Minimizing weight

[Marco Antonitti]

Just to start, I'm new to the site, but have been on it quite often, seeing what's been going on around the different schools. Just to say a bit about myself, I'm from Montreal Canada, I graduated from mechanical engineering, and have a diploma in car mechanics. I'm currently studying aircraft mechanics since I work as a mechanical system designer in the aerospace industry.

I had taken part of the sae team in my school, unfortunately due to budget cuts, we got the short end of the stick. Regardless, my dream is to build my very own.

I'm not planning on using this car to compete in SAE, but I would like to follow the rules to some extent. I'm working on figuring out what I want out of the race car. I'm a huge fan of light weight/strong systems.

In short, my question is, how many of your cars have batteries in them, and who has replaced them with other means, such as capacitors? THis is the start of my modification. In fact, the use of capacitors to run the electrical system in the race car will be my test for my next modification.

I'd really like to know what you guys are doing. thanks!

[Marco Antonitti]

Just to start, I'm new to the site, but have been on it quite often, seeing what's been going on around the different schools. Just to say a bit about myself, I'm from Montreal Canada, I graduated from mechanical engineering, and have a diploma in car mechanics. I'm currently studying aircraft mechanics since I work as a mechanical system designer in the aerospace industry.

I had taken part of the sae team in my school, unfortunately due to budget cuts, we got the short end of the stick. Regardless, my dream is to build my very own.

I'm not planning on using this car to compete in SAE, but I would like to follow the rules to some extent. I'm working on figuring out what I want out of the race car. I'm a huge fan of light weight/strong systems.

In short, my question is, how many of your cars have batteries in them, and who has replaced them with other means, such as capacitors? THis is the start of my modification. In fact, the use of capacitors to run the electrical system in the race car will be my test for my next modification.

I'd really like to know what you guys are doing. thanks!

[PBnG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">In short, my question is, how many of your cars have batteries in them, and who has replaced them with other means, such as capacitors? </div></BLOCKQUOTE>

You could replace the simple and reliable lead-acid battery with super capacitors. Forgive me if I am wrong, but I'm under the impression that super-capacitors offer an order of magnitude less energy density than even lead-acid batteries. There are more energy dense chemistries available that fit this application.

[Marco Antonitti]

that's right, I would replace them with super-capacitors. Can you explain what you mean by "less energy density than even lead-acid batteries"?

I would like to do this as a test, my intentions for the race car will be to go completely electric. I would use a motorcycle engine (suzuki gsxr 600 engine...something I have available) as a temporary installation. Get the chassis and suspension setup, and then start swapping pieces. Obviously it won't be that simple, but that's the direction.

So does anyone in sae use super-caps instead of batteries. Just in electrical systems alone, a lot of weight can be saved as well as reduce maintenance.

[jaca]

I've seen battery eliminator kits for carb'd motorcycles before that are basically just a big capacitor. For an FI engine, things get more complicated.

If you're bump starting the car, you'd at least need a small power source to keep the engine electronics online before the alternator starts generating power. Keep in mind that the instantaneous current draw of a 4cyl COP ignition can be around 10 amps, plus the injector draw, plus ECU.

If you're using an external battery to crank the car you could probably get by with just a big capacitor, assuming that you're producing well in excess of the current that the car draws.

Sizing the cap is left as an exercise for the reader, and don't stall it off the line http://fsae.com/groupee_common/emoticons/icon_smile.gif

[exFSAE]

Now I'm no electrical guru...

...but don't capacitors just rapid discharge? How would you run a car off this? Just to crank the thing initially and then run everything off the alternator? If that's the case hell, don't have a cap at all, just jump start it.

But then of course you can't restart.

I'd run a battery. There are really good, small ones out there.

[PBnG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">"less energy density than even lead-acid batteries"? </div></BLOCKQUOTE>

Energy density: Wh/kg or MJ/kg. If you require a certain amount of energy storage, you minimize the weight of your energy storage device by using choosing one with a <STRIKE>lower</STRIKE> higher energy density (lower weight for a given energy capacity.)

The energy density of a lead acid battery is around ~0.1 MJ/kg. Lithium batteries for a similar application are ~0.3 MJ/kg. Super/Ultra capacitors have somewhere around a tenth of these energy densities. This comes out to approximately 10x the weight for the same amount of energy storage.

Capacitor technology has come a long way, though.

[Marco Antonitti]

1) TO Jaca, it would be for a FI engine. MY intentions are to definitely use the capacitor to start the engine. Also, I can use multiple capacitors. I have already gone to visit a company who will be providing super-caps for our public buses and they have a super cap (don't remember the rating) that weighs pretty much nothing, and capable of starting an engine. sizing the cap is something I'll be working on along with this company.
2) To exFSAE, yes capacitors do rapid discharges, which is great for starting, as long as we can get enough current to the electric starter motor; however, there are ways of controlling it's discharge. I'm going to be trying to use the cap in the same way the battery is used. Yes most electrical requirements will be provided by the alternator, but the cap will always have to be charged correctly.
3) To PGNG: I will have to look into their energy density, once again, I'm a mechanical guy, i just have a great interest in trying something new. Even if it doesn't work, mind as well try. This technology may not be relevant to small racecars, but maybe useful in other domains.
I'll be doing some more homework on this topic. I'll let you know what I find. So I take it that no schools are doing this as we speak?

[PBnG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Marco Antonitti:
I'm a mechanical guy </div></BLOCKQUOTE>

No worries, dude! Trying something new is what FSAE is all about. Don't fear the fog!

BTW: I'm a computer guy and have laughable knowledge of mechanical systems. Even the new members get a kick out of me.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Marco Antonitti:
So I take it that no schools are doing this as we speak? </div></BLOCKQUOTE>

I haven't heard of any teams using a supercap to start their car, but that doesn't mean it hasn't been done. They don't let me out much.

I think a super-cap matched with a smallish (comparatively) low cranking amp battery in a "hybrid" setup could be interesting. That could provide a lot of "oomph" for that initial stall current of the starter!

[Shashi]

We would be going for a Lithium ion Polymer battery this year. I don't have any hard numbers on it, but I think it gets down the weight of the battery from 3.8-4 kilograms right down to some 0.6 kilograms.

[DG]

They also blows up in spectacular style when they overheat, as an added bonus

[Shashi]

Yeah. I heard about that too. And also some quick discharge problems. Sorry, I don't have a clue why that happens. That was a problem some teams had in FSG 2009.

[PBnG]

Thermal events aren't pretty, ask Sony. Choose battery chemistries wisely Sparky-san.

[Zac]

just a word of caution. when you are looking at energy density don't forget to include the weight of the charging system in your calculations. having a battery with 3x higher energy density doesn't help you out very much if it requires another 10 pounds (gross exaggeration) of electronics to integrate it into the car.

[Kirby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Shashi:
We would be going for a Lithium ion Polymer battery this year. I don't have any hard numbers on it, but I think it gets down the weight of the battery from 3.8-4 kilograms right down to some 0.6 kilograms. </div></BLOCKQUOTE>

Might want to run those numbers again chief.

As Zac mentions, you forget the charging system:
-Rectifier (Diode Bridge or 'Smart' Rectification)
-Voltage regulator (needs to be increased for Li-Po float voltage)
-Controller uC
-Charge FETs
-Discharge FETs
-Big Heatsink to bleed off all those Watts
-Enclosure for cells

Or alternatively you could just run the UWA method of Lithium Ion....

Then remember that advanced chemistry is $65/kg in cost compared to $3/kg for SLA.


I dare say that 3.8-4kg is on the heavy side of SLA's that teams run.

[PBnG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">the UWA method of Lithium Ion.... </div></BLOCKQUOTE>

And what would that be?

[Shashi]

I think that weight is only for the battery and not for the entire system. I'll cross check it nevertheless.

[Kirby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PBnG:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">the UWA method of Lithium Ion.... </div></BLOCKQUOTE>

And what would that be? </div></BLOCKQUOTE>

Circa 2008:
3 packs in parallel, under the seat.
No controlled cell balancing, no charge/discharge controller.

And rumored to get hot enough to feel through the seat after enduro.

[Thrainer]

We're in the 21st century, why are you using lead in your car? http://fsae.com/groupee_common/emoticons/icon_wink.gif

For the lightest setup, I'd use LiPo batteries without an alternator. Just take enough capacity for the endurance and don't forget to recharge for longer testing.
For the lightest reliable setup, I'd use LiFe batteries and keep the alternator. The last two years, we were using a 0.6 kg battery. No additional equipment required.

Thomas
AMZ

[Fred G]

See, we're not the only ones running LiPos http://fsae.com/groupee_common/emoticons/icon_wink.gif But we do run our alternators.

Power consumption has reduced considerably now, so bottom heaters are of little concern.

Fred

[Adambomb]

Yeah, I think I remember seeing those Li-Po 0.6 kg batteries, they looked like just several standard Li-Po cells in a standard motorcycle battery-sized case. Very pricey, like $600 range.

I gave another variation of this idea some thought a couple years ago, using some of those 1/2 F "Lightning Caps" they use in high-end car audio systems. Definitely an interesting idea. I once drove 75 miles with my battery disconnected in my pickup when the ground terminal fell off as I was driving. It acted a bit funny, as in dash lights dimmed with the turn signals, and there was a lot of alternator whine in the radio, but it made it without catching on fire or anything, just wouldn't start again http://fsae.com/groupee_common/emoticons/icon_razz.gif . Adding a capacitor would likely add the "damper" to the system needed for voltage stability, if the rest of it could be made to work.

[dazz]

There are fuel injected dirt bikes on the market that don't require a battery to work. Can't remember the make right now, but I remember reading that it was designed suck that a dead battery would not leave the rider stuck out in the middle of the bush somewhere. Say for example ending up with a flat battery after de-watering a bike after a failed attempt at a river crossing. (ie. after a couple of kicks of the back-up kick starter, the bike would start. No idea how they managed getting fuel pressure etc.)

[Adambomb]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by dazz:
There are fuel injected dirt bikes on the market that don't require a battery to work. Can't remember the make right now, but I remember reading that it was designed suck that a dead battery would not leave the rider stuck out in the middle of the bush somewhere. Say for example ending up with a flat battery after de-watering a bike after a failed attempt at a river crossing. (ie. after a couple of kicks of the back-up kick starter, the bike would start. No idea how they managed getting fuel pressure etc.) </div></BLOCKQUOTE>

This reminds me of some absolutely fantastic brainstorming we did after switching to a dirtbike single. We were trying to come up with ways for the driver to operate the kick-starter from the cockpit. First idea was a fold-down kick lever next to the brake pedal, although we determined that if it kicked back there was a good chance the driver would shatter his kneecap on the front roll hoop. The next idea, which was my 2nd favorite, was to run a pull-cord system through the car and attach it to the steering wheel, so to start the car the driver simply needed to hit the quick-release and pull on the steering wheel (this of course would require considerable strength training). The best one was a sliding seat and linkage design, where the kick starter was connected to the back of the seat, which was mounted on a sliding track. The driver would simply remove a locking pin, and use a squatting motion to slide the seat backward to run the kick-starter. This idea, of course, progressed into an integrated "butt shifter" idea, where the sliding track was also used with a damper system and attached to the shift lever, so that the car would shift automatically after a pre-determined delay as the driver's mass was accelerated rearward or forward. And things sort of went downhill from there...

[RenM]

If you have a closer look at the available Lihium Battery technologies you´ll find a cell type that has the perfect voltage range for your car, doesnt require balancing or a charge system and that can easily provide enough current for your starter.

We are using them since 2 years and we had no problems at all. In the same time we killed 2 lead racing batteries....