help - where is my voltage

[KeithD]

I seem to have wiring problem which is getting worse and which is flattening the battery. So much so it has killed a battery in 3 months, and no amount of recharging will recussitate it. Wont even start off the charger now (70 amps). I have an ammeter. In words of one syllable could someone advise what i should do to try to track down where the fault is. Once isolated if I cant get at the offending wire, I can just put an isolation switch in for when it is parked. Guess I could do that for the whole system, but would rather not. Thanks.

[Mike Hippert]

1: Hook up your amp meter to the red lead on the Battery.
2: Measure the Current.
3: Pull fuses until the Current goes down.
4: Add cutoff switch, or follow the circuit further back until you find the bad circuit.


Once you check step 2 let us know what you get (you can kind of ruff calculate how long a battery will last). This is a common problem with Defenders so don't be surprised if you cannot find the problem.

[KeithD]

Thanks Michael - I will try and see what happens.

[KeithD]

Mmm. As I suspected. I get a reading from the battery of 10.26 volts. how can pulling the fuses cause any change? I must be doing something wrong or not using the right setting on the ammeter. I did pull all the fuses anyway and no change on the readout. More help please.

(later) Ok I am confusing current and voltage (Doh!) but the ammeter manual is just not clear enough for me, and has all sorts of no more than 10 amp warnings. I really need babying through this.

[KeithD]

I think what you may be suggesting is:

remove battery terminals

attach red cable on meter to red battery lead.

attach black cable to ground

set multimeter to ? - ohms or volts? which jack on multimeter

start pulling fuses.

see when things change

I'll keep trying - thanks for the help.

[Tom Morrison]

Sounds to me like your battery is toast. I had the same problem with my Optima yellow top, but it would discharge in just over a month. Problem would get worse as it got cooler.

With the key off, the drain on the battery should be way less than 10 amps, should be less than 1 amp I would guess, unless there is a fault. or an after market accessory that is wired into an always on circuit like an inverter.

You could disconnect the pos terminal and put the battery on a fast charge for a couple of hours. If it won't turn the starter after that (low voltage that drops when the starter is engaged) I would very much suspect the battery is bad.

BTW, I'm running a 300 TDI in High River

Tom

[KeithD]

Thanks Tom - nice weather today eh?

300 TDi - lucky you - I will check out your bio after this (and lunch)

the battery is no good for sure but I am pretty sure also that the car has caused this - the last battery only lasted three years, this one 3 months. I'll get half back on it from Can Tire (actually it cost me nought as it was within free replacement period).

I am doing some more checks this afternoon and will report.

[Mike Hippert]

1: Your battery should not read less then 12 volts. If it does then it is drained real low or dead. If it reads less then 11 volts then it is toast.
2: for most DMMs (digital multy meter) to measure current you have to wire the ampmeter in line with the circuit. to do this:
a: disconnect the positive (red) lead of the battery.
b: connect the red lead of the DMM to the + post on the battery.
c: connect the black lead of the DMM to the red battery cable.
d: connect the black lead of the DMM to the COM port on the DMM
e: Connect the red lead fo the DMM to the 10 amp MAX Fused port of the DMM.
f: turn the dial of the knob on the DMM to 10 amp scale.
g: measure away
Disclamer: Different DMMs have different names or tags on them, some are not fused, if yours is not fused then I would recommend putting a 5 amp fuse inline with what you are measuring so you do not fry your DMM.

This should be good to get you going. You may need a new battery to do measurements as yours sounds like it is toast.
If I am unclear on something just reply because i am often very unclear.

[KeithD]

Thanks again. well the leakage is only 1 microamp and removing the fuses makes no difference to this. It is the lowest amount the meter can read so it cant be significant. The alternator is outputting a pretty stable 13.5 volts so that is OK. May just have been unlucky in getting two dud batteries. I will change this one and see how the next one does. After a drive the battery's output increased from 10.5 to 12.2 volts but still not enough kick to turn the engine over.

I will try to get some sort of isolator just as a precaution.

[Tom Morrison]

Hey Keith,

1 uA seems low to me. I think the clock would draw a bit more than that. I wonder if maybe the fuse in your DMM might be gone (assuming it has one).

I am out of town at the moment, I am headed back Wed. I'll follow up when I get home. One thing I wonder about if there is a bit of a surge current when the initial closing of the circuit happens.

The tech. reason is that if the load has much capacitance in it, it is like a short circuit for a split second when the power is first applied.

Tom

[Mike Hippert]

I'm with Tom 1 uA is too low something is not right.

[KeithD]

we did the same test on my mates Ford Tempo (he has a series IIA so don't be too hard on him...) and that showed no leakage at all. We also did test with one of those light bulb things which also showed no leakage. Other tests with the meter were fine so I went out and got a new battery free again - one month within 3 year free replacement period, thank you Canadian Tire. Will install later today and see what happens. No fuse in the meter btw. I am still suspicious that I could have had two bad batteries in a row. and Can tire said very unusual.

any other suggestions - how can I test for your capacitance theory Tom?

[Tom Morrison]

Hey Keith,

Just got round to testing the current drain on my 90.

With a battery voltage of 12.6 using the 10 Amp circuit on my meter (Fluke 83 (industrial grade)) It showed .017 Amps.

Interesting thing though my clock would quit working when the current was going through the meter. Sorry for the techy lingo, but this told me that the voltage drop across my multimeter was enough to stop the clock motor.

Tried the same test using my 400mA circuit and I got a reading of approx. 30 mA (0.030 A) and the clock continued to run.

As my 90 no longer has an ECU in it, and there is a problem with the always on circuit to my radio (The voltage isn't getting to the deck so it has no memory and therefore no current drain) The only thing I can think of that is drawing power with the key off is the clock.

As such I am sure, that unless you aren't running anything with the key off, your results of 1 uA are in error.

The way to confirm that your meter is working correctly would be to connect it in series as Mike described with a known constant and reasonable current source of say 50 to 200 mA. You could rig this up with say a battery and about a 1 Kohm resistor .25 W with a car battery that should give a current of around 130mA. You could get it at Radio shack.

All that said (probably as clearly as mud), I could take a look at it for you, for the price of a can of ale or two.

Cheers, Tom

[Mike Hippert]

Fluke 83! I have the same meter! I bought it years ago and it still works great! I guess great minds think alike!:grin

[Tom Morrison]

Aye,

Fluke makes some really nice test equipment, had mine for years as well. The other week I was playing around with it to determine the external power source current draw of my GPS and I managed to blow the 400 mA cct fuse ($15.00 touch). I wanted to see how much current a solar pannel would deliver to a rechargeable battery without the LED I had wired in series. So I tried to by-pass it with my meter.

Doh! Carefull who you compare yourself to ;)

[KeithD]

I have some boddingtons in my fridge usually Tom!

[Tom Morrison]

Hey Keith,

I'm more a Kokanee drinker, but I'm not that fussy.

I've got a fair bit of spair time on my hands these days so give me a call and we'll put this issue to rest.

You can reach me at 606 1477

Cheers, Tom

[Mike Hippert]

Hey! don't forget to let the rest of us know what you find.;)

[Tom Morrison]

Will do Mike! ;)

[KeithD]

Thanks Tom - I have left a message. would like to see your TDi.

[Tom Morrison]

Got over to Keith's this afternoon and we had a look at his rig's battery drain. Turned out it was drawing about 270 mA. By my guess, this could drain a battery in about 2 weeks if the vehichle is not used.

We went through all the fuses on the interior pannel, none was responsible for the significant drain. The one possable culprit I think, is the aftermarket cd player that is wired in such a way that it is able to play without the key being on.

Unfortunately we did not have the time to pull the deck to disconnect it to verify my theory. I think Keith is going follow up on that.

While we were at it, we did the same tests with Keith's meter (low end auto store type). It gave a reading of 170 mA, apretty significant difference. Pretty sure my Fluke is the one to trust though.

Cheers all, Tom

[KeithD]

My thanks to Tom for checking it out. Don't know for sure it is CD player (can the memory really be pulling this much juice? - hard to think something that small could kill such a big battery in a couple of weeks - surely a digital watch carries just as much memory, and goes for years on a button battery. But as none of the fuses have any affect on the drain hard to see where else the blame can be. may be simpler tyo have a battery isolation switch and just live with the cd/rasdio losing its memory. anyone have any idea how/where to get such a thing?

Nice to hear a 300TDi in my driveway. Before it started up I asked my son 11 year old if he knew whay the vehicle was.
Its a NAS90 he said, proud of himself. started it up. Hey, that's a diesel?!

I have put the charger on 2amp setting and will charge it very few days for a while.

[KeithD]

well I have fitted the switch - Joseph Pollak Master Disconnect - from Gregg Distributors here for about 18 bucks US. Very simple job and works a treat - drilled a hole through the battery box (passenger side on my RHD vehicle) and wired it up. Least I can now use the vehcile without having to charge the battery all the time. Remains a mystery where the leak is but least the vehice is fully usable now (apart from needing new drums (on order)) . Kind of desireable to have a battery cut off switch anyway, and the job is so easy we should all do it. I had a fuse box fire once and could only stop melt down by pulling the leads off the battery. a switch solves the problem.

[Toddco]

I have left my GPS on, Radar detector on, the clock that allways runs in the dash, radio memory, and had the alarm on for 3 weeks, while it was parked at an airport and it started right up. I would not give up on the search. You have to have a small short somewhere, something is eating the juice!

[Tom Morrison]

I'll stand by my diagnosis of the aftermarket cd player. Alberta gets more than a little colder and for a lot longer than Tennessee, and that takes its toll on car batteries.

We pulled all the fuses and the alternator wires, and saw no change in current. This left the cd player, or a short that was after a 44 ohm ( 12 / 44 = 270 mA resistance and before any of the fuses we pulled.

Depending on the size of battery you have and the type of GPS, detector and alarm system, your claim of 3 weeks sounds reasonable to me as long as it wasn't -20 C.

I know with my deck, there is a wire that is supposed to be connected to the always on circuit, but there is also a wire that is connected to the ignition switched circuit as well.

When we reconnected the ground to the battery with the key off, we could hear the motor in the deck start up and then stop. So the deck was doing more than just keeping memory set. The other circuits that sense and load a cd were powered, and probably the 270mA current sink.

I could be wrong, but I'd bet a beer I'm right...

And being a Scot, I hate losing...

Booze:grin

[KeithD]

well the cd is taking some juice for sure, and the clock, but there must be a short too. I just think it is so much work to find it. I suspect it may have something to do with the CDs wiriing and that is where I will look first - all the wires are so crammed in there it aint healthy. getting at all this stuff is a real PINA though.

[Tom Morrison]

Hey Keith,

I can't beleive we lost at Culoden to you guys :grin

Actually I was looking at a car audio forum, and came across a couple of related posts. According to them, anything over 25 mA is a "parasitic" draw(that is a bit low in my opinion) and your setup with the head unit always fully powered will drain a battery. I would test it on my unit, but getting at my unit isn't easy either.

I have a GPS that draws between 140mA and 200 mA so it seems very reasonable to me for head unit to draw the same or more.

Anyhow, I was out of out of province the last couple of weeks, but should be available if you guys head out some weekend. By all means drop me a line.

Cheers, Tom