info on inverters ?

Inverters fall into two groups, large 3 phase powered, and small single phase powered.

The smaller inverters ( up to 3 kW = 4 Hp ) can run of a standard 13 amp plug, and give a three phase *** 230 V *** output, not a 400 V output.

Many modern three phase motors will run on either a 230 or 400 V supply, This requires only a change of the jump links in their connection box. Such motors are marked 230/400 ( or 240 / 415 ) V on their rating plate. 415 V star connection motors can be converted...sometimes :-(.

The three phase plug is for 415 V. You will need to wire the motor directly into the inverter.

Any inverter will run a motor smaller than it's rated capacity... Trying to run an oversize motor will cause trouble.

Hope this helps

Just to clarify what Jonathan is saying, 3-phase comes in various flavours and voltages:

The most common are:

1) Star connected, four wire (3phases plus neutral) plus earth, 240V phase to Neutral and 415 phase to phase, can be reconnected if the motor is suitable to: 2) Delta connected, 3 wire plus earth , 230V phase to phase. 3) Delta connected, 3 wire plus earth, 415 phase to phase. Not reconnectable to anything else.

Motors that are reconnectable 'generally' have the star and delta symbols on the rating plate with the two voltage ranges labelled. In my experience it is usually 6 terminals with reconnection bars to enable star or delta connection.

'YMMV'

Peter

-- Peter A Forbes Prepair Ltd, Luton, UK snipped-for-privacy@easynet.co.uk

thanks for the replies ! even if a little beyond my electrical knowledg

8-( !!! i'm thinking the best idea is for me to get the new lathe an then post my queries when ive got the job in front of me ! ive been t see it today and its a nice machine, only drawback is i'll have t strip it to get it into the back garden .i have been impressed with th quality of the myford , its the smallest machine ive ever used ,when worked in engineering i was lucky , the first 6 years i used dsg' langs and herberts and colchesters for several years after that

-- willowkevi

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hello again , i'm now the proud owner of a colchester student ! with

phase electrics . the sparky where the lathe came from said it wa wired as a star but he took the panel off and said he's changed it t delta (the back of the panel has the diagram for both , the motor i

2.25 kw (i think) and is dual voltage . so what do i do now ? the moto has terminals u1 u2 u3 v1 v2 v3 . will i be able to get an inverte that's foolproof :rolleyes: or to put it another way , will the pape work that comes with an inverter be sufficient for me to muddle throug ? i'm not bothered about having a speed controller , i just want fowar and backwards ! help !

-- willowkevi

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Presumably the motor has got:-

v1 connected to u2 v2 connected to u3 v3 connected to u1

or something very similar. In this case, you can connect the three output leads from the invertor to the three junction points above and it will work. If, by any chance, the motor turns backwards when the invertor says it should be going forwards, then just swap any two wires over and it'll be ok.

HTH

Mark Rand RTFM

after removing the motor , ive found it to be rated 380-415 volts an

2.2 kw . does this mean its not going to be able to be run from a inverter ? if i cant use it what are my options

-- willowkevi

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4 options I can think of 1 open up the motor and see if you can get to the star point, split the three wires and bring out the three new connections and wire up in delta format with a standard 240v inverter. This needs to be done carefully and the new joints well insulated (at high temperatures !) . Tie the new wires into the existing windings to keep them away from the rotor. Be aware that older motors normally use the type of enamelled wire that you need to scrape the enamel off not the newer stuff that comes off when you solder it. Converting to delta is usually successful but it can sometime be difficult. bear in mind that the motor is not much use to you at the moment so if you do ruin it you've not lost much. 2 look out for an inverter that steps up the voltage - there are a few around. 3 look out for a 240 - 415 transformer Use with a 415 volt inverter after checking that it will accept single phase input - some do others shut down thinking a phase has failed. Best to use an inverter with a bit higher power rating as single phase input will need higher current in the rectifier than the equivalent power output run from a 3 phase source. 4 Change the motor for a modern 6 terminal star delta 240/415v unit.

hth

Bob

I've just been looking around on ebay. It appears that the price of a step up inverter is much more than the combined price of a new motor and a 240 in/ 240 out inverter

eg

3 HP 240 in/out inverter 3HP 240/415 motor 3HP 240 in 415 out step up inverter

NB I have no connection with the vendor and just the items to illustrate my point on pricing.

I think this rules out option 2 above

hth

Bob

well ,after a weeks studying i think i want a converter , in the futur

i hope to buy a vertical mill with a long enough bed to skim heads o which would be three phase . its a step up for me this , as machine ive used in the past were allready plugged in ! i can see on eba coverters selling at £3-£400 .does anyone on here go to machiner auctions/sales etc ? and if so could they give me an indication of 2n hand prices

-- willowkevi

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