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Car Forum / MINI / February 2005Fried battery
Have anyone ever had a similar experience or heard of? A few years back I bought a maintenance free Bosch 81080 12V 40Ah car battery from an auto electrical specialist in west London for my 1978 Mini Clubman. Actually it was my second battery from them as the first one was faulty and lost its charge within a week. The second battery had given me years of trouble free power. That is until recently when, after about five minutes of starting the car and driving along the road, the engine began to cut out. I pulled over quickly to the side of the road whereupon I nearly collided head-on into a metal fence as my brakes had completely failed. When the car came to a halt I opened the bonnet amidst acrid smoke billowing from the engine bay with a smell of burnt plastic or rubber. I called a roadside recovery service who established that the battery had short circuited and the smoke was most likely caused by the main battery cable overheating and melting its plastic sleeve. As for the brake failure, not convinced that it was mere coincide as the recovery man suggested, I noticed that there was the presence of a fresh white powdery coating on the otherwise dirty metal brake lines in the engine bay bulkhead. I could only conclude that the current that melted the battery cable casing must also have heated the brake lines causing the brake fluid to boil away leading to total brake failure. The master cylinder and lines are very close to the earth strap. After the initial burn out, the battery generated a lot of heat, which in the end took hours to cool. It also appeared to have switched poles and was no longer providing any more power to the car. Fitting a new battery and bleeding the brakes fixed the problems. Worrying or what? The car now appears to be going fine but I was wondering about any unseen damage it may have caused. >Worrying or what? The car now appears to be going fine but I was wondering >about any unseen damage it may have caused. Very worrying :o( I can't think of anything that could go wrong with the battery which would cause damage to wiring under the bonnet. It sounds like there was a short under the bonnet, which has killed the battery and the wiring. If you only changed the battery, then the cause for the short is still in the car somewhere, waiting to happen again. I'd replace the battery cables as well - sounds like they're now seriously knackered. Cheers, Colin. >> Worrying or what? The car now appears to be going fine but I was >> wondering about any unseen damage it may have caused. [quoted text clipped - 5 lines] > the battery cables as well - sounds like they're now seriously > knackered. You could also try to put a main fuse in the cable at the "-" pole. IIRC it should be 60 A. If this fuse blows up, there is a short, but no fume anyway ;) Cheers, Timo > You could also try to put a main fuse in the cable at the "-" pole. > IIRC it should be 60 A. If this fuse blows up, there is a short, but > no fume anyway ;) > > Cheers, > Timo This won't work on a Mini as it would have to take starter motor current and that can be over 100 amps. If you fit a main line fuse, it has to go in the main lead off the starter motor lead. These normally come off the starter solenoid/switch on Mini's. At least they did on the older ones. John Hi, It is fairly common for the hot exhaust to move or vibrate and touch the main battery cable where it rubs under the car. It burns through the plastic insulation and shorts the cable to earth. This could be where your burnt plastic smell came from. Check this out as it could happen again. Keith > > You could also try to put a main fuse in the cable at the "-" pole. > > IIRC it should be 60 A. If this fuse blows up, there is a short, but [quoted text clipped - 9 lines] > > John >> You could also try to put a main fuse in the cable at the "-" pole. >> IIRC it should be 60 A. If this fuse blows up, there is a short, but [quoted text clipped - 4 lines] > normally come off the starter solenoid/switch on Mini's. At least > they did on the older ones. Ah, didn't know that the starter current will go that high... Timo, without electricity problems at the moment (touch wood ;-) ) hi your brakes wouldnt just fail, they are double redundant . I would say that as the engine stopped working there was no longer any pressure in the manifold to maintain the servo so not having a servo means you almost have to stand up in the seat to brake with the same force. fragged > Have anyone ever had a similar experience or heard of? > [quoted text clipped - 25 lines] > Worrying or what? The car now appears to be going fine but I was wondering > about any unseen damage it may have caused. > hi > your brakes wouldnt just fail, they are double redundant . I would say that > as the engine stopped working there was no longer any pressure in the > manifold to maintain the servo so not having a servo means you almost have > to stand up in the seat to brake with the same force. There should be a non-return valve in the vacuum line that prevents this happening. They have been known to fail. Easy check, see if the brakes work with the engine off. I would go with the original suggestion that a short circuit (or heavy load) put a high current through the brake pipes. Since the car now works this may have been due to a sticking starter solenoid. Is the alternator OK? if the main diode pack fails S/C that can draw a lot of current. The car should be designed so that the brake pipes never take any current. Check all earth paths, e.g. engine, front subframe, rear subframe. If the main + battery lead shorted to either subframe, it may only earth through the brake pipes. John Thanks for your suggestions but I'm still a little unsure. First of all it's a '78 Clubman therefore no servo assistance and brakes work exactly the same with engine off. The engine was running for less than five minutes and still cool. The exhaust pipe is fine and nowhere near the cable. All evidence suggests it was an electrical problem coming from the battery causing the brake lines to heat up. When the car came to a halt the was no electrical power and when the recovery man connected jump leads to the battery there was still no power and nearly a fire in the boot as now the earth lead was beginning to melt and smoke. The hot lead had melted a hole in the battery casing and was starting to leak. When he disconnected the old battery, which was now very hot, the car started fine. He disconnected the brake pipe at the bulkhead union and it took more than four pumps on the pedal before we saw any fluid come out. He then reconnected the union and bled the wheel cylinders. The old battery still had power but it was as if the poles had switched. Everything appears to be working normally now with a new battery. Never had a problem with starter motor or alternator. I'm just curious as to how a battery could suddenly do this? >Thanks for your suggestions but I'm still a little unsure. First of all >it's a '78 Clubman therefore no servo assistance and brakes work exactly [quoted text clipped - 15 lines] > >I'm just curious as to how a battery could suddenly do this? I probably didn't put this forcefully enough in my first reply, but it's just not possible for a battery fault to cause any of these problems. If you had smoke under the bonnet, then the original short was under the bonnet - the smoke will appear between the short and the battery. Once the original short had caused the cable insulation to melt, all sorts of possibilities will have opened up for secondary shorts to keep things nice and toasty until you finally manage to disconnect the battery. The original short may well have cleared itself by then, and moving the leads to replace the battery probably cleared any remaining shorts by fluke. So you put the new battery on, and everything seems fine. The problem is that the insulation on the cables is now probably all burned and crumbly and the cause of the original short still hasn't been found. The brakes are a different matter. They may even be unconnected to the electrical problem, but your theory that heat from the cables caused fluid in the pipes to boil is as plausible as any other. Dual circuit brakes might well not protect against that. Cheers, Colin.
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