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nice and clean Jacob's Ladder

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Alexandre

Thu Jan 28 2010, 01:30PM

Registered Member #1228 Joined: Tue Jan 15 2008, 01:08AM
Location: Curitiba, Brazil
Posts: 162

Last night I decided to build a simple design but well done.
A beautiful and well done Jacob's ladder. For the structures used the legs of an old chair that was here at home and not have danger of burning wood, with which it was fixed, I put 4 insulators.

Look at the pictures:

The power supply used in this test, is a Dual-Mot, with a ballast.

Video:

Alexandre - Brazil

HV Enthusiast

Thu Jan 28 2010, 04:35PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

That jacob's ladder should really be enclosed. MOTs are downright lethal and if you or someone accidentally touch the jacob's ladder output, it will likely be fatal. NST powered jacobs ladder are not lethal because the current is relatively low. But with MOTs, the output current is on the order of pole transformers.

Be very careful.

Mrkva

Thu Jan 28 2010, 05:01PM

Registered Member #2655 Joined: Wed Jan 27 2010, 04:09PM
Location: Czech Republic
Posts: 18

NST output current isn't lethal? Really? Typical NST is rated about 30mA output current which is, at 50Hz, capable of causing a heart fibrillation and death.

Dr. Dark Current

Thu Jan 28 2010, 06:04PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Currents up to 30mA are considered "safe". I once saw a chart which showed how much time is needed to fibrilate a heart at a given current, and even at current way higher than 30mA (don't remember exactly, hundreds of mA or more) I believe it was more than 1 second.

Coherent

Thu Jan 28 2010, 08:45PM

Registered Member #1886 Joined: Sun Dec 28 2008, 02:55AM
Location:
Posts: 73

It's only dangerous if you touch it while it's running and if you manage to do that you'll at least win a nice Darwin Award. Also even if he enclosed the ladder he would need to also protect the mots and all of the connections. Overall too much effort to idiot proof something that idiots should never have access to in the first place.

Alexandre

Thu Jan 28 2010, 09:55PM

Registered Member #1228 Joined: Tue Jan 15 2008, 01:08AM
Location: Curitiba, Brazil
Posts: 162

Thank warnings, but this experiment is really only for myself, if you want to show someone certainly put something back, but it's just an experiment quickly.

Alexandre-Brazil

radiotech

Fri Jan 29 2010, 01:59AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

RE: Dangerous NST's can burn you deeply at the arc contacts site.
Other dangers:- 'let go' current which if passing through body paralyses muscles needed to breeth and disengage.
Electrical workers are trained to pull such cases away without becoming caught themselves.
A fellow electrician , who grabbed a 2300 V busbar thinking it was dead, was 'dropkicked' free by a crewmate and dragged back. he had handburms and the bussbar had his handprint burned into it.

MinorityCarrier

Fri Jan 29 2010, 06:34PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

At Hughes Aircraft in Carlsbad California, in 1981, a maintenance tech working on a HV power supply (~5KV) for an inductively-coupled hivac evaporator, accidentally hit the power switch with his knee while he had his hands inside the unit. While the involuntary muscle contraction caused him to recoil from the cabinet, and he yelled out to other technicians present, his heart stopped and fellow workers were unable to get his heart to re-start. He died before the Emergency Ambulance team arrived.

radiotech

Fri Jan 29 2010, 07:13PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

that was exactly rhe position the guy was in in my post. Kneeling with hands insides a dolly switch that was supposed to disengage when pulled to that position.

HV Enthusiast

Fri Jan 29 2010, 08:02PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

wrote ...

Other dangers:- 'let go' current which if passing through body paralyses muscles needed to breeth and disengage.

"Let Go" current threshold has nothing to do with body paralysis or breathing. Its merely the point where the flexor muscles in the arm contracts involuntarily and prevents someone from removing themself from the conductor. This threshold is typically around 9-15mA in males (60Hz AC), and about 62mA (DC).

However, you are correct that contact with an NST can be dangerous, but typically this very rare. Most due to the fact that an NST is internally current limited to a relatively low current (15-60mA), and hand contact with the NST will simply current limit the NST and the voltage will fold-back considerably.

A MOT on the otherhand does not have internal limiting and can put out just as much current as you can feed into the primary side. If you make contact with a MOT, the arc will be able to supply HUGE amounts of current (as denoted by those flaming jacob's ladders photos) and is EXTREMELY dangerous.

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