Sevenman's TVR (was SAAB) Blog

December 31, 2006

Mondeo Voltage

Filed under: Saab — Administrator @ 4:17 pm

I used my gf’s Mondeo for a comparison test, again using the cigarette lighter for a voltage measurement.

After starting, voltage hit 14.55 volts, and by the end of a 20 min run had settled to 14.2V running and 14.15V at idle.

Restarting was at 14.0V, but then climbed back to 14.3V, and then subsided again to 14.2/14.15V when stopped.

Headlights dropped the voltage by ~0.1V

Using headlights, front and rear heated screens and blower on maximum dropped to 13.6V, similar to my tests.

It looks like this car keeps a much higher charge all the time than mine, with my best voltage being less than the lowest normal voltage when the Mondeo is warmed up.

A 9000 from UK Saabs has been tested, and found to produce :

“Idling on the drive, with a reasonably charged battery, it was sitting at 14.05V. With the headlights on, it went down to 13.98V.”

Which is probably close to what mine does at startup.

Perhaps my current battery is very sensitive to inadequte charge, or something else is going on which I haven’t thought of yet…

Contacting the battery manufacturers is my next step…

December 30, 2006

Voltage update

Filed under: Saab — Administrator @ 12:08 pm

Just took the car for a drive using a cable from the cigarrette lighter attached to a multimeter to read voltage.

The battery voltage when the car had been left overnight was 12.3V. I attached it to the charger which took a few mins to bring it up to 15v before it dropped to the 13.6 maintenance charge.

On starting, voltage dropped to 9v and it started easily.

At idle after starting voltage was 14.1

While driving with normal driving lights and the climate control running it was 14V, dropping to 13.9V at idle.

Adding rear-screen demister, both heated seats, full beam and air-con running flat out dropped the voltage to 13V.

We stopped the car for 15 minutes and when restarted voltage was 13.7 volts.

Over the 15 min drive home this voltage crept up to 13.9V.

Switcjing from daytime running lights (dipped beam) to sidelights made the voltage drop by around 0.05 volts.

The in-dash voltmeter consistently under-read the real voltage, more so on the drive back, possibly confirming my theory that something heat-related is affecting the system.

December 18, 2006

Not charging enough?

Filed under: Saab — Administrator @ 8:50 am

The car spent has now spent over a week with the battery in and it works fine.

Over the 6 days when it was connected and not driven the voltage dropped was 12.7 to 12.4 volts.

It started perfectly, and terminal voltage was 14.3V at idle immediately after starting.

The car had a number of 30min+ drives on Saturday and Sunday, which I would have though was enough to fully charge the battery.

After I washed the car on Sunday I connected the battery charger, and it took about 1 hour to raise the voltage to 15v at which point it drops to a 13.6 holding voltage.

Does this mean the battery is only at 90% charge when the car is driven? If the battery is never becoming fully charged through driving this could be a potential cause of sulfation and battery failure. Although if it had sulfated, would it have recovered fully as it now seems to?

December 10, 2006

Can’t find anything wrong…

Filed under: Saab — Administrator @ 4:15 pm


I did a bit more research on modes of battery failure and none of them looked that likely.

I managed to recharge the battery this time, and it seemed to charge to the proper voltage and stay there.

I then started doing some tests connecting it to the car. The first couple of time I connected and disconnected there was a current drain of 0.5 to 0.7 amps.

when I had an assistant ready to start pulling fuses, the drain dropped to 0.03 amps and has stayed there ever since. The battery has been in the car for a couple of days now, and all seems to be ok. The voltage drops to 12.6 volts overnight which seems perfectly acceptable.

If I can’t find a fault, I can’t fix the problem! I will be keeping a daily check on voltage to see if I can catch it when a problem occurs.

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