Transfo Troubles

[rinias]

Hi all !

I picked up the 3-Axis Pro Stepper Motor Driver Kit from HobbyCNC and things are coming along smoothly I had a few questions as to where I could get some of the components needed to finish the kit, however, as I am in Switzerland and I might be building several machines, I would want to get as local as possible...

The first real problem is the transformer. The kit states that I should pick up a 24 VAC 10 A transformer (like http://www.alliedelec.com/Search/Pro...D4B7002C2A617F ) I've been searching around quite a bit, though I am not sure where to look. I've tried Conrad ( www.conrad.de - site in German) and Distrelec ( www.distrelec.com - site in French) without finding anything "sure."

The main problem stems from the fact that they are not giving the current output but instead the power (in VA). I'm not sure what the calculations are to convert from one to the other - for single phase AC I used VA = V*A which means 24*10 = 240 VA. I'm not sure, however, and it seems more likely that I have 3-phase AC, so - VA = 1.732*V*A which gives about 400 VA (415 to be "exact"). If the second calculation is right, then I would need something that takes 230 V 50/60 Hz and has a power output of 400 VA. So I "chose" something like this

What I don't understand is that it costs about $130 (compared to $40 from Allied...) and looks way too "nice" compared with the one suggested in the kit. Even the one rated at 250 VA is going to be around $90.

What I'm asking, then, is :

- Are my calculations completely flawed ?

- Are these transfos too "complex" for the task ? (there's a note saying that they "start" with little current, are good for control, security and "galvanic separation" applications and that there's a "draw off" or "forced drainage" of +/- 5% on the primary side to adjust the voltage)

- If so, can someone suggest a dealer in the EU (or US with Int'l shipping) that is closer to the recommended component ? (Remember that it needs to accept 230 V 50/60 Hz input )

The other question was does anyone know of a dealer in the EU (or US with Int'l shipping) for the Pactec DM-4 ? ==> link

Thanks in advance for your help !

Rinias

[bebson]

Read this great tutorial...
http://www.campbelldesigns.com/files...ply-part-1.pdf

I dont belive that you have 3phase AC in home in Switzerland. I think that first calculation is OK.

[rinias]

Thanks so much for the link ! It seems to be what I need

According to what he says in the document, I would use the simple VA = V*A calculation so then I would go with around a 250 VA transfo...

Just need to find a supplier who doesn't want so much for this thing !

Rinias

PS - The document looks interesting - I'll have to look through it when I get home ! Thanks again

[bebson]

By those calculations, ideal transformer would be 250 VA, 24V. That woult give abbout 12 Amps at 33 Volts.
I have troubles with purchaseing transformer also. 250-350 VA (sutable for our PS) is weighting to much, so shipping is way to expensive for single piece of equipement. I Also live in Europe (Croatia)...America is great for buying components :-(

[rinias]

Well, after some serious searching - and armed with the knowledge that I needed around 250 VA) I scoured the internet for something local (Switzerland). I came up with Bächli ( http://www.baechli.com ). It was almost pure luck that I found them.

They sell a transformer that does 230 VAC @ 50/60 Hz to 24 VAC @ 300 VA for a mere 58 swiss franks (that's a bit more than 35 euros) for one. 10 costs only 55 sfr./pc and more than 10 they're willing to make a deal with you

The transformer I'll getting to test is the 960 226 109 in this PDF :
http://www.baechli.com/fileadmin/use...formatoren.pdf

It's all in German but they speak English as well and have proven (up til now) to be speedy and curtious.

I'm ordering 2 to give them a go - I'll let you know if there's anything else to report !

Rinias

PS - They also have power supplies and a bunch of other power related components. A good place to check out, I'd say !

PPS - No, I don't know anyone in the company and I'm not phishing. I have just been having a pleasant time doing business with them.

[mike@mikebeck.o]

I'll be happy to ship to you. I keep 24 volt, 10 amp 230 volt PRIMARY, and the Pactec DM-4 enclosures in both "Black" and "Bone", in stock at all times. I charge ABSOLUTELY NO MARKUP. I sell to hobbiests that have difficulty getting what they need strictly as a way of helping them, and therefore helping the hobby of CNC. I am brand new to CNC Zone, so do not know what is considered appropriate, or not. my e-mail is mike@mikebeck.org