Another reason the OEMs put alternator control in the ECU is for strategies like: - idle up if its asking for max output from the alternator - idle up when voltage drops - use alternator activity as an input to stabilizing idle; an alternator is a constant power load thus tends to load down the engine when idle drops
Here's an interesting quote: "If the ... charge lights come on during revving of the engine then it's a sign that the carbon alternator brushes require replacing...About half of the auto electric shops in your local yellow pages sell carbon alternator brushes and copper solenoid starter contacts for about $5/pair. " http://groups.google.com/group/alt.autos.toyota.trucks/browse_thread/thread/43bf5b94cb8a094c That suggests output drops at high RPM due to worn brushes. --- On Sun, 9/7/08, Bill Cardell <[EMAIL PROTECTED]> wrote: From: Bill Cardell <[EMAIL PROTECTED]> Subject: RE: More alternator stuff To: [EMAIL PROTECTED], [email protected] Date: Sunday, September 7, 2008, 7:33 PM Another option might be to go back to the trouble-free 94-97 alternator, before Mazda in their infinite wisdom decided the ecu needed to control the alternator based on air temp and rpm inputs. The theory is the intake air temp will tell the ecu the battery's temperature (in the trunk!). Just need to move a wire or two and the earlier piece fits right on there with self contained regulation. TurboDog's Dad Bill Cardell www.flyinmiata.com 1-800-FLY-MX5S 970-464-5600 tech support Don't miss our Open House! August 14-17 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ian McCloghrie Sent: Sunday, September 07, 2008 8:24 PM To: [email protected] Subject: More alternator stuff As you may recall from my previous email to the power list on this topic, I've been having some problems with alternator output on my 99 FM2 w/ Hydra. The symptoms are that, in certain conditions, the system voltage sags to less than 13 volts (12.5, sometimes as low as 11.8). Basically this happens with all electrical accessories on (blower on high, both Spal fans, AC fan clutch, rear defroster, headlights), and at both low RPMs (less than 1500) and high (above 5000). Jason Cuadra and I did some investigating today and came up with some more info: - It doesn't seem to be a problem with the Hydra alternator control. The Hydra claims it's driving the field coil as hard as it will go, and even clamping the field coil to max by just hooking it to the power line makes no difference. - Hooking up an oscilloscope shows that the diodes in the alternator are all working. - With a clamp-on ammeter, the alternator will make ~ 70 amps at 3000 RPM. At 800-1000 RPM it's only making 50ish amps. At 6000 RPM it's only making 40ish amps. - The alternator belt was a bit loose (presumably from having stretched after being replaced), but tightening it made no difference to the current output. ~70 amps is about what it's rated at, and I'm guessing I just need to turn up the idle a bit to get it to work better at the low end. The high end is a different story, though. I think the voltage is sagging enough that the GReddy boost controller isn't working, because above 5000 RPM with the accessories on I'm only getting 7 psi (the mechanical wastegate setting). I'm pretty sure the high RPM voltage sagging isn't normal, because I don't think the car used to do it. Any thoughts on what might be causing it? Jason speculated that it might be failing slip rings? Does anyone know if you can replace them without replacing the whole alternator? I can't be the only person to put Spals on an NB and then try to take it to redline at night with the AC on, can I? (When you do this it's really noticable because the headlights get a lot dimmer) On another topic, does anyone know of a higher current OEM-style alternator that fits the NB? The aftermarket modified alternators gain higher current do it at the expense of low RPM operation, which is already marginal so I'd rather not push that farther if I don't have to. --Ian _______________________________________________ Miatapower mailing list [email protected] http://list.miatapower.net/cgi-bin/mailman/listinfo/miatapower _______________________________________________ Miatapower mailing list [email protected] http://list.miatapower.net/cgi-bin/mailman/listinfo/miatapower
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