HobbyCNC UK Transformer

[Emcore]

Hi all,
I know nothing about transformers - except they are in pretty much everything, and I know very little about choosing the right one. I am trying to find a UK or Ireland source for 240VAC Input 24VAC Output 10A Transformer as required for the hobbycnc 4 axis package kit.
Maybe I have got this wrong also.
Everything I look up seems to reference the input voltage 240VAC, then they vary with things like 12-0-12 or 24VAC, and then, to make matters more confusing they start using VA (volt-amps).
Of course I can find what I assume is the correct spec in the US on http://www.mpja.com/productview.asp?product=7846+TR , but they will only accept international orders of $100 minimum!
I just want to know what I would need to buy if I bought this kit.

Thanks,
Matt

[Al_The_Man]

Originally Posted by Emcore I just want to know what I would need to buy if I bought this kit. Thanks, Matt

I don't think it is a kit, rather just the transformer.
12-0-12 means that it can be used as 12v centre tapped source or use the 12-12 ends and ignore the 0 centre tap for 24vac supply.
As well as the transformer the basics you will need is a bridge rectifier 25a 100v would be fine ( it is no cheaper to size it precisely) and electrolytic capacitors.
If you do a search here for power supply design there already has been raft of information discussed.
Al.

[HobbyCNC]

Originally Posted by Emcore Hi all, I know nothing about transformers - except they are in pretty much everything, and I know very little about choosing the right one. I am trying to find a UK or Ireland source for 240VAC Input 24VAC Output 10A Transformer as required for the hobbycnc 4 axis package kit. Maybe I have got this wrong also. Everything I look up seems to reference the input voltage 240VAC, then they vary with things like 12-0-12 or 24VAC, and then, to make matters more confusing they start using VA (volt-amps). Of course I can find what I assume is the correct spec in the US on http://www.mpja.com/productview.asp?product=7846+TR , but they will only accept international orders of $100 minimum! I just want to know what I would need to buy if I bought this kit. Thanks, Matt

Below is right from our support group:

"I've just looked up the details on the RS site.. The transformer
stock code is 223-8257 and the price is £27.20 ex VAT..hope this helps"

Dave Rigotti
HobbyCNC.com

[Emcore]

Perhaps you could advise me on how this is calculated.
VA is the input Volt Amps.
So to work out how much you can draw off this?
I assume it is 500 VA (input volt amps) / 25V (output voltage) = 20Amps.
Because you have 2 outputs that can share the 20 Amps, if you only used one output, it would give you 10 Amps.
If so, and I used both outputs, could I potentially have access to 20 Amps.
If it only draws 10 Amps, then it could have a benefit of only drawing 5amps per output, and thus reducing the heat?
Perhaps it doesnt work like that - is this logic flawed?

For those of you referring to this at a later date, the specs are as follows:

RS Stock no. 223-8257
RoHS Status
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Manufacturer Nuvotem
Manufact. part no. 0500P1-2-025
Name Transformer,toroidal,500VA,0-230V pri,50/60Hz,2x0-25V sec
Catalogue page 2-177

Attributes
Category Chassis Mounting Transformers
VA Rating 500Va
Input Voltage 230V(ac)
Output Voltage 2 x 0 - 25V(ac)
Output Current 10A
Dimensions (L x W x H) 60 (H) x 136 (Dia) mm
Regulation (Typ.) 6%
Temperature Rise 68°C
Weight 3.5kg

[daedalus]

You are probably aware of this, but just to make clear, the transformers are rated in AC volts, which is not the same as the final dc voltage you get out of the powersupply after you rectify and smooth this AC voltage. If you want 25VDC out then you dont want to be buying a 25VAC transformer. If your unsure about any of this i suggest you do a good search of the forums before buying anything, as this has been covered many times.

[Al_The_Man]

VA is the 'apparent' power or wattage rating of a transformer, and is considered the maximum rating.
Because the current and voltage do not neccessarily peak coincidentally, you cannot calculate this as actual wattage as normally done for a resistive load as in W=VA. There is something called power factor involved.
For all practical purposes, most use this as a guide as to the max. supply current they can draw, if you use this reasoning then a 500va Tfmr would allow the 25v winding to draw 20amps.
If a toroid states two 24v windings, they are often wound together, and can be connected in parallel in order to power the load up to the max VA (2x10a).
If you visit sites like Plitron Toroid, there is technical information that may be of interest.
Al.

[Emcore]

Thanks to all who replied - you guys certainly know your stuff.
I really appreciate your help.

Thanks again,
Matt

[diarmaid]

Hi Emcore.
I need to get a suitable transformer in Ireland. Do you mind me asking where did you find to get a transformer in the end and what one?
Thanks.

[Davidh]

@dairmaid

http://www.radionics.ie


...which is RS except it is for the Irish market, they have a trade counter in Dublin

[sanjiv]

Being a Mechanical Engineer, it is very hard to understand the designing of electronics/electrical. But fortunately i came to understand about designing a transformer. i saw many friends searching for specific voltage transformer on cnc zone.
so for building a transformer, first survey the core. it may be I section, E section or toroidal.
If u found some in junk, pl. strip it.
Let us assume u found E section core
step:
1. the basic formula for calculating " Number of turns per Volt per square inch" is 7 ( it is universal after studying numerous books having very complex designing & calculations)
now assuming u want to make a transformer rating 240 V to 24V. u found core having X sectional area of 3 sq. inch.
Hence for primary winding:
7divide by 3 multiply by 240= 560 turns
Secondary winding
7 divide by 3 multiply by 24= 56 turns.
it is so simple & used.
For gauge of wire for desired current, pl refer to supplier of winding wire.
Sanjiv

[diarmaid]

Wow! Thanks sanjiv.