need advice, dimming problem

hey all, maybe someone out there can give me some ideas here. im having a dimming headlight/dash light issue, kinda annoying. ill post all the wiring and gear below. incase i forget to include what brand things are, its all rockford fosgate except for the waveguides.....

big 3 upgrade-0/1 wire(fosgate)
new battery-xs power 3400
new alt-250 amp

1x rf power 1500bd amp for 2 12" rf power hx2 subs running@ 2 ohm(birth sheet shows 1724 rms@2 ohm)
1x rf power 550x amp(birth sheet shows 724 rms@2 ohm) for a set of usd audio waveguides on front 2 channels(i believe they are 8 ohm) and a set of rf fanatic q components on rear 2 channels(4 ohm)
1x rf power 250m amp(dont have birth sheet) for a set of rf 6.75" he subs in front kicks(2 ohm)
1x rf 25 farad carbon cap(maybe useless from what ive been reading lol)

as for the wiring, all fosgate....

0/1 gauge from battery to cap then 4 gauge from cap to distro block then 4 gauge to amps
0/1 gauge rear chasis in rear to cap then 4 gauge to distro block then 4 gauge to amps

i also have an audio control eqs which i may have to much boost in some areas as i dont have access to an RTA, every shop i know wants to charge an arm and a leg to do it....rediculous

any ideas or help will greatly be appreciated

So you only have one battery?
That's the first problem.

It's a deep cycle battery. That's the 2nd problem.

Is the cap on the light circuit? That's where it should be to prevent dimming lights (unless you move the AGM battery adjacent to the amps in which case mount the cap with the battery (to protect the battery)), but your case is one of insufficient power distribution.

wow i didnt think upgrading my factory battery to the deep cycle would be an issue here. what are you reffering to the cap being on the light circuit?

To stop headlights dipping, a cap can be used across the light supply though as I have often written, a battery is better (even if a 1.2AH AGM etc). But you also have dash light dimming and that's a separate circuit.


If a single main battery is used with big audio, then it's usually a cranking battery since they can supply a higher current better (and without less damage to the battery - especially if it's an AGM).
And if your alternator is big enough, then there is no need for a deep cycle unless you want to run the audio with the engine off (ie, alternator not operating).

But big audio systems are usually multi-battery installations - namely a normal cranking main battery, and then audio batteries (usually) located with the amps connected to the main battery/alternator via a battery isolator.
That provides the local surge reserve for burps as well as ensuring cranking independence should the amp battery run too low.

The audio batteries can be deep cycle if a long reserve time is desired, though cranking batteries are better for surging amp draws.

In secondary audio battery systems, caps are only used to protect AGM batteries from high surge currents, but that is only relevant for systems above 2-3kW output (assuming normal large sized AGMs).
But even then, an extra battery is a better solution. IE - it doesn't take a large battery to beat even a 25F cap (1.2AH should be more than enough) but the extra battery(s) is to reduce the surge on a single AGM, hence usually 2 (or more) matched batteries.

Long term paralleling of multiple audio batteries should be avoided, but they could be manually isolated if unused for long periods (ie, for days etc).
If high power audio is not required without then engine running, the main battery isolator could be used as a master control for separate relays - ie, between the main/cranking battery and audio battery, and relays between that audio battery and each of the other audio batteries.   
Of course the inter-audio-battery relays can have a manual switch to parallel them when the main isolator is off.

well i did forget to mention....i did have, as you stated, a 2 battery set up before this. i had the xs power 3400 and a xs power 975 with the battery isolator. i had to remove the xs 975 due to it had a swelling issue and i didnt want it blowing up under the hood. removed the isolator as well.....but while  i did have the 2 battery/isolator setup, i still had dim issues. i do know that dodge has that can-bus crap(which mine has). could that have anything to do with this issue? i have a digital volt gauge on the driver a pillar which never drops below 14.1 even on heavy bass/music but the lights are dimming. i took a reading at the rf 1500bd amp and it was showing 14.15 volts

What is the voltage when charging at the main battery? It should not exceed 14.4V long term (unless specs (Optima LOL) say different).
Overcharging kill AGM batteries and can cause swelling.
However the swollen AGM may have had a collapsed cell etc.


Refit the isolator. One bad battery brings down the other. And for AGMs, thermal runaway can occur (selling, heat & BANG!).

The 2nd battery should show the same voltage as the main battery when connected, less any voltage drop due to its load. But of course that drop should be minimal.

i figured maybe since the 2 batteries where of different sizes, maybe thats why i had the swelling issue on the smaller battery. i had the smaller battery as the cranking/starting battery and the big one as the 2nd for stereo and what not

No, the swelling has nothing to do with battery size.
And when charging, battery differences are irrelevant (assuming they are both 12V lead acid - ie, wet cell or AGM - and not failed).

Only when batteries are left connected in parallel when not in use (charging or supplying a load) are mismatches a problem.
But that is not size related - it is terminal voltage and self discharge (profile) related.
In short, long-term or permanently connected batteries should be matched and symmetrically connected (ie, equal +ve & -ve interconnects, and for 2 batteries with +ve out from one battery and -ve out from the other). However that is academic in most automotive situations since the batteries are not collocated (hence different temperatures) and have differing loads and current paths, hence becoming more unmatched as time progresses.   
Besides which, even 2 matched batteries left permanently paralleled and unchecked means double the failure rate with both batteries being lost (ie, you replace 4 batteries in the time you'd normally replace just one from its statistical "self failure" failure rate).

Even shorter, that's why battery isolators are used. Hence because batteries are isolated when NOT being charged, their size, capacity, charge profile, history etc become irrelevant (except in cases of cell failure).
Batteries can be paralleled when charging, but otherwise only as required - eg, to provide extra capacity for a load.

well like i said, i had an 500amp isolator for the batteries and the thing swelled....took to auto store for them to dispose of. maybe my amp gains are up to far too?

The isolator did not cause the swelling. In fact, if not for the isolator, it could easily have turned into a fire.


Think about it.
When an isolator is not active, the 2 batteries are isolated.
Are you saying the battery swelled just sitting there, or when connected to a non-charging alternator?
When an isolator is activated (ie, when the alternator is charging), the 2 batteries are connected and it's the same as a direct link without an isolator. Do you think it more likely that that's when battery swelling occurred?

If the latter, then either the alternator is overcharging (its voltage is too high), or the swollen battery had a failed cell or cells.
If it's failed cells/s, then if it's still connected to the other battery when not being charged...
And since an AGM battery can supply more current than a 250A alternator (not that it would into a not too failed battery) and itself heat up... ie thermal runaway of both AGMs.


Get an isolator, else manually disconnect the 2nd battery when not being used and check its temperature (heat meaning high discharge or charge rate, or a fully charged or faulty battery).

ok, so im going to install a 2nd battery with that 500 amp isolator as well just like before. my only other battery is an autocraft gold series(regular not agm) rated at 1000 crank amp/850 cold crank amp/150 reserve. the xs power 3400(agm) is rated at 1000 crank amp/65 reserve/3300 max amps. would using these 2 with an isolator be a problem(mixing reg battery and agm style)?

Mixing any (same voltage) lead acid batteries is NEVER a problem PROVIDED an isolator is used.

However that assumes the paralleling is only when being charged (else when in use, but NOT when merely sitting and paralleling for long periods)...
AND that both batteries are in reasonable condition - ie, no collapsed or partially collapsed cells etc.


But whether AGM or wet/flooded, small and large, old and new, full or discharged does not matter when paralleled AND being charged.
Anyone that says otherwise usually does not understand batteries - nor sometimes even basic electrics! (Ohms, Thevenin, Kirchov Laws & Theorems) - though there can be some valid arguments - eg, as per jump starting vehicles with very flat batteries; etc.

ok man, i greatly appreciate all of your valuable advice......ive read other forums and some say its ok and some say its bad to mix the 2 types as well as different brands/models. i dont see it being an issue as you stated(both being 12 volts) along with the isolator. i do remember with the 2 batteries/isolator hooked up before, i always heard a faint clicking noise when turning the key ign/run, so im assuming that means the isolator was doing its job then?

LOL! Tell me about the varied advice!! Recently on mp3car I've had a... er... battle with someone re that issue. He insists that paralleled batteries WHEN CHARGING must be matched. Now despite someone else pointing out that in a car, no batteries will ever be matched when there are not co-located and do not share a symmetrical (and diagonal) +ve & -ve power path, he still persists. But he also insists that two batteries when paralleled see different voltages which not only defeats his own "matching" arguments, but also defies basic electrical theory (ie, parallel devices have the SAME voltage).


There are 2 types of battery isolator - ignoring diode and MOSFET isolators which aren't even worth mentioning - other than their avoidance (except for certain rare requirements but at the expense of battery life) - namely being the common commercial offering of voltage sensing aka smart isolators, or an alternator or charge-light controlled isolator.

I use the latter since it's cheap (merely a relay of your choosing), I have a charge light, and I'm not as gullible as other charge-lighters that think voltage sensing is somehow superior (in fact they are almost always inferior in behavior), I am able to find and attach to the charge light circuit, and I hate spending an extra $50 - $400 when it isn't required.   

Anyhow, the basic charge light controlled isolator is only connected when the charge light is not illuminated.
The voltage sensing types almost always have a turn-on delay after charging commences (eg, after the voltage exceeds 13.5V etc) and usually don't disconnect until some time after charging ceases (that can be hours depending on battery surface charge).


But no isolator should connect with mere ignition unless it's intended to parallel the batteries for cranking. But they should disconnect if the engine stalls - ie, no longer charging - noting what I said earlier about the different turn-off delays.

However some use the ACC or IGN to control their isolator (relay) which is better than permanent paralleling - just don't forget to turn off the IGN or ACC!
The main feature with those is that at least with IGN/ACC off, the relay/isolator is off and hence the batteries are isolated, and that's what we want wrt to not having long-term paralleling of batteries.


Note too the situation I am talking about. I am NOT talking about paralleling batteries permanently or long term to supply a load.
I am talking about paralleling batteries that probably have different loads connected AND are ONLY paralleled when charging (and maybe on select occasions for extra reserve - eg, cranking, winching, etc) and do not share location nor balanced charge/discharge paths.

The number of times people choose to argue with me yet they are referring to long-term connected balanced systems....!!!!   

As to sites that do not understand the difference, or fail to point out such differences... But many make a fortune from misinformation, so why not battery & accessory suppliers?

ok, so the isolator i have like i said is a pac 500 amp....has 4 inputs on top(2 small and 2 bigger). one small input is grounded, the other small input is remote. the 2 bigger input studs are for main power wire(in my case ill be using 0/1 gauge).....from battery 1 positive post(reg battery),  power wire runs to fuse(200 amp circuit breaker in my case) then to 1 of the bigger input studs on the isolator. then a power wire from other bigger input stud on isolator to rear of vehicle to another fuse(my other 200 amp circuit breaker) then to positive post of 2nd battery(agm). then from battery 2 positive post to capacitor positive(if i still need it).....does this sound correct?

It's the smaller "remote" that is controlling the PAC, so whatever that is connected to. (If you mean HU or amp remote, then whenever that "remote" is +12V.)

That PAC is merely a relay aka contactor aka isolator - whatever you want to call it. It has no smarts.


BTW - you need a fuse or breaker for the 2nd battery too! (ie, batt1 - fuse1 - isolator - fuse2 -batt2.)

Yea I wrote that I have another breaker for the other battery too sorry. So that schematic will work in my previous post?

I can't find any schematic. But as I wrote - batt1 (main battery) - fuse1 - isolator - fuse2 -batt2 with each fuse/breaker as close to its respective battery as possible. The fuses/breakers are to protect the interlink cable (and respective battery, and isolator if involved) if there is a short to ground along the interlink.

ok sounds good and once again thanx

hey man, just a quick note....ive been working on a fiberglass sub enclosure now and today i finally got it done for the two 12's.....anyways, i hope this doesnt sound rediculous but here goes. as a substitute box for the 12's i had a sealed that i bought yrs ago, the reason why i hated it was because it had a shared chamber for the 2 subs. is it possible the box type was for some god reason giving me issues with the lights? reason i ask is now after today when i finished all the wiring for the new box, i have very faint light dim. i did not readjust and settings on anything, they are where they were with the substitute box......anyways, just curious as i dont get it lol. may not need the 2nd battery now which im happy with....

Well, as soundnsecurity wrote in 2100w rms to 15 kicker l7?, the box can impact current draw.

And then there's the question if vibration is having an impact...