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Author Topic: Capacitor discharge unit for solenoid  (Read 1147 times)
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Can someone point me in the right direction on how to make a capacitor discharge unit and how it works? its to make a solenoid kick. or should i try another approach. im definitely not sticking batteries in parallel/series. i need to save space and weight.
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I'm not aware of any general references on this topic. Can you tell us what the application is, what are the voltage and current ratings of the solenoid, and how long you need to activate it for?
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You'll probably just have to experiment...  maybe try a 1000uF cap, and see what happens...  The bigger the better... Have you got any caps on-hand?

Do you have the specs for the solenoid?  If the solenoid needs to hold, a capacitor isn't going to help that much...    If the solenoid just needs to activate for a fraction of a second, and then return to it's resting-state, a capacitor should help.   Or, it might help if you have a borderline case where the solenoid "almost activates" without the cap.   (It takes more voltage to activate/pull the solenoid than it takes to hold it.)

Once the capacitor discharges (probably a fraction of a second with a solenoid-coil as a load) the capacitor is not going to do anything.

You can look-up Capacitors on Wikipedia if you want to know how to calculate the discharge-rate.   There is something called the "R-C time constant" which is the discharge rate/curve into a resistor.  (A coil will be slightly different.)
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Ebay has some nice 1F 5v caps for pretty cheap I think 3 for 5$ I got
you could put them in series until you get the proper voltage rating and then use extra space to put them in parrallel
say 3 in series to get 15v then with say a 1 ohm solenoid resistance you get 15 amps max, 5 amps a sec later, 2 amps another sec later then less and less
Less resistance will make it more amps for a shorter time, more resitance means less amps for a longer time
and these I saw are pretty small you could probably get 12 on the space of an arduino, so if you added in series and charged them with 60 volts you can get 60 amps thru your 1 ohm resistance, which I would suggest not being around when that happens lol
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Ebay has some nice 1F 5v caps...  for pretty cheap I think 3 for 5$ I got
you could put them in series until you get the proper voltage rating...
I would NOT recommend that!  With capacitors in series, you cannot count on the DC voltage being divided equally.  Due to internal variations, the caps won't charge-up equally.   One capacitor is probably going to end-up with most of the voltage across it...  'till it "blows".  Then, it's going to short-out and the voltage will "move" to a different capacitor, and it will blow, etc.

Also, when you put capacitors in series you decrease the capacitance.   

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... so if you added in series and charged them with 60 volts you can get 60 amps thru your 1 ohm resistance, which I would suggest not being around when that happens lol...
I don' thave the specs, but due to the capacitor's internal series resistance (and the initial inductive reactance in the coil), it's very unlikely that you could get that much current.
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Well for in theory it works lol
and I though capacitence stays the same in parallel? And voltage is the same in series
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ok solenoid specs are 36v, takes in 2amps. any amendments?
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ok solenoid specs are 36v, takes in 2amps. any amendments?
Get (or build) a 36V/2A power supply and forget about the capacitors & "voltage multipliers".   That's 72 Watts!  You need to get 72 watts of power somewhere.

How big is yyour batttery?   Do you have a 72W battery?   If you are running off a car battery, you can get/build a power inverter to boost the voltage at that kind of current, but in that situation it makes a lot more (economic) sense to use a 12V solenoid.  And, it's not problem getting 72W (6 Amps @ 12V) form a car battery if you need a solenoid with that much power.
« Last Edit: March 13, 2012, 06:56:46 pm by DVDdoug » Logged

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i've got a 7.4v lipo. which is why i wanted to use a capacitor
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An LM350 linear power regulator can give you 33 Volts at up to 3 Amps. Scrounge a couple of small caps, four diodes and a power transformer with a step down greater than 35 Volts and you could put that together in under 30 minutes.  (It will take you longer to scrounge parts.)

Better than batteries and realistic possibility.

You'll want the LM350K in a TO-3 package with a heat sink pulling the Amps you require.

Watch for electronics put out at the curb on trash day. You'll find a wealth of parts. The only bug-a-boo will probably be the transformer.
« Last Edit: March 13, 2012, 09:45:52 pm by Rod_D » Logged

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Quote
... so if you added in series and charged them with 60 volts you can get 60 amps thru your 1 ohm resistance, which I would suggest not being around when that happens lol...
I don' thave the specs, but due to the capacitor's internal series resistance (and the initial inductive reactance in the coil), it's very unlikely that you could get that much current.

Well once the magnetic core of the solenoid saturates the inductance will drop to next to nothing, so yes it could easily jump to 60A - not very useful, that's more likely to vaporise the winding than anything else...  High voltages get the solenoid to response faster, but you want to limit the capacitance so it doesn't then just waste energy heating/melting the windings...
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