generator charging/voltage drop test

Post by **misha** » 08 Feb 2009, 19:39

Voltage readings on battery terminals when i start my car in the morning are 13.9-14v at idle and 13.8v with headlights and heater blower at 2000rpm.
After 30 min of driving,with headlights,defogger and blower at 2000 rpm it's 13.3-13.4v???At idle 13.2v!

Is this normal?
I performed voltage drop test on negative side(-batt.terminal and generator housing)with headlights,blower and defogger at 2000rpm and it's 0.0v.So that's ok.
But,on positive side(+batt.terminal and generator b+)with headlights,blower and defogger at 2000rpm it's 0.4-0.5v,sometimes 0.6v!So there's some resistance!
Do i need to replace the positive cable?
I checked it from b+ to starter and from starter to battery + and there's no corrosion.
Thanks!

Post by **MadeInJapan** » 08 Feb 2009, 21:09

Seem you might have a parasitic leak. Check your glove box to see if it's closing all the way to turn off your light. This is a common problem as the car ages and the glove box door doesn't shut good enough to turn the light off.

Post by **BEJinFbk** » 09 Feb 2009, 00:00

The ground leads are every bit as important as the positives.
Check Everything.

Post by **misha** » 09 Feb 2009, 10:02

As i wrote:
voltage drop on negative side 0.0v.
voltage drop on positive side 0.5-0.6v.
Should i replace positive cable or is it something else?
Thanks!

Post by **MadeInJapan** » 09 Feb 2009, 14:14

I really don't know the answer to that...I would hate for you to replace the cable and find it's something else.

Post by **misha** » 09 Feb 2009, 14:20

Ok,thanks.

I'll drive the car to electrician.

Post by **misha** » 24 Nov 2009, 17:55

Time for update:

I added one more cable from extra connector at positive battery clamp to starter without removing or disconnecting existing/stock one.

Now i have 14.2v at idle without any load & 13.9-14v with load(headlights,heater blower,stereo),when i add a defogger voltage is 13.8 at idle & 13.9 at 2000rpm.

Voltage drop at positive side now is below 0.1v...before was 0.6v!

I did this job without disconnecting battery terminals(some of members knows why i did it)...and yes i was very carefull.I wrapped the tool i worked with with a tape and was wearing a thin latex gloves.

Before i started this job i had check engine light on for about 4 years because of(as much as i know)bad air pump & sas valve.

After i completed this job and started a car to check charging voltage,my check engine light went off!!!

...and didn't came back all day.

First...i thought that the bulb was blown,so i turned the engine off to see is it on with the ignition in position II...YES it is.I started engine again and no check engine light!!!

....but it could be back every day,because of a bad air pump.

Mission completed!!!!

PeteB · Post by **PeteB** » 18 Oct 2017, 13:19

I'm an EE with experience in reliability analysis and thought I'd throw in my 2 cents.
There are what we call gas tight and non-gas tight connections, gas tight are highly
reliable, non are not. A crimp is not a gas tight connection, it will oxidize raising the
resistance, then get hot and corrode more. I would open the crimp clean it with a
solvent, brush it with a wire brush or sand paper, add non-acid flux and solder it
with something like a Weller gun (+200W) which makes it a gas tight connection,
close the crimp, solder it closed for more contact area.
Obviously remove it from the studs so that the heat does not go into the equipment.

Post by **abscate** » 20 Oct 2017, 04:36

Old thread alert, but even more relevant as these cars age.

The cables themselves can develop resistance away from the connectors, and one can detect this with an IR gun ( temperature change) or just replacement, of course