sufficient alternator amperage

     Car; '96 Audi A4 Quattro, 120 amp alternator.

     Amplifiers; 1300/5, 180 amp fuse rating - 1000/1, 100 amp fuse rating.

     These amps are not in my car right now as I'm waiting to pick up a H.O. alternator. The alternator is 225 amps, 120 at idle. So far it's the biggest one I can find for my car (if there's a bigger one for around $300, I'd like to know). My goal is to install said amps and turn their gains up 1/3 to 1/2. I have bass knobs for both that will in most cases be turned down. There are times I'd like to turn those knobs up though.

       So I have 270 amp fuse rating and a 225 amp alternator. I know they don't match and I know I can't listen to my music with my bass knobs turned up all the time. I'm probably too old for that level of listening anyways. I want to know if I can get away with running the amps at the" moderate" level I mentioned, reserving the right to flex my windows on occassion, without killing my electrical system.

     Sorry if this post seems fragmented, I'm in a hurry. I didn't list names because the fuse ratings probably give you an idea these amps do what they say ( I hope ) plus I think there's something about name dropping in the posting rules. If more info is needed, I'll include it. And please refrain from suggesting power caps. I have enough "friends" who include caps with their two cents. Thank you.

Fine the employers.

When your alternator can't keep up, the voltage will drop from ~14.2V (typically; 13.8V - 14.4V) and discharge the battery. (The battery will normally be ~13.6V (surface charge) and drop to under 12.7V (being the full voltage of 12.67V less the internal resistance loss - maybe 0.015 Ohms x its current.) That is no problem provided there is enough battery reserve time, and that enough recharge occurs thereafter. And it assumes the amp does not overstress the battery, but that is more of a problem for AGM batteries and large amps (>2kW). Flooded batteries do not have the same sensitivity (their higher internal resistance (typically twice that of equivalent AGMs) limits the current - ie, typically half the short-circuit current of AGMs; plus they can boil-off electrolyte to keep cool).     Many people use a 2nd battery for the amp. Typically an AGM (legally that is, if not mounted in the engine bay else in a sealed enclosure vented to outside) mounted next to or as close as practicable to the amp. (Through a battery isolator (IMO) of course!) That helps overcome voltage dips during high-current surges along the main-battery to amp current path (including ground) as well as providing independence so you still have cranking power if you forget to turn the amp off. I wouldn't worry about the alternator fuse. It is really only there to protect the alternator-battery cable in case it shorts to ground (the fuse should hence be near the battery). The fuse is not - and probably will not - protect the alternator. (Not that alternators should need fusing - by nature they are be self limiting and their design should handle that. Although you probably have a Bosch alternator - their power diodes were underrated in at least their 1980 to late '90s alternators!) Don't forget the Big 3, that will reduce voltage drops. (And maybe prevent ground-path burn outs which can be VERY expensive after resulting equipment damage - cables, EMS, electrical accessories etc - anything with a ground path.)

Thanks oldspark. The reason I mentioned amperage is because I've been told that the alternator needs to match or beat the fuse rating of the amp. But since I have the vehicle I do, and I don't know any cool people, the biggest I can get right now is 225. And I've been told I need at least 270. I'm not concerned about blowing my amp fuse. I just wanted to make sure I could power everything sufficiently and not watch my voltmeter drop constantly. And I think you answered that anyways. I already have 0awg set aside for my big three. And I have a couple yellow 6v batteries wired up under the hood, (that's what runs the car). I have a 3rd 6v I'd like to isolate in the trunk but I'm not sure that would even work and I think I'm probably breaching another topic. Thanks for the info.Fine the employers.

Thanks for the thanks. I feel like the Devil's Advocate because I too say - in principle - that the alternator should exceed the amp rating. (Or rather, that batteries etc won't make up for an undersized alternator as far as keeping >13V is concerned. They will however extend the reserve time (available capacity), but they still need to be recharged (hence reduced amp current at the end of the driving session, or grid charging, etc.) However that statement "the alternator needs to match or beat the fuse rating of the amp" isn't strictly true, but hopefully my writings explain that (ie, if under 13V is okay, and the battery is recharged...).    But yeah - normally I argue the other way... "get a bigger alternator".   I guess I just like giving the alternate scenarios or views - even if they are my own. (I constantly fight myself, but not as much as I fight back; hence I usually lose.) Probably my best summary would be to prioritise the alternator, then worry about batteries. (Unless more batteries are needed to reduce (AGM) damaging current surges.) Though the Big 3 should be #1 since that is required eventually, and in the mean time, it reduces voltage losses which IMO is never a bad thing. [ Likewise, as big as practicable cables from the battery, or alternator, to the amp; especially ground which can be overlooked, and people often forget that grounds may be common with cranking, headlights, etc. Plus if the ground is from alternator to (engine to) chassis and battery to chassis, and then chassis to amp, they are only short lengths to double up on to halve its resistance (keeping in mind that that total ground resistance will be less than the +12V feed with the same gauge, so it's not as if you halve the total resistance - you just halve the ground resistance "cheaply". The again, if that resistance is negligible - but then I argue for ground redundancy - lose one ground and the other(s) should cover it. As I wrote, losing ground can be very expensive. Who had the Hummer with 7 DVD screens and burnt the lot out? Several $thousands worth of damage just by losing a ground. Losing the +12V is cheaper - things merely stop working. ]    Oh dear, repeating my same again? Or maybe emphasising, and with a different slant or extra case studies...? 6V batteries? !! ?? Fine in terms of 2 big capacity 6Vs to get a big capacity 12V, though a 12V monoblock otherwise is better. (It's not like you can replace one 6V and not the other, though series is not as touchy as parallel, though one failed series 6V means the other gets far more than 6V, hence boiling (the heating, then fire?) Ok - done with my due diligence info.... But I wanted to check that your aren't considering adding the 3rd 6V battery... It must be 12V that is added - in parallel. That's probably obvious, but I have known people to add a 6V battery in series with 12V for 18V to boost output power (it works - the vehicle electrics burn far more powerfully than a mere 16V over-voltage!). And I have known people with 2 series 6V to parallel one 6V with another thinking it will help. Whilst is does reduce the paralleled 6V effective resistance, you cannot recharge them; the current sufficient to charge the single battery is only half sufficient for the paralleled. Hence early failure of the parallel batteries, and over-voltage of the single battery. 3 failed batteries usually within days. And maybe a fire too.    Alas the later stuff above is obvious to many, but I understand the (flawed) logic. It reminds me of a kid that once connected 1.5V batteries in series with a little cassette... er, mp3 player to boost output. It was obvious logic at the time. Rumor has it that he or she now writes authoritatively (allegedly!) about batteries, battery isolators, and alternators. (So there is hope for some!) As to Audis, geez man, I'm cool and I considered Audi! And that's not bad for someone with the same Car Marque since driving age (and still the same vintage LOL!). [Not that that is what makes me cool. it's just that my jumper is in the wash....] Besides, I have seen some real hot looking Audis. I mean, cool looking. [ Unfortunately I no longer trust them. They released a model here some years back that was known to have a gearbox that would fail after about 6 months. Instead of the (allegedly!) guilty Agents getting justice, it was transferred to "industrial espionage" by 2 guys - namely the ones that raised the local alarm. Foisting crap on consumers - bad. Criminalising innocents (knowingly and deliberately IMO - unforgivable. ]      ( Maybe moderators should cut that [last bit] out? It's not like I am one that normally publicises events like that.... ) But 12V in the engine bay, and an optional battery (but recommended for big systems) in the boot/trunk; irrespective is 2x6V + 1x12V or 4x6V etc, but each battery "matched" to the other one in its string (ie, series) if it's 6V.    And an isolator when not in use to avoid parallel battery interactions. Maybe the UIBI? (A relay controlled by the charge light or "is charging" signal - ie, off when not charging.) And with a high-impedance input MOSFET version on the horizon (at the moment it's 2 years closer to that horizon LOL), I suspect easy configuration even for EMS controlled alternators (ie, DP etc types as opposed to traditional UIBI D+ or SL or SIL types.) Dang! Even my short "thanks for the thanks" replies are long! Best wishes.

Sorry this takes so long to get to. I'm in school and that's where my focus is. Ya, big three along with existing + - including extra ground upgraded to 0awg in the works. The batteries are of the gel variety and take the place of a worthless one. They are a reputable brand, and they were aquired by a friend of mine who passed the savings on to me. So amperage remains the same while the voltage was taken up to 12 (13.5). They've never gotten hot or drained. But I don't beat on my system either. Also, I do have the third one but I wasn't going to use it without asking someone. The math in my head just didn't work for it. Anyways, everything's temporary until I upgrade the alt. Thanks again, oldspark.Fine the employers.