# Hi and Lo VAC

Discussion in 'General Electronics Chat' started by mbxs3, Oct 14, 2009.

1. ### mbxs3 Thread Starter Active Member

Oct 14, 2009
143
3
Hello All,

If a component is receiving 23.5 VAC HI and 23.5 VAC LO. Does this just mean that the VAC on the HI input is positive and the VAC on the LO input is negative? If anyone could clarify this for me I would greatly appreciate it. Any references would be great. Also, what is the purpose of a HI and LO VAC input? Thanks.

-Mike Brandon

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Can you provide a source for the notation? An AC voltage is one that has excursions above and below the measuring point, as voltage is always relative to some part of the circuit. A DC voltage always remains positive or negative relative to the measuring point.

Your 23.5 VAC sounds like the output from a transformer. A voltmeter measuring across the secondary winding will read that AC voltage. The HI and LO notation is not really informative, unless there is some context.

3. ### mbxs3 Thread Starter Active Member

Oct 14, 2009
143
3
The source voltage is 115vac, single phase, 400 hz. It goes into a component called a compass coupler where, among other things, 23.5vac is sent out to a component called a flux valve, one wire is labeled as 23.5vac HI and the other wire is labeled as 23.5vac LO.

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Without the circuit diagram to provide some context, the notation seems to be arbitrary.

5. ### mbxs3 Thread Starter Active Member

Oct 14, 2009
143
3
Hope this is sufficient.

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6. ### wr8y Active Member

Sep 16, 2008
232
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I suspect the 23 volts ac rides on both conductors, one is called "low" because it is either tied to ground, closer to ground or referenced in some way to ground.

Or, it is (as has been pointed out) an arbitrary notation.

If you measure 23 vac from the "high" side to ground and 23 vac from the "Lo" side to ground, it is an arbitrary notation.

If you measure 23 vac from high to ground, and 0 from lo to ground, it isn't all that arbitrary. But I still suspect it's simply a 23 vac output from the power supply section of your device(s).

7. ### BillB3857 Senior Member

Feb 28, 2009
2,402
348
Some circuits that use AC input tie one side of the AC to the logic or power ground bus of the device being powered. In that instance, the 23.5 AC HI would indicate the "ungrounded" line of the AC and the 23.5VAC LO would indicate the side of the line that is tied to the appropriate ground bus of the device.

wr8y, you type faster than I do or else you got a head start!.. BG

8. ### mbxs3 Thread Starter Active Member

Oct 14, 2009
143
3
Thanks for all the input. It has been really helpful. wry and Bill, I think you are correct that it references a connection to the ground point of the device that is sending the 23.5vac. When you all say "an arbitrary notation" are you basically saying it is an undetermined or unsupported description in the schematic? Thanks again!

-Mike Brandon

9. ### wr8y Active Member

Sep 16, 2008
232
1
Well, if you (and you don't here, I don't think your source is from a transformer, but just saying) have a transformer with a secondary output driving a load, it does not matter to the TRANSFORMER what end of it's secondary is "hi" and what is "lo".

But they MAY tie one side to ground ...

or...

They may just call one "lo" and one "hi" more to make circuit descriptoins easier to read, etc. It's easier to say that than to say "the end of the transformer secondary with the blue wire, not the end with the white wire", see what I mean?

Also, there MIGHT be circuits where the PHASE of this secondary winding does something in the circuit (like an audio circuit) that has to work with the signal from another source and therefore phase is important. (Probably not the case in your application). In this case, "hi' and "lo" again help us to describe what end of the secondary is being referenced to.

10. ### wr8y Active Member

Sep 16, 2008
232
1
I learned to type in junior high at the age of 13.