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3 phase converters

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Artiglio

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Good day all

I’ve been offered a good deal and first refusal on some retirement machinery, however its all 3 phase and i don’t have it.
Talking to a supplier of convertors, i’m told my needs will be met nicely by a 7.5kw rotary convertor unit. (I’ve supplied ratings of the machines)
I’ve no experience of such things , what experiences does anyone have of such units and any advice would be appreciated.
I’ve no problem in terms of the incoming single phase loads.

Many thanks phil
 

Billy_wizz

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I don't know much about converters but it sounds high to me check if it's designed for the highest single load (machine with biggest motor)or for the total load(all machines running together) and hopefully someone with proper knowledge will come along! Also would be helpful to know what sized motors we're talking about
 

Artiglio

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The saw and planer are both rated at 4kw and the extractor at 2kw, convertor supplier explained that going that bit higher made for a better starting current that would be kinder to the motors. Plus if in the future i was to get something larger ( very unlikely) it would cover most small workshop sized machines. It would only be one machine at the time plus extraction.
 

Sideways

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For the task you have described, that sounds like sound advice on the sizing of the converter.
I imagine a rotary converter of that size will cost you a fair bit north of £1000 but will have a resale value when you no longer want it.
Rotary converters are pretty simple and have a long life. You are paying for a sizeable motor (the rotary bit), a heavy copper and iron "autotransformer" inside the box to step the voltage up to 415V, and a bunch of big but simple components including some large capacitors which although good, are a component prone to ageing and failure after perhaps several years use.

What is your alternative ?
ONLY IF the machinery has motors that can be reconnected to run on 240V three phase "delta connected" (some can, some can't)
2 off 4kW rated variable frequency drives from a decent brand plus a 2kW one for the extractor might cost about the same as a rotary converter . Generic Chinese VFD's, much less.
I personally like the control afforded by electronic motor drives. No more worries about startup surges for example.

So take your pick, check your prices and figure £1000 - £1500 into your buying decision for the machines.
 

TFrench

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Go with the rotary. It's big enough to handle the kit, they're kinder on the motors than static converters and cheaper than fitting a VFD to everything. I just bought one on ebay (used) and it wasn't cheap, so they hold the money well.
 

porker

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One big difference that hasn't been mentioned is that the rotary converter is essentially plug and play. VFD's usually require a direct connection of their output to the motor and all the controls as inputs which depending on the electrical complexity of the machine can mean rewiring of the internals.

I've used VFDs on lathes and a milling machine but in your case it looks like a rotary convertor is the way to go.
 

Artiglio

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Cheers gents, looks as though the advice i was given by the vendor was sound. The price is well north of 1k at nigh on 1800 to my door. I’ll get back to the machinery vendor and see if a deal can be done.
 
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