Stepdown transformer 230v prim 220v sek. where to get?

[Setze]

Hi there,

I was searching the net for a step down transformer 230v to 220v since I dont want to damage my v76. Seems to be hard to buy one in a regular store. Where do I find parts like this in Switzerland or Germany? My local dealer does not offer it.

Best Regards
Setze

[nosebleedaudio]

Thats only 5%, I would not worry about it, normal AC power varies that much...

[Matt Syson]

Hi
The cheapest way is to use a 'standard' transformer as an 'autotransformer'. (See Google).
In this you would use a 230 to 12 Volt transformer (very standard stock value) and wire the secondary in SERIES with the incoming mains. Primary is connected to the mains normally.
In this way you get either 230 Volts PLUS 12 Volts (242V) or 230 Volts MINUS 12 Volts (218 Volts.
The transformer is only supplying a small amount of POWER for this operation so for a couple of V modules a 1 Amp transformer (12VA) would be plenty.
You would mount this in a little box with a socket on top to connect the V module to.
Matt S

[Setze]

Yes, you are right but since it is mentioned in so many other threads, I thought I'd take kare of that anyway. And as it easy to do, why not do it.
Besides I am looking for other parts in good quality for other projects. A link to a store with a good assortment would be helpful.

[Setze]

Ah, thx Matt, good Idea!

[Matt Syson]

Hi
I feel Switzerland is a bit thin on the ground for electronics parts. However Farnell have offices somewhere (not the large warehouses as in UK) and there is Conrad in Germany. RS components also have some presence, again probably a small office.
Matt S

[Setze]

Thanks a lot for your useful tips! thumbsup

[Setze]

I've built the power supply Matt supposed and it works just perfect. thumbsup

[drtechno]

put a 1.6 ohm ,20-25 watt resistor in series with the primary and that should work.

or
if you have to do that to multiple pres,
stick a 300w one to your cage (if you have one) in series to the mains power.

[Matt Syson]

Hi
The disadvantage of a resistor is that you have to calculate it correctly but certainly for a multiple rack it would need to vary with the number of modules connected. With a transformer it is rather more predictable.
I can't remember the actual current consumption for one of these units but even if it consumes 25 watts (very unlikely) you would need a dropper resistor of about 85 Ohms. I would expect it to actually draw about 7 or 8 watts so a resistor of about 250 Ohms would be needed.
Matt S

[drtechno]

according to the docs I have they draw 16w typically.

the power requirements is 220V +5%/-15% if you stay in the margin its ok.

card cages was buit on 20 W max current per module opening.

the reason for the 20-25 watt resistor is you want dissapation overhead even though with the fuse rating of 17.6 watts ( 80 ma fuse )

I oops it on the calculation. 138.8 ohms is what it should be. 140-150 ohm resistor should work with the 72 mA current draw.

[Geoff_T]

Originally Posted by drtechno

according to the docs I have they draw 16w typically.

the power requirements is 220V +5%/-15% if you stay in the margin its ok.

card cages was buit on 20 W max current per module opening.

the reason for the 20-25 watt resistor is you want dissapation overhead even though with the fuse rating of 17.6 watts ( 80 ma fuse )

I oops it on the calculation. 138.8 ohms is what it should be. 140-150 ohm resistor should work with the 72 mA current draw.

Hi

The resistor may work, given a constant load, but it has to be well protected from prying fingers and mounted rigidly so that it doesn't move around and rest on power wiring.... even 7 or 8 watts gets blooming hot.

I go along with the view as to not bother... use the 230v.