Lesson in complacency, Batteries they're safe or are they?

[Gordon]

Cor some scary stuff here. It just goes to show familiarity breads contempt. Just check out how little current it takes to cause cardiac or respiratory failure. Roughy a few tens of milliamperes less than it takes to light a torch. Do the sums a 10 watt inverter (if you could get one ) has the potential to kill. Even one of those innocent little inverters that plug into a lighter socket could be lethal. The most expensive inverter in the world won't differentiate between a human connected fully across the 240volt output and an appliance. As someone already has said neither with a trip. As for batteries. Yes those little bubbles are hydrogen. As already stated fun to play with but mixed with a little air becomes a lethal bomb. In my earlier days with Bt large glass lead acid batteries were used for all sorts if things and the bank of batteries to start a standby generator were a bank of 12 cells all made of glass and each cell was very big. These were kept under a careful maintenance charge so did not appear to gas. I did witness the aftermath of an explosion whereby the engine went to start an internal fault in the battery caused a spark. There were shards of glass and acid all over the room. Anyone who had been there to test run the engine ...well shudder to think. We were then sent round to top the water up well above the links within the battery to limit the hydrogen. Later they decided that was silly and took a load out. Then jelly cells were inventedi

[Gordon]

An amusing anecdote from schoolboy chemistry days. As many will remember the test for hydrogen is a lighted splint held at the mouth of a test tube the result was a harmless squeaky pop. Now on one open day one lad was given the job to demonstrate this he happily sat generating his hydrogen filling it by bubbling into the test tube through water and applying the test all good fun and quite safe. However the head came round with the dignitaries ,if I remember it was chairman of governors and the mayor. Protocol dictated that the pupil stops immediately and exchanges conversation with the honoured guests. Perfect timing he had got the hydrogen into the tube and by the time the worthys were ready to observe he continued. Because air had got in the resulting explosion of the glass tube over the mayor was well worth it. I believe the chemistry master proudly related this tale to schoolboys for the rest of his carreer.

[Guest]

Cor some scary stuff here. It just goes to show familiarity breads contempt. Just check out how little current it takes to cause cardiac or respiratory failure. Roughy a few tens of milliamperes less than it takes to light a torch. Do the sums a 10 watt inverter (if you could get one ) has the potential to kill. Even one of those innocent little inverters that plug into a lighter socket could be lethal. The most expensive inverter in the world won't differentiate between a human connected fully across the 240volt output and an appliance. As someone already has said neither with a trip. As for batteries. Yes those little bubbles are hydrogen. As already stated fun to play with but mixed with a little air becomes a lethal bomb. In my earlier days with Bt large glass lead acid batteries were used for all sorts if things and the bank of batteries to start a standby generator were a bank of 12 cells all made of glass and each cell was very big. These were kept under a careful maintenance charge so did not appear to gas. I did witness the aftermath of an explosion whereby the engine went to start an internal fault in the battery caused a spark. There were shards of glass and acid all over the room. Anyone who had been there to test run the engine ...well shudder to think. We were then sent round to top the water up well above the links within the battery to limit the hydrogen. Later they decided that was silly and took a load out. Then jelly cells were inventedi

 

Absolutely  right Gordon "The most expensive inverter in the world won't differentiate between a human connected fully across the 240volt output and an appliance".

 

Even though the main topic of the opening post was about dangerous charging, it's absolutely crucial to not lull people into a false sense of security with 240v AC, at even the smallest of amperages.

 

In my earlier days with BT (the "GPO"), I well remember the basements of the exchanges occupied by acid filled individual cells the size of washing machines, connected with massive busbars to supply the 50v DC, before generators were introduced.

[Gordon]

Absolutely but it must be emphasised that all charging is dangerous. Hydrogen is always produced hopefully is escaped pretty instantly

[ranworthbreeze]

I remember those banks of batteries, but with me they were in the Southern Island P.O., I worked subcontract for Tomas Ward's of Sheffield, our company made the control panals for the twin Dorman Detroit Diesels that were installed into the basements of the Post Offices over there in the early 70's.

I had to commission the installation (with the diesel fitter) and load test the two 3 phase half megawatt generators. These genorators were mains failure units that started and were on load within 15 seconds.

The cost must have been enormous even for the time and just to keep charging the batteries.

Regards

Alan

[Gordon]

Did those big boys have electric start? I remember a pair of Blackstone three phase half mega watt generators being installed in an exchange basement and these had compressed air start. No idea how that worked I assume a pressure vessel must have been kept blown up all the time

[ranworthbreeze]

Hi Gordon,

 

They were electric start, on mains failure both started and one took the load and then the second one came on line when it matched phase rotation.

 

These were dirty great big units with 7 foot square radiators, the bed framework was in fact the fuel tanks.

 

 

Regards

Alan

[DaylightGate]

Strewth!!!

 

Are all boaters in Norfolk ex BT (GPO)? That's where I started back in '68 London SE Region.

 

Gary

.

[Gordon]

Hi Gary welcome aboard. Yes there are a few of us about. Hope we are not guilty of hi jacking the thread for an old PO mans rememiscence. The message of the thread still remains. Respect those batteries they have more than one way of killing you

[ranworthbreeze]

Hi Gary,

Not all but going by the posts we have on the various topics a lot of us are ex BT or electrical engineers.

The company I worked for would not make me up an Approved Electricial when I was 25 ( a difference in those days of 2P per hour from £1.23 to £1.25 per hour) so I left and worked as a service engineer for a fruit machine operator (rather than taking the job as the works engineer at Crosby Kitchens) for 5 years until I went self employed in 1980, the rest as they say is history.

When we were in the Dublin Post Office we needed to speak to a supplier in the UK and the exchange engineer showed us how quick he could monitor a line (a bit against the official Secret act that every BT employee in this country had to sign).

Tan used to work in BT sales and my father in law was high up in the drawing office.

Regards

Alan

[DaylightGate]

Hi Gary welcome aboard. Yes there are a few of us about. Hope we are not guilty of hi jacking the thread for an old PO mans rememiscence. The message of the thread still remains. Respect those batteries they have more than one way of killing you

Hi Gordon

 

Sorry I didn't mean to go off at a tangent. Power is  very dangerous at all levels and must be treated with respect.

[webntweb]

As well as regular servicing we have our shared boat Lightning checked by the boatyard's engineers every time it returns to base (about 40 times a year); batteries used are a quality brand and enclosed in vented boxes yet we still had one explode last year.

 

Roy

[ranworthbreeze]

Hi Roy,

Sadly it does happen, just goes to show even preventative maintenance does not always work.

Regards

Alan

[Viking23]

I just come across is thread, and what struck me was that most isolator switches are preferred by BSS to be located as close to the battery as possible.

This thread clearly shows the dangers of hydrogen gas given off from a battery even during normal charging.

So under fault conditions, which could cause an increase of hydrogen and oxygen to be given off, then we would normally switch off the isolator...

However, the isolator switch might well be in the same localised atmosphere as the batteries, so the explosive gas mixture too, I don't believe that the cheap plastic isolated battery switches are explosion proof, or even sealed against the ingress of the explosive mixture.

So there is a risk that the battery isolator could create a spark within the confined area of the switch contacts causing an explosion that ruptures the switch housing and then the exposed flame or spark can ignite the explosive gas in the battery compartment...

I have worked and designed industrial systems for use in hazardous areas, and this set up would not be allowed.

So is the BSS wrong with this set up, and should battery isolator switches be mounted in an area away from the batteries?

[grendel]

the battery isolator should be close to the battery to minimise the run of wiring, personally I would have a isolator solenoid with a remote switch for preference, this would be a fail safe method as you would be remote while switching. in an explosion rated package.

I have also been the subject of a battery explosion (internal fault - battery exploded when I turned the key on a van) in my case I was in the van and the battery in the engine compartment, so I avoided the spray of acid, but battery shrapnel was found up to 30 feet away, so presumably the acid went at least that far.

Suffice to say, having seen that I dont want to be around if a battery goes up.

I have also seen the effect a battery has on someones finger when they accidentally short across the terminals when using a screwdriver and their wedding ring touches screwdriver and the other battery terminal, having the wedding ring cut off was the least of his worries, for a while they were worried about saving the finger. (moral, take your rings off when working with batteries).

I too work in the electrical industry (in the drawing office) we work at up to 33,000Volts, so we have a great respect for the stuff.

Grendel

[Guest]

.....I have also seen the effect a battery has on someones finger when they accidentally short across the terminals when using a screwdriver and their wedding ring touches screwdriver and the other battery terminal, having the wedding ring cut off was the least of his worries, for a while they were worried about saving the finger. (moral, take your rings off when working with batteries)........

 

You've reminded me of a poster they used to show new apprentices in the GPO when I joined in the 1960's.

 

It showed the result of such an accident.

 

The exchange "bus bars" were only 50 volts DC, but they carried thousand of amps, so the ring had vaporised in a split second. 

 

The effect from a 12v 110 amp battery would be pretty bad too, because the "110 amps" just means that it's nominal capacity is 110 amps continuously for one hour. In the case of a dead short with a metallic object, the momentary current would be many times 110 amps.....