American rotary ADX-60 high amperage on idle?

[idontrunntoofast]

I just installed a brand new ADX-60 rotary phase converter in my new shop.
The documentation for the ADX-60 claims that idle amperage draw should be approx 7.45A.
My clamp meter is showing a 36 amp draw on idle. No loads hooked up.
Now all wiring is per the manual and correct according to American Rotary, all wire sizing exceeds requirements in installation guide and NEC requirements.
When talking to American Rotary I was just told that it is normal and to just run it.
I would like help understanding this. Is this normal? If so why do they claim 7.5 A idle? If not what might be going wrong? Someone else told me it my be due to the way the RPC works, regenerative power flowing back and and forth measuring 36amps total. This would obviously be impossible to measure with a clamp meter or normal multimeter. Anyone else have a RPC they can clamp a meter on during idle?
Btw this is my first post on practicalmachinist, been a lurker for a long time. Let me know if I am breaking posting protocol or something.
Thanks for the help !

 

[jim rozen]

Hmm. Clamp-on meter giving a peculiar indication. Who's gonna start this one?

 

[idontrunntoofast]

Hmm. Clamp-on meter giving a peculiar indication. Who's gonna start this one?

Since the question was running long I didnt mention in the original post, I have 3 clamp meters a fluke 325 a fluke 323 and an older analogue GB clamp meter. All 3 show the same amperage draw.

 

[idontrunntoofast]

Oh and I understand (at least somewhat) about reactive power and motor inductance. But even accounting for that 36A seems a bit high to me. I guess what I am looking for is someone who has a a little free time, an RPC and a working clamp meter to snap it onto L1 or L2 and check the reading when the idler is running without any load...
My old shop had 3 phase power and this is my first attempt at running my machines off a RPC and I want to make sure this 7k motor is running right before turning things up.
-Thank you.

 

[JST]

What is the output voltage when you have it idling at no load?

The spec given on the website is 0.9 kW which I assume is the basic "real" power required to operate the unit on idle. At 230V, that would come to about 4A.

Motors at idle are strongly inductive, and draw considerable "lagging reactive current". The 7.5A may assume the use of power factor correcting capacitors.

The unit may include power factor correcting capacitors on the input, which reduce the current draw by canceling out the "reactive current" drawn by the motor, which would leave only the "real" or "power producing" current. Those capacitors may or may not be included in your actual unit, but I suspect they are not.

If your unit included them, then the 7.5A might be possible. It would take only a power factor of a bit over 0.5 to get there, based on their stated 900 watts in total losses.

Without any power factor correction, the 36 amps sounds reasonable, based on a power factor a bit better than 0.1, and taking their 900 watts of losses as the correct number.

 

[idontrunntoofast]

What is the output voltage when you have it idling at no load?

The spec given on the website is 0.9 kW which I assume is the basic "real" power required to operate the unit on idle. At 230V, that would come to about 4A.

Motors at idle are strongly inductive, and draw considerable "lagging reactive current". The 7.5A may assume the use of power factor correcting capacitors.

The unit may include power factor correcting capacitors on the input, which reduce the current draw by canceling out the "reactive current" drawn by the motor, which would leave only the "real" or "power producing" current. Those capacitors may or may not be included in your actual unit, but I suspect they are not.

If your unit included them, then the 7.5A might be possible. It would take only a power factor of a bit over 0.5 to get there, based on their stated 900 watts in total losses.

Without any power factor correction, the 36 amps sounds reasonable, based on a power factor a bit better than 0.1, and taking their 900 watts of losses as the correct number.

Thank you JST,

T3 is manufactured line
With the idler running and nothing connected I get the following voltages.

Voltage from T1 -T2 (244.4)
Voltage from T1 -T3 (249.4)
Voltage from T2 -T3 (242.9)

The control unit has 15 different large capacitors in it. I would be lying if I said I knew what they all did... But I included a picture of the inside of the control box.


It would be very disappointing to me if this unit really is using 36 amps at idle. When I was told by American rotary that it would be drawng 7.5 amps idle. After all I did just drop $7K on it...
Can you think of a way to measure the "Real" power that this thing actually uses?
I mean I guess I could just get a proper power meter and put it in line before the RPC. Sadly the meter provided by my utility company is digital and does not show current power draw only total KWh.

 

[Mark Rand]

It's possible that the power factor is leading rather than lagging at no load due to the capacitors being sized to provide the reactive current at normal working load. You could work that out without a proper watt/power-factor meter by seeing if the current stayed the same or even fell slightly when driving a lightly loaded three phase motor with the converter.

 

[jim rozen]

"Without any power factor correction, the 36 amps sounds reasonable, based on a power factor a bit better than 0.1, and taking their 900 watts of losses as the correct number."

Thank you.

Amp clamp meters read the sum of in-phase and out of phase current and can give misleading results when attempting to find power consumption of highly reactive loads.

1) is the converter in a residential bulding? If so it is probably fed through a watt-hour meter. If so then turn off all other loads and run only the rotary converter for a known time. Calculate the power used.

2) buy borrow or steal a meter that can determine power factor.

 

[idontrunntoofast]

It's possible that the power factor is leading rather than lagging at no load due to the capacitors being sized to provide the reactive current at normal working load. You could work that out without a proper watt/power-factor meter by seeing if the current stayed the same or even fell slightly when driving a lightly loaded three phase motor with the converter.

So if I wire up and run a lathe and the current stays the same that will tell me that the power factor is leading. If the current increases that'll tell me the power factor is lagging. Right?
Assuming most of this is reactive current that means I shouldn't be getting billed for it. Right? The power company's meter is seeing current traveling back and forth and only billing me for the "real" power traveling in. Would I be correct in assuming that?

 

[idontrunntoofast]

"Without any power factor correction, the 36 amps sounds reasonable, based on a power factor a bit better than 0.1, and taking their 900 watts of losses as the correct number."

Thank you.

Amp clamp meters read the sum of in-phase and out of phase current and can give misleading results when attempting to find power consumption of highly reactive loads.

1) is the converter in a residential bulding? If so it is probably fed through a watt-hour meter. If so then turn off all other loads and run only the rotary converter for a known time. Calculate the power used.

2) buy borrow or steal a meter that can determine power factor.

Yeah that's what I was hung up on I guess. I realized that I was reading some reactive current but didn't know that it would be that high.
The RPC is in a residential building but the meter the power company supplied is a newer digital one that only shows KWh with no decimal point. So I guess I can set up a camera on it and run the RPC with nothing else in the shop running and see approximately what the usage is.

What meter would you recommend if I were to buy or borrow? Sounds like it could be expensive.

Thanks Jim

 

[BT Fabrication]

3 phase draws about 2.5amp at 230V so that being said can be up to 150A. ususally unloaded they run anywhere from 20-30% of max amp draw with just idling and can easily go as high as 300 on start up and heavy loads. i believe i have mine saying about 4.7A for my 10hp and 10.3 for my 20hp. so being 3x the 20 hp and more mass to turn you are in the clamp on ball park. its not actual KVA used but that will only be bearing friction and rotor losses which id guess is around 10-15 amps on yours or about 5-10% of max

 

[BT Fabrication]

So if I wire up and run a lathe and the current stays the same that will tell me that the power factor is leading. If the current increases that'll tell me the power factor is lagging. Right?
Assuming most of this is reactive current that means I shouldn't be getting billed for it. Right? The power company's meter is seeing current traveling back and forth and only billing me for the "real" power traveling in. Would I be correct in assuming that?

yep the residential houses under 200A have a direct reading through the meter base. anything over 200A has a coil around the cables incoming to measure power, and the power company might or might not be measuring it for power factor and max load per hour like they do around here.
anything over 200 amp is just too large to be directly measured from our local power utility and uses a current transformer style socket

 

[BT Fabrication]

Thank you JST,

T3 is manufactured line
With the idler running and nothing connected I get the following voltages.

Voltage from T1 -T2 (244.4)
Voltage from T1 -T3 (249.4)
Voltage from T2 -T3 (242.9)

The control unit has 15 different large capacitors in it. I would be lying if I said I knew what they all did... But I included a picture of the inside of the control box.
View attachment 376493

It would be very disappointing to me if this unit really is using 36 amps at idle. When I was told by American rotary that it would be drawing 7.5 amps idle. After all I did just drop $7K on it...
Can you think of a way to measure the "Real" power that this thing actually uses?
I mean I guess I could just get a proper power meter and put it in line before the RPC. Sadly the meter provided by my utility company is digital and does not show current power draw only total KWh.

the black round things are start electrolytic capacitors and only used until the motor gets up to speed and one of the contacts drop it out of the circuit from what looks to be the small circuit board controlling it, they give the motor a kick in the ass because the one leg doesn't have power supplied from single phase and needs the umph to get it to rotate. there are bleed down resistors on top to discharge them after they come out of circuit.
the silver are oil filled run capacitors and ususally in an metal case to hep dissipate any heat that builds up from the oil and is used to hold a charge on the generated leg so the voltage doesn't drop out too low.
the black start caps have a service life and start leaking or shorting out after about 10 years normally

looks about 3000mfd on the start caps approx
1330 on the red/blue run leg and guessing generated leg is the blue/black like normal with about 1500mfd on it

 

[JST]

You appear to have 3 groups of capacitors. Yes, the black ones are "probably" the start caps.

The other two appear to be 2 groups of run capacitors. it does not appear that there are any power factor capacitors (I am assuming they use wire color consistently).

Your voltage readings indicate there is no excess current being used by the "balance" capacitors. So that is not causing the higher reading.

If their specifications are any good, and show what it seems, you already know the "real" (power producing) current. It is about 4A, to supply the 900w of losses.

IF they had power factor capacitors, they would not be likely to have them compensate at full load, but more likely at no load, where the power factor is lowest. Under load the power factor of a motor increases (the "good" direction) and generally maxes out at between 0.6 and 0.8. The ideal is 1.0, which means that all the current is producing actual power. In reality, the powerco is very happy to have the power factor at 0.9, that is generally what they aim for.

A motor at no load usually has a power factor between 0.1 and maybe 0.2. That means 80% to 90% of the current draw at no load is reactive current. In the US, residential meter does not read reactive power, or if it does, that number is not (yet) used. A commercial meter does, and you get charged for low power factor in various punitive ways.

So there is no really good reason to worry about reactive power for a residential installation. You can simply ignore the "extra" current, it really only bothers the powerco.

 

[idontrunntoofast]

the black round things are start electrolytic capacitors and only used until the motor gets up to speed and one of the contacts drop it out of the circuit from what looks to be the small circuit board controlling it, they give the motor a kick in the ass because the one leg doesn't have power supplied from single phase and needs the umph to get it to rotate. there are bleed down resistors on top to discharge them after they come out of circuit.
the silver are oil filled run capacitors and ususally in an metal case to hep dissipate any heat that builds up from the oil and is used to hold a charge on the generated leg so the voltage doesn't drop out too low.
the black start caps have a service life and start leaking or shorting out after about 10 years normally

looks about 3000mfd on the start caps approx
1330 on the red/blue run leg and guessing generated leg is the blue/black like normal with about 1500mfd on it

3 phase draws about 2.5amp at 230V so that being said can be up to 150A. ususally unloaded they run anywhere from 20-30% of max amp draw with just idling and can easily go as high as 300 on start up and heavy loads. i believe i have mine saying about 4.7A for my 10hp and 10.3 for my 20hp. so being 3x the 20 hp and more mass to turn you are in the clamp on ball park. its not actual KVA used but that will only be bearing friction and rotor losses which id guess is around 10-15 amps on yours or about 5-10% of max

yep the residential houses under 200A have a direct reading through the meter base. anything over 200A has a coil around the cables incoming to measure power, and the power company might or might not be measuring it for power factor and max load per hour like they do around here.
anything over 200 amp is just too large to be directly measured from our local power utility and uses a current transformer style socket

Lots of good info here BT Fab!

Thank you for taking the time out of your day to help me with this. I'll check the printing on the caps when I am at the shop later to see what the ratings are on them.

After all this I feel a lot more comfortable running this machine.
Didn't want to rush into it, because I didn't want to be billed by my electric company for a idler drawing 5x what it was supposed to all day... And if there was something wrong with it I wanted it corrected ASAP. Not just the $7k RPC at stake but I have a lot invested into the 4 CNC machines that will be hooked up to it.
My old shop had 3 phase already so I didn't have to worry about a RPC.

I assume that if this were your machine you would feel comfortable running it at this point?

 

[idontrunntoofast]

You appear to have 3 groups of capacitors. Yes, the black ones are "probably" the start caps.

The other two appear to be 2 groups of run capacitors. it does not appear that there are any power factor capacitors (I am assuming they use wire color consistently).

Your voltage readings indicate there is no excess current being used by the "balance" capacitors. So that is not causing the higher reading.

If their specifications are any good, and show what it seems, you already know the "real" (power producing) current. It is about 4A, to supply the 900w of losses.

IF they had power factor capacitors, they would not be likely to have them compensate at full load, but more likely at no load, where the power factor is lowest. Under load the power factor of a motor increases (the "good" direction) and generally maxes out at between 0.6 and 0.8. The ideal is 1.0, which means that all the current is producing actual power. In reality, the powerco is very happy to have the power factor at 0.9, that is generally what they aim for.

A motor at no load usually has a power factor between 0.1 and maybe 0.2. That means 80% to 90% of the current draw at no load is reactive current. In the US, residential meter does not read reactive power, or if it does, that number is not (yet) used. A commercial meter does, and you get charged for low power factor in various punitive ways.

So there is no really good reason to worry about reactive power for a residential installation. You can simply ignore the "extra" current, it really only bothers the powerco.

Awesome! Thanks JST!
You have been a big help and this is just what I wanted to hear!
This RPC should allow me to run up to any 2 of my CNC machines and a manual machine at the same time without issue. Glad that it is going to work out for me.
If things go my way I am going to get one of my Lathes moved in, wired up and powered on today.
Thank you for the confidence boost.
I was woried for a while that something was up with my setup or the Idler itself.

 

[idontrunntoofast]

You appear to have 3 groups of capacitors. Yes, the black ones are "probably" the start caps.

The other two appear to be 2 groups of run capacitors. it does not appear that there are any power factor capacitors (I am assuming they use wire color consistently).

Your voltage readings indicate there is no excess current being used by the "balance" capacitors. So that is not causing the higher reading.

If their specifications are any good, and show what it seems, you already know the "real" (power producing) current. It is about 4A, to supply the 900w of losses.

IF they had power factor capacitors, they would not be likely to have them compensate at full load, but more likely at no load, where the power factor is lowest. Under load the power factor of a motor increases (the "good" direction) and generally maxes out at between 0.6 and 0.8. The ideal is 1.0, which means that all the current is producing actual power. In reality, the powerco is very happy to have the power factor at 0.9, that is generally what they aim for.

A motor at no load usually has a power factor between 0.1 and maybe 0.2. That means 80% to 90% of the current draw at no load is reactive current. In the US, residential meter does not read reactive power, or if it does, that number is not (yet) used. A commercial meter does, and you get charged for low power factor in various punitive ways.

So there is no really good reason to worry about reactive power for a residential installation. You can simply ignore the "extra" current, it really only bothers the powerco.

One quick question though, If I had Power Factor Capacitors their only benefit would be to reduce the Reactive current in T1 and T2 lines right?
So no real benefit to me due to the fact that the power company doesn't charge me for reactive current.
Am I correct in that assumption?

 

[JST]

That is the point, yes.

Don't forget, all current is "real" as far as the breaker is concerned. Extra current draw is extra current draw, so if you have breaker issues, or wire size issues, or transformer issues, there can be an advantage to power factor capacitors.

That's why the powerco hates reactive current and charges for it separately. They pay to generate it, but nobody pays them for it unless the powerco measures it and assesses a charge. Old style residential meters had an actual adjustment to cancel out any reading of reactive current. New meters can measure it.

 

[jim rozen]

In my area (con ed, NY) residential meters measure only watts (W-hrs...) which is real power but industrial meters typically measure VARs (volt-Amp reactive) or the sum of real and imaginary current. If you have the first type you can determine power draw by integrating over a time interval, noting the meter reading before and after. If the real power draw is that low you may want to make the interval fairly long, an hour or two. Be sure to note the time interval.

 

[idontrunntoofast]

That is the point, yes.

Don't forget, all current is "real" as far as the breaker is concerned. Extra current draw is extra current draw, so if you have breaker issues, or wire size issues, or transformer issues, there can be an advantage to power factor capacitors.

That's why the powerco hates reactive current and charges for it separately. They pay to generate it, but nobody pays them for it unless the powerco measures it and assesses a charge. Old style residential meters had an actual adjustment to cancel out any reading of reactive current. New meters can measure it.

That is a good point, I have 200 amps available at this shop, and from my load calculations it should be enough for now. All the wires are more than sufficient.
But is possible to install power factor capacitors if I need to in the future?
I imagine that I would need to have the capacitor bank hooked up through a contractor controlled by an ammeter so that they turn off when there is sufficient power draw on T3?
Dispite my mediocre understanding of induction motors and reactive current I can design and build a circuit board of necessary.