Hopefully a simple one..
I need to work on my car tomorrow and it's been advised that I disconnect the battery, now does that mean remove both cables or can I just take off either the positive or negative and if so is one better than the other?
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One cable is fine.
Best to disconnect the negative. The reason being that if your spanner accidentally touches the engine or body work whilst you are doing it, no harm will happen to you or the battery.
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Be careful! Some (many) cars are not very tolerant of battery disconnection nowadays. Do a good internet search first, then consider either working round it or using a power saver thing.
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Make sure you have your radio code or you won't have a radio afterwards..
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It may be an old wives tale but some cars engine ECUs need to relearn the optimum settings so if it isn't an OWT the car may run a little rough for a few miles after the power down (reset).
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You may have to reprogramme your electric windows.
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I heard something about possibly having to reprogramme the windows, no idea how I would do this, I'll check the handbook before I attempt to disconnect the battery. I've been lead to believe that the radio code is stored in the ECU somewhere so it sorts itself out when you reconnect.
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>>I heard something about possibly having to reprogramme the windows, no idea how I would do this
>>
On my car it is a case of doing each window in turn. Power fully down and pause with button active then power fully up and pause with the botton active.
It then remembers what it has learned.
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Not an OWT. The C8 forgets my James May driving style after a battery disconnect and becomes more sprightly. No trace of roughness though.
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Really depends what the job is. H&S and backside covering has implemented a trend for recommending that the battery is disconnected on every occasion when really it isn't.
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Agreed, I've seen "disconnect the battery" advice for jobs where one does not go near anything electrical.
Some vehicle alarms go off on a secondary battery if the main one is disconnected - car handbook should cover what to do.
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>> Best to disconnect the negative. The reason being that if your spanner accidentally touches the
>> engine or body work whilst you are doing it, no harm will happen to you
>> or the battery.
>>
No "best" about it. ALWAYS disconnect the negative terminal first if you are either changing the battery or doing other work which necessitates disconnection. Anyone doing otherwise risks severe burns and/or car damage if the spanner touches something metallic.
And while we're on this subject; a wise person removes wedding or signet rings before dealing with batteries. I've seen the effects of a dead short on a fellow mechanic's finger and it ain't pretty.
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>> And while we're on this subject; a wise person removes wedding or signet rings before
>> dealing with batteries. I've seen the effects of a dead short on a fellow mechanic's
>> finger and it ain't pretty.
>>
Oh, and a wise man uses a condom to insulate the floppy bit (oooerrr, missus!) as well.
Well, that's my excuse as to why I keep a pack-of-three in the boot toolbox.
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I fully agree with the concerns over safety around batteries - the speed which a short produces heat is amazing and surprising if you've never seen it before.
One reasonable way around this problem is to drill a small hole into the top of the negative battery terminal, and use a self tapper screwed into the soft lead of the terminal to connect a length of wire fitted with an inline fuse, with the other end of the wire connected to the car's body.
So, when you remove the negative battery lead, the battery is then only connected to the car's electrics via a fuse. Thus, any electronic memories are saved, but, in the event of a short, the fuse blows, protecting you and the car. As there's no actual disconnection of the car's electrics, there's no sparking as you remove the earth lead.
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An old workmate nearly blew himself up when he managed to spark a spanner across the terminals of a freshly charged lorry battery, the explosion of gases blew the battery apart showering him and me in a lovely acid bath, he took the full blast in the face but had 70's style Dreary of Cornation Street glasses on which protected his eyes.
Lesson learned.
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I learnt my high current/battery lesson in spectacular fashion - threading a copper oil pressure pipe thro the bulkhead. It touched on the battery terminal and grounded elsewhere - A very neat way to anneal copper tube!
Never worn a metal watch strap or rings since.
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When i was an apprentice, we were taken to the industrial accident museum, and presented with rows of formaldehyde jars with eyeballs with nails in, severed fingers, severed hands, and various burned and mangled body parts. Even someones scalp with hair on I seem to recall.
Many pictures of near burned off wrists and fingers cause by current through rings and watches.
My father would never wear a wedding ring, because one of his young firemen jumped down from the access ladder of the engine to the ground, leaving his wedding ring and finger behind caught on a loose bolt.
Last edited by: Zero on Sat 2 Mar 13 at 23:26
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>>...leaving his wedding ring and finger behind caught on a loose bolt.
Not just in an industrial context.
Daughter of an ex neighbour lost her wedding finger when she slipped exiting the loft.
I also learned that when testing mains use the back of you hand and when working on ceilings with the risk of live mains then keep one hand in your pocket .
Elf n Safety? Wots that!
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Pal of mine "degloved" his ring finger when the ring caught on some metal racking as he jumped down. The hospital stitched it up, but it went bad and ended in amputation.
I'd never worn a ring and I wasn't tempted after that.
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Back in the mid 80's when we lived in a flat next to The Tate Mod with the view of St Pauls Cath and Father Thames filling our windows, I used to look after one of these www.carandclassic.co.uk/car/C361849 for a couple of gingers who lived near by.
I charged the sealed-for-life battery for them overnight and the lady one came to collect it in the morn.
A few minutes later we heard an almighty BANG where he must have shorted the critter causing said battery to explode.
The man one died a short time after that from an acquired disease, they were a nice couple of chaps ISTR.
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Many years ago whilst working under the bonnet of my Mini wearing a metal watch bracelet, the bracelet came into contact with live terminals in the fuse box, a quick flash & a puff of smoke later i recovered to find 2 of the small links on the bracelet had been welded together. Fortunately i escaped unburnt, but my Y-fronts were a write off!
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" young firemen jumped down from the access ladder of the engine to the ground, leaving his wedding ring and finger behind caught on a loose bolt."
As a result we have to tape up rings or remove for work. Where did your dad serve Z?
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Stratford TMD, Shedcode 30A.
Think he jumped from a LNER B1 class.
There is more than one kind of fireman! ;)
Tho my grandfather was in the LFB during the war. Canning Town Fire Station, Prince Regent Lane. They were a tad busy in 1941.
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>> There is more than one kind of fireman! ;)
No, there's still only one.
The others are now firefighters.........
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>>No "best" about it. ALWAYS disconnect the negative terminal first if you are either
>>changing the battery or doing other work which necessitates disconnection.
Unless the car is positive earth!
All moderns though are negative earth, positive is generally from the mid 30s to early 60s where it was thought (erroneously) to be a good anti corrosion measure.
Last edited by: Slidingpillar on Sun 3 Mar 13 at 09:09
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You should visit an old, Strowger, telephone exchange. They have 50v, open bus-bars, although they are protected by a fuse - 200A IIRC. You'll often see lumps of metal welded to them.
I had to make a 'hot' connection to one when adding new racks of equipment, on the unprotected side of the fuse! We're talking about an aluminium plank, about 300mm x 30mm. Colleagues decided to drop a metal dustbin lid at an inappropriate moment. Oh how I laughed.
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Colleagues decided to drop a metal dustbin lid at an inappropriate moment. Oh how I laughed.
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Bad boys indeed, did you return the favour?.
The mechanics at my first haulage yard would creep up the stairs to the room above the fleet engineer's office, then carefully raise a lorry wheel to head height and drop it on to the wooden floorboards just over Franks head..;)
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Bathtub - I've broken a breaker on an open copper busbar carrying 1.5 volts at 1000A
Now all ripped out, but the 100kW regional transmitters dating from the mid 30s at the Moorside Edge radio transmitting station were powered by diesel generators that were powered by what were really ship's engines. The generators produced 230 volt DC to an open copper busbar system with the HT and other supplies for the transmitters produced by rotating machines.
The rotary converter motors were started by progressively throwing open knife switches to a resistance box starter while making sure the current taken was within limits.
According to the station permanent staff at the time a visiting Health and Safety bod threw a fit and marched out. He later returned with his boss who took a far more pragmatic view since although one could touch lethal busbars etc, no untrained staff were admitted to the building. Presumably the staff didn't tell him such transmitting stations used to run vistor days in the 50's and early 60's.
I do have a final output valve of the type fitted. 7.5kW, water cooled, with 20 volt heaters and what is known as a bright emitter or heater cathode type. Transmitter ran 12 in parallel with two more as 'hot' reserves.
Last edited by: Slidingpillar on Sun 3 Mar 13 at 10:33
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Was project manager for the second batch of the replacement BR Diesel Railcars in the 90s - class 150/2 for the spotters.
Electircity supplied at 28V from a 200A engine driven alternator (there was a joke if there ever was one)
Unfused side of the distribution board had to have a safety screen as an unfused supply was "dangerous", Fused supply did not need one as it was fused.
Maximum design output of the alternator was 200A at 28V, the fuse that protected the distibution board was - 200A!
The joke was that on test the alternator would only supply 80A - Greenbat didn't last much longer.
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Battery disconnect question - Tigger
