2:1 step down transformer for 240V to 120V

[quadwould]

I am modding a powerconditioner (actually many but all the same unit) and i need a stepdown transformer to step the newer 240V to a 120V to feed to the voltage meter in the unit.

As this will only be used got the meter, not much current will go through it. ther rest of the unit will be in 240V... the meter with be reagin on a 120V scale.. but will reflect the real voltage.. i will just doubple what the front panel graphics say.. (so 90= 180, and 120=240,and 130=260 etc etc)

is there a small ( in size) transformer out there that i can fit in a 1U rack that can handle 240V-to->120V stepdown??.... i have had a really hard time so far trying to find one... the all are way too large in size.

 

[PRR]

Why not one or two resistors? What kind of meter is this?

 

[quadwould]

the unit is a Furman PL PLUS and i want to Mod it to their PL PLUS E version which is their EU/UK version.

the meter is an LED array ranging from 90 to 130V in 20 steps (with 20 LEDS)

i can send ypou the PDFs of the schemats and PCB layout. it is a Rev F that i have...

the odd thing is that there are 2 E vesions one with and one without the Transformer. the one without is a little harder to understand how to mod, the one with is very simple to mod... the transformer , cut 2 traces, and ditch one diode. rather simple. (maybe a resistor value change as well...)

But the thing that makes me think is this:

if i step the voltage down to 120V range with an xfmr.. why would have to change anything else....? would it not just work the same, and represent a voltage that is double that is silkscreened on the front panel???


thanks for helping :guinness:

 

[sismofyt]

they're probably made in asia, they do revisions like mad. if it's similar to the Gemini knock offs, i seem to remember the LED being capacitor coupled to the grid? a simple 2:1 transformer will do the trick, but low power types aren't common so you'll probably have to get a custom job done. i'd like to see the schematic

 

[APEX JR.]

How many VA- Watt stepdown transformer are you looking for.
I have stock on some, problem is the 1U restriction.
Topaz makes a ultra isolation transformer or power conditioner
with dual inputs, wouldn't that be a better bet?
Steve @ Apex Jr

 

[PRR]

Digi-Key Part Number MT2113-ND or any small dual-primary power transformer. 2113 is under 1.5" tall.

Ignore the secondary, wire the primary for 230V, take "115V" from one of the two windings.

This assumes the load is less than a watt or so. It isn't just the voltmeter input, there seems to be a chip and multiple LEDs to power.

 

[quadwould]

PRR
indeed you are right. there is a chip some caps some resistors some diodes.. and dthe LEDs...

Good thinking outside the box.. i could wire a transformer and jjst used the primaries... but why the 1 watt limit...?

i can email you the schematics for both units.

email me at [email protected] for the pdfs



APEX..
this is the thing.. i am not sure how many VAs i need... i can send the PDFs..... i talked to the engineers at Furman.. and they were not too helpful either... you would think they would know their own products... seemed like i knew more about the units

Also , yes i am restricted to the 1U rack that these are in.


also i do not want to have to sell these and buy others.... that will be much more expensive and i really dont have the energy to sell these all individually....

 

[quadwould]

So i found out the specs of the transformer froom Furman.. Finally..

120/240V stepdown 100ma so its really small.....

made by CUI INC..

dunno who they are....


also trying to track down the varistors... made by Uppermost...

 

[PRR]

> 120/240V stepdown 100ma so its really small.....

120V*100mA is 12VA, not all that small, you can get smaller.

> why the 1 watt limit...?

The core I pointed to was, I think, 1.2VA. As a 2:1 autotransformer, only half the power flows in the core, so it might be good for a couple watts. Heat could be an issue because we are only using half the copper on the core, so I hate to push it. Still, a few-VA core usually won't overheat, especially screwed to metal.

But if the LED board has ten LEDs each fed 10mA, that's 100mA so we could need the full 12VA of the original.

Does the LED board get hot? (Don't get killed checking!)

> made by CUI INC.. dunno who they are....

http://www.cui.com/ , the brand is available at DigiKey but not their transformers.

With the plugs, varistors, and strict UK electrical regs, I'd be inclined to just get UK-market power strips.

 

[quadwould]

[quote author="PRR"]> 120/240V stepdown 100ma so its really small.....

120V*100mA is 12VA, not all that small, you can get smaller.

> why the 1 watt limit...?

The core I pointed to was, I think, 1.2VA. As a 2:1 autotransformer, only half the power flows in the core, so it might be good for a couple watts. Heat could be an issue because we are only using half the copper on the core, so I hate to push it. Still, a few-VA core usually won't overheat, especially screwed to metal.

But if the LED board has ten LEDs each fed 10mA, that's 100mA so we could need the full 12VA of the original.

Does the LED board get hot? (Don't get killed checking!)

> made by CUI INC.. dunno who they are....

http://www.cui.com/ , the brand is available at DigiKey but not their transformers.

With the plugs, varistors, and strict UK electrical regs, I'd be inclined to just get UK-market power strips.[/quote]


there are 20 leds....

Just rang CUI.... the part is a 120/240 110ma 10VAC

I dont bloody get it!!! if the PCB is getting 120V in the US version, why the hell give it 10V for the EU version....????

the only things that are different are R1 is 6.98K fo rthe EU version instead of 91K, thre is a jumper added at R8, 2 traces cut, C6 and R9 and D5 are not used....

looking at the various schematics i have.. only makes it more confusing......

 

[sismofyt]

according to the two block diagrams, both versions use a stepdown transformer? i find them confusing (the PDFs)

 

[quadwould]

you are right.. theey are rather Crap..... they include the transforemer there becuase it is supposed to be there for some, but not for others... and i suppose it saves space (in pages)...

i am looking to make my units into the "Euro 230V Unit" versions from the current "US 120V Unit" version of the PL Plus. i will do it either with or without transforemer.. i just want to do it right.......

you may notiece an old schematic on page 11 in the PLPlus.pdf file from i think 1988... it seems very straight forward for the EU version.. just add (2) 1.2K 3Watt resistors in parallel .. one on the Hot (live) and one on the Cold (neutral) for
maybe i will do that...


anyone else out there that i cam email these PDFs to to get a second opinion???? PM me with email address, or email me using the email button

i just want these to work without electrocuiting me or causing fire... and it seems like a very sinple Modification... just nead to make sure its safe and correct.

cheers
-david

 

[sismofyt]

**** that ****. use a small 2:1 transformer or do the PRR trick. a transformer certainly is the 'right way' to do it and the safest. i fixed plenty of those Gemini PL100s ( a total Furman knock off) because the LED board went up in smoke. it was connected directly to the grid through a capacitor and resistor. they too had multiple versions of the schematic allthough none had a trannie as fas as i can remember. it's probably, for both the Furman and Gemini, because of different electrical codes in various parts of the wolrd

i know i would sleep a LOT better if it was transformercoupled. and transformers are cool. the LEDs may light up in a more analog and phat way with a trannie