Moss Motors, Ltd

Hi, the battery in my 1993 Mini goes flat very quickly. Even if it is a new battery, if I leave the car without using it for a couple of weeks the battery will drain and then I can't start the car. I fitted a Discarnet Immobiliser without fitting the auxiliary by-pass and still the battery drained! Is this possible??? Does it mean I've got some sort of leak somewhere? Any help will be gratefully received.

Regards and thanks in advance, Stephen

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TCB in a Flash!

sound like you have a leak somewhere in the system! 1st port of call would be to check you have a good earth! Its very common for the main earth to deteriorate... this causes all kinds a weird and not so wonderful things to happen. Next would be to locate the clump of wires under the bonnet slam panel! pull them apart one at a time...clean them and push them back together! after that check the reverse side of the fuse box this is also a problem area that often neglected. That's the first things I would check... don't forget to report back. 

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Oz Cooper
Classic Mini Product Manager UK


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Disclaimer: Working on automobiles is inherently dangerous. Moss Motors, Ltd. is not liable for injury or damage due to incorrect installation or use of their products. All products are sold with the understanding that the safe and proper installation and use of the products is the customer’s responsibility. Follow factory workshop manual procedures and instructions, but use current shop safety standards and common sense. Some tasks will require professional advice or services which Moss Motors cannot provide.

If you have a battery isolator connected and it still goes flat then it's an odds-on favourite to be the Earth as pointed out by the other poster.

 

If the isolator is the first thing in the live side circuit (and isn't faulty .. which is unlikley on a new unit) then it can't be anything other than a bad earth somewhere.   If it were a short it would go "crackle-spit-pop-bang" rathert than just 'fade-away'

To trace it you need a lamp-based tester and work your way around the entire car tracing the earth route and using the lamp in series at each of the connection points.

 

Good luck... they're a real *** to find at times.  Just be patient and methodical and it'll come alright. 

 

Ian   

If it were a bad Earth ("ground" in the US), then your battery would NOT be going flat by just sitting. A bad connection there would limit the output current and make it SEEM like the battery has drained. Of course this works in reverse as well, a bad earth connection would inhibit your charging system and your battery would not get fully charged either, but that scenario would only be present while running the engine.

If its going flat while just sitting unattended, then you have at least a partial short to ground. Much can be determined quickly with an Ohm meter.

• Disconnect either side of the battery.
• Check resistance from the negative battery wire (the terminal that goes to the battery), to the chassis of the car. Make sure that you choose a non-painted surface that is clean. Here you want to see 0Ω of resistance. If you have any more than a few ohms, (more than 10), then you have a bad Earth connection.
• Now check from the positive battery cable to ground, (make sure that every switch in the car is OFF), here you want to see infinite resistance, my guess is that you won't. It sounds to me as if somewhere you have an unwanted current path to ground that is allowing your battery to drain when unattended.

If there is an unwanted path, isolate it by removing all the fuses and retest (positve wire to chassis). If you have infinite resistance here, then start replacing fuses one at a time and you'll soon identify the circuit with the problem. If you DON'T have infinite resistance, then the problem is located before current even gets to your fuse block!

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On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"

Not sure what the standing load on the battery would be for an SPI but an MPI will drain flat as a pancake after 3 - 4 weeks. With the car standing, the immobilser will take some current and so will the radio, probably a few other bits and bobs too. Check out the electrics but I think you will find that there is nothing actually wrong and its just the standing load killing the battery.

You can test the drain current quite easily by disconnecting the earth and sticking a reasonable digital multimeter set to amps in the way. It doesnt actually matter if you use the battery live or the earth wire, its just easier to get to the earth wire. The reading will tell you what the drain current is. If it seems unreasonable high, remove the fuse for the radio and see what happens and then disconnect the immobiliser and see what happens.

Enjoy

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Mini 40....its a wicked ride

The current draw from those loads would be in the micro-amps (.000,080 amperers or thereabouts), I really doubt that they could kill your battery in only a few weeks...a few years maybe? 

What is the Amp-Hour rating of the battery? If unknown, how about the CCA (cold cranking amps)?

Did the battery always go flat, or is this a recent problem?

What is the ambient temperature?

Is you car stored inside, or subject to moisture?

The suggestion to use an ammeter is an excellent one. What is the exact current that is read when using the meter? This will be a huge clue.

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On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"

What you are forgetting though davey, is good old British engineering

Trust me, 3 - 4 weeks and an mpi is dead [:'(]

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Mini 40....its a wicked ride

Perhaps you are right! I am troubleshooting in the dark. I have no experience with Minis, just electronics, Sprites and MGs!

I'd love to read up on the topic. Is there a web address at which I can peruse the schematic for this car? 

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On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"

I am not aware of a web site that has that info on it, but I bought a CD off of ebay for about £4 or about $7-8.

Lots of pages of schematics so its not easy to post a couple of pics either. I was only interested in the MPI info but the CD came with Rover and MGF info.

Our mini is in hibernation at the moment with the battery off and trickle charging so I cant get out and test it, but when I bolt it back in I will test it just out of curiosity.

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Mini 40....its a wicked ride