Spitfire Current Leakage, 1978 Spitfire

[Joe_Pinehill]

My battery is tending to die over 4 or 5 day of not using the car. I checked the current from the negative cable to the negative battery terminal when disconnected, and the car off, and I get 9 mAmps of current. I know its old car, and bound to be some leakage. Is 9 milli Amps typical? Wondering if I have a bad battery or have to hunt the source of the leaking current.

I was going to leave the negative off, and see how much charge it holds over night. Its a relatively new battery, less than 2 years old.

There just isnt that much wiring on the unswitched electrical bus wondering if it maybe the key switch. I dont have a radio.

 

[martx-5]

Nine mAmps is not a lot. It's typical of modern cars to draw between 10-20 mAmps. That shouldn't kill a battery for at least several weeks or longer. There shouldn't be anything drawing on your car, especially if you have no radio with a memory. Try disconnecting the big lead from the battery on the alternator and see if the draw goes away. Sometimes the diodes will leak, but I'm still not convinced that should be enough to kill the battery after 4-5 days. The proof would be to disconnect the battery and see if it still goes flat. That would indicate a bum battery.

 

[Andrew Mace]

Is there a light in the trunk on the late Spitfires? If so, perhaps that's not shutting off?

 

[TR3driver]

If only 9ma is killing the battery in 4 or 5 days, then IMO the battery is seriously weak and should be replaced. That's only about 1 amp-hour, and your battery should be good for at least 40 ah (especially at such a low rate).

As Art says, it could also be the battery self-discharging, which would also mean a new battery.

Another thing to check, perhaps, would be that the battery is getting fully charged in the first place. A bad connection or a wonky voltage regulator might be putting barely enough into the battery to start a warm engine once.

But I've also seen several cases where the leakage varied over time, measured quite low but became higher under some circumstances. My motorhome had that problem; turned out to be mud caked around a solenoid terminal that would become much more conductive when moist from dew or rain.

Most severe case I ever saw was my 1970 Audi, where the relay for the rear window defogger would pull in when it got damp! Never would have solved that one, if I hadn't happened to walk by the car one night and seen the indicator lamp glowing on the dash! Probably, the phenolic relay base had just gotten contaminated with salt and dirt, but I replaced it anyway.

 

[Twosheds]

Look for a puddle of electrons under the car, then follow the electron trail to the leak.

 

[DrEntropy]

John's solution has my vote. Just be sure to check that they're actually genuine Lucas Positive Earth electrons an' not an earlier spill from some domestic system. :smirk:


<span style="font-style: italic">EDIT: Go with Art 'n Randall's suggestion, tho. Seriously, sounds like that battery is FUBAR.</span>

 

[Don_R]

Doc,
Its a 78 Spit. It shouldn't spill positive earth electrons. The car is Neg earth. It would be very hard to seperate these electrons from a domestic source.

 

[DrEntropy]

eep! Neglected t' notice which year Spit! mybad.

Y'd have to pass a sampling of th' spilt suspect 'trons thru a Lucas smoke capacitor then.

Too much argie, wot wif exchange rates, shippin', VAT an' all.... Jus' replace th' battery.

 

[DrEntropy]

...Joe's gonna hate us....

 

[Joe_Pinehill]

Ha Ha, thanks for all the help

 

[71MKIV]

What's the voltage reading first thing in the morning after running the car the day before.

anything less than about 12.5 vdc, your battery has issues.

This will sound stupid, but I've had it work for me. Take it out of the car, and bounce it on the ground a couple of times, and slosh it back and forth. sometimes that will shake the lead sulfate out of the plates enough to buy you some time.

 

[DrEntropy]

...ummm.... I wouldn't do that.

 

[TR3driver]

I'd certainly be VEERY careful with the "bouncing" part. Those things are surprisingly fragile, and you probably won't enjoy the bath in sulfuric acid.

And just a spirited drive around the block should give it about all the "sloshing" it can stand

 

[71MKIV]

What kills the batteries in our little cars is the lead sulphate flaking off the plates and building up in the bottom of the batteries until it shorts the plates. The longer the warrenty of your battery, the deeper the sump is at the bottom of the battery.

I agree that the term "bouncing" connotates something a little harsher than what I had in mind. tapping maybe?

a small discharge, described here, might be dealt with by tapping and rocking the battery back and forth, and save the owner the expense of purchasing a new battery.

And no, driving the cars does not rock the battery enough to accomplish that.

I am assuming here that the owner of the car is very fussy about the appearance of his car, and keeps the top of his batter very clean in keeping with the rest of his car.

 

[TR3driver]

And no, driving the cars does not rock the battery enough to accomplish that.

All a matter of how you drive, I suppose
And FWIW, I don't think I've ever had a battery fail that way in a TR. It has happened, sometimes, in the family "grocery getter". But even there, usually the batteries just lose too much capacity, rather than developing a shorted cell.