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I'm going to install an ammeter inline between a 220v outlet and my VFD to use as a load meter. It has one in and one out, so I figured I would just hook up one leg of the 220v line.

The question is, will this accurately display the load or do I need a two-leg ammeter? Is there such an animal? Should I just double whatever it reads to get a total load? What do I do?

Thanks in advance,

John

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John Watkins
CNC Guitar Parts

Man, I knew I should have taken a foreign language...

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

I'm not an electrician type, but I do own a couple of multimeters, one of which has an 'amps' setting. This meter reads amperage across a circuit with only two probes, which amount to the same thing as the 'one in and one out' that your VFD has. I'd guess it would work fine that way, but I'd wait to hear from one of the resident experts here.

Best,

Michael

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Live to Play, Play to Live

[QUOTE=John Watkins] I'm going to install an ammeter inline between a 220v outlet and my VFD to use as a load meter. It has one in and one out, so I figured I would just hook up one leg of the 220v line.

The question is, will this accurately display the load or do I need a two-leg ammeter? Is there such an animal? Should I just double whatever it reads to get a total load? What do I do?

Thanks in advance,

John[/QUOTE]

If the device ( I don't know what VFD stands for) uses ONLY 220 volts, you're doing the right thing to measure just one side of the line. In that case, the current in both sides of the 220 line will be the same.

If it also uses some 110 V power ( in that case, there would be a neutral wire - probably a fourth white wire - in addition to the two black 220 wires and a green or bare ground) then a single ammeter won't tell you the total current draw.

In any case, though, an ammeter won't tell you what the actual power draw is. To do that, you need a watt meter. The problem is that, with AC, knowing the current is not enough. You also have to know the phase between the voltage and the current. The actual power will always be less than what you calculate by multiplying your measured current x 220V. ( Maybe as little as half as much in some cases).

But,if your goal is to measure current draw just to make sure you don't overload the line and breaker, then the ammeter will serve that purpose well.

Phil

John--You should get an accurate indication of the load with the ammeter wired in series with one leg.

Looks like Phil and I were posting simultaneously. He must have been on the other leg.

Hi John,

Assuming you have a balanced load, you only need to read one leg to measure current. Each leg should read the same. You can verify by using a clamp on multimeter to check.

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Paul Bordeaux
http://www.bordeauxinlay.com

[QUOTE=npalen] Looks like Phil and I were posting simultaneously. He must have been on the other leg. [/QUOTE]

Ditto.... A man steps out for a cup of coffee and....

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Paul Bordeaux
http://www.bordeauxinlay.com

That's what I needed. Thanks, guys!

VFD stands for Vector somethin' Drive. It's an inverter for my 3-phase spindle.

I really just need a relative indication of how much I'm pushing the tool and whether I'm anywhere close to blowing a circuit breaker. The documentation says it can draw as much as 20 amps.

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John Watkins
CNC Guitar Parts

I have used an ammeter that clamped over a wire very successfully to balance loads in an electrical panel. No wiring necessary, it simply clamps over the wire in question and gives a readout in various voltages/ amperages.

Not knowing what you have exactly, I'm not sure how to tell you how to use it. But the tool used for measuring this on a spot check and could be used indefinitely I suppose is not really all that expensive. It does have to make contact with itself all around the wire in question.

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http://www.dickeyguitars.com

[QUOTE=John Watkins] That's what I needed. Thanks, guys!

VFD stands for Vector somethin' Drive. It's an inverter for my 3-phase spindle.

I really just need a relative indication of how much I'm pushing the tool and whether I'm anywhere close to blowing a circuit breaker. The documentation says it can draw as much as 20 amps.[/QUOTE]

"variable frequency drive" It converts the analog voltage to digital and then allows you to change frequency and thus speed of a synchronous motor. For example; if a motor is designed to run at a synchronous speed of 1800 RPM (1725-1750 with slip) at 60 Hz, then changing the invertor to an output of 54 Hz (10% less) will cause the motor to run 10% slower.

The upside is obvious becasue you can now take a single speed moter and give it many of the properties of a vaiable speed DC motor. The downside is that the motor has to be designed for it as it will run hotter if run slower. Running faster is actually easier on the motor up to a point. An 1800 RPM motor has been balanced at probably 3000-3500 rpm and the bearings were chosen for the same speed range. Some mfrs brag about their bearings being 4000 rpm bearings (Baldor comes to mind).

Also, as you slow a motor down, you lose torque, especially if the motor wasn't designed for it. Its torque curve drops very sharply. There are motors that will give 90%+ torque at speeds of less than 1 rpm but they are VERY expensive and require special programming. Ont he other hand, if the motor is lightly loaded, you may be able to gat away with it.

Hope this helps, Steve

PS There is such a thing as a vector drive. It's the ultra variable motor I alluded to. It is also Baldor's trade name, I think. They are impressive!sfbrown38857.7350578704

I use a VFD on my buffer. They've come down in price and size considerably in recent years and the fact that you can run a cheap three phase motor off of 230VAC single phase is a plus. (John, I know that the router motor you're running is NOT cheap)
The VFD's are programmable for such things as maximum and minimum speed, acceleration and/or deceleration rate, electronic braking, reversing etc.
I really need to retrofit my 6x89 edge sander with a VFD as it would be really nice to slow it down sometimes and reversing capability would be a plus also.