Car Battery spikes n noise

12v noise suppressor

hi all...
i want to ask and hope all of you can help me..
how i eliminate the spike and noise from the car battery? or at least minimizing it..
i have small problem on my project device, if i start the engine the device is malfunction..

can anybody have design how to filter spike and noise from car battery?

sorry for my bad english, i hove all you guys understand what i mean..

Thanks and Best regards


Erio

12v noise filter

Try power line noise suppressors like the first one on this page
http://www.electronixwarehouse.com/car/accessories/noise-sup.htm

car noise filter schematic

These filters are generally inductors placed in series with the +12V power line and capacitors connected across the lines. An example circuit can be seen at

**broken link removed**

You can experiment with whatever inductors and capacitors are easily available to you. Make sure that the inductor can handle the current that your project draws. Inductors from the "scrap box" are never marked with a current rating, so it can be hard to judge. Stay away from inductors with very fine wires. Signs that your inductor cannot handle the current is the inductor gets hot or the filter does not seem to work all the time. These are signs that the inductor is saturating. One place to look for inductors is a dead computer power supply.

Also make sure to use capacitors with a minimum 25V rating. A 50V rating would be better.

12v car noise filter

@ Banjo : thanks for the idea..my project draws only 150mA..basically my project is Car Immobilizer.. it implement touch switch to activate the ignition circuit of the car...so if you do not touch the touch sensor, the engine wont start..however, the circuit is so sensitive to engine cranking or spike from car circuitry..when we start the engine, sometimes it false triggered..


sorry for my bad english, i hope all of u guys understand what i mean..

thanks

car line noise

banjo said:

These filters are generally inductors placed in series with the +12V power line and capacitors connected across the lines.

Click to expand...

I have seen most filters contain active circuitry rather than only inductors & capcitors.

simple car noise suppressor circuit

OK, touch switches are very sensitive. This could be radiated noise rather than conducted noise via the power supply. Since your current draw is so low, here is how to troubleshoot. Get a nine volt transistor battery and connect this to power your circuit rather than the car battery. Keep your circuit connected to ground which is the car frame. Just connect the nine volt battery from the +12V input to your circuit and the car's frame. Start the car and see if the same problem exists. If the problem goes away, then the noise is conducted on the +12V input to your circuit. ( I am assuming that your circuit contains a linear regulator down to some lower voltage like +5V. If this is the case, then you have enough headroom to reduce the input from +12V to +9V. If you are using the +12V directly, then you may have to include two 1.5V batteries in series with the +9V.)

If the problem remains, then the noise is either radiated through the air and is being picked up by your touch plate, or the noise is being conducted through the car's frame which is the ground circuit of the electrical system. To determine which, you will be required to completely float your circuit. Completely isolate your circuit. You will probably have to replace its normal output with an LED to see what state your circuit is in. If the noise remains when completely isolated, then this is radiated noise.

One last thought, since your circuit is disabling the ignition, it is possible that the noise is coming in from the output wire that would disable the ignition. You may need a relay there, or at least better isolation between the driver and the output circuit.

With regard the CMOS's comment about active circuitry, I have disassembled the filters from both Radio Shack and the local auto parts stores. They contained only inductors and capacitors. Some may contain active circuits, but I doubt the ones that sell for $20 and can handle 60Amps have any active components. Just my opinion.

car on board computer power filter noise

banjo said:

OK, touch switches are very sensitive. This could be radiated noise rather than conducted noise via the power supply. Since your current draw is so low, here is how to troubleshoot. Get a nine volt transistor battery and connect this to power your circuit rather than the car battery. Keep your circuit connected to ground which is the car frame. Just connect the nine volt battery from the +12V input to your circuit and the car's frame. Start the car and see if the same problem exists. If the problem goes away, then the noise is conducted on the +12V input to your circuit. ( I am assuming that your circuit contains a linear regulator down to some lower voltage like +5V. If this is the case, then you have enough headroom to reduce the input from +12V to +9V. If you are using the +12V directly, then you may have to include two 1.5V batteries in series with the +9V.)

If the problem remains, then the noise is either radiated through the air and is being picked up by your touch plate, or the noise is being conducted through the car's frame which is the ground circuit of the electrical system. To determine which, you will be required to completely float your circuit. Completely isolate your circuit. You will probably have to replace its normal output with an LED to see what state your circuit is in. If the noise remains when completely isolated, then this is radiated noise.

Click to expand...

OK banjo, very thanks for the lenghty info, it very helped me..
i have tried all of your suggestion to troubleshoot my problem..and my problem still exist
its look like i must filtering both the power supply section and the touch plate..

banjo said:

One last thought, since your circuit is disabling the ignition, it is possible that the noise is coming in from the output wire that would disable the ignition. You may need a relay there, or at least better isolation between the driver and the output circuit.

Click to expand...

i use an optocoupler driving BD139 transistor to drive the relay which is use to connect/disconnect the ignition.

anyone can help me to design the touch plate filter?

battery inductor noise

Completely disconnect the touch plate from your circuit with the power source being the +12V car system. Is it stable? If the noise is not present, then all the problems originate with the touch plate.

Filtering the touch plate depends on exactly how you are detecting the touch. There are several methods. The capacitance method detects the change in capacitance when the plate is touched. In these methods, you can sometimes add a series inductor or a series resistor to the wire connecting the touch plate to the circuit. The series element tends to form a low-pass filter and limits the noise impulses picked up by the touch plate.

What is your touch plate? We had problem many years ago with a touch circuit. A fluorescent display behind our board was radiating lots of noise. The solution was to place a ground plane behind the touch sensor. This changed the overall capacitance and we had to retune everything, but it really helped.

I spent several years working on touch sensors. Getting a touch sensor to work is only the first step. Making the system immune to false switching is not easy. One trick is to place a second sensor around the existing sensor. False triggers will affect both sensors at the same time. Therefore, you need to test for touch events on the first primary sensor and NOT on the secondary guard sensor. We were using a microcontroller to detect the touches. I wrote lots of assembly code to perform filters of the raw touch data. If you are using a microcontroller, can you require that touch plate be continually touched for a second or so? This should eliminate the effect of spurious noise.

spikes on 12v in a car

banjo said:

Completely disconnect the touch plate from your circuit with the power source being the +12V car system. Is it stable? If the noise is not present, then all the problems originate with the touch plate.

Click to expand...

yes my circuit seems to be stable, i think the problem originating from the touch sensor..

banjo said:

Filtering the touch plate depends on exactly how you are detecting the touch. There are several methods. The capacitance method detects the change in capacitance when the plate is touched. In these methods, you can sometimes add a series inductor or a series resistor to the wire connecting the touch plate to the circuit. The series element tends to form a low-pass filter and limits the noise impulses picked up by the touch plate.

What is your touch plate? We had problem many years ago with a touch circuit. A fluorescent display behind our board was radiating lots of noise. The solution was to place a ground plane behind the touch sensor. This changed the overall capacitance and we had to retune everything, but it really helped.

Click to expand...

my touch sensor is simply "50Hz hum" sensor using BC557 and BC547 transistor, (see the attachment) i have a plan to change it to capacitance sensor since "50Hz hum" is unreliable but i must troubleshoot this problem since 20+ of my friends complaining the device that cannot work reliably.

banjo said:

I spent several years working on touch sensors. Getting a touch sensor to work is only the first step. Making the system immune to false switching is not easy. One trick is to place a second sensor around the existing sensor. False triggers will affect both sensors at the same time. Therefore, you need to test for touch events on the first primary sensor and NOT on the secondary guard sensor. We were using a microcontroller to detect the touches. I wrote lots of assembly code to perform filters of the raw touch data.

Click to expand...

currently i`m not using microcontroller, currently under development and will be released next year maybe,

banjo said:

If you are using a microcontroller, can you require that touch plate be continually touched for a second or so? This should eliminate the effect of spurious noise.

Click to expand...

yes...this is what i want, a delayed function to eliminate noise. i have month of studies in PICBASIC how to implement this delayed function in my next microcontrolled car immobilizer..currently, i`m implementing interrupt to lock on the relay..

battery noise filter

A 50 HZ hum detector will only work in areas close to powerlines. If you drive the car into the countryside away from powerlines, the switch may not work any more. Remember, the 50HZ hum is a man made effect, not a natural one.

Since operating frequency is so low, I would place a low pass filter between the touch plate and the base of Q1. Use a resistor between the touch plate and the base of Q1 and a capacitor from the base of Q1 to the +12V rail. This forms a low pass filter. The 3dB frequency of the filter is 1/(2*pi*R*C). You want the 50 HZ signal to be unattenuated, so set the frequency much higher than that. Try R=10K and C = 0.1uF. This gives cut-off frequency of about 159HZ. Test if you are stable and also test if the switch still works. If its stable, but the switch quit working, then lower the resistor value to increase the cutoff frequency of the filter. If its still unstable, but the switch still works, increase the resistor to lower the cutoff frequency.

A delayed function in PIC is easy. You just have a timer that fires every so many milliseconds. Then each time the timer fires you test whether the touch switch is active. If the switch is active, increment a counter. If the switch is not active, zero the counter. Then state that the delayed output requires a counter value of 100, for example. This insures that the switch was stable for 100 intervals of our timer. It is very similar to switch debouncing, just with longer timer intervals.

car noise filter circuit

The touch circuit is bad in many respects. As banjo clarified, it can't work in a car. If I remember right, there are plenty of application circuits for capacitive (higher frequency AC driven) touch sensors with uP available at the internet. That's definitely the way to go in a none-mains powered enviroment.