PDA

View Full Version : What's a capacitor bank for



Square Wave
08 December 2010, 1021
I saw this on Ebay:
http://cgi.ebay.com/Electric-Car-EV-Capacitor-Bank-DC-Motor-Controller-/200550403471?pt=LH_DefaultDomain_0&hash=item2eb1bc4d8f
Is this a legitimate performance enhancement? What does it do?

lugnut
08 December 2010, 1042
I saw this on Ebay:
http://cgi.ebay.com/Electric-Car-EV-Capacitor-Bank-DC-Motor-Controller-/200550403471?pt=LH_DefaultDomain_0&hash=item2eb1bc4d8f
Is this a legitimate performance enhancement? What does it do?

First off, I bet it is 6400uF, not 6400mF as he states. And I think it is just a couple of electrolytic capacitors in a box. Likely from a poor attempt at a homemade DC motor controller. See his other items. What does it do? Likely nothing, possibly filter out a bit of ripple, but a decent motor controller will do that on its own. You can buy electrolytic capacitors for less than this.

harlan
08 December 2010, 1230
No, I bet it really is 6400mF. A capacitor bank will improve your performance but not significantly, or even noticeably, unless you spend lots and have that kind of room to spare.

I installed a 5F cap bank in my bike rated for 81V and placed it in parallel with my battery pack. It did reduce voltage sag slightly on acceleration but the problem is, the only way to get energy out of a cap is to drop the voltage. If you do the math you'll figure out you need a whole of of capacitors to make it worth it. Caps are able to discharge at extremely large rates but the disadvantage is that they are expensive and not as energy dense as batteries. You money is better spent on upgrading your battery pack.

If you do however want to experiment with them, I have a used set of ultracaps available for purchase. Five of these to be exact: http://www.tecategroup.com/store/index.php?main_page=product_info&cPath=26_30_73&products_id=1225

lugnut
08 December 2010, 1319
No, I bet it really is 6400mF.......http://www.tecategroup.com/store/index.php?main_page=product_info&cPath=26_30_73&products_id=1225

If I was a betting man, I'd take your bet. 6400mF = 6.4F And he says it is for 200V and in a 6 x 6 x 4 inch box. You reference an ultracapacitor P/N PBL-25/16.2. That is 25F and 16.2V in a 3.7 x 2 x 2.25 inch package. Just by volume, only 8.5 of those would fit into his box. And to get near 6.4F at 200V, you will need 36 of the Tecate modules. And 36 of the Tecate modules will cost $4500. I think it is 6400uF on the ebay item.

harlan
08 December 2010, 1334
It looked bigger in the picture but now seeing the reservoir in the foreground and the battery in the back, you're probably right. Too small of a box for 6.4F at 200V. You win.

BaldBruce
08 December 2010, 1427
YEP. I see people misuse the "m" prefix instead of using the appropriat "u" prefix when stating the capactiance value all the time. I've even seen a rare capacitor salesman screw this up! With the current status of materials in the supercapacito field, no way you fit that much capacitance in that small of a box.