How to choose an AC Powerline Filter

[mitchzizzle]

Hi everyone,

I am working on servicing a pinball machine, it has two screens and one of them resets occasionally from power interference. I would like to add a Powerline filter internallt between the IEC connector input and the machines power supplies that would reduce interference and hold performance over voltage fluctuations. How do I go about choosing an input filter that will suit? I know I need 120v. 15amp., what other specs are important? I would like it to deal with voltage drops as well as spikes.

Thanks for any help anyone can offer!
Mitch

 

[Harald Kapp]

Something like this should work. This is a very general type of mains filter suitable for a wide range of applications. Unless you know very specific details about the nature of the interference or noise on the mains line, it makes no sense to even try to design a dedicated filter.

No filter will deal with voltage drops as no filter can restore the missing amplitude of the voltage when it dips. A typical and proven way of dealing with voltage drops on the primary (mains) side is to add buffer capacitors on the secondary (low voltage) side of the power supply. Or on the primary side in case of switch mode power supplies.
Depending on the age of the pinball machine you may see a transformer based power supply, where the buffer capacitors (unmistakeably to be identified by their bulky size) are on the secondary side and on the order of hundreds to thousands of microfarads in capacitance. You can easily replace these by ones with the same rating (voltage and capacitance), although modern ones will probably be much smaller in physical size. Observe the polarity of these electrolytic capacitors, it is clearly marked on the component.
If the pinball machine is of a more modern make, the power supply may be a switch mode type with the bulk of the capacitors being on the primary side. In that case I recommend you swap the complete power supply for a new one. Trying to repair such a power supply without sufficient expertise is dangerous and potentially lethal as there are high voltages and currents involved.