Greetings!

Researching a project, and came across something that seems ambiguous (at least to me).

Coil voltages. What should be used? I see things all over the place with this ... seems like some machines were 24V and others were 50V ... but this is where it gets ambiguous (for me) the same kind of coils were used. Is that correct?

The 50V, apparently, gives more power which allows for a faster game, and steeper ramps. I understand that. But do these coils really support twice the voltage, which means twice the current, which means four times the power and not melt?

It gets stranger. In reading another thread here a little way down the forum asking about power supplies, someone said they bought an Antec supply from pinballcontrollers. I went to that website and they only have a single power supply ... and it's 70V! Now, that website is all about using P-ROC (which I'm not interested in) so I don't know if they're doing something with that voltage (stepping it down)?

What also peaked my interest is it was a 400W power supply which sounds very low to me considering, for example, an FL-11629 flipper coil is only 4 ohms. At 50V that's 625W and at 70V that goes up to 1225W!!! Now, I realize that's only for milliseconds until the EOS switch is hit, but on the flip side (ha!) the player can hit both flippers at once and on top of that it could be during multiball when other coils are firing. So.... something seems fishy to me?

Along those lines, are all the coils in a game run off the same voltage, or do some of the others run on lower voltages (like pop bumpers, pop targets, slingshots, etc)?

I was looking at getting a 50V transformer, which after being rectified would be ~47-48 volts. Close enough to 50. What I don't know is what VA rating I should go for. I was looking at a 1000VA which could easily do 20 amps. That's not quite the 25A both flippers would be simultaneously, but they do say at 60 Hz you can squeeze an extra 10% out of it just fine. 22 is pretty close to 25. However, that website selling a 400W (aka 400VA) one makes me wonder if I'd be going overboard. It's $50 vs $100 bucks, so twice the cost. Not exactly breaking the bank difference, but why waste money if it's not needed?

Sorry for the long-winded post, I'm just excited to plan out such a project

I'm confused. V=IR. If R is 4 ohms, like in the case of the flipper, that gives:

50V = I * 4, I = 12.5 A

24V = I * 4, I = 6A

The current doubles, does it not?

Since P = V^2/R, that also supports that a doubling of voltage results in a quadrupling of power.

Is there a chart or something that gives guidance on what coil to use for what voltages?

Do most machines run coils off a single voltage, or do they have a mix?

Thanks for all the info and answering my dumb questions, I appreciate it!

I've thought of doing that, but I like the idea of the flippers being independent of the MCU and having zero input lag.

But, using PWM means the EOS switch is no longer needed. Tradeoffs.

I just wanted to pop back in with an update. Part of the purpose of this project was I wanted to learn new things that I don't have experience with. I ended up deciding to build my own supply and through the process I learned quite a lot.

One of the big things is I was thinking about the solenoids entirely the wrong way. While the steady state current usage of the flippers would be 12.5A at 50V, that's only once steady state is reached. At the start of the stroke, it won't be at steady state. I forgot the cardinal rule of inductors and capacitors. A capacitor can have instantaneous current change, but not voltage. Inductors are the opposite, they can have instantaneous voltage but not current. The solenoid, as an inductor, will ramp up in current. Bottom line is, 1000VA isn't needed. As a point of comparison, studying pictures of old Williams transformers I found they're rated for 750VA and they're providing power for everything in addition to the solenoids.

Anyways, this epiphany came to me after I had already ordered the 1000VA transformer, so the 1000VA transformer it will be! The thing is massive in size and a hefty 18 lbs. Who knows, maybe I'll build 4 machines and power them all off this one transformer

I built up a prototype 50V unregulated power supply and it worked wonderfully! The first time I turned it on. The second time tripped the circuit breaker. Ugh. Why? Inrush is why. Toroidal transformers have high inrush, plus the 13.6 mF of capacitance is just too much for a breaker to handle if you catch it at the wrong time in the AC cycle. To fix that, I added a 10 ohm 16W resistor on the primary. This limits the input to 17A peak maximum. While that's higher than my 15A breaker, the duration is really short (couple milliseconds) and most breakers aren't guaranteed to trip until beyond 135% anyways (and even then take a while). They only instantly trip on really high loads or short circuits.

Now, you may have ballparked the math to realize that 17A through a 10 ohm resistor is 2890W of power which is orders of magnitude higher than the 16W it's rated for. Even if it didn't melt down, it would be a colossal waste of power. To counter that, I put a 48V relay in parallel with the resistor that once the output voltage rises to ~36V will switch on and the resistor is then bypassed. This all happens in a couple milliseconds, so the resistor doesn't even get hot.

The other thing I failed to realize at first but did before I ordered the transformer, is that I forgot these are all rated at RMS values and not peak. So a 50V transformer really would have been 1.414 times higher (70.7 volts). So really I only needed a 115V/35V transformer. Since US power is 120V it works out to be 51.6 volts peak. The bridge rectifier then drops that down to nearly 50V.

I'd like to once again thank everyone who popped in with suggestions.

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