Not sure of the circuit

Thread Starter

Janchris

Joined May 2, 2024
18
Hi, I have attached a pic of a circuit of a transformerless power supply. I keep damaging components. I am not sure if the resistor path is correct. I would be grateful if someone can check the circuit to see if it's correct. The two lines at the start of the circuit I have built in a fuse.

Thanks
 

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Jerry-Hat-Trick

Joined Aug 31, 2022
588
If I understand correctly what you are trying to do I’d say that it’s incredibly dangerous. It looks as if you are using a mains voltage input, half wave diode rectifier and a 4.7uF capacitor rated at 300V to smooth the voltage which has a peak value of 340V if it’s a 240V line

The pin out of the transistor suggests that you are putting this voltage into the base where you probably intended it to go to the collector. The 100K resistor followed by the 10K potentiometer is probably intended to give you a voltage at the wiper of between 0 and 30V which you meant to put into the transistor base but it’s going into the collector

You need to learn a whole lot more about electronics before you meddle with mains voltage. This is a very dangerous circuit incorrectly assembled, you could kill somebody
 

Thread Starter

Janchris

Joined May 2, 2024
18
Hi Jan,
Which components are failing in your circuit?
E
Hi, I've had a 100V capacitor, Zener diode, 10K Pot, resistor & transistor fail. I am not sure about the connection where the resistor connects to the zener diode, 100v Cap & the 10K Pot. Or if anyone can assist with a better transformerless 220vac to 24Vdc power supply. I've tried to find software where I can test the circuit before building it.
 

Thread Starter

Janchris

Joined May 2, 2024
18
If I understand correctly what you are trying to do I’d say that it’s incredibly dangerous. It looks as if you are using a mains voltage input, half wave diode rectifier and a 4.7uF capacitor rated at 300V to smooth the voltage which has a peak value of 340V if it’s a 240V line

The pin out of the transistor suggests that you are putting this voltage into the base where you probably intended it to go to the collector. The 100K resistor followed by the 10K potentiometer is probably intended to give you a voltage at the wiper of between 0 and 30V which you meant to put into the transistor base but it’s going into the collector

You need to learn a whole lot more about electronics before you meddle with mains voltage. This is a very dangerous circuit incorrectly assembled, you could kill somebody
Hi, Thanks for the heads up, I am not familiar with electronic circuits at all. I have downloaded the diagram from the internet. I am trying to bypass loadshedding and that's why I am converting some of my alarms from 220v to 12volt.
 

boostbuck

Joined Oct 5, 2017
568
Why transformerless? The great advantage of a transformer is the safety of the isolation. Even an off-line SMPS supply will use a transformer. Your 'internet' circuit is too unsafe to use.
 

Thread Starter

Janchris

Joined May 2, 2024
18
Why transformerless? The great advantage of a transformer is the safety of the isolation. Even an off-line SMPS supply will use a transformer. Your 'internet' circuit is too unsafe to use.
Hi, it's all to do what's available and cost. I'm in South Africa.
 

Thread Starter

Janchris

Joined May 2, 2024
18
How much Current do You expect to deliver with this cheezy "Regulator" ?
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Hi, I need 15vdc. I require a couple of them as I am powering a 12volt lead acid battery charger and a pir. So, the battery charger and the pir get's it's own "cheezy" power supply.
 

ericgibbs

Joined Jan 29, 2010
19,091
Hi Jan,
My Son lives in RSA , PE, he has also had to convert his alarms to 12Vdc.
He uses a 12V SLA battery and mains charger.
Don't use that circuit you have posted, it is useless and very dangerous.

Get a 230Vac to 15Vac 50VA mains transformer, the 12V regulators are low cost to buy and should give you a reliable and safe system.

E
 

Thread Starter

Janchris

Joined May 2, 2024
18
Hi Jan,
My Son lives in RSA , PE, he has also had to convert his alarms to 12Vdc.
He uses a 12V SLA battery and mains charger.
Don't use that circuit you have posted, it is useless and very dangerous.

Get a 230Vac to 15Vac 50VA mains transformer, the 12V regulators are low cost to buy and should give you a reliable and safe system.

E
Hi, That appears to be a better and safer option. Thanks for the assistance. Stay well and be safe.
 
Hi, it's all to do what's available and cost. I'm in South Africa.
Have you got any laptop power supplies left over? I never throw them away when the laptop dies and they are typically around 19V outputs at 3 amps. You can then use a LM317 linear voltage regulator (or a power transistor) any a voltage divider circuit to produce and voltage you want from around 17V to zero.
 

Thread Starter

Janchris

Joined May 2, 2024
18
Have you got any laptop power supplies left over? I never throw them away when the laptop dies and they are typically around 19V outputs at 3 amps. You can then use a LM317 linear voltage regulator (or a power transistor) any a voltage divider circuit to produce and voltage you want from around 17V to zero.
Hi, Thanks, I don't have any but I'll remember the option.
 

LesJones

Joined Jan 8, 2017
4,226
Apart from being unsafe that design will consume much more power than the load. For example with the output voltage set to 24 volts it will convert about 9 times the power used by the load into heat. with the output at 12 volts it will convert about 19 times the power used by the load into heat. so with a 12 volt load consuming 5 watts the power taken from the mains supply will be about 100 watts. This will require a very large heatsink on the mosfet. From the mosfet datasheet it's maximum disipation is 75 watts with a case temperature of 25Deg, C The cost of a plug in 12 volt 1 amp switch mode power supply would be paid for by the saving in the cost of the electricuiy wasted by the design that you want to use in a short time. And it would be safe.

Les.
 

Thread Starter

Janchris

Joined May 2, 2024
18
Apart from being unsafe that design will consume much more power than the load. For example with the output voltage set to 24 volts it will convert about 9 times the power used by the load into heat. with the output at 12 volts it will convert about 19 times the power used by the load into heat. so with a 12 volt load consuming 5 watts the power taken from the mains supply will be about 100 watts. This will require a very large heatsink on the mosfet. From the mosfet datasheet it's maximum disipation is 75 watts with a case temperature of 25Deg, C The cost of a plug in 12 volt 1 amp switch mode power supply would be paid for by the saving in the cost of the electricuiy wasted by the design that you want to use in a short time. And it would be safe.

Les.
Thanks Les.
 

MisterBill2

Joined Jan 23, 2018
19,398
Certainly that non-isolated linear (sort of) regulated supply can be a serious hazard if you don't understand that it is directly tied to the mains. It is also a rather poor design, not being able to deliver a useful amount of current at any voltage. That particular design is very poor and with those components none of the voltage ratings are suitable for use with 220 volt mains.

A supply with an isolation transformer that also reduces the voltage is what is required, because the alarm system plus the PIR sensor will need some current. One source of a transformer not mentioned is a doorbell transformer, if those are available in your area, which I see is South Africa.
So I have no idea as to what salvage resources are available. BUT ANY of the older small plug into the wall supplies will have a transformer of some rating.
For a power supply delivering 12 volts at two amps you will need a transformer rated for at least 25 watts.
If you are willing to do some transformer re-winding, a scrapped microwave oven power transformer can be a good start towards a 12 volt power supply able to deliver at least 100 watts. AND there is quite a bit of information available about rewinding those transformers.
 

Thread Starter

Janchris

Joined May 2, 2024
18
Certainly that non-isolated linear (sort of) regulated supply can be a serious hazard if you don't understand that it is directly tied to the mains. It is also a rather poor design, not being able to deliver a useful amount of current at any voltage. That particular design is very poor and with those components none of the voltage ratings are suitable for use with 220 volt mains.

A supply with an isolation transformer that also reduces the voltage is what is required, because the alarm system plus the PIR sensor will need some current. One source of a transformer not mentioned is a doorbell transformer, if those are available in your area, which I see is South Africa.
So I have no idea as to what salvage resources are available. BUT ANY of the older small plug into the wall supplies will have a transformer of some rating.
For a power supply delivering 12 volts at two amps you will need a transformer rated for at least 25 watts.
If you are willing to do some transformer re-winding, a scrapped microwave oven power transformer can be a good start towards a 12 volt power supply able to deliver at least 100 watts. AND there is quite a bit of information available about rewinding those transformers.
Hi Bill, Thank You so much to you and everyone that has assisted in advising me. It is much appreciated. I am taking note of all the advice. Stay well and be safe.
 
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