Modern phone chargers (and most low voltage power packs these days) no longer use a transformer. Instead, they use circuits containing zener diodes, a curious electronic component which allows the designer to take just a slice of the input AC sine wave and output it as a low voltage for USB, etc.bgd wrote:So these are used to step down from say 240 to 120.
What about phone chargers? Are they step down transformers with an inverter? Given the number of stories about phone and charger fires, are we looking at auto transformers as being the likely cause?
I see the problem with the design. Can good quality materials get around the inherent problems, or would the cost increase negate the advantage (cost) of an auto transformer?
And thanks for the very clear explanation.
I learn something new everyday. Thank you. DC to DC converters (variations of the buck circuit) are used for high efficiency voltage changes (high to low).PNGMK wrote:Actually they are switched PSUs I think. Extremely high frequency down verters. AC rectified to DC and then switched into a extremely high frequency wave form and transformed down to a voltage and then rectified again. The extremely high switching frequency allows for a tiny transformer and full isolation.
I have CHS syndrome myself... but I do like a sound system that puts out the bass. 44 Hz is the lowest note on a bass guitar. I've got a woofer that will make 32 Hz at 3 dB rolloff... amazing how much more expensive things get to get down even a few more Hz.PNGMK wrote:I've never been much of an amp / audiophile guy. Bad hearing etc...
What are you trying to do here? These are isolation for safety (but do not transform the voltage up or down). You use these on wet or dangerous sites where there is a risk of electrocution.x9200 wrote:I am thinking of buying an isolation transformer but looking for a cheaper alternatives to what PNGMK recommended earlier.
I found this one which seems the right thing (except for no stock and I see no drawing) but would appreciate your opinion:
https://sg.rs-online.com/web/p/safety-s ... s/1237376/
And then, there is this one (a few of this type):
https://docs-apac.rs-online.com/webdocs ... 51be93.pdf
even cheaper, but I sort of don't follow the idea of having the output winding split and grounded in the middle. What is this 55V about? Safety related to limit max voltage to 55?
And another one:
https://sg.rs-online.com/web/product/sa ... s/2604272/
Why do you say they don't transform down if the spec says they all do? Did you read the linked information and looked at the diagram in the brochure?PNGMK wrote:What are you trying to do here? These are isolation for safety (but do not transform the voltage up or down). You use these on wet or dangerous sites where there is a risk of electrocution.x9200 wrote:I am thinking of buying an isolation transformer but looking for a cheaper alternatives to what PNGMK recommended earlier.
I found this one which seems the right thing (except for no stock and I see no drawing) but would appreciate your opinion:
https://sg.rs-online.com/web/p/safety-s ... s/1237376/
And then, there is this one (a few of this type):
https://docs-apac.rs-online.com/webdocs ... 51be93.pdf
even cheaper, but I sort of don't follow the idea of having the output winding split and grounded in the middle. What is this 55V about? Safety related to limit max voltage to 55?
And another one:
https://sg.rs-online.com/web/product/sa ... s/2604272/
Any or all of those transformers appear to be center tap to earth. No issue there. That is a design which enables the secondary winding to be grounded because the exact middle of the coil is 0 volts, relative to the ends. You get 110 volts across the ends because when one side is +55 volts, the other side is -55 volts.x9200 wrote:I am thinking of buying an isolation transformer but looking for a cheaper alternatives to what PNGMK recommended earlier.
I found this one which seems the right thing (except for no stock and I see no drawing) but would appreciate your opinion:
https://sg.rs-online.com/web/p/safety-s ... s/1237376/
And then, there is this one (a few of this type):
https://docs-apac.rs-online.com/webdocs ... 51be93.pdf
even cheaper, but I sort of don't follow the idea of having the output winding split and grounded in the middle. What is this 55V about? Safety related to limit max voltage to 55?
And another one:
https://sg.rs-online.com/web/product/sa ... s/2604272/
I missed the step down part (it's at the bottom). Apologies.x9200 wrote:Why do you say they don't transform down if the spec says they all do? Did you read the linked information and looked at the diagram in the brochure?PNGMK wrote:What are you trying to do here? These are isolation for safety (but do not transform the voltage up or down). You use these on wet or dangerous sites where there is a risk of electrocution.x9200 wrote:I am thinking of buying an isolation transformer but looking for a cheaper alternatives to what PNGMK recommended earlier.
I found this one which seems the right thing (except for no stock and I see no drawing) but would appreciate your opinion:
https://sg.rs-online.com/web/p/safety-s ... s/1237376/
And then, there is this one (a few of this type):
https://docs-apac.rs-online.com/webdocs ... 51be93.pdf
even cheaper, but I sort of don't follow the idea of having the output winding split and grounded in the middle. What is this 55V about? Safety related to limit max voltage to 55?
And another one:
https://sg.rs-online.com/web/product/sa ... s/2604272/
No idea. Maybe a more popular model and made in volume hence cheaper? There's no apparent difference in the specs (apart from load rating) or safety standards it meets.x9200 wrote:Thanks SE.
~120W self-freezing ice cream making machine. It's TEC (Peltier) based so no compressor/electric motor except perhaps a cooling fan to remove the heat.
Nb. I don't understand why this one:
https://sg.rs-online.com/web/p/safety-s ... s/1226711/
is so cheap. It's rated 2k2W and it is cheaper than the 750W one:
https://sg.rs-online.com/web/p/safety-s ... s/1237376/
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