Car Charging

[Engine Dude]

Can anyone tell me how long the cars need to stay on for, during the competition?

Also, can you start the cars using a portable charger?

Cheers

Sam.

[Engine Dude]

Can anyone tell me how long the cars need to stay on for, during the competition?

Also, can you start the cars using a portable charger?

Cheers

Sam.

[Agent4573]

They normally run for whatever you want to warm them up(2-5 minutes), acceleration is about 1 minute per run, normally 2 runs are done back to back, autocross would probably run for about 2 mins(1 minute waiting in line, 1 minute running the course), with 2 runs also done back to back. Same for skidpad. Endurance the car is on for about 15 minutes, off for 3 minutes, then on again for 15 minutes.


I would strongly suggest making the car charge itself so that you can start it without a portable charger. The drivers WILL stall the car somewhere, either just screwing up or when they spin out, but your car will shut off on you at least once at competition when you don't want it to. If you can't restart it on its own, you just took yourself out of that event.

[Engine Dude]

What if you had a battery that could supply enough Watts to your energy consuming sources (ECU, Elec water pump and thermofan) for an hour. Then use no altenator and just swap batteries every hour, having the other one on charge.

With all the sources running at full load i calculated about 12 Amp hours required. Would the car not be able to be started if the altenator was ripped off?

Is this a violation of the rules? The Stator and Rotor drains about 1 to 2 HP on the F4i I have been told, and I was looking at taking it off to also for space considerations.
Regards,

Sam.

[B Lewis @ PE Engine Management]

Sam,

Something else to cosider. The ignition coils and injectors also require battery voltage to operate. As the battery discharges, there is less potential available to these components which changes their characteristics drastically. Once the voltage drops to a certain level, the injectors won't open in a timely matter and the coils will just stop firing (this occurs long before the battery is discharged). Even if the injectors and coils operate over the range of voltages you will see for the long events, you will need to map your engine at several different supply voltages to make sure you have accounted for the changing characteristics.

[Chris Boyden]

Another thing to consider is the balancing effect of the rotor. I know a mini sprint racer that wears out crank bearings when he changes the rotor. He's able to run the engine, but it reduces it's lifetime, which is fine if you're ready, willing, and able to deal with it. But, it may catch you by suprise if you're not looking for the oil pressure to suddenly drop, indicating a worn out bearing.
You may want to keep the rotor and ditch the stator if you really want to go down this road.

[Buckingham]

Batteries last a lot longer if you don't deep cycle them like that.

Best way to figure out how much the charging system actually hurts you is on a load-controlled dyno. Best way to waste dyno time is to spend it analyzing your charging system when you should be optimizing your engine's breathing and/or maps.

[Kevin Hayward]

Sam,

Treating the electrical system this way is possibly valid for a competition. However your result will probably be much more dependant on the effectiveness of your testing program than whether you have 1 or 2 more hp at comp time. During testing you will start and stop the car a lot. Each start takes a lot of juice.

Do some quick calcs etc to find out what the extra horsepower will give you for on-track performance. Weigh it up against the saftey margin you will be taking away.

Our team has been through a number of battery and charging related problems. We take a very conservative approach to the area now. You only have to look at where the first non-endurance finishing car ends up. In the 6 comps I have been a part of, not finishing endurance in Australia 2003 was the worst feeling I could ever imagine. It makes it impossible for me not to have sympathy for teams that don't finish and also impossible to understate the importance of reliability.

So there goes.

Alternator gives reduced pain in testing and a safety margin in the comp. I think worth the weight and horsepower disadvantages.

Cheers,

Kev

ex-UWA Motorsport

[J. Schmidt]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Alternator gives reduced pain in testing and a safety margin in the comp. I think worth the weight and horsepower disadvantages.
</div></BLOCKQUOTE>
I agree, Kev. A couple years ago the total loss (non)charging system was our hot ticket. Turns out our battery guy wanted to make it too complicated by using two batteries, one for starting and one for operation. When it finally came down to it we did ran 2 batteries AND the alternator, due to a little miscomunication (among other things).Good info though. I with we had asked back then.

And about starting the car, rule 3.5.1.7 states "Each car must be equipped with an on-board starter, and be able to start
without any outside assistance at any time during the competition."

[Z]

I agree that you should be careful with your electrical system - it is possibly the most common reason for DNFs.

If you want to ditch the alternator it might also be a good idea to do the same with the starter motor. The most reliable electrical component is the one that isn't there! http://fsae.com/groupee_common/emoticons/icon_smile.gif A lot of racecars use pneumatic starters, which are generally lighter and more compact than electric motors with the same power output. They also don't drop the battery voltage just when the spark coils need it most.

This would really only make sense if the car had a compressed air tank, or better yet a CO2 bottle, already on board for some other purpose (eg. gearshifting, etc.). "Recharging" a compressed air bottle is also a very quick and easy operation. However, I'm not sure about the legality of onboard "energy" sources?

Z

[Colin]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> The most reliable electrical component is the one that isn't there! </div></BLOCKQUOTE>

Pretty much goes for any system on the car Z, not just electrical http://fsae.com/groupee_common/emoticons/icon_wink.gif. "Electrical Failures"� are often blamed for DNF's but I bet you'll find 99% of the time it's the wiring and not the component. If you brake an A-Arm you don't blame the off the shelf spherical bearing you blame the bloke who designed\manufactured the A-Arm but as soon as a starter motor doesn't turn over everyone point's the finger at it rather than the bloke who thought it would be a good idea to run 22 gauge wire to it to save weight. If as much design went into the loom as goes into geometry then "Electrical Failures"� would be very rare

[MikeWaggoner at UW]

I always thought it'd be pretty easy to 'fool' the charging system into thinking it had more voltage whenever you had the throttle over say, 80% so it wouldn't charge. The load would be higher at lower RPM's, but you'd get ok charging and the same peak power as if you had no alternator (except no rotating mass advantage like you get from scrapping it).

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Colin:
"Electrical Failures"� are often blamed for DNF's but I bet you'll find 99% of the time it's the wiring and not the component. </div></BLOCKQUOTE>

I remember hearing (from an UNreliable source) that "electrical failures" are something like; 50% connectors, then in decreasing order of occurance, wiring, sensor failure, electronic (solid state) components, and lastly electrical motors/coils/etc.

Z

[Colin]

yea, that sounds reasonable Z, but I reckon wiring (including wiring at connectors) would account for more failures than that at FSAE in particular.

As for "'fooling' the charging system"� mike, remember the alternator only works has hard as it needs to that's what the reg's there for.

[Gabriel Descamps]

It IS true. I´m not sure wiring is 99% of the problems. However, I AM sure it IS 100% of the problem. The least connections you have, the better. The more connections you have, the more sources of failure you´ll get.

You should use AWG 20 wires, it´s the lightest you should use.... As for the starter, you should try AWG 12 (that way you´ll be ensuring enough current goes for the starter, which uses A LOT).

The car WILL start without the alternator, however, the battery won´t last very long.

Building a reliable wiring system is tough, but not impossible. Just make sure nothing´s hanging out, and that everything´s protected from water. Also avoid black tape and the sort, and never make a connection between two wires without a connector (like a knot or something).

Also, don´t let any Mechanic Engineer near it http://fsae.com/groupee_common/emoticons/icon_biggrin.gif Wires, well, they just don´t come naturally to them.
(Just kidding guys)

Good luck with that.

Cheers

[Chris Boyden]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">If as much design went into the loom as goes into geometry then "Electrical Failures"� would be very rare </div></BLOCKQUOTE>

Very true and very necessary given the complexity of the fuel injection systems.

I agree that connectors probably account for more electrical failures than any other part of the electrical.

A proper crimp with a ratcheting aerospace quality crimper is definitely worth the money.
While most teams don't want to spend the $250 or so on the nice crimper, I sleep at night knowing that the connections it makes aren't gonna fail.
Milspec or Deutsch connectors are also definitely worth the money. Soldering can work well too, but I worry about the "hardening" effect soldering has on the multistrand soft and flexible copper. If you solder, make sure and strain relief the wire from the connector to prevent the solder joint/wire from work hardening and breaking. Several connector systems offer shrink boots that will provide waterproof strain relief and look nice. A decent connector system also makes it easier to design and wire the car electrical and makes the whole job more reliable and more professional. Waterproof connectors are also a nice touch, especially since it's so dry in Michigan during comp.

Anyway, what does this have to do with charging systems?

[Cement Legs]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Gabriel Descamps:

Also, don´t let any Mechanic Engineer near it http://fsae.com/groupee_common/emoticons/icon_biggrin.gif Wires, well, they just don´t come naturally to them.
(Just kidding guys)

Good luck with that.

Cheers </div></BLOCKQUOTE>

Another electrical engineer who thinks setting up his new surround sound stereo counts as a co-op term.... http://fsae.com/groupee_common/emoticons/icon_razz.gifhttp://fsae.com/groupee_common/emoticons/icon_biggrin.gifhttp://fsae.com/groupee_common/emoticons/icon_wink.gif

[Gabriel Descamps]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Another electrical engineer who thinks setting up his new surround sound stereo counts as a co-op term....
</div></BLOCKQUOTE>

Nah, not electric, electronic....

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Anyway, what does this have to do with charging systems?
</div></BLOCKQUOTE>

And well, about the charging systems. Why mess around with it? Alternator works just fine, just plug the thing, use a small battery (7-8 Amp-H), and it should work fine. I wouldn´t look into complicating already complicated things.

[Engine Dude]

My Chassis dude is making a full (Straight tub)aluminium monocoque and thinks the engine is too wide.

Being asked to look into a external altenator and run a drive system off the end of the crank or the diff. The rotor weighs a bit though and someone else posted balance issues could arrise. In all honesty it looks like a bit of messing about for little (space) gain.

Cheers

Sam