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Required power for solenoid

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OhmEigaMan

New Member
Greetings Gurus:

As an experiment, I'm trying to trigger a 50V pinball solenoid from a 5v logic pulse, but I'm a little confused (and my electronics knowledge is introductory at best). I'm basing my circuit on a schematic from a pinball machine.

On this schematic, there's a 50V supply and 3.0 Amp slo-blo fuse. So I purchased a 48V 3.3 Amp supply thinking it would work fine. Then I checked the solenoid. The coil is 4 ohms. If I'm doing my math right, that means it's going to pull a whopping 12A.

Now, also on the schematic (before the fuse) there's a 100uF/150 volt capacitor and a 10K 0.5W resistor in paralell. I'm guessing this is to allow for the spike in Amps? I searched the internet for RC circuit info, but couldn't really find anything for these in paralell, only info on how long it would take to discharge/charge if in series.

I'm wondering:

1) If I energize the solenoid for 0.1 seconds (or even 0.25 seconds), am I going to destroy my power supply? And if there's any info or links you know of that would explain the paralell cap and resistor, that'd be great.

2) And if I energize the solenoid for that amount of time, will I destory my 100V 4A rated Darlington Transistors? Or can they tolerate that amount of current for a brief time? The schematic actually uses a TIP102 transistor, but I found this board with the Darlington transistors and the necessary protection diodes (for when the coil de-energizes) already in place.

Thanks in advance for any insights and thoughts!
 

Mr RB

Well-Known Member
I doub't its a 50v solenoid anyway, and doubt it even more when you said 4 ohms coil resistance. It's NOT a 600 watt solenoid!

Get your bench variable PSU and slowly turn the voltage up and find what volts/amps the solenoid actually NEEDS to operate whatever you are connecting it to (which you failed to mention).

Then choose an appropriate power supply voltage based on that.
 

OhmEigaMan

New Member
Thanks for the reply, Mr. RB.

It's a flipper coil and I intend to use it as a flipper. My friend has asked me to help him make a scaled down pinball machine with just a couple solenoids. My understanding is that these coils are triggered at high voltage to provide the kick to the ball, but are never on for more than a brief period of time (i.e. less than 1/2 second, maybe 1/10 second or so). There's a second "hold" winding in the coil for holding the flipper up once activated. That pulls less than 1A, so I'm not worried about it - only concerned about handling the big, brief initial kick without burning everything out.

(BTW I was probably wrong about the cap/resistor in parallel. I looked again and they are right after a bridge rectifier, so now I'm thinking they are part of the AC-DC conversion and have nothing to do with providing extra power to the coils).

Thanks again!!
 

ericgibbs

Well-Known Member
Most Helpful Member
T
(BTW I was probably wrong about the cap/resistor in parallel. I looked again and they are right after a bridge rectifier, so now I'm thinking they are part of the AC-DC conversion and have nothing to do with providing extra power to the coils).

Thanks again!!

hi,
The resistor across the cap is to discharge the cap when the main power is switched off,, big caps can hold a charge for quite a while, which can be hazardous if accidentally touched.
 

hdc090360

Member
Solenoid Power

Your power supply is probably enough to drive a single solenoid, but you couldn't hit both flippers at once.

The flipper solenoid is designed to have a switch shorting the hold coil which opens when the flipper is at nearly full travel. This gives enough power to kick the ball but doesn't burn the solenoid when you hold it on.

The back emf from the solenoid should limit the current until the switch opens.

I tracked down a schematic on the web and a commercial machine has a 7A fuse on the 43V solenoid rail so I imagine they don't draw more than 4-5A max.
 

OhmEigaMan

New Member
ericgibbs: Thanks for the info. That makes perfect sense.

hcd090360: Yes, I have the end-of-throw switch all wired up. Guess I'll need to up the amperage of my supply a bit. No fun to only hit one flipper at a time :) And thanks for looking up a schematic. I'll try to scan and post the relevant parts of the one I'm using for reference. I didn't because there are whole sections that aren't related to what I'm doing and it's spread out among multiple circuit boards/drawings - a big file.

I appreciate all the input! Thx!
 

Mr RB

Well-Known Member
I can't understand why you would want to drive the coil the old fashioned way with unreliable pull-in contacts arcing away at a silly voltage?

Your first post said you were going to drive the solenoid with a logic level pulse ie implying you would use a FET etc to operate the coil. Just choose a better voltage power supply and then program the appropriate pulse length to give good flipper action.
 

OhmEigaMan

New Member
I do plan to trigger the flipper via a 5v signal. I'll scan the switches and send the signal to my comp (via a MIDI encoder), then send a 5v pulse from the comp (via a MIDI decoder) to activate the solenoid. I've found a decoder board with Darlington transistors rated 100V/4A each.

I had, however, planned to use the old-fashioned wiring for the flipper itself (ie. 50V across the coil and keeping the end-of-throw switch to break the hi-power circuit). Are you suggesting to actually trigger the low power and high power windings separately? I hadn't thought of that - seems like it might be a good idea. But won't I still need the high voltage to provide the speed and power in moving the ball around even if the pulse is longer?

Thanks!
 

Mr RB

Well-Known Member
You wont need that much power. Your scaled down machine wont need that much, and even on the full size machines the flipper button contacts and pull-in contacts burn real quick and have a few ohms, they rarely ever run at full power for more than a few days. So they design them to be way over powered than they have some life before you need to replace the contacts again.

The pull-in contacts are unreliable and arc like crazy.

The best solution would be to use a fixed pulse length long enough to give good pull-in, the reduce to a PWM (to reduce average coil current) for the hold in. You only need the one coil winding and one driver transistor.

And personally I would use less than 50v, 24v even 12v should be fine for a scaled down table. Test your flipper setup with a variable bench supply and work out how much flipper power you need (like I said in my first post).
 
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