UWA starter?

[Jersey Tom]

Curious.. we were in line next to you guys for auto-x or some event and I heard the car start up.. starter sounded way different than I've ever heard on an F4! You guys still use the F4, yea?

Any hints as to whats different? Or is it some crazy Australian technology I don't even know about.

[Jersey Tom]

Curious.. we were in line next to you guys for auto-x or some event and I heard the car start up.. starter sounded way different than I've ever heard on an F4! You guys still use the F4, yea?

Any hints as to whats different? Or is it some crazy Australian technology I don't even know about.

[Steve Yao]

I believe they run a non-12V power system. Like 18V with NiCd or lithium-polymer packs?

[benjo]

Yeah, I think its 17 volts though. Close enough http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[Jackness]

Still with the F4i and yes we run a 17V system so the alternator makes a pretty sound (obviously not its main purpose)

[benjo]

What is the advantage of running the 17 volt system?

[Chris Boyden]

alternator makes a pretty sound?, you mean starter?

[Steve Yao]

Well, I would imaging the high voltage lowers current requirements, which allows the use of a smaller, lighter NiCd or lithium polymer battery pack(which cannot deliver as many cranking amps as automotive lead-acid batteries)? maybe even smaller gauge wires and packing flexibility.

Also probably has something to do with the design question I keep hearing about "how long does your battery last?" For the vast majority of us who do not mess with the electrical system much, this is not something we think about. We assume the stock system is good, and do not optimize further. However, the stock system is for a production bike ridden perhaps every day. An FSAE race car needs to run 22 km plus pit driving, plus a little contingency capacity.

Assuming the alternator does not fail and can keep the car running sans battery, the battery really only needs to provide juice for a few engine starts.

[Jackness]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Chris Boyden:
alternator makes a pretty sound?, you mean starter? </div></BLOCKQUOTE>

yeah sorry starter, too many late nights doing assignments really mess your head about

[Chris Boyden]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Well, I would imaging the high voltage lowers current requirements, which allows the use of a smaller, lighter NiCd or lithium polymer battery pack(which cannot deliver as many cranking amps as automotive lead-acid batteries)? maybe even smaller gauge wires and packing flexibility </div></BLOCKQUOTE>

well, the current requirements would be lower IF you rewired the starter to be a higher resistance. If the starter has the original windings, then you get a higher cranking speed, which is what I believe they have done, and Current goes up.
V = IR , R constant and V higher, I is higher.
so instead of ~50 amps the starter probably draws 70 or so with 17V.

that same general rule applies to the rest of the subsystems, unless the impedance is raised, current draw will go up with higher voltage.

switching regulators presented with 17V can use the current efficiently and will result in lower current draw. That's probably what is on the front end of the off the shelf ECU's DAQs etc.. linear regulators would just dissipate extra voltage drop from 17 to 12 wasting power.

My guess would be that the higher voltage system allows them to have higher starting rpms which makes for easier starts. As for the rest of the system, Li-Ion has a higher energy density...and would just save weight vs. lead acid. but you pay in cost and slightly more complexity and charging challenges. Li-ion is a more sensitive battery to discharges etc...

[Mike Flitcraft]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Chris Boyden:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Well, I would imaging the high voltage lowers current requirements, which allows the use of a smaller, lighter NiCd or lithium polymer battery pack(which cannot deliver as many cranking amps as automotive lead-acid batteries)? maybe even smaller gauge wires and packing flexibility </div></BLOCKQUOTE>

well, the current requirements would be lower IF you rewired the starter to be a higher resistance. If the starter has the original windings, then you get a higher cranking speed, which is what I believe they have done, and Current goes up.
V = IR , R constant and V higher, I is higher.
so instead of ~50 amps the starter probably draws 70 or so with 17V.

that same general rule applies to the rest of the subsystems, unless the impedance is raised, current draw will go up with higher voltage.

switching regulators presented with 17V can use the current efficiently and will result in lower current draw. That's probably what is on the front end of the off the shelf ECU's DAQs etc.. linear regulators would just dissipate extra voltage drop from 17 to 12 wasting power.

My guess would be that the higher voltage system allows them to have higher starting rpms which makes for easier starts. As for the rest of the system, Li-Ion has a higher energy density...and would just save weight vs. lead acid. but you pay in cost and slightly more complexity and charging challenges. Li-ion is a more sensitive battery to discharges etc... </div></BLOCKQUOTE>

More or less a new twist on an old hot rodder's trick. Wiring 6v electrical systems for 12v and keeping the 6v starter. Motor started much faster, but the starters died much faster as well, they weren't meant for that kind of usage.

You'll see the same thing quite often on the trails, but with 24v instead of 12v.

[Pete Marsh]

Yes the bateries are lithium, and yes we have to biuld our own charging regulator to manage them. The voltage is required to use the chemistry as less cells would be too low and the higher voltage is better for power electronic functions we run, eg Gear and clutch. The fast crank speed is with a stock starter and is no bad thing IMO. To date there have been no failures or problems with it. For those that don't know our team's history we went out of a couple of endros with failure to start due to low voltage when the car and battery where hot. Not ever going to happen again!!!

Pete