What is a "Digital Capacitor"
What is a "Digital Capacitor"
(OP)
I see these "Digital Capacitors" being advertised for car audio and they just seem too good to be true. They claim to be 24V capacitors with values from 1 to 5 Farads! They only cost between $30 to $150 dollars. When I look at anything that comes close from digikey it costs around $3000 dollars. Could someone explain what this discrepancy is all about.
I am looking for a low cost capacitor bank for a spot welder I am designing. Heck, if these things are for real they would provide a voltmeter for free. Something tells me this isn't going to work though.
Thanks for reading,
Ashard






RE: What is a "Digital Capacitor"
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If we learn from our mistakes I'm getting a great education!
RE: What is a "Digital Capacitor"
You may need to discharge a set sequentially so you don't get a very high initial discharge and next to nothing the following few hundred milliseconds. It depends. If you are working with heavy plates (all is relative) like car body work, then you need several hundred milliseconds. But if you are welding thin material, a single discharge will work quite well.
If you tested these capacitors about ten - fifteen years ago, you would have been very disapointed. They had a rather high internal resistance and could typically be used as a memory back-up supply only. That has changed drastically.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: What is a "Digital Capacitor"
Definitely using ear plugs and safety glasses for this test. I'll let you know how it goes.
Thanks for your thoughts,
Ashard
RE: What is a "Digital Capacitor"
The ghetto blaster usage can be pretty close to short circuiting also.
I think it will be fine.
I've seen builds using them for spot welding.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: What is a "Digital Capacitor"
Inductance in the loop will probably play a greater role than your .04 ohms. So, try different lead configurations. As close as possible is usually best for highest discharge rate and minimum ringing.
And, for measuring the current pulse, use a fast Rogowski coil. The ones from Fluke have limited band-width and do not work. Also, their current range is too low. A coaxial shunt is usually best for these measurements.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...