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Short Circuiting Batteries


cuthound

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3 minutes ago, cuthound said:

Found this video, originally issued by BT as a training video to show budding power technicians what happens when you short batteries out.

 

 

 

Impressive. I particularly liked how far the main cable that’s coming from the top of the rack jumped when the current flowed through it; the right hand rule in action. 

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2 minutes ago, WotEver said:

Impressive. I particularly liked how far the main cable that’s coming from the top of the rack jumped when the current flowed through it; the right hand rule in action. 

 

Yes, strangely despite working for them for 35 years on critical power, i have never seen this video before. It was brought to my attention by a closed Facebook group for ex BT power staff.

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6 minutes ago, Loddon said:

I remember those yellow batteries, many years ago I had some on the boat as leisure batteries. I seem to remember the voltage being odd but cant remember exactly in what way it was odd.

 

 

They were 6 volt VRSLA (valve regulated sealed lead acid, AKA recombination batteries or AGM's) monoblocs of 100 amp hour capacity.

 

The video is a bit misleading calling them 54 volt batteries, there were 8 monoblocs giving a nominal 48 volts. 54 volts was the rectifier output voltage.

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37 minutes ago, cuthound said:

 

They were 6 volt VRSLA (valve regulated sealed lead acid, AKA recombination batteries or AGM's) monoblocs of 100 amp hour capacity.

 

The video is a bit misleading calling them 54 volt batteries, there were 8 monoblocs giving a nominal 48 volts. 54 volts was the rectifier output voltage.

IIRC I had 4 of the 100amp ones, may be the charging voltage I had to play with as in those days I didn't have an intelligent charger, just one that kept going up and up......

 

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A friend of mine who worked in a BT exchange back when I was with them too, managed to put the exchange out of service briefly - the most serious of all BT crimes - by shortcircuiting the 48v supply with his spanner and blowing the fuses while connecting up a new rack. As a penance he was "promoted" to general cleaning duties, and in his first week he carefully set up a (wooden) ladder so that he could clean the inside of the windows then climbed up it and set down his galvanised metal bucket, full of water, on to the two main bus bars. Not only did he shut down the exchange for a much longer time but the incredibly loud bang left everybody deaf for a few seconds, and then the cloud of steam from the water which had instantly boiled made it impossible to see across the exchange.

 

Of course BT never actually sacked anybody back then. He was "promoted" again, to toilet cleaner - and told that if he did well they might get him a new bucket after a few months; he resigned.

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48 minutes ago, Keeping Up said:

A friend of mine who worked in a BT exchange back when I was with them too, managed to put the exchange out of service briefly - the most serious of all BT crimes - by shortcircuiting the 48v supply with his spanner and blowing the fuses while connecting up a new rack. As a penance he was "promoted" to general cleaning duties, and in his first week he carefully set up a (wooden) ladder so that he could clean the inside of the windows then climbed up it and set down his galvanised metal bucket, full of water, on to the two main bus bars. Not only did he shut down the exchange for a much longer time but the incredibly loud bang left everybody deaf for a few seconds, and then the cloud of steam from the water which had instantly boiled made it impossible to see across the exchange.

 

Of course BT never actually sacked anybody back then. He was "promoted" again, to toilet cleaner - and told that if he did well they might get him a new bucket after a few months; he resigned.

 

Very early in my career with BT I witnessed a similar event.

 

A cleaner rested his galvanised bucket full of water on the exchange bus-bars, apparently something he had been doing for years. The exchange, being an old one in need of refurbishment, had bus-bars insulated with impregnated cloth insulating tape, rather than the later practice of insulating them with continuous PVC covering.

 

The bucket must have disturbed the crumbling insulation tape and shorted the bus-bars, which were carrying 1600 amps at the time.

 

There was a blinding flash, a loud bang, a cloud of steam and a scream. The cleaner was unhurt, but physically shocked, the ceiling was blackened and covered in splashes of metal. That was all that was left of the bucket!

 

Fortuneately the exchange wasn't dropped. Would have been a different story with the later electronic and digital exchanges.

 

 

Edited by cuthound
Clarification
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So I don't get accused of thread drift the object below is battery connected (gedit) and is ex BT, Alan should recognise it.

 

One of my jobs in BT was to get redundant repeater stations ready for disposal. This was "rescued."

IMGP4711.JPG

Edited by Ray T
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I worked in power stations where we had larger batteries at voltages of 50, 110, 240 and 500V. The cells of the 500V were small dustbin size. A short on those would be truly scary. The 500V load was basically to 100kW motor generator sets.

 

The video is exactly what trainees should be shown so that they get the idea of how dangerous this stuff can be.

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4 hours ago, cuthound said:

Found this video, originally issued by BT as a training video to show budding power technicians what happens when you short batteries out.

 

 

 

Why didn't they show this sort of stuff at school, if I knew jobs were available that allowed people to blow shit up I might have shown an interest in physics rather than biology 

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7 minutes ago, tree monkey said:

Why didn't they show this sort of stuff at school, if I knew jobs were available that allowed people to blow shit up I might have shown an interest in physics rather than biology 

You could have been a "Blaster Bates."

 

 

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43 minutes ago, tree monkey said:

Unfortunately by the time I started in the tree surgery world routine stump removal with explosives was over, it was a real thing 

 

Blaster Bates was more of a "tree funeral director" than a "tree surgeon". ??

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1 hour ago, PeterF said:

Perhaps people buying hybrid boats, or gas free boats with 48V battery banks should watch this video.

I have a 72 volts LifePo4 battery bank 30 of them they have fantastic terminal covers and then a wooden lid srewed on so I can so I cant screw up!!

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3 minutes ago, peterboat said:

I have a 72 volts LifePo4 battery bank 30 of them they have fantastic terminal covers and then a wooden lid srewed on so I can so I cant screw up!!

Just make sure the screws don't hit the terminals ...

 

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... and don't ask me how I know this!

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5 minutes ago, TheBiscuits said:

Just make sure the screws don't hit the terminals ...

 

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... and don't ask me how I know this!

They are in large insulated wooden boxes so over 25mm from the wodden sides, have you ever seen what it does to a 13mm deep socket when its dropped between the terminals? instant short socket ?

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13 hours ago, PeterF said:

Perhaps people buying hybrid boats, or gas free boats with 48V battery banks should watch this video.

 

Any battery is potentially dangerous, because if you short the terminals you can't turn them off.

 

50 volts and below is considered safe. Above that it is good practice to break them into 50 volt or lower sections when isolating them, by putting each 50 volt section through a multiple isolating switch..

 

At onr time one of the roles I had in BT was to investigate and report on any major power and cooling outages and near misses. I had one, where a guy thought an old Paper Insulated Lead Cable (where the lead outer sheath was earthed) was PVC insulated because the cable was painted black.

 

He broke almost every safety rule, he forgot to isolate the power plant, leaving the cable lug at 50 volts, didn't remove or tape up his rings, watches & medallions, and used an ordinary socket and ratchet (rather than insulated tools or wrapping ordinary tools in 2 layers of insulating tape).

 

As he undid the nut on the cable lug, his wedding ring scratched the surface of the paint on the lead cable, creating a short circuit from the live nut, through the socket and ratchet, through his wedding ring to the earthed lead insulation.

 

He was lucky not to lose his finger, which was burned down to the bone where his ring had been. He had to have numerous skin grafts and never worked on power equipment again.

 

So even for small jobs on batteries, always remove jewellery, use insulated or taped up tools and protect against accidental contact by putting and indulating matetisl (cardboardwill do) between the work and the hull or any other earthed components. 

 

 

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5 minutes ago, cuthound said:

So even for small jobs on batteries, always remove jewellery, use insulated or taped up tools and protect against accidental contact by putting and indulating matetisl (cardboardwill do) between the work and the hull or any other earthed components. 

One of the reasons I have never worn and still dont wear any rings or watches made of metal.

That and seeing someone lose a finger to a flight case catch on a steep ramp.

 

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