-Remove fuse 4,5,6 and 12 (these fuses were the ones where I saw the 1.04 or 0.55V) = 50.4 mA
-Remove fuse 10, 21 only = 13.3 mA
-Remove fuse 10 only = 50.4 mA
-Amp draw for keyless entry (atached directly to battery) = 8.7 mA
So, the stuff on circuit 21, which includes the glove box light, flashlight (dont have), key and seatbelt warnings (only ignition key one works), interior lights (only have the two above the rear doors), radio memory, luggage compartment light (disconnected for test), active check control (dont have), SI, OBC (dont have), fuel delivery, tach/fuel economy gauge, digital clock (dont have), Multi function clock.
So it seems that between the multi-function clock and the radio memory (and whatever else on fuse 21 might have a memory, etc), I pull 37.1 mA. Is this high? The whole rest of the car only pulls 4.6 mA (considering the keyless takes 8.7), which isnt bad.
I should extend to say that in the last 4 months, my car has sat 4 times for a month at a time, and the battery was A-OK when I returned, and the car started, so this draw seems OK - but is it high, normal or low in the big scheme of auto operation?
Any comments, ideas or suggestions???
Thanks again for all the help,
JMH
My 91 BMW 318i has an issue with its service interval computer, that caused my tach and MPG meter to stop working. Ill be fixing it soon, but it prompted me to look a bit more into the electrical system.
I checked voltage at the battery, and with the key off, had 12.39V, and with it on, 12.13V. This is a bit too low, right? I know it is charging properly, as with the car on, I get 13.68V.
The strange thing is that at a number of fuses, I got 1.04 V (and when I checked them again today, noted that I had 0.55V at them). I thought this was a potential issue, but did a parasitic load test and found that it is not an issue that these voltages are liek that. All the same, why would I have a very low voltage at a few circuits, which then go to the proper 12.xxV when the car is on?
OK, now, parasitics... how much parasitic load is considered normal?
I found that my car has 50.4 mA parasitic load w/ trunk light disconnected, and everything off (the battery is in the trunk, thus why I had to disconnect that light). I found the following:
-Amp draw @ battery = 50.4 mA
-Remove fuse 4,5,6 and 12 (these fuses were the ones where I saw the 1.04 or 0.55V) = 50.4 mA
-Remove fuse 10, 21 only = 13.3 mA
-Remove fuse 10 only = 50.4 mA
-Amp draw for keyless entry (atached directly to battery) = 8.7 mA
So, the stuff on circuit 21, which includes the glove box light, flashlight (dont have), key and seatbelt warnings (only ignition key one works), interior lights (only have the two above the rear doors), radio memory, luggage compartment light (disconnected for test), active check control (dont have), SI, OBC (dont have), fuel delivery, tach/fuel economy gauge, digital clock (dont have), Multi function clock.
So it seems that between the multi-function clock and the radio memory (and whatever else on fuse 21 might have a memory, etc), I pull 37.1 mA. Is this high? The whole rest of the car only pulls 4.6 mA (considering the keyless takes 8.7), which isnt bad.
I should extend to say that in the last 4 months, my car has sat 4 times for a month at a time, and the battery was A-OK when I returned, and the car started, so this draw seems OK - but is it high, normal or low in the big scheme of auto operation?
Any comments, ideas or suggestions???
Thanks again for all the help,
JMH
You should consider adding some extra ground straps, between places like the alternator, head light buckets and other power loads and back to the engine block which should have an extra ground right to the battery. I went through this with an Audi. Their electrical system is just terrible. Before adding ground straps I had problems with the tach and other gauges. I tried cleaning connections and making everyting perfect. It finally progressed to the point where the alternator was being fooled by open grounds and putting out way too much current. It fried several batteries and a couple of alternators. The ground straps fixed everyting, including the wondering gauges. I also had to wire a seperate complete circuit for the fuel pump, with it's own inline fuse. Some of these German cars are rolling short circuits.
That's because of the ****** wiring insulation they used on underhood wiring harnesses.
It breaks down due to the heat. Road salt does the rest.
It breaks down due to the heat. Road salt does the rest.
.... and lousy German wiring, too. Some German cars are self propelled short circuits. The Audi dealer could not keep my Audi safe from electrical gremlins. They were good about replacing batteries and alternators but until I added all the ground straps, it was a pain keeping that pile running. They copied the fix for others that were having problems. At least that Audi was fun to drive, while it was running.
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