HO Alternator Idle Conundrum

[bananapehl777]

I wouldn't remove any of your factory grounds. You could check for corrosion on contact points and maybe clean them. If you want, you could add another ground wherever you think that the factory grounds are bad. I've seen and heard many times from long-time installers that sometimes people doing an extra motor to frame ground actually made a car run better, because the factory ground was so old or used up that it just wasn't flowing properly. Corrosion creates resistance, because the corrosion does not conduct electricity like when the metal is in good shape. Dirt and grime and things like that are the same, if it's on a contact surface.

Something you could look into is a real capacitor setup. There's some high quality capacitors that actually have a bit of storage, and that might help your idle voltage, if you get an actual proper setup. There's different types of batteries and power storage that work better than just AGM batteries, and they do cost more money (from what I've seen).

I ran all of my batteries on a closed loop system, basically, in multiple vehicles. I ran + and - directly from alt to directly from battery in the exact same sized wiring. Then from front/factory battery I ran both + and - in the same exact size to my battery bank. I did not ground to the frame with anything except the front batter and alt casing. The entire battery bank in the back went to the front battery.

Thank you for that info. I am a bit confused on how I could run that closed loop set up that you mentioned on my car with just two batteries. How would it help my voltage? Car is an 05 Subaru Outback XT (2.5 L 4-Cyl Turbo)

Also, UPDATE: This weekend I went through the grounds for both batteries and the engine ground. I cleaned them up and stripped paint to ensure a good connection and verified connection with my multimeter. Measured 00.0 ohms on all of them. (Turns out the original shop that did my big 3 did not upgrade engine ground, so I added 0 AWG for engine ground.) I also went ahead and increased my idle speed to ~950 rpm. Based on the alt specifications and pulley ratio, that gets the alt to about 180 A. Took it for a test drive today, and cranked it to full volume but still saw a minimum of about 12.5 - 12.8 V and headlight/gauge cluster dimming. This feels pretty frustrating given all this equipment for 1700 W, but I'm thinking an overdrive pulley might be the next option. Still, I would think 180 A would be enough for this system power.

 

[Buck 5,000+ posts]

Thank you for that info. I am a bit confused on how I could run that closed loop set up that you mentioned on my car with just two batteries. How would it help my voltage? Car is an 05 Subaru Outback XT (2.5 L 4-Cyl Turbo)

Also, UPDATE: This weekend I went through the grounds for both batteries and the engine ground. I cleaned them up and stripped paint to ensure a good connection and verified connection with my multimeter. Measured 00.0 ohms on all of them. (Turns out the original shop that did my big 3 did not upgrade engine ground, so I added 0 AWG for engine ground.) I also went ahead and increased my idle speed to ~950 rpm. Based on the alt specifications and pulley ratio, that gets the alt to about 180 A. Took it for a test drive today, and cranked it to full volume but still saw a minimum of about 12.5 - 12.8 V and headlight/gauge cluster dimming. This feels pretty frustrating given all this equipment for 1700 W, but I'm thinking an overdrive pulley might be the next option. Still, I would think 180 A would be enough for this system power.

It's not quite a true closed loop. I just did it with the idea that the more batteries in between a frame ground and the amps would possibly result in less random feedback getting into the amps with the batteries maybe acting as a dampener in between them.

The problem you're having with alt power at idle is a common problem. I faced the same problem in my Explorer, and I had a 300 amp alt charging at a set 14.8-15v. My alt only did like 60-80 amps at idle, something not very much. You could always get another alt. I had a Batcap 3000 up front and 3 sort of generic group 31 100ah batteries in the back, and I'd still drop to the 12's or even 11's after a pretty short time if I didn't rev the motor up. Only 2400 w rated RMS, and it still did that. But at about 1800 RPM, I was playing high 140's across a pretty good bandwidth, and wouldn't drop below ~13.5v on the lowest notes (below 27 hz or so). Most notes would keep me in the ~13.8v range.

Be careful over spinning your alt. If you engine revs high, then a smaller alt pulley could over spin your alt at high engine RPM's. From my experience, the higher your engine revs, the worse alt output you're going to have at idle. I've seen some older HO alts not even turn on until like 800 rpm on some motors like Honda 4 cylinders because the alt wasn't spinning fast enough. So, I would check on the gearing ratio between your current crank and alt pulley, and see if the alt would over spin if you put a smaller pulley on there. Some alts have bigger pulleys on them for a good reason.

I just turned the volume down a lot when I was at a stoplight or something. That's really the easiest solution haha