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Jan 22, 2013, 07:29 PM
Registered User

Help Me Build a KERS system (Non RC Related)

Hello All, Long story short, one of my many hobbies is racing Karts. No, not the go karts you rent at an amusement park.... These are F1 training tools. WE pull 3+ lateral G's in corners, our acceleration and braking forces are spot on with Formula 1, and there is nothing that compares to Fromula 1 other than Race Karts. On a side note, F1 Drivers almost always use Karts to train during their off season.

Back on topic, I race a class called Tag. We have 40-45bhp (horsepower at the rear wheels), and we weight in at 365 pounds on the scale. These karts can go anywhere from 80-100+ depending on gearing and the track. 365 pound weight is a class spec rule, and we MUST weight 365. That being said my 135-140 pound human body, and 180 pound kart needed to strap on 50 pounds of weight to be "legal."

Well, thats Karting in a nutshell. However we often get caught bragging about the similarities between race karts, and F1, and now I am on a mission to bring us one step closer. I want to create a KERS system.

Here is an explanatory video for your viewing pleasure.
BBC F1: The KERS Unit Explained with Andy Cowell and Gary Anderson (2 min 2 sec)

My Idea is Very simple. If you look in the Attached pics, our brakes have two master cylinders actuated by ONE rod to the brake pedal. We adjust brake bias by screwing the bolt left to right either pulling harder on the front, or rear master cylinder.

In the class I race we are not allowed to have front brakes, So my Idea was to have a Hydraulic clutch actuated by the (front brake) master cylinder. This would allow you to adjust the differential between the hydraulic brake, and the electrical motor braking. This system would put electric energy into either Capacitors, or Batteries. The clutch and gear for the Electronics would be the opposite side of our engine.

After a few corners (braking) the system would have enough power to provide 3-10kw of power (or 4-13hp) available in quick bursts, strategically used coming out of a tight corner. This would provide a 15-30% boost in power, trumping that of F1 who gain 80bhp at a mere 11-13% gain in power. However their system weighs in at a total of 50 pounds with an output of 80bhp.

I estimate with the right execution I could have this system weigh in between 15-30 pounds providing 3-10kw of "boost" power.

Any of you Electrical Guru's willing to help on this one?

I know Eddie has done some pretty promising work with his gas powered electric generator powered multi rotor! Seen here:

And Here is a some onboard Karting Video for your Pleasure. No, t is not sped up. Skip to 6:15, as the rest of it was Jumped starts (causing 2 re-starts).
SKUSA SuperNationals XVI - TaG Sr. - Heat 2 (GoPro) (16 min 44 sec)

Rotax MAX Challenge Grand Finals 2012 - Race Day (4 min 46 sec)
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Jan 22, 2013, 07:58 PM
Registered User
you want 3-10 kw at what voltage?

Edit: I think you are trying to build this from scratch - so voltage is in the air..

That being said....

Generally you will end up with a clutch grabbing the electric motor which will need to go to a rectifier and then to caps.

Now then... your best power to weight will be with super capacitors (maybe). They have a caveat though. They can only handle 2.7 volts max each so you will need to use several in series. They also have a lower discharge rate then regular electrolytic caps. But they have MASSIVE capacitance compared to electrolytics.

Just some stuff to think on
Jan 22, 2013, 08:05 PM
Registered User
I was thinking a recovery of 40-50 volts.

The Electric motor wont be able to provide as much power as the gas at top-end but it will give me quite a bit of bottom end pull. With proper gearing this means that my braking (which occurs at higher speeds) would provide a high enough input, to hopefully get 40-50 volts back at or around 150-200 amps.
Jan 22, 2013, 08:09 PM
Registered User
I think supercaps may be out then - I just looked at some data sheets. They don't provide enough current.

The next question is, how many seconds do you need this boost?
Jan 22, 2013, 08:15 PM
Registered User
2-5 seconds.

5 Optimal, but really even 2 would be huge. It would need to gain this approximately 2 seconds each lap. A lap is about 50-56 seconds with 10-15 turns. This would allow for 7-10 braking points.

If I could regain 2 seconds each lap, that would be awesome. If I could save it over 2-3 laps and get one 6 sec, or two 3 second bursts (or 3:2 etc...) that would be even better...

The 80-150cc Electric equivalent motors I have seen operate between 40-50 volts and 150-200 amps. KV is only a concern to me for charging, as the powered side of it will be geared accordingly. The motor would have a pinion gear between 20-25T and would run on a 80-85T chain ring.

I am also not against having a flywheel so the motor can maintain charging a bit longer, however I wouldn't want that flywheel to effect output power. The other concern is a 20-30 pounds overall package. (should be pretty easy, the 150cc equivalent motor weighs 5.5 pounds.)
Jan 23, 2013, 05:44 AM
Life begins at transition
Just running some quick numbers...

5 of these 3kF caps would weight in at 2.5kg. 12.5kw peak power (in the 5cap stack), at 12.5V.
Around $270 per piece.

35 of these 400F caps would weigh 2.5kg too. Peak power isn't specified in the datasheet, but it'll be similar to the above. 87.5v all in series, or 42.5v in 37s2p.
$70 per piece ($2500 in total!)

I sized these off the 5second, 10kw requirement (50kj) Seems reasonable so far, depending on budget
Jan 23, 2013, 11:20 AM
Registered User
Most really large caps are homemade. Commercial ones are just too expensive. Look up some of the info on tesla coils. Those guys have lots of guides on making large, high-voltage caps.

You might also want to look at regenerative braking systems for electric bikes, I know there are several out there.
Jan 23, 2013, 02:19 PM
Registered User
hmm I will look into that.

The Capacitor doesn't have to be large, it only needs to be able to put out ~140 amps for 2-3 seconds at 45-50 volts. I would understand large batteries or capacitors if I were asking for thousands of volts, or thousands of amps.

Thanks for the help thus far guys!
Jan 23, 2013, 02:52 PM
AndyKunz's Avatar
How many Joules is that? That will tell you how to size the system better.

Jan 23, 2013, 02:58 PM
Registered User
The system is fairly simple. Even with unefficient energy regeneration, the amount of kinetic energy wasted in corners is huge. Our braking forces are huge, and the 2-3 sec burst is quite small.

I am a professional aircraft electrician by trade. The wiring, and mechanical set up is simple. I am just having trouble figuring out how to retain and temporarily store the power.

IE, it needs to hold charge for ~2 minutes, with a discharge capacity of ~1 amp hour, or even less. I only need 140 amps for 2-5 seconds. So realistically (less than) .3-.7 usable amps, with a discharge of up to 140/150, at a voltage of 40-50v
Jan 23, 2013, 03:11 PM
Registered User
So I need a regeneration of about 18,000-45,000 Joules.

This would be 9,000 watts (or 12 horsepower) for a total of 2-5 seconds of burst. (2 being 18k joules, 5 being 45k joles)

Now this would be for the "most powerful" set up using the 12-13 horse 150cc equiv motor. If I use the 100cc or 80cc, it would still be more than enough power, and way lower in needed energy.
Jan 23, 2013, 03:19 PM
Registered User
I don't know much about what caps/batteries would work best for you. But I have seen quite a bit of info on making large caps. They roll up plastic and insulate with oil for the big ones. Maybe some of that info will be of use to your project. Building your own will hopefully save money and let you build ones as big as you need. Good luck, and let us know how it turns out!
Jan 23, 2013, 03:22 PM
Registered User
The problem with batteries so far is the size (capacity, I dont need much), to charge and discharge rate (which needs to be really high)
Jan 23, 2013, 03:24 PM
Registered User
You might parallel up a bunch of smaller batteries to get the current and charge rate you need. LiPo will take somewhat of a sophisticated charge/discharge system though. Probably not all that difficult if you know what you're doing and/or are any good at uC programming.
Jan 23, 2013, 05:02 PM
Life begins at transition
For a 5second charge/discharge cycles, you can pretty much forget batteries (unless you're happy using 1/10th of their useable capacity)

A 5 second burst of braking is a 120C charge rate!

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