starting problem, killing battery

[Antileon]

My Spider 76 1800 only make a poor attempt to crank, unless it fires immediately, the battery is drained.
The battery is brand new and fully charged but looses power after a few moments. Alternative batteries respond the same way.

all instruments lights are on as they should, battery terminals are clean and having good contact,. the main ground in the trunk is solid. Car out of gear.

There is no smoke and I have not been able to locate any hot parts after the starting attempts.
Only peculiar thing is a week humming sound from the cars rear end, when the battery is connected ( I have a main emergency switch in the trunk ) this is before ignition is on. I can not locate or identify the source of this sound.

Any suggestions are highly appreciated.

Thanks

[baltobernie]

Sounds like you have ruled out a bad battery, but I must say it is quite unusual to have a single start sequence completely drain a healthy battery. A current drain of that magnitude would result in very warm battery leads, to say the least.

The only other thing back there (depending on your model and PO mods) may be an electric fuel pump. If it was running 24/7, it would drain the battery in a day or two. If you have one, it is in the left-side well of the trunk. If you remove the panel covering the spare tire, and the spare itself, it will be on the forward and left side under a separate panel. You would be able to hear it clearly if you remove the spare.

If it's not an electric fuel pump running continuously, we need to investigate your "main emergency switch" in the trunk.

[Antileon]

Hi
It can not be anything draining the battery while on stand-by, as the new fully charged battery has not been connected before my first start attempt-. so it can not be any kind of leakage..
The emergency switch ( car has been styled for rally ) is a simple boat type breaker with a very high A rating., it can not drain anything and if it was providing a poor contact, it should generate a lot of heat/smoke while draining a new 70A battery in a few moment. Could it be the starter motor that is not working correctly ?
It is indeed a mystery.
I will remove the spare, to find the source of the noise.
Thanks for the tip.

[aj81spider]

There's something weird going on. A 70Ah battery is rated to supply 70 amps for an hour. Doing a little math: Assume you drain it on a single start episode, say 30 seconds of cranking, and assume that if the battery loses half it's capacity it can't crank the car any more, then you would have to draw 35 (half the capacity) x 120 (30 seconds is 1/120 of an hour) = 4,200 amps to take half the power out of the battery.

Assuming the battery could put it out (which it can't) 4,200 amps will cause quite an explosion.

There's something else going on other than draining the battery.

If you try to start and it doesn't - and is then dead - disconnect the battery and measure its voltage. If the voltage looks good then reconnect it and try again. If it turns over once then it's not the battery getting drained, the act of starting is changing the state of the car and preventing it from starting again. Disconnecting the battery is then resetting the state.

[DieselSpider]

Mine was doing that and it was the contacts inside the starter solenoid that were failing along with the end of the battery cable attached to the starter solenoid along with the connecting points between it and the starter being dirty. Even with a 1010 CCA battery it was iffy starting the car until I replaced the starter solenoid and cleaned up those connections. The diesel has to be spun up fast to generate enough compression to ignite so it was blowing a lot of smoke as if it was a fuel problem due to the fuel building up while it cranked without starting. A local vender had the solenoid in stock so it took very little cash to resolve the problem by installing a new solenoid.

[spider2081]

If you have a bad connection causing the starting problem that would not drain the battery's charge. It would actually draw less current than a good connection. Are you sure the battery is dead after cranking??

You need to get a volt meter and make some measurements while the car is cranking.
1. Measure voltage on the battery posts. (not the cable connectors on the posts)
2. Measure the voltage on the battery cable terminal of the starter solenoid.
3. Measure the voltage on the starter terminal of the starter solenoid.

Let us know what you find with these tests.

[gspear]

I had the same problem this week.
I checked all the wires and connectors, recharged the battery, no luck.
I removed the starter from the car and tested it on the bench using booster cables and the same battery, no issues it all worked well.
Cleaned the starter and the area where the started sat against the engine.
All was working normal after i re-installed the starter, started the car at least 10 times today.
I suspect the full charge was not getting to the starter due to poor ground to the starter caused to gunk, and possible so loose bolts.

Regards
Greg
79 spider in Montreal

[Antileon]

The problem did not make sense, power does not just dissapear.

I suspected that the battery ( brand new ) had a defect and had i replaced,. the situation repeated itself again with the new battery.
I returned this battery also and went to another supplier for a battery of a different brand.,. and the car came to life instantly.
I guess that the first shop had a defective batch of batteries.

At least it forced me to check my connections so it was not a total waste of time.

Thanks for the support guys.