Want to build a power line monitor

[chuckworkb]

I have been thinking of building a power line monitor.

A simple display of AC line voltage, and AC current.

I was thinking of using an old digital multimeter, and some how leaving the current and voltage probes in all the time and switching between the two with a relay.

Does this sound nuts - what do you think? :yes::no:

[Rick james]

I don't think it's nuts but OTOH what's the point? If your rig sounds good it is good, why add something that might make you think there's something wrong when there isn't? If your worried about voltage fluctuations run a dedicated AC line to the box.

[chuckworkb]

I like gadgets - and I thought this fit the bill.

I have a dedicated line, but that doesn't mean the display will always stay on 120.

I am interested in watching the current flow as well.

It is just the tinkerer in me.

[speakerfritz]

the power line monitor info will surprise you. my avs2000 and htps7000 can provide voltage and current info. Voltage swings in the NYC area are as high as 19 volts. This could be problematic if left uncontrolled for tube gear due to the bias requirements. If you bias your tubes when the voltage swing is low, you run the risk of operating tubes in an over bias senerio when the voltage swings high. Also, keep in mind that the rail voltage in tube gear often is 3X higher than the incoming voltage. so 19 volts could result in 47 volts of an increase in your rail voltage. This could be a problem if caps are used with close tolerance voltage ratings. for example I once worked on a tube amp that had 450 volt caps. the amp was designed to work on 110 - 117 volts. However, voltages in NYC often glide along at 126 volts. Rail voltage went from 448 to 472 and as you can see is higher than what the caps are rated at. The amp had noise if used over 117 volts as a result.

[bricktop]

I like gadgets - and I thought this fit the bill.

ha! me too. You can get some DMM panel meters for dirt cheap that will give you what your after. They are on ebay all the time, all colors and sizes. I also like the look of old school simpson/tripplett meters too, if your into that. Usually you can find them used there too, which is no biggie.

I was recently thinking of doing this all in a cabinet with a variac b/c some of my tube gear requires it (line V is 125 here).

[NicoR]

the power line monitor info will surprise you. my avs2000 and htps7000 can provide voltage and current info. Voltage swings in the NYC area are as high as 19 volts.

In my house in Brooklyn, we've got about 127 volts coming out of the wall. It's a bit high, but at least none of my equipment seems to care too much (Although we burn up fluorescent bulbs like a b**).

[NicoR]

Oh, also, keep in mind that many multimeters will only read DC current, not AC current.

Also, the way the probes would get connected for measuring voltage and amperage are different, so in the end, you might just be better off with two multimeters/guages.

[chuckworkb]

They make multi-meters that read AC current - I own one Fluke model 77 I think it is.

This thing gets more and more complex as I think about it, and I am beginning to think that by the time I build this with two meters and remotely display of the data it will cost $$$$$$$$$$$$$$$$.

I have two meters I don't use that i was trying to figure out how to do this with. I have a clamp on I could use more safely for current, and another Multimeter I could use for voltage.

We shall see - I am going to mess with it maybe next week.

Thanks for all the feedback

[Glen B]

I have been thinking of building a power line monitor.

A simple display of AC line voltage, and AC current.

I was thinking of using an old digital multimeter, and some how leaving the current and voltage probes in all the time and switching between the two with a relay.

Does this sound nuts - what do you think? :yes::no:

The way to go would be to purchase digital AC voltage and current panel meters and install them in an enclosure. Connect the voltmeter across the AC line and the load thru the current transformer of the current meter (see product choices at the link below).
http://img.villagephotos.com/p/2003-5/191557/ac_mon.JPG

http://www.metercenter.com/cgi-bin/webshop.cgi?config=zxcvbnm&uid=lnanyixn120115131637&command=link--da142.htm

Alternately, you could save yourself the trouble of DIY and buy a basic Furman line conditioner that reads AC voltage and current.

http://www.furmansound.com/product.php?div=01&id=PM-8_II

[PakProtector]

hey-Hey!!!,
Get a small, cheap DMM from one of the big chain stores and set it for AC in the proper range. Attach a plug to the leads and you're OFF. One could pot the thing in acrylic but battery maintainance would be difficult...:) Fuse the line with something itsy-bitsy just in case it gets plugged in w/o the meter.
cheers,
Douglas

[Glen B]

But the OP also wants to monitor (continuous) current draw. A multimeter set up to read AC volts alone won't accomplish this. A meter with one leg of the load passing thru a current transformer will. :)