How do I prevent video interference caused by electric motors

so what specifically needs to change in my original 'wiring diagram' so that it becomes a star ground wiring system?

This will be interesting to see what changes, as all the grounds seem connected. If you can change your wiring which you said you couldn't) then there may be other solutions.

it's only when the power door lock motor is on it's own battery power supply that the problem goes away.

it's only when the power door lock motor is on it's own battery power supply that the problem goes away.

Bummer

yea, that doesn't help. How do you simulate two separate power supplies using one?

so what specifically needs to change in my original 'wiring diagram' so that it becomes a star ground wiring system?

Look in the link I've pointed you at twice now.

oric_dan(333):

so what specifically needs to change in my original 'wiring diagram' so that it becomes a star ground wiring system?

Look in the link I've pointed you at twice now.

ok. I read it. It talked about using a main capacitor to absorb voltage spikes and drops. I tried using a 1000uF, 35v cap. It didn't have any effect. So, back to where we left off at. It flickers even when a charged cap is applied, it doesn't flicker when a the power door lock is being powered by batteries that share the same ground as the original power supply. Given these clues, what specific tests can be performed to find out what needs to be added to calm the voltage or current? What about an inductor? Maybe the capacitor isn't large enough?

Look in the link I've pointed you at twice now.

I looked at the single link i see posted that led to other links, and in a quick scan of the resultant pages didn't see anything helpful to the current issue (well maybe if a capacitor the size of a microwave oven is used). If the OP can't change the power supply or make any modifications to his current setup, his project is toast. It is what it is, and no amount of wishful thinking will change that fact. The laws of physics generally ignore fantasy thinking.

If you want to run both the motor and the battery from the same 12V supply, then at the very least the motor should have its own power and ground cables between the it and the power supply. Do not share any part of the motor power or ground lines with the power feed to the video camera. But this probably won't be sufficient, because switch mode power supplies don't react instantaneously to large changes in load current.

1000uF is probably nothing like large enough to supply the current peak when the motor starts up. 20000uF would be more like it.

Consider adding slow-start to the motor. This will reduce the current surge when it switches on and give the power supply time to react. One way is to replace the switch with a mosfet, and feed the mosfet with a slowly-increasing PWM signal. Don't forget to put a diode across the motor if you do this. Similarly, use slow-stop.

What you're saying makes a lot more sense and matches the results I get through experimentation. Wouldn't an inductor of the right size smooth out current spikes and solve it?

David82:
Wouldn't an inductor of the right size smooth out current spikes and solve it?

An LC filter between the power supply and the motor, and/or between the power supply and the video camera, would fix it. But the inductor needed would be very large, so I don't think this is a practical solution.

wow. I've been messing with this for days now and tried so many things. Is there someone I can pay to solve it with the constraints I mentioned?

Here is the challenge:

while everything is powered on and working, connect an uncharged capacitor, motor, or any other device that draw significant current to terminal A, with any additional components, such that the video feed does not flicker. You cannot change the wiring. Everything shares a ground as illustrated including the ground portion of the video feed.

Can you make a list of how much current and voltage your components use, like what they are rated for VS what your able to supply? Also a visual picture and/or video would be helpful too.

And if you want to pay someone to do this for you, you need to make a post in "Gigs and Collaborations".

ok, I'll post in there too. It seems like this problem will occur throughout a WIDE range of possible component specs (amp draw, voltage etc.) making that question not only very hard to answer, but largely irrelevant. I'll humor the idea anyway though. the power supply is a 90W computer power supply. All sorts of stuff can be hooked up to terminal A to make the video flicker so specs on that don't exist. The specs on the camera and LCD screen are unknown and don't seem to be relevant anyway..

This problem should be immediately recognizable to someone with the proper experience.

This problem should be immediately recognizable to someone with the proper experience.

Sure, you most likely have an inadequate power supply.

The same effect is seen even when using 8AA batteries instead of the pc power supply :confused:

David82:
The same effect is seen even when using 8AA batteries instead of the pc power supply :confused:

The wires from the power supply may be too small to pass sufficient starting current to the motor resulting a brownout of the camera. Particulalry if your AA batterys are in one of those radio shack battery holders, that could be an issue. If the cam could operate at 11v instead of 12v, then a diode in the cam + wire with a big capacitor between the diode and the cam, your problem might be solved. If you can't change any thing, then note the below.

Insanity: doing the same thing over and over again and expecting different results.
Albert Einstein

a quick scan of the resultant pages didn't see anything helpful to the current issue (well maybe if a capacitor the size of a microwave oven is used). If the OP can't change the power supply or make any modifications to his current setup, his project is toast.

Maybe a more through scan would help too. First off, it describes the use of star grounding
that G_M originally mentioned. If properly implemented, this helps keeps the motor current
noise from getting onto the power and ground leads of the video ckt.

Secondly, the Main Capacitor needs to be placed correctly [as indicated on the link cited], and
its job is to help compensate for the inductance of overly long leads [meaning more than a
couple of inches] from the battery/power supply to the board being powered. It probably won't
help much if the motor load is so great it shorts the buss temporarily, or if it's located in
the wrong place.

Thirdly, it was pointed out back in reply #17, and probably also by others, that what OP has
been trying to do all along is find one patch/fix for a crappy design, rather than build a
better design from the getgo. Further, he seems intend on abandoning every "fix" that
doesn't solve the problem completely, whereas he's been told that a good design has many
aspects, not just one bit of magic.

Fourthly, the reason for pointing OP to the links in the first place was because some of
us don't believe in simply spoon-feeding proverbial loaves'n'fishes to neophytes. Ultimately,
the object is to learn something about what you're doing.

Fifthly, relative to item #4, it might be helpful to look up the concept of "Cargo Cult". See
especially "In an attempt to attract further deliveries of goods, followers of the cults engaged
in ritualistic practices such as building crude imitation landing strips, aircraft and radio
equipment, and mimicking the behavior that they had observed of the military personnel
operating them".

See also,

My only suggestion now for the OP is to start making sacrifices to some diety. I suggest starting with a 20 piece bucket of KFC extra crispy. Below is how I brownout protected a servo control chip back in the day.

zoomkat:
The wires from the power supply may be too small to pass sufficient starting current to the motor resulting a brownout of the camera. Particulalry if your AA batterys are in one of those radio shack battery holders, that could be an issue. If the cam could operate at 11v instead of 12v, then a diode in the cam + wire with a big capacitor between the diode and the cam, your problem might be solved. If you can't change any thing, then note the below.

That's a good suggestion. I tried moving the batt pack right up to the camera power leads but still had the same issue. remember, even just placing a uncharged cap anywhere on the + - rails will still cause the momentary camera blackout.

Ideally, the problem would go away if I didn't have to have all of the ground leads connected together. I could use two power supplies to completely isolate the camera power from everything else so that it's power wouldn't be interfered with. That's not possible with this design so i need to simulate the same thing. I need to make it so that the camera power is unable to experience any voltage drops or spikes and the same with current.

Does you door lock, stay energized? If so, it might be putting on additional resistance to your battery, which will want to eat up more current from the battery. If it is doing this, it could be taking current from the camera.

If not, then it is with your power supply. It might not be able to handle everything. This would explain why it improves when you added the second power supply.