Hi I was reading in a different forum that someone had a vintage power supply which had 2 neons 1 from each side of the centre tapped secondary which normally just glowed but at switch off they would flash bright blue because of the inductive kick from the transformer and from the smoothing choke the idea being to protect the rectifiers by clamping the spike. Also the PSU was designed to run motor generator sets feeding them 28 volts DC obviously motors are also a bit inductive so guess these nons helped with that too.. My question is do you think there's any mileage in using neons across the mains to act as surge arrestors? I'm thinking they could be a cheap option instead of MOVs etc what do you think? Am I miles out here or on to something?
I have used neons to clamp lower voltage lines than mains - antennas and so on, but . you need to be aware they are not really up to dissipating much energy , probably only a joule or so before they shatter. The other problem is that once they enter the impact ionization arc state- the blue flash is the onset of an arc, they have a very low voltage drop, typically less than 10V, and the current must be interrupted for several milliseconds before they extinguish, and go back to the glow discharge that drops 70-90 V..
Normal signal neons run off the mains rely on a current limiting resistor of perhaps 100k ohms to limit the current to ~ 1mA to stay in the orange light glow discharge
state.
There are ceramic bodied gas discharge tubes with higher power ratings , but again they go near-short circuit when lit, so need a bit more thought and cannot be just left across the mains without additional ADS measures.
So not really up to the job of surge protection then. I guess if they were some manufacturer would of taken advantage by now. In the PSU I mentioned the neons only flash at the moment of switch off which must be what saves them from destruction it does prove though that spikes on AC lines are a real thing.
Neon lamps can be used as surge arrestors and have the merits of low cost and simplicity. More applicable to low power and ELV circuitry than for mains power supplies.
Can be used between chassis and the aerial of vehicle mounted radio equipment, to protect against high voltages from capacitive coupling when the vehicle passes under high voltage lines.
Also can be used to shunt 24 volt or lower voltage relay and contactor coils so as to limit the back emf when the coil is de-energised. A neon lamp works with DC of either polarity or with AC unlike the commonly used silicon diode. A neon lamp also allows the relay or contactor to open more promptly.
The internal contacts in a door bell or buzzer may be shunted with a neon lamp to reduce contact wear and radio interference.
24 volts nominal (up to about 30 volts actual under worst case conditions) is probably the safe limit for neon lamps as surge arrestors. Much more than that might result in the lamp striking due to a surge and then remaining lit and blowing up.
Private telegraph, telephone, or intercom lines may be earthed each end via neon lamps as a defense against static electricity.
