How to design a control or sensor circuit for following

[Jayesh]

Hi
There is a transformer which has got different tappings on it for
120,208, 277V.
Now I want that whatever the supply voltage is say 120, 208, 277 that
switch should turn on from the tappinngs i.e switches are connected at
tappings and heating coil should be connected to that so for that I
need to sense it but iam not aware of the way I can sense it or can any
one guide me with circuit that can be usedto sense it.
Thanks
Jayesh

 

[Dan Hollands]

The approach would be:

use a diode and capacitor to peak detect the AC voltage and convert it to a
DC voltage

Use 3 OpAmps or comparitor IC's set to detect a voltage below 120, between
120 and 208, between 208 and 277

Apply logic (relay or solid state ) to determine which taps to connect.

Can't be any more specific with the minimum information you have supplied

Dan

--

Dan Hollands
1120 S Creek Dr
Webster NY 14580
585-872-2606
[email protected]
www.QuickScoreRace.com

 

[Jayesh]

thanks

Can u plz elaborate on wat u mean by peak detect the AC voltage and how
much value shall i convert to dc voltage i.e whats the valueof dc
voltage .
And abt op-amp i have no ideaso iam goin thru it now so will get back
to u later with doubts.

Thanks
Jayesh

 

[Dan Hollands]

Use a diode and capacitor to make a simple dc power supply from the ac in
put voltage
The dc voltage will be approximately 1.4 times the AC voltage



--

Dan Hollands
1120 S Creek Dr
Webster NY 14580
585-872-2606
[email protected]
www.QuickScoreRace.com

 

[Jayesh]

ok
so if its say 120-277V ac then dc will be (120-277 )* 1.4 DC
But i cannot supply such large voltage to Op-amp so what do i do

Thanks
jayesh

 

[Rich Grise]

ok
so if its say 120-277V ac then dc will be (120-277 )* 1.4 DC
But i cannot supply such large voltage to Op-amp so what do i do

You would use what's called a 'voltage divider' - two resistors in
series, such that the voltage drop is proportional to their resistance.

Maybe if you need to ask this question, you shouldn't be messing
with 277 volts!

Can this voltage change unexpectedly? You could simply install
a switch, or give the user three input jacks, so they could plug
the unit in to either power at the site.

But automatic switching isn't that hard - you could use what's
called a "signal transformer" or some such - a 277/12V ordinary
transformer, and when the input is 120V, the output will be
12 * (120/277) V. That's way easy territory for an opamp.

Good Luck!
Rich

 

[Jayesh]

thanks but can it be done without using a transformer what abt power
loss at resistor .

Jayesh

 

[Fred Bloggs]

Hi
There is a transformer which has got different tappings on it for
120,208, 277V.
Now I want that whatever the supply voltage is say 120, 208, 277 that
switch should turn on from the tappinngs i.e switches are connected at
tappings and heating coil should be connected to that so for that I
need to sense it but iam not aware of the way I can sense it or can any
one guide me with circuit that can be usedto sense it.
Thanks
Jayesh

1) what power level are you talking about?
2) the load on the transformer secondary is a heater?
3) why do you need this voltage sensing to be automatic? how come a
terminal jumper will not work? a consumer item?