Weird battery volts, 2v less via chassis

[Danglerb]

Problems with my feet had both 928's parked for a couple months, finally got around to checking them and the US 83 has some weirdness.

Battery is a new Bosch, fully charged and disconnected with a battery switch when parked. Now measured 11.98v at the battery posts, but a bit less than 10v across the battery switch (through the chassis and CE panel etc).

Meter used is my Solar BA5 battery tester, which I am not sure about in terms of input impedance, but would be surprised if it wasn't megohms, so any current through the meter should be tiny, a few ma a most, not what I would expect to see a 2v drop from.

Car started and runs fine, no doubt the troubleshooting will be entertaining.

[Mrmerlin]

find another car and do a similar test with your meter,
then use another to do the same test,
your meter may have a weak battery

[harborman]

What does the car volt meter read? Is it normal? I prefer to use a volt/ohm meter myself, not one limited to battery testing. You can pick up a cheap one at Lowes but better ones are like a Simpson 260 or ones made by Fluke.

[Danglerb]

I actually have both a Simpson 260 and 360 (VTVM), Solar BA5 has no battery, so first thing will be checking with something else.

Volt meter in the pod is a very loose suggestion on the actual voltage.

I plan to give it another look tomorrow, and with luck put a 100 miles or so on the 85 Euro and get it smogged again.

[harborman]

Originally Posted by Danglerb

I actually have both a Simpson 260 and 360 (VTVM), Solar BA5 has no battery, so first thing will be checking with something else.

Volt meter in the pod is a very loose suggestion on the actual voltage.

I plan to give it another look tomorrow, and with luck put a 100 miles or so on the 85 Euro and get it smogged again.

I was just wondering if you noticed a change on the dash meter. I know it's not that accurate.

I found the braided battery cable on my car to be bad. It had a voltage drop inside the crimped end where it attaches to the frame. Also, I cleaned the motor to frame ground. Something you might check.

[Danglerb]

I bought new heavy braided cables from Waytech, overpaid thanks to nasty shipping costs, and put top quality 3m adhesive shrink on them. The shrink set hard so the bend barely fits in the battery box, plus its a few inches too long, and again not very flexible, but I get no drop across the ground strap.

I was measuring with the battery disconnect open, so no reading on dash meter. Car started normally and dash meter looked normal.

Didn't get to check it this week, maybe early next week.

[Alan in AZ]

Originally Posted by Danglerb

I was measuring with the battery disconnect open, so no reading on dash meter.

Why? this is not a very logical measurement to make

You are completing the circuit with your meter - which is indeed high impedance, this makes this a virtually meaningless measurement.

Measure a different way - keep the battery switch closed and measure from the chassis to positive post

Alan

[Danglerb]

Few have accused me of being logical.

[harborman]

Originally Posted by Danglerb

Few have accused me of being logical.

Funny! When I had a problem with this, I measured the voltage from the jumper terminal up in the engine compartment to chassis ground. It showed about 10 volts. I measured across the battery, 12.56 volts......hummm. I jumpered the braided ground cable.....12.56 volts! The darn cable looked new but......inside that crimped end it was all powder.