Ultra-Capacitor Powered Car - Page 1
Forum section: electronics / beginners

author: GrantRitchie
author_rank: Newbie
timestamp: November 09, 2015, 09:08:03 pm
content: I'm working on a project to design and build a 1/10th scaled ultra-capacitor powered electric car. I'm a Mechanical Engineer & I really want to focus on the the building and testing of the vehicle - not the electronics, which is why I need your help!As I have a limited electronics knowledge I was hoping that I could run my initial control system design past some of you in the hope you'd be able to confirm my ideas and maybe point me in the direction of some suitable hardware. Or help correct my errors.Here is a basic modular outline of my design: Modular Diagram[Modular Diagram][http://s8.postimg.org/3pw1hnlh1/Screen_Shot_2015_11_09_at_16_52_51.png]The plan is to have 3 ultra-capacitors connected in series using the Maxwell Integration Kit. I know I need a Buck-Boost converter with the voltage and current rating of the motor. Ideally I'd like something off the shelf - I was investigating these modules from Linear Technology ([http://www.linear.com/solutions/Supercap,_Capacitor_*_Battery_Back-Up_Solutions]). Would these do the job? Or is there something better out there without creating one from scratch?I'd also like some motor controller which integrates some form of speed control and outputs the speed, distance travelled etc. I've not researched this in too much detail yet as it's an added extra and not essential.The motor can then be decided based on the parameters of the rest of the control system but I require a minimum motor torque of around 0.2Nm. I'll probably go for a DC brushless based on efficiency.The vehicle is intentionally simple and the target is to drive a 50m straight journey at a constant speed.Thanks in advance for your time and please let me know what you think.

author: max_torque
author_rank: Super Contributor
timestamp: November 09, 2015, 09:40:22 pm
content: If you are just interested in the mechanical build of the car, do yourself a big favour and just use an "off the shelf" powertrain with batteries!

author: tszaboo
author_rank: Super Contributor
timestamp: November 09, 2015, 09:44:16 pm
content: Hi,I did recently calculations for these capacitors. You need to be aware that the capacitors have very little energy stored in them. I mean these big cells have less energy than a AA battery, and fraction of a similar sized Lithium battery. Probably 50m is a good estimate, but calculate the power.You should be using a buck boost if you need to have the voltage below or above the capacitor voltage. Since your output voltage is going to be 12V or 24V (how much power do you need for the motor?), you need a boost converter, not buck-boost.There should be several demo boards which are available from the manufacturers. It is not rude to ask them to send you it for free. If you are a student, or your work goes into publication, I'm quite sure they help you. Otherwise they cost around 50-100 Euros/USD/GBPs.Same goes for the motor controller. Texas Instruments claims that they have brushless controllers, which you can get spinning in 5 minutes.And just for the 'mericans: A 10F capacitor contains half the amount of energy of a 9mm bullet, as the Dicovery channel would say.

author: SL4P
author_rank: Super Contributor
timestamp: November 09, 2015, 10:15:54 pm
content: Quote from: NANDBlog on November 09, 2015, 09:44:16 pmAGREED. Stepping in here... please correct me.I see a lot of magic being offered for super caps, but this seems like a big problem...in my understanding, (any caps) are great at charging very quickly, and really good for holding energy when you need to use it slowly over a period, or for a heavy dump in an instant. Both things that batteries are not very good at.But as a battery replacement in cases like this (a motor under load), they're virtually useless for continuous operation.. other than acting as a capacitor to filter out supply noise.Please set me straight.I'd love to know what science these stories are based on. I've used Supercaps for clock backup, or peak power smoothing, but can't see any practical goal, if I have to carry a massive power supply around - in order to recharge every 30 sec between discharges!?

author: nidlaX
author_rank: Frequent Contributor
timestamp: November 10, 2015, 02:35:27 pm
content: If not constrained by cost, maybe you can consider using lithium ion capacitors instead?Sent from my LG-E970 using Tapatalk

author: SL4P
author_rank: Super Contributor
timestamp: November 10, 2015, 02:42:48 pm
content: Dave, or any other suitably savvy engineer with experience in DC power electronics...Can you shed some clarity in this discussion?Ive read about Supercaps being used to power everything from mobile phones to buses... where's the truth?

author: Delta
author_rank: Super Contributor
timestamp: November 10, 2015, 02:43:08 pm
content: A small 2-stroke engine sounds ideal for this application.

author: tszaboo
author_rank: Super Contributor
timestamp: November 10, 2015, 02:56:19 pm
content: Quote from: wilfred on November 09, 2015, 11:41:35 pmI think the viability is questionable at best. I was doing calculations for a moving vehicle, the LiFePO4 solution went for a few hours, a similar size supercap went a few tens or meters. An then you need recharging. The LifePO had a dedicated charging station, with an off the shelf battery charger, the supercap solution had several, kilowatt sized power supply, where you need to add extra current limit, high current contacts (or a wireless with kilowatts of electrosmog), Buck boost for the power... The built in power supply capacity overall was like 10 times than the battery solution. Than we realized that if the vehicle gets stuck between charging stations, it is really stuck. While with a battery, you can still go minutes when the battery is at 10%.They did supercap bus in China. It doesn't make sense IMHO. Use a trolley bus, that is proven technology for the last decade. And yes, I had 1000F+ ultracap in my hands, it is impressive and scary.

author: timb
author_rank: Super Contributor
timestamp: November 11, 2015, 01:14:47 am
content: Quote from: wilfred on November 09, 2015, 11:41:35 pmBuses and other large vehicles use the caps for regenerative braking. That is, when stopping, the electric motors are disconnected from the battery bank and connected to the super capacitor bank. This puts a load on the motors, which now act as generators; the extremely low ESR of the caps looks almost like a dead short. This heavy load on motors acts as an EMF brake, slowing the bus and charging the super caps.Then the stored energy in the super caps is used to get the bus moving again once the stop is over with. This both saves wear and tear on the conventional leaf spring or drum brakes *and* extends the run time.I've also seen this system used in garbage trucks. (It works well for any heavy vehicle that makes frequent stops.)The reason super caps are used is because they can charge/discharge quickly and have a long life compared to a battery.Sent from my Tablet

author: SL4P
author_rank: Super Contributor
timestamp: November 11, 2015, 01:29:24 am
content: So the bottom line seems to be that caps are only viable to augment other traction power or braking systems - and not a solution in themselves ?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 11, 2015, 04:14:25 am
content: Until supercaps get another few orders of magnitude more super they won't be the primary source for traction power. What they can do is allow designing the battery and charging system for the average power draw of the system, using the supercap to supply/absorb short term transients. That is not a negligable contribution.I wouldn't totally reject the possibility of supercaps getting that much more super. I can certainly remember when any engineer in the world would tell you that you were into the funny juice if you talked about capacitors measured in even fractions of Farads (unless they were some physics experiment filling a warehouse). Available capacitors have gone up roughly 5 orders of magnitude in capacitance since I was in high school, with stored energy up by maybe an order of magnitude less.