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MG Midget and Sprite Technical - Power puzzle!!!

OK, I have a really odd problem here.

I noticed the battery going dead on me after two weeks without driving. Upon investigation I noticed a 250ma leak with the ignition switched off.
Quick math will explain the battery going from full to empty in approx 8 days with that kind of leak.

So I started looking for a culprit. I just started pulling fuses until I saw the leak disappear. Hit the jackpot with fuse nr 2.
But what struck me as odd: when I pushed the fuse back in, the leak didn't return!
Only after running the engine and switching off, the leak was back again. Tried again with the same result.

The wiring on this car isn't very good, that was Nick's weak point. When I look at the original diagram there shouldn't be any power anywhere with the ignition off, but thats not the case with this car. All the lights work with ignition off.

What kind of device on the car could explain this behaviour?

I will investigate further on Sunday, but maybe one of you guys have an idea where to start looking!

Cheers,

Eddy
Eddy Veuger

Eddy.

Not that electrics are my 'thing' but could the 'leak' be related to a bad earth on the lighting system at all....?

Just remember, NEVER let the smoke escape from the wires.....!

Mark.
M T Boldry

Eddy is there a radio or an alarm fitted?

250mA could be a memory drain for a pushbutton radio or the sort of drain that a sensor for a car alarm might maintain

or if the drain were higher I might have suspected the boot to have a light that is controlled by a faulty switch.

It is incorrect to think the lights cannot work without the ignition being on. All of my lights work without the ignition, except that the headlight flasher has been wired to require the ignition to BE ON. Mainbeam, dipped beam and side and tail lights all work off the battery. Reversing lights, indicators and stop lights DO NEED the ignition to be on.

I know this doesn't help yet but at least you have an idea what ought to be available without the ignition

keep throwing it at us and we can all join in.

:-)
Bill sdgpm

Yes, there is a radio and CD changer on board...but 250ma seems mighty high for a memory...that's 6ah per day mind you!
And it also doesn't explain why the "leak" is not coming back after reinserting the fuse....

it has no boot light, so thats one less thing to worry about! :-)
Eddy Veuger

Eddy - Try pulling the plug out of the back of the alternator. I've heard of similar symptoms with a dodgy alternator - even if it's charging ok.

Cheers, Matt
Matt

I was just about to advise the same, if the diode pack in the alternator is faulty this can happen
Bill sdgpm

That was a new alternator just last summer! Old one packed up at Croft, as far as I recall.

Guy
Guy Weller

Don't let the fact that the alt. is <1 yr old fool you into dismissing it as the culprit. If you do find its the alt. you might consider swapping the Lucas for a GM or Japanese model. Easy swap: Great results.
Phil
Phil

Not that you should not fix the problem but you can cure the symptom easly with a batery cut of switch.

just make sure you get the one that shuts down the ignition wire as well

works fine for me and always a good start
Onno Könemann

250mA. Could be what a relay coil takes - 50 ohmish. What's on the circuit that is covered by the fuse?
Steve Church

I plug mine in one of these when parked in the garage

http://www.accumate.co.uk/it010003.html

Keep on looking for the leakage but with an Optimate plugged in at least the car will start after 4 weeks
Alex Sturgeon

I too think it sounds like the voltage regulator within the alternator. Simple to check, just pull the plug out odf the alternator while watching the meter for leakage.

If not we then it is thinking cap time!!
Robert (Bob) Midget Turbo

I wasn't suggesting that it couldn't possibly be the generator because it was so new!
Just saying that it had been replaced - bearings had gone on the old one IIRC.

The real answer is of course to drive it every day, then you don't need to worry about a little leakage (battery that is!)
Guy Weller

and fit a cut off switch
no problems here starting after 2/3 weeks
Onno Könemann

Im with Onno on this.
I also have a "massa schakelaar" in my footwell and as soon as i switch off the engine i turn the key on it and take it out: All power down = no current leaks or "kortsluiting".
And a bit tuffer for thieves to start the engine(unless they have a key = universal and for sale at Hallfrauds at € 1,-)

Sorry for the dutch words you all, i just coundt remeber the english translation for them. :)

Eddy, best tho to find the source of the leak first.
Arie de Best

-battery cut of switch
-short circuit

just to translate my fellow dutch men
Onno Könemann

Hi All,

Thanks for your input!

I first suspected the alternator as well, but unplugging it did not cure the leak.

It was getting more and more complicated, the leak would now appear at random, sometimes it didn't come back after starting and sometimes it would come back without starting.

First I pulled the radio and I soon discovered what caused the problem to be so erratic. The radio had a very dodgy groundwire. Small bolt in a big hole with paint not removed and it was loose too.
Radio grounded > leak. Not grounded > no leak.

What remains is the fact that the radio+changer combination pulls 250ma which is a lot.
I pulled the unit now and I don't really need a radio in the car (drove it today without the hood, the engine note is all the music I need!).

Anyway, problem "solved" or at least eliminated!

Cheers,

Eddy
Eddy Veuger

Eddy

You could connect the radio to the green wire on the fuse box (ignition fused = green). Then there will be no 'leak' when the engine's off.

Hard to understand why the radio should take 1/4 amp when not in use... this is a whopping current for 'standby'.

A
Anthony Cutler

This thread was discussed between 20/02/2009 and 23/02/2009

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