System Voltage

[digitech]

Perhaps someone could tell me this, what is the voltage at the battery, engine running, with a full electrical load, i.e., cooling fan on, lights on, hazard flashers on and trans. shifted into reverse?

[majicwrench]

Well, there is no precise number. But is should be higher than the battery at rest, and it will go up a bit as you rev motor. And it depends how many amps you alternator can produce. So....
At idle, likely gonna be about 13v. A couple k rpm, likely 14v.
Keith

[digitech]

I have 13.5v, engine running, with the system unloaded (just the radio on) and it can drop to 12v with everything on.

[majicwrench]

Then you are not producing enough amps. What does it do reved to 2k?

[Schnauzer]

Digitech: Don't know what year your Spider is so we don't know which alternator it has. My 76 had a 45 amp alternator. My son's 79 2000 had a 55 amp alternator. Neither could keep up to a full load. We both had dim dash lights, slow flashers, nearly inoperable windshield wipers. We installed Mark's 95 amp replacement alternator kits. Now with a full load of lights and accessories we still get 14.6 volts at the battery at 2000 rpm. Definetly an upgrade where the results far out weigh the cost. It is easy too.

Good luck,

Jim

[digitech]

Thanks for all the replies and advice - think I have the problem narrowed down. I have a '79 so it has the 55 amp alt. which was removed and checked out by an alt./starter repair shop and also just had the whole system tested at Advance Auto.

What is happening is the alt. and battery voltage are working fine, voltage is at 13.8, tapering off slightly as battery is brought up to full charge and dropping a few tenths under full load. But the B+ voltage at my coil drops increasing amounts as the electrical load increases,implying a voltage drop somewhere.

Chased through the entire electrical path, found a few gnds. less than secure and some issues on my pass. side tailight ckt. board - fixed everything and issue is much better but still there. Started voltage drop troubleshooting and found I lose .6 -.7 volts through the associated ign. switch contacts with increasing load - fully loaded, it can drop a volt.

I have another used switch so I am going to disassemble/rework it, using the various repair guides some people here have kindly written, and then swap it out. And then, knock on wood, that should be my last issue and I can finally just enjoy the car. Won't be able to make FFO this year after all but hoping for next year.

[kmead]

You might consider using relays to reduce the loss across the ignition switch contacts and help you ignition switch last much longer.

This means removing most of the wires leaving from the ignition switch to the accessory circuits and placing them onto the load side of several relays and then running a wire from the ignition switch to the switching side of the relays (these only carry a tenth of an amp or less). This way the system behaves like it should and reduces both load on the switch and improves the load path reducing voltage drop.

Relays are cheap, easy to replace and can create much safer systems.

You can also use them to create a load reduction relay as well as a nice starter relay. This images shows a load reduction relay approach:


In the image above, the 87 post of the left most relay would got to the starter solenoid engaging the starter and giving it a clean source of power and taking that high amp load off the switch.

One would use a third relay for things you want to be powered when the ignition is in either position such as the coil for example.

What is not shown are appropriate fuses on the 30 supply side before the relays. The "Brown Wire Mod" would be the source for the power supply to the relays.

One nice side benefit to this is you don't need to cut out any existing wiring, you are just moving it and adjusting the position.

Karl

[digitech]

Good idea Karl, I believe I will move at least that circuit to a relay as I have a couple leftover from when I did my headlights; I put my wipers on a relay a couple of years ago as well so outside of my cooling fan (which does not run through the ign sw), this my last high current draw ckt.