Capacitor Energy Density / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Capacitor Energy Density

1 2 next

Move Thread

LAN_403

Weston

Thu Sept 29 2011, 11:31PM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

What is a normal range for capacitor energy density (Joules/cubic inch) for electrolytic and film capacitors?

I just got a pule cap off ebay and was surprised on how small it is. Its poly film and 1440 VDC and 500uf. The dimensions are 4.1" by 5.5" by 1.4". This equates to a energy density of around 15 joules/inch^3

By comparison, a random electrolytic cap I have has an energy density around 4 joules/inch^3

Is the cap mislabeled? (It has a Aerovox manufacture sticker though) Or has film capacitor technology significantly improved?

Dr. ISOTOP

Fri Sept 30 2011, 02:47AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Almost certainly not a pulse cap.
An oil-paper Maxwell stores 250J and is ~12"x8"x2", which is a joule or two per inch^3.
A *good* poly film cap will be significantly lower, (maybe 100mJ per inch^3 for a nice pulse cap).

Weston

Fri Sept 30 2011, 03:38AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

The label says "Energy Discharge Capacitor 500uF 1440VDC"
Its made by aerovox. They make pulse capacitors and defibrillator capacitors.
I think it might be a defibrillator capacitor.

Turkey9

Fri Sept 30 2011, 03:45AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

I doubt that the label is correct. Those wires coming out of the top are no where near large enough to handle the current that a pulse cap of that rating would produce. They also look like they could only hand 120V DC not 1.4kV. Maybe a decimal point was worn off and they are rated for 144V DC. That would seem way more likely a voltage for a defibrillator.

The description also says that the wires are rated for 10 KVA which is a strange rating for a pulse capacitor. It would be much more likely for wires of a cap to be rated in amps.

All in all this thing seems a little fishy to me. Careful charging it when you come to that.

2Spoons

Fri Sept 30 2011, 04:28AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

Look at the Aerovox website: seems to have similar devices with similar dimensions.

Being a defibrillator cap, it may not be capable of 1000A discharges. I'm sure 10A is enough to give someone a hefty kick.

Weston

Fri Sept 30 2011, 04:43AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

I am holding one of the caps right now. It is clearly 500uf and 1440vdc. I think the "10KVA" rated leads are just seller hype. This weekend I am going to hook it up to the flashlamp for my er:yag laser head and see how it preforms.

Turkey9

Fri Sept 30 2011, 06:19AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

Wow must be some new technology that I haven't heard of. I hope you can get a lot out of that capacitor!

2Spoons wrote ...

You know that's a good point. 100mA across the heart can cause fibrillation.

Weston

Fri Sept 30 2011, 04:36PM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

From the aervox site, the capacitor could either be a pulse cap or a defibrillator cap.
Their line of poly film pulse caps have an energy density of up to 1.1 j/cm^3. The defibrillator capacitors have an energy density of up to 1.47 j/cm^3.

My cap has an energy density of 0.83 j/cm^3

Based on the custom part number and the lower voltage/higher capacity then the defibrillator capacitors, I beleive that it migh be a pulse cap for a flashlamp or something similar.

Forty

Sun Oct 02 2011, 10:22PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

I just put in a bid for one. If it does turn out to be legit then it would be a pretty sweet deal.

klugesmith

Mon Oct 03 2011, 03:36AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Weston wrote ...

From the aervox site, the capacitor could either be a pulse cap or a defibrillator cap.
Their line of poly film pulse caps have an energy density of up to 1.1 j/cm^3. The defibrillator capacitors have an energy density of up to 1.47 j/cm^3.

My cap has an energy density of 0.83 j/cm^3

Based on the custom part number and the lower voltage/higher capacity then the defibrillator capacitors, I beleive that it migh be a pulse cap for a flashlamp or something similar.

You taught me something here, Weston: the surprisingly high energy density of modern metallized film pulse capacitors.

There is no question, this is an Energy Discharge Capacitor a.k.a. a Pulse Capacitor. The closest I found on Aerovox website is QL232EW195, 195 uF & 2330 V. Practically identical to yours in energy and volume.

You may be right about the flashlamp application. Though whether for that or for a defibrillator (typical load is around 50 ohms resistive),

, I bet these guys are not designed for sub-millisecond discharge times and the associated high currents. Metallized film is known for self-healing around dielectric defects, not for ultra-high currents.

Can you tell us if the wire insulation marking includes "10 kV" ? Then the ebay seller saying "10 kVA" would be an excusable error.
If you tell us the wire gauge, we could determine the minimum discharge time if limited by wire heating (I bet it isn't).

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob