Help with Automotive Project Please.

[soundcatcher]

I'm working on a project that is pushing my knowledge to it's limits. I'm totally self taught and I pick up knowledge as I encounter stuff that I don't' understand or tackle new challenges. On this occasion I've come a bit un-stuck.

I'ts good old auto-electrics this time that has me tearing what little hair I have left out! I have a custom car that has solenoid doors. I decided that I wanted something a little bit different so I have decided to use a Capacitance Switch to trigger the doors to open, rather than use a pushbutton or remote control. This switch works fine by iteself but when you trigger an unrelated device like the electric windows, a spike gets sent back up the powerline and triggers the door switch and they then get stuck in a loop and go crazy! Not great if you're driving down the road and need to adjust your window and the doors open!

So after a bit of searching I think I have 1 solution... Unless you guys can think of a better one. I'm thinking about using a transient voltage suppressor across the sensor circuit to hopefully stop the unwanted triggering from happening.

So far so good but at this point I don't know which one to choose and I don't know how to work out or where to measure to find the parameters that will narrow down the choices?

Does anyone have any experience with TVS and can you please guide me gently in the right direction as to what to do. I've read dozens of articles, but as yet they all say the same thing, but don't give me the laymens version so that I can grab a meter and start to work it out? I have a feeling that once It's been explained I will kick myself. But at the moment I feel as though I am banging my head against the wall on this one.

Many thanks in advance...

Andy

 

[Reloadron]

At the present time, before all else, do the installed solenoids have diodes across them to snub the inductive kick from the solenoid when the field collapses? Do the motors driving the windows have a cap (.001 uF) across them?

Ron

 

[KeepItSimpleStupid]

The automobile environment is a very hostile place. The above advice is first order.

 

[OlPhart]

An O'scope would Really help. Vehicular electronics is impressively nasty. Using touch switching is a bold move, high impedance = high sensitivity.

TVS (MOV) is more for destructive protection, you first need noise level suppression. I'd start by adding .1uF ceramic and 1uF tantalum caps (parallel) along with a 5-30 ohm resistor (series) to the power feed of the door sensor. Good Hunting with this, it may not be easy... <<<)))

P.S. this is along with previous posted suggestions

 

[soundcatcher]

At the present time, before all else, do the installed solenoids have diodes across them to snub the inductive kick from the solenoid when the field collapses? Do the motors driving the windows have a cap (.001 uF) across them?

Ron

Erm, no and no. Having said that the solenoids are attached to the touch switch and don't appear to be causing any issues....I might just fit some diodes just in case. What diodes do you suggest please?

Not sure where to put the cap on the window motors? They are an after market style that reverse the polarity in the motor. Should I just put the cap across the positive feed before the switch and the negative wire?

 

[KeepItSimpleStupid]

In4004 or 1n5404.

Caps at the motor itself. Ceramic caps are polarity insensitive. They help reduce brush noise and RF emissions.

 

[soundcatcher]

In4004 or 1n5404.

Caps at the motor itself. Ceramic caps are polarity insensitive. They help reduce brush noise and RF emissions.

Thanks...I'll give that a go!

 

[soundcatcher]

An O'scope would Really help. Vehicular electronics is impressively nasty. Using touch switching is a bold move, high impedance = high sensitivity.

TVS (MOV) is more for destructive protection, you first need noise level suppression. I'd start by adding .1uF ceramic and 1uF tantalum caps (parallel) along with a 5-30 ohm resistor (series) to the power feed of the door sensor. Good Hunting with this, it may not be easy... <<<)))

Thanks for the advice. An O'scope isn't in my arsenal of tools as yet.... Bold or stupid, only time will tell!? Got to love ebay though...Found the parts within a 5 min search! So the next bit is to understand how to fit them. Sorry if I appear thick........ So the two caps go across the +'ve and -'ve feed to the sensor circuit and the resistor goes in line between the caps and the sensor circuit on the +'ve feed?

Oh and just a thought......5-30 ohm resistor. Is that one of those any size between 5-30 will work just fine or is the resistor size dependant on something else? Just thought I'd ask as I'm having a shopping spree I may as well get optimised parts....

 

[ronv]

Noise reduction

Here is a good link for your window motors:

https://www.electro-tech-online.com/custompdfs/2011/06/motor-noise-reduction.pdf

And a schematic of the filters for the sensor.

Sounds like the window motors may be the culprit.

 

[OlPhart]

The resistor is to provide some separation, between the power source and the touch sensor circuit. Its' value is just high enough to not cause much (<1V) voltage drop in operation. Both capacitors go in parallel, across at the sensor power, after the resistor. Note that this is just for the sensor, Not the driver & solenoid. Also, the tantalum IS polarized.

 

[Diver300]

If you have a solenoid, it is basically a coil like a relay coil. You can put a diode in parallel to stop the inductive spike. The diode has to be in the direction that it takes no current when the solenoid is operating. (The cathode of the diode, usually marked with a line connects to the positive side of the solenoid).

However, you should be aware that some items called "solenoids" in car door locks are not solenoids at all. They are motors with gears arranged to give a short push - pull action. The motor is connected in reverse to reverse the direction of travel. You cannot suppress them with a diode, as it will blow in one direction. Capacitors can help. An other way of suppressing the inductive spike is a resistor in parallel. I suggest 22 ohms 5 W. A bidirectional TVS rated at 16 - 20 V in parallel with the motor is a good way of dumping the inductive energy effectively.

 

[soundcatcher]

Thanks for those last few bits of info and help.

The components landed on my door-mat on mass this morning. I've just got to get permission from my wife and children to start fitting them to the car!

 

[soundcatcher]

Hi Folks,

So I managed to get some time on the car today as the weather has finally cleared up.

The diode on the solenoid didn't work unfortunately. I had a plan 'B', which was to put a delay circuit inbetween the output relay on the sensor circuit and the solenoid. That appears to have sorted the solenoid feedback issue for now.....unless it was just dumb luck?

As for the window motors. For some reason which I don't understand if you start with the windows all the way down and press the button and make the window go up the sensor circuit doesn't activate. But when you wind the window down it causes the sensor circuit to activate. Go figure? I have a single cap on the window motor at the moment. Next time I get out there I'll try using 3 caps and see if that makes a difference!?

I'll keep you posted on how things go.

In the meantime if you guys have any other suggestions I'll give 'em a go.

Cheers,

Andy

 

[soundcatcher]

So things haven't exactly gone according to plan. I've tried all of the suggestions and none of them worked unfortunately. I think this is because of the oversensative nature of the sensor circuit. So I plan to get another circuit to use after the sensor circuit. This will be a delay circuit with **broken link removed**. The main reason is that the sensor and solenoid together cause an electrical loop. By not retriggering the solenoid it will break the loop.

As for the windows, I think I have a solution. I'm after automation, so I have thrown together this circuit to do the job...

**broken link removed**

Yes it's very basic but it works on the principal of when a motor has power, the relay is activated and the solenoids circuit will be broken and untriggerable even if the sensor circuit is activated.

To explain, the two lightbulbs attached to the relay are instead of the solenoids, And the 4 switches and lightbulbs were used to show what happens when each of the 4 wires that receive +ve volts to activate the windows

This is a bit of a bruce force solution on both parts. But hopefully it'll do the trick. I'll let you know how i get on once I have the delay circuit and the relay I need to make the simple circuit in the diagram....

 

[soundcatcher]

Hi folks. So I've had a bit of a break on this project whilst I opened our new shop. So now things have got a little easier on the time side I'm getting back into the swing of problem solving.

I've fixed the retriggering by using a non retriggerable timer circuit after the sensor circuit. The next issue I have is that the negative power lead on the sensor circuit is acting like a trigger when there's a spike from another system or even if you touch the connector where it is fitted to an earth tab.

So I'm back asking for help again...... I think if I had a 12v dc to 12v dc something that isolates the + & - inputs from the + & - outputs so that spikes cannot travel across from the power source to the circuit that'll solve that issue.

Does such a thing exist or how do I go about building such a thing???

Thanks in advance...Andy

 

[Reloadron]

There are turn key DC to DC converters out there along these lines that provide output isolation for a span of input voltages. For example the ZUS 61212 runs off 9 to 18 volts and outputs (isolated) 12 VDC @ 0.5 amp. They get much larger but also can be pricey for higher currents. One merit is the wide input voltages for automotive applications. The link just being an example as there are many manufacturers and prices.

Ron

 

[soundcatcher]

Thanks for that. I take it I can just 'bolt' this inline or do I need any external components for smoothing purposes??

 

[Reloadron]

Pretty much plug and play. A few caps added and that is about it. Maybe .1 uF in and out just to be sure about noise (automotive systems are notorious for noise) and maybe a few 470 uF in and out for filtering. While DC to DC converters can be built sometimes it is advantageous to get a plug and play solution. The 470 uF was based on a .5 amp unit. It's all about cost I guess. Remember, the link was just an example. They come in all sizes shapes and currents as well as voltages from a host of manufacturers.

Ron