Hey Folks-
So, I upgraded my dead electric fan to a 4k cfm unit out of a ford taurus. This fan draws 33 amps when on. I am also running MSD and plan on installing a stereo in the future, so I upgraded the stock alternator to a Powermaster 8002 100 amp unit. At idle, my system is at 14.4 VDC. When I turn the fan on, it drops to 12.0 VDC. I wired the alternator as a one wire unit per the instructions, but I hooked the factory 10 AWG charge cable back up. Does this alternator need a larger wire to charge the battery and run my accessories? Thanks!

MD, #10 wire is rated at a max load of 100 amps. #8 rated at 150 amps. Maybe you need to look into what amperage your alternator is actually producing at idle.

That's the plan, I'm going to pull it out in a minute and see where it's at. I just don't want to take it on the road and have it die on me. Thanks!

Looks like I don't have a tool that can read that high. I took a cruise around the block, volts came back up to 13 with the fan on. I let it idle in my driveway for a while, 13 steady.

Would it be better to set up this alternator as a 3 wire and hook up the original leads to the external regulator? I picked up the (- -) connector in case I have to go this route and replace the (| |) connector.

MD, I just went through this same problem, I run dual 13" fans, electric fuel pump etc...I was running a 100 amp alternator, I believe "SI-12". It was wired as a one wire alternator and used a #10 straight to the battery. Battery would not keep up. My alternator was good but did not produce anywhere close to the stated output at idle. I went to a local shop and asked for reccomendations. He built me a 140 amp "CS-130" alternator that produces enough current at idle to run everything. He wired it as a one wire and had me change to a #8 wire to the battery. Problem solved. I do want to research and confirm wire size is large enough.

Keep in mind with a 1-wire, your rpms have to hit a certain point to "turn on" the alternator. My 140amp unit turns on at 1,200rpm initially and stays on regardless of rpm until the key is off. For mine a #6 wire was even recommended. So if you are checking the power before you have given the motor a lil rev to turn on the alternator, then you are just reading battery.

Thanks, these voltages are read after the bump to start charging. I am going to have the alternator tested and see what's up.

Alternator passed testing. Did you run #8 wire to the battery and have an additional wire to the junction block? That is my last guess.

#8 should be run to the horn relay, not the battery.

Ron

Thanks -- it was mentioned in a different thread that I run #8 to the junction block and the starter solenoid, what do you think about that?

+1. I am running the CS-130 as well. Mark VIII fan. #8 wires.

When that fan hits, it REALLY pulls a lot of current. Over time you may find that killing that 100 amp alternator/battery setup.

Especially if it is a hot day when engine temp already over 190 turning on the electric fan at the start and running a high current mini starter....something will have to give.

MD, I just went through this same problem, I run dual 13" fans, electric fuel pump etc...I was running a 100 amp alternator, I believe "SI-12". It was wired as a one wire alternator and used a #10 straight to the battery. Battery would not keep up. My alternator was good but did not produce anywhere close to the stated output at idle. I went to a local shop and asked for reccomendations. He built me a 140 amp "CS-130" alternator that produces enough current at idle to run everything. He wired it as a one wire and had me change to a #8 wire to the battery. Problem solved. I do want to research and confirm wire size is large enough.

Whenever you upgrade the alternator you also need to upgrade the power cable from the alternator. An 8g would probably be an absolute minimum depending on cable length. Longer cables need to be bigger.

Next forget about the battery, power when running comes from the alternator. Think about things from this perspective as you go about designing wiring and measuring things. It actually can be a good thing to run larger power cable to the power bus and smaller wire to the battery. Battery charging does not require that much current and generally there is less power required when the engine is off. So the battery connection can be smaller.

If you have to run, or really want to run, a one wire alternator you will have to measure voltage at the alternator. That is where the alternator measures and adjusts it. If it is 14v there the alternator is doing it's job just fine. Personally I would not run a one wire alternator. I much prefer an internal regulator using an external/remote voltage sensing wire. That way the regulator/alternator can adjust voltage to get 14v at the power bus (means driving it a bit higher at the alternator if you have voltage loss in the alternator power cable...).

Don't forget the ground side of the circuit here either. Higher power devices will also require higher current ground connections.

Be conservative on the connections on all high power circuits. Any resistance in a connection can create a lot more heat than most folks realize. Alternator power cables should always have soldered terminals and never just crimped.

One more question: could all of this be caused by a bad ground at the fan?

MD, my battery is in the stock location. The one wire goes straight to the battery so its only 18"-20". My car was already wired like this when I bought it. I have seen numerous post advising not to run straight to the battery, but none explained why. I would definitely be willing to change mine if neccesary.

Digging in a little deeper, I found a questionable ground connection at the battery in the trunk. The clamp on the terminal was a normal "crimp-on" lead battery connector, but the ground cable was not crimped in. Instead, it was wedged in the clamp part of the connector and clamped in. i am going to replace this with a new battery connector. I added two big fat grounds from the block to the frame. I also added an 8 AWG wire to the junction block from the alternator. I am going to try it like this tomorrow when I get the new connector and see what happens.

If all of this doesn't work, I am going to get a new electric fan or switch to a mechanical one. Ugh.

Ok... all those upgrades didn't work. One more try, new battery tomorrow. Already ordered the mechanical fan stuff. I bet this electric fan is on its way out.

If by clamp on connector you mean those cheesy .99 bat terminals that clamp the cable under a strap held down by 2 1/4" bolts, you're asking for trouble. Those things give nothing but grief. The ground side especially is so short it is crazy not to replace the whole cable. A crimped or soldered end is much better, even a short repair cable that crimps onto the original cable about 6" from the bat is better, as it gets the connection away from the bat acid. jim.

Yep, it was one of them, but the wires weren't clamped by the 2 1/4" bolts.. they were stuff around the terminal.

Thursday morning update: Battery failed the load test! New battery in the back of the subaru, I'll see what it does this evening.

Car runs great -- fan hits, volts come back up to 13.5. I idled her for 20 mins, temps stayed steady with fan on!