The V8 Owners Forum -

Hi,

Had my Chimaera just 3 days, and it already packed up on me! Wouldn't start in work's car park this evening and had to call the AA. Flat battery.

Will be buying a new one, but it seems a bit odd: it had plenty of juice in the morning and previously, with no signs of getting tired. I hadn't left anything on, except the radio is a bit iffy in that when you press the off button once it comes up with an error message and you have to press it a second time to switch off. I must have forgotten to press it the second time, because the LCD display was still on when I returned to it after work 8 hours later. But I can't imagine just the radio LCD flattening the battery in that short space of time.

The electrics were going crackers though: the indicators kept coming on, and then switching themselves off. I'm wondering if maybe they'd shorted out during the day -- it's been pissing down all day here -- and they'd flattened the battery, although all the fuses and relays in the passenger foot well looked dry. Could that have been just random electrical faults from the flat battery and all the gubins for the immobiliser and alarm and stuff? All seems fine now.

Sounds like a poor earth to me. Probably will take ages to find too. Sorry!

richardpope50 wrote:Sounds like a poor earth to me. Probably will take ages to find too. Sorry!

Thanks. Lol, don't apologise -- I knew what I was letting myself in for. New battery now -- which was a sod to change -- so I'll see what this does in the next few days.

When looking and replacing earth connections, make sure the connection is very clean under the washer(s) so it is direct metal to metal. Also, don't (as me) assume SS bolts are best as they will not rust. They actually act as a resistor and will (could) melt your loom wires as they become the same as a bar fire.

(Mine melted a fuse and holder twice until I found this out. Also reduces voltage.)

Even if the problem is not an earth, good earths mean you can easily discount them as a problem area.

Interesting, Richard. What grade of SS?

I've measured the resistance of a 4 x 40mm SS one against a steel one using a bridge device designed to measure ultra low resistance, and can't really see any appreciable difference. But can between steel and brass.

I have cocked up with stainless too. If you get any sort of arc, the stainless goes high resistance. So if you use it for a contact (like in a starter solenoid like I did), you'll get one contact, then it won't work any more as the mating surfaces are high resistance.

Chris.

ChrisJC wrote:I have cocked up with stainless too. If you get any sort of arc, the stainless goes high resistance. So if you use it for a contact (like in a starter solenoid like I did), you'll get one contact, then it won't work any more as the mating surfaces are high resistance.

Chris.

Ah. That might make some sense. However, you'd not normally use any type of steel for a contact.

Be interesting to know just how that connection was made. Difficult to see in that pic.

With a normal ground connection to a chassis, the direct path should be between the ring terminal on the wiring, and the chassis it is clamped to. So even a plastic nut and bolt (if it could be tightened sufficiently) should be ok. Indeed, this method is often used on production car tail lights, where a fixing screw is used to secure the ground to the body. And that fixing screw goes into the plastic of the lamp unit. As on the SD1, and plenty others.

Problems come where the 'chassis' is painted before the wiring fitted. You then rely on the bolt providing the ground path either via its thread if into a rivnut type of thing, or from the nut and spring washer on the back. One of which must break through the paint somewhere to get a contact.

As regards long term reliability, it comes down to the chemistry of the materials in contact, when current flows between them. If it starts out a poor connection, the current flow between the materials will be higher, so any chemical reaction that much faster. Would seem that SS is a poor choice in these circumstances.

What actually melted in the above pic is the main fuse holder from the battery immediately prior to going into my distribution bar for all the12v (ignition and permanent) feeds. Logic was battery > 70 amp fuse > perm 12v distribution bar and 12v Ignition on via relay. From distribution bars > all circuits via fuses > earth.

Originally I used SS bolts for all distribution bar connections and all earths. All earths were 6mm SS bolts into rivnuts in the chassis. NB all rivnuts were covered up with a bolt when I painted so no problems there.

Above pic shows SS M8 bolts acting as a terminal for the feed from battery and the output to distribution. Dist bar uses about 2 x 5 M5 bolts.

I was only achieving around 12v even when engine was running. The first version used a wooden holder which burnt. Assuming it was the paint that burnt / conducted electricity I made a new holder up using plastic.conduit trunking.

I now have zinc plated bolts and 13.6v.

Do not use SS!

This is very good feedback. I've never seen the high resistance through st/st before and luckily not experience the difficulties mentioned. For earthing straps I would always tap out the body threads first, assemble earthing point and cover with a transparent sealer. The thread's timing is perfect as I'm just starting the rewiring of the dash electrics and was going to use st/st screws on the under dash ground screws...well, not now...