How dangerous is a Nixie Power Supply? HV Advice please

[NivagSwerdna]

I have built the driver board for my Nixie clock.  It has two power supplies one is 5V the other is a HV PSU (https://threeneurons.wordpress.com/nixie-power-supply/ design)...

The board takes 9V at around 150mA (when driving six tubes) currently from my bench supply.

The question I was asked was... how dangerous is it?  I was unable to answer that question and thought that was a bit of knowledge I really needed.

The board is currently on my desk attached to tubes but otherwise unprotected until I build a case.

So... is it potentially lethal? 

I'm planning on building a case of 1mm clear perspex.  I'm assuming that is adequate protection but ideally I would have a potential gaps, around the vertical tubes, where on a really bad day someone could spill their cup of coffee etc.

Please could someone quantify the dangers of this.  Is it just a nasty shock risk or something I should care alot more about?

Thanks in advance

[ebclr]

Not dangerous at all, nixies needs 170 to 200 volts, but current available isn't enough to burn an ant, in worst case scenario you will get a small electric shock.

If you use a pacer on your heart, this can be a problem, otherwise, it's very low risk.

I noted you are from UK, in UK anything higher than 12 V is considered dangerous

[Gyro]

I noted you are from UK, in UK anything higher than 12 V is considered dangerous

 Huh?   Maybe you should set your country flag!

[DaJMasta]

My nixie clock project used a separate DC converter module to get the high voltage, capable of 10W or so and set to about 140V (plenty for the tubes I was using).  Shocked myself accidentally on the bus running on the bottom of the boards, was definitely noticeable, but not especially painful.  Still felt a tiny bit of the whole-body tightness that can be associated with a bigger shock, but not really pain and not so strongly that my hands tensed up or anything.

I would treat it as your normal high voltage - mains voltage but lower current - but if something does happen, it probably won't be very painful.  You never want to just subject yourself to a high voltage shock, and you could look at this as a good opportunity to develop better habits in terms of probing and where to put your hands.... but I don't think it would be lethal unless it was over paddles across your heart.  Just touching it shouldn't do any lasting damage.

[Zero999]

I noted you are from UK, in UK anything higher than 12 V is considered dangerous

 Huh?   Maybe you should set your country flag!

He's probably from some dodgy country where no one gives a toss about safety and climbing up 12kV power lines to connect up a pirate transformer to steal electricity is the norm. 

I have built the driver board for my Nixie clock.  It has two power supplies one is 5V the other is a HV PSU (https://threeneurons.wordpress.com/nixie-power-supply/ design)...

The board takes 9V at around 150mA (when driving six tubes) currently from my bench supply.

The question I was asked was... how dangerous is it?  I was unable to answer that question and thought that was a bit of knowledge I really needed.

The board is currently on my desk attached to tubes but otherwise unprotected until I build a case.

So... is it potentially lethal? 

I'm planning on building a case of 1mm clear perspex.  I'm assuming that is adequate protection but ideally I would have a potential gaps, around the vertical tubes, where on a really bad day someone could spill their cup of coffee etc.

Please could someone quantify the dangers of this.  Is it just a nasty shock risk or something I should care alot more about?

Thanks in advance

To be picky, this is nowhere near high voltage, which is classed as >600V or >1000V, depending on the country.

As mentioned above, the circuit generates around 180VDC, at a limited current (under 50mA), which poses a small safety hazard, compared to the mains, even in 120V countries. The reason this is much less dangerous than 120VAC mains is because: the current is restricted and DC is much less likely to cause ventricular fibrillation than AC.

This doesn't mean you shouldn't be cautious, there's still a tiny risk it could kill you, it's just highly unlikely. Keep all the connections to the hazardous voltage insulated from the end user.

[Ian.M]

You've also got to consider energy storage in the output reservoir capacitor
https://www.physicsforums.com/threads/at-what-capacitance-do-hv-capacitors-become-dangerous-to-human-touch.688975/ should give you some idea of the issues, and help you find the standards and recommendations you should be adhering to.

If you cant meet your desired ripple specs with a smaller capacitor, consider using an active capacitance multiplier to attenuate the ripple without increasing stored energy and charge.

[mmagin]

Getting the nixie supply across the heart with sweaty hands, it could kill you if you're particularly unlucky.  There's the apocryphal tale of the guy that electrocuted himself with pointy meter probes on an old VOM (that uses 30V on some ohms ranges.)

If it's floating with regard to ground and you try to always keep one hand away from the supply while it's on, you probably won't even get a tingle.

If you do get a tingle off of it, consider it a lesson.  Stop, turn things off and think about what you were doing before you do anything that stupid again.

Also, as a reminder, all your antistatic wrist bands, table mats, and floor mats should be at least 1M ohm to ground.  Before you go messing around with high voltage, you might want to verify that.

[Zero999]

You've also got to consider energy storage in the output reservoir capacitor
https://www.physicsforums.com/threads/at-what-capacitance-do-hv-capacitors-become-dangerous-to-human-touch.688975/ should give you some idea of the issues, and help you find the standards and recommendations you should be adhering to.

That's an interesting thread. You raise a valid point about the capacitor. As I'm sure you're aware, It's the energy stored in the capacitor, just as much, as the voltage which makes it dangerous. However, the voltage will be important too with lower voltages being less hazardous, given the same amount of stored energy. If I remember rightly, most safety standards say capacitors should be discharged to below 120V in under a few seconds, after the power has been removed, which suggests <120V is fairly low risk. This is from memory only so, don't take my word for it. I'll have to do some research.

There's the apocryphal tale of the guy that electrocuted himself with pointy meter probes on an old VOM (that uses 30V on some ohms ranges.)

I've heard that one before too but  find it very hard to believe.

I think the one about someone being electrocuted, when they touched a 24VDC system on a small boat, when they were immersed in salt water from the waist done, had soaking wet hands and the regulator was probably faulty (the actual voltage was much higher than 24V) more plausible.

The dampness of the environment is taken into account, when looking at the risk of electrocution. For example, exposed 48VDC would be fine in a dry environment such as on a workbench, but it wouldn't be acceptable in a wet room.

[james_s]

I'm not going to make a blanket statement here because some nixie tube power supplies are capable of delivering a lot more current than others. It's important to remember that under the right circumstances it only takes some 10mA across the heart to cause death so don't get careless. A typical nixie PSU is probably not going to kill you but speaking from experience, getting zapped by one hurts! Just use common sense, treat it like you'd treat mains from the wall, it's generally quite a bit safer but why chance it?

[Paul Moir]

For perspective, just a few years ago people held substantial a capacitor charged to 350VDC to their faces every time they wanted to take a picture.

[ebclr]

How many volts do you need to take 10 ma on heart ?

[calexanian]

Anything with more than 42 volts is potentially dangerous according the the NEC.

Now that that is out of the way.....

Its only as dangerous and you would be careless. You should keep your wits about you and best practices with any higher voltage circuit. I have been careless and been zapped several times, and every one of those times counted my blessings and moved on. being in the states 120 vac is what gets you the most and its an interesting feeling. something you never want again.

Keeping your work area orderly is key. Its the thing you are not thinking about that gets you. Design the job to lessen risks.

Look at it this way though. Driving a vehicle can be dangerous. We practice best procedures to be safe. Electronics is no different.

[nowlan]

I was under the impression DC was worse, because it never lets go like AC.

[NiHaoMike]

A 2.2uF cap charged to around 200V isn't particularly dangerous, giving a little sting similar to static electricity. The converter itself, however, could deliver a dangerous current.

Not dangerous at all, nixies needs 170 to 200 volts, but current available isn't enough to burn an ant

Doesn't take very much current at all to zap an ant. Know that from when I experimented with small high voltage circuits and I made a 500V or so supply that was so low powered that (so long as the output capacitance is kept very low) the current can't even be felt, but it would zap ants with ease.

[mmagin]

For perspective, just a few years ago people held substantial a capacitor charged to 350VDC to their faces every time they wanted to take a picture.

I never came in direct contact with one of those while operating a camera!

[Siwastaja]

I was under the impression DC was worse, because it never lets go like AC.

50/60Hz AC is bad because it messes up the rhythm of the heart. The near-zero current periods in the AC are too short for muscles to let go.

Depending on legislation/standard, the "safe" limits differ, but it's usually around 50V of 50/60Hz AC, or 100V of DC. These are typically called extra-low voltages or safety voltages, and it means it should be safe to actually touch them; even though touching 50V AC or 100V DC is definitely not fun!

[NivagSwerdna]

Many thanks for all the replies so far. Looks like I haven't created a definite kill device which is a great relief.

I am indeed UK based and have been told from birth how scary 240V mains supply is.

Sounds like a simple acrylic box (i.e. not earthed) to keep prying fingers away is sufficient.

(I do need to get an enclosure ASAP due to the conductive tools etc floating around my desk).

Thanks to those who have touched their Nixie power supplies so I don't have to! I am very happy you are still here! 

[mikerj]

I'm planning on building a case of 1mm clear perspex.

That sounds a little too thin to create a reasonably robust case IMO.

[NivagSwerdna]

I'm planning on building a case of 1mm clear perspex.

That sounds a little too thin to create a reasonably robust case IMO.

Indeed. You are correct.  I mean either 2mm or more probably 3mm.

[Zero999]

I was under the impression DC was worse, because it never lets go like AC.

50/60Hz AC is bad because it messes up the rhythm of the heart. The near-zero current periods in the AC are too short for muscles to let go.

Depending on legislation/standard, the "safe" limits differ, but it's usually around 50V of 50/60Hz AC, or 100V of DC. These are typically called extra-low voltages or safety voltages, and it means it should be safe to actually touch them; even though touching 50V AC or 100V DC is definitely not fun!

Yes, that's true.

The safe voltage limits also vary depending on the surface area of the metal conductors and whether the equipment is designed for use in dry, damp or wet areas.

[GoneTomorrow]

If it is powered from an isolated power supply (bench PSU, and most SMPS's) then the risk is even lower. You'd have to contact both the positive and negative output of the 'HV' PSU to create a circuit with yourself included. Simply touching one leg of the output is fine.

[NivagSwerdna]

It's only attached to my bench supply during development, ultimately it will be powered by a 9v wall wart.

[CJay]

Probably not that dangerous unless you've a weak heart and manage to stick it across your chest but why take chances, treat it as dangerous and apply safe working practice anyway, that way you form the habit and when you do come across a supply that's capable of damaging you it's second nature to be safe. (reminisces about all the stupid things I've done))

[westfw]

The board takes 9V at around 150mA (when driving six tubes) currently from my bench supply.

Conventional wisdom is that the output current of HV or moderate voltage supplies like this (power by a low-voltage source) is limited by a lot of other factors to relatively safe levels.  Say you replace the bench supply with a 200ma 9V wall wart.  It can now provide about 1.8W, so your HV converter delivering 180V can only deliver about 10mA, even under ideal circumstances (ie not through real components, and real skin contact, and etc.)  And that should be below the levels "generally recognized as dangerous."  You can mess it up, of course - stick a couple of thousand uF of electrolytics on the output of the supply, and you might be able to build up a fatal charge; eventually; if something doesn't burn out first.  And you can definitely FEEL 180V at low current; you could surprise yourself and fall off the ladder you were using to mount the clock on the wall, onto the sharp corner of your glass coffee table, and kill yourself...

(This is OLD conventional wisdom, from the sort of "electronics projects for teens" books published in the 60s - "Build a shocking prank device" - "the output power of this is limited by the low power you can get out of the battery used to power it."   (Those were carbon zinc cells.  I've often wondered if someone has managed to hurt themselves by building one of those projects and powering it with a modern Alkaline or rechargeable battery...))

[ZeTeX]

Only 1 way to find it out: touch it.

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