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Author Topic: What size capacitor needed to power solenoid?  (Read 3906 times)
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Montreal
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Well, It is unlikely to see fireworks on a circuit that supply just 50 Amps, probably even less.
I know, that Capacitive Discharge Spot Welder delivers >2000 Amps in the same time frame.

http://www.shearconnectorwelding.com/capacitor-welding-machines.html
http://www.philpem.me.uk/elec/welder/
http://ultrakeet.com.au/index.php?id=article&name=cdWelder

And there is a link to capacitor selection tab:

http://frikkieg.blogspot.com/p/capacitor_04.html

Plus video:
http://frikkieg.blogspot.com/2009/06/homemade-capacitor-spot-welder.html



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Fort Worth, Texas
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I have reconsidered the capacitor vs. battery solution. I don't want a capacitor exploding inside my control box. I do have a few SLA batteries laying around I can use...20ah capacity. I would rather use a 12v trickle charger to maintain the battery and keep this part of the project separate from other power needs (stepper motor and Arduino). Terry, I don't have an Oscope, but will take your advice and use a suitable diode across the solenoid terminals. As for switching...do you prefer the FET board over using a SSR good for 40 or 60 amps? As you mentioned, pulling 40 amps in 50ms isn't going to happen.

Thanks,
Cris
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Manchester (England England)
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Quote
Well, It is unlikely to see fireworks on a circuit that supply just 50 Amps
Not sure what planet you are on but 50 Amps is a lot of current on this one. You can get quite spectaular with that amount of current.

Quote
I know, that Capacitive Discharge Spot Welder delivers >2000 Amps in the same time frame.
And did you see the size of those things, they weren't cobbled together by an amateur.
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Red Sea, Saudi Arabia
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I As for switching...do you prefer the FET board over using a SSR good for 40 or 60 amps? As you mentioned, pulling 40 amps in 50ms isn't going to happen.

...

If you can get a DC type SSR like that it sounds like a good solution.. 

Let us know what works out so we learn too  smiley-cool
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Regards, Terry King  ..On the Red Sea at KAUST.edu.sa
terry@yourduino.com  LEARN! DO! (Arduino Boards, Sensors, Parts @ http://yourduino.com

Fort Worth, Texas
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Well I ordered a Chinese build 40 amp DC to DC SSR, but I'm going to order that FET board as well...I'll try out both and report back on how things work out.

Thanks,
Cris
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Turn-on time for a DC SSR will be considerable slower than a FET.  This might have a bearing on how quickly you can get the required energy into your solenoid, the inductance of which will itself tend to slow down the current in-rush.
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Bute, Scotland
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Came across these today. U.K supplier :
http://www.distel.co.uk/Asps/details1.asp?ID=HP23
The coil on these is low current but you could drive them in series from the 24 volts without the 24 to 12 volt conversion and with contacts on the relays in parallel
from a relatively low power transistor I think.
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Fort Worth, Texas
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Well, I was trying to stay away from a mechanical relay. Received the SSR I ordered from the west coast and it pulls the solenoid in pretty good, only problem is my Arduino doesn't have the power to pull in the SSR! Now I've got to either use a power transistor or reed relay to pull in the SSR..... Just added more complexity to the whole thing.

Cris
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