Battery Drain...

[andy-w]

Hi guys,

Just a quick question as i dont have the bible here at work with me.

I have just been to the car during my lunch break to try and find out what is causing the power drain on the chim. with the ignition off it was drawing 12 volts....i pulled one of the relays and the power draw stopped...

Now the only thing that appears to not be working are the horns which were definately working on saturday for the mot (which the car passed with flying colours - no recommendations and no faults..... :-)
).

so are the horns on a relay or fuse and is anything else on the same circuit...checked lights/indicators/wipers/washers and all seems ok...???

[That Daddy]

Hi Andy they should be relay fed as you have 2 horns and i cant see a basic horn switch taking that kind of load,maybe the relay as gone AWOL,hows things?

Edited by That Daddy on Wednesday 9th July 14:33

[andy-w]

Hi TD,

Been ages since i have been on here....i have been tied up with work/sorting out the car when i can/more work...its been a hectic few months. If it is ok i shall give you a buzz tonight if you are around??? and if you would send me your mobile number again!!!!

That makes sense with the horns being on the relay...i might swap it over with another one and see what happens...

If i fully charged the battery it would flatten with a day...so far it is still going strong...also if i was to disconnect the battery earth and place a light bulb in between the earth and the battery would you expect it to light up with the ignition switched off and no electrics(or minimal, radio led, remote control sensor etc) turned on?

[BryanWilton]

I know someone who had a Battery drain problem & others on here have also had it
I believe its usually one of the relays in the passenger footwell causing it, can't remember which relay the culprit usually is
Sorry couldn't be of more help...

[Cider Andy]

What do you mean by "it's drawing 12V"? You should find 12V all over the place: at the fusebox, at various switches etc. What you need to measure is the current being drawn. Set your multimeter to the 20A range, disconnect the positive battery terminal and connect the multimeter red wire to the battery positive post; connect the meter's black wire to the wire(s) you just removed from the battery. You can start with the heavy wire as it's only connected to the starter motor and alternator. If there's no current being drawn there you can ignore this wire and just leave the thinner one(s) in the circuit.

Certain systems in the car, especially the alarm and immobiliser should draw a tiny current, probably milliamps. This will show up on the meter. Any more than this and you need to start pulling fuses to try to identify the circuit that's drawing a bigger current. You'll also need to simulate the doors being shut by taping over the switch in the sill (as it will be impossible to pull fuses without having the door open). If the battery's not in good condition, even a normal tiny current will drain it a lot quicker than a good battery.

[BryanWilton]

Just checked, there should be one horn relay (controlling only the horn/horns) & one 15 Amp Horn Fuse

[BryanWilton]

Agree with Cider Andy, the Alarm for example will draw a small current even when its not set
Still believe problem is likely to be duff relay though...

[andy-w]

yes - appreciate that it will be 12v...its just when i pulled the horn relay it totally broke the circuit...tha alarm, stereo and anything else that could draw power had already been disconnected....including the interior light relay....unless there is a lose wire/short behind the fuse box...

I shall have a look tonight when i get in and post the results tomorrow.

[grumbledoak]

Er, what "Cider Andy" said. It'll be Amps that she is 'drawing', hopefully milliamps.

Even if the battery is good and the wiring is fine, the Alarm/Immobiliser/ECU never entirely switch off, so you cannot just leave them and expect them to start. But if she is draining a good battery quickly (say, less than a week) then something has gone wrong. It probably won't be easy to find, but I'd start with the bits that get wet - front of the bonnet, or in the doors.

Good luck.

[andy-w]

grumbledoak said:

if she is draining a good battery quickly (say, less than a week)

Try a fully charged battery in less than 10 hours....plus i have tried another (new) battery and exactly the same...!

[BryanWilton]

Agreed, should be milliamps

If its draining in say a day, then you pull the horn relay for example (only the horn relay) & the draining is cured then its a duff horn relay
Apparently this problem is normally one of the relays, but could be something else that normally stays 'live' when the ignition is off (like the electric windows or door solenoids)

If the horn relay you suspect doesn't cure the problem i would then pull all the relays in the footwell & see if that cures it
At least that narrows it down to the footwell relays (or tells you its not a relay in the footwell)

You could check if any of the relays have gone 'closed circuit' with a multimeter, this is best done by unplugging them & checking for continuity across the 'switch' terminals
I wouldn't advise checking for 12 volts on the switching side of the relay with them in situ, as you can get back feeds & it may show 12 volts even if it isn't switching

[grumbledoak]

Ten hours? Sounds like something is badly fked. I think I'd disconnect the battery in case that 'something' gets hot.

It shouldn't be on the ignition circuit. (With a TVR, "can't" is an unwise word...) But I'd still be looking at the wet bits and the courtesy light first.

Hopefully someone who does this for a living will be along...

[Cider Andy]

andy-w said:

Try a fully charged battery in less than 10 hours....plus i have tried another (new) battery and exactly the same...!

The battery will have a capacity of around 72Ah. That means it can supply a steady current of 1A for 72 hours. If yours is dying within ten hours you could reasonably expect to find something drawing over 7A. That's a heavy drain, more than a headlamp! Something should either be lit up or getting hot. I'd start at the alternator: is it warm?

[BryanWilton]

Wonder if anyone makes a 12-Volt Clamp Meter (measures Current) & you wouldn't even have to disconnect the Battery to measure the drain?
This would make finding the fault a lot easier
If not you need to wire an Ammeter(or multimeter) in series with the battery to measure it (as Cider Andy has said)
Make sure its set on Amps & will measure at least 10-Amps

I would guess the normal current drain should be between 100-200mA (very roughly)
If your Battery is for example an 80-Amp Hour (should say rating on it) & its going flat in 10 hours then your car is drawing roughly 8-Amps
Thats assuming you started with a healthy battery
Sorry, i'm sounding a right geek now!

Then maybe pull the fuses one at a time(& put back) until the drain drops right down, at least this will tell you which circuit the faults on
Then check the relay on said circuit....