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Location:
Brisbane
Registered:
March 2004
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Location:
Adelaide
Registered:
May 2002
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Re: do brakes suck fuel?
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Wed, 16 June 2004 09:53
 
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Load on the alternator, hence drive system from illuminating brake lights
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Location:
Brisbane
Registered:
March 2004
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Re: do brakes suck fuel?
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Wed, 16 June 2004 10:27
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Dude, you rock. Answer staring me right in the face  That would explain lower idle speed at night time versus day too. Sooo is there an option to upgrade or recondition the alternator so that doesn't happen?
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Location:
Newcastle
Registered:
April 2003
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Re: do brakes suck fuel?
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Wed, 16 June 2004 11:10
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| amwtoy wrote on Wed, 16 June 2004 20:27 |
Sooo is there an option to upgrade or recondition the alternator so that doesn't happen?
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If its a Bosch alt then yes it's easy.
If it's not a Bosch alt then yes but you would need to see a leco for what can be done.
I got an external reg 40 amp alt upgraded to a 55 amp internal reg done at the electricans a while ago so it can be done.
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Location:
Montrose, VIC
Registered:
May 2002
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Re: do brakes suck fuel?
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Wed, 16 June 2004 11:12
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Well, where's the alternator meant to get it's power from if not the engine?? Has to come from somewhere...
Thing is, most (well, apart from the old ones!) EFI engines use an idle speed motor with feedback, to bring the idle speed back up once the load of AC, PS, alternator, selecting drive etc. has brought it down.
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On Probation
Location:
North East NSW
Registered:
December 2002
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Re: do brakes suck fuel?
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Wed, 16 June 2004 12:24
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i don't know how an ra40 with an 18rg is set up, but it could also be the brake booster sucking some intake charge from the inlet manifold, if the car does have a brake booster
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Location:
Brisbane
Registered:
March 2004
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Re: do brakes suck fuel?
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Wed, 16 June 2004 14:32
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These are some really interesting replies, thanks guys! So how does an alternator work exactly? It sounds like what you guys are saying is that something in the alternator creates a physical resistance so the crankshaft has to do more work to produce more current. Does that mean it doesn't always produce maximum current? I'm trying to understand why it affects my idle speed and not the other way round - why doesn't my idle speed stay the same and have the brake lights dim/fail when there is less current?
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I supported Toymods
Location:
Perth, WA
Registered:
May 2003
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Re: do brakes suck fuel?
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Wed, 16 June 2004 14:39
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same way a electric motor works but in reverse
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On Probation
Location:
North East NSW
Registered:
December 2002
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Re: do brakes suck fuel?
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Wed, 16 June 2004 22:52
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an alternator sucking rotational power away from the engine when throttle condition isn't changing? call me skeptical, but i don't think the bits inside the alternator are strong enough to generate enough resistance even slightly slow down the few-odd foot pounds of rotational torque your engine will be making at idle
if anything, you'll probably find the extra load on the electrical system from switching the brake lights on is using a bit of ignition voltage, hence weaker spark, hence rpm drop
sit and flick your headlights on and off and the rpm rises and falls, that's the same thing. mine does that, in fact when i have high beams, fans, interior light and indicators on, the charge light dimly blinks. it's probably a slightly worn alternator, or insufficient it's only a 35A corolla one, but it charges the battery enough so i dont care
you can get your alternator reconditioned at an auto elec, last time i checked it was about $150. i'm told that if your car has a bosch type alternator, you can use a stronger bosch alternator (eg: 60A from XF falcon) and your existing front pulley, and some longer stator bolts and it all just bolts up
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I supported Toymods
Location:
melbourne
Registered:
June 2002
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Re: do brakes suck fuel?
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Wed, 16 June 2004 23:04
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there is a really easy way to check this, next time you are stationary at a stop light, turn your headlights on instead of pushing the brake, headlights will suck more current than your pissy brake lights.
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Location:
Montrose, VIC
Registered:
May 2002
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Re: do brakes suck fuel?
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Thu, 17 June 2004 00:05
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| Super Jamie wrote on Thu, 17 June 2004 08:52 |
call me skeptical, but i don't think the bits inside the alternator are strong enough to generate enough resistance even slightly slow down the few-odd foot pounds of rotational torque your engine will be making at idle
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Hey, skeptical! Think about it: 60A x 14V = 840W (0.84Kw). Remember that the alternator is far from 100% efficient, and that at idle your engine is only producing single KW power figures. It has to come from somewhere, y'know.... (Of course, that'd only be when the alternator is producing a full 60A, which wouldn't be too often, but hey)
The only reasons I didn't suggest vacuum is that usually a vacuum leak will cause engine speed to INCREASE, as well as the fact you mentioned it idles slower at night time too 
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: do brakes suck fuel?
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Thu, 17 June 2004 02:21
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when police are around, i sometimes turn on my headlights and internal fan and .. (well they're about the only electrical items in my car  ) to slow the idle speed down a bit 
with headlights on, you are sucking...at least a few more amps... say maybe 10 more.. internal fan, 5 more...
as for alternators, the Bosch 60A XF guts can be chucked into KE70 Bosch with a few alterations...
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On Probation
Location:
North East NSW
Registered:
December 2002
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Re: alternators (was: do brakes suck fuel?)
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Thu, 17 June 2004 06:35
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but does idle speed decrease because of resistance in the alternator spinning against the crank pulley, or because you're stealing ignition voltage and weakening the spark in the combustion chamber?
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Location:
Brisbane
Registered:
May 2002
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Re: alternators (was: do brakes suck fuel?)
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Thu, 17 June 2004 06:56
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You're not "stealing" voltage from your ignition system, unless your alternator and battery are totally stuffed that is. The car's electrical system should never drop below 12v when the engine is running, and 12v is plenty for the ignition system.
Besides, if the ignition system was breaking down you'd get an audible miss, the engine wouldn't just slow down (as was described).
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I supported Toymods
Location:
Epping, Sydney
Registered:
May 2002
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Re: alternators (was: do brakes suck fuel?)
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Thu, 17 June 2004 09:53
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how come I've never seen the might yello-rolla round newtown?
I'm a bit of a barfly there... maybe it's already tucked away for the night whenever I'm in the area
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Location:
Newcastle
Registered:
April 2003
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Re: alternators (was: do brakes suck fuel?)
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Fri, 18 June 2004 07:07
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An alt will only make as much amps as needed by whats on in the car at the time it is running.If you let the car idle and pull the high beam on then you should hear the revs drop as the alt loads up to compensate for them.At full load it can take up to 10kw to drive an alt on the modern cars so yours will certinaly take some power from the engine to drive it so hence the rev's drop.
But like we have said if it's a Bosch alt then the guts of an XF Falcon alt will fit in your case.You can't fit up the whole falcon unit unless you make a new alt bracket.
If a electrican tells you it can't be done then go somewhere else as he either doesn't want the job or doesn't know how to do it.
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On Probation
Location:
North East NSW
Registered:
December 2002
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Re: alternators (was: do brakes suck fuel?)
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Fri, 18 June 2004 14:54
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i was doing some work at a local auto elec workshop today, and asked the dude to show me what happens when you load up an alternator
he started an electric motor, connected to an alternator by a fan belt, it was spinning fairly fast, and the alternator was charging. then he spun a dial to increase load on the alternator and lo and behold the electric motor slowed down. you could just speed up the motor, load the alternator more and it would slow down again
he reckons he's seen some alternators actually STOP and the belt just slips, slowing the car's engine down dramatically. it was amazing to see happen like that. now i want a new alternator too
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Location:
Brisbane
Registered:
March 2004
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Re: alternators (was: do brakes suck fuel?)
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Sun, 20 June 2004 13:55
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Thanks for all the information guys I'll definitely see if i can get anything done next time i visit the mechanic...
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