30amp Watt Meter

[Punx]

I'm plugged into a regular 30a service at my marina. I was wondering if there were any products available that would show me how many watts I'm currently drawing. I do have a regular household watt meter as well as a converter cable from marine 30a to a regular household plug, but I didn't know if this would actually work, and I wanted to check before I tried it out. Any suggestions?

[zeehag]

i use the total number of items i have and i read each one before purchase so i know how many i am drawing so i dont exceed my limit of 30 amps. yes, i presume a lot, in that i presume the item i bought doesnt exceed the number of amps declared on the item. i have been doing this since 1990, and have gotten decent at counting to 30. i limit my usage to 28 amps at peak so i dont exceed.
i also presume the 30 amp circuit on the dock really is 30 amps. sometimes is less--i generally look at the dock sockets to make sure the provision is actually 30 amp0s, not 15 or 20 or 50.

[Punx]

I want to get a reading of the watts though, not amps.

[Lancerbye]

To get a proper watt reading the eequipment has to read current and voltage. There are inexpensive plug in types for 120 volts 15 amps easily available from electrical supply places, however 30 amps moves you up to a commercial level. Here is a link for a supplier (no affiliation) that handles what you need. You will need a 100amp ct and the metering device to go with it.Watthour Meter Selection Wizard & Online Store.

[noelex 77]

The new blue seas vsm422 looks like it will do what you want.

[zeehag]

to keep the boat from pulling on plug, i make a loop and tie it to dock box, whereon the electrical outlet is mounted. i also keep a lot of slack in my cord, and i make sure it doesnrt fall into sea.

[DotDun]

I use a Blue Sea 8247

AC Digital Meters - Blue Sea Systems

[hellosailor]

You can buy a gizmo called a "Kill A Watt" for about $20-25. You plug that into a regular 110V wall socket, and then plug any device into it, and it shows both instant power usage (watts) and totallized usage (watt hours) over a time.

You'd have to fiddle about with the plugs and wiring to plug it into a dock plug unless they've got a model with marine power plugs, but at th eprice maybe it is something you can put to use, i.e. plug it in oboard to see what each device is pulling.

Or you buy a clamp-on AMMETER and clamp it over the AC line running into the boat. That gives you amps, then you multiply by voltage to get the watts. I don't know that there are any clamp-on wattmeters...it would be possible but I've never met one. Clamp-on AC ammeters run $50-100 and up.

[Punx]

Originally Posted by hellosailor

You can buy a gizmo called a "Kill A Watt" for about $20-25. You plug that into a regular 110V wall socket, and then plug any device into it, and it shows both instant power usage (watts) and totallized usage (watt hours) over a time.

You'd have to fiddle about with the plugs and wiring to plug it into a dock plug unless they've got a model with marine power plugs, but at th eprice maybe it is something you can put to use, i.e. plug it in oboard to see what each device is pulling.

Or you buy a clamp-on AMMETER and clamp it over the AC line running into the boat. That gives you amps, then you multiply by voltage to get the watts. I don't know that there are any clamp-on wattmeters...it would be possible but I've never met one. Clamp-on AC ammeters run $50-100 and up.

Yeah, I've got a kill-a-watt meter thing, and a converter to plug my shore power line in. I just didn't know if I would melt anything by doing this.

[Blue Stocking]

Originally Posted by Punx

I want to get a reading of the watts though, not amps.

Multiply amps X volts= watts..

You do have an amp guage on your shore current supply--don't you?

[hellosailor]

"I just didn't know if I would melt anything by doing this. "
Set up a cooler full of cold beer, on a hot day the fireman appreciate it.<G>

I never looked but I'd hope there's some kind of fuse in there, or something that blows as a fuse. I've used them on 15A loads (AC or fridge) which is the max that the normal unit is rated for. Turn on your loads one at a time, see if the numbers are showing a 15A load and if they are--stop. Shut those loads, turn on the other ones, just note down which gizmos are pulling how much power, and you can always add the numbers back up to get your total power draw.

[goboatingnow]

Originally Posted by hellosailor

Or you buy a clamp-on AMMETER and clamp it over the AC line running into the boat. That gives you amps, then you multiply by voltage to get the watts. I don't know that there are any clamp-on wattmeters...it would be possible but I've never met one. Clamp-on AC ammeters run $50-100 and up.

Just a point about clamp meters. Firstly simply putting them over the shore power cable won't read anything. You have to measure the live wire separately

Also many posts make reference to using then to measure DC currents. Most clamp meters still use a CT so they cannot read DC. Even though the spec mentions it, usually the Dc is measured via the leads like a conventional meter.

Good hall effect meters are quite expensive and typically have a smaller clamping head.

[btrayfors]

+1 about measuring only one wire with a clamp-on ammeter. I have made up a special little pigtail from a section of shorepower cable, about 3' long with 30A male and female connectors on the ends, and the with the external yellow insulation stripped off the middle so each wire can be individually measured if needed. Made one for 15A household circuits, too.

RE: DC current measurement, there are numerous clamp-on meters which do a very good job of measuring DC currents, even fairly small ones. One such meter which I like very much is the Mastech MS2108. I like mine better than my Fluke 337 which costs about five times as much. The Mastech can be found from a U.S. supplier in NJ for $67 these days...an incredible bargain IMHO. It's a real RMS AC/DC clamp-on ammeter with in-rush, frequency, and other useful measurements.

A meter like this can save your bacon, and cuts troubleshooting time way down.

Bill

[hellosailor]

"Firstly simply putting them over the shore power cable won't read anything. You have to measure the live wire separately "

Ah, the "live wire" to any one device on the boat is still drawing all current through the shore power cable. If the shore power cable shows no current being drawn--there is no live wire, nothing on the boat is drawing any current. Everything bottlenecks through that shore power cable.

DC current being of course a nice bonus, but not the issue here. At $67 though, "Dear Santa!" <G>

[btrayfors]

I think you missed the point.

You can't just use a clamp-on ammeter around the shore power cord to read the amperage being drawn. It must go around only one wire, preferably the hot (black) wire.

Similarly, when measuring DC current with a clamp-on ammeter you need to clamp around just one wire, positive or negative, not around both.

Bill