Not sure what could be the issue here, i upgraded to a DC power alternator (180 amp) and it's not charging the battery above 12v.

My car is an S4. Wiring has been modified to accept an S5/FD alternator. L terminal is the resistive load in the dash, and the S terminal is going directly to the battery positive. B terminal feeds the battery through the 80a main fuse with 4awg wire.

As advertised, the alternator was plug and play (for the most part). Car started right up and ran fine. But volt gauge never showed anything above 12v. Whether hot or cold, stayed the same
Turning on electrical loads does cause the voltage gauge to blip slightly (volvo power steering pump, turning on the headlights).

Here are pictures for reference. Any insight is much appreciated

 

Also, forgot to mention, the 80A main fuse is not blown, and none of the electronics malfunction under engine load. Drove the car for 20-30 minutes, really giving it the beans, and the voltmeter stayed pinned at 12v the whole time

 

Is the alternator casing coated (could be clear anodized or powder coated)? When I installed an anodized side mount alternator bracket I lost about 2V because the alternator wasn't properly grounding to the engine block through the coating. In my case, this was resolved by running another ground cable from the engine to the (uncoated) alt cage.

You could sand a small, out of the way spot on the casing and test the voltage between the alternator casing and the positive terminal - this will tell you if the alt is actually charging low or if there's a connection issue.

 

Didn't think of that. Interesting. I don't believe it's anodized (although the company doesn't explicitly say that it's NOT), it says it's just standard billet aluminum. But I will try that. I'll test the B post against the casing to make sure the regulator is doing it's job, and if so, I'll try adding a ground to see if that changes anything. Any specific gauge of wire needed for the ground? Is 16awg sufficient you think?

 

Have you verified the reading with a multimeter? My voltage gauge is a consistent 1.5-2V low at all times.

Plus, a rewound alternator doesn't usually charge as well at low engine speeds. I know you went for a drive, just mentioning it since it could compound the problem from a wonky gauge.

 

I have not, but the gauge was reading correctly when I had my FD alternator. Unless by the will of god, the gauge went out of wack when I swapped to the new alt. Lol.

I'll verify with a gauge as well and see where that gets me

 

I used a short piece of 4 AWG wire. The ground path (whether through the casing to bracket to engine, or external cable) has to be capable of returning all current that the alt is putting out. Small gauge cable will likely just burn up if forced to carry that much.

If you don't have the time or resources to make a good cable, you could also try sanding the inside of the mounting ears on the alt cage (where the main bolt goes through) and the corresponding mating surfaces on the alt bracket to try to get a better electrical connection there.

Either way testing with a multimeter is a must to ensure there actually is an issue (like WondrousBread suggested), and then to isolate the issue. Be sure to sand a small spot for your negative probe to be on the casing before testing the alt output voltage. The aluminum cage likely has some sort of coating on it, otherwise it would oxidize and get the ugly white powder on it like the stock aluminum parts do.

 

Got around to verifying everything with a multimeter

Battery voltage at idle is 12.3 volts. Alternator pushing out 12.2 volts at idle. Seems like the back part of the alternator casing is cast, rather than anodized aluminum. Seems to be properly grounded

What else could be wrong here? I'm stumped

 

Have you had the alternator tested? It could simply be defective.

 

$600 alternator, i hope it's not defective, lol. I have not. Any local parts store should be able to test it, correct?

 

I usually go to my local alternator shop. If you don't have one, some parts stores test it. It's worth calling ahead to see.

$600 is pretty crazy; it had better work well for that much money. Neat that the case is compact. I'm using a 170A Taurus unit and it's pretty bulky.

 

Gotcha. I'll call around and see if i can get it tested and report back with my findings
yeah it's pretty compact. Fits in the same footprint as an S5 or FD alternator, but cranks out 180A

 

Have you checked to ensure the the L terminal wiring isn't just an open circuit? What's the resistance measurement from the L terminal (at connector, unplugged from alternator) to ground?

 

I have not checked. How would I go about doing this? If i unplug the connecter with the car running, it will stall out, correct?
Or do you mean test resistance with the car off?

If so, am I testing the L terminal against any good ground? (ie. Engine, chassis, starter, battery negative), or does it have to be the battery negative?

Also what should the resistance be? How many ohms is within spec?

 

I'll skip the boring stuff, and suggest that you wire the L terminal to 12V with an 12v bulb placed inline.

If that circuit has failed somewhere in the dash, it will cause exactly what you're mentioning.

 

How much resistance does the L terminal need to see? FSM puts it around 1-3 volts. Not sure what size resistor could be used to step 12v down to 3. Ohms law not doing me any good here, lol

 

It needs to not be infinite (open circuit) with the connector off, car off, measured between that pin and any solid ground. If it's infinite, well, that's an issue.

Who knows what previous owners may have done/not done... but if you wire 12v and a bulb as per that above diagram, even just temporarily, that will rule it out.

The bulb should be lit with the car off, but key in "run," and off with the engine running. Any map light bulb will work.

 

Roger Roger. Will give that a shot and see where that gets us.

Going to get the alternator tested in the next couple days. If it passes, then I'll wire in a bulb, and see what happens

Will update when I have more results

 

I edited that picture above to show a couple of things... one being power should come from a switched source if you go down this route permanently. Second, I wired in a resistor so that in case the bulb burns out, the alternator would still charge.

 

Update on this issue for anyone following along, or anyone else that comes across this thread in the future
Rather than pull the alternator and take it to get tested, i figured I'd just to the bulb test and get it out of the way.

You were 100% correct! Dash circuit failed. Infinite resistance at the L terminal. Hooked up a bulb in series with the alternator, and it's charging at 15v, absolutely perfectly.

 

This may be a stupid question, but what kind of connector are your using for the alternator? My S5 has a square 2-pin connector.

 

Glad to hear it!

 

The S5's and FD's have the same connector type. The alternators are plug and play with each other. They are both LS style alternators whereas the S4's were LR style.

here's a picture of the connector I'm using, in case you still needed it. I'm actually running an upgraded S5 alternator.

 

Glad it's sorted out!

I'll need to look into my alternator wiring again. It charges fine, but if I take the belt off and start the car the battery light still doesn't illuminate.

 

S5 and FD have the SAME CONNECTOR but are NOT wired the same

That would have been your PROBLEM.

S5 and FD needs the wire pin positions reversed to switch between each other.