Power

Electrical separation

With any electrical cabling, wires generate an EMF or electromagnetic field around the wire. This can ‘induce’ voltage into other wires and anything conductive running nearby, even with the correct rated insulation on your wires. The best practice for installation is to segregate, as much as possible, all mains wiring away from the 12 volt cabling. Rule of thumb (and Australian standard when wiring cable lower than mains volatage) is a spacing distance of 50mm or 2 inches.

Keep all electrical wiring away from – speaker cables, your PC (Especially if it is not in a case), network cables and all monitor cables as much as practicable. Too close to speaker cables will induce a hum and too close to monitors can induce interference.

Try to keep you wiring as neat as possible. Wire looming is an art form but it’s amazing what can be done with a packet of cable ties. Also consider using what is known as slotted trunking. It keeps everything super neat and adds more insulation. Also great for fault finding because it means you don’t have to cut the million cable ties you just put on to trace a wire. Another method that is common is to twist the wires together. This can be even done using a drill but putting the group of wires into the chuck and running the drill until the twist is reasonably tight. This will make securing cables easier and the whole job a lot neater. The down side is that if you have a fault, it’s hard to separate your cables to find the problem.

I will be using and recommend using bootlace ferrules but they may not be worth the added expense for most. They stop any faults caused by stray strands of wire finding their way to a spot they shouldn’t be.

Power supply and fuses

The power supply I am using is a DIN rail mount, 10 Amp Meanwell unit DR-120-12. Chriz99 has used the enclosed 12.5 Amp Meanwell unit SP-150-12. Both do the same job.

Now the fusing spiel. Fuses are used to protect both the wire and the object at the end of the wire from damage. They are also used to protect things on the other side of the fuse from faults that happen downstream. For a simplified example, from your nearest power station they have fuses (or circuit breakers to be factual but same principle) to protect the generator from overload or short circuit from the wires to the switch yard. From the switch yard they have fuses at the start of the wires to your street, from your street they have fuses to your house and your house has fuses for your lights, and another from your power points and another from your hot water system.......

Each step is protected by a fuse at each change. In your pinball machine it should be similar. This is again a personal preference to some extent as you can under protect but never over protect.

If you change wire size at all, make sure you protect the wire used with a fuse rated at or below the rating of the wire. Again to quote a Jaycar primer, to select the correct fuse size –

“So the correct fuse rating is found by dividing the operating current level by 0.75 . e.g. in a circuit normally carrying 750mA, a 1A fuse would be used. When this derating is done, fuses will generally operate almost indefinitely in equipment running at room temperatures of 25°C or lower.”

For the shaker, knocker and gear motor, a 10 amp slow blow fuse will be used. Slow blow fuses are used here because of ‘inrush current’. When a motor starts, it draws a lot of current for a short time and a fast blow fuse may blow although there is no fault. For the LED’s and other lights, a 500 milliamp fast blow fuse and for the contactors, a 500 milliamp fast blow fuse also.

That way if one thing dies I can fault find quickly and it won’t take the rest of the ship with it.

Also, grimwasere had an issue with a contactor coil that had failed and shorted out. The weakest link between the power supply and the coil (now a short circuit) was the LEDwiz. It took out 3 of the 4 drivers on his LEDwiz board, practically killing it. The question was raised if it is possible to install fuses on the negative wires? Because fuses work on current, all current that flows through the positive, must pass through the negative to complete the circuit so fuses on the LEDwiz outputs will work fine. 500 mA fuses will protect the LEDwiz and still run the contactors, Cree LED’s, relay’s etc.

Never put fuses on the Neutral of mains voltage.

Multiple Power Supplies

Some people are using a single 12 volt power supply for everything, others are using an ATX power supply and using the 5 VDC and 12 VDC rails, while some are using two (or more) separate power supplies. This can cause issues with multiple negatives and how to hook things up to the LEDwiz.

The correct way to connect multiple power supplies is to create what is known as a ‘star’ point. This can be a bolt, a bridged terminal strip, basically anything that connects all the negatives together. No doubt you have heard the negative referred to as a ‘common’ or ‘ground’.

Skipping all the technicalities, with the power supplies that we are using (if using the ones recommended) the negative wire is electrically connected to earth, and there should be no difference in voltage between each negative. (Yes that is skipping the tech.  )

So you should run a decent gauge wire from each power supply to the star point and then run a wire from the star point to all things that require a negative, if it’s being fed from the active on the power supply (LEDwiz, front control push button lights, coin button lights, fans, etc) I have used a 12 and a 24 volt supply in my example but any DC voltage is the same. I sent LEDwiz techs an email regarding this. The response was -" This should be fine. However, when tying multiple grounds from different supplies together, it's good practice to use a meter to make sure there is no potential between any of the grounds you intend to tie together. Usually, you can check for continuity between all of them and they will be common through the grounded mains plug. " So it’s good practice to use a multimeter on DC volts and test between the negatives on each power supply. If you have a more that a couple of volts, check you connections and test again. This can cause damage to components.