ATC529R

Hey all. I'm wiring a 90 alternator (80 amp) into a 1980 rx7 conversion. I do not have the original wiring as this is not a rotary. Can someone tell me where the 2 wires from the plug go to. I've seen conflicting info and their mainly direct SC to FB conversions.


The main positive I assume goes to the starter or battery?

Thanks

jjwalker

Main goes to the battery, the S wire goes to the battery, and the L wire is for the dash light.

ATC529R

thanks. could you just jump the s to the main going to the battery?

jjwalker

You could, but I'd run it to the fuse block personally.

jackhild59

iTrader: (7)

If you do, the voltage will be regulated at the alternator end of that wire, rather than at the battery end. Volts will be slightly lower at the battery and charging will be slightly compromised. It will operate same as a one wire alternator, with reduced volts output.


No need to half-*** this while you are completely redoing the charging system. Do it once do it right.

jjwalker

To expound on what jack said...

What jack said is the reason why I said run the S wire to the fuse block. For instance, let's say its cold outside and you got your blower motor blasting and headlights on at a stop light. With the engine running that is a **** load of current draw from the alternator as it is powering everything else making the car run, plus the Headlights, parking lamps, brake lights and so on. An S5 alternator is maxed out at 80 amps but you can't get 80 amps out of the alternator until about 2000 rpm, so at idle, it's quite a bit less.

So if you are drawing more current than the alternator can supply, how come you still have power? The extra current comes from the battery. The math gets crazy when you have two different voltage sources on the same DC circuit but I'll simplify it.

Voltage = Force
Current = electrons transferring energy

If our alternator wasn't in a rough situation like described above, the whole DC circuit on the car would be 14.4v and all current coming from the alternator. The alternator post and the battery post would be at 14.4v. The 12.6 battery voltage is null as no current is being pulled from it.

In a very demanding situation, as described above, the situation is very different!

Let's say your car is drawing 60 amps, the alternator is providing 50 amps of that and 10 amps are coming from the battery. The current coming from the battery is going to have a voltage of 12.6v, and the rest of the current will have a voltage of 14.4v. Well, You can't have both on a DC circuit. The entire circuit voltage will fall to 12.6v. In this situation, you can still read with a multimeter full "voltage" output from the alternator, but at the battery side it's going to be 12.6 or lower depending on how much current you are drawing.

The mathmatical median of 14.4v and 12.6v at a 10 amp disparity is exactly 12.6v

Super long story short, connect the S wire to the fuse block

ATC529R

Will do guys. I don't have a fuse block....threw away too much on this conversion. Guess I'm gonna need one because right now I have the main power to the harness, a main to two amplifiers, this wire from the alternator, MSD ignition poisitive to the battery etc. thats a lot of wires with single in line fuses.

so much to do. Any thoughts on a universal fuse block?

FYI, my battery is on the passenger now after moving it and making tray etc. by the firewall. so I have had to cross everything over from the drivers side. It's quite a few wires...and the less the better which is why i asked about jumping it.

jackhild59

iTrader: (7)

jjwalker

LOL, Jack!