4 batteries, 2 caps, stock alternator

I know that this topic has been beat to death, and I expect to get some opinionated responses.. but unless you can tell me exactly WHY my system runs as well as it does when the car is running and WITHOUT the h/o alternator, then please don't just tell me to just go buy a h/o alt. Here's my setup:

1997 Plymouth Grand Voyager Minivan (soccer practice never sounded so good..)

1 x standard car battery

I have the three ran parallel with a relay/isolator at the car battery. I have a Kole 2.5 farad cap and a Power Ackoustic 6 farad cap.

I'm trying to figure out how my extra batteries and caps make a HUGE difference when my car is running. My lights don't dim anymore, my system sounds great and everything stays charged. Regardless of how many of you say that extra batteries do not help when the car is running, this works and I'm trying to understand why. The digital readouts on my caps usually say about 13.7 volts when the car is on. Before adding the deep cycle batteries that number would dip down to 11 volts or lower during loud bass hits. Now it never goes below 12.5 and usually stays pretty steady in the mid 13’s.

You know, I think I just answered my own question. The alternator supplies power as much as it can until the draw brings the voltage down to the level of the batteries. At that point the power is drawn from the batteries keeping the voltage from dropping below 12v. Does that make sense? If so, then the extra batteries and caps DO help and all those statements I have read about them being useless with the engine running are very misleading.

The other question is concerning my charging system. I plug a 12v deep cycle battery charger in at my home about once a week or so and let it charge the system over night. I don’t disconnect the batteries but just hook it up to the positive of one 6v and the negative of the other. It usually seems to charge all the batteries without problem and I keep a close watch with my multi-meter. This morning I unhooked it and I guess the automatic turn-off didn't kick in and the batteries are reading at around 15v (each 6v is at like 7.8). What happens if a battery gets over-charged? Should I do something before I start my car?

Your system runs fine the way it is because everything is new and fresh, the batteries at least. They will continue to do so for a while, until a point comes where they need to be recharged, then your alternator will be taxed tremendously in order to recharge all of those batteries and caps.

I think the real question that should be adressed here is why you have two 12's and a 15"

Thanks for the reply.. although I wasn't asking if it was going to damage my alternator. I have a relay that prevents that. You must have missed the part where I explained my charging system. My question had to do with the benefit of running multiple batteries even when your car is running.

Why wouldn't I run two 12's and a 15? I have a pair of 10's I will be putting back in soon as well. I have an active crossover system and some serious sound processors with my 29 speaker set-up. If you heard my system you would probably change your opinion on that matter.

Thanks for the valuable input. Just to clarify, I'm not trying to say that a H/O alternator would not help my system. I know it would, and eventually I intend to upgrade this aspect of the system. I am unsure if I intend to keep this vehicle, so that has been the main deterrent for this upgrade. As far as the elaborate set-up is concerned.. it's been an ongoing experiment. Phase and cancellation, crossover adjustments, wiring configurations, etc. etc.. I just want to know how all of it works and eventually I will tone it down to what I like the best.

The reason for this thread was to find out WHY the batteries and caps were making a difference in my set-up because I kept reading other threads stating that they were useless while the car was running. It’s not that I am trying to talk my way out of buying the h/o alt, it’s that I already know I need that. I just didn’t understand how the batteries were making such a difference and I wanted to find that out instead of just hearing more of what I already know. Now I understand that they are not useless, but I cannot rely on my alternator to keep them charged. I don't think I need to charge the batteries at my house on a weekly basis either.. I probably just have too much time on my hands. The two 6 volt batteries say 200 AH – 20 hour rate to 1.75 VPC @ 77 degrees F. I don’t ever run the system for longer than 30 minutes or so at a time and I’ve never seen any of the batteries drop below 12 volts (or 6) although I see what you mean, arrow12, that I haven’t dropped the full load on the alternator yet.

As far as spending money on the batteries.. they were all free from a friend who does back-up power supplies for business servers. I have like 60 of them. I get the caps and much of the other stuff through auctions for practically nothing because that’s the line of work I’m in. Although I haven’t come across a H/O alternator at the auction yet..

So you think the use of different size subs is so uncommon? I tried running all 12’s, all 10’s, all 15’s.. I tried different combinations.. I just like the tightness of 10’s for the kick drum and the fat lows that the 15 can hit. And the DD 12’s are just ungodly. You guys will probably have a hay-day with this next part but here is the layout for the 29 speaker setup. I crossover each set of speakers starting at the subs with my ultra-low (15") to my mid-lows (12") to my high-lows (10"). If you work your way up with low-mids (6x9)(6.5), mid-mids (5x7)(5.25), and high-mids (4" & 3") and then the highs (tweeters) counting any two-way speakers as two separate drivers you will come up with the 29 speakers. It’s a lot, but it’s really more of an experiment than anything. The sound processors were set-up by a friend who does acoustic design for theaters and the purpose is primarily to adjust the phase of each set of speakers to prevent excessive cancelation. It sounds complicated, but I’m telling you, the system sounds amazing. I’ll post some pictures once I finish cleaning up the install.