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  1. #21
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    Quote Originally Posted by Peter from Holland View Post
    Ross
    Or 60 Hz Single phase 120V 2phase 220 volts 3ph 120/208 V or 277/480 V or 120/240 V or 240 V / 480 V and those that I forgot
    Like 347/600, which seems to be common here in Canada...

    Anyways, I apologize for derailing this otherwise perfectly reasonable thread with my prejudices .

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    I also wonder what's wrong with the world..... ;-)

    In the UK it seems like they often have 240V single phase - and the fuse is in the plug
    (which protects the device - but not the wiring in the house).

    So they sell 1-3 phase VFD's in the UK. Those are rarely seen here, unfortunately.

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    Quote Originally Posted by Erik View Post
    I also wonder what's wrong with the world..... ;-)

    In the UK it seems like they often have 240V single phase - and the fuse is in the plug
    (which protects the device - but not the wiring in the house).

    So they sell 1-3 phase VFD's in the UK. Those are rarely seen here, unfortunately.
    The general idea is to have the same voltage all over the EU
    We used to have 220 Volts Now it is 230V Then 240 volts is within limits of 5%
    There are plenty 1 ph input 3ph output VFD `s available if that is what you mean
    I am sure in Danmark too If not I can sell you some

    Peter

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    They also sell 230V single phase input, 415V 3 phase output VFDs (no transformer) here as well. I'm not suggesting they are a good idea, but they are available and can make powering a machine with a motor that cannot be wired in delta easier.

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    Quote Originally Posted by billmac View Post
    They also sell 230V single phase input, 415V 3 phase output VFDs (no transformer) here as well.
    I didn't realize that such things were available. I thought that if you want 400V output you need 400V input, because all that a VFD does is provide phase-shifted versions of the input, perhaps at *reduced* voltage.

    Could you please provide a link or part number?

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    Quote Originally Posted by ballen View Post
    I didn't realize that such things were available. I thought that if you want 400V output you need 400V input, because all that a VFD does is provide phase-shifted versions of the input, perhaps at *reduced* voltage.

    Could you please provide a link or part number?
    Great deals from Drives Direct Inverters LTD in DIGITAL-240-TO-415-INVERTERS- | eBay Shops

    If you think that the inverters look like standard inverters you would be correct. The UK supplier does some internal modifications so that the output is 415V rather than 230V. I have some notes somewhere about how that is done, but I would have to look for them. The changes are not complicated. I do not think that the inverter OEM would necessarily endorse the modifications, so just to be clear this is not a recommendation.

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    Quote Originally Posted by billmac View Post
    Great deals from Drives Direct Inverters LTD in DIGITAL-240-TO-415-INVERTERS- | eBay Shops

    If you think that the inverters look like standard inverters you would be correct. The UK supplier does some internal modifications so that the output is 415V rather than 230V. I have some notes somewhere about how that is done, but I would have to look for them. The changes are not complicated. I do not think that the inverter OEM would necessarily endorse the modifications, so just to be clear this is not a recommendation.
    Here in Germany I have 3 phase 400V @ 32A in my home workshop, so I don't need this for myself. But this looks like a great solution for people who want to run a European 400V/3-phase machine on 230VAC single-phase. Thanks very much for the link, as I wrote earlier, I did not know that such things existed.

    If you have time to explain to me how it works, I would be interested. My 'mental model' of a VFD is that the input is a bridge rectifier and capacitor that create an internal DC bus at sqrt(2) x input AC voltage. Then some mosfets or igbts are switched at ~10 kHz to make PWM facsimiles of three phase-shifted sinusoids. Do the devices you linked to have some sort of high-frequency 'buck converter' to boost the voltage before the DC bus?

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    Quote Originally Posted by Peter from Holland View Post
    The general idea is to have the same voltage all over the EU
    Peter
    Well, Peter - it looks like they solved that problem with Brexit. ;-)

    I read in the UK that three phase supply is not standard unless you live near industrial areas.

    And therefore expensive to get if you live in an older residential area. I do hope that situation has become better.

    In Denmark three phase supply is delivered everywhere - and I suppose in the Netherlands as well.

    I know Norway have 3x230Volt supply instead of 3x400 - strange.

    Another fun fact: 100 impulses (50 Hz) per second is what causes your muscles to cramp up completely.

    At lower frequencies you may be able to let go of the connection. (tested in Biology class on frog muscle)

    Back to topic - I know Danfoss make 1->3 phase VFD's. I just haven't seen any physically.

    My reason for using one would be because the three phase VFD's trip my RCD. But I don't really need one.

    And I have two NOS 3 HP Danfoss (VLT2822) VFD's I won't/can't use.

    Cheers
    Erik

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    In Europe almost all single speed motors up to 5Kw are dual speed 230 400 volt Above that some are 400-690 volts
    So the only time one needs a 1ph 230V input to 3ph400 output VFD is with a dual speed motor As most of these are single voltage
    And even then I prefere to switch the motor to a single speed motor if possible
    A possible candidate for such a VFD is a Deckel FP1 You can eighter put u new motor on it and go with a 1ph 220 to 3ph 400 VFD or keep the old motor and use a 1ph 220v to 3Ph 400volts VFD I have heard mixed opinions about the 1ph 230 to 3ph 400volts VFD so for now I prefer the solution with another motor should the need be there

    Peter

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    Single Voltage motors are fairly common here. These have the star point connection buried in the windings. To convert them from 415V to 230V delta connection, you need to open the windings (in the right place) disconnect the star point, solder in connection wires and route them out through the terminal box. Now you need to tape everything back up and preferably dip the windings or apply some kind of insulating compound. A 230V to 415V inverter is a reasonable alternative to this process when the motor cannot be economically replaced.

    I agree about the dual speed motors. My lathe had a three speed motor; I wanted a inverter drive for various reasons, but after a lot of thought I decided that keeping the original motor was going to be extremely complex so I replaced it with an inverter rated dual voltage motor.

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    Quote Originally Posted by ballen View Post
    My 'mental model' of a VFD is that the input is a bridge rectifier and capacitor that create an internal DC bus at sqrt(2) x input AC voltage. Then some mosfets or igbts are switched at ~10 kHz to make PWM facsimiles of three phase-shifted sinusoids.
    Do the devices you linked to have some sort of high-frequency 'buck converter' to boost the voltage before the DC bus?
    I really don't remember the way in which this is done, but I do recall that it isn't at all complicated, certainly not an additional buck-converter; that would involve a number of new components. My vague memory is that it is just a reconfiguration of how components are connected up that involves driving them with higher voltages than the oem had in mind. I will see what I can find.

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    Quote Originally Posted by ballen View Post
    If you have time to explain to me how it works, I would be interested. My 'mental model' of a VFD is that the input is a bridge rectifier and capacitor that create an internal DC bus at sqrt(2) x input AC voltage. Then some mosfets or igbts are switched at ~10 kHz to make PWM facsimiles of three phase-shifted sinusoids. Do the devices you linked to have some sort of high-frequency 'buck converter' to boost the voltage before the DC bus?
    There are two ways to do this that I know of:
    1. A capacitive voltage doubler.
    2. A boost converter, perhaps doubling as a power factor correction.

    The former is possibly a "simple" modification to an existing item, though the device would have to be built to allow this, I'd think. Here's an image of what this'd look like (ignore the transformer):

    It's essentially a pair of half wave rectifiers, each with it's own capacitor. Note that this puts much higher stresses on the diodes and capacitors than a full-wave rectifier as each capacitor has to hold up its rail for a full mains cycle, rather than half of one.

    Siggi
    Last edited by sigurasg; 04-04-2021 at 02:19 PM. Reason: Noticed the transformer should be ignored for a VFD/inverter..

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    The doubler circuit looks plausible for an easy modification of an inverter. I took a quick look at the manuals for a few of the inverters that I have used. Most do not give any circuit information beyond how to wire them up, but I did find some examples with maintenance details, including replacement of the main smoothing capacitors(C1 and C2) in the schematic above. In these VFDs, a pair of large value capacitors were used and they had either screw or spade terminals. I would expect a 3 phase modular full diode bridge, but with the example I have in front of me it would be very simple to reconnect this in the way shown. The change could therefore be made with very simple wiring modifications; no additional components, no need for changes to PCBs.

    That said, I don't like the idea much.


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