Ultra-Capacitor Voltage Regulation - Page 1
Forum section: electronics / projects

author: 6963641
author_rank: Newbie
timestamp: August 25, 2014, 05:17:33 am
content: Hi Everyone,This is my first post on this forum so if I do it wrong, please advise.I am currently designing a Battery Pack to be used in a solar powered vehicle for the World Solar Challenge.(Team Aurora).While my skills with battery control are half/decent, I wish to use a Capacitor Bank as a secondary energy storage module.My aim is to use the Capacitors for high loads such as acceleration and regenerative braking, however I am running into difficulty working with the 2.7/2.85 voltage limits.Capacitor energy storage rises as more are connected in parallel, however the voltage remains at 2.7/2.85. I will be building a test circuit with a 12V BLDC motor to run some tests But I am having a hard time finding a cheap voltage regulator that can handle 0.5V - 5V input - 12V output.If anyone has any insights on how to work with these components, any help would be greatly appreciated^^.Also does anyone know if I can use similar battery balancing techniques to Lithium Ion batteries to balance capacitors?This is my Final year project for Robotics Engineering at Swinburne University.Cheers,Edwin

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: August 25, 2014, 05:36:35 am
content: I'd worry about temperature too.

author: LabSpokane
author_rank: Super Contributor
timestamp: August 25, 2014, 05:48:33 am
content: You're really looking for a boost converter to go from low to high voltage.I looked into using banks of super caps a few years back. Make sure you read the manufacturers recommendations on cap balancing. There are/were some issues there. Do consider the prefabricated cap banks that places like Maxwell sells. Not cheap, but the hard work is already done for you.http://www.maxwell.com/products/ultracapacitors/products/16v-large-modules

author: IanB
author_rank: Super Contributor
timestamp: August 25, 2014, 05:49:02 am
content: Quote from: Alex Eisenhut on August 25, 2014, 05:36:35 amOn watching Mike's recent video on the satellite fish transponder buoy it seems that ultra-capacitors may have a very wide operating temperature range.

author: IanB
author_rank: Super Contributor
timestamp: August 25, 2014, 05:53:19 am
content: Quote from: 6963641 on August 25, 2014, 05:17:33 amI think you most likely would need to put enough capacitors in series to get the voltage you need. With high loads as you describe, putting a voltage converter in the middle is going to be inconvenient.The comment above about prefabricated capacitor banks makes a lot of sense.

author: David Hess
author_rank: Super Contributor
timestamp: August 25, 2014, 05:54:41 am
content: Quote from: 6963641 on August 25, 2014, 05:17:33 amThere are not any which will meet your power requirements at such low voltages; the IR losses at low voltages are just too high. Since most of the energy from the capacitors is available at higher voltages, this is not much of a loss.QuoteThere sure is and I would consider it mandatory in this sort of application. The balancing currents however will be high to match the high power densities involved. I looked into this when considering how feasible it would be to use a bank of ultracapacitors in place of a starter battery. I found several articles on the subject of balancing ultracapacitors but nothing was particularly unexpected except that ultracapacitor life decreases 10 times for every increase of 0.2 volts.

author: Artraze
author_rank: Contributor
timestamp: August 25, 2014, 02:26:00 pm
content: Quote from: IanB on August 25, 2014, 05:53:19 amSince capacitors don't provide a constant voltage supply it would be hard to avoid a converter anyway. Granted, the motor driver probably works from variable supply voltages without issue (being a current-mode device, I hope!). However working only in the range of 12V - 16V means under utilizing the caps by around 12^2/16^2 = 56%, in likely the best case. Increasing the max voltage helps, but adds more troubles too (e.g. generating it with a 12V motor, limits of the motor drive).Also, what sort of power are you looking at?

author: David Hess
author_rank: Super Contributor
timestamp: August 25, 2014, 03:27:06 pm
content: Quote from: Artraze on August 25, 2014, 02:26:00 pmIn the past with similar circuits, I assumed a 4:1 range at low powers and a 2:1 range at higher powers. The later yields almost 75%.

author: Marco
author_rank: Super Contributor
timestamp: August 25, 2014, 05:51:14 pm
content: Quote from: 6963641 on August 25, 2014, 05:17:33 amYou need current based load balancing and bidirectionality any way, just getting it to 12V isn't enough. For bleeding edge efficiency this stuff really should be rolled into the motor controller, otherwise you're compounding losses ... I think it would be master level thesis work though.

author: DanielS
author_rank: Frequent Contributor
timestamp: August 25, 2014, 06:51:47 pm
content: This is a bit like trying to get the maximum performance out of lithium: ideally you would want a charge controller monitoring and charging/balancing every cell individually... put the baseline charge current through the whole stack and then use per-cell DC-DC converters to increase charge current to cells that are falling behind.A less efficient balancing scheme would be to shunt power on cells that have higher voltage than others.

author: David Hess
author_rank: Super Contributor
timestamp: August 25, 2014, 09:51:13 pm
content: Here is a link to the article I found most useful about UltraCapacitor balancing:http://hal.archives-ouvertes.fr/docs/00/41/14/82/PDF/ESSCAP2006_Venet_2.pdfThe only problem with a high power design is that balancing will require proportionally high currents so passive balancing is out because of heat dissipation.

author: 6963641
author_rank: Newbie
timestamp: September 01, 2014, 05:26:25 am
content: Thank you everyone for the feedback and advice put forward^^.For the low power system 11-15V, I will be hacking into an accucel6 balance charger to change the voltages for ultra-capacitors(hopefully).Just a thought,If I were to use 2 series lithium ion cells in parallel with 3 ultracaps. Would the ultracaps take the priority on high loads due to the lower internal resistance?This way I could use a single battery balance controller to keep everything under control?Has anyone attempted this?

author: IanB
author_rank: Super Contributor
timestamp: September 01, 2014, 06:27:44 am
content: Quote from: 6963641 on September 01, 2014, 05:26:25 amI'm not sure how that could work. Battery balancers use intermediate voltage taps between the cells to sense each cell voltage. With two lithium ion cells you would have one center tap, but with three capacitors you would have two taps at different intermediate voltages.