Need desperate help with electric motors going from 60 to 50hz country. Rectifier 115VDC to 115VAC

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Hello everyone

As some of you all know I teach internationally and frequently move from country to country.

Currently I am in a country with 115v AC and 60hz.
I am moving to a country with 230v AC and 50hz

My Glycol cooler for my soft drink bar uses a refrigeration compressor that runs at 115vac and 60hz @ 8a
and the glycol pump is a 1/3hp induction motor that runs on 115vac and 60 hz @ 8a

Now the cost to replace these 2 pieces is cost prohibitive to replace the units with 230vac 50/60hz

So what I want to do is to take my 10kva (10,000w) isolated transformer and drop the line voltage from 220vac to 110vac.
Then I want to take and make a full wave rectifier to convert it from 110AC to 110DC (this will eliminate, or make manageable the flux in the motor)
I was going to add a bank of capacitors to smooth the DC out more.

Here is were I am stuck.
Is such thing as an inexpensive 110vdc inverter to 110vac?? I could even do a 220vdc to a 220vac unit and then drop the voltage with my isolated transformer.

If this does not exist cheaply commercially does any one know what I would need to build one?

My concern is the hertz frequency, I have been told that using a 115vac with 60hz will overheat and destroy my 1/3hp motors on the 115vac 50hz
Other folks say it is not a problem.

It should be noted that the compressor and the glycol pump motor will be running 24/7/365.

Any help you folks can offer would be great. I am not new to wiring things up, my weakness is in the theory of things.
 

MaxHeadRoom

Joined Jul 18, 2013
20,879
Personally I would not consider 1/3hp motors in any danger running on 50hz instead of 60hz.
Unless in the bush, is there not these facilities available locally where you go?
Max.
 

Reloadron

Joined Jan 15, 2015
5,504
During the early 80s I was required to live in the Naples Italy area for 3 years. I got a sweet deal on an American Specification 19 Cubic Foot refrigerator freezer designed for 120 VAC 60 Hz. It ran 3 years 24/7 just fine on the 50 Hz power and using a 220 Volt to 120 Volt transformer to reduce the voltage. The compressor motor likely ran a little slower on 50 Hz and maybe a little warmer but the unit ran fine. I wouldn't worry about it until you know for sure the 50 Hz is a problem.

Ron
 

dendad

Joined Feb 20, 2016
3,564
I think you will have to try it and see.
One test could be to measure the current on the 115V 60Hz supply and then on the 110V 50Hz supply. If it is not over maybe 20% more, it is probably going to be ok. The trouble can arise if there is not enough magnetic material there for 50Hz and magnetic saturation occurs. If that does, I would expect the current to rise sharply.
I have seen it in a power transformer.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Hey max
the refridgeration compressor that is on the glycol unit only comes in 115v, and there is nothing comparable as it is a proprietary compressor.
The motor for the glycol pump is just a plain jane induction motor. So No I can not change the compressor motor out on the glycol cooler or the freezers.

Personally I would not consider 1/3hp motors in any danger running on 50hz instead of 60hz.
Unless in the bush, is there not these facilities available locally where you go?
Max.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
If the equipment that I have was from the 80's I would not worry about it as they built them like abrams tanks. However in todays world with the companies have "improved" i.e. making things lighter and cheaper, built like a disposable lighter, I am concerned..

I mean I have ran my 1/3hp Lem 115v 60hz grinder that has an induction motor in Ethiopia dropping down the voltage with a transformer to run on 115v 50hz, but the grinder would only be run for periods of maybe 10-20 min not really long enough to get too hot like a motor running 24/7

I think you will have to try it and see.
One test could be to measure the current on the 115V 60Hz supply and then on the 110V 50Hz supply. If it is not over maybe 20% more, it is probably going to be ok. The trouble can arise if there is not enough magnetic material there for 50Hz and magnetic saturation occurs. If that does, I would expect the current to rise sharply.
I have seen it in a power transformer.
During the early 80s I was required to live in the Naples Italy area for 3 years. I got a sweet deal on an American Specification 19 Cubic Foot refrigerator freezer designed for 120 VAC 60 Hz. It ran 3 years 24/7 just fine on the 50 Hz power and using a 220 Volt to 120 Volt transformer to reduce the voltage. The compressor motor likely ran a little slower on 50 Hz and maybe a little warmer but the unit ran fine. I wouldn't worry about it until you know for sure the 50 Hz is a problem.

Ron
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Let me ask you folks another question

A electric motor 1/3hp 115v 60hz @8A when it starts up what type of amp draw does it usually have till it gets to speed. Some folks say 3X the rated Amp, so in my case 24A? does this sound correct? it seems way too high.

The reason I am trying to find out is because I am thinking of running a smaller more cost efficient transformer for the designated motors rather than my 10kva transformer.

Any feed back would be great!
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Good to know Albert, I did know this but have forgotten over the years.
So how do I get the rectified 155VDC inverted to 115vac at 60hz? This is where I am having the difficulty.
Alternatively we could rectify 220vac 50mhz to 325vdc but again how do I invert that amount of voltage to 220vac 60hz? I can drop the 220vac down to 115vac with my transformer after it is inverted at 60hz.

And remember I need fairly large draws. The compressor takes 8a draw @115vac@60hz and the pump takes 7a draw @ 115vac@ 60hz so a total of 15-16a + I guess 3x for its startup spike (or so I have been told) so about 45a @ 115 @60hz.

I'm not an expert at running motors on the wrong frequency but I can tell you that if you rectfy and smooth AC you get 1.4142 (square root of two) times the voltage so 110VAC will give you 155VDC.
 

ebeowulf17

Joined Aug 12, 2014
3,274
Let me ask you folks another question

A electric motor 1/3hp 115v 60hz @8A when it starts up what type of amp draw does it usually have till it gets to speed. Some folks say 3X the rated Amp, so in my case 24A? does this sound correct? it seems way too high.

The reason I am trying to find out is because I am thinking of running a smaller more cost efficient transformer for the designated motors rather than my 10kva transformer.

Any feed back would be great!
@MaxHeadRoom is probably the one to answer your starting current questions, although he may need more detail on the motors first.

I can tell you from my own experience that more than 3x is easily possible, depending on the nature of the motor. I regularly work with 1/3HP carbonator pump motors which use a centrifugal switch start system. Ours are actual set up for dual voltage capabilities. You just move a few jumper wires to configure it for either 120 or 240V nominal voltage and 50-60Hz is acceptable (although motor speed varies in direct proportion to line frequency.)

With the centrifugal switch start, the motor draws over 14A (on 240V) initially, and then as it gets up to speed (~0.2 sec when I tested with an oscilloscope) the centrifugal switch trips and greatly reduces the current to around 2.4A. So, in our application starting current is roughly 6x the running current. I imagine every motor and every application will yield different results, but there's on data point for you.

Usually we just check amp draw on these things with an amp clamp multi meter, and the high current draw passes too quickly to measure, but one time I hooked up a current transformer and oscilloscope to view the current draw. I thought it was pretty interesting. The attached image is the same one test run shown several times with cursors in different spots to get p-p measurement values for conversion.
motor-current.png
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Unfortunately for my glycol cooler pump the &£"(^&^$) seller said he would send me a dual voltage dual hz motor, but when I got it here in Taiwan, it was a 115v 60hz Jacka$$. But I guess though it would not make too much of a difference though because as I said the compressor is also 115v60hz, so I would had to change it out (if could change it out which I cant (nothing comparable).


@MaxHeadRoom is probably the one to answer your starting current questions, although he may need more detail on the motors first.

I can tell you from my own experience that more than 3x is easily possible, depending on the nature of the motor. I regularly work with 1/3HP carbonator pump motors which use a centrifugal switch start system. Ours are actual set up for dual voltage capabilities. You just move a few jumper wires to configure it for either 120 or 240V nominal voltage and 50-60Hz is acceptable (although motor speed varies in direct proportion to line frequency.)

With the centrifugal switch start, the motor draws over 14A (on 240V) initially, and then as it gets up to speed (~0.2 sec when I tested with an oscilloscope) the centrifugal switch trips and greatly reduces the current to around 2.4A. So, in our application starting current is roughly 6x the running current. I imagine every motor and every application will yield different results, but there's on data point for you.

Usually we just check amp draw on these things with an amp clamp multi meter, and the high current draw passes too quickly to measure, but one time I hooked up a current transformer and oscilloscope to view the current draw. I thought it was pretty interesting. The attached image is the same one test run shown several times with cursors in different spots to get p-p measurement values for conversion.
View attachment 153426
 

Sensacell

Joined Jun 19, 2012
2,568
Just my 2 cents...

I moved from a 110 VAC 60 Hz country to a 220 VAC 50 Hz one and also had the grand idea to use converter transformers to solve the problem.

But... Human nature and Murphy's law take a heavy toll, eventually, I stopped this silly practice after everything "110 VAC only" got blown up.
It's almost impossible to keep others from randomly plugging things in, even with giant tags on the plugs, still happens.
Even with different plugs- still happens! ("clever" people find adapters!)

I blew a few up myself, it's just too easy.

The only real solution would be to hard-wire the transformer to the device.
 
Just my 2 cents...


The only real solution would be to hard-wire the transformer to the device.
Very good move. thats what you have to do when you have to run some 100 V, 60 Hz Japanese stuff (Scanning Electron Microscopes) at 120 V.

Some stuff is rated for 50/60 Hz and that's what you would like.

50 Hz stuff may not run on 60 Hz power because there is more iron in the 50 Hz stuff to avoid saturation.

There is always the possibility to use a VFD (Variable Frequency Drive) for critical stuff.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
This is what I was envisioning to fix the hz problem, maybe I am nuts but I don't know of any other way. So the line voltage is 220v 50hz, now to drop that down to 110vac is not an issue just use a transformer, simple enough.

Next I was thinking of rectifying the voltage from 110vac @50hz, Now as Albert reminded me, when I rectify 110vac to dc the voltage jumps up to 155vdc. I was then thinking of putting the 155vdc thru a bank of capacitors to smooth out the voltage. Then I was thinking of building an inverter to switch from the 155vdc to 115vac@ 60hz...

Would this crazy idea work? I know this sounds like a lot of work (I have plenty of time) but to replace all my 115v equipment would cost me some where near $5-8k usd.

I know how I could do this by connecting 115v to 12vdc power supplies then connecting a mess load of 12v to 115v car inverters but there has got to be a cheaper way and less hassle by just rectifying the line voltage.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Well We have been living over seas for the past 20 year now with smaller 115v equipment and just a transformer, and I am very happy to say we have never blown up anything yet. It also helps not having kids to screw with things. We have noticed some of our smaller equipment does not run as smoothly but never popped anything. My concern now is since I have gotten inventive and make our own sodas/soft drinks (they don't have my favorites outside of the states like mellow yellow, root beer, grape, fresca, diet pepsi, dr pepper,... and it is a mess load to make you own, I make mine for less than $2.58 per 5 gallons. We save about $3k per year on softdrinks when compared to the US costs.) But like I say my inventiveness has required some rather pricy motors and pumps to get a proper pour.


Just my 2 cents...

I moved from a 110 VAC 60 Hz country to a 220 VAC 50 Hz one and also had the grand idea to use converter transformers to solve the problem.

But... Human nature and Murphy's law take a heavy toll, eventually, I stopped this silly practice after everything "110 VAC only" got blown up.
It's almost impossible to keep others from randomly plugging things in, even with giant tags on the plugs, still happens.
Even with different plugs- still happens! ("clever" people find adapters!)

I blew a few up myself, it's just too easy.

The only real solution would be to hard-wire the transformer to the device.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
From what I know having run 220v 50hz on 220 60hz it actually is no problem the reason like you said there is more iron on the 50hz things. The only thing that you get is the motor runs about 20% faster. as long as you have adequate cooling this is not a problem. We have done this for years.

The potential problem comes with the 60hz gear on 50hz lines it can as you say saturate the core due to the flux of the mg field. This is what I don't know about. I know I have ran 60hz gear on 50hz lines in the past with just a transformer but like I say it is only for a short time and not enough time to build up a saturation to damage the motors.

What I don't know is the 24/7 duty cycles and if this would be a problem. Hence my desire to build a "frequency converter".

Very good move. thats what you have to do when you have to run some 100 V, 60 Hz Japanese stuff (Scanning Electron Microscopes) at 120 V.

Some stuff is rated for 50/60 Hz and that's what you would like.

50 Hz stuff may not run on 60 Hz power because there is more iron in the 50 Hz stuff to avoid saturation.

There is always the possibility to use a VFD (Variable Frequency Drive) for critical stuff.
 

ebeowulf17

Joined Aug 12, 2014
3,274
Everything I've seen and read makes me think that building a high power vfd or inverter and getting reasonably clean power out of it is a very high level job. This isn't something you can just whip up with a few simple components. Getting DC from AC is trivial, but going the other way is not! I think you're better off buying an off the shelf unit.

As others have mentioned, a VFD (variable frequency drive) does exactly what you need - it takes AC power, converts it to DC, and then generates AC power from it at whatever frequency you want. I think this is your simplest solution, although I'll admit my first couple searches didn't find many options with 230V in and 115V out.

The other option, if you're confident in your ability to generate DC, would be to buy an inverter to handle switching back to AC at 50Hz.
 

MaxHeadRoom

Joined Jul 18, 2013
20,879
Let me ask you folks another question
A electric motor 1/3hp 115v 60hz @8A when it starts up what type of amp draw does it usually have till it gets to speed. Some folks say 3X the rated Amp, so in my case 24A?
Any feed back would be great!
An AC induction motor is essentially a transformer with a shorted turn secondary at switch on, so the inrush can be high momentarily and is only limited by the DC resistance of the winding.
Then there is a decreasing current until running rpm is reached.
1ph Motor VFD's are not popular when using them to vary speed, but If you can find one and set it to a fixed run speed of 60hz then it should overcome some of the drawbacks normally seen when varying the rpm.
This is the reason for the use of 1ph in 3ph out for 3ph VFD motor control as these work well over the whole rpm range.
Max.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Max one of the issues I am having is the inrush. I have a freezer with 1.45a running draw at 115. which equals 166 watts, for testing here, I connected my BA transformer to the wall mains, which was able to push 220v @ 3000watts I then connected a small 200 watt transformer to my 3000w unit to drop the voltage down from 220 to 110v (this simulated 220v in Egypt) when I powered it up and the compressor kicked in pop went the fuse on the 200w transformer, So this is telling me that the start up / inrush exceeds 200 watts. Now I know how to use the Nema code for motors to find out the start up draw, but how do you figure it out for refridg compressors?

An AC induction motor is essentially a transformer with a shorted turn secondary at switch on, so the inrush can be high momentarily and is only limited by the DC resistance of the winding.
Then there is a decreasing current until running rpm is reached.
1ph Motor VFD's are not popular when using them to vary speed, but If you can find one and set it to a fixed run speed of 60hz then it should overcome some of the drawbacks normally seen when varying the rpm.
This is the reason for the use of 1ph in 3ph out for 3ph VFD motor control as these work well over the whole rpm range.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
20,879
Just measure the across line resistance of the motor and you will get an idea what your supply is seeing at the moment of switch on!
It's going to see that for at least one cycle.
Max.
 
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