Using a 120 VAC to 5VDC PS to sense 120 VAC - how to handle 277VAC?
Using a 120 VAC to 5VDC PS to sense 120 VAC - how to handle 277VAC?
(OP)
Hi,
I needed to make a device to remotely detect whether or not a 120VAC circuit was live. We make a micro-based device that measures 0 to 5 VDC and converts it into a 10 bit number. Being in a rush and not wanting to screw around the best idea I could come up with was an open frame power supply (85 to 264VAC input, 5VDC output) wired to the switched 120VAC. Close the switch, the PS puts out 5V, my A/D says 1023 or thereabouts, and all is great.
Now I'm told I need to sense 277 VAC (one phase of a 3 phase supply to a 480 VAC pump). I have found a 120 - 370 VAC to 5 VDC supply (h ttp://www. powerconve rsion.com/ assets/nlp 65_ds_1216 436331.pdf) but it's $80 and I need 4 of them. And I'm concerned about inserting the device into one of the 3 phases to the motor.
1. Will the pump still pump OK with the power supply inserted into one of its phases?
2. Could I use a voltage divider to cut the 277 VAC in half and use the first supply?
3. Is there...a better way?
Thank you for any help.
Rob
I needed to make a device to remotely detect whether or not a 120VAC circuit was live. We make a micro-based device that measures 0 to 5 VDC and converts it into a 10 bit number. Being in a rush and not wanting to screw around the best idea I could come up with was an open frame power supply (85 to 264VAC input, 5VDC output) wired to the switched 120VAC. Close the switch, the PS puts out 5V, my A/D says 1023 or thereabouts, and all is great.
Now I'm told I need to sense 277 VAC (one phase of a 3 phase supply to a 480 VAC pump). I have found a 120 - 370 VAC to 5 VDC supply (h
1. Will the pump still pump OK with the power supply inserted into one of its phases?
2. Could I use a voltage divider to cut the 277 VAC in half and use the first supply?
3. Is there...a better way?
Thank you for any help.
Rob





RE: Using a 120 VAC to 5VDC PS to sense 120 VAC - how to handle 277VAC?
Using the same basic idea, couldn't you just do a full-wave, or half-wave rectification, resistor-divide and measure the resultant voltage? Not only would you know that the input is live, you'd actually be able to figure out the numerical value of the voltage.
TTFN
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RE: Using a 120 VAC to 5VDC PS to sense 120 VAC - how to handle 277VAC?
http://www
See page 21 of the catalog.
Rafiq Bulsara
http://www.srengineersct.com
RE: Using a 120 VAC to 5VDC PS to sense 120 VAC - how to handle 277VAC?
Ideally, if building anything on your own, one would include an optocoupler stage in the circuit to provide some inherent protection for the poor micro.
If you can't find any off-the-shelf voltage measuring interfaces, then there must be off-the-shelf 3-phase current measuring gadgets. If you have current, then the voltage is probably there.
RE: Using a 120 VAC to 5VDC PS to sense 120 VAC - how to handle 277VAC?
The controller for the motor may have a 480V:120V control transformer. Just connect a 120V coil relay onto the output of this transformer.
Or, just buy a voltage relay like the one already posted.
RE: Using a 120 VAC to 5VDC PS to sense 120 VAC - how to handle 277VAC?
Just sensing voltage to a motor isn't evidence that it is running. If you don't sense current I would use a phase relay.
RE: Using a 120 VAC to 5VDC PS to sense 120 VAC - how to handle 277VAC?
Roy
RE: Using a 120 VAC to 5VDC PS to sense 120 VAC - how to handle 277VAC?
Mike Halloran
Pembroke Pines, FL, USA