There are a variety of ways to set up one’s neon bombarder controls. The method chosen will depend in part upon the specific installation, equipment purchased, and personal preferences. In any case, safety must be the primary concern.
The output of a typical bombarding transformer is quite dangerous if one is not respectful of the power involved. Get yourself shocked by a regular 30ma neon sign transformer and it will give an unpleasant bite to remind you not to be so clumsy. …..but come across a bombarder whose current ranges anywhere from 200ma to a full amp and the likelihood of death is very real and second chances to learn from the mistake are rare. In all probability, you’d be dead before hitting the floor. Even if you only got a partial hit of some of the current, and even if not instantly deadly, the shock can and likely will be severe enough to cause heart rhythm disruptions and other odd symptoms (sore muscles, burning sensations, metallic tastes, etc) that may last for a while afterwards. So needless to say, this is a big deal. You’ve been warned.
Any system, be it commercially purchased or homebuilt, should incorporate a few basic shut off points, indication lamps, and always be well grounded. Some go as far as safety cabinets with interlocks, but even if you don’t go that far, you can build in a few basic and effective safety points.
Grounding. First and foremost. Build all your hardware with a good dedicated grounding point and use it! This is so basic, yet sometimes overlooked and in at least one case I am aware of a failed ground connection ruined a person’s day and almost killed them. Don’t skimp on this. Make certain the ground connections are in good order. Make it part of your inspection routine prior to operations.
Disconnects. Provide a good reliable main supply voltage shutoff point that is close to your control point. A master switch. Be it a simple 2 pole switch or a disconnect pull or an additional circuit breaker downstream of the building’s breaker box. Something close to your working location at the bench that when you turn it off, the entire system is absolutely and positively disabled.
The contactor (relay) and footswitch or push button. When you hit the button or footswitch, the contactor coil is powered and this causes the heavy contacts to close and send power to your choke and bombarding transformer. These should be good momentary switches with adequate guards and, again, properly grounded. Do not put a simple toggling household light switch here! (yes, I’ve seen it done in a few shops….. Just. Don’t.) My personal preference is for a big, safety guarded foot switch with a momentary spring loaded contact. If you step off of it, it turns off. A so-called (but hopefully not) “deadman” switch. And as a matter of good practice, keep your hands to yourself when you press it. Errant hands can provide an entry point and pathway for current.
Additional safety switching. Although many would be content to turn on one switch and then hit the button, I am not. I suggest adding at least one more switch ahead of the power to the button. The idea being to add deliberate decision points in the steps leading up to activation of the power.
Indicators. Lamps or meters or some other tell-tale device to indicate when parts of the system are energized. I have three. …and may add a fourth, more on this later.
The first lamp is illuminated anytime that the main master disconnect is on. This lets the operator know that it is possible that voltage could be present elsewhere in the system. My procedure is that if this lamp is on, nothing on the processing table is to be touched. Connect your wires to the unit….then turn on the master. If some hookup doesn’t look right, turn the master off and then correct it.
Next is a safety capped toggle switch with another lamp. This is the arming switch. Lifting the cap and turning this on illuminates the next lamp and supplies power to the footswitch. After this stage, pressing the footswitch will activate the contactor and bombarder. (The safety cap is of the aircraft type and if the cover is pushed shut, the toggle is returned to the off position.)
When the main and arming switches are on, and that footswitch is pressed, one more lamp will illuminate along with power being applied to the transformer. Of course, at this stage, you should hear the clunk of the contactor and the hum of the transformer and also see the unit being processed illuminate. But in the event of some issue preventing all of that, at least you’d see the third lamp come on.
Below is a sketch of how I set up my controller, I drew this schematic for another bender and showed the choke as a generic box because it is possible to connect any of the popular choke arrangements at this point. My system uses a large variac as a source of variable inductance. (see “The wrong way to connect a variac…” http://www.novioljourneys.com/?p=581 ) Others opt for the slide chokes or the DC reactance chokes (aka saturable reactor, or “Superchoke” and similar products)
Note that I used a 3 pole contactor and also made use of the 120/240 conventional 3 wire arrangement with the neutral lead. Three pole contactors are very common since they often get used in 3 phase circuits. The use of the neutral allows me to tap 120v for the foot pedal, contactor coil, and indicator lamps without having to provide a separate dedicated 120v line for this purpose. In addition, if you do use a saturable DC reactance type choke, you can tap into part of the 120v portion to power the reactor’s small variac and rectifier control circuit. If this is your situation, I recommend tapping this ahead of the contactor so that your control power is on and available to saturate the core prior to the contacts being closed to apply power through the AC choke winding and bombarder. This will lower the surge current as you will only be adding this load rather than simultaneously adding the load of the DC control power too. Also, if some minute lag exists in building the magnetic flux in the control core, this will eliminate that having an effect on the bombarder output at the moment of being powered…..but follow the manufacturer’s wiring recommendation.
Also note that I placed my main power indicator lamp across the neutral and one of the hot leads of the power. Then I put the next lamps on the neutral and the other hot lead. This was purposeful. It allows a quick check that power is on both legs of the incoming line. If one lamp fails to illuminate, it is a clue to check things. Sometimes breakers fail….and dual pole breakers sometimes loose one pole and not the other.
The fourth lamp. Presently, there are only three lamps used, but I am thinking about adding a fourth. This additional lamp will be placed on the main input in tandem with the one that is already there but it will be connected to the other hot lead, thus allowing instant verification of main power on both poles and also provide redundancy in case the first lamp were to fail.
You can also replace these lamps with meters, or omit the use of the neutral and go with 240 volt lamps and a 240v contactor coil if your purposes or parts bin contents suit doing so.
Add a warning sign. If not for you, for the possible visitors who may wander by. It need not be elaborate. It need not even be a purchased item. ….of course, if you happen into a few choice antique porcelainized high voltage signs from around the world, you could make an art piece out of it.
Of course, in spite of all these efforts and ideas, how well it works and how safe it is will ultimately be dependent upon you. Just like a pilot’s checklist (and yes, you can make a neon processing checklist too!) and your training plus your experience, these are all just tools to help you avoid making mistakes. And since it is so damn easy to make mistakes anyway, you might as well try to build your system so as to make it harder to make those mistakes.
I have little doubt that this critical information may very well save someone’s life. Well done, and thank you my friend.
– Lee Colwell