battery drain

[V8 Vum]

I believe that exposing my silly problems, warts and all on this forum, (not the personal ones, I hasten to add!) rather than getting macho about hiding them, will hopefully help others in their build.

For those who don't know, I am in the middle of all the spagetti wiring that needs to be sorted in the cockpit before final fit.

The engine compartment is all but complete, with a few tweaks to do, and the enine now reliably bursts into life whenever I need a fix/motivation, or to annoy or scare someone (like my neighbours )!

And so, I regularly leave the battery negative disconnected inless I need to test something.

Now I do have a little car electronics experience, but no way would I call myself an electrician, so I was a little surprised when I started to notice that each time I reconnected the battery negative (ign off) I saw a tiny spark on contact between the neg post and the wire socket. It could easily be missed, its is very small, but nontheless I don't think I should be seeing any spark at all?

This leads me to suspect that something is pulling current when the ign is off, and unless I get and find the cause I may have battery-drain issues later.

With all the wires draped all over the place I need to check all are insulated from the chassis, and since I have stalks I need to be sure these controls are all switch off.

Has anyone else had a similar situation?

I suppose what would help is to see what the current is being pulled which may help indicate what is going on?

cheers

Keith

[spatz]

you assume right there is a significant current that is creating the spark, you will need to pull the fuses one after the other and have ampmeter connected between battery and either positive or ground terminal to see when you found the source for the current. Depending on your configuration you need to located circuits that are not switched off by the key switch and go from there if you have a current even if the ignition key is out.

[Pb3]

Somethings may well draw current even with the ignition switch off. Many ECUs have a permanent battery supply (does yours?) as well as an ignition switch input. As stated try to eliminate one circuit at a time. Obviously you do not have a direct short otherwise a fuse will have blown and the next time round you would get no spark! My battery will last about 10-14 days, before I have a battery that will not turn the engine over fast enough. But I have an alarm and a PIC micro taking current continuously.

[GarethGTR]

Hi

I would not worry too much yet!

Most of the electronics / ecu etc. have capacitors on the battery input. These will draw an instantaneous high current, causing small sparks. Connect the lead, then remove and reconnect as quick as you can. Sparks still there? if not then this is simply capacitors charging. (they take a small while to discharge hence no sparks on quick reconnect.)

Very important: measure static current draw!

Gareth

[Steve_D]

Radio, alarm, immobiliser, ECU etc will all have a small drain.

If you don't have your immobiliser installed yet you may want to do that before putting the body on as most of the lines you want to connect to will be under the dash.

Steve

[V8 Vum]

Thanks Guys,
It is comforting to know that!
Yes I have an LS7, and the ECU is connected directly to the battery, but I wasnt aware that it draws any current although briefly as mentioned.
Very worthwhile checking - thanks