ho alternator

From my understanding it shows the temperature ratings. So a cable rated at 125*c can carry more amperage. as it can take more heat? some cables are rated at 80*c so depending on what amperage ur pushing it shows what size cable u will need. 1 guage 80*c can only push 160 amps. 2/0 SGX is rated at 125*c should be fine with a 270 amp alternator. i Know nothing about voltage drop and resistance. I used to have my memphis mojo amp 4kw push 2 12's 2200RMS. ALL i had was an extra optima battery in the trunk next to the stock battery. Ran that for a long time. Now that i got a custom box made i figured i should do things right this time. 270 amp alternator. XSpower 3100 battery same amp and 12's. Amp will be down to 1 ohm. Since the battery is in the trunk i have to run a wire from the alternator to the battery. 18ft run approx. my concern is what size cable do i need. SGX is rated at 125*c SGT (standard cable) 80-85*c now that 1/0 knukonceptz.com cable says 105*c But on that chart 105*c is only good for up to 242 amps.

gstacks wrote: From my understanding it shows the temperature ratings. So a cable rated at 125*c can carry more amperage.

Aha! I interpreted that a given gauge can carry a higher current at a higher temperature, and that is incorrect. What it is saying is that if its insulation is rated for a higher temperature, it can carry a higher current. Why - because that's how bluddy hot that cable will get! Bad luck if your 125C rated cable is running at 120C next to 85C rated insulation and paint etc. (fusing, maybe fire!) But again, the voltage drop from such a high temp cable would be awful - plus dangerous (you would burn yourself!) Be aware that the heat in a cable is its voltage drop times its resistance which is the same as its resistance times its current times its current (ie, R x I x I, aka I-squared x R). IOW, double the current thru a cable and you have (2x2=) 4 times the heat. Heat is the "power" generated in the cable (Watts) and that increases temperature, though power to temperature is another conversion formula. As to the rest, like I said, you should already have a suitable cable - ie, battery in rear to starter motor up front. (Not that I am familiar with your vehicle.) Hence you should not need a new cable from the alternator to the battery. You probably only need new cable from the alternator to the starter assuming the existing starter cable is big enough - noting that it need only carry starter current for up to a minute etc (ie, may not handle that current long-term). So find out what your existing battery to starter-motor wire gauge is, and hence its current carrying capacity (85C assumed?). Then check your battery to amp, and battery to chassis and chassis to engine cable capacities.    As to resistance and voltage drops - and batteries for big audio and audio voltage dips - there should be plenty of info available. It is usually a key part of any audio power design. And I would design for the standard 80C or 85C whatever - even though I think a cable self-generating to that temperature means a BAD design - ie, too big a voltage drop.

so u think the 18 foot run of 1 guage thats in the car stock should be fine with the 270 amp alternator? I have a big 3 kit installed. Grounds the chassis to motor in 2 different locations with 4 guage. Grounds the alternator to engine 4 guage. Transmission ground cable 4 guage. Also i have 0 guage in the trunk to the negative side of the battery. Whatever i use in for the amp i use for the negative side of the battery. i been searching for 2 weeks on and on about battery power cables lol. Its driving me crazy. so u think 1 huge battery will be fine aswell? or 2 decent size ones

oldspark, thank you for pm-ing me about the update. so far it is a moot point, as dc power engineering has still failed to deliver product, and it has been 6 months. maybe i'll have to see how much mechman will charge for a custom....

Glad you are here... gstacks made me realise I missed what you were probably after - ie, whether changes to distribution (wiring) were required. I don't know why I was looking at it from the "car electrics overloading" POV - other than that I had been verballing to someone else why that is a non-issue (ie, rubbish). With a bigger alternator, the ground from the alternator (engine) to be load must be increased. The +12V and ground from the battery to the load must also handle the load demand as well as increase current the battery might receive from the alternator. The short of that is to upgrade engine to body and battery grounds, and alternator +12V to fuse-box and battery - unless they already handle the amperage of the alternator etc (noting that a load can take alternator AND battery current). Actual setups depend on the application.    For example, gstacks' last question(s) cannot be answered due to lack on information. (Actually they have already been answered in my previous replies.) And whether you even need an HO alternator.... Bottom line there is that an voltmeter across the battery should provide that information unless you have very good data on your driving & alternator & load profiles - not that that will warn you when your alternator or battery is failing (unlike the voltmeter). Now as to two threads with the same name being updated at the same time with overlapping contributors...

i was planning on upgrading the wiring for the charging system when i installed the alternator (alt to chassis, engine & batt), so your original answer was right on target with what i was really asking anyway. the fusing from the alt to the fuse panel is something i need to look into though. my factory electrical (for everything not having to do with my stereo) should be fine as is though?

IMO - The alternator fuse should be sized to protect the cable, and if alternator to battery, should be near the battery. Alternator fusing is an interesting topic that nobody seems to address, but I'll ramble about that later. And good - so I was correct in assuming you were going to do the "obvious" upgrades... Not that that excuses me from not emphasising that in my first reply (the big-3 etc) - unless your upgrade intent and knowledge was obvious. (Geez OldFart, maybe I should just re-read the original post!) But yes - other than where the higher currents could run - ie, from alternator to battery, and (therefore) all the grounds (alt/battery/body/chassis) - there is no change to the rest of your system. A bigger load (audio etc) will require +12V & GND cabling to suit its power requirements. It is assumed that that is taken car of in its own right (hence upgraded battery-body-alternator grounds for it).    Your traditional radio and lights and whatever still take the same current they always did. Ok - in reality, maybe a bit more if your old alternator couldn't keep up its (say) 14.2V output that the bigger alternator can, but that is merely the loads getting what they should be getting (and they should tolerate 15V if not 16V etc). The main point being that a bigger alternator cannot "push" more current into the same old loads. Current is determined by voltage and resistance. The load resistance hasn't changed, the voltage should be the same, therefore the current should be the same. I = V/R (from V=IR - Ohm's Law). I'll leave it there. The following rambles are optional.... (LOL!) They expand the above, and include the unthinkable - a car battery with incorrectly labelled polarity!! Ramble #1: Though obvious, that "bigger power source" can be tricky to comprehend (whether it be a bigger alternator or battery). I like to analogize with water... You have a full water tank with a tap 1 meter (~3') down from the top. You open the tap and get a certain water flow - ie, a pressure that - thru that tap size - supplies water at a certain rate. You order your partner to expand the tank in preparation for the coming drought. She, or he, digs & builds for a while. You know have a tank that holds the Pacific Ocean (desalinated of course!). Ok, I exaggerate, let's assume it's just the Hoover Dam. The same tap is still 1M down from the water surface. The tap still produces the same water flow. Even though there is the entire capacity (mass or volume) of the Hoover or whatever behind that tap, the tap still sees the same pressure (1 meter down) as it would in a fish tank (also 1m down). Hence no effect on the rate of flow. Voltage is the "pressure". Current is the flow or flow rate - the amount per unit time. The resistance is the tap - the size of the restriction. So the same amount of current (water) will flow whether it's a fish tank or the Pacific Ocean. The same current will flow whether it's a 160A or 16000A alternator. Same if from a 100AH or 100000AH battery. Mind you, a bigger battery can accept more charge (from the alternator) than a smaller one...    /end ramble #1 Ramble #2 - Alternator fusing Alternator fusing (usually to the battery) is IMO an interesting topic. AFAIK cars never used to have it. Then in the 1970s , they began inserting fusible links between the alternator and battery. But the sizing was strange - often with ~20A flinks for 45A alternators etc. I began asking why. I got every combination - ie, to protect the alternator; to protect the alternator power diodes in case of reverse-connection of the battery; to protect the battery; and sometimes even to protect the cable (but in that case, shouldn't there be 2 fuses - one at each end?). My sensical conclusion was, that if required, the alternator-battery fuse was: - to protect the cable from the battery (as per normal fusing practice). - it shouldn't be to protect the cable from the alternator unless the cable is underrated - an alternator should limit its current to not much above its maximum rated current if that. (If higher, then add an alternator-end fuse.)     IMO it was not to protect the alternator. In cases of over-current, the alternator should self limit (due to its electro-magnetic behaviour, saturation, back-EMF, and good design with appropriately rated diodes). In cases of reverse-polarity battery connection, I generally found that fuses did not help - fused (protected) diodes blew whilst un-fused diodes survived. (More below.) More recently I found that nothing protects a Bosch alternator - specifically those from the 1980s & 1990s. Even a flat battery would blow the Bosch power diodes. I hence learned that the old bullsh spouse tale to "keep the jumper battery connected for a while after jump starting (to prevent alternator damage)" was in fact not bullsh. My 1960s-1970s Japanese vehicles have no flink. (In fact the first fuse is ~2m away diagonally opposite in the engine bay!) The battery is next to the alternator. IMO, their alt-battery "protection" is the same as the battery-starter cable - it is physical protection or security rather than electrical. It is assumed that with adequate insulation, secure routing and termination, a fault/short will not occur. (Or they figured the lead battery terminals is the "fuse" protection.) I have never had a blown power diode to my knowledge. A few years ago a mate with the same 1966 car as mine rang for help. He had a new battery but it "sparked" when he connected it. Some 2,000km later I arrived at the scene. Sure enough, sparks. Everything looked good. No alternator diodes were shorted. But the battery terminals were incorrectly labelled! This was a typical plastic-cased lead-acid battery with + & - clearly molded next to the terminals. But they were WRONG! We reversed the connections (so it seemed he had a +ve chassis vehicle) and everything was fine. But what got me was that after SEVERAL reverse connections to this unfused alternator, the alternator appeared to be ok. (She charged fine and I could not detect any dropped output nor high AC content.) Yet alternators that were fused often blew their main diodes at the sniff of a reverse connection. Granted - it's a 25A alternator versus my sampled 45A - 100A Bosch alternators, but it was 1965 componentry. And 12V through a 25A alternator's diode should be more destructive than for 110A alternators! (All being typical 0.6V silicons.) Anyhow, 2 rambles to scare the crud out of those that merely see the bulk of text. But a valuable lesson that NEW components can be faulty - ie, a car battery with incorrectly case-molded polarity! IE - never assume ANYTHING! And IMO an interesting saga as to why people think things are done despite obvious self contradictions, or a case of how "someone though it was a good idea", and everyone has since followed - despite all the problems it causes.

And *I* always overbuild no matter WHAT the charts say! *ONE* four gauge? Pshaw... Two, please!It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."