I am currently repairing a holiday display piece for a customer, and I am having some isues with led lights that flicker due to alternating amp draw.
The piece I am working on is a Lemax Halloween front yard. It has about 20 led lights of varying sizes/colors, to moving elements that run off 3v dc motors, and two characters in swings. The swinging characters are causing the issues, because they use pulsating electro magnets to "push" the swings away from center. (There is a standard magnet in the bottom of each swing.
The original PCB was fried, so I decided to make my own. Power input is 4.5v dc @ max of 1000mah. This is the largest amperage available for these pieces.
I have used resistors of varying sizes to isolate the led lights on their respective circuits, according to power requirements.
I have used resistors to bring the power down to 3v to run both dc motors.
I am running a full 4.5v to the swings, but when the electro magnets "pulse" on, the lights flicker and the motors slow. I have tried to find the proper size resistor to allow the swings to work, but not affect the lights. I've tried everything from a 1.2k up to a 4.5m Ohm. None allow the swings to move, but obviously the flickering stops with them in place.
I'm not an electronics "guy", I have more of an automotive background. I'm wondering if I need to try a higher resistor (10M?, 20M?) or possibly a capacitor? Any help or direction pointing would be greatly appreciated.

 

What is the rating of the power supply?

How much current the magnet take?

Can you control the length of the pulses? That would be a better way to control the power to the magnets than using a resistor.

If you do use a resistor, it would need to be Ohms, not KOhms.

Bob

 

What is the rating of the power supply?

4.5v DC

How much current the magnet take?

That will be difficult to check with my meter, because they pulse a few times per second. My meter can't keep up with the changing amp draw.

Can you control the length of the pulses? That would be a better way to control the power to the magnets than using a resistor.

If I change the pulse timing, the swings won't work properly. They have to fire in synch with the pendulum. My thinking is a smaller pulse, will create a shorter pendulum swing.

If you do use a resistor, it would need to be Ohms, not KOhms.

The last resistor I tried was a 4.5M

Bob

 

Sorry, without knowing the current capability if your power supply or the current draw if the magnets, I can’t help you. All I can say is that it is insufficient.

I didn't say to change the timing of the pulses, I said the length.

A 4.5 Meg resistor would limit the current from a 4.5V source toone uA! AsI said, ypu need a resistir on the order of 1 to 10 Ohms. Not Kilohms or worse yet Megohms.

Bob

 

You need to estimate current used by each portion of the circuitry and look at the ground resistance back to the power source.

It would be helpful if you posted a schematic and pictures of the layout; identifying areas of high current draw.

If is a commercial product, they probably already considered the issue you're addressing. I'd be checking for capacitors that are no longer working well enough.

Just noticed this part (after reading your post several times to pick out relevant details).

The original PCB was fried, so I decided to make my own.

You need to look at your power distribution.

 

A 4.5 Meg resistor would limit the current from a 4.5V source toone uA! AsI said, ypu need a resistir on the order of 1 to 10 Ohms. Not Kilohms or worse yet Megohms.

Bob

Thanks, Bob. I'll start with a 10Ohm, and work up or down from there to find the right balance.

 

I'm currently running it with a 10Ohm inline for the swings. They just barely move, and there is still a slight flicker. When running everything off my stand alone power supply, I'm seeing the amp draw peak at just under 700 mah when the swings activate. The lights are not affected at all.
When they switch off, it will drop to 190 mah. The plug in power adapter is a 1000 mah unit, and I tried a 30 watt, adjustable voltage unit set at 4.5 v. Still getting a slight flicker.