[dboss]

I'm working out some electrical issues on my 67 catalina 2+2. I want to replace my existing alterator and external voltage reglator with a 3-wire 10SI internally regulated alternator. I've already ordered a 10SI that's rated at 105 amps. I went to order an engine harness from M&H Wiring and the tech I talked to said my alternator at 105 amps was too much and could fry the wiring. Is this true? From all I've read here, I thought that 100 or so amps would be great to have. Also, the alternator output wire is part of the engine harness and goes into the firewall plug and elsewhere before reaching the battery, so my question is should I run another wire from the alt output directly to the battery? I know I run a wire from terminal 2 on the alt to the battery. Many thanks.

[george kujanski]

An alternator only produces the amount of current that the loads require, plus some charging current into the battery.

Assume the battery is charged, the alt output voltage is 14.0 and you have your headlights and heater on and the engine running. The loads amount to, say, 20 amps as an example, plus at 14.0 volts, the battery will take about 4 amps when it's fully charged.

The alt will therefore output 24 amps.

If you manage to start the car when the battery is very low, (by jump starting), the alt will output much more current into the battery, the amount determined by the actual battery discharged condition, but the current could be fairly high. Also using a electric radiator fan and/ or a high power stereo can put high current demands on your alt, (which, of course is why you get a high output alt in the first place).

I would recommend upsizing your alt output cable to the next even gauge, i.e. if you have a 8 Ga., go to a 6 Ga., or double up what you have. The fusible link will probably need to be increased also. An additional cable directly to the battery will bypass the fusible link and therefore is not as safe. If your exisitng harness was for a 37 A alt, the fusible link may be too small for your alt and should be upgraded. If you had a 62 A alt, chances are it'll be ok, given that the max output really only happens on rare occasions (unless you add the loads as mentioned above.)

George

[dboss]

Thanks George for your input. Since the output cable is part of the engine harness and only 10 gauge, I believe, should I ask M&H to make that cable 6 gauge?

[george kujanski]

A 6 ga, fine-stranded cable is a good size for a high-output alt, shouldn't need more than that. Have them adjust the fusible link size as well.

They probably have their own guidelines as to wire sizing, etc. Let them know your plans for the electrical system and I'm sure they will advise you.

George