Mains converter to power Aussie scientific machine in the USA.

[VK3DRB]

Hi.

I need to find a non-battery power solution for a very sensitive scientific machine. The machine uses two compressors and is designed to use two single phase Australian 230 VAC, 50Hz inputs - one input for each compressor.

However, this machine is going to be demonstrated in the USA where the nominal mains voltage is a single phase 110VAC, 60Hz. A step-up transformer is no good because it would change the frequency. I have been told (to be confirmed) a modified sine wave output is no good either, but a pure sine wave output is required. I do not know what, if any, feedback mechanisms are in the equipment, but if it were used in Australia, typical variances in mains amplitude obviously isn't an issue.

There are two 230V compressors, one draws 6A and the other 4A. I have also been told "the inrush current is 20A for as long as 200ms". I assume that is for each mains input - more to the 6A compressor I assume.

The machine can have its code modified so only one compressor switches on at a time, hence the inrush current at any one time need not exceed 20A.

I want to use something off-the-shelf, but if required we can build such a converter in a box with two 230V mains outlets and one (maybe two) 110V mains inlets and get it electrically certified. But maybe something is already complete ready to work. Of course, two independent power supply converters would work too, but one might be a more attractive option.

This device needs to be reliable. I searched in the WWW and it is flooded with solar inverters made by every man and his dog.

I normally work in microelectronics and PCB design, but not much in this area. If anyone has any suggestions or tips on where to get such a mains power converter, please let me know.

cheers,
Dave

[Ian.M]

The usual US 120V outlet is NEMA 5-15R, rated for max. 15A, and it is unwise to exceed 80% of its rating for an extended duration.   20A NEMA 5-20R outlets do exist, but they aren't commonly installed except in areas where the use of high load current 120V appliances is anticipated.

You need 10A @230V, which is 2300VA just for the compressors, ignoring any conversion losses and other loads in your machine.  At 120V, that's fractionally under 19.2A, pretty much 'redlining' a NEMA 5-20R outlet, which will almost invariably be on a 20A breaker. 

If your machine has two completely electrically separate power inputs (i.e. absolutely no interconnection between the two Lives or Neutrals) for the two compressors, with appropriate voltage and frequency conversion for each, and if loss of either power source wont cause problems other than an unintended shut down, you could feed it from two NEMA 5-15R outlets on separate breakers, but ensuring the outlets are on separate breakers will be difficult without the cooperation of the venue's electricians, so its probably preferable to require the venue has a 240V outlet available.

Frequency conversion is a whole other can of worms.  There are companies that make mains frequency converters (e.g. Georator no endorsement intended) but it doesn't come cheap.

Check with the compressor manufacturer if 60Hz operation is permissible.  If not, do they have a 'drop in' replacement that *IS* rated for 60Hz operation?

[BradC]

I need to find a non-battery power solution for a very sensitive scientific machine. The machine uses two compressors and is designed to use two single phase Australian 230 VAC, 50Hz inputs - one input for each compressor.

I'd use a pair of single phase to 3 phase VFD. Feed it with the 220V 60HZ American power and connect the machine between 2 phases of the output with it set to full beans and 50HZ. Multiply by 2.

Another solution would be to use a grunty double conversion UPS with the output set to 230V 50HZ. I know some of the older Liebert and APC units could do conversion, but haven't looked seriously for years. The batteries would supplement the inrush, but you'd need a pretty big unit to manage it.

[electr_peter]

You require significant power from converters. I would look into other direction - get a gasoline generator rated at 3kW or more. For example, Honda makes EU3000 with true sine wave output at 230V/50Hz.

[jpanhalt]

First off, I wouldn't assume that you will not have our "220V" with ground and probably a common available.  Any commercial laboratory or exposition hall will probably have 220V available and may likely have 3-phase.  A business office might be a different story.  However, most modern commercial facilities will probably have at least 220V available.  Residential is a different story.

Second, are you sure the pumps will not run on 60Hz?  I have two Savant two-stage vacuum  pumps (1/2 HP each) and both are rated 50/60 cycle.  If you are planning to sell the instrument internationally, it would be best to incorporate dual frequency ability.

[jeroen79]

The device may be sensitive but are you sure it is sensitive to mains voltage and frequency?


Can't you do a one off (partial) conversion?
I.e. change whatever won't run on 110V/60Hz for something appropriate.

Presumably if you're going to demonstrate it in the US you're going to want to sell it in the US.
Then you would make a better impression with something that doesn't need a big expensive converter.


The gasoline generator can probably be rented for just the demonstration.

[VK3DRB]

First off, I wouldn't assume that you will not have our "220V" with ground and probably a common available.  Any commercial laboratory or exposition hall will probably have 220V available and may likely have 3-phase.  A business office might be a different story.  However, most modern commercial facilities will probably have at least 220V available.  Residential is a different story.

Second, are you sure the pumps will not run on 60Hz?  I have two Savant two-stage vacuum  pumps (1/2 HP each) and both are rated 50/60 cycle.  If you are planning to sell the instrument internationally, it would be best to incorporate dual frequency ability.

I have been told the compressors will not work at 60Hz. They cool down to below -80deg C and apparently the system is precise with set point, ramp rates etc. They say they don't have the time to get them to work at 60Hz. They won't be used in a hall, but in a special medical facility over a period of weeks or months, where power needs to be reliable, so I can imagine a petrol driven generator wont cut it.

The three phase idea has the 60Hz issue.

[VK3DRB]

The device may be sensitive but are you sure it is sensitive to mains voltage and frequency?


Can't you do a one off (partial) conversion?
I.e. change whatever won't run on 110V/60Hz for something appropriate.

Presumably if you're going to demonstrate it in the US you're going to want to sell it in the US.
Then you would make a better impression with something that doesn't need a big expensive converter.


The gasoline generator can probably be rented for just the demonstration.

Sorry, I should have been clearer. The demonstration is clinical trials. Eventually they will use an alternative compressor arrangement (eg: a variable speed compressor).

[VK3DRB]

Check with the compressor manufacturer if 60Hz operation is permissible.  If not, do they have a 'drop in' replacement that *IS* rated for 60Hz operation?

Apparently not, unfortunately. That is why I initially suggested a step up transformer but they said it won't work due the frequency.

[VK3DRB]

I need to find a non-battery power solution for a very sensitive scientific machine. The machine uses two compressors and is designed to use two single phase Australian 230 VAC, 50Hz inputs - one input for each compressor.

I'd use a pair of single phase to 3 phase VFD. Feed it with the 220V 60HZ American power and connect the machine between 2 phases of the output with it set to full beans and 50HZ. Multiply by 2.

Another solution would be to use a grunty double conversion UPS with the output set to 230V 50HZ. I know some of the older Liebert and APC units could do conversion, but haven't looked seriously for years. The batteries would supplement the inrush, but you'd need a pretty big unit to manage it.

The big VFD seems a possibility, providing it can provide the current on two phases and the inrush current and the third phase has no load. I have never played with a VFD in my life (except a Vacuum Fluorescent Display ). I'll need to research this more. Thanks.

Batteries in a UPS would not be good, because this is to run for a long time.

[BradC]

The big VFD seems a possibility, providing it can provide the current on two phases and the inrush current and the third phase has no load. I have never played with a VFD in my life (except a Vacuum Fluorescent Display ). I'll need to research this more. Thanks.

Batteries in a UPS would not be good, because this is to run for a long time.

I have several high current VFDs here that I've used experimentally to provide ~230V single phase with a variable frequency. I'm told some VFDs don't cope with an unbalanced phase load, but all of the ones I have comfortably run a single phase motor on 2 of the 3 outputs. They won't boost a voltage, but at the end of the day all they do is rectify the incoming mains to DC and then chop it up, so they should be fine with US 220V 60HZ.

The batteries in the UPS are only there to provide that extra starting oomph. In a double conversion UPS the input current is only a relatively long term load average. The batteries just absorb the peaks and average the load.

[tpowell1830]

Hi.

I need to find a non-battery power solution for a very sensitive scientific machine. The machine uses two compressors and is designed to use two single phase Australian 230 VAC, 50Hz inputs - one input for each compressor.

However, this machine is going to be demonstrated in the USA where the nominal mains voltage is a single phase 110VAC, 60Hz. A step-up transformer is no good because it would change the frequency. I have been told (to be confirmed) a modified sine wave output is no good either, but a pure sine wave output is required. I do not know what, if any, feedback mechanisms are in the equipment, but if it were used in Australia, typical variances in mains amplitude obviously isn't an issue.

There are two 230V compressors, one draws 6A and the other 4A. I have also been told "the inrush current is 20A for as long as 200ms". I assume that is for each mains input - more to the 6A compressor I assume.

The machine can have its code modified so only one compressor switches on at a time, hence the inrush current at any one time need not exceed 20A.

I want to use something off-the-shelf, but if required we can build such a converter in a box with two 230V mains outlets and one (maybe two) 110V mains inlets and get it electrically certified. But maybe something is already complete ready to work. Of course, two independent power supply converters would work too, but one might be a more attractive option.

This device needs to be reliable. I searched in the WWW and it is flooded with solar inverters made by every man and his dog.

I normally work in microelectronics and PCB design, but not much in this area. If anyone has any suggestions or tips on where to get such a mains power converter, please let me know.

cheers,
Dave

First of all, the US mains are split phase 240 VAC, 60 Hz. Since the 60 Hz, will probably make the motors on the compressors run faster, your ramp times, etc. will be different. Most wall units in the office or hospital rooms will only have 120 VAC, 60 Hz. outlets, however, if you are doing your trials in a lab like room, it may have the 240 VAC 60 Hz. outlets or can easily be installed.

Second, you said that there are 2, 230 VAC, 50 Hz, inputs, one for each compressor which means that your solution, whether it is a VFD or something else will require 2 separate outputs. Most 240 VAC outlets in the US are single outlets. If you can use a single 240 VAC, 60 Hz. input on your VFD or other solution, no worries. There are different current ratings that are common for 240 VAC outlets: 30 amps and 50 amps, which each should have the proper sized wire to accommodate these currents.

Third, If you come up with a 120 VAC, 60 Hz. solution, keep in mind that most 120 VAC wall outlets in the US are rated at 15 amps. There are 20 amp outlets available, but the NEMA configuration for the power chord is not common and would be a "special" installation, which may be a deal breaker.

Fourth, if you know where you will install this unit, you might talk to the maintenance or technical liason in the building and this person may work a solution for you. It can't hurt to ask. Most places in the US are very accommodating and understand the 60 Hz/50 Hz dilemma.

I know this didn't answer your original question, but at least you have more facts about US power outlets, etc.

Hope this helps...

[mikeselectricstuff]

An online UPS ( which has configurable frequency) might be an option, it's the sort of thing you might find cheap as surplus.
Kikusui make some AC power supplies, these are popular for running valve guitar amps on tour - expensive though.
VFDs are probebly the best bet - these may also be able to do soft-start to reduce the effect of inrush.

[jpanhalt]

Sorry, I should have been clearer. The demonstration is clinical trials. Eventually they will use an alternative compressor arrangement (eg: a variable speed compressor).

If the instrument is going to be used to validate some clinical intervention, then there will be no problem with a "make do" solution.  However, if the instrument itself is being validated for use in the US, then the one used in the trials needs to be the one sold here.  There is some wiggle room, but any change to an instrument, and you would be surprised at how minor a change the FDA considers as change,* will need to be recertified.  That recertification doesn't need to be as extensive as the original  validation, but it needs to be done and approved.  I suspect our FDA would not consider a change in motors as a minor change, since as you stated, the operating conditions are extreme.

Changing a couple of motors would seem to be a lesser headache.

*We had an instrument that reported date as day/month/year in a rural environment.  It was the only instrument in that lab that reported in that fashion circa 1990 and caused confusion, so the lab changed the format to month/day/year.  A subsequent inspection by the FDA cited that change as a major infraction, namely "not following the manufacturer's directions."  The lab had to change the date format or get the manufacturer's approval for the alternative format.  Our FDA has a very limited range of infractions, and there is no grey area between "not following directions" that may cause result errors and any other type.  Another example is with drugs.  The FDA not only approves the drug per se, but its formulation and package.  That is, if the approved package (e.g., vial) is 1 g, then another vial with 5 g is considered an experimental drug and needs an NDA (new drug approval).  That was a real problem when we used drugs as reagents for some tests.

[mag_therm]

As ex-Australian migrant to USA, I have been through variations of this problem, including taking systems from Australia to demo/install in USA, and vice-versa.

Firstly , as jpan mentioned, industrial exhibition halls normally have booths with higher power outlets, like 220 V or even 480V 3 phase.
You would need to check with the venue, also it might mean location of the booth in a particular area.

Secondly, I would recommend to price changing to 60 Hz variants of your pumps, compared to a frequency converter.
That means not only the motors, but the innards of the pumps and maybe the mounting dimensions are different, to end up with similar pump specs.

Thirdly check that all parts of the control circuit are compatible with 60 Hz, including power supplies, relays etc.

The last place you want glitches is in an exhibition. On one occasion, before leaving Melbourne,  we rented a D_Genset that the supplier adjusted to 60 Hz for testing.

[Zero999]

Have you searched for 60Hz to 50Hz converter?

The old fashioned way is with motor generator set, which has the advantage of being resistant to overloads, and low electrical noise, but is bulky and subject to mechanical wear.
https://www.piller.com/en-GB/203/motor-generator-set-50-60hz-from-12kva-up-to-1500kva

There are also inverters specifically designed to convert 60Hz to 50Hz and some also do the voltage conversion.
https://www.kccscientific.com/50hz-60hz-guide-frequency-converter-power/
http://www.gohz.com/how-to-convert-60hz-to-50hz

What is it? Is it a new kind of oxygen generator, or ventilator for COVID-19 patients?

[ajb]

Third, If you come up with a 120 VAC, 60 Hz. solution, keep in mind that most 120 VAC wall outlets in the US are rated at 15 amps. There are 20 amp outlets available, but the NEMA configuration for the power chord is not common and would be a "special" installation, which may be a deal breaker.

It's quite common to install 15A receptacles on 20A circuits in the US, this is specifically allowed for 20A circuits by code as long as there is more than one receptacle (and apparently a single duplex counts as 'more than one').  I would expect any kind of relatively modern commercial or light industrial facility like a lab to have 20A circuits.  It may or may not have 20A receptacles, but more likely to have, IME, than not.  In any case, the 20A NEMA 5-20R will accept 15A 5-15P plugs and all of the wiring materials are the same other than the orientation of one connecter blade, so it's really a non issue.  Plus we're talking about 20A *inrush*, not steady state, so it's very unlikely for this to be an issue anyway since breakers are inherently designed to deal with inrush currents via their trip curves. 

Of course the wiring needs should be verified with the location ahead of time to be sure you know what you're walking in to.

[CaptDon]

Why is your instrument so sensitive to the frequency change??? Granted the compressors will run faster but your control loop should compensate. If the control loop is pushed outside its limits consider a U.S. set of P.I.D. variables for 60hz and a different set for 50hz. As for the compressors themselves they should run fine with no damage anticipated. 50hz 'iron' seems to run even cooler at 60hz.

[bdunham7]

Some of this has already been said, but the USA is not a '110V' country, you will find 240V almost everywhere, although you may need a circuit installed to the exact location.  A 240V (single phase) 40A circuit should be sufficient for your needs, this will allow 32A continuous and ~10X that for inrush/starting surge.

As for you conversion, you need a single-phase VFD and I'd recommend two, one for each compressor.  Single phase VFDs are used to control the speed of single phase motors in certain instances like slowing a fan down to save energy.  I'd look at the 1.5 kW version for your needs.  They can both be run off the same 240V 40A branch circuit.

https://www.ato.com/single-phase-vfd?affiliate=ads&gclid=Cj0KCQiAys2MBhDOARIsAFf1D1csbn6z7__hinmd3R93qVvJUlC9ZWAP6XdHuveh3OUxoQF193yIvq4aAhITEALw_wcB

You might need to program the VFD for a soft start to limit the surge current, but that shouldn't be an issue.

[LaserSteve]

In a Medical situation in the US we have a higher grade of wiring standards for leakage current and construction  in a patient care situation. 

For example medical grade plugs and outlets  have green dots on them.  Switching power supplies have to meet additional standards and testing.

If your device is going into a clinical situation that involves human patients, it will need to pass those requirements and will need an FDA form for import as a trial device.  US Customs may hold it for compliance testing etc.. A US citizen may need to agree to accept it, and promise to either export or destroy it after one year.

I'd strongly suggest you seek the advice of the Biomedical Engineering staff at where ever it is going to be used.

I haven't done that kind of importing / wiring  twenty odd years, so I will not try  point you to relevant code.

I do know in a medical setting the Biomedical Engineering staff will leakage test it, and the idea of it being on more then one plug makes me shudder. I spent a year working on CT machines and our control PCs were rack mounted and met severe grounding. Isolation, and interlock requirements. Our non-patient training devices were in the inventory system as medical devices.

So you need to define if it has human use or not before you proceed.

Don't forget about Rotary Converters, which are available in the US.

Last time I checked, clinical test, demonstration or marketing medical devices fell into the standard rules unless exempted by a variance report submitted and approved by FDA.

I'd modify the whole unit and or reprogram it.

On the other hand, if its going to a university lab and non human use, no problem.

In the US, FDA has jurisdiction over lasers, medical or otherwise, which is why I have some limited knowledge of this.  That and a year at the CT plant.

Steve

[mag_therm]

Why is your instrument so sensitive to the frequency change??? Granted the compressors will run faster but your control loop should compensate. If the control loop is pushed outside its limits consider a U.S. set of P.I.D. variables for 60hz and a different set for 50hz. As for the compressors themselves they should run fine with no damage anticipated. 50hz 'iron' seems to run even cooler at 60hz.

If these compressors are centrifugal and if  the  single phase motors are not speed controlled, and for a given impeller, (details I don't think are stated)
the affinity laws state that
flow goes up in proportion to rpm
pressure goes up by square of rpm

therefore shaft power goes up by cube of rpm.
 60/50 Hz ^3 : 1.73 times

[TimFox]

Before I retired (in US), we had the opposite problem:  our small company exported equipment with reasonably high power requirements to countries that used 50 Hz power (and to Japan, where we had to check carefully to see on what side of the 50 Hz/60 Hz line the customer was located).  Some of the subsystems were frequency sensitive.  The only sensible solution for us was to rent a Diesel-powered generator with appropriate output voltage that could be set to 50 Hz, in order to test thoroughly the equipment before shipment.  Such generators are readily available from rental companies in the US.
As stated above, "normal" domestic power (as in my city house) is 240 V with center ground, suitable for single-phase loads at 120 V (most everything) and 240 V (used for clothes driers and air conditioning).
A common power feed to commercial/small industrial power is 208 V (line-to-line) three phase, which allows 120 V (line-to-neutral) loading as well.
The "20 A" NEMA sockets mentioned above differ from the "15 A" type by an extra short orthogonal slot on the neutral side, but it is compatible with the standard 15 A NEMA three-pin plug.  I have never actually seen the mating plug that will only fit into the 20 A socket.  Sometimes, three-phase power uses a "twist-lock" connector pair that seems to be unknown outside of North America.

[BrokenYugo]

The double conversion UPS idea is probably the most straightforward and portable solution. Do the homework on what sort of high current 240V socket you'll be provided, there are many varieties.

Do these compressors run continuously? I recall reading many VFDs don't care for the load coming on and off as many refrigeration compressor applications tend to do, I think they're really only meant for direct connection to a motor. I'm also not sure if they tolerate one phase floating, that's generally a bad thing with 3 phase and the VFD may be programmed to object to it.

The "20 A" NEMA sockets mentioned above differ from the "15 A" type by an extra short orthogonal slot on the neutral side, but it is compatible with the standard 15 A NEMA three-pin plug.  I have never actually seen the mating plug that will only fit into the 20 A socket.

I saw a 120V one once on a commercial pressure washer, factory molded plug, somebody had twisted the pin to make it sort of fit in a standard 120V 15A socket.

[TimFox]

Defeating the 20 A prong:  "Fools are infinitely ingenious."

[VK3DRB]

Have you searched for 60Hz to 50Hz converter?

The old fashioned way is with motor generator set, which has the advantage of being resistant to overloads, and low electrical noise, but is bulky and subject to mechanical wear.
https://www.piller.com/en-GB/203/motor-generator-set-50-60hz-from-12kva-up-to-1500kva

There are also inverters specifically designed to convert 60Hz to 50Hz and some also do the voltage conversion.
https://www.kccscientific.com/50hz-60hz-guide-frequency-converter-power/
http://www.gohz.com/how-to-convert-60hz-to-50hz

What is it? Is it a new kind of oxygen generator of ventilator for COVID-19 patients?

The machine is used in research. An NDA forbids me to say what it is. But your GoHz may fit the bill nicely. A big thank you. I have contacted them with some specs and we will see what they come back with. The compressors can be switched on at different times to reduce inrush current.
I will need to run some tests or see some data to verify the load claims of the compressors. I am also interested to know why they cannot use a feedback loop to control the work of the compressors if they run at 60Hz.

GoHz has a 5kVA model that might be suitable.

In any case, if the GoHz solves our problem, I owe you a beer  .