I'm having trouble starting my car and now think I might have two separate but related problems: something draining the battery and a dodgy starter. Right now I'm trying to figure out the battery drain issue but am technically challenged (though willing to learn). I've read through many of the threads here and think I get the general concept that I need to measure the draw on the battery when the car is off and then remove fuses to figure out what is causing the abnormal draw. I've got a multimeter (and am armed with a vague sese of what it does) and have two questions:

1) how specifically do you measure the power being drawn from the battery? and

2) what is the 'normal' draw (for the clock and whatever else 'normally' draws power from the battery whilst the car is resting)? Presumably, one needs to know this in order to figure out whether something abnormal (a stuck switch, hood light, etc.) is draining the battery?

(background: I had the battery replaced about 6 weeks ago, worked fine for about a week, then dead, recharged fully, ran for about a week,then dead, recharged, went to Kenya for 10 days, came back, started fine for a couple fo days, then dead (again)

 

Do you have a dvm ? A digital volt meter ?

 

I'm not an EE but delve further into electronics than I should on my cars. You're on the right start to check your voltage and what variations as you see as you pull various fuses to narrow down where your problem may lie. Despite what I consider to be a pretty good skill set for automotive electronics and first rate equipmet what I may suggest is something else. There are excellent electronic troubleshooters out there who can cut to the chase a lot faster than most of us backyard mechanics. I would suggest you go to one of them. On one of my "British" cars I had the same problem,--battery drain unless I drove the car at least every 3 days. The shop I went to found the problem in one hour. To me, it was absolutely worth the $60 or whatever it was.

 

There's quite a few good threads on this subject:

https://rennlist.com/forums/964-foru...ent-draw.html?

is one. Do a search on "Current drain" or "battery drain", etc...

Basically, you use a voltmeter set to microamps to detect the amperage drain by disconnecting the negative lead from the battery and then connecting the volt meter in between the negative battery lead and negative battery post. You then can sequentially pull each fuse and relay to see if something is causing current drain. If that doesn't detect anything then likely you have and unfused aftermarket circuit like a car stereo or alarm causing the problem.

Usual suspects are door light switches, glovebox light switch, decklid switches, etc...

Best of luck!

 

This statement tells me you do not have a serious battery drain. You went 10 days idle, and the battery when you drive it. Do the simple maintenance thinks first. Clean both battery terminals and the ground connection. That fixes the problem at least half the time.

To troubleshoot, you need a decent digital DMM, which costs about $35. Simply clip the two leads on the battery terminal and read the voltage. 12 to 12.5 is about right for a full battery. With the engine running at idle, and the headlights on, the voltage should read 13.8 or something very close. If cleaning the terminals does not work, I think you will quickly find you need an alternator. Read up on the DMM instructions how to read current draw. You need to disconnect one battery lead. Keep a couple of spare DMM fuses handy if this is your first go at measuring current draw.

Good luck!

 

Thanks for the responses (and Edgy1 I'm sure you're right about having qualified experts work the problem but I'm sort of using this as an opportunity to learn a bit more about how the car works. This seems like a problem that I can diagnose without causing much harm and that I'll learn something useful in the process. My own psychosis I guess!) and some progress has been made.

With a couple of friends and with the help of Adrian's book we were able to measure the draw and it seems fine. Measured about .39 which seems to be well within range (The after-market stereo seems to draw about .05 which I guess makes sense. We pulled the fuses of the usual suspects while we were at it and didn't find anything unexpected.)

We then went thru the procedure suggested in the book for testing the alternator and Springer3 may well have made the right prediction. Not sure whether the results are conclusive or whether the meter just isn't that precise but here's what happened. Battery was at 12.7 v. During start it did not go below 9 (good according to Adrian). At idle around 1000 it was around 13 and it was over 3000 before it got to the mid-13s but as the throttle was increased it never went above 13.6 (the book says it should get to 13.7 at around 1800-200) and according to the guys looking at the meter the voltage tended to go DOWN as throttle was increased above 4000. So now I'm not sure whether that's a useful 'finding' or is it just an imprecise meter?

The battery terminals/connections are clean (the battery is new).

Any other thoughts?

 

What type of meter are you using (brand and model)? Are you reading 0.39 amps? That is quite high. I recall mine was at 0.108, and it thought that was too high. I can go a month and still start, so your 10 day trip to Kenya was about the max with your drain.

Voltage readings sound like a bad alternator, but I would get an expert to check before buying a new one.

 

Radioshack '29-Range Digital Multimeter' (22-813). Was about $30. I followed the procedure in the Adrian's Streather book (it says in there that .3 is ok?) but don't really have any intuitive understanding of what I'm doing (so maybe I'm doing something wrong?). I have an aftermarket stereo which appears to draw about .5 by itself (that is to say the meter drops to .34 when I disconnect the stereo fuse) and a rudimentary alarm system but nothing else non-stock that I'm aware of. I did have all kinds of problems with the electric seat (driver's side) and it's now disconnected. I could go back and systematically pull each fuse and figure out exactly how much is drawing from where. We stopped after looking at the ones specifically referred to in the book.

I also ordered (should arrive today) a voltmeter that plugs into the lighter. From my reading here and over at the pelican forums it seemed that that would give me some sense of what's happening with the alternator/recharging process?

Equus 3721 Battery and Charging System Monitor http://www.amazon.com/gp/product/B000EVWDU0

 

Your meter is fine, but cheaper ones like that can get fooled reading DC volts if there is AC noise caused by failing diodes in the alternator. It should work just fine on DC amps to hunt for leakage.

Here is how to tell how long your battery will last:

Full charge on the battery is about 80 amp-hours (one amp draw can be sustained for 80 hours, 2 amp draw for 40 hours, 4 amp draw for 20 hours, ect). I don't think the car will start after the battery 3/4 discharged, so usable draw is about 60 amp-hours. If you are pulling 0.39 amps, you can last only 6 days before the car will not start. I don't see how the car started after your 10-day Kenya trip unless the draw declines with time. Can you check after the car has sat overnight with the key off? That might explain the discrepancy.

Get the draw down to 0.1 amps, and you can last 600 hours (25 days) before the car is a non-starter. My car draws 0.1 amps, but I made the measurement after the car sat overnight. I have not had a not-start issue since I drive the car at least once or twice every week.

Your alternator voltage is low, but still in a range that should keep the battery charged. Definitely check with a more accurate meter before tearing into the alternator.

Good luck

 

I got the voltmeter that plugs into the adapter and drove around for a while. It never got above 14. When the engine is off the battery is at 12.7. In neutral at around 1000 rpms it's in the low 13s. It stays in the mid-high 13s no matter what the rpms. Similarly when driving. There doesn't appear to be any correlation between rpms or speed, just stays between 13.5 and 13.8.

I'll go thru the process of checking the amps and taking out fuses more systematically as per your advice above (to see if I can get the draw lower) later this weekend. Thanks for your help. If you have any thoughts on the above re-charging scenario let me know.

 

Use your dvm on another car so that you can see what it reads on a known good car .