Excuse me if this is a dumb question, if i have a 320v center tapped secondary winding, i.e. 160v-0-160v is there any reason why i cant use half of it as a 160v winding and ignore the other side? Basically is there any downside, or side effect to having half the secondary floating?
I wanted a transformer with a 150 or 160v secondary, and a 6.3v ~4amp winding which is proving hard to find. I then found a bunch of 300v center tapped transformers like the Edcors which gave me the idea of using half the winding.
If you can get full power from half a winding then its ok to do that.
If not then look up "full wave rectifier" where you can use both halves.
If not then look up "full wave rectifier" where you can use both halves.
Aha, a full wave center tapped rectifier looks perfect, right voltage, and all the amperage. Thanks again!
The full wave only uses 2 diodes, whereas if you used one winding you would need 4 diodes to form a bridge rectifier.
This saves 2 diodes but will not give any more available power vs. using a single winding with a bridge rectifier. You will only get roughly half the power rating on the transformer. Since you are only using one winding per half cycle you are still limited to the current rating of a single winding.
Depending on how the transformer secondary is rated, you can typically use half the winding for 71% of the rms current that normally would be the full winding rating. If you can see the winding structure, then choosing the winding closest to the outer surface is probably a better choice.
Now i'm getting a little confused. This is the transformer i was looking at https://www.edcorusa.com/xpwr196 , if i use it with a full wave center tap rectifier to get 150v out what current load will it support?
Power transformer for a 120V, 60Hz. or 240V, 50/60Hz. line to 300V (150-0-150) at 120mA center tapped, 6.3V at 4A and 5V at 2A.
answer:
120mA at 212volts DC.
answer:
120mA at 212volts DC.
This is the sad thing about manufacturers giving feeble specs - perhaps edcor have an app note on their current ratings - because it will be different for choke versus cap input filtering, and for rectifier configuration - and the current may be winding rms, or DC load current.
The total secondary loading is 71.2VA
The 150-0-150Vac winding has a 36VA capability.
The MAXIMUM continuous AC current into a resistive load is 120mAac.
Once you connect a rectifier, the allowable continuous maximum current changes, a lot !!!!!
Look up the manufacturer's datasheet for determining the output with different styles of rectifier and smoothing.
The 150-0-150Vac winding has a 36VA capability.
The MAXIMUM continuous AC current into a resistive load is 120mAac.
Once you connect a rectifier, the allowable continuous maximum current changes, a lot !!!!!
Look up the manufacturer's datasheet for determining the output with different styles of rectifier and smoothing.
The manufacturers datasheet, and website don't seem to mention the subject.
If you could shed some light on how to calculate a transformer current requirement from a known DC current load it would be greatly appreciated as i cant seem to find a straight answer. Assume i will be using a center taped full wave rectifier with a CRCRC power supply behind it.
Or to put it another way, if i design an amp that creates a load of 100ma @200v, how do i calculate the size of transformer i will need? i know half the answer is 150v.
Does the Full Wave Center Tap math on this page looks correct? PowerVolt Application Notes
Assuming so for a 100ma load it implys i would need a 120ma rms rated secondary (1.2 x .100 = .120ma RMS)
Assuming so for a 100ma load it implys i would need a 120ma rms rated secondary (1.2 x .100 = .120ma RMS)
It depends very much on whether the duty cycle is 100% (i.e. continuous DC current load), or medium duty, say 30% to 60% of maximum continuous DC current),
or low duty cycle say << 30% of maximum duty cycle.
Take the last figure in the table:
full wave centre tapped (bridge rectifier) feeding a capacitor input filter.
They state 1.6 to 1.8times the DC load current.
I use 2times for the maximum continuous DC current.
I recommend that for cool running you use around 50% for continuous DC current.
There is no doubt in my mind, that using the figures from the table will result in VERY hot transformers, if you use 100% duty cycle.
or low duty cycle say << 30% of maximum duty cycle.
Take the last figure in the table:
full wave centre tapped (bridge rectifier) feeding a capacitor input filter.
They state 1.6 to 1.8times the DC load current.
I use 2times for the maximum continuous DC current.
I recommend that for cool running you use around 50% for continuous DC current.
There is no doubt in my mind, that using the figures from the table will result in VERY hot transformers, if you use 100% duty cycle.
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