Use of step down transformer as a step up transformer

[whizz90]

I recently puchased several electrical items (Widescreen TV ETC ) and they are from abroad ( U.K.) they are capable of running on 50/60 Hz supply but require 230-240VAC. Ok thats not the problem i have several transforms capable of suppling correct voltage but i would like to have them all running of a single one but i require about 200-300W allowing for future devices. the largest transormer i have is an EN60-742 0.1kVA 50/60Hz 862 im doubt that this will suffice any suggestions? Size is an important issue as transformer (in its Housing ) is visible....


Any help appreciated..

Martin

 

[Alex68]

I understand that:
1- you have a lot of very little transformers
2- you wish to connect them to obtain an equivalent transformer able to feed a 300W load

Please clarify the meaning of the object:"Use of step down transformer as a step up transformer". What is the relationship with your wishes?

First impression:
a transformer able to feed a 300W load (about 380VA) is a little transformer; if your biggest one is 0.1kVA sized, you need at least 4 transf in parallel. Connecting transformers in parallel is never a simple problem, above all if they are different.

Suggestion: buy a new transformer of 0.4kVA

 

[whizz90]

Thanks ALEX 68


To clarify the object i have found it easier to find step step down transformers 230vac - 110vac . iknow that transformers dont see polarity in the respect of direction of use (ie wether or not it is stepping down or up ) so i intend to use this ability as access to said transformers is easy. my main concern was from overheating from pulling to much current by overstepping the wattage maximum. the tv ai rated @ 93w max the other devices need 50w and 23w respectivly. i have a large margin of error due the desgin of british tv,s can draw more than the 20% tolerance specified as they use cheap imported transformers in some parts of the circuits. in addition i may add another device or two so i wanted some lea-way.


i could just use a feed from the 240vac drier output but i would rather have the portability of being able to move from socket to socket.

 

[Alex68]

Maybe I understood:
you have a TV transformer with one input and some outputs; since the transf. is a reversible machine, you wish to feed a load with different main voltages, connecting it to the input (now output) and a socket to one of the output (now input). And your question is: Is it possible without overheating the transformer?

If the problem is this, I say: perhaps!
Consider the TV transformer with one input and some outputs: the input is sized (electrically and thermally) to supply all the loads connected to all the outputs at the same time; on the other hand, each output is sized (electrically and thermally) to feed its own load.
If you invert the power direction, you must verify the sizing of each couple of winding involved in the circuit.
Be aware of what you do!

 

[busbar]

A step-whatever transformer rating of 0.1kVA may not be adequate/safe for powering a widescreen television; introducing a basic fire hazard. Line current in an SMPS will typically be larger. Seriously consider the task of verifying by measurement load [VA not watts] rating. It is possible the transformer vendor could provide application/sizing assistance.

It is common for small power-frequency stepdown transformers to contain a low-side ‘compensating’ turns to winding so the if served from the low-voltage side, the loaded high-voltage-winding output may be undesirably/damagingly be higher than labeled.

Set aside the dryer-plug thoughts.

Now, as for variations in broadcast formats, I am not qualified to address. It may be wise to ask before incurring needless equipment-shipping expense.

 

[whizz90]

Thanks Busbar




my basic application is to supply 230vac at a maxium of 5 ampres, this is to supplied from 110vac. specifacations of uk electrics require a live a fused nuetral and an earth or second un-fused nuetral. i dont wish to change the internal transformer of the TV but merely supply the correct volatge and current load without incurring any heat issues ( ie fire risk ) i want to do this the safest way possible. hence the reason i opened forum on this subject all information is received with many thanks. please note its not a price issue but a saftey issue. i can do the electronic work but its calculation of current/voltage/wattage seems to me directly relate to heat dissapation.

 

[benray]

1.5 KVA 120/240 single phase transformers are a standard KVA size. The physical size is 10"H, 6"W, 6"D. Weight 40 lbs.
This procedure is common for voltage matching. Safety considerations are; Ambient temperature, duration of load at full demand, Temperature rise is 115ºC, ventilation is necessary. Core temperature can get high.

 

[whizz90]

excellent benray


this answers my questions 1.5kva will suffice and i will incorperate a thermistor controlled cooling fan....



thanks to all who answered any additional data that you think i might need is appricated.....

 

[busbar]

whizz— Pardon me, but my comments may have been a bit tainted by a visit to a big hobby/appliance/electronics store and seeing a shelf full of cheesy 2:1 transformers in various sizes—claimed to be for that purpose. Some had fairly open, barely covered "universal" terminals, little if any identification of ratings or manufacturer, no instructions and most of all, having no user-resettable/replaceable overcurrent protection or no indication of containing any sort of thermal protection. [And oddly, being not too many miles from one of a larger nationally-recognized electrical product-testing facilities.]

Responders here don't know of your experience and qualifications; hence the rather basic comments.

 

[whizz90]

busbar with regards exp & quals



i an IT professional with electronics servicing, analogue and digital circuit design in addition i have also had minimal electrical experiance in LV applications. both electrical installation and repair. minimal meaning 3 years as an subcontractor fitting and rewiring domestic locations.


this should help ....

 

[peebee]

There is a reasonable chance that you'd end up burning down your house and insurance would not cover you due to your off-listing modifications. I'd strongly recommend buying a new transformer or power supply.