DC limiter

Asbjørn · 2006-11-10T00:01:42+00:00

The halogene spots in the elevator outside my appartment repeats going out - because of malfunctional electronics from the elevator company, the voltage rise from the normal 12V and up to 30V. In OrCAD PSpice I have tried designing a simple circuit with a 12V zener diode keeping the DC voltage at 12V at varying input 12-30V. But it doesn't work... anyone have an better idea?!

Nov 10, 2006 23 Replies

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DaveM 19 years ago

Ross Herbert skrev:

Well, yes, I have just downloaded the PSpice ver. 15.7, so I had do practice some simple circuits... Their are some crack heads - writing: you gunn'r kill somebody etc. - so thats why I need to mention my upcoming bachelor degree, telling them... well I'm not an 13 year old kid making some fun!! I need some practical study as well, and everybody nedds to start somewere...

I will return with some more information, when I have spooken to the electricians - a part of the difficulty in the task is not knowing the exact circuit of the halogenspot, the voltagesupplier (trafo), average time of overvoltage, exact maximum voltage level etc. My motivation was, well: just use a 12V zener, that should do it - but know I've learned :)

Perhaps if you had asked the electrician about Gov't regulations concerning elevator maintenance, he might have told you that modifications to electrical controls and components are very restrictive as to who can make the mods and install them. Usually, only licensed elevator maintenance people can repair an elevator, and only within specific limits.

Perhaps the maintenance company needs to hire a qualified engineer to properly diagnose and repair the equipment.

Cheers!!

Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Some days you\'re the dog, some days the hydrant.

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AJ 19 years ago

Maybe a Polyfuse followed by a decent sized TVS like15KP13A? Any voltage above 15.9V max will be clamped and if it remains for a while the polyfuse kicks in so the TVS isn't damaged.

Regards

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Ancient_Hacker 19 years ago

Well, a little thought beforehand might have helped, along the lines of:

** The elevator is not owned by me.

** Therefore I am not responsible for the equipment in it.

** An elevator is a device which is entrusted with the lives of people.

** So it's likely there are rules, standards, norms, laws controlling who can service an elevator.

** So I should NOT even think of doing anything to it.

-------- Also:

** Just about every incandescent light bulb is run off AC.

** A Zener only regulates DC.

** Therefore a Zener is not a good match for regulating an incandescent lamp.

** This looks like a 25 watt lamp.

** Most Zeners I've seen are like 400mW to 1W.

** For a Zener to regulate it has to be fed from a higher voltage source. We only have 12V available, which is also the output voltage. Oops.

** To regulate a 2X overvoltage will require the Zener to dissipate Y times the delivered power. Y depends on the value of series resistance.

** It's going to take 20 to 50 1W Zeners at the very least to do this.

** The zeners are going to dissipate 20 to 50 Watts. Where is this heat going to go?

** Zeners require a series resistor to limit the current BUT in this case the resistor has to be very low value to pass 12V with a 12V input. What will the resistor value have to be? How many watts will it dissipate? Where is this heat going to go?

Things to think about.

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