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What are your opinions about this circuit and how to fix voltage

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anas az

New Member
How can i fix the voltage at 220V , when I connect the voltmetre with no load it shows 220V but when I add a lamp it drops to 87V
What can I do to improve the circuit and what are your opinions about it
Help please !
 

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unclejed613

Well-Known Member
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EDIT: on second thought (i'll leave my original reply below, so you can read it and use the information in it after you fix the big problem) i noticed while looking at the schematics a second time: you have 12V lamps on the secondary. these will have a very low resistance compared to a 220V lamp. the very low resistance could be what's loading the secondary down to 60-80V.
solution #1, change lamps to 220V

if the problem persists after that, read my original response below:


first, measure the 12V at the center tap of the transformer when you have a lamp on the secondary. if the 12V supply voltage drops when you connect the lamp, you need a beefier 12V power supply.
if the 12V stays the same (or drops less than 10%) put a second set of FETs in parallel with the ones already there, and use a higher wattage transformer. you don't need source resistors like you do with bipolar transistors, because FETs don't do the "current hog" thing like BJTs do.
 
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ronsimpson

Well-Known Member
Most Helpful Member
What is the light bulbs? (voltage, current, watts .... any data)
What information do you have on the transformer? Winding resistance?
 

anas az

New Member
EDIT: on second thought (i'll leave my original reply below, so you can read it and use the information in it after you fix the big problem) i noticed while looking at the schematics a second time: you have 12V lamps on the secondary. these will have a very low resistance compared to a 220V lamp. the very low resistance could be what's loading the secondary down to 60-80V.
solution #1, change lamps to 220V

if the problem persists after that, read my original response below:


first, measure the 12V at the center tap of the transformer when you have a lamp on the secondary. if the 12V supply voltage drops when you connect the lamp, you need a beefier 12V power supply.
if the 12V stays the same (or drops less than 10%) put a second set of FETs in parallel with the ones already there, and use a higher wattage transformer. you don't need source resistors like you do with bipolar transistors, because FETs don't do the "current hog" thing like BJTs do.



Hi !
I changed the lamp to 220V but the problem still persists , the 12V supply voltage indeed drops when I add a lamp ( to 4.5V) I put a second set of FETs in parallel and the current and voltage increases but when I add a lamp the voltage drops again ( but to a higher value this time ) I can only change the value of voltage in the DC source in the software .
another thing is that when I increase the lamp internal resistance the voltage increases but the current decreases.
thank you for your help
 

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anas az

New Member
What is the light bulbs? (voltage, current, watts .... any data)
What information do you have on the transformer? Winding resistance?
Hi !
the light bulb has 220V as nominal voltage and 24ohms as internal resistance that's what I can view and change
for the transformer please see the picture below
thanks for your help
 

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ronsimpson

Well-Known Member
Most Helpful Member
It looks like the transformer has a 1:18 turn ratio.
On the secondary you have 6 amps so the primary current might be 110 amps.
Back when you had two MOSFETS; The on resistance is about 0.07 ohms. (depends on who makes the part) Some parts are 0.05 ohms.
110 amps and 0.07 ohms = 7 volts drop across the MOSFET. About 1/2 of your power is lost in the MOSFETs.
With four MOSFETs then the voltage loss due to the transistors is 3.5 to 2.5 volts. (more or less)
With no load you have 12V across the primary of the transformer. At load you only have 10 to 9 volts on the primary. That gets us close to the 147 volts you see.
upload_2018-2-24_17-37-21.jpeg
 
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