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Kill switch for Instrumentation

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p.lewis View Drop Down
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    Posted: Mar/31/2010 at 10:12am
How do people navigate rule 22 with regards to tachometer/speedometer/odometer computers with internal batteries? Do you add a circuit to the kill switch and hack the computer's battery connection to put in a shutoff?
 
Thanks!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GT Steve Quote  Post ReplyReply Direct Link To This Post Posted: Mar/31/2010 at 12:21pm

In my experience, this has been one of those rules that is in the book, but is not strictly enforced as written.  We had a full data system on the car for several years, which the engine kill switch didn't touch, and i can't remember ever being called on it.  We had one "master" switch for all of the electronics, but it was seperate from the engine kill switch entirely.

This may have changed more recently, but I suspect not.
 
It sounds like your instruments are entierly enclosed and battery operated, and I don't believe the intent of this rule is to have you void your warrentees by hacking into the case.
 
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p.lewis View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote p.lewis Quote  Post ReplyReply Direct Link To This Post Posted: Mar/31/2010 at 12:50pm
I see there being two reasons for the kill switch on electrical systems:
1) eliminate electrical shock hazards to drivers, courseworkers, and officials
2) eliminate electrical fire ignition sources in the event of a rollover with a gas spill
 
I think that within this interpretation of the intention of the rule, a small watch battery in a tachometer/speedometer instrument does not need a kill switch. But that is just my opinion, and it doesn't technically agree with the way the rules are written.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rhillson Quote  Post ReplyReply Direct Link To This Post Posted: Mar/31/2010 at 1:56pm
I'm also from p.lewis's team.

The way I see it, having the kill switches (which are normally-open type) shut off the engine and all the accessories (all the 12 volt data acquisition stuff) at the same time is impossible, unless you bend the rules in some fashion, like:

1) Use a normally-open-normally-closed type kill switch (But the rules state you can only use a certain type of kill switch)
2) Insert a relay in the accessories circuit (But that requires a power source)
3) Have a separate shutoff switch for the accessories circuit (But this is obviously doesnt fufill the rules requirement)

Has anyone successfully shutoff their engine AND 12V accessories circuit with the normally-open kill switches?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Waffles Quote  Post ReplyReply Direct Link To This Post Posted: Mar/31/2010 at 2:27pm
Surely all formula SAE cars have instruments, how do they deal with this?  Do those rules make more sense?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CobraCommander Quote  Post ReplyReply Direct Link To This Post Posted: Mar/31/2010 at 2:40pm
I've never looked into this but couldn't you use a double pole single throw switch so that your systems are still separate but can be shut off with the same kill switch?
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p.lewis View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote p.lewis Quote  Post ReplyReply Direct Link To This Post Posted: Mar/31/2010 at 3:02pm
Because they differentiate functions between the cockpit kill switch and primary external kill switch, the FSAE rules leave less room for interpretation. However, implementing their rules seems a bit more straightforward. Since most of the formula car runs with controls off of battery power, their normally closed kill switches easily shut down most of the vehicle's systems without a complex electrical system design.
 
Our shorting type (normally open) kill switches are difficult. I don't think we can create a circuit that responds to short circuit to shut itself off without consuming power. Open circuit feedback is child's play. But I'm an ME, so I might be overlooking a relatively simple analog circuit that the EEs would quickly put together.
 
The little watch battery won't source much more power than a relay or transistor circuit would, so I say it does not need a kill switch.


Edited by p.lewis - Mar/31/2010 at 6:27pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Old Greg Quote  Post ReplyReply Direct Link To This Post Posted: Mar/31/2010 at 8:12pm
We ran a dash last year, and the tech inspectors at Wisconsin did enforce that rule; our car wasn't compliant.

What I did to get the car legal was to run the dash power through the second pole of both kill switches (the Polaris ones).  It worked perfectly.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ffriolet Quote  Post ReplyReply Direct Link To This Post Posted: Apr/01/2010 at 10:29am
Originally posted by p.lewis p.lewis wrote:

How do people navigate rule 22 with regards to tachometer/speedometer/odometer computers with internal batteries? Do you add a circuit to the kill switch and hack the computer's battery connection to put in a shutoff?
 
Thanks!


Originally posted by SAE Rules SAE Rules wrote:

22.2 Onboard Instrumentation/Data Acquisition/Electronic Controls
Onboard instrumentation, data acquisition, and electronic controls of the suspension and transmission are all allowed; the power for these components must come from approved batteries per 22.1 if the battery is being charged by a Briggs alternator.


I think Onboard instrumentation includes tachometer/speedometer or odometer. So internal batteries should not be legal.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote EAD Motorsports Quote  Post ReplyReply Direct Link To This Post Posted: Apr/01/2010 at 7:41pm
FSAE's cockpit switch only kills the ignition and fuel pumps.
FSAE's master switch kills all power, period.
NASA and SCCA require master switches that kill all power.
 
Baja's rule is sorta a mix between the two FSAE switches. The wording suggests you must kill everything but the brake/reverse light and reverse alarm. I would guess the intent is to kill the engine and anything controlling the drivetrain while still having a brake light left on to serve as some modicum of warning to other oncoming cars during endurance the disabled car ahead of them on course is either slowing or stopped. Eliminating fire hazards due to sparking may be one reason to kill all accessories, but keeping the brake light circuit energized seems to contradict this line of reasoning; unless it is felt the warning afforded by the brake offsets the liability from fire. 12V systems generally don't pose an electrocution hazard, so that shouldn't be a reason to shut down power.
 
I would email bajarules@sae.org and get their input. Are they going to enforce the rule as written, or as intended (and what is that intent)? Keep in mind we're within the 2 week period of Baja SAE Carolina, so the techs may not answer your question before then.
 
ffriolet, I think rule 22.2 either has a typo or is poorly written. Instrumentation and data acquisition has, at least back to 2000, never needed to come from the alternator. On the other hand, electronic controls have always needed to come from the alternator. I believe the section after the semi-colon is in reference only to "electronic controls of the suspension and transmission". Otherwise any team running instrumentation/data acq needs an alternator, which is a pretty big deal.


Edited by EAD Motorsports - Apr/01/2010 at 7:45pm
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