We have a SDK 10K14 varistor between the 12V battery connector and ground.
After the fuse a 1N4004 diode, then a 7805 Regulator with 2
electrolytic capacitors 100 uF on the input and 10uF on the output pins.
We have a ceramic capacitor between Vss and Vdd pins underneath the PIC socket.
The measured Vdd is 6V95 !
The REGULATOR and the PIC do not like it !
The measured voltage on the car battery (with no load) is 16V90 almost 17V for a 12V car battery ?
How can we solve this issue ?
Thank you for your help
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Hi,
Is your voltmeter well calibrated ?
A new battery has a voltage of MAX 2,65V for each element
With a 12V you may have 15,9V instead of 16,9V as you find.
Try with another voltmeter . Or if it's not that reason I think your 7805 is HS !
Regards
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You are right vith 2 other voltmeter I have 12,15 and 12,16 V.
Then the 7805 is not good, this is the third time I put a new one !
I don't understand why it is dead with no PIC on the socket ?
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Car batteries charge to more than 12V (almost 14V), and when the car is running the charge voltage can get way up to maybe 18 V (if the battery is low).
When I run a PIC off a car battery I normally use a zenner to do the dropping especially if the current draw of the PIC is low. Standard regulators will draw about 10mA which can be unacceptable for battery operation.
What exactly is the SDK10K14 supposed to do?
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Some suggestions :
1) Put a 100nf at the 7805 input yo avoid oscillations
2) Your 7805 output must never be "open" if you want to have a correct regulation . You can put a Led with a 470 ohms resistor for instance
3) I often use another regulator before too high voltage to reduce dissipation on 7805 ( ie : 7809 which is a medium -size voltage ) .
4) I have sometimes invert inadvertantly input and output of regulator , causing its destruction ! Often with LM317 or 7905 because they have no same pins ! lol
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you will see the 100nF at the 7805 input pin, and a 10uF at the output pin. Also a 100nF on the PIC socket. The varistor SDK 10K14 is supposed to avoid peaks above 14V from the car battery
Studying the Data sheet this is what I understood so far.
The car battery regulator is supposed to keep charge voltage below 14V, I did not measure this.
I read the 7805 is supposed to accept up to 18V.
I do not see any need for cascading with a 7809 regulator.
I do not understand why , where and which Zener could help in my power design ?
At the moment everything work fine with this power design. My problem was weak batteries on my 2 digital Voltmeters, put new 9V batteries and made a calibration with the scope.
I do not think the 7805 output can be seen as open with the PIC on the board and other items like the Hall Sensor TLE4905 but I did not take any measure for that point.
.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
The power design looks basic but do not work:
http://capaction.free.fr/PowerSupply.jpg
We have a SDK 10K14 varistor between the 12V battery connector and ground.
After the fuse a 1N4004 diode, then a 7805 Regulator with 2
electrolytic capacitors 100 uF on the input and 10uF on the output pins.
We have a ceramic capacitor between Vss and Vdd pins underneath the PIC socket.
The measured Vdd is 6V95 !
The REGULATOR and the PIC do not like it !
The measured voltage on the car battery (with no load) is 16V90 almost 17V for a 12V car battery ?
How can we solve this issue ?
Thank you for your help
Hi,
Is your voltmeter well calibrated ?
A new battery has a voltage of MAX 2,65V for each element
With a 12V you may have 15,9V instead of 16,9V as you find.
Try with another voltmeter . Or if it's not that reason I think your 7805 is HS !
Regards
You are right vith 2 other voltmeter I have 12,15 and 12,16 V.
Then the 7805 is not good, this is the third time I put a new one !
I don't understand why it is dead with no PIC on the socket ?
Car batteries charge to more than 12V (almost 14V), and when the car is running the charge voltage can get way up to maybe 18 V (if the battery is low).
When I run a PIC off a car battery I normally use a zenner to do the dropping especially if the current draw of the PIC is low. Standard regulators will draw about 10mA which can be unacceptable for battery operation.
What exactly is the SDK10K14 supposed to do?
Vdd and Vss is taken across the electrolitic 'C3' , 10k resistor is a bleeder one and their open side must be conected to grownd. PCS.
Some suggestions :
1) Put a 100nf at the 7805 input yo avoid oscillations
2) Your 7805 output must never be "open" if you want to have a correct regulation . You can put a Led with a 470 ohms resistor for instance
3) I often use another regulator before too high voltage to reduce dissipation on 7805 ( ie : 7809 which is a medium -size voltage ) .
4) I have sometimes invert inadvertantly input and output of regulator , causing its destruction ! Often with LM317 or 7905 because they have no same pins ! lol
Thank you for all your suggestions on the design I made:
http://capaction.free.fr/PowerSupply.jpg
you will see the 100nF at the 7805 input pin, and a 10uF at the output pin. Also a 100nF on the PIC socket.
The varistor SDK 10K14 is supposed to avoid peaks above 14V from the car battery
Studying the Data sheet this is what I understood so far.
The car battery regulator is supposed to keep charge voltage below 14V, I did not measure this.
I read the 7805 is supposed to accept up to 18V.
I do not see any need for cascading with a 7809 regulator.
I do not understand why , where and which Zener could help in my power design ?
At the moment everything work fine with this power design. My problem was weak batteries on my 2 digital Voltmeters, put new 9V batteries and made a calibration with the scope.
I do not think the 7805 output can be seen as open with the PIC on the board and other items like the Hall Sensor TLE4905 but I did not take any measure for that point.
.