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

born2dive00

Joined Oct 24, 2016
285
Hello Ebowulf

I can do high level if I know what parts to get and have a schematic. I have created a base station for a project that runs on ac 110, ac220, 12vdc or off lipos, and has a collapsing circuitry made with relays to automatically switch to which ever voltage is available and if on 110 or 220 to charge the lipos or lead acid batteries. Nothing has been made for a FPV base station.

The problem that I am encountering with this is 2 fold. 1 I can not find a cheap 10,000watt VFD, and 2 I can not find a 10000 watt vfd that has 220v @ 50hz in and 110v @ 60hz out. Either it has not been made or there is not much demand.

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.

born2dive00

Joined Oct 24, 2016
285
I don't have an osliscope to measure it on the start up cycle, and the multi meter wont catch it cause the in rush is too fast.

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.

born2dive00

Joined Oct 24, 2016
285
Are you saying use my multi meter and measure the ohms when it is off? or use an oscope which I don't have.?

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.

born2dive00

Joined Oct 24, 2016
285
I have a question about the VFD's
I have found a 7500w VFD, it goes from single phase 220 50hz or 60hz in, but the out put is 220v 3 phase. Now I have always been told that you can not run a single phase motor or appliances or irons or hair driers on a 3 phase is this true?

What I mean is can I connect my transformer to the VFD which is on a 3 phase 220? I have always connected it to 220v single phase.

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.

born2dive00

Joined Oct 24, 2016
285
If you are saying to use my multi meter, do I measure the resistance of the motor only or do I measure the resistance with the capacitor an the motor?

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.

Joined Jul 18, 2013
25,010
Using a 3ph VFD for anything but what it is intended for, (3ph motor) is a gamble, especially if using a 1ph device, the VFD generally does not like it.

The reason you cannot find too many 1ph VFD is a already mentioned, those that select them for speed control are generally disappointed.
Just measure the resistance across the pair of input AC supply leads to the motor.
Max.

born2dive00

Joined Oct 24, 2016
285
Understood not to run a 1 phase equipment on 3 phase.

Now here is the question on the VFD's the large ones I have seen 7500w seem to be 3 phase out, Does this mean that each phase is on separate terminals or does it mean that all 3 phases are sent to one terminal block?

The reason I am asking is if the 3 phases are on separate blocks can I not just connect to only 1 to get 1 phase?

Using a 3ph VFD for anything but what it is intended for, (3ph motor) is a gamble, especially if using a 1ph device, the VFD generally does not like it.

The reason you cannot find too many 1ph VFD is a already mentioned, those that select them for speed control are generally disappointed.
Just measure the resistance across the pair of input AC supply leads to the motor.
Max.

Joined Jul 18, 2013
25,010
Now here is the question on the VFD's the large ones I have seen 7500w seem to be 3 phase out, Does this mean that each phase is on separate terminals or does it mean that all 3 phases are sent to one terminal block?

The reason I am asking is if the 3 phases are on separate blocks can I not just connect to only 1 to get 1 phase?
You can get much smaller 3ph out VFD's than 7.5Kw.
The output of a VFD is electronically produced 3 phase wave form across the three terminals.
With 3 phase, the use of any two phases is regarded as single phase.
This is what you would need to connect to, but generally a VFD designed for 3ph output generally throws an error in this condition.
Max.
.

born2dive00

Joined Oct 24, 2016
285
Hey Max I did what you said.
here are the results with my multi meter set to 200 ohms I got

On the small freezers
across the run and common I got 8.98 ohms
across the start and common I got 8.30 ohms
across the run start I got 16.6 ohms

On the 1/3hp glycol pump motor
I got 33.5 ohms across the 2 blades on the plug.

So if I did my math correctly for the freezers with 16.6 ohms at 115v that should give me 6.92 amps or 800 watts (rounded up) on the start up in rush is that correct?

If I did my math correctly for the 1/3hp Glycol pump I get 33.5 ohms @ 115, that should give me 3.43 amps, or 400 watts (rounded up) on the start up in rush of the motor is that correct?

But why on does the sticker on the 1/3hp motor say that it is at 7Amps????

I will get the measurement of the 1/2hp glycol refridg compressor shortly.

Now I think I know the answer but why is a tiny refridg compressor in the freezers taking almost double the amp draw of the 1/3hp glycol pump??

Next question is regarding the small transformer for the freezers, I have always followed the rule of 1.5 X the max watts so with the small freezer taking 800 w that would be 1200w But seeing that it is a momentary pulse, do you think I could get by with a 1000w transformer? I mean it is still above the 800w needed to start the unit. will that momentary pulse of 1200w screw a 1000w transformer?

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.

Last edited:

ArakelTheDragon

Joined Nov 18, 2016
1,353
I did not get why we need to create a 115VAC signal?

You are moving from a 115VAC country to a 230VAC country? What's wrong with a transformer to lower it to 115VAC, rectify it, make it a 60Hz signal and feed it to a second transformer?

ArakelTheDragon

Joined Nov 18, 2016
1,353
Or even better, buy a notebook charger 19VDC and after it just make the VAC part?

Edit: You can probably put a battert after the notebook charger and buy a solar invertor DC to VAC.

born2dive00

Joined Oct 24, 2016
285
Hello Arakel
First off we are dealing with a relatively large refrigerator compressors 1/2 these are not that common in a residential use
as well as 1/3hp water pump, 1/3hp meat grinder and 2 freezers with smallish 1/10hp ref. compressors plus several other house hold appliances with induction motors.

Yes I can buy transformers for each item but that is going to get expensive fast to get proper size, for example the little 1/10hp freezer motor has a start /inrush operating amp draw of around 3.4A BUT it has a locked rotor draw or 15 amps. Now while it might be ok to use a smaller transformer say we are using the 3.4A measurement, this would be required to have 400w + 50% so a 600W transformer, But if that motor locks up for any reason, (as I understand it) @ 15 A we would need a transformer that is 1725W + 50% so a 2587w transformer. If we used a smaller transformer (as I understand it) and the motor locked up, the transformer would blow a fuse at the least, potentially burning the coils.
So I would need to get at a minimum of 1 huge transformer, and run extension cords, OR get several smaller transformers, Either way it gets pricey both for the number of transformers or for the size of the transformer + each of the VFD's

If I could find a VFD with 115vac @60hz then I would only need to get a VFD for each of the pieces of equipment that has induction motors.

A small note book charger to get power is way too small, I have calculated (perhaps in error) that I would need 1 large 20kw transformer with 1 30kw VFD for all my gear, OR (2) 3kw, and (3) 6kw transformers and VFD's

And transformers weigh a ton when trying to ship air freight. (estimated 300lbs @ $2.50/lb so around$700 just for transformers). So as you can see it would be very beneficial to find a large VFD with a 220v 50hz in with a 110v 60hz out.

I did not get why we need to create a 115VAC signal?

You are moving from a 115VAC country to a 230VAC country? What's wrong with a transformer to lower it to 115VAC, rectify it, make it a 60Hz signal and feed it to a second transformer?

born2dive00

Joined Oct 24, 2016
285
Max here is the numbers for the 1/2hp danfoss SC12G /SC15G
Across the common to run it is 1 ohm
across the common to start is 4.2 ohm
across the run start it is 5.2 ohm

So if I did my math right that = 22.1 A @ 115v or 2550 watts,+ 50% = 3825 watts for the transformer
BUT
the locked rotor amps are at 42A. so about 7660 watt transformer

Which one do I go with?

What I am thinking of doing is running a 5000w transformer to a 20a circuit breaker, then to a plug to the motor
If I am right, the circuit breaker should trip before ever reaching the 42a locked motor rating. but the question is would the transformer suffer a potential burn up until the circuit breaker tripped?

You can get much smaller 3ph out VFD's than 7.5Kw.
The output of a VFD is electronically produced 3 phase wave form across the three terminals.
With 3 phase, the use of any two phases is regarded as single phase.
This is what you would need to connect to, but generally a VFD designed for 3ph output generally throws an error in this condition.
Max.
.

born2dive00

Joined Oct 24, 2016
285
Now I just checked my 1/3hp motor and it says Code S I am guessing that is the nema code
if correct it says 18. so 18X.33X1000/115 = 52A or 5994w

But you said that I should measure the resistance across the lines which = 33.5 ohms which is 3.4A @ 115v or 391W
But the tag says 6.9A @115v or 793w

So which set of numbers should I use? when getting the transformer
but when I look at what circuit breaker is commonly used for a 1/3hp on 115v they say use a 15A or 1800w

So which is correct?

You can get much smaller 3ph out VFD's than 7.5Kw.
The output of a VFD is electronically produced 3 phase wave form across the three terminals.
With 3 phase, the use of any two phases is regarded as single phase.
This is what you would need to connect to, but generally a VFD designed for 3ph output generally throws an error in this condition.
Max.
.