3/5/2017 – Why bulk capacitance matters

Rarely is there a single change that can be made, where cause and effect is so evident in electrical engineering.  After looking through the equations for solenoid power and running some calculations, I noticed that reducing the amount of turns on a solenoid doesn’t really affect things that much because at the same time, I would be increasing the amount of current in each turn.

Because of that, I came to the conclusion that I would need to throw in a higher voltage power supply.  I had a super cheap 48V supply laying around, and tossed it into the machine just to reset the drop bank targets.  After trying it, it just didn’t work well at all.  Then I decided to add a big bulk capacitor to store some charge so it could respond easier to the firing of the solenoid.  (10mF)  It more than made up for the inability of the power supply to provide the instantaneous current to fire the solenoid.

Here is the video that shows the difference with an without the capacitor:

8 responses to “3/5/2017 – Why bulk capacitance matters

  1. Quite the difference. I can’t seem to find documentation on building the power filter board, or for that matter the neopixel wing. Can you point me in the right direction? Thanks. I’m just getting started and look forward to using OPP for my project.

    • I’ve been suggesting to people to not use the neopixel wing board, but instead to use a Fade Candy board. There is no MPF support for the Neopixel wing, and I don’t think that there is really enough communication bandwidth available for people to be happy with the light shows that it could do. (It also uses a color table to store 32 colors for each pixel. It would be very difficult to explain that only 32 colors are available, and if a new color needs to be added, it will replace one of those 32 colors.)

      The power filter board is done, and you can grab it from the Mezels. The only missing part is the BOM materials. That will live on the OPP section of pinballmakers.com. (I started a section, but haven’t finished filling it out). Because it can be populated multiple different ways, it is going to require some explanatory text. That’s why it has been taking so long. Maybe I can finish that this week, but there are no promises.

  2. Thanks for the reply, Fade Candy was the plan and then I saw your board and thought maybe I could use that instead, but fade candy will work great.

    I actually just ordered one of the power filter boards from Mezels the other day while I was ordering the rest of my boards, and was looking for the bom to add parts to my Mouser order, but it can wait as I’m a ways from actually building my machine just getting a head start gathering materials.

    Thanks again for all your work, this is all pretty cool.

  3. Well, here is a quick BOM assuming that you are using the power filter board for a single 48V high voltage:
    3 bulk caps (8.2mF, 63V), 598-SLPX822M063H5P3, $4.28 each
    1 NTC thermistor (inrush current limit), 995-SG26, $2.28
    1 PChan MOSFET (only necessary if turning on/off high voltage), 511-STF10P6F6, $.85
    1 Indicator LED (5mm or T-1 3/4), 626-SLX-LX5093ID, $.06
    10 100K Resistors (only need 3 or 4, but cheaper if buy 10), 588-OK1045E-R52, $.018 each
    1 900K Resistor (Used as voltage divider and assumes 48V power supply), 660-CF1/4CT52R914J, $.15 each
    2 Molex 6-pin 4.2 mm Mini-Fit Header, 538-35317-0620, $.28 each
    12 Molex Crimp-Style 4.2 mm 24-18AWG Female Pins, 538-39-00-0039, $.19 each
    2 Molex 6-pin 4.2 mm Mini-Fit Housing, 538-39-01-2065, $.52 each
    1 6 pin 100 mil header (use leftovers from 40 pin headers)

  4. Sweet, thanks. I’m actually going to be using a 24V powersupply, build will be Gottlieb late em/system 1 era style using period Gottlieb components that originally were 25vdc.

  5. So for the voltage divider, assuming the processor reading the input is a 5V processor, you would use a 402K resistor, or 603-MFR-25FRF52-402K. That should make the input so it reads as a high. Of course, if you don’t care about reading if the voltage is on/off you can simply not populate those components. Same thing with the PChannel MOSFET. If you aren’t going to turn the voltage on/off, you simply use a jumper wire instead of the MOSFET.

  6. go ahead and still use the same (63V) caps though? and yeah I really don’t care about turning the voltage off, if the machine is on we’re all go.

  7. You can drop the ratings of the caps. I’m just trying to give a general guideline, and most people are using 48V supplies, so 63V is a really good value. Typically for caps you want about a 20% buffer from their rating, so at 24V, the caps should be rated for about 30V (or whatever the standard cap voltage is near that point). That should save you some coin. If you don’t care about turning on/off voltage, don’t buy the P-Channel MOSFET and jumper across it to pass the high voltage directly to the 2nd connector.

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