# Voltage Sensor

#### Elevatorinfo

Joined Jul 12, 2015
20
Have one for you Wiz Kids,

Trying to cobble up a detector/sensor that will detect/sense a 12 to 220 VDC voltage/potential. Just need to know it's there. Out put could be LED, transistor/relay driver. I can tame the high voltage down with a voltage divider. Power supply is 12 VDC. Preferably need to turn a relay that is on a relay that's on a relay input/output module.

Thanks

#### MikeML

Joined Oct 2, 2009
5,444
Can the 220Vdc input share a common ground with the low voltage power supply that runs the relay logic?

Joined Jul 18, 2013
28,482
Do you need to detect the actual level/value or only if it is above 12vdc?
Which you imply in the first sentence, if so it could simply be done with a LM393 etc.
Max.

#### MikeML

Joined Oct 2, 2009
5,444
If the grounds can be common, here is a simple circuit that turns on at ~2.5Vdc and tolerates inputs up to 250Vdc without dissipating hardly any power.

The X-axis of the plot is V2 sweeping from 100mV to 250V (log plot).

ps. Forgot to add: L1 is the 12Vdc Relay coil, DC resistance >= 80Ω

Last edited:

#### Elevatorinfo

Joined Jul 12, 2015
20
Can the 220Vdc input share a common ground with the low voltage power supply that runs the relay logic?

Yes it can and actually it does. The way we want it to work is: Look at 12 thru 220 VAC/VDC thru bridge rectifier then thru voltage divider to lower voltage then on to relay module board that turns on it's relays on the ground side. Hope I explained it well enough.

Jim

#### Elevatorinfo

Joined Jul 12, 2015
20
Do you need to detect the actual level/value or only if it is above 12vdc?
Which you imply in the first sentence, if so it could simply be done with a LM393 etc.
Max.
Thanks Max,

Just detect any DC voltage above 12VDC (220 VDC Max)

#### Elevatorinfo

Joined Jul 12, 2015
20
This is getting good,

In either case (Max/Mike) we can eliminate the voltage divider? For Mike "L1" is?

Thanks Again,

Jim

#### MikeML

Joined Oct 2, 2009
5,444
...For Mike "L1" is?

#### Elevatorinfo

Joined Jul 12, 2015
20
DUH.........................................

Joined Jul 18, 2013
28,482
Do you want it to snap over at exactly 12vdc?
Max.

#### Elevatorinfo

Joined Jul 12, 2015
20
12 volts is the lowest voltage we are looking at so it could be less

Joined Jul 18, 2013
28,482
So essentially anything?
Max.

#### mcgyvr

Joined Oct 15, 2009
5,394
If your voltage is 220V AC then when you rectify it you will see 300+ DC volts...

#### Elevatorinfo

Joined Jul 12, 2015
20
YOU ARE CORRECT THANKS FOR THE HEADS UP. DEAL IS THE 220 SITUATION IS THE RAREST OF RAREST SO FORGOT TO PAY MUCH ATTENTION TO IT. THIS WOULD BRING BACK THE VOLTAGE DEVIDER. ATTACHED IS WHAT WE ARE TRYING TO DO HERE. AS DRAWN IT'S UP AND RUNNING BUT STILL NEED TO DETECT VOLTAGE

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#### Elevatorinfo

Joined Jul 12, 2015
20
More......after some thought. There might be a chance that the guy using this thing might reverse the polarity. Don't think we can share grounds.

Max might have it with the regulator turning on a relay and using it's dry contacts out.

Max would you have some values to share so I can order parts.

Thanks All,

Jim

#### Elevatorinfo

Joined Jul 12, 2015
20

Joined Jul 18, 2013
28,482
Max might have it with the regulator turning on a relay and using it's dry contacts out.

Max would you have some values to share so I can order parts.
Jim
I think MikeML quoted the relay, although the comparitor would sense a voltage level, and it seems you don't really need this so only a simple mosfet might work.
Max.

#### MikeML

Joined Oct 2, 2009
5,444
If you really do need galvanic isolation from 240Vac (USA) or 220Vac (EUR) then this becomes a very different project involving transformers and/or opto-isolators. That is why I asked the question way back in post #2!!!

#### ian field

Joined Oct 27, 2012
6,536
Have one for you Wiz Kids,

Trying to cobble up a detector/sensor that will detect/sense a 12 to 220 VDC voltage/potential. Just need to know it's there. Out put could be LED, transistor/relay driver. I can tame the high voltage down with a voltage divider. Power supply is 12 VDC. Preferably need to turn a relay that is on a relay that's on a relay input/output module.

Thanks
There was a Steinel voltage/continuity tester that used a thin film PTC on a little ceramic tube as the current limiting element in series with an inverse-parallel pair of indicator LEDs. Its voltage range was about 4 -450V.

One of those PTC units and an AC input optocoupler would do the job and give you isolation into the bargain.