Battery won't charge with headlights on

[dbcjmc]

Hi! Hope you can help me source the issue. It's a '77 280Z with a new(ish) alternator. Bypassing the voltage regulator it puts out over 15V. The battery (also newish) and measures about 12.4V with engine off. At idle, V = about 13.2 to 13.4V and will charge up to 14.5V at high rpm.

BUT, turn on the headlights, and V = 12.8.

I tightened the alternator belt, clened the fusable link connectors, and other accesible connectors.

I have Zondabrain headlight wiring harness upgrade and the H4 headlights from MSA. Is it possible the relay in the headlight harness is faulty?

[Nissanman]

My initial guess is the brushes in the alternator are worn out.

When worn down they have very little spring tension on them and, providing the Voltage Regulator is doing the right thing, the exciter current doesn't increase in the rotor therefore the stator doesn't increase in output voltage.

So once again, providing the VR is good, I'd suggest pulling the brushes out to check their integrity:bulb:

Edited May 12, 2011 by Nissanman

[JohnnyO]

...Snip, the exciter current doesn't increase in the rotor therefore the stator doesn't increase in output voltage....Snip

I'd have to agree with what Nissanman said because I have no idea what it means

[240260280z]

The voltage regulator is not regulating or the alternator has a fault and can not support the load.

You can try cleaning the yellow sense wire contacts. It feeds back the battery voltage to the regulator and sets the target set point voltage. If the contacts are bad or loose then the feedback does not work.

Try installing a ZX distributor with built-in regulator. Here is how to do it on a 77 280z:http://www.atlanticz.ca/zclub/techtips/alternatorswap/index.html

Edited May 12, 2011 by Blue

[dbcjmc]

Hi Folks,

I upgraded to a ZX alternator (brand new from Carquest) and followed the wiring instructions exactly. I went the extra mile and ordered a 70 AMP alternator for an '83 ZX Turbo. No improvement tho.... I get ~ 13.5V at idle and it'll charge up to ~ 13.7V at higher rpm. But charge drops below 12V with the lights on. Connecting the +tive directly to the alternator gets me 14.5 to 14.7V.

Is my voltage reader bad? Doubtful, but will check it this weekend at the service station.

Could there be some fault with the headlight wiring upgrade? How to check it?

What else could be wrong?

As always, all suggestions welcome.

[240260280z]

I think there is a bad wire or connection in your circuit that is preventing the alternator from knowing what the battery is doing.... the alternator is supposed to work with the battery as a team and the yellow sense wire is how the alternator knows what the battery is doing.

It is also possible that the fusible link is current limiting the output of the alternator. It could be corroded.

Two 70watt headlight bulbs will only draw ~11 amps so the alternator should be able to handle that no problem.

Try this:

1. Connect a new wire to the "S" connection on the alternator and connect the other end to the +pos post on the battery. If this works then your sense wire in the harness and its connections need to be refreshed.

2. Clean all +12V cable connections between battery and alternator. The path is:

- Battery to starter

- Starter to fusible link

- black fusible link

- fusible link to alternator

You can check the wiring path interconnections on this drawing: http://www.atlanticz.ca/zclub/techtips/wiringdiagrams/F77ZCAR-WIRING1.pdf

[240260280z]

I just edited wiring diagram to make it easier to follow. See attachment.

[dbcjmc]

Thanks for your help Blue! Making progress but still not quite right.

- The jumper test from the S connectoor (yellow) to +tive terminal yielded no different result.

- The fusible link for the Alternator & Ignition Relay is super hot to the touch. In fact, after about 15 minutes of running the motor while trying to troubleshoot, the platic housing started to smoke (melt) it was so hot!

- I disconnected the #2 and #3 (White&Red to Yellow) that I tied together at the old V regulator connector, and now get 14.3V without lights on, and 13.5 to 13.7V with the lights on.

Is it OK to leave these these 2 wires diconnected?

What would cause the fusable link to get burning hot?

[SteveJ]

A hot fusible link happens during an overcurrent condition. Check & clean all your fusible links. Replace the bad one. Courtesy Nissan does have the fusible links available.

[240260280z]

Heating is due to current and resistance. The resistance of a fusible link and connections should be ~0 ohms therefore the heating should be ~ 0 Watts however if the connections to the fusible link are loose and/or corroded.... or the wiring to the bottom of the fusible link holder is corroded then this adds resistance and, in turn, heating.

Heating is proportional to I²R where I is current and R is resistance. As mentioned your lights draw ~ 11 amps however the resistance of the link should be ~ 0.01 ohms so the radiated power should be ~1.2 W

If the resistance of the fusible link was increased to just 1 ohm due to corrosion then the heat would be ~ 120Watts... try holding your finger on a 100W light bulb to get an idea of that much energy.