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My 72 Midget fails to start at the moment. Within 4 or 5 goes of the starter motor the battery is unable to turn the engine any more. I have checked the voltages and with the ignition off the battery is holding a friendly 12v. Once I turn the ignition on the battery voltage drops to 8.5v.
This is even before trying to turn the engine over. I have tried jump starting from another car and I can hear the engine start to labour in the jumper motor as the voltage is sucked out of that battery as well!
Any suggestions will be greatly received.
Sounds like your battery is u/s. Hearing the other car labour as it's alternator tries to cope with the demand from yours is a classic symptom of this. You could try putting your battery on a slow charge for 24 to 36 hours. If that makes little difference, then borrow a known good battery from another car and see how that behaves when directly fitted. I assume you have removed, cleaned, checked and refitted the battery termainals, starter motor terminals and engine-to-body earth strap......
Since no one has answered your question, I assume that they are a clue-less as I. Have you tried a new battery? It may be that you have a shorted cell which is causing this problem. For a definitive answer, jump up to the B bulletin board and post your problem to the attention of Paul Hunt. Paul is an electro-mechanical engineer who handles most of the electrical trouble shooting problems on the B. He should be able to help you.
FYI a car battery has 6 cells in it.Each cell is or should be 2.1 volts dc so if you are reading 12v dc on your DMM or for you purist your Simpson meter then your battery is dead.
P.S.
When you have your car running use your meter on the battery and see what the charge rate is,
ball park of 13.5
to much and you cook your battery
to little you use up the charge that is in
it and you don't put a good charge on it and over time you kill it.
I'm a purist and gave up my Simpson long ago. We (purists I know) use Fluke 87s.
If the drop in voltage is when you start have you considered a bad earth connection. Check the main earth strap is in good condition and undo and reconnect the bolt to the body.
I havn't checked stuff like the starter motor leads yet, when I do I'll repost with my (hopfully) good news.