aluminum battery terminals

Hello again! I bought a new truck recently and I'm wanting to upgrade a bit. Due to the power I plan on running I plan on doing the "big 3" with some large gauge wire. Anyway, I have a sheet of 5/8" aluminum and I was thinking of just making my own custom application terminals. I know aluminum and copper don't play well together though, but I'm not sure if galvanic corrosion would be an issue in a spot like this. Bad idea? If so I'll just order some brass, but the stuff isn't cheap! I'm talking about blocks something like this, simple hole with a set screw kinda thing. I'd do it a bit different though, matched to fit the stock wiring and maybe even build in a few fuses into the positive block. https://i.walmartimages.com/i/p/00/03/39/91/99/0003399199215_500X500.jpg Also, I plan on running a combined 800WRMS or so of equipment. This is in a chevy colorado, so no runs loner than 6 feet or so. Would 4 gauge be enough? According to my figuring, I'm looking at around 120A of draw and I think 4 gauge is good for about 125A at 10ft right? Would I put less strain on my charging system if I used 1/0? Thanks for looking!

Yes, bad idea. Do not use aluminium. You'll put less demand on your charging system if you use 4G because that means higher resistance (than 0G) and hence lower current. [ Why do people think it's "harder" or "more strain" for an alternator to supply poor wiring or grounds etc? The alternator merely supplies less current (which come equate to "less strain"). That "more strain" etc is such a common statement.... Do they confuse a poorly functioning load with a straining alternator? ]

oldspark wrote: Yes, bad idea. Do not use aluminium. You'll put less demand on your charging system if you use 4G because that means higher resistance (than 0G) and hence lower current. [ Why do people think it's "harder" or "more strain" for an alternator to supply poor wiring or grounds etc? The alternator merely supplies less current (which come equate to "less strain"). That "more strain" etc is such a common statement.... Do they confuse a poorly functioning load with a straining alternator? ]

I see, kinda figured mixing aluminum and copper would be bad. I also assumed that the larger voltage sag from a higher resistance load would strain the alternator more, is that not sound thinking? Wouldn't the amplifier simply use more current to compensate for the extra voltage drop from the extra resistance?

If amps use an SMPS as all big amps must use (eg, >200W into 1 Ohm; >50W into 4 Ohm etc) then yes, their current - and hence alternator current - will increase as the amp's voltage drop increases. However, many amps seem not to exhibit such behavior based on their specs (some act as if they are purely resistive; other reduce output power as voltage decreases). IE - An amp with SMPS should put out constant power irrespective of input voltage. Ignoring extra copper losses etc, 300W out could mean 28A @12V or 24A @14V (336W in). And whether more current means more "strain"...? Sure, more fuel is burnt & more pressure (ie, mechanical strain) on belts and some parts, but whether that means more wear or worse operational conditions and hence "straining" it - IMO that is not strain per se, it's merely normal operation. (I would say my alternator works harder with headlights and wipers etc, but I would not call it a "strain".) But for the more typical resistive & non-SMPS loads, increased path resistance means a lower supply/alternator current, hence less alternator "work".

oldspark wrote: If amps use an SMPS as all big amps must use (eg, >200W into 1 Ohm; >50W into 4 Ohm etc) then yes, their current - and hence alternator current - will increase as the amp's voltage drop increases. However, many amps seem not to exhibit such behavior based on their specs (some act as if they are purely resistive; other reduce output power as voltage decreases). IE - An amp with SMPS should put out constant power irrespective of input voltage. Ignoring extra copper losses etc, 300W out could mean 28A @12V or 24A @14V (336W in). And whether more current means more "strain"...? Sure, more fuel is burnt & more pressure (ie, mechanical strain) on belts and some parts, but whether that means more wear or worse operational conditions and hence "straining" it - IMO that is not strain per se, it's merely normal operation. (I would say my alternator works harder with headlights and wipers etc, but I would not call it a "strain".) But for the more typical resistive & non-SMPS loads, increased path resistance means a lower supply/alternator current, hence less alternator "work".

I see, I'm running a Kenwood KAC-9105D (900WRMS@2ohm) and a KAC-8405 (60WRMSx4@4ohm) I believe both are advertised as Mosfet power supplies, which I thought were linear? Regardless, less load on the alternator would mean that extra overhead could be used to charge the battery which would keep the voltage more stable and make it less likely to damage parts of my charging system (like Vregs) or at least that's always been my way of thinking. I've only got a 125A alternator, and my system is likely to draw 115A+ of that momentarily. I believe I'm well into headlight dimming territory which I'd like to avoid. Either way, I believe the miniscule amounts we're taking about between 4 and 1/0 are pretty insignificant especially because I don't think my amps are SMPS. I went ahead and ordered some good quality 4 gauge. If I have to I'll upgrade the alternator later. Thanks for the discussion and advice! I always like learning new stuff.

From V=IR & P=VI, V = root(PR) = root(900W x 2 Ohms) = root 1800 = 42V. Hence it must be SMPS since you need (at least) 42V for 900W into 2 Ohms. MOSFETs are often used in SMPS - they are superior to transistors in such switching paplications. But there are also MOSFET amps. And no doubt some advertise MOSFET PSU/SMPS powered bipolar transistor amps as "MOSFET amps". It's not so much a case of having extra overhead to charge the battery, but keeping the alternator voltage as high as possible - ie, 14.2 or 14.4V. Normally a battery is NOT charging - not wrt "lots of Amps". By that I mean that most of the battery recharge (due to cranking) is done within minutes - usually at rates of 10 Amps or more. The charging current gradually drops and though "in theory" it continues forever, it will only be maybe 1A within tens of minutes for a few hours - plus it's "float current" - the current a battery continues to accept even when it is fully charged. The float current of typical car batteries can be from 100mA to 1A or maybe 2A. (More than 1-2A may mean it's partially compromised or damaged - eg, near end of life.) Anyhow, though I have often read that vehicle manufacturers "only supply the least they can" - ie, that alternators do NOT have much overhead - the way I see it is that manufacturers must allow for reasonable worst case situations. IE - during peak hour traffic with aircons or heaters and lights, the battery shall not flatten. IOW the alternator should have enough overhead to provide charge at low RPM with headlights & wipers etc etc.    Remove the lights and wipers and that's a 10A - 20A overhead gain. From here the arguments can go on infinitum. But to roll a whole lot together and even address audioforum needs for capacitors etc... Suppose you have a demand that outweighs the alternator's output (maybe stop lights and flashers as you are idling in peak hour traffic with your lights, aircon & wipers during a nighttime tropical downpour and your engine electric cooling fan blasting away).. The voltage will drop to the battery voltage which will be about 13.7V due to the battery's surface charge (after charging at ~14V). That surface charge gradually depletes and you then have the "normal" battery full "rested open circuit" voltage of ~12.7V (12.67V @ ~25C/75F in theory).   [ That detail is for the benefit of those that argue for caps to avoid amp dips. Surface charge can take 24 hours or more to deplete. Some sources reckon "15 minutes on high beams" to remove surface charge. How much is that in Farads? ] When the system hits 12.7V, the battery begins its normal chemical discharge to supply the alternator shortfall. Hence load inputs like amps have dropped from (say) 14.2V below 12.7V - a drop of 1.5V or more. Now as I said, an input drop of over 14V to (say) 12.5V should not make any difference to an SMPS amp, but that's where I find some amp specs and audioforum bullsh somewhat overwhelming. FYI - I reckon most vehicles should survive at least one hour running without an alternator and a near full battery with headlights on. Driving alternator-less all day (up to 12 hours) is not unlikely without headlights and other drains. But IMO the bottom line is to have (1) an adequately sized alternator that outputs 14.2-14.4V over an acceptable engine RPM range (peak hour versus highway cruising etc) and (2) distribution (wiring etc) that does not have any voltage drops - or in practice minimal voltage drops (don't overlook grounds!).    That overcomes your (valid!) point about a lower amp voltage meaning a higher current, and many audioforum arguments (many reckon to get more or bigger batteries BEFORE upgrading the alternator! That is advice I cannot understand - except where battery reserve is more important than having a system voltage of over 14V - but then they won't be arguing for caps will they?). And hence "the big 3" as so often pushed by this forum of experienced and practical minded gurus... First fix your distribution to see if that solves the bulk of voltage drop issues - ie, harden your engine/battery/chassis grounds. And (or is that or my big 4 etc?) harden your alternator to load and battery to load (and hence alternator to battery) +12V distribution. Load/amp grounding and +12V distribution is implicit. Only after that do you upgrade alternators if voltages still dip too low too often. [ The big 3 or 4 should be sized for the intended (future?) max load. IE, IMO may as well size the 120A alternator to battery for the possible 250A alternator required for the 3kW audio system. ]    As to caps - they are only good (1) to protect AGM batteries against high current surges (typically only for audio systems with 3kW output and higher) or (2) at lights to negate voltage dips or (3) where there is no secondary battery and there are distribution shortfalls and you want to avoid amp burp dips of up to a few milli- or tenths- of seconds and you cannot fit a battery instead. IOW, if you experience headlight dimming, place the cap (else battery) at the lights (NOT the amp!)