Vibrator relay keeps melting.

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RayRay1132

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I've recently built a high voltage circuit with an old 50's car radio vibrator relay which turns on an off a transformer which is connected in series with a power supply. I've noticed the relay arm will get red hot and start melting if I short out the secondary of the transformer or put a big load on it. (or sometimes just randomly starts arcing). I'm using the correct voltage(12VDC), for the relay. Is there any way to stop the arcing between the relay arm and the contact? I know a while back someone mentioned adding a capacitor somewhere in the circuit but I can't quite remember where? Any help would be greatly appreciated.
Thanks in advance -Ray
 
Is it a changeover type vibrator & centre tapped transformer, or a single on-off contact?

If it's a changeover one, you can use diodes across the contacts to suppress any high voltage. A single ended one needs a diode and series resistor to limit the spike voltage without allowing the current to continue to circulate too long.

Another problem with single-ended drive is that the transformer core can very easily saturate if the magnetic field builds up too much (as it never reverses), unless it's a transformer designed with that use in mind.
Saturation means the inductance drops off and the winding pretty much becomes a short circuit...
That could be your problem.

Also make sure you have the correct connections on the vibrator; some have multiple connections, with the vibrator drive contact and power contacts having different timings. Getting them mixed up will reduce efficiency.
 

Are you serious? - second stupid dangerous question of the morning. Why on earth are you shorting out the secondary, or overloading the transformer?.
 
There are two types of vibrator, synchronous and non-synchronous. the former is obvious due to the absence of any rectifier on the transformer output.
DC produced by the switching.
 
Nigel Goodwin said:
Are you serious? - second stupid dangerous question of the morning. Why on earth are you shorting out the secondary, or overloading the transformer?.
Click to expand...
I was shorting out the transformer because i'm trying different transformers to see which one will work best for powering a homemade neon tube. The argon/mercury "neon" tube I made has a very low resistance one started hence the short.
 
RayRay1132 said:
I was shorting out the transformer because i'm trying different transformers to see which one will work best for powering a homemade neon tube. The argon/mercury "neon" tube I made has a very low resistance one started hence the short.
Click to expand...

So what about the ballast? - you don't short a transformer out.
 
No, but I would keep someone close by with phone, and an Ambulance on speed dial - heading for potential blindness and death.
 
Nigel Goodwin said:
Putting a dead short across the secondary of a transformer?, hoping a sheet of glass or plastic will prevent high power UV radiation from causing severe damage to you.

You're certainly not 'careful'.
Click to expand...
some glass does block most of the uvc wavelength, I just forgot which one. As for the transformer I have no excuse lol.
 
When I was in high school 50+ years ago I had a factory made vibrator type 12vdc to 120vac converter. In those days they were called converters but now days they are call inverters. The factory made vibrator converter had a current limiting choke transformer. I think the choke coil was on the output is the step up transformer but not 100% sure. The convert was low power about 100w.

I built an inverter once many years ago just for a learning project using a 555 as the 60Hz driver to turn a mosfet 5% on & 95% off time. Mosfet over heats just like the vibrator with 50/50 duty cycle. 400Hz worked better than 60Hz. The circuit still sucks.

Harbor freight inverters will run a 12v battery dead with the switch off. Remove alligator clamps when not using the inverter.
 
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Not at all, the FET overheats if you designed and built it wrong - which was obviously the case. It's not as trivial a design as you might imagine.
 
Years ago, many years ago, I played around with the vibrators from car radios. I suggest you look at some of those old car radio circuits and note the rectifier tubes/valves used. Then look at some of the old tube/valve data sheets. You will notice the maximum forward current those tubes/valves could handle. The tube/valve plates in those old radios did not use much current at all. When you overload something the end result is generally smoke or in the case of a vibrator some molten metal and contacts. When the gas in a neon tube ionizes the current draw is low but many neon tubes require from 1.0 KV to 15 KV.

This would go much better if you had data on the neon tube you are using. Today there are inexpensive solid state neon sign transformers designed for safe use. You may want to look that way. Unless you are using something like a little NE2 lamp. It's all in the details.

Ron
 
I wish I had a datasheet, I made these tubes myself and they are nitrogen/mercury filled. They strike around 1.5-2kV. I've switched to using my own homemade 3kV transformer with a ballasting air gap, now the problem I have is as the temps of the tubes go up so does the maintaining voltage, sort of like an old hps lamp at eol.
 
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