1982 Supra Alternator B+ cable to 12 volt battery terminal voltage drop

[captainbuford]

After replacing my alternator on my 1982 Supra I did a voltage drop test from the B+ terminal on the alternator to the + battery terminal. At 2000 rpm I am measuring a .46 voltage drop with the fan and headlights turned on. At idle with the fan and lights off the voltage drop is .30 volts.
The voltage at the battery is 14.0 volts with the engine running at idle without fan and headlights.
I was thinking about making up a test cable with 6 gauge multistand wire with a 60 amp fuse in series with the test cable and running it from the alternator B+ terminal to the battery + terminal. I would remove the original wire from alternator B+ terminal. There is no voltage drop across the 1.0 yellow fusible link inside the fuse and relay panel in the engine compartment.
I forgot to mention something. The voltage on the alternator B+ post to battery ground is 14.3 volts at idle.So I am dropping .3 volts between the alternator B+ post and the + Battery post
I would like to get rid of the voltage drop from the alternator to the battery.
Has anyone done this?

[1982 Dragon]

I have a huge draw from my windows, my lights dim bad. Garage says I check out fine, they replaced alternator last year.
I'd say check your grounds, but these cars a super old. I just put up with it

[Donn29]

Do you mean that you have a drop when the loads come on? Or do you have a voltage drop across the wire? IE from Ground to the alternator terminal is 14, but from ground to the battery positive is 13.5?

If it is the first one, that there is a drop when loads come on, that is totally normal. At idle, if you are above 13.7 with few/no loads on, you are good. If you are above 13.7 at 2000 with most normal loads on, you are also good. Once you drop under 13.7 it is unlikely you are charging the battery enough to put back the energy it took to start the car. Also, you might just be adding more loads than the alternator was designed for. OEM is about 50-60amps, and a single fan could be about a quarter to a third of it's max output.

If you are getting different readings at different spots on the positive from the Alternator to the battery, you could try just using a jumper cable. Just be careful not to short it out. On a 5M it is a pretty long run, but there shouldn't be too much of a drop. Check the ends to see if there is any corrosion inside the wire insulation.

[MrBubbles00482]

The voltage drop you are seeing when lights and and fan are on aren't a whole lot...

These cars don't have a big alternator at all to begin with like 50-60 amps, my lights dim when I roll my windows up, HID's draw my voltage down...etc...
ANY added current draw on that small of an alternator is going to have voltage drop. As long as you are in the 13.5+ you are okay, 12V batteries tend to rest around 12.8~...
If you start dropping below 13.5, all your alternators current is being used and you are starting to pull battery power.

If you're really worried about that drop, measure your resistance between the alternator and fusible link, the resistance on the fusible link, see what you get, you can add charge cables to cut down on resistance and maybe stabilize that drop, but I doubt it will help since it's such a small drop.

If anything add another charge line, 4 gauge with it's own fuse holder, and add engine/battery grounds.

[captainbuford]

Do you mean that you have a drop when the loads come on? Or do you have a voltage drop across the wire? IE from Ground to the alternator terminal is 14, but from ground to the battery positive is 13.5?
Donn I have a voltage drop across the wire. Voltage at alternator B+ post is 14.3 volts to ground. At the battery + post the voltage is 14.0 volts. So I
am dropping .3 volts across the wire.
If it is the first one, that there is a drop when loads come on, that is totally normal. At idle, if you are above 13.7 with few/no loads on, you are good. If you are above 13.7 at 2000 with most normal loads on, you are also good. Once you drop under 13.7 it is unlikely you are charging the battery enough to put back the energy it took to start the car. Also, you might just be adding more loads than the alternator was designed for. OEM is about 50-60amps, and a single fan could be about a quarter to a third of it's max output.

If you are getting different readings at different spots on the positive from the Alternator to the battery, you could try just using a jumper cable. Just be careful not to short it out. On a 5M it is a pretty long run, but there shouldn't be too much of a drop. Check the ends to see if there is any corrosion inside the wire insulation.

The 2 wire ends look ok. I didn't peel them back as I am planning to replace the total lenght of the wire run and eliminate the engine fuse, relay box that has the 1.o yellow fusible link in series with the white and blue wires that are plugged into the fuse, relay box printed circuit board.

[captainbuford]

The voltage drop you are seeing when lights and and fan are on aren't a whole lot...

These cars don't have a big alternator at all to begin with like 50-60 amps, my lights dim when I roll my windows up, HID's draw my voltage down...etc...
ANY added current draw on that small of an alternator is going to have voltage drop. As long as you are in the 13.5+ you are okay, 12V batteries tend to rest around 12.8~...
If you start dropping below 13.5, all your alternators current is being used and you are starting to pull battery power.

If you're really worried about that drop, measure your resistance between the alternator and fusible link, the resistance on the fusible link, see what you get, you can add charge cables to cut down on resistance and maybe stabilize that drop, but I doubt it will help since it's such a small drop.

If anything add another charge line, 4 gauge with it's own fuse holder, and add engine/battery grounds.

Mrbubbles I am going to replace the charge line and add a 60 amp fuse in series. The resistance of my fusible link is less than 1 ohm measured at the disconnected Alternator B+ terminal and the other end disconnected at the battery. There is no voltage drop across the yellow 1.0 fusible link inside the engine relay, fuse box

[MrBubbles00482]

Mrbubbles I am going to replace the charge line and add a 60 amp fuse in series. The resistance of my fusible link is less than 1 ohm measured at the disconnected Alternator B+ terminal and the other end disconnected at the battery. There is no voltage drop across the yellow 1.0 fusible link inside the engine relay, fuse box

If your resistance is that low then I highly doubt replacing the charge line will help that much, if at all. No resistance is ideal, but that little isn't going to hurt anything.

[Donn29]

Ya, all seems fine. You might want to run a larger gauge wire if you upgrade the alternator though.

[captainbuford]

If your resistance is that low then I highly doubt replacing the charge line will help that much, if at all. No resistance is ideal, but that little isn't going to hurt anything.

I made up a test jumper 7 and 1/2 feet long with a 60 amp fuse in series. I am not sure is it is 4 awg or 6 awg. Battery voltage at idle is now 14.2 volts at idle. That's higher voltage than in 1982 when my car was new. When I install the jumper permanently it will be several feet shorter than now so the voltage may be higher.

[MrBubbles00482]

Very nice!