vnova94

Ok.... i got tired of my lights dimming at stop lights so i installed an FD alternator. I really need the extra current output since my two amplifiers draw alot of current.

I still have dimming lights however..... and when im driving..... i see the voltage gauge move when the windshield wipers are on intermittently...... evey time they start.... voltage drops....

Am i asking for too much? Is an FD alternator not going to help at idle since the 100+ amps requires i guess 1500 rpms?

Plus my windows are slow as nuts...... and if the car isn't running i feel like punching them out, they are sooo slow.

Thanks,

Matt

rx7_ragtop

Try running a couple extra wires (or one REALLY heavy one) from the "hot" post of the alternator to the battery positive terminal. The stock system is pretty weak there. Check/upgrade your grounds too. I have this alternator on my car, it was a great upgrade, BUT, I have an (electronically) stock car except for the electric fan.

Brad

TristanTII

Where did you guys get the FD alternators from? how much? and how hard of an install was it?

Icemark

Slow windows are usually dirty switch contacts or dirty window tracks.

With a digital multi-meter what is the voltage of the car while running at idle (700 rpm)? how about with the lights on? how about with the lights and brake pedal pressed? It should stay above 13.5 volts. If it is not then have the alt checked.

Also you should have upgraded your battery ground and engine grounds. You should not expect to get any additional amperage if you are using 15 year old grounds that were weak when new.

remember only as much amperage/voltage can get out of the battery and electrical circuit as can get back in. Think of the electricity making a big loop through the car. If you have little tiny wires going back into the battery and engine, it doesn't matter if you put 2 AWG wires coming off the alt.

gorockrx

Go to Autozone and get one of the 4 guage ground straps from the battery section. Install from the engine ground at the rear of the intake manifold where the engine lift point is and go to the firewall where the old ground wire is. Replace that and maybe put an extra ground from the battery to the chassis.

Might want to put a larger size wire to the alt. Make sure you have good batt voltage at idle and if not, maybe you have a bad alt anyway.

If all this doesn't help, try a large capacitor on your stereo system amps where the batt voltage comes in. This could help a lot.

Just some ideas I hope will help.....

HuggyBear

get a cap for your sound system

Aaron Cake

iTrader: (1)

A capacitor will not help. They are only for instantanious current draw, NOT steady draw...The capacitor can only provide current for a fraction of a second.

vnova94

Here's what i measured:

At 750rpm idle: 14.92V

with headlights: 14.72V

with headlights
and brakes: 14.57V

with all of the above and my stereo system: 13.7V (13.2 initially and climbs up to the mid 13's)

goes back up to 14.4V with increased rpm's.


so i guess the stereo is just too much even for the FD alternator? I do have a large gauged ground running from the negative battery terminal to the chassis. Also from the positive terminal to the alternator.

Matt

vnova94

^ any thoughts?

KNONFS

iTrader: (14)

What Battery are you using? Might want to try the Optima RED top.

vnova94

I have a Sears Diehard Gold

KNONFS

iTrader: (14)

Ok, sorry I meant how many amps, etc. People with sound systems have had VERY good results with the optima batteries, we use them in our demo car back in the days with very good results.

copandengr

Stereo systems place an extra high demand on your rex's power supply. Since amps dissipate a considerable percentage of their consumed power in heat, it is a good assumption that you need about 150 percent more power available for the amps than they put out. For instance, a 200 watt amp will need 300 watts of power input capability. Understand of course that amps do not draw anywhere near their maximum current drain most of the time. Loud bass sounds use mucho current.

Watts divided by volts will give you the amperes needed. For example, 300 watts divided by 13.8 volts gives 21.7 amperes. Looking at the power requirements this way it isn't hard to understand the tremendous current drain your alternator is fighting. Add the other loads together, such as lights, the fuel injection system, ECU, A/C, wipers, etc. and you can see that even the 100 amp FD alternator is overwhelmed. I have found on my rex that the fuel injection system is very voltage dependant. Allowing the voltage to drop to the 12 volt range really messes the performance of my car up. The 3,800 RPM hesitation becomes very pronounced at lower voltages. You also need to understand that alternators are rated at a rotor speed of 3,000 RPM. Though they put out considerably more voltage and current at idle than the old generators did, they still need speed to work well enough to maintain a high load demand.

Delco has several configurations of 150 to 180 amp alternators that are stock on many pick-up trucks and cars made by GM. Though I have never tried to install one of these on a Rex, I have used them on numerous tractors, airplanes and boats. They are plentiful at salvage yards, have an internal regulator, are very dependable, and around here go for 25 to 45 bucks. A little effort with some tools and imagination and you could install one of these on your car. Problem solved.

Icemark

I actually prefer the Diehard gold myself, 100 to 150 more CCA, higher (750) amp/hour rating, and a lower passive discharge rate than either the red or yellow top optima batteries.

vnova94 It sounds like the alt is running fine, what is the actual rated wattage of the amps you have added?

vnova94

I have a 4-channel Adcom.... 40W x 4 and a 2-channel Nakamichi.... 80Wx2.

Matt

Icemark

thats only 320 watts... I wouldn't think you should have a problem with that little.

I'd go back to the ground situation... sounds like there is a bad one.

Replace or add a 2 awg ground wire from the battery to the car body, and double check your engine grounds. replace or upgrade them as well.

vnova94

What gauge to ground the engine? The only grounding straps i can find are 10awg. Is that sufficient? The only large braided cables i could find have a battery terminal on one end for grounding the battery.....

Matt

vnova94

What gauge to ground the engine? The only grounding straps i can find are 10awg. Is that sufficient? The only large braided cables i could find have a battery terminal on one end for grounding the battery.....

I have two 10awg braided bare copper straps..... from what i can find is that 10awg handles up to 60A. But there are so many ground points this should be fine? Otherwise i would need something like a 4awg for 125A. Figured i'd ground my exhaust also..... especially since i have noise in the stereo...


Matt