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Have a read through Section 8.2 of this:
http://sound.westhost.com/xfmr2.htm , you are looking at toroidal transformers, doughnut shaped, so you can be 99% certain that parallel operation is safe but it is well worth the time to quote:

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The transformer manufacturer's specifications will indicate if parallel operation is permitted. If you are unsure, measure the voltages carefully, and avoid parallel connection if the voltages differ by more than a couple of hundred millivolts. There will always be a difference, and only the manufacturer's winding tolerances can predict what it will be. With toroidal transformers, the windings are often bifilar, meaning that the two windings are wound onto the transformer core simultaneously. The tolerance of such windings is normally very good, and should cause no problems.

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Sections 8.1, 11.3 and 12.1 are also worth a quick once over.

This is a must read for anyone playing with mains: http://sound.westhost.com/articles/electrocution.htm

If you're bored then http://sound.westhost.com/xfmr.htm is also worth looking at. In fact bookmark the site for a rainy day, there's lots of info in the Articles part and a lot of good projects too. Rod Elliott, the site owner is knowledgeable and well respected, if you are ever uncertain about anything electrical then it's always worth a visit to see if Rod has any advice.

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Originally Posted by Jonathan

The position of the black dot on the diagram shows the relative polarity of the windings, so if a primary wire with a dot is connected to one without, and the other two are connected to the mains that's correct for 230V. If the dotted wires are connected together, then to the mains and similarly for the wires without the dot then the primary windings are in parallel and in phase, so 115V is required - i.e. ideal for the countries with 115V mains (e.g. USA). Any other connection is not permitted since it will involve connecting the windings 180° out of phase, so they'll approximately cancel and you'll get nothing.



If you put the two secondary windings in series then yes you would get 70V, however we want them in parallel to get 35V at twice the current as if they were in series. Most transformers are wound with at least two secondaries to give you this option.

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so secondry in series on the diagram would be red 70v+ , yellow and black joined. orange -v

sorry here is a good detailed page.. http://www.routoutcnc.com/PowerSupply.pdf

ok so i got it, apparently times your ac voltage by 1.4... right gonna go with it i think.. been looking at maplins,?

off the shelf 225va 2x35 3.2a,39.99. not as good as your link to rapid johnathon, i know but what do ya think.

thanks all

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Originally Posted by crossleymarko

ok so i got it, apparently times your ac voltage by 1.4... right gonna go with it i think.. been looking at maplins,?

off the shelf 225va 2x35 3.2a,39.99. not as good as your link to rapid johnathon, i know but what do ya think.

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The proper figure is the square root of 2, which is roughly 1.412, however the rated output voltage of the transformer is with the it under the rated load, so off load the voltage is normally a few percent higher, and you need to allow that mains voltage can drift up and down, so you need to allow some margin for error.

Also check out http://www.airlinktransformers.com/ for transformers.

thanks what range of va am i looking at. ie 300va 0-35 0-35

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Originally Posted by crossleymarko

thanks what range of va am i looking at. ie 300va 0-35 0-35

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For 4 motors you want a minimum of 500VA.

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Originally Posted by John S

So what happens when the onboard fuse goes or does that behave differently ?

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That fuse is a much higher current rating than what you might expect (20 amps if I recall correctly). If it blows the driver is probably already gone so I bet it's more there to prevent fire.

so would 600va 2x35v cover me for all motor upgrades... dont wanna be spending twice...

why would you use axis a by the way for milling... ?

add vat to the rapid prices,, doh,,! another tenner mate. 49.50 so with caps etc how much do you acctualy save?

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Originally Posted by crossleymarko

add vat to the rapid prices,, doh,,! another tenner mate. 49.50 so with caps etc how much do you acctualy save?

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Not so much how much you save but how much better for the drives and your machine it will be.? . . Well worth it my reply.!!!
(Remember the drives debate and back EMF in the other post.!!)