Voltage Detection Circuit

[tulum]

Hello,

I am looking to make a small circuit that is capable of detecting 600Vac. All it would need to do is detect if the voltage was present and then turn on a dry contact.

I need it to be small, so I was thinking electronics...otherwise I would just use a PT.

Any ideas...

Regards,
TULUM

 

[Comcokid]

Optocouplers such as the Avago (formerly Agilent, formerly Hewlett Packard) HCPL-3700 is made for AC threshold detection up to 240 VAC input.The output of this device could then drive a very small relay, or could be buffered by a transistor to drive a large relay.

For 600 VAC, you might have to use a low current transformer to step-down to the maximum voltage of this device. Optionally you could put some series high-voltage power zeners to step down for the device.

600 VAC is more in the HVAC realm, so a proper "small circuit" does leaves some questions on isolation, safety, and agency issues. Just what is your application?

 

[ScottyUK]

We know it must detect 600V AC, but what voltage must it not detect? 599? 500? 100? This will have a significant input to whatever method you use.
More info needed!

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Sometimes I only open my mouth to swap feet...

 

[tulum]

Scotty,

Basically, I just want to know definitly when the power is on.

With the system it does not matter when it drops out (I was thinking of sealing in the contact after it is picked up)

As far as detecting when it pickups up... it should be in the realm of 80% full voltage (like a relay) or if possible 90-95%.

Just looking for a point in the right direction to a power electronics device that I can start a read on...

Regards,
TULUM

 

[jraef]

Why does it have to be an electronic device? Why not just use a simple relay with a 600V coil? That's what most people do.

JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[tulum]

Interest sake more than anything...

 

[jraef]

The problem is, in the manufacturing process for semiconductor devices only the smallest percentage of production will pass testing for 600V applications, making them more expensive and more difficult to find on the shelf if they ever need to be replaced. For this reason, most device manufacturers opt out of direct sensing of 600V, choosing instead to ask users to step it down prior to going into a sensor (or building in the step-down xfmr). You could make your own by rectifying the 600V and then dropping the DC down with resistors to a workable voltage for whatever else you want to do. Of course you will need to deal with the heat of the dropping resistors and smoothing caps for the DC ripple, etc. etc. I just don't know of anything out there that would do this already.

By the time you are done with it, a $15 relay with a 600V coil will be looking pretty good to you.

JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[nbucska]

Tulum:
If you just want to indicate, use a neon lamp with a
resistive voltage divider

If low power is important, use a comparator and divide
down the input VTG.

You can use a series cap to drop the voltage without
generating heat.



Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>

 

[OperaHouse]

If using a series cap, use two or three in series to lower the voltage on each cap. Single foil caps suffer from corona damage over about 200V. I'v used three 0.47 caps in series to operate 48VDC relays with rectifier. Put a 470K resistor on each cap to drain charge. Caps in series with AC relays can be chancy. Hit that RL series resonance and the voltage can skyrocket. I operate 220V fans on 120VAC with a cap in series to boost the voltage on the motor!