3 Phase converter.

[Darkwood]

Example ..I have here in my hand a 4kw Omron inverter 1ph to 3ph now given that a 4kw motor will have an flc of approx. 8amps the plate rating gives a input demand of 40amps so do the maths that is 5 times the motor flc rating because you generate it from a single phase supply .... now take the OP example 7.5 KW motor and do the same.... with approx' 14amps flc x 5 this could see a demand of up to 70amps on the 1ph supply of which has a cutout fuse carrier stamped 100amps although this may not be the fuse rating within. As silva has pointed out once motors start getting beyond 4kw the duty on a single phase supply becomes so large it not commercially viable to make a product that would see little demand although you can get them they aint cheap .. don't mix this up with 3ph in 3ph out inverters which come in all size as ive just fitted a 33kw inverter myself.

 

[snowhead]

You are suggesting a motor inverter. The largest off-the-shelf one I could find was 2.2kw. Please link us to a 7.5kw one you know of. Or regurgitated manuf. spec of input supply requirements.

.

See my post, No.2. link to 10hp 1 to 3 ph.

From spec "At FULL LOAD this unit would require a 220 Volts feed of 50 Amps",

 

[brman]

Example ..I have here in my hand a 4kw Omron inverter 1ph to 3ph now given that a 4kw motor will have an flc of approx. 8amps the plate rating gives a input demand of 40amps so do the maths that is 5 times the motor flc rating because you generate it from a single phase supply .... now take the OP example 7.5 KW motor and do the same.... with approx' 14amps flc x 5 this could see a demand of up to 70amps on the 1ph supply of which has a cutout fuse carrier stamped 100amps although this may not be the fuse rating within. As silva has pointed out once motors start getting beyond 4kw the duty on a single phase supply becomes so large it not commercially viable to make a product that would see little demand although you can get them they aint cheap .. don't mix this up with 3ph in 3ph out inverters which come in all size as ive just fitted a 33kw inverter myself.

Ok, I think you might have to educate me.
Keeping it simple and only looking at power in vs power out.

Are you saying the plate rating of the 4kW inverter is 40A at 230V? That would be 9.2kW.
I am finding it hard that if it is giving 4kW out it is taking 9.2kW or only 43% efficient - that is pretty damn inefficient whatever the technology it has inside and it must get pretty hot!

snowheads spec sounds better to me. 220V at 50A is 11kW. 10hp being 7.5kW. So 68% efficient assuming

What is wrong with my logic?

I should add that I have limited experience of inverters but I do have a 1.5hp one on my lathe. Its manual quotes 230V @ 12A in vs 230V at 6A out. Given that is 6A per phase I make that 2760W in vs very roughly 2400W out if I have done my sums right.

 

[TF and the wire]

Sorry but I still can't see what the problem is. He has a 10HP (7.5kW) 3 phase motor that he needs to supply. If he uses a 230v single phase in/230v 3 phase out invertor, he would have to connect the motor in delta to accept this 230v.

If the invertor was 100% efficient it would be 7.5kW in/7.5kW out. As we know it will not be that efficient so you could expect to have to put in more than you take out. The input is unlikely to be treble the output because each phase is 120 degrees apart will be closer to 1 over root 3 (1.732).

Forget about using the motor in star for 400v operation as it is perfectly capable of working at 230v in star. To get a 230v single phase in/ 400v 3 phase out would be unecessarily expensive.

These are widely used in industry, and Routeco have them for example.

 

[silva.foxx]

Sorry but I still can't see what the problem is.

These are widely used in industry, and Routeco have them for example.

Firstly, interpretations of converter are being crossed here, I think. I believe the OP was inquiring about supply converters rather than motor inverters.

Secondly, please link to a single phase 7.5kw inverter drive on Routeco as I can't locate, but this phone is awkward for browsing.

.

 

[Darkwood]

A lot of confusion here...
Motor rating 10hp ...7.5kw which would equate to approx. 14.5 amps a phase (3ph 400v)
You have a single phase supply and want to use and inverter to gain 3ph to run the machine so you can either fit a motor inverter and do the necessary control and connection alterations or you can get a mains inverter that stands alone before the machine ..which ever way you do this you have to gain 14.5amps 3ph from 1phase and this can only be done by putting a 2 to 3x duty on the 1ph supply i.e. approx. 45amps but dependant on inverter and whether its mains or a motor can mean up to 5x the rating of the motor plate... how can I explain it any simpler

 

[Darkwood]

Sorry but I still can't see what the problem is. He has a 10HP (7.5kW) 3 phase motor that he needs to supply. If he uses a 230v single phase in/230v 3 phase out invertor, he would have to connect the motor in delta to accept this 230v.

If the invertor was 100% efficient it would be 7.5kW in/7.5kW out. As we know it will not be that efficient so you could expect to have to put in more than you take out. The input is unlikely to be treble the output because each phase is 120 degrees apart will be closer to 1 over root 3 (1.732).

Forget about using the motor in star for 400v operation as it is perfectly capable of working at 230v in star. To get a 230v single phase in/ 400v 3 phase out would be unecessarily expensive.

These are widely used in industry, and Routeco have them for example.

Yes 3ph is 120 degrees apart but to generate it from 1ph will put triple duty (double duty can be achieved with clever electronics and software but often not better than this) .. motor full speed will be 50hz you cant turn 7.5kw 1ph into 7.5kw 3ph or we would have free power for everyone as you could take a 1ph supply turn it into 3ph use the second phase to power the inverter and the 3rd phase would be free power ... physics conservation of energy applies here thing about it you think you really can input 1ph 7.5kw and get 3ph 7.5kw out that a 66% energy gain from nothing!

Converting a motor from 400v star to 230v delta only works with duel voltage motors so its an assuming comment to say it can be done regardless, and lastly show me any motor inverter or mains converter 1ph to 3ph that has the same power in ratio to power out i.e. 7.5kw in 1ph 7.5kw out 3ph and you'll be teaching me that the laws of physics are wrong.

I you want a 15amp 3phase supply and you convert it from 1ph you need 30-70 amps (differnet models vary this amount) of the 1ph supply minus control losses you can't put 15amps 1ph in and get 15amps 3ph (15amps per phase) out as it electronically steps the single phase into 3ph and creates the 120 degrees off 1ph.

 

[brman]

A lot of confusion here...
Motor rating 10hp ...7.5kw which would equate to approx. 14.5 amps a phase (3ph 400v)
You have a single phase supply and want to use and inverter to gain 3ph to run the machine so you can either fit a motor inverter and do the necessary control and connection alterations or you can get a mains inverter that stands alone before the machine ..which ever way you do this you have to gain 14.5amps 3ph from 1phase and this can only be done by putting a 2 to 3x duty on the 1ph supply i.e. approx. 45amps but dependant on inverter and whether its mains or a motor can mean up to 5x the rating of the motor plate... how can I explain it any simpler

Ok, I think I am following you now. 14.5A a phase at 400V is about 10kW (ie. 14.5*400*1.73). Am I right?

45A at 230V is 10.35kW. That is 97% efficient (ignoring power factors) so I'd be happy with that.
Like you said, in reality it probably is not that good but it matches the inverter snowhead quoted at 50A for 10hp.

I think I must have been confused by your post 16 which gave an example of 43% efficient.

 

[brman]

Yes 3ph is 120 degrees apart but to generate it from 1ph will put triple duty (double duty can be achieved with clever electronics and software but often not better than this) .. motor full speed will be 50hz you cant turn 7.5kw 1ph into 7.5kw 3ph or we would have free power for everyone as you could take a 1ph supply turn it into 3ph use the second phase to power the inverter and the 3rd phase would be free power ... physics conservation of energy applies here thing about it you think you really can input 1ph 7.5kw and get 3ph 7.5kw out that a 66% energy gain from nothing!

Converting a motor from 400v star to 230v delta only works with duel voltage motors so its an assuming comment to say it can be done regardless, and lastly show me any motor inverter or mains converter 1ph to 3ph that has the same power in ratio to power out i.e. 7.5kw in 1ph 7.5kw out 3ph and you'll be teaching me that the laws of physics are wrong.

I you want a 15amp 3phase supply and you convert it from 1ph you need 30-70 amps (differnet models vary this amount) of the 1ph supply minus control losses you can't put 15amps 1ph in and get 15amps 3ph (15amps per phase) out as it electronically steps the single phase into 3ph and creates the 120 degrees off 1ph.

I think this is where the confusion is. I think when TF (and I) were talking about output power he didn't mean power per phase, he meant overall power. ie. the power that is the motor hp.
So 3ph 400V at 7.5kW is 10.8A per phase (7500/(400*1.73) (EDIT: took out the kw per phase as it is confusing...)
So he isn't trying to get a 166% efficiency, just 100%.
Am I right TP?

I think we are all saying the same thing, just in different ways

Whether it solves the question of whether the compressor should (as apposed to could) be run off a single phase supply or not I am not sure!

 

[Darkwood]

Yes I can see where the confusion has risen but don't take the 3x as a guide its just a ball park you can get units that have a 5x and down to just 2x its really all about the brand and cost so always check. Yes I was referring to 7.5kw in 1ph ---- 7.5kw (10hp) per phase out as motors are listed this way. A 3ph motor that has a plate saying 400v 3ph - flc 8.1amps will be 8.1amp per phase not 8.1 shared across the phases, so an inverter would have to generate that rating on each phase off a 1ph supply.

 

[TF and the wire]

Blimey this is getting bogged down. I can give you an example of where I have seen this in practive.

A machine where I work has several invertors, single phase 230v input, each supplying a 3 phase motor connected in delta (230v use).

I am just picking these figures from memory, I think the motors are 1.5kW. The single phase input current is around 8amp. Which equates to around 2kW single phase in to give 1.5kW 3 phase out. Difference is due to lack of efficiency of the invertor.

So I would expect a 7.5kW motor connected in this way to take around 10kW from a single phase supply, 40 odd amp. These are estimations.

If the motor is a standard 3 phase type, it will almost certainly have the 6 connections to connect in either star or delta.

 

[bigbaddave]

At least my post was more useful than #9!

Hes not a spark.. hes a basket baller you see

 

[ajelec10]

I have a 7.5Hp motor dual voltage wired in delta, connected to a 7.5 Hp inveter 1 phase 230 input 3 phase digital output 230v inverter from inverter supermarket about £450.00. When the motor runs without load it only draws around 10amps on the single phase side the inverter soft starts it very well.

 

[Outspoken]

Try this LINK

Lots of complicated talk when all you had to do was provide a link to the equipment he wanted.

The simplest and cheapest method is the single phase to 3 phase inverter, but above 3kW these start to get expensive.

Of course the other route is to convert the 3 phase motor to single phase, which is not as complicated as it sounds, but you will certainly need a supply capable of handling it.

Sell the compressor and buy a single phase unit...simples...:waving:

 

[silva.foxx]

... buy a single phase unit...simples...:waving:

See post #4 that was deemed useless!