My battery seems to be running down after 3 days. I measured a quiescent draw of 800 ma. That seems excessive.

AFAIK, the only thing that should be drawing power is the clock/trip computer. I dont have any anti-theft devices that I know of.

A new alternator was installed, so Im going to disconnect the B+ from that tomorrow.

Any other ideas?

 

My first thought is 'how old is the battery?'

 

Bought new at the end of June. Car was stored while I was off sailing. Came back 3 weeks ago. It was on a trickle charger.

I had it tested both by Autozone and an independent mechanic.

The issue is that 800ma is pretty high. Thats almost 20 AH per day of draw. The Group 34 batteries are typically 50-60 amp capacity, so at a draw of 20Ah per day, its essentially dead in 3 days. And that parallels with what I am experiencing

 

scottpeterd,

You haven't said what car you've got, but I'm guessing you might have the standard Jaguar security systems installed?

The most common causes of inadvertent current drain on XJS are:

- boot light switch
- radio aerial
- security system
- alternator rectifier pack
-
One way to check is to pull the relevant fuses one by one until you find the circuit that's causing the problem. I know some owners who have literally pulled every fuse and then replaced them one by one to identify the culprit. The difficulty is that there are some inline fuses not mounted in the core fuseboards.

Good luck

Paul

 

MY92

Those are my thoughts as well. I am not sure they mech pulled the bulb out of the light switch when he measured the draw.

After that, I suspect the alternator diode pack, as the car didnt have this problem before the new alternator went in.

I cannot find any reference in my owners manual as to a security system. I have owned the car for 6 years, but only driven it for 1,000 miles or so. I only get to see it once a year for a couple of weeks. And for over 3 of those years its been in a body shop

 

If you have a small rocker switch and a red led on the steering column, or look by the aerial in the boot/trunk if you find an big white connector connected then you do. If its not connected you don't have the Jag alarm fitted.

 

My experience of battery drain was with the electric aerial.
If its the aerial fault I had, turn off the ignition, open the boot and listen and you'll hear the motor turn on very briefly every so often.
I only tracked it down as on the way back from a trip to the UK my Ferry to Ireland was delayed and I sat in the car waiting in the middle of the night and heard this intermittent 'wurring' sound.

Good luck tracking it down

 

Another afternoon spent on the car. Most of the morning was helping a Rennlist member look at a 928 I found in the hood yesterday.

There is no alarm. So that rules that drain out.

Pulled the fuse for the antenna. Drain is still there.

Tomorrow I will check for a shorted diode in the alternator. After that I will start pulling fuses.

 

I just located the load dump module on the car. This could also be the source of the drain. I didnt know the car had one

 

My parasitic drain ended up being the right side AC blower. Mine read .8ma when I tested it as soon as I pulled that fuse it went to zero.

 

Thats rather disturbing. Aren’t the blowers on an ignition powered circuit?

Following the battery distribution diagram from the electrical manual, I was just testing fuses for the non-ignition circuits

 

scottpeterd,

There's a nuance in the wiring structure which means that if the Darlington transistor corrodes, the fan can draw current without the ignition circuit being live.

Paul

 

Whoa...

Did you find that on a wiring diagram, or after finding that is was the fan and examining how that happened. I dont see that in the wiring diagrams

Great tip. Thanks.

I hope there are not many more like that

 

I did the old fashioned pull fuses and see when it drops. It's weird because the fan seems to work perfectly, but has the draw. It doesn't make any noise when off, just draws power. I did end up putting the fuse back in and unplugging the connector to the fan behind the glove box ,only because I wasn't sure if other parts of the air\vent system used the fuse too. No I didn't really look into the wiring diagram, just wanted to see if the fan alone was the draw. As soon as I unplugged the connector it dropped to zero again

 

Sorry if I missed it, but have you ruled out the trunk /boot lights staying on with a closed lid? That is usually the problem....my 95 was having a “drain” after a full repaint where the boot lid was removed and now if I don’t use force to close it , the lights stay on and drain the battery

 

Yea, Ive done that. The drain is still there with the switch unplugged and the bulb removed

 

scottpeterd,

As I interpret the wiring diagram, there are two reasons why the fan circuit can get power without the ignition on.

Firstly a relay can get stuck in an open position and thus feed the power to the fan circuit without being initiated through the ignition being on. Pulling the fuse will stop that.

The second is that the fan control module is fed battery power. The Darlington transistor (effectively controlled through ignition) stops the power. So, if the transistor fails, then the fan control module will constantly receive battery power and thus feed the fan circuit. But there's no fuse circuit to protect that, so you'd have to disconnect the battery.

Of course, I may have misread the diagrams!

Cheers

Paul

 

As one having both a BSc and MSc in Electrical Engineering, I feel somewhat qualified to ask...

Where did they find the guys who designed these things??

 

Hey Paul, where are you seeing a relay for the AC fans? Just wondering. I didn't see one in the XJS electrical file I downloaded, but I'm really curious if there is one. It would make sense

 

TiR,

Sorry, I may have confused you. I don't think there are any external relays involved in the aircon system (other than the a/c compressor clutch relay). But there is a high-speed relay inside each blower motor.

I THIN K that the way it works is that the fan motor receives power in from a direct battery feed. It is then earthed out through either the Darlington transistor or the high-speed relay. The Darlington transistor controls variable fan speed but only when the fan switch is in Pos 2 (late facelift cars) If the High-Speed is not called for and the relay is thus open, the DT circuit operates and the fan earths through that. If the High speed relay is closed, then the motor earths through that. So a failure in either can potentially constant current flow (depending which orientation they fail).

To make it more confusing, the 2 high-speed relays seem to be linked, so I think that a failure on one side could cause a current circuit to the other side?

I hope that helps (or potentially is more confusing!)

Cheers

Paul