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PSU with variable AC input; overvoltage protection.

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Diy1995

Member
Hello, I am building Arduino Uno based voltage regulator for my homemade generator.
As a part of this project I must build power supply for Arduino and overvoltage protection for Arduinos analog input.

1.)Power supply:
How can I make Power supply that can take up to 500VAC and put out from 7v to 12v (1A would be good).
Im planing on using 220VAC to 8VAC transformer> bridge rectifier> 8v voltage regulator... Would this be OK?

2.)Overvoltage protection for analog input pins on Arduino:
What component can I use to cut off voltage if its get over 5v? And it must not affect voltage lower than 5v? (Arduino can accept voltage from 0v to 5v to analog input, i will use transfromer and rectifier to drop down 0-500VAC to 0-5VDC, but on error voltage could get higher than 500VAC and i dont want to damage Arduino).

Thank you for your anwsers!
 

awesomelumens

New Member
If it is giving 8V on 220V input. Then increasing volts at primary to 500V will give 18V at secondary. It can be handled by Lm78xx.
Precise zeners 5.1-5.3 volts of high wattage accompanied by a 1 amp fuse.
 

Les Jones

Well-Known Member
Most Helpful Member
You can't more than double the voltage on a transformer winding as the core will saturate which will cause the winding to draw a large current and burn out. (This is assuming that the frequency of the AC is not changed.) What I would suggest is to obtain two IDENTICAL transformers with 250 volt primaries and 8 volt secondaries. Connect the primaries in series and the secondaries in parallel. You must ensure that the phasing of the windings is correct.

Les.
 

spec

Well-Known Member
Most Helpful Member
Once you have done as Les suggests in post #3 above, rectify the 8V RMS from the composite winding with a bridge rectifier and reservoir capacitor which will give you 9.3V off load. Then use a switch-mode power supply to give a stabilized 8V supply, or within reason, any other voltage you require: http://www.ebay.com/sch/i.html?_fro...oost+.TRS0&_nkw=buck+boost+converter&_sacat=0

15V windings, to give you a 19V rectified voltage off load, may be a better option, as this will allow for a greater variation of your mains supply voltage.

You could even set the switch-mode power supply to your final target voltage, presumably 5V, to improve performance and make the system more efficient.

Another approach would be to connect two 240V to 120V transformers together with the primaries in series and secondaries in series. Then simply use an 85V to 264V AC input, off-line switch-mode power supply to generate your final target voltage, presumably 5V: http://www.ebay.co.uk/itm/5-volt-DC-power-supply-enclosed-switch-mode-5V-5-0A-25W-/221523877656

spec
 
Last edited:

Diy1995

Member
You can't more than double the voltage on a transformer winding as the core will saturate which will cause the winding to draw a large current and burn out. (This is assuming that the frequency of the AC is not changed.) What I would suggest is to obtain two IDENTICAL transformers with 250 volt primaries and 8 volt secondaries. Connect the primaries in series and the secondaries in parallel. You must ensure that the phasing of the windings is correct.

Les.
I like the idea, but what if I mechanicly limit trottle of engine, so voltage wont rise above 400v, I can use single transformer than, because I wont be even doubling voltage on primary than? Voltage will be close to 250VAC, because voltage will be regulated with help of arduino, but on error can get higher.
 

Diy1995

Member
Once you have done as Les suggests in post #3 above, rectify the 8V RMS from the composite winding with a bridge rectifier and reservoir capacitor which will give you 9.3V off load. Then use a switch-mode power supply to give a stabilized 8V supply, or within reason, any other voltage you require: http://www.ebay.com/sch/i.html?_fro...oost+.TRS0&_nkw=buck+boost+converter&_sacat=0

15V windings, to give you a 19V rectified voltage off load, may be a better option, as this will allow for a greater variation of your mains supply voltage.

You could even set the switch-mode power supply to your final target voltage is, presumably 5V, to improve performance and make the system more efficient.

Another approach would be to connect two 240V to 120V transformers together with the primaries in series and secondaries in series. Then simply use an 85V to 264V AC input, off-line switch-mode power supply to generate your final target voltage, presumably 5V: http://www.ebay.co.uk/itm/5-volt-DC-power-supply-enclosed-switch-mode-5V-5-0A-25W-/221523877656

spec
I like the idea with buck converter and higher voltage transformer, i will stick to it :) thanks!
 

Diy1995

Member
If it is giving 8V on 220V input. Then increasing volts at primary to 500V will give 18V at secondary. It can be handled by Lm78xx.
Precise zeners 5.1-5.3 volts of high wattage accompanied by a 1 amp fuse.
I think I will use switch-mode regulator...
Precise zeners 5.1-5.3 volts of high wattage accompanied by a 1 amp fuse
Is this ment for overvoltage protection for analog input? thanks
 

Les Jones

Well-Known Member
Most Helpful Member
I think a 220 volt transformer will saturate long before 400 volts. Transformers will be made so they do not saturate at their rated voltage plus a reasonable safety margin. Making them with a larger saturation voltage would make them larger, heavier and more expensive.

Les.
 

spec

Well-Known Member
Most Helpful Member
Is this ment for overvoltage protection for analog input? thanks
Primarily, the twin transformer> off-line switch-mode power supply approach is intended for simplicity, reliability, and low cost and good performance. One of the benefits will be will be protection for the power input to the processor.

But the protection of the other inputs/outputs are a separate issue and will require designing.

The inputs to most chips are protected, to a limited extent though.

The protection measures required will greatly depend on what you intend to connect to the inputs/outputs.

spec
 

Diy1995

Member
I did some research and found out that I could use MAX366 for overvoltage protection for analog inputs. However I can't figure out how to set when voltage will cut off. Will voltage cut off when input will be greater than V+?
 

Diy1995

Member
I think a 220 volt transformer will saturate long before 400 volts. Transformers will be made so they do not saturate at their rated voltage plus a reasonable safety margin. Making them with a larger saturation voltage would make them larger, heavier and more expensive.

Les.
I'm sorry, but i don't understand what are you trying to tell me. So I should use two transformers anyway?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I did some research and found out that I could use MAX366 for overvoltage protection for analog inputs.
You're vastly overthinking this, all you need is either:

a) A simple series resistor to limit the current.

b) A potential divider to scale the input, and limit the current should the input still go too high.

These are basic things you do for any analogue input.
 

Diy1995

Member
Primarily, the twin transformer> off-line switch-mode power supply approach is intended for simplicity, reliability, and low cost and good performance. One of the benefits will be will be protection for the power input to the processor.

But the protection of the other inputs/outputs are a separate issue and will require designing.

The inputs to most chips are protected, to a limited extent though.

The protection measures required will greatly depend on what you intend to connect to the inputs/outputs.

spec
I did a research and arduino have no protection on analog input pins. I found out that I could use MAX366 for overvoltage protection.
 

Diy1995

Member
You're vastly overthinking this, all you need is either:

a) A simple series resistor to limit the current.

b) A potential divider to scale the input, and limit the current should the input still go too high.

These are basic things you do for any analogue input.
A b) potential divider would be a diode? Thanks
 

Diy1995

Member
I found this schematic on internet. This would do overvoltage protection?
5v that I marked red... At this voltage diode would cut off? For example if this voltage would be 7v diode would cut off at 7v?
How can I calculate value of r1, r2 and d1? Thanks

 

Nigel Goodwin

Super Moderator
Most Helpful Member
A b) potential divider would be a diode? Thanks
No, a potential divider would be two resistors - R1 and R2 in your diagram of post #15.

Assuming your AVR doesn't have protection diodes built-in? (PIC's do) then you could add two diodes as well, input pin to Vss and input pin to Vdd - same orientation as D1 in said diagram.
 

ronsimpson

Well-Known Member
Most Helpful Member
1) You need two diodes.
upload_2016-12-29_9-52-28.png
2) Read about your Arduino ANALOG inputs and see what the maximum input voltage is. It might be from -0.6 volts to +5.6 or maybe 4.0V. So the bottom diode connects to ground but the top diode connects to +3.3 or +5.0 depending to the answer. (5V in your case)

3) R1/R2 I think you want 0 to 500V to be 0 to 5V.
That is 100:1 divider.
In round numbers: If R1=500k ohms and R2=5k then you would have 101:1. (close)
Common numbers: 470K and 4.7K R1 will need to be 1 watt. Or 1M ohm and 10k 1/2 watt.
Many small resistors are only good for 200 to 300 volts. You can series resistors. example 220k + 220k = 440k that can with stand more voltage and wattage. I would use 1% resistors but you can use more standard 5% if you can live with that.

4) The Arduino is using the power supply as reference. So the 5V of off by 3% all you measurements will also be off a little. If you are using 5% resistors then there is more error. You can measure the voltage with a good meter and then teach your computer about the error. Example: If you really have 220V but because of all the errors the computer reads 230V (about 5% off) then include a "error number" in software. (read the voltage then multiple by 0.95 to get a good measurement)
 

Diy1995

Member
No, a potential divider would be two resistors - R1 and R2 in your diagram of post #15.

Assuming your AVR doesn't have protection diodes built-in? (PIC's do) then you could add two diodes as well, input pin to Vss and input pin to Vdd - same orientation as D1 in said diagram.
I see now, thank you for anwser
 

Diy1995

Member
1) You need two diodes.
View attachment 103310
2) Read about your Arduino ANALOG inputs and see what the maximum input voltage is. It might be from -0.6 volts to +5.6 or maybe 4.0V. So the bottom diode connects to ground but the top diode connects to +3.3 or +5.0 depending to the answer. (5V in your case)

3) R1/R2 I think you want 0 to 500V to be 0 to 5V.
That is 100:1 divider.
In round numbers: If R1=500k ohms and R2=5k then you would have 101:1. (close)
Common numbers: 470K and 4.7K R1 will need to be 1 watt. Or 1M ohm and 10k 1/2 watt.
Many small resistors are only good for 200 to 300 volts. You can series resistors. example 220k + 220k = 440k that can with stand more voltage and wattage. I would use 1% resistors but you can use more standard 5% if you can live with that.

4) The Arduino is using the power supply as reference. So the 5V of off by 3% all you measurements will also be off a little. If you are using 5% resistors then there is more error. You can measure the voltage with a good meter and then teach your computer about the error. Example: If you really have 220V but because of all the errors the computer reads 230V (about 5% off) then include a "error number" in software. (read the voltage then multiple by 0.95 to get a good measurement)
Thank you for explanation, what kind of diodes can I use?
 
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