Flat Battery

[WallerZ]

Morning all,

 

I came back to my car after the IVA test to find my battery was completely flat (car had been standing a couple weeks) I ended up buying a new battery as it was the original one out at MX5. However, I've put the new battery in last night, had a little blast, and over night the car is completely flat again! Nothing at all!

 

Nothing has changed since the IVA electrically and there is nothing to be left on (even switches for things not installed I.e. windscreen wipers/radio)

Its a new problem and the car has been sat with nothing done to it so I can't even undo something that changed!

 

Does anybody have any ideas???

[richyb66]

It could be the alternator, I had them fail so that the battery drains back thought them when the car is left standing. Unplug the alternator, charge the battery and see if it holds the charge.

 

Has the ignition light stay on or glow when the car's running which might indicate it's not charing either?

[ozz]

I have a small denso alternator on mine, the multi plug on the back came off at a rolling road session, this disconnected the warning light and prevented the alternator from charging the battery.

 

I have put a blob of sealant on it now and always check the light comes on before starting.

 

Check this and the alternator wiring if applicable.

 

Ozz

[Grim]

You could take fuses out and measure current draw through the fuse holder pins on each circuit to find where the fault lies.

[WallerZ]

Yeah the charge light comes on but then goes off again once started.

Yeah a quick look at some forums shows the fuse route to find the circuit, the alternator is a quick and easy check too.

If anyone is near Tamworth today, has jump leads and nothing better to do, you're more than welcome to have a look. I've got nothing to get the car charged until my dad is home tonight with his jump leads. Tea/coffee on tap too

[Tazzzzman1]

Zach

 

Agree with the above, check that your Alternator is charging

Also check if it is the immobiliser....

I have this issue that it will drain the battery within hours if left on, although admittedly I am using a dry cell race battery. Over come this by using battery cut off switch..

[WallerZ]

Yeah I'll check the alternator first as that's more likely to have failed whilst driving to the IVA that a short circuit coming about to drain it?

I removed the immobiliser when I was putting the wiring in so that would have flagged up an issue earlier.

[fry61]

When you have power in the battery again; & about to put the car to bed----disconnect the battery & wire a lamp/bulb of high wattage in series --- between disconnected lead & battery terminal---- if test lamp glows/is bright there is something still connected -----try switching on/disconnecting circuits ---- brighter/dimmer test lamp will result ---- you're aiming for NO GLOW on test lamp.

[WallerZ]

I've concluded that its the cooling fan circuit thats causing the issue. Cold engine, got some power to the battery via jump leads, fan came on full tilt, relay and/or fuse disconnected and it cut out.

Left the car with the fuse and relay out from Friday to Sunday afternoon and the car started fine, no issues, battery was putting out about 12.1V.

I've got a battery cutoff switch and planned on fitting it anyway as a further anti-theft device. Will see how that works. Easier fix than ripping the circuit out again as my free time has vanished for a couple months....

[Bob Tucker]

Sounds like the thermostat switch has stuck closed (ie connected)...should be easy to check with bulb, wires & a battery.